JPH0738060B2 - Exposure control device for electronic still camera - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera, and more particularly to an exposure control apparatus that controls exposure so that the level of its output signal is constant.

BACKGROUND ART As its name implies, an electronic still camera can obtain a video signal of only one field or one frame exposed by opening a shutter. Proper exposure is required to obtain a proper reproduced image, that is, a visually natural reproduced image. In the electronic still camera, proper exposure must always be obtained for one shot of video signal as described above. Proper exposure means that the luminance signal or G signal obtained from the solid-state imaging device used has a substantially constant level without depending on the light intensity of the field.

Therefore, in the exposure control of electronic still cameras, a method similar to that of conventional silver salt film still cameras, for example, the transmitted light of a shooting lens is measured by a photodiode, and the shutter and aperture values are adjusted accordingly, and solid-state imaging is performed. A method of giving a proper exposure to a device is used.

A video movie camera usually uses an auto iris that controls the aperture value by feedback control from the video signal so that the output level of the video signal becomes constant. However, such a feedback control system for movies cannot be used in the electronic still camera, because quick response is required to obtain one shot image.

Solid-state imaging devices such as charge-coupled devices (CCD) used as imaging devices for electronic still cameras have a narrower dynamic range than ordinary silver halide photographic film, and the solid-state imaging device and photometric photodiode are different in color temperature depending on G Since the sensitivity of the signal or the brightness signal is different, the light transmitted through the taking lens is simply measured by the photodiode, and the shutter and aperture values are adjusted accordingly to control the exposure, which can be obtained from the solid-state imaging device. It was not possible to make the luminance signal or the G signal constant.

For example, photometric photodiodes have different photosensitivity characteristics from solid-state imaging devices such as CCDs. 4 and 5 show the case where the output of the auto iris sensor is made constant in the case of a silicon photodiode.
The difference in the output of the CCD sensor due to the color temperature is shown.

As can be seen from FIG. 4, the output of the G signal changes depending on the change of the color temperature. For example, when the color temperature is low at about 3000 ° K, the output of the CCD sensor is low because of the low sensitivity of the G signal.

Also, as can be seen from FIG. 5, the luminance signal Y = 0.3R + 0.
The 59G + 0.11B output (dashed-dotted line) also changes with changes in color temperature, and when the color temperature is low at around 3000 ° K, the output is low because the sensitivity of the luminance signal of the CCD sensor is low.

Therefore, in the method of adjusting the values of the shutter and the aperture according to the photometric value of the photometric element, for example, the photodiode, depending on the bias of the spectral component of the incident light from the field,
In some cases, the level of the G signal or the luminance signal of the output signal from the CCD image pickup device was not adjusted to a constant appropriate value, and thus a video signal representing a good image could not be obtained.

For example, when the color temperature is about 3000 ° K, the sensitivity of the CCD image pickup device is low, so even if the shutter and aperture values are adjusted so that the G signal or the luminance signal becomes constant according to the photometric value of the photometric element. , The output of the G signal or the luminance signal from the CCD image pickup device becomes low and is not constant.

As described above, in the conventional electronic still camera, it is difficult to control the exposure so that the output G signal or the luminance signal is constant because the photometric element and the solid-state imaging device have different sensitivity characteristics with respect to color temperature. .

An object of the present invention is to provide an exposure control apparatus for an electronic still camera which solves the above-mentioned drawbacks of the prior art and eliminates the unevenness of the output due to the difference in the sensitivity characteristics with respect to the color temperature of the photometric element and the solid-state imaging device. With the goal.

DISCLOSURE OF THE INVENTION According to the present invention, an exposure control apparatus for controlling exposure of an electronic still camera that captures a field by a solid-state imaging device and forms a video signal representing an image of the field is provided from the field. Light detection means for receiving the incident light and outputting a signal according to the amount of the incident light, color temperature detection means for detecting the color temperature of the object field, and output from the light detection means for output from the color temperature detection means The exposure control means controls the exposure of the electronic still camera by the output from the light detection means and the output from the color temperature detection means. The exposure control means controls the solid-state imaging device and the light. The exposure of the electronic still camera is controlled according to the amount of incident light detected by the photodetector so as to compensate for the difference in sensitivity due to color temperature between the detectors.

