JP2006324851A - White balance adjusting device and digital camera, white balance adjustment method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white balance adjusting device, a digital camera, a white balance adjusting method and a program capable of carrying out white balance adjustment with high accuracy at strobe photography, even under constitution or photography conditions in which an objective distance can not be obtained. <P>SOLUTION: At photography with strobe light, a control unit 8 acquires a ratio between brightness of photographed image and brightness of an image displayed as a through-image just before on a display unit 10, and white balance adjustment is carried out based on the ratio. At the white balance adjustment, the white balance adjustment value is set by weighting, according to the ratio, between a first adjustment value of non-strobe photography and a second adjustment value of non-strobe photography. At the strobe photography, the white balance of photographed image is adjusted according to the degree of influence of strobe light, so that white balance adjustment with high accuracy can be performed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a white balance adjustment device suitable for use in a digital camera, a digital camera, a white balance adjustment method, and a program used for realizing them.

  Conventionally, in a digital camera, white balance adjustment for a captured image is generally performed by controlling the gains of R (red) and B (blue) components in an image signal to values corresponding to, for example, the type of light source in a shooting environment. ing.

As a technique for performing the optimum white balance adjustment at the time of flash photography, for example, in Patent Document 1 below, R gain and B gain of an image signal, that is, white balance adjustment values for non-strobe photography and strobe photography are used. Is a technology that controls the actual adjustment value to a value that changes the weighting of the adjustment value for non-strobe shooting and the adjustment value for strobe shooting according to the subject distance. Are listed.
JP 2004-166310 A

  However, in order to perform the above-described white balance adjustment, it is indispensable to acquire the subject distance during flash photography. Therefore, it cannot be implemented in a configuration in which the subject distance cannot be acquired, such as a digital camera that does not have a focus adjustment function or a distance measurement function. Even when the subject distance can be obtained, a precise white balance adjustment is necessary when shooting in a shooting environment where the subject distance cannot be obtained, such as when the subject cannot be measured because the subject is dark. There was a problem that could not be done.

  The present invention has been made in view of such a conventional problem, and enables white balance adjustment with high accuracy in strobe shooting even in a configuration and shooting environment in which the subject distance cannot be obtained. An object of the present invention is to provide an adjustment device, a digital camera, a white balance adjustment method, and a program used for realizing them.

  In order to solve the above-mentioned problem, in the invention of claim 1, in the white balance adjustment device that adjusts the white balance of the image captured by the image sensor, the image is captured by the image sensor during non-strobe imaging without strobe light emission. First luminance acquisition means for acquiring the first subject luminance from the captured image, and second luminance for acquiring the second subject luminance from the captured image captured by the image sensor during strobe imaging in accordance with a photographing operation involving strobe light emission. And a change degree acquisition means for acquiring a change degree of the second subject brightness acquired by the second brightness acquisition means with respect to the first subject brightness acquired by the first brightness acquisition means. And a white balance for adjusting the white balance of the photographed image based on the degree of change acquired by the degree-of-change acquiring means. It was that a settling unit.

  In such a configuration, the white balance of the photographed image is adjusted based on the degree of change in subject brightness between the image at the time of non-strobe photographing and the photographed image at the time of strobe photographing according to the photographing operation. In other words, highly accurate white balance adjustment can be performed by adjusting the white balance in the captured image in accordance with the degree of influence of the strobe light.

  In the invention of claim 2, the first subject luminance acquired by the first luminance acquisition unit and / or the second subject luminance acquired by the second luminance acquisition unit is Brightness correction means for correcting according to the difference between the shooting conditions set for non-strobe imaging without strobe light emission and the shooting conditions set for strobe imaging with strobe light emission according to the shooting operation; The change degree acquisition unit acquires the change degree based on the first subject brightness and / or the second subject brightness after being corrected by the brightness correction unit.

  In such a configuration, even when the shooting conditions are different between non-strobe shooting and strobe shooting, white balance adjustment is performed based on the exact degree of influence of strobe light that reflects the difference between the two shooting conditions. be able to.

  According to a third aspect of the present invention, the first luminance acquisition means acquires the first subject luminance from an image captured in a shooting standby state immediately before the shooting operation is performed.

  In such a configuration, it is possible to eliminate a wasteful imaging operation without strobe light emission for white balance adjustment of a captured image taken with a flash.

  According to a fourth aspect of the present invention, the white balance adjusting unit is configured to adjust the white balance of the photographed image based on the degree of change acquired by the degree of change acquisition unit and the amount of flash emission at the time of the strobe imaging. Was to be adjusted.

  In such a configuration, it is possible to perform white balance adjustment according to the color difference of the strobe light that varies depending on the amount of strobe light emission.

  According to the invention of claim 5, brightness acquisition means for acquiring the brightness of the subject at the time of the strobe imaging, and shooting operation corresponding to the brightness of the subject acquired by the brightness acquisition means. Adjustment value acquiring means for acquiring a white balance adjustment value for strobe imaging with corresponding strobe light emission, wherein the white balance adjustment means accompanies the degree of change acquired by the change degree acquisition means and the strobe light emission. The white balance of the photographed image is adjusted based on the white balance adjustment value for non-strobe imaging and the white balance adjustment value for strobe imaging acquired by the adjustment value acquisition unit.

  In such a configuration, it is possible to perform white balance adjustment according to the difference in the amount of steady light during shooting.

  According to a sixth aspect of the present invention, the image processing apparatus includes a light source determination unit that determines a light source type at the time of the non-stroboscopic imaging based on a captured image obtained by the non-stroboscopic imaging. The white balance of the photographed image is adjusted based on the degree of change acquired by the degree-of-change acquiring unit and the light source type determined by the light source determining unit.

  In such a configuration, the white balance can be adjusted according to the difference in the characteristics of the light source under the shooting environment.

