JPH0723287A - Imaging device - Google Patents

Abstract

(57) [Summary] [Purpose] Imaging that can obtain an output image with rich gradation expression over the entire screen, even if gradation correction is performed on an image with strong normal light to strong backlight. Provide a device. [Structure] The correction characteristic determination circuit 117 determines a correction coefficient based on the characteristic amount obtained from the input video signal by the characteristic amount extraction circuit 116. The aperture control and the gradation correction are linked by the determined correction coefficient. The iris control unit corrects the iris by a correction coefficient to prevent the high brightness part from being crushed, and the tone correction circuit 1
Reference numeral 06 makes it possible to obtain an output video signal rich in gradation expression by simply changing the gradation correction characteristic by a correction coefficient and performing gradation correction suitable for all subjects from normal light to backlight.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus capable of obtaining an image with a rich gradation expression by performing gradation correction on a blurred main image of a main subject due to backlight photography or the like. It is a thing.

[0002]

2. Description of the Related Art In recent years, many imaging devices have been developed. As a conventional imaging device, for example, Japanese Patent Laid-Open No. 1-120
It is disclosed in the imaging device (first conventional example) of Japanese Patent No. 969.

The image pickup apparatus of the first conventional example will be described below. FIG. 22 is a block diagram of a conventional image pickup apparatus disclosed in the publication. In FIG. 22, 1501 is an imaging lens, 1502 is an iris, 1503 is a solid-state image sensor, 1504 is an amplifier, 1505 is a maximum value detection circuit,
1506 is a minimum value detection circuit, 1507 is an average value detection circuit, 1508 is an iris control circuit, 1509 is a subtractor,
Reference numeral 1510 is a comparison circuit, 1511 is a control voltage generation circuit, 1
Reference numeral 512 is a DC level shift circuit, 1513 is a shift amount calculation circuit, and 1514 is an adder.

The operation of the image pickup apparatus of the first conventional example constructed as described above will be described below. The light input from the subject passes through the imaging lens 1501 and its power is adjusted by the iris 1502.
Image on 3. The video signal converted into an electric signal by the solid-state image sensor 1503 is amplified by an amplifier 1504, and
Maximum, minimum, and average detection circuits in the field 1
Input to 505, 1506, and 1507, respectively. The output s of the average value detection circuit 1507 is input to the iris control circuit 1508 via the adder 1514, and iris control is performed. The output x of the maximum value detection circuit 1505 and the output y of the minimum value detection circuit 1506 are subtracted by the subtractor 9, and z =
xy, this value z is compared by the comparison unit 1510, and when this value z is smaller than a preset specified value a, the control voltage generation circuit 1511 opens the iris 1502 and z =
to be a. In a backlit subject, the image quality of the main subject and the background can be improved.

Another example (second conventional example) of a conventional image pickup device with a gradation correction function is disclosed in a gamma correction device disclosed in Japanese Patent Laid-Open No. 2-206628. The second conventional example of the image pickup apparatus with a gradation correction function will be described below.

FIG. 23 is a block diagram of a conventional image pickup device with a gradation correction function shown in the publication. In FIG. 23, 1601 is an imaging device, 1602 is a gain control circuit,
Reference numeral 1603 is an attenuation control circuit, 1604 is a level range dividing means, 1605 is an average value detection circuit, and 1606 is a gain control data ROM. Reference numeral 1607 is a gamma correction control circuit.

The operation of the image pickup apparatus having the gradation correction function of the second conventional example constructed as described above will be described below. The image signal obtained by the image pickup by the image pickup device 1601 is divided into a predetermined signal level range by the level range dividing means 1604, and the average value detection circuit 1605 detects the average value or integrated value of the image signals in each level range. In the gain control data ROM 1606, the gain or the attenuation amount in the gamma correction control circuit 1607 is set according to the average value of the video signal in each level range. In the gain control circuit 1602 and the attenuation control circuit 1603, by controlling the gamma correction characteristic according to the output signal of the gain control data ROM, it is possible to prevent the occurrence of white crushing and black crushing.

[0008]

However, in the above-mentioned first conventional example, since the difference between the maximum value and the minimum value of the video signal is large in the case of a backlit subject, the iris should match the average value of the video signal. There is a problem in that the gradation of the low luminance portion and the high luminance portion is controlled and disappears. Further, there is also a problem that the gradation is totally lost and an unnatural output image is obtained for a subject having a gradation from low luminance to high luminance in a normal-light subject.

Further, in the above-mentioned second conventional example, the gain of the low luminance part is increased to prevent the black crushing, and the attenuation amount of the middle luminance part and the high brightness part is controlled to prevent the white crushing. Therefore, white crushing can be prevented, but instead there is a problem in that the gradation of the high-luminance portion is lost.

Further, the above-mentioned conventional example has a problem that even if an attempt is made to correct the gradation from a normal-light subject to a backlight subject, the correction characteristic cannot be easily changed.

Further, in the above-mentioned conventional example, since it does not support moving images, there is a problem that an unnatural output image which is not stable is obtained when gradation correction is performed on the moving image.

The present invention solves the above-mentioned problems of the prior art, and can prevent an underexposure or underexposure and provide an output image with rich gradation expression over the entire screen from a normal light subject to a strong backlit subject. It is an object of the present invention to provide an imaging device that can obtain a natural gradation correction image even for a moving image.

[0013]

In order to achieve this object, an image pickup apparatus of the present invention comprises an image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, and a maximum output video signal of the image pickup device. A maximum value detection circuit for detecting a value, an average value detection circuit for detecting an average value of the output image signal of the image sensor, a maximum value detected by the maximum value detection circuit, and an average value detected by the average value detection circuit A weighted average circuit for weighted averaging by a weighting coefficient, a comparison circuit for comparing an output result of the weighted average circuit with an exposure amount target value, and a control signal generation circuit for controlling the exposure control circuit according to the output result of the comparison circuit. A feature amount extraction circuit for obtaining a feature amount of an output video signal of the image sensor, and a correction feature for determining a gradation correction characteristic to be corrected based on the feature amount extracted by the feature amount extraction circuit and outputting a correction coefficient. A decision circuit, in which a gradation correcting means for correcting the respective output image signal of the imaging element by the gradation correction characteristic and the correction characteristic determination circuit has determined.

The image pickup apparatus of the present invention includes an image pickup element,
An exposure control circuit for controlling the exposure amount of the image pickup device, a luminance signal generation circuit for separating or synthesizing a luminance signal Y from an output video signal of the image pickup device, and a maximum value detection circuit for detecting the maximum value of the luminance signal. An average value detection circuit that detects an average value of the luminance signal, a weighted average circuit that performs a weighted average of the maximum value detected by the maximum value detection circuit and the average value detected by the average value detection circuit by a weighting coefficient, A comparison circuit for comparing the output result of the weighted average circuit and the exposure amount target value, a control signal generation circuit for controlling the exposure control circuit according to the output result of the comparison circuit, and a feature amount extraction circuit for obtaining a histogram of the luminance signal. A correction characteristic determination circuit that determines a gradation correction characteristic to be corrected based on the histogram obtained by the feature amount extraction circuit and outputs a correction coefficient, and the correction characteristic determination circuit The determined gradation correction characteristics is obtained and a gradation correction means for correcting the respective output video signal of the image sensor.

The image pickup device of the present invention includes an image pickup element,
An exposure control circuit that controls the exposure amount of the image sensor, a maximum value detection circuit that detects the maximum value of the output video signal of the image sensor, and an average value detection circuit that detects the average value of the output video signal of the image sensor. A minimum value detection circuit for detecting the minimum value of the output video signal of the image sensor; a subtraction circuit for subtracting the minimum value detected by the minimum value detection circuit from the maximum value detected by the maximum value detection circuit; A first comparison circuit for comparing the output result of the subtraction circuit with a specified value; and a weighted average circuit for weighted averaging the maximum value detected by the maximum value detection circuit and the average value detected by the average value detection circuit by a weighting coefficient. ,
A second comparison circuit for comparing an output result of the weighted average circuit with an exposure amount target value; and a control signal generation circuit for controlling the exposure control circuit according to the output result of the second comparison circuit,
A feature amount extraction circuit that obtains a feature amount of the output video signal of the image pickup device, and a correction characteristic determination circuit that determines a gradation correction characteristic to be corrected based on the feature amount extracted by the feature amount extraction circuit and outputs a correction coefficient And a gradation correction means for correcting each of the output video signals of the image pickup device with the gradation correction characteristic determined by the correction characteristic determination circuit.

The image pickup device of the present invention includes an image pickup element,
An exposure control circuit for controlling the exposure amount of the image pickup device, a luminance signal generation circuit for separating or synthesizing a luminance signal from an output video signal of the image pickup device, and a maximum value detection circuit for detecting a maximum value of the luminance signal, An average value detection circuit that detects the average value of the luminance signal, a minimum value detection circuit that detects the minimum value of the luminance signal, and a minimum value that the minimum value detection circuit detects from the maximum value that the maximum value detection circuit detects. A subtraction circuit for subtracting a value, a first comparison circuit for comparing an output result of the subtraction circuit with a specified value, a maximum value detected by the maximum value detection circuit and an average value detected by the average value detection circuit are weighted. A weighted average circuit for weighted averaging by a coefficient, a second comparison circuit for comparing an output result of the weighted average circuit with an exposure amount target value, and an exposure control circuit controlled by an output result of the second comparison circuit. A control signal generation circuit, a characteristic amount extraction circuit for obtaining a histogram of the luminance signal, and a correction characteristic determination circuit for determining a gradation correction characteristic to be corrected based on the histogram obtained by the characteristic amount extraction circuit and outputting a correction coefficient. And a gradation correction means for correcting each of the output video signals of the image pickup device with the gradation correction characteristic determined by the correction characteristic determination circuit.

Further, the gradation correction means of the image pickup apparatus of the present invention generates a first gradation correction characteristic from the input video signal, and a first gradation correction characteristic circuit, and a second gradation correction from the input video signal. A second gradation correction characteristic circuit for generating a characteristic; an average value detection circuit for obtaining an average value of the input video signal; an adder for adding the average value and the correction coefficient determined by the correction characteristic determination circuit; A weighted average circuit that outputs a correction gain by performing a weighted average of the first gradation correction characteristic and the second gradation correction characteristic according to the output signal of the adder, and the input video signal by the correction gain obtained by the weighted average circuit. It is provided with a configuration called a correction means for correcting each of the above.

[0018]

With the above arrangement, the image pickup apparatus of the present invention obtains the maximum value and average value in one field from the output video signal of the image pickup element. The obtained maximum value and average value are weighted averaged, and exposure control is performed so that the output result of the weighted average and the exposure amount target value match. At the same time, the feature amount extraction circuit extracts the feature amount of the output video signal of the image sensor. The correction characteristic determination circuit determines the gradation correction characteristic to be corrected based on the extracted characteristic amount, and the gradation correction means performs gradation correction on the output video signal of the image sensor. Then, the exposure amount target value is changed according to the determined gradation correction characteristic, and the aperture control linked with the gradation correction is performed, so that a stable gradation correction image can be obtained for any input image. it can.

