JP4412109B2 - Electronic camera having color balance adjustment function and program - Google Patents

Description

The present invention relates to an electronic camera that performs color balance adjustment on flash image data.
The present invention also relates to a program for performing color balance adjustment on image data obtained by flash photography on a computer.

  Conventionally, Patent Document 1 is known as a technique for performing white balance adjustment during flash photography. In Patent Document 1, a non-flash image and a flash image are captured under the same exposure condition, and a luminance difference between the two images is obtained. When the luminance difference between the images is large, white balance adjustment is performed based on the color temperature of the flash. Conversely, when the luminance difference between images is small, white balance adjustment is performed based on the color temperature of external light.

Further, it is known that when photographing is performed under fluorescent lamp illumination, a green fog is generated in the captured image due to the wavelength characteristics of the fluorescent lamp. Patent Document 2 describes a technique for correcting such a green fog.
JP-A-8-51632 (Claim 1 etc.) JP 2003-264850 A (summary)

  By the way, in the case of Patent Document 1, in order to accurately detect a luminance difference due to the presence or absence of flash emission, shooting without flash and flash shooting are performed under the same exposure conditions (the same aperture value, the same imaging sensitivity, and the same). Charge accumulation time). Therefore, in flash photography at long seconds, such as during slow sync photography, photography without flash must be performed over long seconds. In this case, the actual flash photography is delayed, and problems such as missing a photo opportunity occur.

  In addition, since exposure is started by matching the exposure conditions for flashless shooting and flash shooting, the exposure conditions for flash shooting cannot be changed in the middle. For this reason, it is impossible to change the exposure condition of the flash photography in a flexible manner after analyzing the shooting result without flash.

By the way, in night scene shooting and indoor shooting, a complicated lighting environment in which fluorescent lights, light bulbs, and flashlights are mixed is often obtained. If unevenness occurs in how each light hits in such an environment, the green fog also becomes uneven. For example, consider a case where a slow-synchronized shooting is performed by irradiating a person in front with a flash against a background of a high-rise building group (a large number of fluorescent lights can be seen from a window). In this case, a green fog caused by a fluorescent lamp occurs in the light of a high-rise building group that occupies most of the background. On the other hand, the person in the foreground is strongly illuminated by the flash, and no green fog occurs.
If a green fog correction is performed on a captured image in this state as described in Patent Document 2, the red-blue component of a person who does not have a green fog rises too much, resulting in an unnatural magenta fog on the person. .

  In view of these conventional problems, an object of the present invention is to provide a technique for appropriately determining the degree of influence of flash emission even when exposure conditions are changed between flashless shooting and flash shooting.

<< 1 >>
The electronic camera of the present invention includes an image acquisition unit, a luminance ratio detection unit, and a color balance adjustment unit.
The image acquisition unit controls the flash device to acquire a non-flash image captured without flash and a flash image captured with flash.
The luminance ratio detection unit obtains a luminance ratio between different areas A and B in the screen for the non-flash image and sets it as the luminance ratio Rnf. In addition, the luminance ratio detection unit similarly determines the luminance ratio Rf for the flash image. Further, the luminance ratio detection unit obtains a change amount C of the luminance ratios Rnf and Rf with or without flash.
The color balance adjustment unit sets the color balance adjustment with an emphasis on the color temperature of the flash as the change amount C is larger, and performs the color balance adjustment on the main image captured by the flash.

<< 2 >>
Preferably, the luminance ratio detection unit obtains a luminance ratio Rnf of “brightness in the center area of the screen” and “brightness in the whole area of the screen or the peripheral area of the screen” for the non-flash image. Also, the luminance ratio detection unit obtains the luminance ratio Rf of “brightness in the screen center area” and “brightness in the entire screen area or the screen peripheral area” for the flash image.

<< 3 >>
Preferably, the color balance adjustment unit sets the color balance adjustment with an emphasis on the color temperature of the main image or the flash image as the change amount C is smaller, and performs the color balance adjustment on the main image.

<< 4 >>
Preferably, the color balance adjustment unit weakens the green fog correction amount (correction amount that makes the red-blue component relatively larger than the green component) in the color balance adjustment as the change amount C is larger.

<< 5 >>
Preferably, the image acquisition unit includes a sub image sensor and a main image sensor.
The sub-imaging device captures a non-flash image in a state where the flash device is not flashed.
The main imaging element captures a flash image (also serving as a main image) in a state where the flash device is flashed.