  In the invention of claim 7, the white balance adjustment for the photographed image by the white balance adjusting means is performed by using the white balance adjustment value as the first adjustment value for non-strobe imaging and the strobe imaging. According to the degree of change in the white balance adjustment value that is set by the weighting based on the degree of change acquired by the degree-of-change acquisition unit and the white balance adjustment value that is set by the process. And a process of setting a weighting change rate between the changing first adjustment value and the second adjustment value in accordance with the light source type determined by the light source determination means.

  In such a configuration, as the white balance adjustment value, it is possible to obtain a value corresponding to characteristics such as a color temperature difference from strobe light that varies depending on the light source in the shooting environment, and light wraparound.

  In the invention of claim 8, the white balance adjustment for the photographed image by the white balance adjusting means is performed by using the white balance adjustment value as the first adjustment value for non-strobe imaging, or during strobe imaging. It is assumed that the process for setting the second adjustment value is included.

  According to the ninth aspect of the present invention, the white balance adjustment for the photographed image by the white balance adjusting means is performed by using the white balance adjustment value as the first adjustment value for non-strobe imaging and the strobe imaging. It is assumed that a process of setting by weighting with the second adjustment value is included.

  In such a configuration, the white balance adjustment value is changed between the first adjustment value for non-strobe imaging and the second adjustment value for strobe imaging according to the degree of influence of strobe light on the subject. Thus, white balance adjustment is performed.

  In the invention of claim 10, the white balance adjusting means includes a limiting means for limiting an adjustment limit of the white balance adjustment value toward the second adjustment value.

  In such a configuration, accurate white balance adjustment is performed even in the case where the influence of the strobe light is slight even in a shooting environment where the color change is large even if the influence of the strobe light in the photographed image is slight. Can do.

  In the invention of claim 11, the limiting means sets the adjustment limit to the second adjustment value side in the white balance adjustment value, the light source type determined by the light source determination means, or the strobe. The limit was set according to the amount of luminescence.

  Even in such a configuration, accurate white balance adjustment can be performed even in a shooting environment where the change in color is large even in the case of a shooting environment where the change in color is large even if the influence of the strobe light on the captured image is slight. Can do.

  In the twelfth aspect of the invention, the first luminance acquisition unit obtains the first subject luminance from a predetermined region in a captured image obtained by non-strobe imaging without strobe light emission. The second luminance acquisition means acquires the second subject luminance from the predetermined area in the photographed image obtained by strobe imaging with strobe light emission according to the photographing operation.

  In such a configuration, the influence of sudden external light is reflected only on one of the subject brightness of the image at the time of non-strobe imaging and the subject brightness of the captured image at the time of strobe imaging according to the shooting operation. The probability of

  According to a thirteenth aspect of the present invention, a digital image provided with a light emitting means for recording a photographic image picked up by an image pickup device in accordance with a photographing operation on a recording medium as image data and performing strobe light emission as necessary. In the camera, a first luminance acquisition unit that acquires a first subject luminance from a captured image obtained by non-strobe imaging without strobe light emission by the light emission unit, and strobe imaging with strobe light emission according to a shooting operation. Acquired by the second luminance acquisition means for acquiring the second subject luminance from the obtained photographed image, and the second luminance acquisition means for the first subject luminance acquired by the first luminance acquisition means. Based on the degree of change acquired by the degree-of-change acquiring means for acquiring the degree of change of the second subject luminance, Was that a white balance adjusting means for adjusting the white balance of.

  In such a configuration, when the digital camera performs strobe shooting, it is possible to perform white balance adjustment with high accuracy by adjusting the white balance in the captured image in accordance with the degree of influence of the strobe light.

  According to the fourteenth aspect of the present invention, in the white balance adjustment method in the white balance adjustment device for adjusting the white balance of the image picked up by the image pickup device, the non-strobe image pickup without strobe emission and the shooting operation are performed. A step of performing strobe imaging with strobe emission, a step of acquiring a first subject luminance from a captured image obtained by the non-strobe imaging, and a second from the captured image obtained by the strobe imaging. A method including: obtaining a subject brightness of the subject; obtaining a change degree of the second brightness with respect to the first subject brightness; and adjusting a white balance of the captured image based on the change degree; did.

  According to this method, it is possible to adjust the white balance with high accuracy by adjusting the white balance in the captured image in accordance with the degree of influence of the strobe light.

  In a fifteenth aspect of the present invention, a computer having a white balance adjustment device for adjusting white balance of an image picked up by an image pickup device is provided with a computer based on a picked-up image obtained by non-strobe image pickup without strobe light emission. A process for obtaining one subject brightness, a process for obtaining a second subject brightness from a captured image obtained by strobe imaging with strobe emission in accordance with a photographing operation, and the second subject brightness with respect to the first subject brightness. A program for executing a process of acquiring a luminance change degree and a process of adjusting the white balance of the captured image based on the change degree is provided.

  As described above, in the present invention, it is possible to perform white balance adjustment with high accuracy by adjusting the white balance in the captured image in accordance with the degree of influence of the strobe light. Therefore, it is possible to perform white balance adjustment with high accuracy in strobe shooting even in a configuration in which the subject distance cannot be obtained or in a shooting environment.

  In addition, even when shooting conditions differ between non-strobe shooting and strobe shooting, it is possible to perform white balance adjustment based on the precise degree of strobe light that reflects the difference between the two shooting conditions. .

  Furthermore, in the white balance adjustment device of the present invention, it is possible to eliminate a wasteful image pickup operation without strobe light emission for white balance adjustment of a photographed image taken with a flash. Therefore, efficient white balance adjustment can be performed.

  In addition, the white balance adjustment according to the difference in the color of the strobe light that varies depending on the flash emission time, the accurate white balance adjustment according to the difference in the amount of steady light during shooting, and the difference in the characteristics of the light source under the shooting environment The white balance can be adjusted accordingly. Therefore, more accurate white balance adjustment can be performed.

  In addition, as a white balance adjustment value, it is possible to obtain a value corresponding to characteristics such as a difference in color temperature from strobe light and light wraparound depending on a light source in a shooting environment. Therefore, it is possible to perform white balance adjustment with higher accuracy.

