JPH11252442A - Automatic focusing adjustment circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To adjust a focus, even when the high band level of luminance signals is low. SOLUTION: When a luminance level YH is higher than a first reference value REFa, focusing adjustment is executed based on the luminance level. When the luminance level is lower than the first reference value, gain adjustment for turning the color level of G and B to zero is performed, and control is performed so as to turn the luminance level to an R level. When the R high band level RH is higher than a second reference value REFb, the focusing adjustment is executed based on the R high band level. Although eventhough the second reference value is a value smaller than the first reference value, since contour components are included, the focusing adjustment is performed through this. When the R high band level is lower than the second reference value, gain is adjusted so as to turn the color level of R and G to zero. By a B high band level BH obtained at the time, the focus adjustment similar to the one at the time of the R high band level is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an auto focus adjustment circuit. More specifically, by using not only the luminance level but also the color level, the auto focus can be accurately adjusted even in the case of a color image of a subject having the same luminance level.

[0002]

2. Description of the Related Art A configuration as shown in FIG. 4 is known as an autofocus adjustment circuit of a video camera. FIG. 1 shows a signal processing system of a video camera.
Is projected onto an image sensor, in this example, a color CCD 16 via an optical system 14 including an auto-focus adjustment system, and an optical image is converted into an electric signal (video signal). As the color filter, for example, a checkered color filter in which R, G, and B filters as shown in FIG. 5 are arranged in a checkered pattern can be used. Accordingly, the CCD 16 outputs a video signal which is a dot-sequential signal of R, G, and B.

[0003] The analog R, G, B signals (primary color signals)
Is sampled and held, and supplied to an A / D converter 18 to be converted into a digital signal. The digital video signal is supplied to the first white balance adjustment circuit 20, and the gain of each of the R, G, and B signals is adjusted so as to achieve white balance. Specifically, the R, G, and B signals are supplied to a multiplier for white balance adjustment together with a gain level setting signal (point-sequential setting signal) synchronized with the R, G, and B signals.

When a checkered filter is used as a color filter as described above, not all of the primary color signals of R, G, and B are output from one horizontal line. A line delay circuit 22 is provided, and the R, G, and B primary color signals delayed by one horizontal line are similarly supplied to a second white balance adjustment circuit 24 to perform similar gain adjustment. Therefore these two
For the first time, the R, G, and B primary color signals whose white balance has been adjusted at the output side of the two adjustment circuits 20 and 24 are obtained.

The output signals of the first and second white balance adjusting circuits 20 and 24 are respectively supplied to a first low-pass filter 26 and subjected to a filtering process to obtain a first luminance signal Ym. The first luminance signal Ym is supplied to a subsequent signal processing circuit (such as a detection circuit) 28 to obtain a final video signal.

Similarly, the output signals of the adjusting circuits 20 and 24 are also supplied to a second low-pass filter 30, which is for obtaining a signal for auto-focus adjustment. Therefore, a filtering process different from that described above is performed, and the output signal is supplied to the subsequent high-pass filter 32 as a luminance signal (second luminance signal) Yw for focus adjustment, and only the high-frequency component YH is extracted. Is done. When the focus adjustment is complete, the outline of the projected image is clearly displayed, and the level of the high-frequency component YH of the video signal at that time increases.

Therefore, the extracted high frequency component YH is supplied to the focus control circuit 34, and an adjustment signal corresponding to the level of the high frequency component is supplied to the focus drive circuit 36. Since the above-described optical system 14 is provided with a focus adjustment unit (not shown), an output of the focus adjustment circuit 36 is used as a drive signal for the adjustment unit. If the just-focus is not performed, the level of the extracted high-frequency component YH will be reduced, so that the just-focus state can be determined from the history of these high-frequency components.
Therefore, the focus adjustment is actually performed using a microcomputer or the like.

[0008]

By the way, in the auto focus adjustment circuit 10 shown in FIG. 4, the focus adjustment is performed based on the level of the high frequency component (high frequency luminance signal) extracted from the luminance signal as described above. Since it is performed, it is an auto focus adjustment process centering on the luminance level.