<< 6 >>
Preferably, the image acquisition unit includes a sub image sensor and a main image sensor.
The sub-imaging device captures a non-flash image before or after pre-flash of the flash device, and captures a flash image during pre-flash.
The main image pickup device picks up the main image in a state where the flash device performs main light emission.

<< 7 >>
The program according to the present invention causes a computer to function as the luminance ratio detection unit and the color balance adjustment unit according to any one of the above << 1 >> to << 6 >>.

(1)
The electronic camera of the present invention obtains the luminance ratio between different areas A and B in the screen.
If this luminance ratio is greatly changed by the flash illumination, it can be determined that there is unevenness in the way the flash reaches between the areas AB and the reflectance of the object scene. As described above, when the illumination state becomes uneven, it is difficult to appropriately adjust the white balance based on the color temperature estimated from the flash image itself. If forcibly performed, the color of the illumination location different from the estimated color temperature is unnaturally adjusted.

  Therefore, in the present invention, when the change amount C of the luminance ratio between the flash image and the non-flash image increases, color balance adjustment is performed with an emphasis on the color temperature of the flash. In general, a portion that is well lit by flash light is in a shooting environment such as being located in front or facing the camera, so it is highly likely that it is a main subject. Accordingly, the color balance adjustment is performed with an emphasis on the color temperature of the flash as the change amount C of the luminance ratio is larger, so that the color balance of the main subject can be adjusted better with a high success probability.

By the way, the luminance ratio obtained here is a value obtained by taking the luminance ratio between the areas AB in the screen, and is a relative value. Therefore, differences in exposure conditions (imaging device, aperture value, imaging sensitivity, and charge accumulation time) hardly appear in the luminance ratio. For this reason, there is little need to completely match the exposure conditions between the flash image and the non-flash image, and it is allowed to appropriately shift the exposure conditions. For example, in slow sync photography, the charge accumulation time of a non-flash image can be shortened appropriately. In this case, the actual flash photography is not so delayed, and the chance of missing a photo opportunity is reduced.
In the present invention, by analyzing the non-flash image, it is possible to perform advanced exposure control such as changing the exposure condition of flash photography to the occasion.

(2)
Note that the main subject often exists partly in the center area of the screen. Therefore, in the present invention, it is preferable to obtain the luminance ratio from a comparison between “luminance in the center area of the screen” and “luminance in the entire screen area or the peripheral area of the screen”.
By such a method for obtaining the luminance ratio, it is possible to detect without overlooking the flash unevenness occurring in the main subject and other areas. As a result, it is possible to satisfactorily adjust the color balance of the main subject with a higher success probability.

(3)
By the way, when the luminance ratio does not change so much by the flash illumination, it can be determined that the flash illumination state is almost uniform between the areas AB.
Usually, since flash illumination is close to a kind of point light source, unevenness in illumination is likely to occur. Nevertheless, the fact that the illumination state is almost uniform under flash illumination, for example, can be expected as follows.

Case 1: The object scene is a flat plate and the flash is uniformly illuminated.
Case 2: The ratio of outside light is higher than that of flash, and the state change due to the presence or absence of flash is small.
Case 3: The flash illumination is not effectively irradiated because the subject distance is generally long.

  In these situations, if the color balance adjustment is performed with emphasis on the color temperature of the flash, the color balance is unnaturally adjusted in the cases 2 and 3 described above.

  Therefore, in the present invention, it is preferable to set the color balance adjustment in which the color temperature of the main image or the flash image is emphasized as the change in the luminance ratio is small depending on the presence or absence of the flash. In this case, since the illumination state is nearly uniform, the color temperature can be estimated relatively accurately from the main image (or the flash image) captured with the flash. As a result, in any case of the above cases 1 to 3, the color balance of the main image can be adjusted well with a high success probability.

(4)
By the way, when the change in the luminance ratio is large depending on the presence or absence of flashlight, one of the areas A and B in the screen is a place where the flashlight is well applied. This portion has a high proportion of flash illumination, and the green fog caused by the fluorescent lamp is reduced.
Therefore, in the present invention, it is preferable to decrease the green fog correction amount (correction amount for making the red-blue component relatively larger than the green component) in the color balance adjustment as the luminance ratio change amount C is larger.
This operation can reliably prevent magenta fog due to excessive correction of green fog at a location where the flash illumination is well in the screen (the possibility of the main subject is high).

