JP2000165896A - White balance control method and its system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain white balance control to reduce unpleasant color slurring in the case of photographing where different light sources are included in a picked-up frame. SOLUTION: A luminance discrimination means 6 obtains a luminance distribution on the basis of image data for each prescribed areas divided for a photographing frame, the luminance distribution of the areas is compared, and an achromatic range setting means 8 sets a luminance range for extracting an achromatic color to an initial value or a calculated revised value depending on the comparison result so as to exclude other light source area from the object of achromatic discrimination, an achromatic color discrimination means 9 applies achromatic discrimination to the image data within the set luminance range and a gain control means 10 sets a gain control variable with respect to the image data on the basis of the integrated data of pixels discriminated to be chromatic so as to take white balance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RGB single-plate CC
The present invention relates to a white balance control method and apparatus for a digital still camera, a digital video camera, and the like using an imaging device such as D.

[0002]

2. Description of the Related Art Generally, image data picked up by a color image pick-up device such as an RGB single-chip CCD is used for A
After performing processing such as / D conversion and color interpolation, achromatic determination is performed for each pixel data, the RGB values of the achromatic pixels are integrated, and a gain control amount is obtained based on the integrated data.
The white balance control is automatically performed by performing gain control on the R data and the B data of the image data.

Here, in performing such white balance control, a screen division is performed on image data in an image pickup frame that has been subjected to processing such as color interpolation, and the white balance is determined based on color information of each divided area. It is widely known to perform

[0004]

However, in the case of such a conventional method, for example, when taking a picture in a room under a light source such as a fluorescent lamp, a window enters into an imaging frame.
When performing automatic white balance processing when there is an object illuminated by a different light source in the frame, the automatic white balance processing fits outside the window even though the room is being shot, and the indoor white balance However, there are disadvantages such as that the image is shifted, or conversely, when trying to photograph the outdoors from indoors, the white balance is adjusted in the indoors, causing color shifts in the outdoors.

When white balance control is performed on the basis of color information within the entire image or within a certain range in an image-capturing frame, depending on the ratio of different light sources such as windows in the image or within the range. There is also a problem of causing color misregistration.

Therefore, the present invention reduces the unpleasant color shift at the time of photographing by performing white balance control using luminance information even during photographing in which a different light source is included in the image pickup frame. It is an object of the present invention to provide a white balance control method and a white balance control method.

[0007]

According to a first aspect of the present invention, there is provided a white balance control method, wherein a luminance distribution is obtained based on image data for each predetermined area divided for an image pickup frame, and the luminance distribution for each area is calculated. Compare, set a luminance range for performing achromatic color extraction according to the comparison result to an initial value or a calculated change value, perform achromatic determination on the image data within the set luminance range, and determine that the image data is achromatic. White balance is achieved by setting a gain control amount for the image data based on the integrated data of the pixels.

Therefore, the achromatic color determination is performed by changing and setting the brightness range for performing the achromatic color determination based on the brightness information that is the brightness distribution in the unit of area, so that a different light source may be included in the imaging frame. Even when shooting,
White balance processing can be performed accurately.

According to a second aspect of the present invention, in the white balance control method according to the first aspect, when the luminance distribution of each area is different in two or more steps, achromatic color extraction is performed based on the luminance distribution on the low luminance side. The luminance range is set to the calculated change value.

Therefore, since the achromatic color detection on the high-brightness side is not performed based on the brightness information, even when an outdoor scene is photographed indoors, the white balance without a sense of incongruity is eliminated except for the influence of the outdoor data having a high brightness value. Control becomes possible.

According to a third aspect of the present invention, there is provided the white balance control method according to the first or second aspect, wherein the luminance distribution of each area is different in two or more steps within a range where the maximum luminance average value is equal to or less than a predetermined value. The luminance range for performing achromatic color extraction based on the luminance distribution on the high luminance side is set to the calculated change value.

Accordingly, by setting a luminance range for achromatic color detection using luminance information and a fixed value, for example, an exposure control value, in an image pickup frame, achromatic color detection in a luminance range near an object is performed. In addition, white balance processing in which color shift of a subject is suppressed can be performed.