Description of Embodiments Next, an embodiment of an exposure control apparatus for an electronic still camera according to the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, an electronic still camera to which an embodiment of an exposure control apparatus according to the present invention is applied has an image pickup optical system 10, and the optical system 10 includes an image pickup lens 12, a diaphragm 14, a beam splitter 16, and a shutter. 18 is the optical axis of the lens 12 as shown
It is arranged on 20. Behind the shutter 18, a solid-state imaging device 22 such as a CCD is arranged.

The imaging lens 12 is an imaging cell array of the solid-state imaging device 22.
An image of the object scene is formed on 24. The diaphragm 14 is an imaging cell array
It is an exposure adjustment mechanism that adjusts the amount of light incident on the 24
The diaphragm drive unit 28 drives the narrowing as shown in FIG. The beam splitter 16 is arranged at 45 ° with respect to the optical axis 12 and splits a part 30 of the incident light from the lens 12.
A photo-detecting element 36 is disposed in front of the branched light 30 via a lens 32 and a filter 34. The shutter 18 is an exposure mechanism that exposes the imaging cell array 24, and the dotted line 38
The shutter driver 40 controls the opening and closing of the shutter, as shown in FIG.

The light detection element 36, a photodiode in this embodiment,
It is connected to the input of logarithmic amplifier 42. The lens 32 converges the branched light 30 on the light receiving portion of the photodetector element 36. As a result, the photodetector element 36 fulfills the TTL photometric function of exhibiting a conduction state corresponding to the amount of light incident on the imaging lens 12.

The solid-state imaging device 22 is a CCD color imaging device in this embodiment, the drive input 44 is connected to the drive signal output of the synchronization generation circuit 46, and the video signal output 48 is connected to the color separation gain adjustment unit 50. There is. The synchronization signal generation circuit 46 has a reference oscillator that runs at a stable frequency and outputs the horizontal and vertical drive clocks necessary for driving the solid-state imaging device 22 to the output 44 and the horizontal and vertical synchronization signals to its output 52. Output. The solid-state imaging device 22 accumulates electric charges according to the subject image exposed in the imaging cell array 24 by opening the shutter 18, and outputs a color video signal according to the electric charges in response to the driving clock from the driving input 44. Output to.

The color separation gain adjustment unit 50 receives the input 48 from the solid-state imaging device 22.
Amplifies the color video signal input to
It is decomposed into the three color signals of and output to the output 54.

The output 54 of the color separation gain adjustment unit 50 is connected to the input of the matrix circuit 60. The matrix circuit 60 converts the three-color signal RGB input from the color separation gain adjusting unit 50 into the luminance signal Y,
And color-difference signals R-Y, B-Y and output them 62
It is a functional unit that outputs at. The color difference signals RY, B-
Y is output in scanning line order.

The logarithmic amplifier 42 is an amplifier that logarithmically compresses the output signal from the photodetector 36 and outputs it to its output 64. The output 64 is connected to the input port of the auto iris (AE) control unit 66. The AE control unit 66 in this embodiment has an analog-digital converter that converts the signal at the input 64 into corresponding digital data, and a processing system such as a microprocessor is advantageously used. The output ports 68 and 70 of the AE control unit 66 are connected to the diaphragm drive unit 28 and the shutter drive unit 40.
Respectively connected to.

The AE control unit 66 outputs a signal representing the amount of light measured by the light detection element 36 to the overall control unit 58, and the diaphragm drive unit 28 according to the signal representing the corrected amount of light sent from the overall control unit 58 as described later. And a control function unit that controls the shutter drive unit 40 and realizes an automatic exposure function that controls the exposure of the imaging cell array 24.