(5)
By the way, in the present invention, it is preferable that two image pickup devices are provided, a non-flash image is picked up by one sub-image pickup device, and a flash image (also serving as a main image) is picked up by the other main image pickup device.
As described above, the non-flash image sub-image sensor and the flash image main image sensor can be provided separately because the luminance ratio of the present invention is a relative value, and there is a difference between the image sensors in the luminance ratio. It is hard to appear.
Further, even when the number of pixels of the electronic camera (main image sensor) is increased, the image reading time of the non-flash image can be kept short by keeping the number of pixels of the sub image sensor low. As a result, the processing time required for the imaging sequence of the present invention can be shortened.

(6)
In the present invention, it is preferable that the sub-imaging device is used to capture a non-flash image before or after pre-emission of the flash device, and to capture a flash image during pre-emission. In this case, the main image sensor is used for photographing the main image. Therefore, even when the number of pixels of the electronic camera (main image sensor) is increased, the image reading time of the non-flash image and the flash image can be kept short by keeping the number of pixels of the sub image sensor low. As a result, it is possible to further reduce the processing time required for the imaging sequence of the present invention.

(7)
Note that by executing the program of the present invention on a computer, the computer can function as the above-described luminance ratio detection unit and color balance adjustment unit. As a result, the same color balance adjustment as that of the electronic camera can be realized on the computer.

(1) First Embodiment << Configuration Description of First Embodiment >>
FIG. 1 is a diagram for explaining a component arrangement of the electronic camera 11 in the present embodiment.
In FIG. 1, the electronic camera 11 is provided with an electronic flash device 12 and a photographing lens 13. A quick return type mirror 15 is provided on the image space side of the photographic lens 13. A diffusion plate 16 is disposed at the imaging position of the subject light beam reflected by the mirror 15. The user observes the subject image formed on the diffusion plate 16 via the finder optical system 17. The light beam from the diffusion plate 16 is guided to the imaging surface of the photometric image sensor 18 provided at the corner of the finder optical system 17 and re-images the subject image on the imaging surface. Further, behind the mirror 15, a shutter 19a, a recording image sensor 19 and the like are arranged.

FIG. 2 is a block diagram relating to image processing of the electronic camera 11.
In FIG. 2, the output of the photometric image sensor 18 is input to the image memory 22 via the A / D converter 20. The output of the recording image sensor 19 is input to the image memory 22 via the A / D converter 21. The image memory 22 is connected to the bus 23. Connected to the bus 23 are an image processing unit 24, a compression recording unit 25, an imaging control unit 27, a flash emission control unit 28, a microprocessor 29, and the like.

  Among these, the compression recording unit 25 compresses and records image data on a removable memory card 26. The microprocessor 29 is given an operation input from a release button 29a or the like.

<< Correspondence with Invention >>
Hereinafter, the correspondence between the description items of the claims and the first embodiment will be described. Note that the correspondence relationship here illustrates one interpretation for reference, and does not limit the present invention.
The image acquisition unit described in the claims corresponds to the imaging control unit 27, the flash emission control unit 28, the photometric image sensor 18, and the recording image sensor 19.
The luminance ratio detection unit described in the claims corresponds to the “function for obtaining the change amount C of the luminance ratios Rf and Rnf” of the microprocessor 29.
The color balance adjustment unit described in the claims corresponds to “a function for setting and executing color balance adjustment of the main image using the change amount C as a scale” by the microprocessor 29 and the image processing unit 24.
The sub-imaging device described in the claims corresponds to the photometric imaging device 18.
The main image sensor described in the claims corresponds to the image sensor 19 for recording.

<< Description of Operation of First Embodiment >>
FIG. 3 is a flowchart for explaining the operation of the first embodiment.
Hereinafter, the operation of the electronic camera 11 will be described along the step numbers shown in FIG.

[Step S1] Before starting the release operation, the mirror 15 is in the lowered state. Therefore, the subject luminous flux that has passed through the photographing lens 13 forms a subject image on the imaging surface of the photometric imaging element 18 via the diffusion plate 16 and the finder optical system 17.
In this state, the microprocessor 29 uses the imaging control unit 27 to give a drive signal to the photometric image sensor 18. A non-flash image captured without flashing is output from the photometric image sensor 18. This non-flash image is digitized in units of pixels via the A / D converter 20 and then temporarily stored in the image memory 22.