According to a fourth aspect of the present invention, there is provided a white balance control method, wherein a luminance distribution is obtained based on image data for each predetermined area divided for an image pickup frame, and the luminance distribution for each area is compared. As a result, when the luminance distribution of each area is different in two or more steps, the luminance range for performing achromatic color extraction is set to the calculated change value for each of the different luminance distributions, and each of the set luminances is set. Achromatic determination is performed on the image data within the luminance range of each distribution, and a white balance is obtained by setting a gain control amount for the image data according to the achromatic determination result of each luminance distribution. .

Accordingly, since the gain control amount is obtained for each luminance range based on the luminance information, and the gain control amount is appropriately set based on the result and the control is performed, the white balance control can be performed more flexibly and accurately.

According to a fifth aspect of the present invention, there is provided a white balance control device, which obtains a luminance distribution based on image data for each predetermined area obtained by dividing an image frame picked up by an image sensor, and compares the luminance distribution for each area. The achromatic color range setting means for setting the luminance range for performing achromatic color extraction to an initial value or a calculated change value in accordance with the comparison result by the luminance determination means, and the achromatic color range setting means Achromatic color determination means for performing achromatic color determination on the image data within the brightness range, and gain control for the image data so that white balance can be obtained based on integrated data of pixels determined to be achromatic by the achromatic color determination means. Gain control means for setting the amount.

Therefore, the luminance range for performing the achromatic color determination based on the luminance information representing the luminance distribution in the unit of area is changed and set by the achromatic color range setting means, and the achromatic color determination is performed by the achromatic color determination means. The white balance processing can be performed with high accuracy even during shooting in which a different light source is included in the frame.

According to a sixth aspect of the present invention, in the white balance control device according to the fifth aspect, the achromatic color range setting means sets the brightness distribution of each area to two or more levels as a result of the comparison by the brightness determination means. If different, the luminance range in which achromatic color extraction is performed based on the luminance distribution on the low luminance side is set to the calculated change value.

Accordingly, since the achromatic color detection on the high luminance side is not performed based on the luminance information, even when an outdoor scene is photographed indoors, the white balance without a sense of incongruity is eliminated except for the influence of the outdoor data having a high luminance value. Control becomes possible.

According to a seventh aspect of the present invention, in the white balance control device according to the fifth or sixth aspect, the achromatic color range setting means has a maximum luminance average value equal to or less than a predetermined value as a result of the comparison by the luminance determination means. When the luminance distribution of each area is different in two or more steps in the range, the luminance range for performing achromatic color extraction based on the luminance distribution on the high luminance side is set to the calculated change value.

Therefore, the achromatic color range setting means sets the luminance range for detecting the achromatic color by using the luminance information in the imaging frame and a constant value, for example, the exposure control value. Achromatic color detection is performed, and white balance processing that suppresses color shift of the subject can be performed.

The invention according to claim 8 is a luminance judging means for obtaining a luminance distribution based on image data for each predetermined area divided from an image pickup frame picked up by an image pickup device and comparing the luminance distribution for each area. The brightness range in which achromatic color extraction is performed is set to an initial value or a changed value in accordance with the result of comparison by the brightness determination means. If the brightness distribution of each area differs by two or more levels as a result of the comparison, Achromatic color range setting means for setting, for each luminance distribution, a luminance range in which achromatic color extraction is performed in accordance with the luminance distribution to a calculated change value; and for the image data within the luminance range set by the achromatic color range setting means. Achromatic color determining means for performing achromatic color determination, and a gain control amount for setting a white balance according to an achromatic color determination result by the achromatic color determining means. And a control unit.

Therefore, by setting the luminance range for achromatic color detection using the luminance information and a fixed value, for example, the exposure control value, in the imaging frame, the achromatic color detection in the luminance range near the subject is performed. In addition, white balance processing in which color shift of a subject is suppressed can be performed.