Further, the image pickup apparatus of the present invention is configured as described above, and obtains the maximum value and the average value in one field from the output video signal of the image pickup element. The obtained maximum value and average value are weighted averaged, and exposure control is performed so that the output result of the weighted average and the exposure amount target value match. At the same time, the feature amount extraction circuit extracts the feature amount of the output video signal of the image sensor. The correction characteristic determination circuit determines the gradation correction characteristic to be corrected based on the extracted characteristic amount, and the gradation correction means performs gradation correction on the output video signal of the image sensor. By changing the weighting coefficient of the weighted average according to the determined gradation correction characteristic and performing exposure control linked with gradation correction, a stable gradation correction image can be obtained for any input image. You can

Further, the image pickup apparatus of the present invention has the above-mentioned configuration and obtains the maximum value, average value and minimum value in one field from the output video signal of the image pickup element. The obtained maximum value and average value are weighted averaged, and exposure control is performed so that the output result of the weighted average and the exposure amount target value match. Further, the exposure amount target value is changed according to the result obtained by subtracting the minimum value from the maximum value, and the exposure control is similarly performed. At the same time, the feature amount extraction circuit extracts the feature amount of the output video signal of the image sensor. Based on the extracted characteristic amount, the correction characteristic determination circuit determines the gradation correction characteristic to be corrected, and the gradation correction unit corrects the gradation of the output video signal of the image sensor, so that any input image can be corrected. It is possible to obtain a stable gradation correction image.

Further, the image pickup apparatus of the present invention is configured as described above, and obtains the maximum value, average value and minimum value in one field from the output video signal of the image pickup element. The obtained maximum value and average value are weighted averaged, and exposure control is performed so that the output result of the weighted average and the exposure amount target value match. Further, the weighting coefficient of the weighted average is changed according to the result of subtracting the minimum value from the maximum value, and exposure control is performed in the same manner. At the same time, the characteristic amount extraction circuit extracts the characteristic amount of the output video signal of the image sensor. Based on the extracted characteristic amount, the correction characteristic determination circuit determines the gradation correction characteristic to be corrected, and the gradation correction unit corrects the gradation of the output video signal of the image sensor, so that any input image can be corrected. It is possible to obtain a stable gradation correction image.

Further, the gradation correction circuit of the image pickup apparatus of the present invention has the above-mentioned configuration, and performs the weighted average of the first gradation correction characteristic and the second gradation correction characteristic using the average value Ya of the input video signal. By obtaining the correction gain, the brightness is corrected low if the brightness in the vicinity is high, and the brightness is corrected high if the brightness in the vicinity is low, and the gradation correction is performed so that the contrast is maintained even if the gradation correction gain is small. It is possible to obtain a gradation correction image with rich gradation expression.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the arrangement of an image pickup apparatus according to the first embodiment of the present invention. In FIG. 1, 1
01 is an optical system, 102 is a diaphragm circuit, 103 is a solid-state image sensor, 104 is an analog circuit, 105 is an analog / digital converter (A / D converter), 106 is a gradation correction circuit, 1
Reference numeral 07 is a signal processing circuit, 108 is a digital / analog converter (D / A converter), 109 is an encoder circuit, 110
Is a luminance signal generation circuit, 111 is a maximum value detection circuit, and 112
Is an average value detection circuit, 113 is a weighted average circuit, 114 is a comparison circuit, 115 is an aperture drive circuit, 116 is a feature amount extraction circuit, and 117 is a correction characteristic determination circuit.

FIG. 2 is a block diagram showing the internal structure of the gradation correction circuit 106 in the first embodiment. In FIG. 2, 201 is a first gradation correction characteristic circuit, and 202 is a second gradation correction characteristic circuit.
Of the gradation correction characteristic circuit, 203 is an adder, 204 is a weighted average circuit, 205 is a delay circuit, and 206 is a multiplier.

FIG. 3 is a diagram showing an image of one field of the input video signal in the embodiment of the present invention. In FIG. 3, 301 shows an effective screen. The number of samples of the effective screen 301 is 448 in the horizontal H direction and 224 in the vertical V direction. FIG. 3A shows an image of one field of the input video signal, but this image is an example of a subject in which a person stands in front of a window and has a large degree of backlight. FIG. 3B is a diagram showing 7 × 7 block division of the 1-field effective screen. FIG. 3C is a diagram showing center-weighted block division.

FIG. 4 is a histogram of the luminance signal of the effective screen in the embodiment of the present invention. 4A is a histogram of the luminance signal. 4b is the number of low luminance pixels, c of FIG. 4 is the number of medium luminance pixels, and d of FIG. 4 is the number of high luminance pixels.

FIG. 5 is a block diagram showing the configuration of the feature quantity extraction circuit 116 in the embodiment of the present invention. 5, reference numeral 501 is a comparison circuit, 502 is a counter circuit for the number of low-luminance pixels, 503 is a counter circuit for the number of medium-luminance pixels, 5
Reference numeral 04 is a counter circuit for the number of high-luminance pixels.

FIG. 6 is a block diagram showing the internal structure of the correction characteristic determining circuit 117 according to the embodiment of the present invention. Figure 6
In the figure, 601 is a correction coefficient table ROM, and 602 is a filter circuit.

FIG. 7 is a characteristic diagram showing gradation correction characteristics in the embodiment of the present invention. In FIG. 7, Y1 is the first gradation correction characteristic, and Y2 is the second gradation correction characteristic.

The operation of the image pickup apparatus of the first embodiment of the present invention constructed as above will be described below.

In FIG. 1, first, the optical input is the optical system 10.
1 and the diaphragm circuit 102 to input to the solid-state image sensor 103. The analog circuit 104 takes in R, G, and B signals as input video signals from the solid-state image sensor 103. This R,
The G and B signals are converted into digital data of 0 to 255 by the analog / digital converter 105. This 0-2
The R, G, and B signals converted into 55 digital data are supplied to the gradation correction circuit 106 and the luminance signal generation circuit 110 as input video signals. These color data are R = G = B
= 255 indicates white, and a larger value indicates brighter. The luminance signal generation circuit 110 calculates the luminance signal Y from the R, G, B signals. When the luminance of the input video signal is Y, it can be obtained by the relational expression of, for example, Y = 0.30R + 0.59G + 0.11B (1), and the value is also 0 to 255.

The calculated luminance signal Y is the maximum value detection circuit 11
1 is supplied to the average value detection circuit 112 and the feature amount extraction circuit 116. First, the maximum value detection circuit 111 and the average value detection circuit 112 respectively detect the maximum value and the average value of the effective screen of one field from the calculated luminance signal Y. A weighted average circuit 113 weights and averages the maximum value and the average value of the detected luminance signal with a weighting coefficient to obtain an average luminance level. For example, the average luminance level can be calculated by the relational expression of average luminance level = {(maximum value) × (weighting coefficient) + (minimum value) × (100−weighting coefficient)} / 100 (2).

The comparison circuit 114 compares the obtained average luminance level with the target value of the aperture, and the aperture drive circuit 115 causes the aperture circuit 102 to match the average brightness level with the target value of the aperture.
Aperture control is performed by driving.

From the calculated luminance signal Y, the feature amount extraction circuit 116 obtains a three-level histogram of low luminance, medium luminance, and high luminance. From this histogram, the correction characteristic determination circuit 117 determines the optimum gradation correction characteristic for the input video signal and outputs the correction coefficient indicating the gradation correction characteristic. With this correction coefficient, the gradation correction circuit 106 performs gradation correction with optimum gradation correction characteristics for the input video signal. The signal processing circuit 107 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. A digital / analog converter 108 converts the signal-processed digital R, G, B signals into analog R, G, B signals. Finally, the encoder circuit 109 converts the R, G, B signals into a Y signal (luminance signal).
And C signals (color signals) are converted to video signal outputs and output.

Next, the operation of the gradation correction function of the image pickup apparatus of the present invention will be described in detail with reference to FIGS. 2, 3, 4, 5, 6, and 7.

The operation of the feature quantity extraction circuit 116 will be described in detail with reference to FIG. The input luminance signal Y is compared with the comparator 50.
At 1, the thresholds 1 and 2 are compared. Luminance signal Y is threshold 1
When it is smaller, the low brightness count signal is output. When the luminance signal Y is between the threshold 1 and the threshold 2, the medium luminance count signal is output. When the luminance signal Y is larger than the threshold value 2, a high luminance count signal is output. This low brightness count signal,
The counter circuits 502, 503, and 504 count the number of pixels in the effective screen of one field according to the medium-luminance count signal and the high-luminance count signal, and output the low-luminance pixel number, the medium-luminance pixel number, and the high-luminance pixel number, respectively. For example,
FIG. 3A shows an image of one field of the input video signal, but this image is an example of a subject in which a person stands in front of a window and has a large degree of backlight. Feature quantity extraction circuit 1
16 shows the distribution of the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels for one field image 448 × 224 dots of the effective screen 301 of FIG. When asked, b in FIG.
A luminance histogram as shown in c and d is obtained. Looking at this luminance histogram (b, c, d in FIG. 4), peaks are formed at two locations, low luminance and high luminance, and it can be inferred that the subject is backlit.

The operation of the correction characteristic determination circuit 117 will be described in detail with reference to FIG. The correction coefficient table ROM 601 uses the low-luminance pixel number, the medium-luminance pixel number, and the high-luminance pixel number supplied from the feature amount extraction circuit 116 as an address to correct the gradation correction characteristic of a normal-light subject to a backlight subject and a dark subject. The correction coefficient and the like of the gradation correction characteristic for are stored. Therefore, when the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels are input from the feature amount extraction circuit 116 to the correction coefficient table ROM 601, one correction coefficient is determined for the input image. The correction coefficient is filtered by the filter circuit 602 so as to maintain continuity with the previous field, and the correction coefficient is output.

The operation of the gradation correction circuit 106 will be described in detail with reference to FIG. The input luminance signal Y is supplied to the first gradation correction characteristic circuit 201 and the second gradation correction characteristic circuit 202. The first gradation correction characteristic circuit 201 outputs a first correction gain (Y1 / Y) from the input luminance signal Y and Y1 corrected by the first gradation correction characteristic. Similarly, from the second gradation correction characteristic circuit 202, the second correction gain (Y2 /
Y) is output. On the other hand, the adder 203 adds the luminance signal Y and the correction coefficient and outputs an X signal. Next, the weight averaging circuit 204 weights the first correction gain and the second correction gain by the relational expression (3) using the X signal to obtain the correction gain (Y '/ Y).

Y ′ / Y = {(Y1 / Y) · (256−X) + (Y2 / Y) · X} / 256 (3) In the present embodiment, the first correction gain (Y1 / Y ) By the equation (4) and the second correction gain (Y2 / Y) by the equation (5).

Y1 / Y = {1/256 ² · (Y-256) ³ +256} / Y (4) Y2 / Y = Y / Y (5) Finally, R, G, B The delay circuit 205 matches the timing of the signal with the correction gain (Y ′ / Y), and the multiplier 206 multiplies the R, G, B signals by the correction gain (Y ′ / Y), and the gradation-corrected R ′ is obtained. , G ', B'signals are output. In this way, by using the correction gain in common for the R, G, and B signals, it is possible to obtain an output image with good color balance and rich gradation expression over the entire area.

FIG. 7 shows gradation correction characteristics in this embodiment. Y1 is the first gradation correction characteristic, and Y2 is the second gradation correction characteristic. For example, when the correction coefficient is 0, the gradation correction characteristic becomes a in FIG. 7 from the relational expression (3). Similarly, when the correction coefficient becomes positive, the gradation correction characteristic becomes as shown in c of FIG. Similarly, when the correction coefficient becomes negative, the gradation correction characteristic becomes as shown in b of FIG. By changing the correction coefficient in this way, the gradation correction characteristics can be easily and continuously changed. When the correction coefficient of the gradation correction characteristic is changed, the correction gains of the low-luminance portion and the middle-luminance portion gradually increase, and finally the overall correction gain increases.
Therefore, the gradation correction characteristic of Y2 in FIG. 7 is applied to the normal light subject, the gradation correction characteristic of FIG. 7a is applied to the backlight subject, and the gradation correction characteristic of Y1 in FIG. 7 is applied to the dark subject. By performing gradation correction with the correction characteristic, it is possible to perform gradation correction with rich gradation expression for all subjects.