Each unit of these devices is controlled by the overall control unit 58. This electronic still camera has a shutter release button 72
And its output 74 is connected to the input port of the overall controller 58. In the present embodiment, the overall control unit 58 is also advantageously configured by a processing system such as a microprocessor, and responds to a shutter release signal sent from the shutter release button 72 through the control line 74, and the AE control unit 66, color separation gain. It is a control mechanism that controls the adjustment unit 50 and the matrix circuit 60, and thereby performs photographing, that is, exposure of the image pickup cell array 24 and reading of a video signal from the solid-state image pickup device 22.

The output 76 of the color temperature detector 78 is connected to the input port 76 of the overall controller 58. As shown in FIG. 2, the color temperature detection unit 78 detects the light incident on the aperture 80 from the field through the R and B filters 82 and 84 by the photodiodes 86 and 88, respectively, and detects the respective R and B color components. Is logarithmically compressed by the logarithmic amplifiers 90 and 92, converted into a signal showing the ratio of the R signal and the B signal by the differential amplifier 94, and the color temperature data of the field is outputted to its output 76. Have a function.

FIG. 3 shows the relationship between the output of the color temperature detector 78 and the color temperature. As shown in the figure, when the color temperature is high, that is, when the milled color (10 ⁵ / color temperature Tc) is small, the output from the color temperature detecting unit 78 is large.

The overall control unit 58 corrects the signal indicating the light amount obtained from the AE control unit 66 by the signal indicating the color temperature obtained from the color temperature detection unit 78, and sends the signal indicating the corrected light amount to the AE control unit 66. Output. The AE control unit 66 controls the diaphragm drive unit 28 and the shutter drive unit 40 by the signal indicating the corrected light amount.

A storage unit 96 in which a look-up table used to correct such light amount data is stored is connected to the overall control unit 58. The correction of the light amount data performed in the overall control unit 58 is performed by reading a look-up table composed of data as shown by a dotted line in FIG. 4 from the storage unit 96, for example. As shown by the solid line in FIG. 4, the solid-state imaging device 22 has low sensitivity of the G component when the color temperature is low. Therefore, by using the look-up table shown by the dotted line in the figure, for example, it is possible to compensate for the decrease in the sensitivity of the G signal of the CCD sensor at a low color temperature and to increase the G signal at a low color temperature, that is, Correction is performed so that the amount of light incident on the solid-state imaging device 22 is increased.

This is because, for example, in the overall controller 58, the color temperature detector 78
When the color temperature due to the signal from is low, the light amount data sent from the AE control unit 66 is corrected to be small.
The AE control unit 66 that receives the corrected light amount data from the overall control unit 58 has a small corrected light amount, and therefore the iris driving unit 28 and the shutter driving unit to further increase the exposure amount.
Control 40. As a result, the diaphragm and shutter are controlled to increase the exposure amount, and the solid-state imaging device 22
The amount of light incident on is increased. As indicated by the solid line in FIG. 4, the solid-state imaging device 22 has a G value when the color temperature is low.
Since the sensitivity of the component is low, even if the amount of incident light increases, G
The output of the component does not increase and becomes constant.

The sensitivity due to the color temperature of the luminance signal created by the matrix circuit by the output from the solid-state imaging device 22 is shown by the alternate long and short dash line in FIG. 5, so the exposure is controlled so that the luminance signal is constant. In this case, a look-up table shown by a dotted line in the figure may be used to correct the decrease in the sensitivity of the CCD sensor when the color temperature is low as in the case of the G signal.

The overall control unit 58 also adjusts the amplifier gain of the color separation gain adjusting unit 50 independently for each of the three colors in accordance with the output from the color temperature detecting unit 78, whereby the video signals of substantially the same level for each RGB color are output from the output 54. Adjust the white balance so that it is output.

Note that FIG. 1 does not show the recording function part of the electronic still camera realized as the embodiment of the present invention, that is, the function part for recording the video signal of the output 62 on the video signal recording medium such as a video floppy. This is omitted in order to avoid complication of the drawings and description, which is not directly related to the understanding of the present invention, but in order to fulfill the function as a camera, this functional unit is also included in this embodiment. Needless to say.

