JP3273619B2 - Electronic imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic image pickup apparatus, and more particularly to an electronic image pickup apparatus having a wide dynamic range and capable of appropriately picking up a backlight scene or the like.

[0002]

2. Description of the Related Art As shown in FIG. 3, a schematic block diagram of a conventional electronic image pickup apparatus includes a photographing lens 11 and an aperture mechanism 1 for adjusting the amount of subject light transmitted through the lens 11.
2, a CCD 13 as an imaging means for photoelectrically converting the subject light to output a video signal, a CDS 14 for performing correlated double sampling of the video signal, and separating the output of the CDS 14 into a luminance signal Y and a chrominance signal C. A signal processing circuit 15; an encoder 16 for converting these signals into, for example, an NTSC decoded video signal; a video output terminal 17 for transmitting a video signal to an external device (not shown);
An average photometric circuit 20 that integrates the output of the DS 14 and outputs average photometric information; and a comparator 21 that controls the aperture of the aperture mechanism 12 by comparing the average photometric information with a reference voltage Vref.
And C for controlling the vertical transfer pulse and horizontal transfer pulse of the CCD 13 and the application of a substrate voltage for discharging unnecessary charges.
It comprises a CD drive circuit 18 and an SG 19 for generating a timing signal according to the television standard.

In the exposure control in the conventional electronic image pickup apparatus having the above-described configuration, the average photometric information output from the average photometric circuit 20 is applied to the reference voltage Vref applied to the non-inverting input terminal of the comparator 21. Throttle mechanism 1 so that they are equal
The second aperture is controlled so that an image is taken with a predetermined exposure amount.

[0004]

However, in the above-mentioned conventional electronic image pickup apparatus for controlling the exposure so that the average photometry information becomes a predetermined reference level, the dynamic range of the image pickup means such as a CCD is narrow. A problem arises when the brightness difference of the subject is large, such as in a backlight scene.

[0005] That is, when a person 101 as shown in FIG. 4 is photographed under backlight, the person 101 as a main subject has a low luminance, while a background 102 such as a tree or a mountain has a high luminance. Therefore, when the exposure is adjusted to the person 101, which is the main subject, the background 102, which is a high-luminance part, loses its gradation due to overexposure and becomes uniformly whitish.
This causes so-called overexposure, resulting in unsightly images. Conversely, when the exposure is adjusted to the background 102, which is a high-brightness part, the important person 10 who is the main subject to actually shoot is
In the case of No. 1, the gradation is lost due to insufficient exposure, and the image becomes uniformly dark, that is, a so-called black loss occurs.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problem and to shoot a scene in which the luminance difference of a subject is large.
An object of the present invention is to provide an electronic image pickup apparatus that does not cause overexposure or underexposure.

[0007]

An electronic image pickup apparatus according to the present invention is an electronic image pickup apparatus for controlling the amount of exposure of the image pickup means in accordance with the amount of light. Within the photoelectric conversion surface, a discriminating means for discriminating whether or not the level difference of the photoelectric conversion output between the portions exceeds a predetermined value; and When it is discriminated that the level difference of the photoelectric conversion output exceeds a predetermined value, the first exposure control for controlling the exposure amount based on the photoelectric conversion output from the entire photoelectric conversion surface or a specific portion thereof is performed. A second exposure control mode for controlling the amount of exposure based on a substantial peak value of a photoelectric conversion output from a photoelectric conversion surface of the imaging unit corresponding to the unit image. Alternate modes Means for obtaining a signal corresponding to an arithmetic average of a signal corresponding to the photoelectric conversion output in the first exposure control mode and a signal corresponding to the photoelectric conversion output in the second exposure control mode. It is characterized by the following.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of an electronic image pickup apparatus according to an embodiment of the present invention. The same components as those in FIG. 3 in the conventional example are denoted by the same reference numerals, and description thereof is omitted. This will be described below with reference to 1 to 7.

Reference numeral 1 denotes an A / D converter for converting the output of the CDS 14 into a digital value, 2 denotes a field memory for storing image information for one field, and 3 denotes an output of the A / D converter 1 and the field. An adder 4 for adding the output of the memory 2 to the output of the adder 3 is a multiplier for multiplying the output of the adder 3 by a factor of 1/2. The / A converter 6 is a microcomputer, and controls a shutter speed and an aperture by a built-in discriminating means 6a, a first light measuring means 6b, a second light measuring means 6c and the like. 7 is E ² P
Write the saturation level of CCD 13 etc. in ROM,
The signal is supplied to the microcomputer 6.

The discriminating means 6a built in the microcomputer 6
Is for discriminating whether or not the level difference of the photoelectric conversion output between the portions in the photoelectric conversion surface of the CCD 13 as the imaging means corresponding to the unit image exceeds a predetermined value. For example, FIG. This is to discriminate when the brightness difference of the subject is large, as in the case of the shooting in the backlight scene shown above.