For this reason, for example, when a subject 12 having different colors and the same luminance level is imaged, focusing (just focus) adjustment on the subject 12 becomes a problem.

For example, when there is a red flower on a green lawn as shown in FIG. 6, the level of the red flower (R signal level)
Is 50, for example, if the green grass level (G signal level) becomes 25, the red flower level: Yr = R (50) + G (0) + B
(0) = 50 Green grass level: Yg = R (0) + G (50) + B
(0) = 50.

Therefore, since the luminance level does not change at the boundary between the red flower and the green grass, the output level from the high-pass filter 32 is too small for such a subject, so that focus adjustment such as just focusing cannot be performed. Would. This is because the auto focus adjustment is performed with reference to only the luminance level.

Accordingly, the present invention has been made to solve such a conventional problem. The present invention refers to not only a luminance level but also a color component level, thereby enabling auto focus adjustment. It proposes a circuit.

[0013]

According to an aspect of the present invention, there is provided an auto-focus adjustment circuit for a video camera, wherein the auto-focus adjustment circuit is generated from an optical system. Extracting a high-frequency signal of the luminance signal, adjusting the autofocus based on the level of the high-frequency luminance signal, and, when the level of the high-frequency luminance signal is lower than a first reference value, , The autofocus is performed based on the high-frequency signal level of the primary color signal.

According to the present invention, when the high-frequency luminance level is larger than the reference value, the focus adjustment is performed based on the high-frequency luminance level. When the high-frequency luminance level is smaller than the first reference value, the focus is adjusted with reference to the primary color signal level (color level).

That is, when the high-frequency luminance level is smaller than the first reference value, first, gain adjustment is performed so that the G and B color levels become zero, so that the high-frequency signal level becomes a level of only R. To control. This R high frequency signal RH
Is larger than the second reference value, a plurality of adjustments are performed based on the R high band signal level. Even if the second reference value is smaller than the first reference value, since the R high-frequency signal RH includes a contour component, it can be considered to be a relatively large level. It can be said that the signal level is sufficient to perform.

When the R high band signal RH is smaller than the second reference value, the gain is adjusted so that the R and G color levels become zero. B high frequency signal B obtained at this time
When H is larger than the second reference value, focus adjustment is performed based on the B high-frequency signal BH. When both the R high band signal RH and the B high band signal BH are less than the second reference value, the maximum level including the luminance level YH is detected, and the focus is adjusted at the luminance level having the maximum level. .

As described above, since the focus can be surely adjusted based on the color level as well, FIG.
Just focus on a subject like
A clear image can be obtained.

[0018]

Next, an embodiment of a focus adjustment circuit according to the present invention will be described in detail with reference to the drawings.

The basic structure of the present invention is the same as that of the prior art shown in FIG. Accordingly, the subject 12 is projected through an optical system 14 including an autofocus adjustment system onto a color CCD 16 in this example as an image pickup device to obtain a video signal. As the color filter, for example, FIG.
A color filter having a checkered pattern as shown in (1) can be used, but a filter having another filter configuration can also be used. When using the color filter having the configuration shown in FIG. 5,
The CCD 16 outputs a video signal formed as a dot-sequential signal of R, G, and B.

The analog R, G and B signals are sampled and held, and then supplied to an A / D converter 18 where they are converted into digital signals. The digital video signal is supplied to a first gain adjustment circuit 20 that constitutes a white balance adjustment means 21, and the gain of each of the R, G, and B signals is adjusted to adjust the white balance. More specifically, the R, G, and B signals are supplied to a multiplier (not shown) provided in the gain adjustment circuit 20 together with a gain level setting signal (point-sequential setting signal) synchronized with the R, G, and B signals. Then, the gain of the R, G, and B signals is adjusted. As a result, a video signal Ym having a white balance is obtained.

