JPH0568205A - Imaging device - Google Patents

Abstract

(57) [Abstract] [Purpose] Proper exposure can be performed regardless of the position of the subject on the screen, and good imaging can be performed even with an image sensor having a narrow dynamic range. An image pickup optical system, an image pickup device for converting an optical image formed by the image pickup optical system into an electric signal, a processing means for performing a predetermined process on a signal obtained by the image pickup device, and the processing means. And a recording medium for recording the signal processed by
In an image pickup apparatus in which the exposure amount of an image pickup device is corrected based on the brightness of a subject before main exposure, a means for measuring the distance to the subject in a plurality of areas in the screen, and a main subject based on the distance measurement result. And a means for discriminating the area in which the main subject is positioned, which is discriminated by the discrimination means, and the exposure amount in the main exposure is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup device for picking up an image of a subject using an image pickup device such as a CCD, and more particularly to an exposure control device used for controlling exposure.

[0002]

2. Description of the Related Art As a conventional image pickup device, an image pickup device such as a CCD is used to convert an optical image of a subject into an electric signal, and the video signal is recorded on a recording medium such as a magnetic disk, a magnetic tape or an IC memory. It has been known. In such an image pickup apparatus, when the exposure condition of the image pickup element is determined, the brightness of the subject is measured using the photometric element, and the aperture value or the exposure time for the image pickup element is determined based on the obtained measurement value. However, since an image pickup device such as a CCD has a so-called dynamic range extremely narrower than that of a silver salt film due to its characteristics, there is a problem that an exposure determination method using a photometric device is inferior in accuracy.

Therefore, as a method for solving the above problems, for example, an exposure control method as shown in FIG. 4 is known. Note that FIG. 4 shows an exposure control system of a still video camera using a magnetic disk as an image pickup device such as a CCD or a recording medium. In the figure, first, the brightness of the subject is measured using a photometric element such as SPC (S1), and an image of the subject is captured by the image sensor according to the obtained photometric value (S2). Next, the signal of the image pickup device is read (S3), and the level of the signal in the entire screen or in the designated range is compared with the prescribed level. If the result of this comparison is not the prescribed level, the aperture value or exposure time is corrected. (S4). The exposure (main exposure) is performed again under the corrected conditions (S5), and after the main exposure, the signal of the image pickup device is read (S6) and recorded on the recording medium (S7).

[0004]

In the above-mentioned conventional exposure control method, since the main exposure is performed based on the image signal actually taken by the image pickup device, the exposure accuracy is improved. However, there is a problem in that appropriate exposure cannot be performed depending on the arrangement of the subject in the screen, and the exposure accuracy is also inferior.

The present invention has been made in order to solve such a problem, and its purpose is to perform an appropriate exposure regardless of the position of a subject, and to take a good image even with an image pickup device having a narrow dynamic range. An object of the present invention is to provide an imaging device capable of performing the above.

[0006]

The object of the present invention is obtained by a photographing optical system, an image pickup device for converting an optical image formed by the photographing optical system into an electric signal, and the image pickup device. And a recording medium for recording the signal processed by the processing unit. The exposure amount of the image sensor is corrected based on the brightness of the subject before the main exposure. In the image pickup apparatus described above, a means for measuring the distance to the subject in a plurality of areas on the screen and a means for discriminating the area where the main subject is located based on the distance measurement result are provided. This is achieved by an image pickup device characterized in that the exposure amount in the main exposure is controlled by focusing on the area where the subject is located.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the image pickup apparatus of the present invention. Here, an example is shown in which the present invention is applied to a still video camera using a magnetic disk as a recording medium.

In FIG. 1, reference numeral 1 is a photographic optical system composed of a diaphragm, shutter or lens, 2 is an optical driver including a lens drive control circuit for exposure control and focusing, and 3 is an imaging optical system 1. It is an image sensor that converts an imaged optical image into an electric signal. A CCD is used as the image sensor 3. Reference numeral 4 is a signal processing circuit for converting a signal obtained by the image pickup device 3 into, for example, a television signal or a signal suitable for the recording format of the recording medium 7, and 5 further processes the output signal of the signal processing circuit 4,
A conversion circuit for converting a signal suitable for recording on the recording medium 7 and a gate circuit 6 for recording a signal when the signal processed by the conversion circuit 5 is recorded on the recording medium 7. A magnetic disk is used as the recording medium 7, and the drive is controlled by the medium control circuit 8.

Reference numeral 9 is an arithmetic circuit for judging the exposure level of a picked-up image on the basis of the luminance signal obtained by the signal processing circuit 4 and calculating the exposure level for the main exposure. Reference numeral 10 is a control circuit for controlling each part, and CPU It consists of Reference numeral 11 is a clock circuit for generating a clock necessary for imaging and control operations, 12 is a photometric element, and 13 is a distance measuring circuit for measuring the distance to a subject. The clock signal of the clock circuit 11 is sent to the image pickup device 3 and the control circuit 10, and the output of the photometric device 12 is also sent to the control circuit 10. Further, the distance measuring circuit 13 is composed of, for example, a light emitting section that emits three infrared beams and a light receiving sensor corresponding to each infrared beam, and as described later, the distance measuring is performed in a predetermined area on the screen. Is to do. 14 is a distance measuring circuit 13
It is an area control circuit that determines in which area of the screen the subject is present based on the information obtained in step 1, and controls the timing of reading the luminance signal from the signal processing circuit 4 based on the result of the determination. ..