[Step S2] The microprocessor 29 accesses the image memory 22 and obtains a luminance component for each small region (for example, each pixel) of the non-flash image.
It should be noted that each color component constituting the non-flash image is added according to the composition ratio of luminance components (for example, R: G: B = 0.29: 0.587: 0.114, etc.) to generate a luminance component. Is preferred. Further, a color component (G color component or the like) containing a large amount of luminance components in the non-flash image may be regarded as a luminance component as it is.
The microprocessor 29 divides the luminance component of the non-flash image obtained in this way into a screen central area and a screen peripheral area, and calculates an average luminance for each. The microprocessor 29 substitutes these average luminances into the following equation to obtain the luminance ratio Rnf.
Brightness ratio Rnf = (Average brightness in the screen center area) / (Average brightness in the screen periphery area)
Note that it is preferable to add a minute value to the denominator on the right side of the above equation so that the luminance ratio Rnf does not overflow even if the average luminance in the screen peripheral area is zero.

[Step S3] The microprocessor 29 determines whether or not the release button 29a is fully pressed.
If the release button 29a is fully pressed, the microprocessor 29 proceeds to step S4.
On the other hand, if the release button 29a is not fully pressed (half pressed or not pressed), the microprocessor 29 returns the operation to step S1.

  [Step S4] The microprocessor 29 performs pre-emission as follows. First, the microprocessor 29 raises the mirror 15 and projects a subject image on the shutter curtain of the shutter 19a. In this state, the microprocessor 29 causes the electronic flash device 12 to perform minute pre-emission using the flash emission control unit 28. The microprocessor 29 measures the brightness of the shutter curtain during pre-emission using a photometric element (not shown) provided at a position where the shutter 19a is viewed. The microprocessor 29 determines the target light amount for the main light emission according to the brightness of the shutter curtain during the pre-light emission. Information on the target light amount of the main light emission is transmitted to the electronic flash device 12 side.

[Step S5] Subsequently, the microprocessor 29 opens the front curtain of the shutter 19a, and starts projecting a subject image on the imaging surface of the recording image sensor 19.
When single-shot main light emission is performed, the microprocessor 29 causes the electronic flash device 12 to start main light emission when the shutter 19a is fully opened. The electronic flash device 12 monitors the light emission amount of the main light emission, and stops the main light emission when reaching the target light amount for which information has been transmitted in advance.
On the other hand, when the charge accumulation time set for exposure has elapsed, the microprocessor 29 closes the rear curtain of the shutter 19a. When the shutter 19a is completely closed in this way, the microprocessor 29 lowers the mirror 15 downward. Note that the charge accumulation time here is preferably changed flexibly based on the luminance distribution (histogram) of the non-flash image.

  [Step S <b> 6] The microprocessor 29 supplies a drive signal to the recording image sensor 19 using the imaging controller 27. The recording image sensor 19 outputs a flash image (also serving as a main image) captured with flash. The flash image is digitized in units of pixels via the A / D converter 21 and then temporarily stored in the image memory 22.

[Step S7] The microprocessor 29 accesses the image memory 22 and reads a low saturation area (area where the saturation is a predetermined value or less) from the flash image. The microprocessor 29 obtains the chromaticity (R / G, B / G) for each small region (for example, each pixel) for the RGB color components in the low saturation region, and obtains the distribution center of these chromaticities. Subsequently, the microprocessor 29 determines the difference between the distribution center and the black body locus on the chromaticity coordinates.
Further, the microprocessor 29 maps the distribution center onto a black body locus and detects a correlated color temperature on the black body locus.

  [Step S8] The microprocessor 29 calculates a color ratio (R gain and B gain) for shortening the above-described deviation in the green direction, and sets it as a green fog correction coefficient.

[Step S9] The microprocessor 29 accesses the image memory 22, reads the flash image, and processes it into a processed image suitable for comparison with the non-flash image.
In creating the processed image, it is preferable to perform image processing that suppresses the difference between the imaging elements as described below.