The first photometric means 6b built in the microcomputer 6 is used in a first exposure control mode for controlling an exposure amount based on a photoelectric conversion output from a front surface of the photoelectric conversion surface of the CCD 13 and a specific portion thereof. The screen is divided into several areas by the photometric means, and the weight is increased at the center and the weight is reduced at the periphery, so that the main subject located at the center in the backlight scene shown in FIG. Photometry can be performed with emphasis on 101 and the peripheral portion taken into account, and is hereinafter referred to as center-weighted exposure. Further, a second exposure control mode for controlling an exposure amount based on a substantial peak value of a photoelectric conversion output from a photoelectric conversion surface of the CCD 13 as an imaging unit corresponding to the unit image is provided. Since the photometric means sometimes used corresponds to the peak level of the signal, it can be used for photographing in which exposure is adjusted to a high-luminance background in the backlight scene shown in FIG. 4, and is hereinafter referred to as peak exposure.

In the embodiment, the CCD 13 as an image pickup means has a photoelectric conversion surface divided into a plurality of regions, and can separately take out photometric information for each region. When a high voltage is applied to the CCD substrate, unnecessary accumulated charges on the photoelectric conversion surface can be discharged in the vertical direction.

First, the basic operation of the present embodiment constructed as described above will be described.
The first exposure control mode is executed alternately for each field, for example, the first exposure control mode is executed in an odd field, and the second exposure control mode is executed in an even field, for example. A signal corresponding to an arithmetic mean of a signal corresponding to the converted output and a signal corresponding to the photoelectric conversion output in the second exposure control mode is obtained. The signal corresponding to the arithmetic averaging is stored in the field memory 2, adder 3, multiplier 4
In addition, it is required by the microcomputer 6 and will be described in detail below using the timing chart of FIG.

First, each signal in FIG. 2 will be described as follows.

Light metering switching signal: A signal for switching between the first light metering means 6b and the second light metering means 6c in the microcomputer 6.

FLD: Field switching signal.

VBLK: Vertical blanking signal.

TG: a timing signal for transferring the electric charge accumulated in the photodiode of the CCD to the vertical transfer register (actually, the electric charge is transferred by driving the vertical transfer pulse to a high level at this timing).

HD: Horizontal drive pulse.

XSUB: A signal indicating the timing at which a high voltage is applied to the substrate of the CCD imager to discharge charges in the vertical direction, and is output in synchronization with the horizontal drive pulse HD.

The CCD output is the CD shown in FIG.
The output signal of S14 and the output of the adder are the output signals of the adder 3, but are drawn in an analog image so as to be easily understood visually. Further, the video output is a signal waveform of the video output terminal 17.

The CC in which the photoelectric conversion surface is divided into a plurality of areas
The photometry information for each area from D13 is stored in CDS14, A /
When the microcomputer 6 takes in the data via the D converter 1, the discrimination means 6a in the microcomputer 6 discriminates the level difference of the photoelectric output between the central part and the peripheral part in each area of the CCD 13. If the level difference exceeds a predetermined value and is discriminated by the discriminating means 6a, the microcomputer 6 determines that the subject is in a backlight state and sequentially executes the following operations.

When the first field 31 is started at the time t1, a transfer timing signal TG34 is transmitted during the active L period of the vertical blanking signal VBLK33. Then, in synchronization with the TG 34, the discharge timing signal X
., 35n are sent from the CCD drive circuit 18 in FIG.
During the transmission of the SUBs 35a,... 35n, even if the subject light is irradiated on the photoelectric conversion surface of the CCD 13, the photoelectrically converted charges on the photodiodes are discharged to the vertical transfer register, so that the charge is not accumulated.

Therefore, the discharge timing signal XSUB35
The period from n to the transmission of the transfer timing signal TG44 in the next second field is the charge accumulation period in the photodiode of the CCD 13, and the peak exposure in the second exposure control mode is performed. That is, a high-speed shutter operation corresponding to the peak exposure is performed by adjusting the transmission period of the discharge timing signal XSUB.

By the way, the electric charge accumulated corresponding to the peak exposure is read out in the next second field by a CCD.
At output 42, the CCD read out in this first field
The output 32 is obtained by reading out the accumulated charge obtained in response to the center-weighted exposure in the zeroth field preceding the first field by using the transfer timing signal TG34.

The CCD output 32 is the same as that shown in FIG.
Is stored in the field memory 2. actually,
The 0th output prior to the first field is output to the CCD output 32.
During the field period, addition with the peak exposure information 26a stored in the memory 2 is performed. This addition will be described in the next second field, and a description thereof will be omitted.

In the second field 41, during the accumulation period of the electric charge accumulated in the photodiode on the photoelectric conversion surface of the CCD 13, 1/60 second from the transfer timing signals TG44 to TG54, and the low-speed shutter operation by the center-weighted exposure is performed. Is performed. The waveform of the accumulated charge is the CCD output 52 in the next third field 51.