When a checkered filter is used as a color filter as described above, not all signals of R, G and B are output from one horizontal line.
As shown, a delay circuit 22 for one horizontal line is provided, and R, G, and B signals delayed by one horizontal line are supplied to a second gain adjustment circuit 24 which also constitutes the white balance adjustment means 21. Similar gain adjustment is performed. Therefore, for the first time at the output side of these two adjustment circuits 20, 24, R, R,
G and B signals are obtained.

First and second gain adjustment circuits 20, 2
The output signal of No. 4 is supplied to the first low-pass filter 26 and subjected to a filtering process, whereby a first luminance signal Ym is obtained. The first luminance signal Ym is supplied to a subsequent signal processing circuit (such as a detection circuit) 28 to be a final video signal.

In the present invention, a dedicated circuit system for focus adjustment is further provided. Specifically, a second white balance adjusting unit 40 is provided. This white balance adjustment means 40 has the same configuration as the first white balance adjustment means 21 and has two gain adjustment circuits 42,
An undelayed video signal (R, G point sequential signal) is supplied to one gain adjustment circuit 42, and a 1H delayed video signal (G, B point) is supplied to the other gain adjustment circuit 44. Signals are supplied sequentially.

A point-sequential gain adjustment signal Sg synchronized with R, G, and B signals, which will be described later.
2 to give a white-balanced R,
G and B signals are obtained. The R, G, and B signals of the gain adjustment circuits 42 and 44 are supplied to the second low-pass filter 30, and a luminance signal including a band signal necessary for autofocus adjustment is output. This luminance signal is output to the high-pass filter 3
2 and only the high frequency component YH is extracted.

The high-frequency luminance signal YH and the above-described luminance signal Ym are supplied to a control unit 50 composed of a microcomputer. The output signal of the signal processing circuit 28 can be used instead of the luminance signal Ym.

First, the control unit 50 generates a first gain adjustment signal Sg1 to be supplied to the first white balance adjustment means 21 from the luminance signal Ym. The gain adjustment signal Sg1 is a point-sequential signal synchronized with the R, G, and B signals as in the related art.

Next, a second gain adjustment signal Sg2 to be supplied to the second white balance adjustment means 40 is generated using the high-frequency luminance signal YH. The gain adjustment signal Sg2 is a point-sequential signal synchronized with the R, G, and B primary color signals as in the related art, but is used exclusively as an auxiliary signal for obtaining a focus adjustment signal after the white balance adjustment is completed.

The focus adjustment signal generated by the control unit 50 is supplied to a motor driver 36, and the motor for controlling the optical system (lens system) 14 for focus adjustment is controlled so as to perform just focus.

In the present invention, first, the high-frequency luminance level YH is referred to in order to make it possible to perform just-focus even when an image of an object having the same luminance level is captured in different colors. However, when this is above a specified level, focus adjustment is performed based on this high-frequency luminance level, and when it is below a specified level, that is, when the luminance level is such that focus adjustment cannot be performed correctly at that level. Focus adjustment is performed using the color level. Since the G level is almost the same as the luminance level, in this example, focus adjustment is performed with reference to the R or B color level.

This is based on the following reasons. First, FIG.
When the subject 12 is imaged as shown in FIG. 2, a luminance signal after white balance adjustment as shown in FIG. 2A is obtained,
It is assumed that the high-frequency luminance level YH at that time is as shown in FIG. In the case of FIG. 6, the G color signal SG as shown in FIG.
And the R color signal SR shown in FIG.

The G high band level GH at that time is obtained as a signal component corresponding to the outline as shown in FIG. E, and the R high band level RH is a signal component as shown in FIG. Therefore, even if the signal has a relatively large high-frequency level at each color level, since the respective polarities are different, when both color levels are added, a relatively low level as shown in FIG. This becomes the high-frequency signal YH.
As a result, even when the high-frequency signal YH alone does not provide a sufficient focus adjustment signal, a high-frequency signal of a sufficient level for focus adjustment can be obtained at the high-frequency level based on the primary color level. .