  In addition, accurate white balance adjustment can be performed even in the case where the effect of the strobe light is small even in a shooting environment where the color change is large even if the effect of the strobe light in the captured image is slight. I made it. Therefore, it is possible to cope with various shooting situations.

  There is a low probability that the influence of sudden extraneous light is reflected only on either the subject brightness of the image during non-strobe imaging or the subject brightness of the captured image during strobe imaging according to the shooting operation. . Therefore, it is possible to prevent a decrease in white balance adjustment accuracy due to suddenly generated external light.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a block diagram showing the overall configuration of a digital camera 1 according to the present invention. The digital camera 1 picks up an image of an object via an optical lens group 2, a lens driving circuit 3 for driving a zoom lens and a focus lens (including a diaphragm mechanism) constituting the optical lens group 2, and the optical lens group 2. And a strobe circuit (light emitting means) 5 including a CCD 4 as an imaging means, a light emitting tube such as a xenon tube, and a drive circuit for driving the light emitting tube.

  The CCD 4 is scan-driven by a TG (Timing Generator: timing generator) 6 at a predetermined cycle, photoelectrically converts the optical image of the subject collected by the optical lens group 2 for each pixel, and performs analog processing on the analog imaging signal. Output to unit 7. The analog processing unit 7 includes a CDS (Correlated Double Sampling) that removes noise included in the image pickup signal input from the CCD 4, an AGC (gain adjustment amplifier) that amplifies the image pickup signal after noise removal, and amplification. It comprises an AD (A / D converter) for digitally converting the subsequent imaging signal, and outputs the imaging signal (Bayer data) converted into digital data to the control unit 8.

  As shown in FIG. 2, the control unit 8 mainly includes a CPU 81 that controls the digital camera 1, an image processing block 82 that performs various image processing to be described later, and a data input / output interface (not shown). The image processing block 82 includes an interpolation circuit 821, a buffer memory 822, a gain adjustment circuit 823, a gamma correction circuit 824, and a YC matrix circuit 825.

  The Bayer data output from the analog processing unit 7 to the control unit 8 is converted into R, G, B color component data (RGB data) for each pixel by the interpolation circuit 821 of the image processing block 82, and then the buffer memory. The white balance adjustment is performed in the gain adjustment circuit 823 through the gain adjustment of the R data and the B data via the reference numeral 822. Further, after the gamma characteristic (gradation characteristic) is corrected for the RGB data after white balance adjustment by the gamma correction circuit 824, the luminance signal (Y) and the color difference signal (U, U) are converted from the RGB data in the YC matrix circuit 825. Y) data for each pixel consisting of V) is generated.

  The YUV data generated in the image processing block 82 is temporarily stored in the memory 9 and sent to the image display device 10. The image display device 10 includes a video encoder, a VRAM, a liquid crystal monitor, and a driving circuit thereof. The image display device 10 generates a video signal based on the transmitted YUV data by the video encoder, and a display image based on the video signal, that is, a through image of a subject imaged by the CCD 4 is generated. Displayed on the LCD monitor.

  Further, the YUV data imaged by the CCD 4 during the shooting operation in the recording mode and generated by the image processing block 82 is recorded on the image recording medium 11 as compressed image data compressed and encoded by the CPU 81 by a predetermined method. The compressed image data recorded on the image recording medium 11 is displayed on the image display device 10 after being decompressed and decoded by the CPU 81 in the reproduction mode.

  An operation key unit 12 is connected to the control unit 8. The operation key unit 12 includes a mode switching key for switching between a recording mode for shooting and a playback mode for displaying a recorded image, a shutter button, a zoom key, a strobe mode switching key, and setting keys used for various setting operations. The operation state of each switch is periodically scanned by the CPU 81.

  The image recording medium 11 is a flash memory or the like. As shown in FIG. 3, a program area 11b is secured separately from the image storage area 11a for storing the compressed image data described above. In the program area 11b, a control program for causing the CPU 81 to perform various controls such as the above-described compression / decompression of image data, AE control, AF control, control related to white balance adjustment described later, and the like are used. Various data are stored. The various data are a program diagram for through image and shooting used for AE control, a gain acquisition table for through image and strobe shooting, and the like. The gain acquisition table is set in the gain adjustment circuit 823. It is a table which shows the value of R gain for R data and B gain for B data which should be performed.

  In this embodiment, the CPU 81 operates in accordance with the control program as a first luminance acquisition unit, a second luminance acquisition unit, a change degree acquisition unit, a white balance adjustment unit, and a luminance correction unit of the present invention. Function.

  Next, an operation according to the present invention of the digital camera 1 having the above configuration will be described. 4 and 5 are flowcharts showing processing contents in the CPU 81 of the control unit 8 when the recording mode is set by the operation of the mode switching key of the operation key unit 12 by the user.

  The CPU 81 starts the operation together with the setting of the recording mode, and starts imaging with a fixed period by the CCD 4 and display of a through image based on the captured image data (step SA1). Then, the light source type is determined based on the color information of the RGB data sent from the interpolation circuit 821 of the image processing block 82, and a through image gain acquisition table (light source type) stored in the program area 11 b of the image recording medium 11. And the gain value correspondence table), the gain values (R0, B0) suitable for the determined light source type are used as the white balance adjustment R component and B component gain values in the gain adjustment circuit 823. Is stored in its own internal memory (not shown) (step SA2). Further, based on the luminance signal sent from the YC matrix circuit 825 of the image processing block 82, an appropriate Ev value (Ev0) corresponding to the brightness of the subject at that time is determined and stored in its own internal memory (step SA3). ). The Ev value is equivalent to a value obtained by adding the shutter speed (Tv), the aperture value (Av), and the gain value (Sv: ISO sensitivity equivalence value). Also, the Ev value determined in step SA3 is higher than the value determined during flash photography using the through image program diagram (FIG. 3) in order to increase the brightness of the through image and improve the visibility. Also set a bright value. Thereafter, based on the luminance signal sent from the YC matrix circuit 825 of the image processing block 82, the integral value (Y0) of the luminance Y for each pixel in the image data is measured and stored in the internal memory (step SA4).