Now, C in the second field 41
The CD output 42 is connected to the CCD 1 during the first field period.
The signal corresponding to the peak exposure accumulated on the photodiode No. 3 is a signal read by the TG 44 output during the active L period of the VBLK 43. The CCD output 42 due to this peak exposure is the CDS1 in FIG.
4. The signal is supplied to one input terminal of the adder 3 via the A / D converter 1.

On the other hand, the other input terminal of the adder 3
CCD output 32 by center-weighted exposure read in the first field 31 stored in the field memory 2
Are supplied to the CCD output 32, and the adder output 46 is obtained by adding 42 to the CCD output 32. This adder output 46
Is multiplied by で in a multiplier 4 to become a video output 47.
Therefore, the video output 47 is a signal corresponding to the arithmetic average of the CCD output 42 based on the peak exposure and the CCD output 32 based on the center-weighted exposure.

The CCD output 42 is also applied to the field memory 2 to rewrite the memory information of the memory 2. The memory information is rewritten after the addition operation is completed. The microcomputer 6 controls the timing.

Since the CCD output alternately outputs a signal based on the center-weighted exposure and a signal based on the peak exposure for each field, the above operation is repeated from the third field 51 onward, and the CCD output based on the peak exposure and the center-weighted exposure are output. A signal corresponding to the arithmetic average with the CCD output by exposure is obtained. Therefore, as a result, the dynamic range of the video signal is expanded.

As described above, by changing the accumulation time of the electric charge accumulated on the photodiode of the CCD 13 for each field for each field, the discharge timing signal XS for high brightness light such as background light in a backlight scene.
By adjusting the UB transmission time, the exposure time is shortened to prevent overexposure, and for low-brightness light such as a main subject in a backlight scene, the exposure time is set to 1/60 second to increase the blackout. Try to prevent.

In the above embodiment, the exposure time at the time of center-weighted exposure is set to 1/60 second. However, the exposure time can be freely set by controlling the aperture and shutter speed, that is, the charge accumulation time. Also, the description has been given on the assumption of a backlight scene, but the present invention is not limited to this, and can be widely applied to shooting of a subject having a large luminance difference. Further, the present invention can be applied to not only a still image shooting but also a moving image shooting.

According to the above embodiment, the imaging means such as a CCD having a narrow dynamic range can have a wide dynamic range. Therefore, it is possible to photograph a scene having a large difference in luminance of a subject, for example, in a backlight scene.

[0035]

As described above, according to the present invention, it is determined whether or not the level difference of the photoelectric conversion output between the portions in the photoelectric conversion plane of the imaging means corresponding to the unit image exceeds a predetermined value. Is discriminated by the discriminating means, and when it is discriminated that the level difference exceeds a predetermined value, the first exposure for controlling the exposure amount based on the photoelectric conversion output from the entire photoelectric conversion surface or a specific portion thereof is performed. A second control mode for controlling the exposure amount based on a control mode and a substantial peak value of a photoelectric conversion output from a photoelectric conversion surface of the imaging unit corresponding to the unit image;
The two exposure control modes are alternately executed, and the phase of the signal corresponding to the photoelectric conversion output according to the first exposure control mode and the signal corresponding to the photoelectric conversion output according to the second exposure control mode. Since the exposure amount is controlled by obtaining a signal corresponding to the averaging, a remarkable effect of preventing overexposure and underexposure even when photographing a scene in which the luminance difference of the subject is large is exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram of an electronic imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart of signals of each section in FIG.

FIG. 3 is a block diagram of a conventional electronic imaging device.

FIG. 4 is a diagram showing an imaging target in FIG. 3;

[Explanation of symbols]

2. Field memory (means for obtaining a signal corresponding to arithmetic averaging) 3. Adder (means for obtaining a signal corresponding to arithmetic averaging) 4. Multiplier (means for obtaining a signal corresponding to arithmetic averaging) 6. Microcomputer (means for obtaining a signal corresponding to the arithmetic mean) 6a: discriminating means 13: CCD (imaging means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 5/225-5/243 H04N 5/335 G03B 7/28

Claims (1)

(57) [Claims] 1. An electronic imaging apparatus for controlling an exposure amount of an imaging unit according to an amount of light, comprising: a photoelectric conversion output between portions of a photoelectric conversion surface of the imaging unit corresponding to a unit image; Discriminating means for discriminating whether or not the level difference exceeds a predetermined value, and wherein the discriminating means has a level difference in photoelectric conversion output between the portions in the photoelectric conversion surface of the imaging means exceeding a predetermined value. When it is discriminated, a first exposure control mode for controlling the exposure amount based on the photoelectric conversion output from the entire photoelectric conversion surface or a specific portion thereof, and a photoelectric conversion surface of the imaging unit corresponding to the unit image. Controlling the exposure amount based on the substantial peak value of the photoelectric conversion output from
The two exposure control modes of the first exposure control mode and the signal corresponding to the photoelectric conversion output of the second exposure control mode are alternately executed. Means for obtaining a signal corresponding to the arithmetic mean.