For this reason, the above-described control unit 50 executes a focus adjustment process as shown in FIG. First, the high-frequency luminance level YH is compared with the first reference value REFa. If the high-frequency luminance level YH is larger than the first reference value REFa, the focus adjustment is executed based on the high-frequency luminance level YH (steps 60 and 72). When the high-frequency luminance level YH is smaller than the first reference value REFa, the focus is adjusted with reference to the color level.

Therefore, when the high-frequency luminance level YH is smaller than the first reference value, first, the color levels of G and B are set to zero, and the second white balance adjustment circuit 40 is set so that the color signal of only R is obtained. Is performed (step 62). The control unit 50 generates the gain adjustment signal Sg2 for that. As a result, a color signal (R signal) having a luminance level of only R is obtained from the second white balance adjustment circuit 40.

The R signal is supplied to the high-pass filter 32 to extract the R high band signal RH. Next, when the R high band signal RH is larger than the second reference value REFb, the R high band signal RH is extracted. The focus adjustment is executed based on (steps 64 and 72). This is because even if the second reference value REFb is smaller than the first reference value REFa, as described above, R
This is because the high frequency signal RH is often included.

If the R high band signal RH is smaller than the second reference value REFb, the gain is adjusted so that the R and G color levels become zero (step 66). The B high frequency signal BH obtained at this time is compared with the second reference value REFb, and when it is larger than the second reference value REFb, the focus is adjusted based on the B high frequency signal BH (step 68, step 68). 72). However, the B high band signal B
When H is less than the second reference value REFb, the maximum level among the three signal levels obtained by adding the luminance level YH to these is detected, and the focus is adjusted using the signal having the maximum level ( Step 70).

As described above, if the color level is also used as a reference, the focus can be surely adjusted.
Just focus on a subject like
A clear image can be obtained.

In the above description, focus adjustment is performed by using the R high band signal or the B high band signal. First, the G high band signal GH (FIG. 2E) is obtained. The focus can be adjusted by a signal.

[0038]

As described above, in the present invention, the focus is adjusted not only with reference to the luminance level but also with reference to the color level in some cases.

According to this, even when the high frequency signal component of the subject is small, the focus can be adjusted correctly, so that a clear image is always obtained even if the subject has the same luminance level with different colors, for example. Features that can be.

[Brief description of the drawings]

FIG. 1 is a system diagram of a main part showing an embodiment of an autofocus adjustment circuit according to the present invention.

FIG. 2 is a diagram illustrating a high-frequency signal level.

FIG. 3 is a flowchart illustrating an example of focus adjustment.

FIG. 4 is a system diagram of a conventional auto focus adjustment circuit.

FIG. 5 is a diagram of a color filter.

FIG. 6 is an explanatory diagram of a subject.

[Explanation of symbols]

10 Focus Adjustment Circuit 21, 40 White Balance Adjusting Means 42, 44 Gain Adjustment Circuit 50 Control Unit 36 Focus Adjustment Motor Driver 14, 14 Optical system, REFa, REFb
···Reference value

Claims (4)

[Claims] 1. An auto-focus adjustment circuit for a video camera, comprising: extracting a high-frequency signal of a luminance signal generated from an optical system; adjusting an auto-focus based on a level of the high-frequency luminance signal; When the level of the high-frequency luminance signal is lower than a first reference value, autofocus is performed based on a high-frequency signal level of a primary color signal instead of the high-frequency luminance signal. Adjustment circuit. 2. The auto-focus adjustment circuit according to claim 1, wherein primary color signals such as R and B are used as said primary color signals. 3. Autofocusing using a primary color signal is performed first using a red signal. When the high frequency level of the red signal is lower than a second reference value, a blue signal is used instead of the red signal. 2. The auto-focus adjustment circuit according to claim 1, wherein 4. A primary color signal obtained from an image pickup device is supplied to a gain adjustment circuit, and the gain-adjusted primary color signal is supplied to a high-pass filter to extract a high-frequency signal for auto-focusing. When the high-frequency luminance signal is lower than the first reference value, the corresponding single primary color signal is output as an autofocus primary color signal by controlling the gain adjustment circuit. The autofocus adjustment circuit according to claim 1, wherein