On the other hand, the weighting coefficient of the weighted average circuit 113 is corrected by the correction coefficient determined by the correction characteristic determination circuit 117, and the aperture control is performed in conjunction with the gradation correction.

FIG. 8 is a characteristic diagram showing the correction value of the weighting coefficient with respect to the correction coefficient. For example, the correction characteristic determination circuit 117
When it is determined that the subject has a gradation correction characteristic of a backlight subject, as shown in FIG. 8, the weighting coefficient of the weighted average circuit 113 is increased according to the correction coefficient, and the ratio of the maximum value of the luminance signal is increased to increase the average luminance. Try to find a level. Aperture drive circuit 1
Reference numeral 15 drives the diaphragm circuit 102 so that the target value of the diaphragm and the corrected average brightness level match, so that when the average brightness level becomes large, the diaphragm circuit 102 operates in the direction of closing the diaphragm. Normal,
Since the diaphragm drive circuit 115 drives the diaphragm circuit 102 so as to match the diaphragm with the average brightness level, the average brightness level becomes small and the diaphragm opens when the subject is backlit.
High-brightness areas such as outdoors are crushed in white. Therefore, by correcting the weighting coefficient with the correction coefficient, the average luminance level is increased, and by closing the diaphragm, white crushing is prevented. Further, the gradation correction circuit 106 raises the low-luminance portion and outputs the high-luminance portion as it is, so that a video signal output rich in gradation expression can be obtained on the entire screen even for a backlit subject.

As described above, according to this embodiment, the image pickup apparatus of the present invention has an optical system 101, a diaphragm circuit 102, a solid-state image pickup element 103, an analog circuit 104, and an analog / digital converter (A / D). Converter) 105, gradation correction circuit 106, signal processing circuit 107, digital / analog converter (D / A converter) 108, and encoder circuit 10.
9, a luminance signal generation circuit 110, and a maximum value detection circuit 11
1, an average value detection circuit 112, and a weighted average circuit 113
The comparison circuit 114, the diaphragm drive circuit 115, the characteristic amount extraction circuit 116, and the correction characteristic determination circuit 117 perform diaphragm control linked with gradation correction,
It is possible to obtain an output image in which the gradation is not destroyed for all the objects from the backlight object to the normal object and the color balance is good and the gradation expression is rich over the entire area.

The gradation correction circuit of the image pickup apparatus of the present invention is the first gradation correction characteristic circuit 201, the second gradation correction characteristic circuit 202, the adder 203, and the weighted average circuit 204.
By configuring the delay circuit 205 and the multiplier 206 so as to generate the correction gain by the correction coefficient, it is not necessary to have an extra ROM or the like for storing some kinds of gradation correction characteristics. Therefore, the circuit scale can be made very small.

By changing the correction coefficient, it is possible to generate the gradation correction characteristics of a forward-lit subject and a backlit subject. It is possible to obtain an output image with rich gradation expression over the entire area.

Further, since the gradation correction characteristic can be continuously changed, it is possible to perform natural gradation correction even for a moving image.

When the input signal is large, the gradation correction characteristic is set so that the input signal becomes the output signal as it is, so that the gradation of the high-luminance portion is conventionally reproduced by auto knee control and the like can be reproduced clearly. can do.

FIG. 9 is a block diagram showing the internal structure of the gradation correction circuit 106 in the image pickup apparatus according to the second embodiment of the present invention. The difference from the internal configuration of the gradation correction circuit 106 in the image pickup apparatus according to the first embodiment shown in FIG. 2 is that an average value detection circuit (LPF) 207 is newly provided in the gradation correction circuit 106. .

The operation of the gradation correction circuit 106 will be described in detail below with reference to FIG. The input luminance signal Y has the first gradation correction characteristic circuit 201 and the second gradation correction characteristic circuit 20.
2 is supplied. In the first gradation correction characteristic circuit 201,
A first correction gain (Y1 / Y) is output from the input luminance signal Y and Y1 corrected by the first gradation correction characteristic 201. Similarly, the second gradation correction characteristic circuit 202 outputs a second correction gain (Y2 / Y). On the other hand, for the luminance signal Y, an average value detection circuit (LPF) 207 obtains an average luminance value Ya, an adder 203 adds the average luminance value Ya and a correction coefficient, and outputs an X signal. Next, the weighted average circuit 204 weights and averages the first correction gain and the second correction gain by the relational expression (3) using the X signal to obtain the correction gain (Y ′ / Y). Finally, the R, G, B signals are timed with the correction gain (Y '/ Y) by the delay circuit 205, and the R, G, B signals are multiplied by the correction gain (Y' / Y) by the multiplier 206. , And outputs R ', G', and B'signals whose gradations have been corrected. In this way, by using the correction gain in common for the R, G, and B signals, it is possible to obtain an output image with good color balance and rich gradation expression over the entire area.

FIG. 10 shows gradation correction characteristics and input / output characteristics. When the luminance average value Ya obtained by the average value detection circuit 207 is equal to the luminance signal Y of the pixel of interest, the gradation correction characteristic of FIG. 10A is obtained. When the average luminance value Ya is lower than the luminance signal Y of the pixel of interest, In the tone correction characteristic of 10b, when the average luminance value Ya is higher than the luminance signal Y of the pixel of interest, the tone correction characteristic of c of FIG. By performing the gradation correction, the gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and an output signal rich in gradation expression can be obtained.

FIG. 11 is a block diagram showing a specific structure of the gradation correction circuit 106 according to the second embodiment of the present invention. In FIG. 11, 901 is an average value detection circuit (LP
F), 902 is a first adder, 903 is a clipping circuit, 9
04 is the second adder, 905 is the first multiplier, and 906 is the third
An adder, 907 is a first subtractor, 908 is a second multiplier, 9
Reference numeral 09 is a second subtractor, 910 is a fourth adder, 205 is a delay circuit, and 206 is a multiplier.

Hereinafter, the gradation correction circuit 106 will be described with reference to FIG.
The operation of will be described in detail. FIG. 11 is a circuit in which the equations (3), (4), and (5) are directly rendered. Two
56 times, 1/256, etc. are dealt with by bit shifting of data to simplify the circuit. First, when the luminance signal Y is input, the average value detection circuit 901 calculates the average value Ya. Next, the average value Ya and the correction coefficient are added by the first adder 902. The output signal of the first adder 902 is vertically clipped by the clipping circuit 903 with the value “0” and the value “255”.
On the other hand, the average value detection circuit 901 outputs the luminance signal Y to the average value Y.
The luminance signal 2Y doubled by 1-bit shift and the luminance signal Y are added by the second adder 904 to obtain a tripled luminance signal 3Y. Also, the first multiplier 90
In step 5, the luminance signal Y is squared to generate a luminance signal Y ² . The value “3” is output to the output signal of the first multiplier 905 by the third adder 906.
Is added. Next, the output signal of the second adder 904 is subtracted from the output signal of the third adder 906 by the first subtractor 907. Next, the output signal of the clipping circuit 903 is set to the numerical value “25.
6 ”from the second subtracter 909. Second subtractor 90
The output signal of 9 and the output signal of the first subtractor 907 are multiplied by the second multiplier 908. Finally, the output signal of the clipping circuit 903 and the output signal of the second multiplier 908 are combined into a fourth adder 91.
0 is added to obtain a correction gain. On the other hand, the input video signal is delayed by the delay circuit 205, and this correction gain is multiplied by the multiplier 206 to perform gradation correction.

The correction gain is controlled in accordance with the gradation correction characteristics shown in FIGS. 7 and 10 by controlling the correction gain with a correction coefficient, so that the gradation is not destroyed for all objects from the backlit object to the frontlit object. It is possible to obtain an output image that is well balanced and rich in gradation expression over the entire area. Further, the gradation correction characteristic is adaptively changed for each pixel according to the luminance average value Ya to perform the gradation correction, so that the gradation correction is performed so that the contrast is maintained even if the inclination of the correction gain is small, and the gradation expression is performed. A rich output signal can be obtained.

As described above, according to this embodiment, the gradation correction circuit 106 of the present invention is used as the first gradation correction characteristic circuit 201.
A second gradation correction characteristic circuit 202 and an adder 203
The weighted averaging circuit 204, the delay circuit 205, the multiplier 206, and the average value detection circuit 207 are used to generate a correction gain by a correction coefficient, so that several kinds of gradation correction characteristics can be obtained. Extra RO to remember
Since it is not necessary to have M or the like, the circuit scale can be made very small.

By changing the correction coefficient, it is possible to generate the gradation correction characteristics of a forward-lit subject and a backlit subject. It is possible to obtain an output image with a good gradation expression over a wide range.

Further, when the input signal is large, the gradation correction characteristic is set so that the input signal becomes an output signal as it is, so that the place where the gradation in the high-luminance portion has been destroyed by the conventional auto knee control can be reproduced neatly. can do.

Further, the gradation correction characteristics are adaptively changed in pixel units according to the average luminance value Ya to perform gradation correction, so that gradation correction is performed so that contrast is maintained even if the inclination of the correction gain is small. An output signal rich in gradation expression can be obtained.

FIG. 12 is a block diagram showing the arrangement of an image pickup apparatus according to the third embodiment of the present invention. In FIG. 12, 1001 is an optical system, 1002 is a diaphragm circuit, and 1003.
Is a solid-state image sensor, 1004 is an analog circuit, 1005 is an analog / digital converter (A / D converter), 1006
Is a gradation correction circuit, 1007 is a signal processing circuit, 1008 is a digital / analog converter (D / A converter), 1009
Is an encoder circuit, 1010 is a luminance signal generation circuit, 10
11 is a maximum value detection circuit, 1012 is an average value detection circuit, 1
013 is a weighted average circuit, 1014 is a comparison circuit, 1015
Is a diaphragm drive circuit, 1016 is a feature amount extraction circuit, 1017
Is a correction characteristic determination circuit.

The operation of the image pickup apparatus of the third embodiment of the present invention constructed as above will be described below.

In FIG. 12, first, the optical input is the optical system 1.
A solid-state image sensor 1003 passing through 001 and the aperture circuit 1002.
To enter. From the solid-state image sensor 1003 to the analog circuit 1
R, G, and B signals are captured by 004 as an input video signal. These R, G and B signals are converted to analog / digital converter 1
It is converted into digital data of 0 to 255 by 005. R converted into digital data of 0 to 255,
The G and B signals are input image signals and the luminance signal generation circuit 10
11 and the gradation correction circuit 1006. Hereinafter, except for the weighted average circuit 1013 and the comparison circuit 1014, the operation is exactly the same as in the first and second embodiments. That is, the luminance signal generation circuit 1010 calculates the luminance signal Y from the R, G, B signals. First, the maximum value detection circuit 1011 and the average value detection circuit 1012 respectively detect the maximum value and the average value of the effective screen of one field from the calculated luminance signal Y. The weighted averaging circuit 1013 weights and averages the maximum value and the average value of the detected luminance signal with a weighting coefficient to obtain an average luminance level. For example, the average luminance level can be calculated by the relational expression (2). The comparison circuit 1014 compares the obtained average brightness level with the target value of the aperture, and the aperture drive circuit 1015 drives the aperture circuit 1002 so that the average brightness level and the target value of the aperture match, thereby performing aperture control.