[0023]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration example of a color imaging device using the white balance control device according to the present embodiment. First, there is provided an RGB single-chip CCD 1 which is an image sensor for imaging a subject in a desired imaging frame. An analog processing circuit 2 is provided for performing sampling processing on the image data (analog) converted into an electric signal by the CCD 1 by a subtraction method CDS (correlated double sampling) method to remove noise. An A / D converter 3 for converting image data into digital data is connected to a stage subsequent to the analog processing circuit 2. A CCD is provided after the A / D converter 3.
1 is connected to a color interpolation circuit 4 for creating RGB color data for each pixel by interpolation from adjacent pixel data.

Further, at the subsequent stage of the color interpolation circuit 4, a white balance control device 5, which is a feature of the present embodiment, is connected. The white balance control device 5 includes a brightness determination circuit 6 as a brightness determination unit, a buffer memory 7,
It comprises an achromatic color range setting circuit 8 as achromatic color range setting means, an achromatic color determination circuit 9 as achromatic color determination means, and a gain control circuit 10 as gain control means.

The luminance judging circuit 6 obtains a luminance value Y for each pixel by matrix calculation based on the RGB data created by the color interpolation circuit 4, and for example, for an image pickup frame 11 as shown in FIG. The luminance value of each pixel is integrated for each of the five divided areas A, B, C, D, and E, the average value is obtained as a luminance distribution, and the average luminance value of each area is compared. . The buffer memory 7 temporarily stores the image data whose luminance has been determined. The achromatic color range setting circuit 8 sets the luminance range for performing achromatic color extraction based on the comparison result of the luminance determination circuit 6 to a preset initial value or a calculated change value, or is set in advance from outside or the like. The color difference range is set for the achromatic color determination circuit 9.

An example of setting the luminance range by the achromatic color range setting circuit 8 will be described with reference to FIG. FIG.
As shown in (b), for example, when an image is captured using the imaging frame 11 in which the area A includes a window, the luminance integrated value of this area A becomes the luminance integrated value of the other areas B, C, D, and E. The value is higher than the value. At this time, information that the average luminance value of the area A is 200 and the average luminance value of the other areas B, C, D, and E is 120 is obtained from the luminance determination circuit 6. When the initial value of the luminance range setting value of the pixel for which the achromatic color determination is performed is set to 255>Y> 32 with respect to the luminance value Y, the luminance average value of each area is compared, and the luminance average value of the area A becomes A comparison result is obtained that shows different luminance distributions with respect to the average luminance values of the areas B, C, D, and E. When a result that the luminance distribution is different between the divided areas is obtained, the achromatic color range setting circuit 8 changes and sets the luminance range from the initial value so as to exclude the high luminance side. In this case, as a change setting of the luminance range, for example, (200 + 120) / 2>Y> 32, that is, 160>Y> 32 with respect to the above initial value is processed by calculation.

Here, the determination of the difference in the distribution of the average luminance values for each of the original areas (determination of whether or not the luminance distribution has two or more levels) is generally performed in the central area C including the subject. Is used as a reference. That is, if the average luminance value of each of the areas A, B, D, and E is within a predetermined range with respect to the average luminance value of the area C, the luminance range is not changed and set to the initial value, and the luminance value is outside the predetermined range If such an area exists, the change setting of the luminance range as described above is performed.
That is, the allowable fixed range is ΔC, and each area A, B,
The average luminance values of C, D, and E are calculated as EV _A , EV _B , and EV, respectively.
_C, EV _D, when the _{EV E, EV A> EV C} + ΔC EV B> EV C + ΔC EV D> under conditions satisfying one of the _{EV C + ΔC EV E> EV} C + ΔC, luminance range as described above Is set.

The achromatic color determination circuit 9 performs an achromatic color determination on the image data read from the buffer memory 7 in accordance with the luminance range in which the achromatic color extraction is set by the achromatic color range setting circuit 8 and determines that the image data is achromatic. RGB of pixel
Multiply the values. The gain control circuit 10 obtains a gain control amount based on the integrated data of each of the RGB obtained from the achromatic color determination circuit 9 and performs white balance processing by applying gain control to R and B data in the image data. For example, when the integrated data of each of the RGB obtained from the achromatic determination circuit 9 is Rsum, Gsum, Bsum, R,
The respective gain control amounts Rgain and Bgain of B are obtained by the arithmetic processing of Rgain = Gsum / Rsum and Bgain = Gsum / Bsum.