  Thereafter, if the shutter button is not operated (NO in step SA5), the processing in steps SA2 to SA4 is repeated, and the gain value (R0, B0), Ev value (Ev0), and integral value of luminance Y in the internal memory ( Y0) is updated sequentially. When the shutter button is operated (YES in step SA5), the strobe mode setting state at that time is confirmed, and the following processing is performed according to the contents of the set strobe mode.

  That is, when the strobe mode currently set by the user operating the strobe mode switching key of the operation key section 12 is a mode other than the auto strobe mode or the forced flash mode, that is, the flash prohibition mode (step SA6). , SA7 are NO), a normal photographing process is performed, and the photographed image is stored in the buffer memory 822 (step SA8). Thereafter, the RGB data temporarily stored in the buffer memory 822 using the gain values (R0, B0) set in the gain adjustment circuit 823 at the time of shooting operation as they are as gain values for white balance adjustment. Is adjusted (step SA9), and an image based on the RGB data after the white balance adjustment is recorded on the image recording medium 11 (image storage area 11a) (step SA28: FIG. 5).

  If the strobe mode is the forced flash mode (NO at step SA6, YES at step SA7), pre-flash shooting is performed to obtain a shot image (step SA10), and the brightness of the shot image, that is, the image Based on the luminance signal sent from the YC matrix circuit 825 of the processing block 82, the flash emission time (t1) at the time of actual photographing is determined and stored in the internal memory (step SA11). Then, strobe shooting (main shooting) is performed with the light emission time (t1), and the shot image is stored in the buffer memory 822 (step SA12). Thereafter, white balance adjustment processing is performed on the RGB data temporarily stored in the buffer memory 822 in accordance with the degree of influence of the strobe light on the subject (step SA13), and recording based on the RGB data after white balance adjustment is performed. An image is generated and recorded on the image recording medium 11 (step SA28: FIG. 5). The white balance adjustment process is the same as steps SA19 to SA27 described later except for some processes. The detailed description is omitted here.

  If the auto / strobe mode is set as the strobe mode at the time of shooting when the shutter button is operated (YES in step SA6), it is further determined whether or not strobe light emission is necessary (step SA14). Whether or not strobe light emission is necessary is determined based on whether or not the Ev value (Ev0) stored in the previous step SA3 has reached a predetermined limit value. If it is determined that the strobe light emission is unnecessary (NO in step SA14), the processing after step SA8 described above is performed.

  On the other hand, if it is determined that strobe light emission is necessary (YES in step SA14), the Ev value for strobe shooting (Ev1), specifically, a value determined at the time of displaying a through image in consideration of strobe light emission. A dark value is set and stored in the internal memory (step SA15). That is, the shutter speed, aperture value, and gain value for obtaining the Ev value (Ev1) are set based on the shooting program diagram (FIG. 3). Thereafter, pre-flash photography is performed to obtain a photographed image (step SA16). Based on the brightness of the photographed image, that is, the brightness signal sent from the YC matrix circuit 825 of the image processing block 82, the flash emission time at the time of actual photography. (T1) is determined and stored in the internal memory (step SA17). Then, strobe shooting (main shooting) is performed with the light emission time (t1), and the shot image is stored in the buffer memory 822 (step SA18). The stored image is also sent to the subsequent circuit, and the luminance value (Y1) in the stored image (flash image) is measured based on the luminance signal sent from the YC matrix circuit 825 and stored in the internal memory (step SA19). ).

Subsequently, as shown in FIG. 5, the gain acquisition table for strobe shooting is referred to, and the gain value (R1, B1) for white balance adjustment corresponding to the strobe light emission time (t1) is acquired. (Step SA20). Further, in order to correctly compare the luminance of the subject (Y0) immediately before shooting (while displaying a through image) stored in the internal memory with the luminance of the subject at the time of flash shooting, the Ev value (Ev0) immediately before shooting is The brightness value (Y1) at the time of flash photography is corrected from the difference from the Ev value (Ev1) at the time of flash photography (main photography) (step SA21). That is, since the influence of the difference in Ev value on the image luminance is generally doubled at 1 Ev, the corrected luminance (Y1 ′) is obtained by the following equation based on the relationship. The method for obtaining the corrected luminance (Y1 ′) may be other than this.
・ Y1 ′ = Y1 × 2 ^ (Ev1-Ev0)

  Subsequently, the ratio between the luminance immediately before photographing (Y0) and the corrected luminance (Y1 ′) is calculated, and it is confirmed whether or not it is larger than a predetermined threshold (Kmax), for example, “3”. When it is larger than the threshold value, that is, when the degree of influence of the strobe light on the image brightness is large (YES in step SA22), the gain value for white balance adjustment of the gain adjustment circuit 823 corresponds to the strobe light emission time (t1). The gain values (R1, B1) to be set are set, and white balance adjustment is performed on the RGB data on the buffer memory 822 (step SA23), and an image based on the RGB data after the white balance adjustment is recorded on the image recording medium 11. (Step SA28).

When the ratio is equal to or less than the threshold value (Kmax) but is equal to or greater than “1”, that is, when the degree of influence of the strobe light on the image luminance is small (both steps SA22 and SA24 are NO), first, The gain between the gain value (R0, B0) for white balance adjustment (suitable for the light source type) set immediately before shooting and the gain value (R1, B1) corresponding to the flash emission time (t1) Gain value (R2, B2) that is weighted according to the ratio of the luminance value (Y0) immediately before photographing and the correction luminance (Y1 ′) described above (the degree of influence of strobe light on the image luminance) Is calculated by the following equation (step SA25). Note that k in the following equation is a constant specific to the camera model, and the weighting may be performed using another equation.
* R2 = k * {(R1-R0) * Y1 '/ Y0 + R0)}
B2 = k * {(B1-B0) * Y1 '/ Y0 + B0)}

  Then, white balance adjustment by setting the calculated gain values (R2, B2) in the gain adjustment circuit 823 is performed on the RGB data (strobe image data) on the buffer memory 822 (step SA26), and white balance is performed. An image based on the adjusted RGB data is recorded on the image recording medium 11 (step SA28).