Further, the calculated luminance signal Y is supplied to the characteristic amount extraction circuit 1016 and the gradation correction circuit 1007. The characteristic amount extraction circuit 1016 obtains the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels of the luminance signal Y, and the correction characteristic determination circuit 10
Supply to 17. The correction characteristic determination circuit 1017 determines the optimum gradation correction characteristic for the input video signal based on the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels, and outputs the correction coefficient of the gradation correction characteristic. The gradation correction circuit 1006 obtains a correction gain from the luminance signal Y and the correction coefficient. The gradation of the input video signal is corrected with this correction gain. The signal processing circuit 1007 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. This signal processed digital R,
A digital / analog converter 1008 converts the G, B signals into analog R, G, B signals. Finally, the encoder circuit 1009 converts the R, G, B signals into a Y signal (luminance signal).
And C signal (color signal) and output the video signal output.

On the other hand, the operation differs from the first and second embodiments in that the correction target value of the comparison circuit 1014 is corrected by the correction coefficient determined by the correction characteristic determination circuit 1017.
This is where aperture control is performed in conjunction with gradation correction. For example, when the correction characteristic determination circuit 1017 determines that it is the gradation correction characteristic of the backlight subject, the correction coefficient becomes small, and the target value of the aperture of the comparison circuit 1014 is made small in proportion to the correction coefficient. The diaphragm driving circuit 1015 adjusts the diaphragm circuit 1002 so that the target value of the diaphragm and the corrected average luminance level match.
Is driven, so that when the target value of the aperture becomes smaller, the aperture operates in the direction of closing the aperture. Normally, the diaphragm drive circuit 1015 drives the diaphragm circuit 1002 so as to match the target value of the diaphragm with the average brightness level. Therefore, when the subject is backlit, the average brightness level decreases, so the diaphragm opens, and high brightness outdoors. The part is crushed white. Therefore, the target value of the aperture is corrected by the correction coefficient so that the aperture is closed to prevent the whitening. Further, the gradation correction circuit 1006 raises the low-luminance portion and outputs the high-luminance portion as it is, so that a video signal output rich in gradation expression can be obtained on the entire screen even for a backlit subject.

As described above, according to the present embodiment, the image pickup apparatus of the present invention includes an optical system 1001, an aperture circuit 1002,
A solid-state image sensor 1003, an analog circuit 1004, an analog-digital converter (A / D converter) 1005,
A gradation correction circuit 1006, a signal processing circuit 1007, a digital / analog converter (D / A converter) 1008,
Encoder circuit 1009 and luminance signal generation circuit 1010
A maximum value detection circuit 1011 and an average value detection circuit 101
2, a weighted average circuit 1013, a comparison circuit 1014,
A diaphragm drive circuit 1015, a feature amount extraction circuit 1016,
With the configuration of the correction characteristic determination circuit 1017, the target value of the aperture is corrected by the correction coefficient determined by the correction characteristic determination circuit 1017, and the control linked to the gradation correction is performed, so that all the objects from the backlit subject to the forward-lit subject are captured. On the other hand, it is possible to obtain an output image in which gradation is not crushed, color balance is good, and gradation expression is rich in the entire area.

FIG. 13 is a block diagram showing the arrangement of an image pickup apparatus according to the fourth embodiment of the present invention. In FIG. 13, 1101 is an optical system, 1102 is a diaphragm circuit, and 1103.
Is a solid-state image sensor, 1104 is an analog circuit, 1105 is an analog / digital converter (A / D converter), 1106.
Is a gradation correction circuit, 1107 is a signal processing circuit, 1108 is a digital / analog converter (D / A converter), 1109
Is an encoder circuit, 1110 is a luminance signal generation circuit, 11
11 is a maximum value detection circuit, 1112 is an average value detection circuit, 1
Reference numeral 113 denotes a weighted average circuit, 1114 denotes a second comparison circuit, 1
Reference numeral 115 is a diaphragm drive circuit, 1116 is a feature amount extraction circuit, 1
Reference numeral 117 is a correction characteristic determination circuit, 1118 is a minimum value detection circuit, 1119 is a subtractor, and 1120 is a first comparison circuit.

The operation of the image pickup apparatus of the fourth embodiment of the present invention constructed as above will be described below.

In FIG. 13, first, the optical input is the optical system 1.
A solid-state image sensor 1103 that passes through 101 and the diaphragm circuit 1102.
To enter. From the solid-state image sensor 1103 to the analog circuit 1
The R, G, B signals are captured by the input signal 104. These R, G and B signals are converted to analog / digital converter 1
It is converted into digital data of 0 to 255 by 105. R converted into digital data of 0 to 255,
The G and B signals are luminance signal generation circuits 11 as input video signals.
10 and the gradation correction circuit 1106. Hereinafter, except the minimum value detection circuit 1118 and the subtractor 1119, the operation is the same as in the first and second embodiments. That is, the luminance generation circuit 1110 calculates the luminance signal Y from the R, G, B signals. First, the maximum value detection circuit 11 is calculated from the calculated luminance signal Y.
11 and the average value detection circuit 1112 detect the maximum value and the average value of the effective screen of one field, respectively. A weighted average circuit 1113 weights and averages the maximum value and the average value of the detected luminance signal with a weighting coefficient to obtain an average luminance level. For example, the average luminance level can be calculated by the relational expression (2). The second comparison circuit 1114 compares the obtained average brightness level with the target value of the aperture, and the aperture drive circuit 1115 drives the aperture circuit 1102 so that the average brightness level and the target value of the aperture match, thereby performing aperture control. To do.

Further, the calculated luminance signal Y is supplied to the characteristic amount extraction circuit 1116 and the gradation correction circuit 1107. The characteristic amount extraction circuit 1116 obtains the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels of the luminance signal Y, and the correction characteristic determination circuit 11
Supply to 17. The correction characteristic determination circuit 1117 determines the optimum gradation correction characteristic for the input video signal based on the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels, and outputs the correction coefficient of the gradation correction characteristic. The gradation correction circuit 1106 obtains a correction gain from the luminance signal Y and the correction coefficient. The gradation of the input video signal is corrected with this correction gain. The signal processing circuit 1107 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. This signal processed digital R,
The digital / analog converter 1108 converts the G, B signals into analog R, G, B signals. Finally, the encoder circuit 1109 converts the R, G, B signals into Y signals (luminance signals).
And C signal (color signal) and output the video signal output.

On the other hand, the operation differs from the first and second embodiments in that the maximum value detection circuit 1111 and the minimum value detection circuit 1118 calculate the maximum value and the minimum value from the brightness signal Y calculated by the brightness generation circuit 1110, respectively. To detect. The subtracter 119 subtracts the minimum value from the detected maximum value. The subtraction result is compared with a preset specified value by the first comparison circuit 1120. Based on this comparison result, the weighting coefficient of the weighted average circuit 1113 is corrected, and the aperture control linked with the gradation correction is being performed.

FIG. 14 is a characteristic diagram showing the correction value of the weighting coefficient with respect to the difference between the maximum value and the minimum value. For example, when the correction characteristic determination circuit 1117 determines that it is the gradation correction characteristic of the backlight subject, the subtraction result becomes large, and the weighting coefficient of the weighted average circuit 1113 is increased in accordance with the subtraction result as shown in FIG. The ratio of the maximum value of is increased to obtain the average brightness level. Since the diaphragm drive circuit 1115 drives the diaphragm circuit 1102 so that the target value of the diaphragm and the corrected average brightness level match, the diaphragm drive circuit 1115 operates in the direction to close the diaphragm when the average brightness level increases. Normally, the diaphragm drive circuit 1115 drives the diaphragm circuit 1102 so that the average brightness level and the target value of the diaphragm are matched, so that the average brightness level becomes small when the subject is backlit, so the diaphragm opens, and high brightness outdoors. The part is crushed. Therefore, the weighting coefficient is corrected by the subtraction result to increase the average luminance level, and the iris is closed to prevent white crushing. Further, the gradation correction circuit 1106 raises the low-luminance portion and outputs the high-luminance portion as it is, so that it is possible to obtain a video signal output rich in gradation expression on the entire screen even for a backlit subject.

As described above, according to the present embodiment, the image pickup apparatus of the present invention includes the optical system 1101, the diaphragm circuit 1102,
A solid-state image sensor 1103, an analog circuit 1104, an analog / digital converter (A / D converter) 1105, a gradation correction circuit 1106, a signal processing circuit 1107, and a digital-analog converter (D / A converter). ) 1108, encoder circuit 1109, and luminance signal generation circuit 1110
A maximum value detection circuit 1111 and an average value detection circuit 111
2, the weighted average circuit 1113, and the second comparison circuit 111
4, the diaphragm drive circuit 1115, and the feature amount extraction circuit 111
6, the correction characteristic determination circuit 1117, and the minimum value detection circuit 1
118, the subtractor 1119, and the first comparison circuit 1120.
With this configuration, the weighting coefficient is corrected by the subtraction result of the maximum value and the minimum value, and the aperture control linked to the gradation correction is performed, so that the gradation is not destroyed for all objects from the backlight subject to the forward-illumination subject. It is possible to obtain an output image with good color balance and rich gradation expression over the entire area.

FIG. 15 is a block diagram showing the arrangement of an image pickup apparatus according to the fifth embodiment of the present invention. In FIG. 15, 1201 is an optical system, 1202 is a diaphragm circuit, and 1203.
Is a solid-state image sensor, 1204 is an analog circuit, 1205 is an analog / digital converter (A / D converter), 1206
Is a gradation correction circuit, 1207 is a signal processing circuit, 1208 is a digital / analog converter (D / A converter), 1209
Is an encoder circuit, 1210 is a luminance signal generation circuit, 12
11 is a maximum value detection circuit, 1212 is an average value detection circuit, 1
213 is a weighted average circuit, 1214 is a second comparison circuit, 1
Reference numeral 215 is a diaphragm drive circuit, 1216 is a feature amount extraction circuit, and 1
Reference numeral 217 is a correction characteristic determination circuit, 1218 is a minimum value detection circuit, 1219 is a subtractor, and 1220 is a first comparison circuit.

The operation of the image pickup apparatus of the fifth embodiment of the present invention configured as above will be described below.

In FIG. 15, first, the optical input is the optical system 1.
A solid-state image sensor 1203 passing through 201 and the diaphragm circuit 1202.
To enter. From the solid-state image sensor 1203 to the analog circuit 1
The R, G, B signals are taken in by the input signal 204. These R, G and B signals are converted to analog / digital converter 1
It is converted into digital data of 0 to 255 by 205. R converted into digital data of 0 to 255,
The G and B signals are used as input video signals and the luminance signal generation circuit 12
10 and the gradation correction circuit 1206. Hereinafter, except the weighted average circuit 1213 and the second comparison circuit 1214, the operation is the same as that of the fourth embodiment. That is, the luminance signal generation circuit 1210 calculates the luminance signal Y from the R, G, B signals. First, the maximum value detection circuit 12 is calculated from the calculated luminance signal Y.
11 and the average value detection circuit 1212 detect the maximum value and the average value of the effective screen of one field, respectively. A weighted averaging circuit 1213 weights and averages the maximum value and the average value of the detected luminance signal with a weighting coefficient to obtain an average luminance level. For example, the average luminance level can be calculated by the relational expression (2). The second comparison circuit 1214 compares the obtained average brightness level with the target value of the aperture, and the aperture drive circuit 1215 drives the aperture circuit 1202 so that the average brightness level and the target value of the aperture match, thereby performing aperture control. To do.