The shutter release button 72 operates in a two-step stroke. First, when the button is pressed to the first stage, the overall control unit 58 responds to this and activates the AE control unit 66, and TTL photometry by the light detection element 36, color temperature detection by the color temperature detection unit 78, and diaphragm drive. Control of the diaphragm 14 by the unit 28, and shutter drive unit
The shutter 18 is controlled by 40. That is, as described above, the AE control unit 66 measures the amount of light incident from the field through the lens 12 by the photodetector element 36, and outputs the photometric value to the overall control unit 58. In addition, the color temperature detection unit 78,
The color temperature of the incident light incident through the opening 80 is detected, and the detected value is output to the overall control unit 58. As described above, the overall control unit 58 receives the color temperature signal from the color temperature detection unit 78.
The light amount signal from the AE control unit 66 is corrected, and the corrected light amount signal is sent to the AE control unit 66.The AE control unit 66 responds to this signal by the degree of the aperture of the diaphragm 14, that is, the aperture value, and the shutter 18
Determines the opening time or exposure time.

When the shutter release button 72 is pressed to the second stage,
In response to this, the overall control unit 58 controls the diaphragm drive unit 28 and the shutter drive unit 40 in accordance with the determined aperture value and exposure value, respectively, and causes the solid-state imaging device 22 to perform image capturing. The solid-state imaging device 22 accumulates electric charges according to the subject image exposed in the imaging cell array 24 by opening the shutter 18, and outputs a color video signal corresponding to the electric charges in response to the driving clock from the driving input 44. Output to 48.

The color video signal read from the solid-state imaging device 22 is amplified by the color separation gain adjusting unit 50 and decomposed into the three-color signals RGB. At that time, the overall control unit 58 adjusts the gain of the color separation gain adjusting unit 50 independently for each of the three colors in accordance with the color temperature data obtained from the color temperature detecting unit 78. As a result, the white balance-adjusted three-color signal RGB is output to the output 54 of the color separation gain adjustment unit 50.

The three-color signal RGB output from the color separation gain adjusting unit 50 is input to the matrix circuit 60, and the circuit 60 creates a luminance signal Y according to a predetermined synthesis rule. The matrix circuit 60 also
The color difference signals RY and BY are formed, the luminance signal Y is output to the output 62, and the color difference signals RY and BY are generated.
Are output to the output 62 in the scanning line order.

As described above, in the present embodiment, the light amount of the incident light detected by the photodetector 36 is corrected by the color temperature of the incident light detected by the color temperature detector 78, and the solid-state imaging device 22 and the photodetector 36 are corrected. It compensates for the difference in sensitivity due to the color temperature. Therefore, for example, when the color temperature is as low as about 3000 ° K, the amount of incident light is adjusted so as to compensate for the decrease in the sensitivity of the solid-state imaging device 22, so that the solid-state imaging device 22 can adjust the color temperature regardless of changes in the color temperature. It is possible to always obtain a constant G signal output or Y signal output.

Therefore, from the scene through the imaging lens 12 to the imaging device
Even if there is a change in the color temperature of the light incident on 22, the level of the luminance signal Y synthesized from the G signal of the video signal or the video signal output from the solid-state imaging device 22 is properly adjusted. Therefore, a video signal representing a good image can be obtained from the output 62. An exposure error caused by a difference in photosensitivity between the photometric element 36 and the image pickup device 22, such as saturation or smallness of a photocarrier due to incident light, which often occurs in a conventional electronic still camera, is minimized.

As described above, in the present invention, the difference in sensitivity due to the color temperature of the image sensor and the photometric element is adjusted so that the G signal of the output signal of the solid-state image sensor or the luminance signal synthesized from the output signal according to a predetermined synthesis rule becomes constant. To compensate. Therefore, the level of the video signal output from the solid-state imaging device can be properly adjusted even if the color temperature of the light entering the solid-state imaging device from the field changes.