FIG. 2 is a diagram showing an example of an image pickup screen.
The quadrangle surrounded by P ₁ , P ₂ , P ₃ , and P ₄ indicates the entire imaging screen. The range surrounded by P ₅ , P ₆ , P ₈ and P ₇ is from the signal processing circuit 4 to the arithmetic circuit 9 during the first exposure.
The area to be read is shown. This area is P ₅ ,
The area A defined by P ₉ , P ₁₀ , P ₇ and P ₉ , P ₁₂ ,
The area B defined by P ₁₁ , P ₁₀ and P ₁₂ , P ₆ , P ₈ ,
The area C is defined by P ₁₁ . Furthermore, area A,
The three areas indicated by a, b, and c in B and C correspond to the path measurement areas of the distance measuring circuit 13 described above.

Next, the operation of this embodiment will be described with reference to FIG. In FIG. 3, when shooting is first instructed, the distance measuring circuit 13 measures the distance to the subject (S
1), the measurement result is sent to the control circuit 10. in this case,
As described above, the distance measuring circuit 13 performs multi-point distance measuring for measuring distances at three locations by using three infrared beams, and outputs each measurement result to the control circuit 10. At the same time, the brightness of the subject is measured by the photometric element 12 (S2), and the control circuit 1
At 0, the exposure amount of the image sensor 3 is determined according to the photometric value, and exposure is performed (S3). After this exposure, the luminance signal of the image pickup device 3 is read out to the signal processing circuit 4 (S
4). On the other hand, in the control circuit 10, on the basis of the result of the multi-point distance measurement, at which position on the screen the main subject exists, that is, which region among the regions a, b and c shown in FIG. It is determined whether the vehicle is located at (S5).
When determining the position of the main subject, the region having the shortest distance is determined to be the position of the main subject, and the determination result is sent to the region control circuit 14. For example, when it is determined that b in FIG. 2 is the position of the main subject, the area control circuit 14 controls the arithmetic circuit 9 to read the range of the luminance signal of the image sensor 3 as the area B (S6), Only the signal in the area B is taken into the arithmetic circuit 9 from the signal processing circuit 4 by its control operation. Further, when a is determined to be the position of the main subject, the signal of the area A is taken into the arithmetic circuit 9, and when C is determined to be the position of the main subject, the signal of the area C is taken into the arithmetic circuit 9. Be done.

The arithmetic circuit 9 compares the obtained signal corresponding to the position of the main object with a predetermined prescribed level, and if the signal is not within the prescribed level, arithmetic processing is performed to correct the aperture value or the exposure time, and the main exposure is performed. Exposure level is calculated (S
7). Next, main exposure is performed by the image sensor 3 according to the obtained exposure level (S8), and the signal obtained by this main exposure is read to the signal processing circuit 4 (S9). The signal processing circuit 4 performs predetermined signal processing, and the processed signal is further converted into a signal suitable for recording by the conversion circuit 5. The image signal processed by the conversion circuit 5 is recorded on the recording medium 7 by the timing control of the gate circuit 6.

In the above embodiments, the arithmetic circuit 9 fetches the signal of any area where the main subject is located and the exposure level is determined based on the signal of that area. Weighting may be performed with an emphasis on the subject existing area based on the signal. For example, the main subject is area C
If the position is set to, the weighting is A: B: C = 1: 1: 3
And it is sufficient. Further, when the signal is read from the signal processing circuit 4, the signal of the area designated by the area control circuit 14 is read, but the image signal of the first exposure is stored in the memory and then the signal of the designated area is read. You may take out. Further, although the first exposure is performed based on the output of the photometric element 12, it may be performed based on the signal of the image pickup element 3. Further, in the embodiment, the distance measurement is performed in three areas in the screen, but it may be performed in at least two areas.

[0014]

As described above, according to the present invention, since the exposure control of the main exposure is performed by focusing on the area where the main subject is located in the screen, it is appropriate regardless of the position of the subject. There is an effect that various exposures can be performed and the exposure accuracy can be significantly improved as compared with the conventional one. Therefore, even an image sensor having a narrow dynamic range can be effectively supplemented and a high quality image can be captured.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a distance measuring area within a screen.

FIG. 3 is a flowchart showing the operation of the embodiment of FIG.

FIG. 4 is a flowchart showing exposure control of a conventional example.

[Explanation of symbols]

 1 Photographic Optical System 3 Image Sensor 4 Signal Processing Circuit 7 Recording Medium 9 Arithmetic Circuit 10 Control Circuit 12 Photometric Element 13 Distance Measuring Circuit 14 Area Control Circuit

Claims (1)

[Claims] 1. An image pickup optical system, an image pickup device for converting an optical image formed by the image pickup optical system into an electric signal, a processing means for performing a predetermined process on a signal obtained by the image pickup device, A plurality of areas in a screen in an image pickup apparatus including a recording medium for recording the signal processed by the processing unit, and correcting the exposure amount of the image pickup element based on the brightness of the subject before the main exposure. A means for measuring the distance to the subject by means of, and a means for discriminating the region where the main subject is located based on the distance measurement result are provided, and the main exposure is performed with emphasis on the region where the main subject is discriminated by the discrimination means. An image pickup apparatus characterized by controlling an exposure amount in the case of.