Further, the calculated luminance signal Y is supplied to the characteristic amount extraction circuit 1216 and the gradation correction circuit 1207. The characteristic amount extraction circuit 1216 obtains the number of low luminance pixels, the number of medium luminance pixels, and the number of high luminance pixels of the luminance signal Y, and the correction characteristic determination circuit 12
Supply to 17. The correction characteristic determination circuit 1217 determines the optimum gradation correction characteristic for the input video signal based on the low luminance pixel number, the medium luminance pixel number, and the high luminance pixel number, and outputs the correction coefficient of the gradation correction characteristic. The gradation correction circuit 1206 obtains a correction gain from the luminance signal Y and the correction coefficient. The gradation of the input video signal is corrected with this correction gain. The signal processing circuit 1207 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. This signal processed digital R,
The digital / analog converter 1208 converts the G, B signals into analog R, G, B signals. Finally, the encoder circuit 1209 converts the R, G, B signals into Y signals (luminance signals).
And C signal (color signal) and output the video signal output.

On the other hand, the operation differs from that of the fourth embodiment in that
The maximum value detection circuit 1211 and the minimum value detection circuit 1218 detect the maximum value and the minimum value from the brightness signal Y calculated by the brightness generation circuit 1210. The subtractor 1219 subtracts the minimum value from the detected maximum value. The first comparison circuit 1220 compares the subtraction result with a preset specified value. Based on this comparison result, the target value of the aperture of the second comparison circuit 1214 is corrected, and the aperture control linked with the gradation correction is being performed. For example, when the correction characteristic determination circuit 1217 determines that it is the gradation correction characteristic of the backlight subject, the subtraction result is large, and the target value of the aperture of the second comparison circuit 1214 is reduced while being inversely proportional to the subtraction result. Aperture drive circuit 12
Reference numeral 15 drives the diaphragm circuit 1202 so that the target value of the diaphragm and the average brightness level coincide with each other. Therefore, when the target value of the diaphragm becomes small, the diaphragm circuit operates in the direction of closing the diaphragm. Normally, the diaphragm drive circuit 1215 drives the diaphragm circuit 1202 so that the average brightness level and the target value of the diaphragm are matched. Therefore, when the subject is backlit, the average brightness level becomes small and the diaphragm is opened, so that the high brightness portion such as outdoors is exposed. Will be crushed in white. Therefore,
Whitening is prevented by correcting the target value of the aperture with the subtraction result and closing the aperture so that the low-luminance portion is not blackened. Further, the gradation correction circuit 1206 raises the low-luminance portion and outputs the high-luminance portion as it is, so that it is possible to obtain a video signal output rich in gradation expression on the entire screen even for a backlit subject.

As described above, according to the present embodiment, the image pickup apparatus of the present invention includes an optical system 1201, an aperture circuit 1202,
A solid-state image sensor 1203, an analog circuit 1204, an analog / digital converter (A / D converter) 1205,
A gradation correction circuit 1206, a signal processing circuit 1207, a digital / analog converter (D / A converter) 1208,
Encoder circuit 1209 and luminance signal generation circuit 1210
A maximum value detection circuit 1211, and an average value detection circuit 121.
2, a weighted average circuit 1213, and a second comparison circuit 121
4, the diaphragm drive circuit 1215, and the feature amount extraction circuit 121
6, the correction characteristic determination circuit 1217, and the minimum value detection circuit 1
218, the subtractor 1219, and the first comparison circuit 1220.
With such a configuration, the target value of the aperture of the second comparison circuit 1214 is corrected according to the subtraction result of the maximum value and the minimum value, and the aperture control linked with the gradation correction is performed, so that the backlight subject and the forward-illuminated subject can be controlled. It is possible to obtain an output image in which gradation is not overwhelmed with respect to the subject, color balance is good, and gradation expression is rich in the entire area.

FIG. 16 is a block diagram showing the concrete arrangement of the image pickup apparatus according to the sixth embodiment of the present invention. In FIG. 16, reference numeral 1301 denotes an optical system, 1302 denotes a diaphragm circuit, and 13
03 is a solid-state image sensor, 1304 is an analog circuit, 130
5 is an analog / digital converter (A / D converter), 13
Reference numeral 06 is a gradation correction circuit, 1307 is a signal processing circuit, and 130.
8 is a digital / analog converter (D / A converter), 13
09 is an encoder circuit, 1310 is a luminance signal generation circuit,
Reference numeral 1311 is a block memory circuit, 1312 is a feature amount extraction circuit, 1313 is a correction characteristic determination circuit, 1314 is a one-chip microcomputer, and 1315 is an aperture drive circuit.

The operation of the image pickup apparatus of the sixth embodiment of the present invention constructed as above will be described below.

In FIG. 16, first, the optical input is the optical system 1.
A solid-state image sensor 1303 that passes through 301 and the aperture circuit 1302.
To enter. From the solid-state image sensor 1303 to the analog circuit 1
The R, G, B signals are taken in by the input signal 304. These R, G and B signals are converted to analog / digital converter 1
It is converted by 305 into digital data of 0 to 255. R converted into digital data of 0 to 255,
The G and B signals are input image signals and the luminance signal generation circuit 13
10 and the gradation correction circuit 1306. The luminance signal generation circuit 1310 calculates the luminance signal Y from the R, G, B signals. The calculated luminance signal Y is stored in the block memory circuit 13
13, a feature amount extraction circuit 1311, and a gradation correction circuit 1306
To enter. After that, the gradation correction circuit 1306, the characteristic amount extraction circuit 1311, and the correction characteristic determination circuit 1312 operate exactly as in the first and second embodiments. That is, the feature amount extraction circuit 1311 obtains the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels for the effective screen of one field. Next, the correction characteristic determination circuit 1312 determines the correction coefficient of the optimum correction characteristic for the input video signal from the low luminance pixel number, the medium luminance pixel number, and the high luminance pixel number. The determined correction coefficient is processed so as to have continuity with the gradation correction characteristic of the previous field, and the correction coefficient is set in the gradation correction circuit 1306. The gradation correction circuit 1306 performs a weighted average of the first gradation correction characteristic and the second gradation correction characteristic with a value obtained by adding the average value of the input luminance signal and the correction coefficient to obtain a correction gain. At the same time, the delay circuit adjusts the timing of the R, G, B signals to the correction gain, multiplies each of the R, G, B signals by the correction gain, and outputs the R, G, B signals whose gradation has been corrected. The signal processing circuit 1307 performs signal processing such as aperture processing on the gradation-corrected R, G, and B signals. A digital / analog converter 1308 converts the signal-processed digital R, G, B signals into analog R, G, B signals. Finally, the encoder circuit 1309 converts the R, G, B signals into Y signals (luminance signals).
And C signal (color signal) and output as a video signal output.

On the other hand, the operations different from those of the first and second embodiments are the operations of the block memory circuit 1313 and the one-chip microcomputer 1314. In the block memory circuit 1313, as shown in FIG. 3B, the effective screen of one field is divided into 7 × 7 blocks, and the average luminance of each block is obtained. The one-chip microcomputer 1314 reads the obtained average brightness of each block. The 1-chip microcomputer 1314 finds the maximum value of the average luminance of each block. Further, as shown in FIG. 3C, the central block areas 302, 30
3 is weighted and averaged to obtain the average value of the entire effective screen, which emphasizes the average brightness of the central block. The maximum value and the average value of the obtained luminance signal are weighted and averaged by the weighting coefficient to obtain the average luminance level. For example, the average luminance level can be calculated by the relational expression (2). The obtained average brightness level is compared with the target value of the aperture, and the aperture drive circuit 1315 drives the aperture circuit 1302 so that the average brightness level and the target value of the aperture match, thereby performing aperture control.

Further, the one-chip microcomputer 1314 reads the correction coefficient determined by the correction characteristic determination circuit 1312. The weighting coefficient is corrected by the read correction coefficient, and the aperture control is performed in conjunction with the gradation correction. For example, when the correction characteristic determination circuit 1312 determines that it is the gradation correction characteristic of the backlight subject, the weighting coefficient of the weighted average is increased according to the correction coefficient as shown in FIG. 8, and the ratio of the maximum value of the luminance signal is increased. Then, the average brightness level is obtained. Aperture drive circuit 13
Reference numeral 15 drives the diaphragm circuit 1302 so that the target value of the diaphragm and the corrected average brightness level match, so that when the average brightness level increases, the diaphragm circuit 130 operates in the direction of closing the diaphragm. Normally, the diaphragm drive circuit 1315 drives the diaphragm circuit 1302 so that the diaphragm is adjusted to the average brightness level. Therefore, when the subject is backlit, the average brightness level decreases and the diaphragm opens, and the high-brightness portion such as outdoors is crushed. Resulting in. Therefore, by correcting the weighting coefficient with the correction coefficient, the average luminance level is increased, and by opening the diaphragm, whiteout is prevented. Further, the gradation correction circuit 1306 raises the low-luminance portion and outputs the high-luminance portion as it is, so that it is possible to obtain a video signal output rich in gradation expression on the entire screen even for a backlit subject.

Alternatively, another program operation of the one-chip microcomputer 1314 will be described. The correction characteristic determination circuit 13
The correction coefficient determined by 12 is read by the one-chip microcomputer 1314. The target value of the aperture is corrected by the read correction coefficient, and the aperture control linked with the gradation correction is performed. For example, when the correction characteristic determination circuit 1312 determines that the gradation correction characteristic of the backlight subject is set, the target value of the aperture is reduced while being proportional to the correction coefficient. Since the diaphragm drive circuit 1315 drives the diaphragm circuit 1302 so that the target value of the diaphragm and the corrected average luminance level match, when the target value of the diaphragm becomes small, the diaphragm drive circuit 1315 operates in the direction to close the diaphragm. Normally, the diaphragm drive circuit 1315 drives the diaphragm circuit 1302 so that the diaphragm is adjusted to the average brightness level. Therefore, when the subject is backlit, the average brightness level decreases and the diaphragm opens, and the high-brightness portion such as outdoors is crushed. Resulting in. Therefore, whitening is prevented by correcting the target value of the aperture with the correction coefficient and opening the aperture. Further, the gradation correction circuit 1306 raises the low-luminance portion and outputs the high-luminance portion as it is, so that it is possible to obtain a video signal output rich in gradation expression on the entire screen even for a backlit subject.

As described above, according to the present embodiment, the image pickup apparatus of the present invention has an optical system 1301, a diaphragm circuit 1302, a solid-state image pickup device 1303, an analog circuit 1304, an analog / analog circuit.
Digital converter (A / D converter) 1305, gradation correction circuit 1306, signal processing circuit 1307, digital / analog converter (D / A converter) 1308, encoder circuit 1
309, luminance signal generation circuit 1310, feature amount extraction circuit 1
311, a correction characteristic determination circuit 1312, a block memory circuit 1313, a one-chip microcomputer 1314, and an aperture drive circuit 1315 perform gradation correction linked with aperture control by a correction coefficient, so that all subjects from a backlit subject to a forward-illuminated subject can be obtained. It is possible to obtain an output image in which gradation is not overwhelmed with respect to the subject, color balance is good, and gradation expression is rich in the entire area.

Further, when the input signal is large, the gradation correction characteristic is set so that the input signal becomes an output signal almost as it is, so that the place where the gradation of the high-brightness portion has been destroyed by the conventional auto knee control can be reproduced clearly. can do.

Further, the gradation correction characteristic is adaptively changed on a pixel-by-pixel basis by the brightness average value Ya to perform the gradation correction, so that the gradation correction is performed so as to maintain the contrast even if the inclination of the correction gain is small. An output signal rich in gradation expression can be obtained.