(1) Processing for cutting out a processed image from a flash image in accordance with the imaging field angle of the non-flash image.
(2) The flash image is divided into pixel blocks in accordance with the positions of the small areas (see step S4) of the photometric image sensor 18, and luminance components (including pseudo luminance components such as G color) are provided for each pixel block. The requested process.
(3) The maximum gradation value, the average gradation value, and the most frequent gradation of the flash image according to the maximum gradation value, the average gradation value, the most frequent gradation value, and the minimum gradation value of the non-flash image. Processing to normalize and match values and minimum gradation values.
(4) Processing for converting the number of gradation steps and the gradation curve of the flash image in accordance with the gradation characteristics of the non-flash image.

[Step S10] The microprocessor 29 divides the processed image created from the flash image into a screen central area and a screen peripheral area, and calculates an average luminance for each. The microprocessor 29 substitutes these average luminances into the following equation to obtain the luminance ratio Rf.
Brightness ratio Rf = (Average luminance in the screen center area) / (Average brightness in the screen periphery area)
Note that it is preferable to add a minute value to the denominator on the right side of the above equation so that the luminance ratio Rf does not overflow even if the average luminance in the peripheral area of the screen is zero.

[Step S11] The microprocessor 29 obtains a change amount C of the luminance ratios Rnf and Rf accompanying the flash emission.
Change amount C = | luminance ratio Rf−luminance ratio Rnf |

  [Step S12] From the magnitude of the change amount C, the following determination and countermeasure can be performed.

(Case where amount of change C is large)
When the amount of change C is large, it can be determined that there is unevenness in the way the flash emission reaches in the center and the periphery of the screen. For example, there is a situation in which a near subject that is strongly illuminated by flash emission and a distant view where flash emission is difficult to reach are mixed in one screen.
Therefore, the microprocessor 29 sets the white balance adjustment value in which the correction of the color deviation of the flash color temperature is increased as the change amount C is larger (see FIG. 4).
With this setting, it is possible to improve the color reproducibility of a near-field subject (high possibility of being a main subject) to which flash emission is well transmitted.

(Case where change C is small)
On the other hand, when the change amount C is small, the flash illumination is either uniform or does not reach uniformly at the screen center and the screen periphery. With these subject arrangements, it can be determined that there is little unevenness in the illumination light and the illumination uniformity is high.
Therefore, the microprocessor 29 sets a white balance adjustment value in which the correction of the color deviation of the correlated color temperature is strengthened as the change amount C is small (see FIG. 4).
With this setting, a white balance adjustment value that matches the uniform illumination of the entire screen is set, and the color reproducibility of the entire screen can be improved.

[Step S13] As described above, when the amount of change C is large, it can be determined that the flash emission is well delivered to the near subject. For such a near-field subject, the proportion of flash light in the entire illumination light is high, and green fog such as a fluorescent lamp hardly occurs.
Therefore, the microprocessor 29 adjusts the green fog correction coefficient so that the greater the change amount C is, the smaller the green fog correction amount is (see FIG. 5).
With this setting, it is possible to prevent a problem that a magenta fogging in the reverse direction occurs in a near-field subject (which is likely to be a main subject) to which flash emission is well transmitted.

  [Step S14] The microprocessor 29 reads out the “white balance adjustment value” set in step S12 and the “green fog correction coefficient” adjusted in step S13. The microprocessor 29 adjusts the color component gain of the main image captured in step S6 based on the read value, and generates a main image that has been color balance adjusted.

<< Effects of First Embodiment >>
As described above, in the first embodiment, the change amount C between the luminance ratio Rnf in the screen of the non-flash image and the luminance ratio Rf in the screen of the flash image is obtained. If the amount of change C is large, it can be estimated that there is a near-field subject that has received strong flash illumination in the screen. Therefore, in the first embodiment, the white balance adjustment value in which the contribution rate of the flash color temperature is increased as the luminance ratio change amount C is larger. As a result, it is possible to improve the color reproducibility of a near-field subject (large possibility of a main subject) that is stained by the color temperature of the flashlight.

  Furthermore, since these luminance ratios are relative ratios within the screen, differences in the exposure conditions of both images (non-flash image and flash image) are unlikely to appear. Therefore, even if the average value of luminance shifts due to the difference in the exposure conditions of both images, the change amount C can be accurately obtained. Therefore, the charge accumulation time of the non-flash image can be appropriately shortened, and the above-described series of imaging sequences can be shortened.

Furthermore, in the first embodiment, the green fog correction amount is lowered as the change amount C is larger. As a result, it is possible to prevent over-correction of the green fog and appropriately prevent the magenta fog due to the over-correction for the portion of the screen where the flash illumination is well applied.
Next, another embodiment will be described.