Therefore, a video signal representing a good image can be obtained, and the exposure error caused by the difference in sensitivity due to the color temperature of the photometric element and the solid-state imaging device, which occurs in the conventional electronic still camera, is minimized.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of an exposure control device for an electronic still camera according to the present invention, FIG. 2 is a block diagram showing an example of the color temperature detection unit of FIG. 1, and FIG. Fig. 2 is a graph showing the output characteristics of the color temperature detection unit, and Figs. 4 and 5 are graphs showing the change in sensitivity due to the color temperature of the CCD sensor when the output of the auto iris sensor in Fig. 1 is constant. is there. Explanation of symbols of main parts 14 ... Aperture 18 ... Shutter 22 ... Solid-state imaging device 28 ... Aperture drive unit 36 ... Photodetector 40 ... Shutter drive unit 42 ... Logarithmic amplifier 58 ... Overall control unit 60 ... Matrix circuit 66 ... AE control unit 78 ... Color temperature detection unit 90, 92 ... Logarithmic amplifier 94 ... Differential amplifier 96 ... Storage unit

Claims (7)

[Claims] 1. An exposure control apparatus for controlling exposure of an electronic still camera, wherein an image of a field is captured by a solid-state imaging device to form a video signal representing an image of the field, the apparatus comprising: Light detecting means for receiving the incident light from the device and outputting a first signal according to the amount of the incident light; and detecting a color temperature of the object field and outputting a second signal according to the color temperature. Color temperature detection means, and exposure control means for controlling the exposure of the electronic still camera by the first signal and the second signal, the exposure control means comprising the solid-state imaging device and the light detection means. Between the storage means for storing the correction data for compensating the difference in sensitivity due to the color temperature, and the correction data for the first signal based on the correction data in the storage means according to the second signal. , The third signal with the first signal corrected Based on the third signal output from the first control means, which outputs the first signal output from the light detection means to the first control means. And a second control means for controlling the exposure amount of the electronic still camera, wherein the exposure control means responds to the sensitivity according to the color temperature of the solid-state imaging device and the color temperature of the light detection means. An exposure control device for an electronic still camera, which performs exposure control compensating for a difference from sensitivity. 2. The apparatus according to claim 1, wherein the solid-state imaging device forms a color video signal, and the electronic still camera forms a luminance signal from the color video signal according to a predetermined synthesis rule. And a matrix circuit for outputting the output, and the exposure control means is responsive to the first signal from the light detection means and the second signal from the color temperature detection means,
An exposure control apparatus, which controls an exposure amount of the electronic still camera so that a luminance signal output from the matrix circuit means becomes constant irrespective of a color temperature of the field. 3. The apparatus according to claim 1, wherein the solid-state imaging device forms a color video signal, and the electronic still camera forms a luminance signal from the color video signal according to a predetermined synthesis rule. And a matrix circuit for outputting the color image signal in accordance with the output signal from the light detection unit and the output from the color temperature detection unit. An exposure control apparatus, which is controlled so as to be constant irrespective of color temperature. 4. The apparatus according to claim 2 or 3, wherein the apparatus adjusts the white balance of each color signal of the color video signal output from the solid-state imaging device, White balance adjusting means for adjusting based on a second signal output from the color temperature detecting means, and the matrix circuit means includes the white balance adjusting means for adjusting the white balance from the color video signal. An exposure adjusting device for an electronic camera, which forms a luminance signal. 5. The exposure apparatus for an electronic still camera according to claim 1, wherein the solid-state imaging device includes a charge-coupled device, and the photodetector includes a silicon-based photodiode. Control device. 6. The apparatus according to claim 1, wherein the exposure control unit determines the amount of incident light detected by the light detection unit when the color temperature detected by the color temperature detection unit is low. An exposure control apparatus for an electronic still camera, wherein the exposure control is performed based on the correction data having a characteristic of correcting a corresponding first signal to a low level and thereby increasing an exposure amount of the electronic still camera. 7. The electronic still camera according to claim 1, wherein said exposure control means performs exposure control for controlling an aperture and / or a shutter of said electronic still camera. Exposure control device.