Further, even if a moving image is corrected, a natural gradation correction image can be obtained. FIG. 17 is a block diagram showing a specific configuration of the image pickup apparatus according to the seventh embodiment of the present invention. In FIG. 17, 1401 is an optical system, 1402 is a diaphragm circuit, 1403 is a solid-state image sensor, 1404 is an analog circuit, 1405 is an analog / digital converter (A / D converter), 1406 is a gradation correction circuit, and 1407 is a signal. A processing circuit, 1408 is a digital / analog converter (D / A converter), 1409 is an encoder circuit, 1410 is a luminance signal generation circuit, 1411 is a feature amount extraction circuit, 1412 is a correction characteristic determination circuit, 1413 is a block memory circuit, 14
Reference numeral 14 is a one-chip microcomputer, and 1415 is a diaphragm drive circuit.

The operation of the image pickup apparatus of the seventh embodiment of the present invention constructed as above will be described below.

In FIG. 17, first, the optical input is the optical system 1
A solid-state image sensor 1403 that passes through 401 and the diaphragm circuit 1402.
To enter. From the solid-state image sensor 1403 to the analog circuit 1
The R, G, B signals are taken in by the input video signal 404. These R, G and B signals are converted to analog / digital converter 1
It is converted into digital data of 0 to 255 by 405. R converted into digital data of 0 to 255,
The G and B signals are input image signals and the luminance signal generation circuit 14
10 and the gradation correction circuit 1406. The luminance signal generation circuit 1410 calculates the luminance signal Y from the R, G, B signals. The calculated luminance signal Y is stored in the block memory circuit 14
13, a feature amount extraction circuit 1411 and a gradation correction circuit 1406
To enter. Hereinafter, the gradation correction circuit 1406, the characteristic amount extraction circuit 1411, and the correction characteristic determination circuit 1412 operate in exactly the same manner as in the first and second embodiments. That is, the feature amount extraction circuit 1411 obtains the number of low-luminance pixels, the number of medium-luminance pixels, and the number of high-luminance pixels for the effective screen of one field. Next, the correction characteristic determination circuit 1412 determines the correction coefficient of the optimum correction characteristic for the input video signal from the low luminance pixel number, the medium luminance pixel number, and the high luminance pixel number. The determined correction coefficient is processed so as to have continuity with the gradation correction characteristic of the previous field, and the correction coefficient is set in the gradation correction circuit 1406. The gradation correction circuit 1406 performs a weighted average of the first gradation correction characteristic and the second gradation correction characteristic with a value obtained by adding the average value of the input luminance signal and the correction coefficient to obtain a correction gain. At the same time, R,
Adjust the timing of the G and B signals to the correction gain, and
Each of the G and B signals is multiplied by a correction gain, and the tone-corrected R, G and B signals are output. This gradation corrected R,
The signal processing circuit 1407 performs signal processing such as aperture processing on the G and B signals. This signal processed digital R, G,
The digital / analog converter 1408 converts the B signal into analog R, G, B signals. Finally, encoder circuit 1
409 converts the R, G, B signals into a Y signal (luminance signal) and a C signal (color signal) and outputs them as a video signal output.

On the other hand, the operation differs from that of the first embodiment in that the block memory circuit 1413 and the one-chip microcomputer 1414 are
Is the operation. In the block memory circuit 1413, FIG.
As shown in (b) of, the effective screen of 1 field is 7 ×
It is divided into 7 blocks and the average luminance of each block is obtained. The average brightness of each block obtained is calculated by 1-chip microcomputer 1
414 reads. The one-chip microcomputer 1414 finds the maximum and minimum values of the average brightness of each block. See also FIG.
As shown in (c) of FIG.
03 is weighted and averaged to obtain the average value of the entire effective screen with emphasis on the average brightness of the central block. The maximum value and the average value of the obtained luminance signal are weighted and averaged by the weighting coefficient to obtain the average luminance level. For example, the average luminance level can be calculated by the relational expression (2). The obtained average brightness level is compared with the target value of the aperture, and the aperture drive circuit 1415 drives the aperture circuit 1402 so that the average brightness level and the target value of the aperture match, thereby performing aperture control.

Further, the difference between the maximum value and the minimum value of the obtained average luminance of each block is obtained. The weighting coefficient is corrected based on the difference between the maximum value and the minimum value, and the aperture control linked with the gradation correction is performed. For example, in the case of a backlit subject, the difference between the maximum value and the minimum value becomes large, and the weighting coefficient is increased according to the difference between the maximum value and the minimum value as shown in FIG. Increase to obtain the average brightness level. Since the diaphragm drive circuit 1415 drives the diaphragm circuit 1402 so that the target value of the diaphragm and the corrected average brightness level match, the diaphragm drive circuit 1415 operates in the direction to close the diaphragm when the average brightness level increases. Normally, the diaphragm drive circuit 1415 drives the diaphragm circuit 1402 so that the diaphragm is adjusted to the average brightness level. Therefore, when the subject is backlit, the average brightness level becomes small and the diaphragm opens, and the high-brightness portion such as outdoors is crushed. Resulting in. Therefore, the average luminance level is increased by correcting the weighting coefficient with the difference between the maximum value and the minimum value,
Preventing whiteout by closing the aperture.
Further, the gradation correction circuit 1406 raises the low-brightness portion and outputs the high-brightness portion as it is, so that it is possible to obtain a video signal output rich in gradation expression on the entire screen even for a backlit subject.

Alternatively, another program operation of the one-chip microcomputer 1414 will be described. The difference between the maximum value and the minimum value of the calculated average luminance of each block is calculated. The target value of the diaphragm is corrected by the difference between the maximum value and the minimum value, and the diaphragm control is performed in conjunction with the gradation correction. For example, in the case of a backlit subject, the difference between the maximum value and the minimum value becomes large, and the target value of the diaphragm is reduced while making the difference inversely proportional to the difference between the maximum value and the minimum value. Since the diaphragm drive circuit 1415 drives the diaphragm circuit 1402 so that the target value of the diaphragm and the corrected average luminance level match, when the target value of the diaphragm becomes small, the diaphragm driving circuit 1415 operates in the direction to close the diaphragm. Normally, the diaphragm drive circuit 1415 drives the diaphragm circuit 1402 so that the diaphragm is adjusted to the average brightness level. Therefore, when the subject is backlit, the average brightness level becomes small and the diaphragm opens, and the high-brightness portion such as outdoors is crushed. Resulting in. Therefore, whitening is prevented by correcting the target value of the aperture with the difference between the maximum value and the minimum value and closing the aperture. Further, the gradation correction circuit 1406 raises the low-brightness portion and outputs the high-brightness portion as it is, so that it is possible to obtain a video signal output rich in gradation expression on the entire screen even for a backlit subject.

As described above, according to the present embodiment, the image pickup apparatus of the present invention has an optical system 1401, an aperture circuit 1402, a solid-state image pickup element 1403, an analog circuit 1404, an analog / analog circuit.
Digital converter (A / D converter) 1405, gradation correction circuit 1406, signal processing circuit 1407, digital / analog converter (D / A converter) 1408, encoder circuit 1
409, luminance signal generation circuit 1410, feature amount extraction circuit 1
411, the correction characteristic determination circuit 1412, the block memory circuit 1413, the one-chip microcomputer 1414, and the diaphragm drive circuit 1415 perform gradation correction linked to the diaphragm control, so that all objects from a backlit subject to a forward-lit subject can be detected. It is possible to obtain an output image in which the gradation is not destroyed and the color balance is good and the gradation expression is rich over the entire area.

Further, when the input signal is large, the gradation correction characteristic is set so that the input signal becomes the output signal as it is, so that a place where the gradation of the high-brightness portion has been destroyed by the conventional auto knee control can be reproduced clearly. can do.

Further, the gradation correction characteristic is adaptively changed for each pixel according to the average luminance value Ya to perform the gradation correction, so that the gradation correction is performed so as to maintain the contrast even if the inclination of the correction gain is small. An output signal rich in gradation expression can be obtained.

Further, even if a moving image is corrected, a natural gradation correction image can be obtained. 18, FIG. 19, FIG. 20, and FIG.
FIG. 1 is a block diagram showing the arrangement of an image pickup apparatus according to the eighth, ninth, tenth, and eleventh embodiments of the present invention. 18-
In FIG. 21, 1701 is an optical system, 1702 is a diaphragm circuit, 1703 is a solid-state image sensor, 1704 is an analog circuit, 1705 is an analog / digital converter (A / D converter), 1706 is a gradation correction circuit, and 1707 is a signal. A processing circuit, 1708 is a digital / analog converter (D / A converter), 1709 is an encoder circuit, 1710 is a maximum value detection circuit, 1711 is an average value detection circuit, 1712 is a weighted average circuit, 1713 is a comparison circuit, and 1714 is A diaphragm drive circuit, 1715 is a feature amount extraction circuit, 1716 is a correction characteristic determination circuit, 1717 is a minimum value detection circuit, and 1718 is a subtractor.

The operation of the image pickup apparatus of the eighth to eleventh embodiments of the present invention configured as above will be described below.

The image pickup devices of the eighth to eleventh embodiments are the first, second, third and fourth, except that the input video signal is a signal which has generated a luminance signal and a color signal and the luminance generation circuit is eliminated. , Operates exactly as in the fifth embodiment. That is, the correction characteristic determination circuit 1716 determines the correction coefficient based on the characteristic amount obtained from the input image signal by the characteristic amount extraction circuit 1715, and the aperture control is corrected by the correction coefficient so as to be linked with the gradation correction. The gradation correction circuit 17 according to the coefficient
Reference numeral 06 automatically generates the optimum gradation correction characteristic to perform gradation correction. By performing gradation correction linked to aperture control with a correction coefficient in this way, it is possible to prevent blackout and whiteout with a simple configuration, and provide rich gradation expression over the entire screen from normal-light subjects to strong backlight subjects. An output image can be obtained. Moreover, since the gradation correction characteristics can be changed in conjunction with each other, natural gradation correction can be performed on a moving image.

Alternatively, the correction characteristic determination circuit 17 is determined by the characteristic amount obtained from the input video signal by the characteristic amount extraction circuit 1715.
16 automatically determines the optimum gradation correction characteristic, and the gradation correction circuit 1706 performs gradation correction. At the same time, the subtractor 1718
Calculates the contrast difference from the maximum value and the minimum value of the input video signal, and corrects the aperture control by interlocking with the gradation correction based on this contrast difference. In this way, by performing gradation correction linked with aperture control by contrast difference,
With a simple configuration, it is possible to prevent an underexposure and underexposure, and obtain an output image with rich gradation expression over the entire screen from a normal-light subject to a strong backlight subject. In addition, since the gradation correction characteristic can be continuously changed, natural gradation correction can be performed on a moving image.

As described above, according to this embodiment, the image pickup apparatus of the present invention includes an optical system 1701, an aperture circuit 1702,
A solid-state image sensor 1703, an analog circuit 1704, an analog / digital converter (A / D converter) 1705,
A gradation correction circuit 1706, a signal processing circuit 1707, a digital / analog converter (D / A converter) 1708,
Encoder circuit 1709 and maximum value detection circuit 1710
An average value detection circuit 1711 and a weighted average circuit 1712
A second comparison circuit 1713 and a diaphragm drive circuit 1714.
A characteristic amount extraction circuit 1715 and a correction characteristic determination circuit 17
16, a minimum value detection circuit 1717, and a subtractor 1718 are used to perform aperture control in conjunction with gradation correction so that gradations are not destroyed for any subject from backlight subjects to forward-illumination subjects, and color balance is maintained. It is possible to obtain an output image with a good gradation expression over a wide range.