(2) Second Embodiment Since the configuration of the electronic camera in the second embodiment is the same as that of the first embodiment (FIGS. 1 and 2), description thereof is omitted here.
FIG. 6 is a flowchart for explaining the operation of the second embodiment.
Hereinafter, the operation of the electronic camera 11 will be described along the step numbers shown in FIG.

  [Steps S31 to S32] Same as steps S1 to S2 of the first embodiment.

[Step S33] The microprocessor 29 determines whether or not the release button 29a is fully pressed.
If the release button 29a is fully pressed, the microprocessor 29 proceeds to step S34.
On the other hand, if the release button 29a is not fully pressed (half pressed or not pressed), the microprocessor 29 returns the operation to step S31.

  [Step S34] The microprocessor 29 causes the electronic flash device 12 to perform pre-emission, and obtains a flash image from the photometric image sensor 18.

  [Step S35] The microprocessor 29 determines the target light emission amount of the main light emission based on the divided light metering result of the pre-light emission (that is, the flash image).

  [Step S36] The microprocessor 29 divides the flash image into a screen central area and a screen peripheral area, and obtains an average luminance for each. The microprocessor 29 obtains a ratio between the “average brightness in the screen center area” and the “average brightness in the screen periphery area” and sets it as the brightness ratio Rf.

[Step S37] Subsequently, the microprocessor 29 flips up the mirror 15, opens the front curtain of the shutter 19a, and starts projecting a subject image on the imaging surface of the recording imaging device 19.
When single-shot main light emission is performed, the microprocessor 29 causes the electronic flash device 12 to start main light emission when the shutter 19a is fully opened. The electronic flash device 12 monitors the light emission amount of the main light emission, and stops the main light emission when the target light amount is reached.
On the other hand, when the set charge accumulation time has elapsed, the microprocessor 29 closes the rear curtain of the shutter 19a. When the shutter 19a is completely closed in this way, the microprocessor 29 lowers the mirror 15 downward.

  [Step S <b> 38] The microprocessor 29 uses the imaging control unit 27 to provide a drive signal to the recording image sensor 19. A main image is output from the recording image sensor 19. The main image is digitized in units of pixels via the A / D converter 21 and then temporarily stored in the image memory 22.

[Step S39] The microprocessor 29 accesses the image memory 22 and reads a low saturation area (area where the saturation is equal to or less than a predetermined value) from the main image. The microprocessor 29 obtains the chromaticity (R / G, B / G) for each small region (for example, each pixel) for the RGB color components in the low saturation region, and obtains the distribution center of these chromaticities. Subsequently, the microprocessor 29 determines the difference between the distribution center and the black body locus on the chromaticity coordinates.
Further, the microprocessor 29 maps the distribution center onto a black body locus and detects a correlated color temperature on the black body locus.

  [Step S40] The microprocessor 29 obtains the color ratio (R gain and B gain) for shortening the deviation from the black body locus in the green direction, and sets it as a green fog correction coefficient.

[Step S41] The microprocessor 29 obtains the change amount C of the luminance ratios Rnf and Rf accompanying the pre-emission.
Change amount C = | luminance ratio Rf−luminance ratio Rnf |

  [Steps S42 to S43] Same as steps S12 to S14 of the first embodiment.

<< Effects of Second Embodiment >>
As described above, also in the second embodiment, the same effect as in the first embodiment can be obtained.

  Furthermore, in the second embodiment, the photometric image sensor 18 is used to compare the luminance ratio before and after pre-emission. In this case, since both the non-flash image and the flash image have a small number of pixels, the processing cost for calculating the luminance ratio and the change amount C is reduced. As a result, a series of imaging sequences can be further simplified.

<< Additional items of embodiment >>
In the above-described embodiment, the single-lens electronic camera 11 has been described. However, the present invention is not limited to this. For example, the present invention can be applied to a compact type electronic camera. In this case, a non-flash image may be captured by a recording image sensor. In such a configuration, the photometric image sensor 18 is not required, and the configuration of the imaging unit can be further simplified.

  In the above-described embodiment, one color balance adjustment value is determined for the entire image. However, the present invention is not limited to this. For example, the screen may be divided into a plurality of areas, and the color balance adjustment value of the present invention may be determined for each area. In this case, it is possible to determine the uniformity of the illumination state for each region, and determine an appropriate color balance adjustment value for each region according to the uniformity determination.