  On the other hand, when the ratio is equal to or less than the threshold (Kmax) and smaller than “1”, that is, except for the case described above (NO in step SA22, YES in step SA24), the gain adjustment circuit 823 is used for white balance adjustment. White balance adjustment is performed on the RGB data on the buffer memory 822 as the gain value (R0, B0) set at the time of the shooting operation (step SA27), and an image based on the RGB data after white balance adjustment is recorded in the image. Recording is performed on the medium 11 (step SA28).

  Here, the processing in step SA13, which has not been described above, that is, the white balance adjustment processing when the strobe mode is the forced flash mode will be described. That is, in the process of step SA13, the above-described processes of SA19 to SA27 are also performed. In the forced flash mode, unlike the auto flash mode, the Ev value for flash photography (Ev1) is used as the Ev value during flash photography (main photography). In step SA13, the process of correcting the luminance value (Y) during strobe shooting in step SA21 is omitted, and the brightness after correction in steps SA22, SA24, and SA25 described above is performed. A process of using the luminance (Y1) before correction as it is instead of (Y1 ′) is performed.

  As described above, in the present embodiment, the gain value (R2, B2) for white balance adjustment at the time of flash photography is calculated using the brightness value (Y0) immediately before the flash photography and the brightness value (Y1) at the time of flash photography. It is calculated by weighting according to the ratio (forced flash mode) or the luminance value (Y0) immediately before the flash photography and the luminance value (Y1) at the time of flash photography are the difference between the Ev values before and after the photography (Ev1-Ev0) It is calculated by weighting according to the ratio with the corrected luminance (Y1 ′) corrected by (auto flash mode). In other words, highly accurate white balance adjustment can be performed by adjusting the white balance in the captured image in accordance with the degree of influence of the strobe light.

  Therefore, accurate white balance adjustment can be performed in strobe shooting even in a shooting environment where the subject distance cannot be obtained during shooting. Further, in the white balance adjustment method according to the present embodiment, since it is not necessary to acquire the subject distance as described above, the focus adjustment function and the distance measuring function are not provided, and the subject distance cannot be acquired. Even in a digital camera having a configuration, it is possible to perform white balance adjustment with high accuracy during flash photography.

  In the present embodiment, the gain value (R0, B0) set in the gain adjustment circuit 823 at the time of shooting operation is used as it is during normal shooting without strobe light emission, and the buffer memory 822 is used as it is. The white balance adjustment is performed on the RGB data temporarily stored in the buffer memory 822. The light source is determined based on the RGB data temporarily stored in the buffer memory 822, and stored in the program area 11b of the image recording medium 11. By referring to the gain acquisition table for the live image, the gain values (R0, B0) suitable for the determined light source type are used as the gain values of the R component and B component for white balance adjustment in the gain adjustment circuit 823. ), And RGB stored temporarily in the buffer memory 822 It may be the white balance adjustment for over data.

  In the present embodiment, in order to correctly compare the luminance (Y0) of the subject immediately before shooting (while displaying a through image) and the luminance of the subject at the time of flash shooting, in step SA21, the Ev value (Ev0) immediately before shooting. ) And the Ev value (Ev1) at the time of strobe shooting (main shooting), the luminance value (Y1) at the time of flash shooting is corrected, and the degree of influence of the strobe light using the corrected luminance value (Y1 ′) (Y1 '/ Y0) is acquired, but the present invention is not limited to this. From the difference between the Ev value (Ev0) immediately before shooting and the Ev value (Ev1) at the time of flash shooting (main shooting), The luminance (Y0) may be corrected, and the degree of influence of the strobe light may be acquired using the corrected luminance value.

  In the present embodiment, the brightness value (Y1 ′ / Y0) of the strobe light in the captured image obtained by the strobe shooting is obtained using the brightness value (Y0) of the through image immediately before the strobe shooting. Therefore, for example, compared to a case where a separate imaging operation without flash emission is performed immediately before (or immediately after) flash photography, there is no wasteful imaging operation only for white balance adjustment, and efficient white balance adjustment is performed. be able to.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. In the white balance adjustment according to the first embodiment, as described above, the difference in the brightness of the subject before and after the strobe light emission is reduced, that is, as the value of Y1 ′ / Y0 approaches “1”, the white balance adjustment is performed. The gain value for use will approach the gain value (R0, B0) during live view display. Therefore, for example, when shooting under tungsten light, even under slight changes in the brightness of the subject before and after the strobe light emission, under a shooting environment where the color change is large, the subject When the change in brightness is negligible, an accurate value cannot be obtained as a gain value for white balance adjustment.

  In the present embodiment, in order to prevent this, the CPU 81 functions as the limiting means of the present invention, so that the luminance immediately before shooting (Y0) and the corrected luminance (Y1) at the time of flash shooting (at the time of main shooting) are taken. ') The white balance adjustment gain value when the ratio (Y1' / Y0) to the threshold value (Kmax) is less than or equal to the gain value (R0, B0) immediately before shooting is limited. Is.

  Specifically, instead of the processes of steps SA20 to SA28 in the first embodiment, the processes of steps SB20 to SB29 shown in FIG. 6 are performed. That is, the processes from step SB20 to SB23 are the same as steps SA20 to SA23 in the first embodiment. On the other hand, when the determination result in step SB22 is NO and the ratio between the luminance immediately before shooting (Y0) and the corrected luminance (Y1 ′) at the time of flash shooting (at the time of actual shooting) is smaller than the threshold (Kmax). Then, it is confirmed whether or not the ratio exceeds a predetermined lower limit ratio (Klimit), for example, “2” (step SB24).