In this embodiment, the solid-state image pickup device has been described as one block, but the number of the solid-state image pickup device may be one or plural.

In this embodiment, the operation of the exposure control circuit has been described as the diaphragm circuit, but the same effect can be obtained as long as the exposure control circuit can control the exposure amount of the electronic shutter of the solid-state image pickup device. it can.

Although the R, G, B signals are used as the input video signals in this embodiment, the luminance signals, the color difference signals, the composite signals, and the luminance signals are generated instead of the R, G, B signals. The same effect can be obtained by using this signal as the input video signal.

In the present embodiment, the weighted average of the maximum value and the average value was performed and the aperture control was performed in the direction in which the result of the weighted average coincides with the target value of the aperture. The same effect can be obtained even if the difference result with respect to the target value is calculated, weighted averaging is performed, and aperture control is performed in a direction in which the weighted average result becomes smaller. At this time, the maximum target value is corrected by the correction coefficient.

In the present embodiment, the gradation correction means multiplies each of the input video signals by the correction gain to perform the smooth correction, but instead of the correction gain (Y '/ Y), the correction value (Y The same effect can be obtained by adding'-Y) to each of the input video signals. The same effect can be obtained by combining the result obtained by multiplying the input video signal by the correction gain (Y '/ Y) and the result obtained by adding the correction value (Y'-Y) to the input video signal.

In the present embodiment, the input video signal has been described by analog-to-digital conversion into 8 bits, but the quantization bit number may be another value, and the processing bit number of the gradation correction circuit etc. It can be configured according to the number of digitized bits.

In this embodiment, the feature quantity extraction circuit outputs the number of pixels of three brightness levels, but the threshold value of each level may be different, or the number of levels may not be three. .

In the present embodiment, the feature quantity extraction circuit counts the number of pixels for an effective screen having one horizontal pixel number of 448 pixels and 224 lines. However, the counted number of pixels may be different, or a signal indicating the number of pixels. The number of bits may be any number as long as the characteristics of the input image are known.

In the present embodiment, the correction characteristic determination circuit discriminates the input image by using the luminance histogram as the characteristic amount. However, instead of the luminance histogram, other characteristic amounts, for example, R, G, and B signals, respectively. Histogram or any one of the histogram or the effective screen of image data is divided into blocks, and the luminance signal, RGB signal, maximum value, average value, minimum value, etc. of the color difference signals of each block are used as the characteristic amount, and the image is classified as a class. The method is not limited to this method as long as the feature amount can be divided.

In this embodiment, the ROM table is used as the correction characteristic determining circuit, but the gradation correction characteristic is determined by discriminating the image, such as the method using the neural network, the method using the fuzzy control, the method using the template matching, or the like. The method is not limited to one as long as it can determine.

Although the signal processing circuit is arranged after the gradation correction circuit in this embodiment, the same effect can be obtained by arranging the signal processing circuit in reverse.

[0113]

As described above, the image pickup apparatus of the present invention determines the correction coefficient based on the feature amount obtained from the input video signal,
With this correction coefficient, the aperture control is corrected so as to be linked to the gradation correction, and at the same time, the optimum gradation correction characteristic is automatically determined by this correction coefficient and the gradation correction is performed. In this way, by performing gradation correction linked to aperture control with a correction coefficient, it is possible to prevent blackout and whiteout with a simple configuration,
It is possible to obtain an output image with rich gradation expression over the entire screen from a normal light subject to a strong backlight subject. Also,
Since the gradation correction characteristics can be changed continuously,
Natural gradation correction can be performed on a moving image.

Further, the image pickup apparatus of the present invention automatically determines the optimum gradation correction characteristic by performing the gradation correction by discriminating the input image based on the characteristic amount obtained from the input video signal. At the same time, a contrast difference is obtained from the maximum value and the minimum value of the input video signal, and the aperture control is corrected by the contrast difference so as to be linked with the gradation correction. In this way, by performing gradation correction linked to aperture control by contrast difference, it is possible to prevent blackout and whiteout with a simple configuration and to provide rich gradation expression over the entire screen from normal-light subjects to strong backlight subjects. An output image can be obtained. In addition, since the gradation correction characteristic can be continuously changed, natural gradation correction can be performed on a moving image.

Further, the image pickup apparatus of the present invention obtains the correction gain by weighted averaging the first gradation correction characteristic and the second gradation correction characteristic by using the average value Ya of the input video signal.
If the brightness in the vicinity is high, the brightness is corrected low, if the brightness in the vicinity is low, the brightness is corrected high, and the gradation is corrected so that the contrast is maintained even if the gradation correction gain is small. A toned image can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image pickup apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration of a gradation correction circuit 106 according to the first embodiment.

FIG. 3 is an explanatory diagram showing a 1-field image of an input video signal in the first embodiment.

FIG. 4 is an explanatory diagram showing a luminance histogram in the first embodiment.

FIG. 5 is a characteristic amount extraction circuit 116 according to the first embodiment.
Block diagram showing the internal configuration of the

FIG. 6 is a correction characteristic determination circuit 11 according to the first embodiment.
Block diagram showing the internal configuration of 7.

FIG. 7 is a characteristic diagram showing a gradation correction characteristic in the embodiment of the present invention.

FIG. 8 is a characteristic diagram showing a correction coefficient and a correction value for a subtraction result of the maximum value and the minimum value in the embodiment of the present invention.

FIG. 9 is a block diagram showing an internal configuration of a gradation correction circuit 106 in an image pickup apparatus according to a second embodiment of the present invention.

FIG. 10 is a characteristic diagram showing input / output characteristics of gradation correction according to the second embodiment.

FIG. 11 is a gradation correction circuit according to the second embodiment.
Block diagram showing the detailed internal structure of

FIG. 12 is a block diagram showing the arrangement of an image pickup apparatus according to the third embodiment of the present invention.

FIG. 13 is a block diagram showing the arrangement of an image pickup apparatus according to the fourth embodiment of the present invention.

FIG. 14 is a characteristic diagram showing a correction coefficient and a correction value for a subtraction result of the maximum value and the minimum value in the fourth embodiment.

FIG. 15 is a block diagram showing the arrangement of an image pickup apparatus according to the fifth embodiment of the present invention.

FIG. 16 is a block diagram showing a specific configuration of an image pickup apparatus according to a sixth embodiment of the present invention.

FIG. 17 is a block diagram showing a specific configuration of an image pickup apparatus according to a seventh embodiment of the present invention.

FIG. 18 is a block diagram showing the arrangement of an image pickup apparatus according to an eighth embodiment of the present invention.

FIG. 19 is a block diagram showing the arrangement of an image pickup apparatus according to a ninth embodiment of the present invention.

FIG. 20 is a block diagram showing the arrangement of an image pickup apparatus according to the tenth embodiment of the present invention.

FIG. 21 is a block diagram showing the arrangement of an image pickup apparatus according to an eleventh embodiment of the present invention.

FIG. 22 is a block diagram showing a configuration of an image pickup apparatus in a first conventional example of the present invention.

FIG. 23 is a block diagram showing a configuration of an image pickup apparatus in a second conventional example of the present invention.

[Explanation of symbols]

 Reference Signs List 101 optical system 102 diaphragm circuit 103 solid-state image sensor 104 analog circuit 106 gradation correction circuit 110 luminance signal generation circuit 111 maximum value detection circuit 112 average value detection circuit 113 weighted average circuit 114 second comparison circuit 115 diaphragm drive circuit 116 feature amount Extraction circuit 117 Correction characteristic determination circuit 201 First gradation correction characteristic circuit 202 Second gradation correction characteristic circuit 203 Adder 204 Weighted average circuit 205 Delay circuit 206 Multiplier 207 LPF 1118, 1218 Minimum value detection circuit 1119, 1219 Subtractors 1120 and 1220 First comparison circuit

Claims (19)