  In the above-described embodiment, the case where the built-in type electronic flash device 12 is used has been described. However, the present invention is not limited to this. The present invention may be applied to a case in which an external type electronic flash device is used.

  Further, in the above-described embodiment, the case where the color balance adjustment is performed in the electronic camera has been described. However, the present invention is not limited to this. For example, a program for executing part or all of the processing shown in FIGS. 3 and 6 may be created. By executing this program on an external computer, the above-described image processing can be performed on the computer.

  In the above-described embodiment, the magnitude of the difference between the luminance ratios Rnf and Rf is obtained and used as the change amount C. However, the present invention is not limited to this. For example, the change amount C may be obtained by obtaining a ratio (Rf / Rnf or the like) between the luminance ratios Rnf and Rf.

  In the above-described embodiment, the luminance ratio between the screen central area and the screen peripheral area is obtained. However, the present invention is not limited to this. In general, the luminance ratio may be obtained for different areas in the screen. For example, the luminance ratio between the vicinity of the selected AF area and the other area may be obtained. For example, the luminance ratio between the screen center area and the entire screen area may be obtained.

  As described above, the present invention is a technique that can be used for an electronic camera, an image processing program, and the like.

It is a figure explaining component arrangement | positioning of the electronic camera 11 in this embodiment. 2 is a block diagram relating to image processing of the electronic camera 11. FIG. It is a flowchart explaining operation | movement of 1st Embodiment. It is a figure which shows the relationship between the variation | change_quantity C and a color balance adjustment value. It is a figure which shows the relationship between the variation | change_quantity C and the green fog correction amount. It is a flowchart explaining operation | movement of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Electronic camera 12 Electronic flash device 13 Shooting lens 15 Mirror 16 Diffuser 17 Finder optical system 18 Photometric image sensor 19 Recording image sensor 19a Shutter 20 A / D converter 21 A / D converter 22 Image memory 23 Bus 24 Image Processing unit 25 Compression recording unit 26 Memory card 27 Imaging control unit 28 Flash emission control unit 29 Microprocessor 29a Release button

Claims (7)

An image acquisition unit that controls the flash device to acquire a non-flash image captured without flash and a flash image captured with flash;
For the non-flash image, a luminance ratio between different regions A and B in the screen is obtained as a luminance ratio Rnf, and for the flash image, a luminance ratio between the regions A and B in the screen is obtained as a luminance ratio Rf. A luminance ratio detection unit for obtaining a change amount C of the luminance ratios Rnf and Rf with or without the flash;
A color balance adjustment unit that sets color balance adjustment with an emphasis on the color temperature of the flash as the change amount C increases, and performs the color balance adjustment on the flash-photographed main image. camera. The electronic camera according to claim 1,
The luminance ratio detector is
For the non-flash image, a luminance ratio Rnf between the luminance of the screen central area and the luminance of the entire screen area or the peripheral area of the screen is obtained,
An electronic camera characterized in that, for the flash image, a luminance ratio Rf between the luminance in the central area of the screen and the luminance in the entire area of the screen or the peripheral area of the screen is obtained. The electronic camera according to claim 1 or 2,
The color balance adjustment unit
An electronic camera characterized in that, as the change amount C is smaller, color balance adjustment is performed with emphasis on the color temperature of the main image or the flash image, and the color balance adjustment is performed on the main image. The electronic camera according to any one of claims 1 to 3,
The color balance adjustment unit
The electronic camera characterized in that as the change amount C is larger, a green fog correction amount (a correction amount that makes the red-blue component relatively larger than the green component) in the color balance adjustment is weakened. The electronic camera according to any one of claims 1 to 4,
The image acquisition unit
A sub-imaging device that captures the non-flash image in a state in which the flash device is not flashed;
An electronic camera comprising: a main image pickup device that picks up the flash image that also serves as the main image in a state where the flash device is flashed. The electronic camera according to any one of claims 1 to 4,
The image acquisition unit
A sub-imaging device that captures the non-flash image before or after the pre-flash of the flash device, and captures the flash image during the pre-flash;
An electronic camera, comprising: a main image pickup device that picks up the main image in a state where the flash device performs main light emission.   A program for causing a computer to function as the luminance ratio detection unit and the color balance adjustment unit according to any one of claims 1 to 6.

Images