  If the lower limit ratio (Klimit) is exceeded (YES in step SB24), the gain value for white balance adjustment is set to the luminance value (Y0) immediately before shooting as in the first embodiment. After calculating the gain value (R2, B2) weighted according to the ratio to the corrected luminance (Y1 ′) (step SB25), the buffer memory 822 performs white balance adjustment using the calculated gain value (R2, B2). This is performed on the upper RGB data (step SB26). Thereafter, an image based on the RGB data after the white balance adjustment is recorded on the image recording medium 11 (step SB29).

On the other hand, when the ratio is equal to or lower than the lower limit ratio (Klimit) (NO in step SB24), a gain value weighted according to the lower limit ratio (Klimit) is used as a gain value for white balance adjustment. (R3, B3) is calculated by the following equation (step SB27). In the following equation, k is a constant specific to the camera model.
R3 = k * {(R1-R0) * Klimit + R0)}
B3 = k * {(B1-B0) * Klimit + B0)}

  Then, white balance adjustment based on the calculated gain values (R3, B3) is performed on the RGB data on the buffer memory 822 (step SB28), and an image based on the RGB data after white balance adjustment is recorded on the image recording medium 11. (Step SB29).

  With the above processing, in the present embodiment, there is little difference in the brightness of the subject before and after the flash light is emitted, and the gain value for white balance adjustment is the gain value immediately before shooting (suitable for the light source type). Even in the case of approaching (R0, B0), since the gain value actually used is restricted from approaching the gain value (R0, B0) above a certain level, the gain value (R0 immediately before photographing) is always set. , B0) can be a gain value shifted to a gain value (R1, B1) corresponding to the flash emission time (t1).

  For this reason, for example, when shooting under tungsten light, even in a shooting environment where the color change is large even if the change in the brightness of the subject (the degree of influence of the flash light) is slight before and after the flash light emission, In addition, even when the change in the brightness of the subject before and after the flash light emission is negligible, a good white balance can be obtained, and more various shooting situations can be handled.

(Embodiment 3)
Next, a third embodiment of the present invention will be described. In this embodiment, a plurality of the threshold value (Kmax), the lower limit ratio (Klimit), and the constant k for each model, which are fixed values in the second embodiment, are prepared in advance for each type of light source. A constant table 100 (see FIG. 7) showing the above constants (Kmax, Klimit, k) corresponding to is stored in the program area 11a of the image recording medium 11. In this embodiment, by causing the CPU 81 to function as the light source determination unit and the change rate setting unit of the present invention, at the time of strobe shooting, each constant (corresponding to the light source type determined during display of the through image immediately before shooting) Kmax, Klimit, k) are set with reference to the constant table 100, and the processes of steps SB20 to SB29 described above are performed.

  In such an embodiment, by setting each of the above constants (Kmax, Klimit, k) to a value suitable for the determination result of the light source type immediately before shooting, as a gain value for white balance adjustment during flash shooting, Since it is possible to obtain a gain value corresponding to characteristics such as a color temperature difference from strobe light and light wraparound depending on the light source under the shooting environment, white balance adjustment with higher accuracy can be performed.

  In the present embodiment, the processing described in the second embodiment is basically used, and each constant (Kmax, Klimit, k) used during the processing is suitable for the determination result of the light source type immediately before photographing. Although what is set as a value has been described, the present invention is not limited to this, and based on the processing described in the first embodiment, each constant (Kmax, k) used during the processing is determined as the light source type immediately before shooting. It can also be set to a value suitable for the result. Even in that case, the same effect as described above can be obtained.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described. In the present embodiment, the gain value (R1, B1) for white balance adjustment corresponding to the strobe light emission time (t1) is changed according to the Ev value (Ev0) immediately before photographing. More specifically, in the program area 11a of the image recording medium 11, a plurality of types of tables similar to the gain acquisition table for strobe shooting described above are stored for each different Ev value, and the CPU 81 has the brightness of the present invention. By functioning as an acquisition unit and an adjustment value acquisition unit, the following processing is performed during flash photography. That is, in step SA20 described above, the gain value for white balance adjustment corresponding to the strobe light emission time (t1) is referred to by referring to any strobe shooting gain acquisition table corresponding to the Ev value (Ev0) immediately before shooting. (R1, B1) is acquired.

  According to such an embodiment, the imaged image is captured in a shooting environment with a lot of constant light as in the case of so-called daytime synchro shooting, and in a shooting environment with a low amount of constant light as in the case of general strobe shooting. High-precision white balance adjustment can be performed both in a shooting environment where the color of the strobe light is dominant in the color component of the data.

  Note that the white balance adjustment gain values (R1, B1) corresponding to the flash emission time (t1) may be changed according to the brightness of the subject immediately before the flash photography, and the Ev value immediately before the photography is not necessarily required. It is not necessary to change according to (Ev0). For example, an optical sensor for detecting ambient brightness can be provided separately from the CCD 4, and the gain values (R1, B1) can be changed according to the detection result of the optical sensor.

  Further, the gain value (R1, B1) for white balance adjustment corresponding to the strobe light emission time (t1) described above may be changed according to the light source type determined during the display of the through image immediately before shooting. More specifically, a plurality of types of tables similar to the above-described gain acquisition table for flash photography are stored for each different light source in the program area 11a of the image recording medium 11, so that the following processing is performed at the time of flash photography. Let it be done. That is, in step SA20 described above, by referring to any strobe shooting gain acquisition table corresponding to the light source type determined during the display of the through image immediately before shooting, the white balance corresponding to the strobe lighting time (t1). Gain values (R1, B1) for adjustment are acquired.

  Further, not only the processing described in the first embodiment but also the processing described in the second embodiment and the third embodiment corresponds to the flash emission time (t1). If the gain value (R1, B1) for white balance adjustment to be performed is changed according to the Ev value (Ev0) immediately before photographing, the same effect as in the present embodiment can be obtained.