[Claims] 1. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a maximum value detection circuit for detecting a maximum value of an output video signal of the image pickup device, and an output video signal of the image pickup device. An average value detection circuit that detects an average value, a characteristic amount extraction circuit that obtains a characteristic amount of the output image signal of the image sensor, and a gradation correction characteristic that should be corrected based on the characteristic amount that the characteristic amount extraction circuit extracts. A correction characteristic determination circuit that determines and outputs a correction coefficient, corrects the weighting coefficient by the correction coefficient, and displays the maximum value detected by the maximum value detection circuit and the average value detected by the average value detection circuit by the corrected weighting coefficient. A weighted average circuit for weighted averaging, a comparison circuit for comparing the output result of the weighted average circuit with the exposure amount target value, and the output result of the comparison circuit and the exposure amount target value are the same. A control signal generation circuit that controls the exposure control circuit, and a gradation correction unit that corrects each of the output video signals of the image sensor with the gradation correction characteristic determined by the correction characteristic determination circuit, An image pickup apparatus, wherein an output video signal whose gradation is corrected by a gradation correction means is obtained. 2. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a maximum value detection circuit for detecting a maximum value of an output video signal of the image pickup device, and an output video signal of the image pickup device. An average value detection circuit that detects an average value, a characteristic amount extraction circuit that obtains a characteristic amount of the output image signal of the image sensor, and a gradation correction characteristic that should be corrected based on the characteristic amount that the characteristic amount extraction circuit extracts. A correction characteristic determination circuit that determines and outputs a correction coefficient, a weighted average circuit that performs a weighted average of the maximum value detected by the maximum value detection circuit and the average value detected by the average value detection circuit by a weighting coefficient, and the correction coefficient A comparison circuit that corrects the exposure amount target value and compares the corrected exposure amount target value and the output result of the weighted average circuit, and the output result of the comparison circuit is such that the output result of the weighted average circuit and the exposure amount target value are equal. A control signal generation circuit for controlling the exposure control circuit, and a gradation correction means for correcting each of the output video signals of the image sensor with the gradation correction characteristic determined by the correction characteristic determination circuit, An image pickup device, characterized in that the gradation-corrected output video signal is obtained by the gradation correction means. 3. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a luminance signal generation circuit for separating or synthesizing a luminance signal from an output video signal of the image pickup device, and a maximum value of the luminance signal. A maximum value detection circuit for detecting the average value of the luminance signal, an average value detection circuit for detecting the average value of the luminance signal, a feature amount extraction circuit for obtaining the histogram of the luminance signal, and a correction based on the histogram obtained by the feature amount extraction circuit A correction characteristic determination circuit that determines a gradation correction characteristic to be output and outputs a correction coefficient, a weighting coefficient is corrected by the correction coefficient, and the maximum value and the average value detected by the maximum value detection circuit are corrected by the corrected weighting coefficient. A weighted average circuit for weighted averaging the average value detected by the circuit; a comparison circuit for comparing the output result of the weighted average circuit with the exposure target value; and an output result of the comparison circuit. A control signal generation circuit that controls the exposure control circuit so that the output result of the weighted average circuit and the exposure amount target value match, and the output video signal of the image pickup device with the gradation correction characteristic determined by the correction characteristic determination circuit. And a gradation correction unit that corrects each of the above, and obtains an output video signal whose gradation is corrected by the gradation correction unit. 4. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a luminance signal generation circuit for separating or synthesizing a luminance signal from an output video signal of the image pickup device, and a maximum value of the luminance signal. A maximum value detection circuit for detecting the average value of the luminance signal, an average value detection circuit for detecting the average value of the luminance signal, a feature amount extraction circuit for obtaining the histogram of the luminance signal, and a correction based on the histogram obtained by the feature amount extraction circuit A correction characteristic determination circuit that determines a gradation correction characteristic to be output and outputs a correction coefficient, and a weighted average that performs a weighted average of the maximum value detected by the maximum value detection circuit and the average value detected by the average value detection circuit by a weighting coefficient. A circuit, a comparison circuit that corrects the exposure target value by the correction coefficient, and compares the corrected exposure target value with the output result of the weighted average circuit, and the output result of the comparator A control signal generation circuit that controls the exposure control circuit so that the output result of the weighted average circuit and the exposure target value match, and the output image of the image pickup device with the gradation correction characteristic determined by the correction characteristic determination circuit. An image pickup apparatus comprising: a gradation correction unit that corrects each of the signals, and obtains the gradation-corrected output video signal from the gradation correction unit. 5. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a maximum value detection circuit for detecting a maximum value of an output video signal of the image pickup device, and an output video signal of the image pickup device. An average value detection circuit that detects an average value, a minimum value detection circuit that detects the minimum value of the output video signal of the image sensor, and a minimum value that the minimum value detection circuit detects from the maximum value that the maximum value detection circuit detects. A subtraction circuit for subtracting a value, a first comparison circuit for comparing the output result of the subtraction circuit with a specified value and outputting a correction value, a weighting coefficient is corrected by the correction value, and the maximum value is corrected by the corrected weighting coefficient. A weighted average circuit for weighted averaging the maximum value detected by the detection circuit and the average value detected by the average value detection circuit; a second comparison circuit for comparing the output result of the weighted average circuit with the exposure target value; Second ratio A control signal generation circuit that controls the exposure control circuit so that the output result of the weighted average circuit and the exposure amount target value match with the output result of the comparison circuit, and a feature amount that obtains the feature amount of the image signal output from the image sensor. An extraction circuit, a correction characteristic determination circuit for determining a gradation correction characteristic to be corrected based on the characteristic amount extracted by the characteristic amount extraction circuit, and outputting a correction coefficient, and a gradation correction characteristic determined by the correction characteristic determination circuit 2. An image pickup apparatus comprising: a gradation correction unit that corrects each of the output video signals of the image pickup device, and obtains the gradation-corrected output video signal from the gradation correction unit. 6. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a maximum value detection circuit for detecting a maximum value of an output video signal of the image pickup device, and an output video signal of the image pickup device. An average value detection circuit that detects an average value, a minimum value detection circuit that detects the minimum value of the output video signal of the image sensor, and a minimum value that the minimum value detection circuit detects from the maximum value that the maximum value detection circuit detects. A subtraction circuit that subtracts a value; a first comparison circuit that compares the output result of the subtraction circuit with a specified value and outputs a correction value; a maximum value detected by the maximum value detection circuit and an average value detection circuit A weighted averaging circuit for weighted averaging the averaged values with a weighting coefficient; a second step of correcting the exposure amount target value with the correction value and comparing the corrected exposure amount target value with the output result of the weighted average circuit;
And a control signal generation circuit for controlling the exposure control circuit so that the output result of the weighted average circuit and the exposure amount target value match the output result of the second comparison circuit, and the output of the image sensor. A characteristic amount extraction circuit for obtaining a characteristic amount of a video signal; a correction characteristic determination circuit for determining a gradation correction characteristic to be corrected based on the characteristic amount extracted by the characteristic amount extraction circuit and outputting a correction coefficient; A gradation correction unit that corrects each of the output video signals of the image pickup device with the gradation correction characteristics determined by the determination circuit, and the gradation-corrected output video signal is obtained by the gradation correction unit. Image pickup device. 7. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a luminance signal generation circuit for separating or synthesizing a luminance signal from an output video signal of the image pickup device, and a maximum value of the luminance signal. A maximum value detection circuit for detecting, an average value detection circuit for detecting an average value of the luminance signal, a minimum value detection circuit for detecting a minimum value of the luminance signal, and a maximum value detected by the maximum value detection circuit. A subtraction circuit that subtracts the minimum value detected by the minimum value detection circuit, a first comparison circuit that compares the output result of the subtraction circuit with a specified value and outputs a correction value, and a weighting coefficient is corrected by the correction value. A weighted average circuit that performs a weighted average of the maximum value detected by the maximum value detection circuit and the average value detected by the average value detection circuit by a corrected weighting coefficient; and an output result of the weighted average circuit and an exposure amount target value. A second comparison circuit for comparing; a control signal generation circuit for controlling the exposure control circuit so that the output result of the second comparison circuit and the exposure amount target value match the output result of the weighted average circuit; A characteristic amount extraction circuit for obtaining a histogram of a luminance signal, a correction characteristic determination circuit for determining a gradation correction characteristic to be corrected based on the histogram obtained by the characteristic amount extraction circuit, and outputting a correction coefficient, the correction characteristic determination circuit And a gradation correction unit that corrects each of the output video signals of the image pickup device with the gradation correction characteristics determined by the above, and the gradation-corrected output video signal is obtained by the gradation correction unit. Imaging device. 8. An image pickup device, an exposure control circuit for controlling an exposure amount of the image pickup device, a luminance signal generation circuit for separating or synthesizing a luminance signal from an output video signal of the image pickup device, and a maximum value of the luminance signal. A maximum value detection circuit for detecting, an average value detection circuit for detecting an average value of the luminance signal, a minimum value detection circuit for detecting a minimum value of the luminance signal, and a maximum value detected by the maximum value detection circuit. A subtraction circuit that subtracts the minimum value detected by the minimum value detection circuit, a first comparison circuit that compares the output result of the subtraction circuit with a specified value and outputs a correction value, and a maximum value detected by the maximum value detection circuit Value and the average value detected by the average value detection circuit are weighted and averaged by a weighting coefficient, the exposure amount target value is corrected by the correction value, and the corrected exposure amount target value and the output result of the weighted average circuit are corrected. Second to compare the fruits
And a control signal generation circuit that controls the exposure control circuit so that the output result of the weighted average circuit and the exposure target value match the output result of the second comparison circuit, and a histogram of the brightness signal. A characteristic amount extraction circuit that determines a gradation correction characteristic to be corrected based on the histogram obtained by the characteristic amount extraction circuit, and a correction characteristic determination circuit that outputs a correction coefficient; and a level determined by the correction characteristic determination circuit. An image pickup apparatus comprising: a gradation correction unit that corrects each of the output video signals of the image pickup device with a tone correction characteristic, and obtains the gradation-corrected output video signal from the gradation correction unit. 9. The image pickup apparatus according to claim 1, wherein the number of image pickup elements is one or more. 10. A first gradation correction characteristic circuit in which the gradation correction means generates a first gradation correction characteristic from an output video signal of the image sensor, and a second gradation from the output video signal of the image sensor. A second gradation correction characteristic circuit for generating a correction characteristic; an adder for adding the output video signal of the image sensor and the correction coefficient determined by the correction characteristic determination circuit; and an output signal of the adder for the first gradation correction characteristic circuit. A weighted averaging circuit that outputs a correction gain by performing a weighted average of the gradation correction characteristic and the second gradation correction characteristic, and corrects each of the output video signals of the image sensor by the correction gain obtained by the weighted average circuit. The imaging device according to claim 1, 2, 5, or 6, which has a configuration. 11. A first gradation correction characteristic circuit, wherein gradation correction means generates a first gradation correction characteristic from an output video signal of the image pickup device, and a second gradation from the output video signal of the image pickup device. A second gradation correction characteristic circuit that generates a correction characteristic, an average value detection circuit that obtains an average value of the output video signal of the image pickup device, and the correction coefficient determined by the average value and the correction characteristic determination circuit are added. An adder, a weighted average circuit that outputs a correction gain by performing a weighted average of the first gradation correction characteristic and the second gradation correction characteristic according to the output signal of the adder, and calculates the weighted average circuit. 7. The image pickup apparatus according to claim 1, 2, 5, or 6, wherein each of the output video signals of the image pickup element is corrected by a correction gain. 12. The weighted averaging circuit corrects the weighting coefficient of the maximum value in proportion to the correction coefficient so as to increase the weighted coefficient, and weighted averages the maximum value and the average value by the corrected weighting coefficient. Item 1. The imaging device according to Item 1 or 3. 13. The comparison circuit corrects the exposure amount target value in proportion to the correction coefficient so as to reduce it, and compares the corrected exposure amount target value with the output result of the weighted average circuit. The imaging device according to claim 2 or 4. 14. A first gradation correction characteristic circuit in which the gradation correction means generates a first gradation correction characteristic from a luminance signal, and a second gradation correction characteristic circuit in which a second gradation correction characteristic is generated from the luminance signal. A gradation correction characteristic circuit; an adder for adding the correction coefficient determined by the luminance signal and the correction characteristic determination circuit; and an output signal of the adder for the first gradation correction characteristic and the second gradation correction. The weighted average circuit for weighting and averaging the characteristics to output a correction gain, and the correction gain obtained by the weighted average circuit for correcting each of the output video signals of the image sensor. The imaging device according to 4, 7, or 8. 15. A first gradation correction characteristic circuit in which the gradation correction unit generates a first gradation correction characteristic from a luminance signal, and a second gradation correction characteristic circuit in which a second gradation correction characteristic is generated from the luminance signal. A gradation correction characteristic circuit, an average value detection circuit that obtains an average value of the luminance signal, an adder that adds the correction coefficient determined by the average value and the correction characteristic determination circuit, and an output signal of the adder, A weighted average circuit that outputs a correction gain by performing a weighted average of the first gradation correction characteristic and the second gradation correction characteristic, and outputs each of the image signals output from the image sensor by the correction gain obtained by the weighted average circuit. The image pickup apparatus according to claim 3, 4, 7, or 8, wherein the image pickup apparatus is configured to correct. 16. The weighted averaging circuit corrects the weighting coefficient of the maximum value in proportion to the correction value so as to increase the weighted coefficient, and the weighted average of the maximum value and the average value is corrected by the corrected weighting coefficient. Item 5. The imaging device according to item 5 or 7. 17. A second comparison circuit corrects the exposure amount target value in proportion to the correction value so as to reduce it, and compares the corrected exposure amount target value with the output result of the weighted average circuit. The imaging device according to claim 6 or 8. 18. The third gradation correction characteristic Y1 of the input video signal Y is 3 in the form of Y1 = {1 / a ² · (Y−a) ³ + a}.
16. The image pickup device according to claim 10, 11, 14 or 15, wherein the second gradation correction characteristic Y2 follows a linear straight line in the form of Y2 = bY according to the following curve. 19. A gradation correction means, an average value detection circuit for obtaining an average value Ya of an input video signal Y, a first adder for adding the average value Ya and a correction coefficient, and an output of the first adder. A clip circuit for clipping the signal at a value of "0" and the maximum value that the input video signal Y can take, and the input video signal Y
A second adder for adding 3 to output Y and a first multiplier for squaring the input video signal Y and outputting Y ² .
A third adder for adding a constant to the output signal of the first multiplier, a first subtractor for subtracting the output signal of the second adder from the output signal of the third adder, and the output of the clip circuit A second subtractor for subtracting a signal from the maximum possible value of the input video signal Y, a second multiplier for multiplying an output signal of the first subtractor and an output signal of the second subtractor, and the clipping circuit A fourth adder for adding the output signal of the second multiplier and the output signal of the second multiplier, a delay circuit for delaying the output video signal of the image sensor, an output signal of the fourth adder and an output signal of the delay circuit. 16. The image pickup apparatus according to claim 11, wherein the image pickup apparatus has a configuration of a multiplier for multiplying.