(Embodiment 5)
Next, a fifth embodiment of the present invention will be described. In the white balance adjustment according to the first embodiment, since the threshold value (Kmax) and the constant k for each model are fixed values, the following is expected. That is, in general, the color temperature of strobe light tends to increase as the light emission time becomes shorter, and this becomes remarkable in a region where the light emission time is extremely short. Therefore, for example, when the reflectance of the subject is high during macro photography, the light emission time is extremely short and the color temperature of the strobe light becomes higher than usual. Therefore, an accurate value cannot be obtained as a gain value for white balance adjustment under such a shooting environment.

  In the present embodiment, in order to prevent this, the threshold value (Kmax) and the value of the constant k for each model are changed according to the strobe light emission time (t1). Specifically, instead of the processes of steps SA20 to SA28 in the first embodiment, the processes of steps SC20 to SC28 shown in FIG. 8 are performed. As is apparent from the figure, the processing is the same as that of the first embodiment except for the processing of step SC22 and step SC25.

  That is, in the process of step SC22, it is confirmed whether or not the ratio between the luminance immediately before photographing (Y0) and the corrected luminance (Y1 ′) is larger than the threshold value (Ktmax) corresponding to the flash emission time (t1). At this time, a smaller value is used for the threshold value (Ktmax) as the strobe light emission time (t1) is shorter. More specifically, for example, a value that is stored in advance in the program area of the image recording medium 11 and that is obtained from a threshold table indicating threshold values corresponding to different strobe lighting times, or a predetermined reference value and strobe lighting time ( The value calculated based on t1) is used.

In the process of step SC25, the gain value (R2, B2) corresponding to the ratio between the luminance (Y0) immediately before photographing and the corrected luminance (Y1 ′) is calculated by the following equation. At this time, the coefficient kt is specific to the camera model, and at the same time, a larger value is used as the strobe light emission time (t1) is shorter. More specifically, for example, a value that is stored in advance in the program area of the image recording medium 11 and that is obtained from a predetermined coefficient table indicating coefficients corresponding to different strobe light emission times, or a predetermined reference value and strobe light emission. The value is calculated based on time (t1).
* R2 = kt * {(R1-R0) * Y1 '/ Y0 + R0)}
* B2 = kt * {(B1-B0) * Y1 '/ Y0 + B0)}

  According to such an embodiment, even if the ratio between the luminance immediately before shooting (Y0) and the correction luminance (Y1 ′) at the time of flash shooting (main shooting) is the same, the flash emission time As (t1) is shorter, the gain value (R2, B2) for white balance adjustment can be shifted to the gain value (R1, B1) side corresponding to the strobe light emission time (t1). Therefore, for example, even when the reflectance of the subject is high during macro photography, an accurate value can be obtained as a gain value for white balance adjustment, and high-precision white balance adjustment is performed as in other cases. be able to.

  In the present embodiment, the processing described in the first embodiment is basically used, and the threshold (Kmax) used in the processing and the constant k for each model are changed according to the strobe light emission time (t1). However, the present invention is not limited to this, and based on the processing described in the second to fourth embodiments, the threshold (Kmax) used in the processing, the constant k for each model, and the above-mentioned The lower limit ratio (Klimit) may be changed according to the strobe light emission time (t1). Even in that case, the same effect as the present embodiment can be obtained.

  Further, in a configuration in which the amount of light emitted by the flash at the time of flash photography is controlled not by the light emission time (t1) but by changing the amount of light emitted per unit time, for example, the threshold (Kmax) is set according to the amount of light emitted per unit time. Alternatively, the constant k and the lower limit ratio (Klimit) for each model may be changed.

(Embodiment 6)
Next, a sixth embodiment of the present invention will be described. In the present embodiment, one of the processes described in the first to fifth embodiments is performed, and the measurement process of the integral value of luminance Y (steps SA4 and SA19 in the first embodiment) is performed. When performing, the integral value of the luminance Y for each pixel in the cross-shaped luminance detection area 200 intersecting at the center shown in FIG. 9 is measured. That is, the brightness Y0 and Y1 used in the white balance adjustment gain value acquisition processing (steps SA21, SA22, SA24, and SA25 in the first embodiment) at the time of flash photography are set in the through image, and This is an integral value of the luminance Y for each pixel in the cross-shaped luminance detection area 200 intersecting at the center shown in FIG. 9, which is set in the image captured at the time of flash photography (at the time of actual photography).

  In the present embodiment, by setting the measurement target of the luminances Y0 and Y1 to the luminance detection area 200, the luminances Y0 and Y1 are affected by sudden external light compared to the case where the measurement target is the entire image. The degree decreases. Therefore, the degree of influence of the strobe light on the image luminance, that is, the ratio between the luminance immediately before photographing (Y0) and the corrected luminance (Y1 ′) can be determined more accurately. As a result, it is possible to prevent a decrease in white balance adjustment accuracy when sudden extraneous light is generated.

  Note that the shape of the luminance detection area 200 may be any shape that takes into consideration the light distribution characteristics of a typical strobe and the shape of the subject within the range that the strobe light can reach, and an area other than the illustrated shape is set as the detection area. You can also.

It is a block diagram of a digital camera common to each embodiment of the present invention. It is a block diagram which shows the structure of the control part of the digital camera. It is a conceptual diagram which shows the storage area of an image recording medium. It is a flowchart which shows the operation | movement in 1st Embodiment. It is a flowchart following FIG. FIG. 6 is a flowchart corresponding to FIG. 5 illustrating an operation in the second embodiment. FIG. It is a conceptual diagram which shows the constant table used by the operation | movement in 3rd Embodiment. FIG. 6 is a flowchart corresponding to FIG. 5 and showing an operation in the fifth embodiment. It is a figure which shows the brightness | luminance detection area set to the image in 6th Embodiment.

Explanation of symbols

1 Digital camera 4 CCD
5 Strobe Circuit 7 Analog Processing Unit 8 Control Unit 81 CPU
82 Image processing block 821 Interpolation circuit 822 Buffer memory 823 Gain adjustment circuit 824 Gamma correction circuit 825 YC matrix circuit 9 Memory 10 Image display device 11 Image recording medium 100 Constant table 200 Brightness detection area

Claims (15)

In the white balance adjustment device that adjusts the white balance of the captured image,
First luminance acquisition means for acquiring a first subject luminance from a captured image obtained by non-strobe imaging without strobe light emission;
Second brightness acquisition means for acquiring a second subject brightness from a captured image obtained by strobe imaging with strobe light emission according to a shooting operation;
A degree of change acquisition means for acquiring a degree of change in the second subject brightness acquired by the second brightness acquisition means with respect to the first subject brightness acquired by the first brightness acquisition means;
A white balance adjustment device comprising: white balance adjustment means for adjusting white balance of the photographed image based on the change degree acquired by the change degree acquisition means. The first subject luminance acquired by the first luminance acquisition unit and / or the second subject luminance acquired by the second luminance acquisition unit is set in the non-strobe imaging without the strobe light emission. Brightness correction means for correcting according to the difference between the shooting conditions and the shooting conditions set for strobe imaging with strobe emission according to the shooting operation,
2. The white balance according to claim 1, wherein the change degree acquisition unit acquires the change degree based on the first subject brightness and / or the second subject brightness after correction by the brightness correction unit. Adjustment device.   2. The white balance adjustment device according to claim 1, wherein the first luminance acquisition unit acquires the first subject luminance from an image captured in a shooting standby state immediately before the shooting operation is performed.   The white balance adjusting means adjusts the white balance of the photographed image based on the degree of change acquired by the degree of change acquisition means and the amount of flash emission at the time of the strobe imaging. 2. The white balance adjusting device according to 2. Brightness acquisition means for acquiring the brightness of the subject during the strobe imaging;
Adjustment value acquisition means for acquiring a white balance adjustment value for strobe imaging with strobe light emission corresponding to the shooting operation corresponding to the brightness of the subject acquired by the brightness acquisition means,
The white balance adjustment means is a change degree acquired by the change degree acquisition means, a white balance adjustment value for non-strobe imaging without strobe light emission, and a strobe image acquisition time acquired by the adjustment value acquisition means. 4. The white balance adjustment device according to claim 1, wherein the white balance of the photographed image is adjusted based on the white balance adjustment value. Based on a captured image obtained by the non-stroboscopic imaging, comprising a light source determination means for determining a light source type at the time of the non-stroboscopic imaging,
The white balance adjustment means adjusts the white balance of the captured image based on the degree of change acquired by the degree of change acquisition means and the light source type determined by the light source determination means. The white balance adjusting device according to any one of 1 to 5.   In the white balance adjustment for the photographed image by the white balance adjusting means, the white balance adjustment value is set between the first adjustment value for non-strobe imaging and the second adjustment value for strobe imaging. A process of setting by weighting based on the degree of change acquired by the degree of change acquisition means, and the first adjustment value and the second of the white balance adjustment value set by the process, which change according to the degree of change The white balance adjustment apparatus according to claim 6, further comprising: a process of setting a change rate of weighting with respect to the adjustment value according to the light source type determined by the light source determination unit.   The white balance adjustment for the photographed image by the white balance adjusting means includes a process of setting the white balance adjustment value to the first adjustment value for non-strobe imaging or the second adjustment value for strobe imaging. The white balance adjustment device according to claim 1, wherein the white balance adjustment device is included.   The white balance adjustment for the photographed image by the white balance adjusting means is performed by weighting the white balance adjustment value between the first adjustment value for non-strobe imaging and the second adjustment value for strobe imaging. The white balance adjustment apparatus according to claim 1, further comprising a setting process.   The white balance adjustment device according to claim 7, wherein the white balance adjustment unit includes a limit unit that limits an adjustment limit of the white balance adjustment value toward the second adjustment value.   The limiting means limits an adjustment limit of the white balance adjustment value toward the second adjustment value according to a light source type or strobe light emission determined by the light source determination means. The white balance adjustment device according to claim 10. The first luminance acquisition means acquires a first subject luminance from a predetermined area in a captured image obtained by non-strobe imaging without strobe light emission,
12. The white balance according to claim 1, wherein the second brightness acquisition unit acquires the second subject brightness from the predetermined area in a captured image obtained by strobe imaging with strobe light emission according to a shooting operation. Adjustment device. In a digital camera provided with light emitting means for recording a photographic image captured by an image sensor in accordance with a photographing operation on a recording medium as image data and performing strobe light emission as necessary.
First luminance acquisition means for acquiring first subject luminance from a captured image obtained by non-strobe imaging without strobe emission by the light emitting means;
Second brightness acquisition means for acquiring a second subject brightness from a captured image obtained by strobe imaging with strobe light emission according to a shooting operation;
A degree of change acquisition means for acquiring a degree of change in the second subject brightness acquired by the second brightness acquisition means with respect to the first subject brightness acquired by the first brightness acquisition means;
A digital camera comprising: white balance adjustment means for adjusting white balance of the captured image based on the change degree acquired by the change degree acquisition means. In the white balance adjustment method in the white balance adjustment device for adjusting the white balance of the image captured by the image sensor,
A process of performing non-strobe imaging without strobe light emission and strobe imaging with strobe light emission according to the shooting operation;
Obtaining a first subject brightness from a captured image obtained by the non-stroboscopic imaging;
Obtaining a second subject luminance from a captured image obtained by the strobe imaging;
Obtaining a change degree of the second luminance with respect to the first subject luminance;
Adjusting the white balance of the captured image based on the degree of change. A computer having a white balance adjustment device that adjusts the white balance of an image captured by an image sensor,
A process of acquiring a first subject brightness from a captured image obtained by non-strobe imaging without strobe light emission;
A process of acquiring a second subject luminance from a captured image obtained by strobe imaging with strobe emission according to a shooting operation;
Processing for obtaining a change degree of the second luminance with respect to the first subject luminance;
A program for executing a process of adjusting a white balance of the photographed image based on the degree of change.

Images