FIG. 3 is a flowchart showing such a schematic process in order. That is, when image data is captured by the CCD 1 (step S1), noise is removed by the analog processing circuit 2 by the CDS method (S2), and then A / D converted by the A / D converter 3 (S3). The color interpolation circuit 4 performs color interpolation processing (S4). Thereafter, the luminance determination circuit 6 divides the image frame 11 into screens (S5), calculates an average luminance value for each divided area (S6), and calculates the average luminance value for each area as the average luminance value for the central area. Is determined (S7), and it is determined whether or not there is a high-luminance area exceeding a certain range with respect to the luminance average value of the central area (S8). If it does not exist, the luminance range in which achromatic color detection is performed is not changed and the initial value is maintained, but if a high luminance area exists, the luminance range in which achromatic color detection is performed is changed to the achromatic color range setting circuit 8. Change setting by (S
9). In this manner, the achromatic color detection circuit 9 performs an achromatic color detection process while the luminance range remains at the initial value or is set to the changed value (S10), and based on the result, the gain control circuit 10 sets the gain. The control amount is calculated (S1
1) A white balance is obtained by performing gain control on the R and B data based on the calculation result (S12).

Therefore, according to such a schematic configuration and operation, even if the imaging frame 11 includes a high-luminance portion due to another light source or the like, the image data is excluded from the achromatic judgment. It can be seen that good white balance processing without color shift due to image data of a high luminance portion can be performed.

Here, a more specific configuration example and operation of the present embodiment will be described below. First, a filter 12 having an arrangement as shown in FIG. That is, a green filter (blue) Gb is provided in the column of the blue filter B, and a green filter (red) Gr is provided in the column of the red filter R, so that RGB becomes the target pixel. On the other hand, a filter based on a 3 × 3 matrix adjacent to each other is configured.

The color interpolation circuit 4 is configured, for example, as shown in FIG. That is, A / D converted by the A / D converter 3
/ D output for three lines with reference to the pixel clock CLK.
Two line buffers 13 for storing 9 pixels
a, 13b, nine registers 14a to 14i, and a selector & adder 15 for appropriately interpolating each pixel data stored in these registers 14a to 14i and outputting as R, G, B data. Have been. That is, R, G, and B data are obtained by performing interpolation for each color based on image data of 3 × 3 pixels around the pixel including the target pixel.

FIG. 6 shows a flowchart of an example of color interpolation processing in the selector & adder 15. R, G (Gr, Gb
, B is the image data of the pixel corresponding to the filter 12 array, COL NUM is the number of pixels in the horizontal direction of the CCD pixel size, RAW NUM is the number of pixels in the vertical direction of the CCD pixel size, and the array [i, j] Indicates a pixel position where the pixel data is stored. First, if the image data of the pixel of interest is Gr (Y of S21), R = ([i
−1, j] + [i + 1, j]) / 2, G = [i, j], B =
A color interpolation process of ([i, j-1] + [i, j + 1]) / 2 is performed (S22, S23, S24). If the image data of the target pixel is R (Y in S25), R = [i, j] and G = ([i−1, j] + [i + 1, j]) for R, G, and B, respectively. +
[I, j-1] + [i, j + 1]) / 4, B = ([i-1, j-
1] + [i + 1, j-1] + [i-1, j + 1] + [i + 1, j + 1])
/ 4 is performed (S26, S27, S2
8). If the image data of the target pixel is Gb (Y in S29), R = ([i, j-1] +
[I, j + 1]) / 2, G = [i, j], B = ([i−1, j]
+ [I + 1, j]) / 2 is performed (S3
0, S31, S32). If the image data of the pixel of interest is B (Y in S33), R = R
([I-1, j-1] + [i + 1, j-1] + [i-1, j + 1] +
[I + 1, j + 1]) / 4, G = ([i-1, j] + [i + 1,
j] + [i, j-1] + [i, j + 1]) / 4, B = [i, j]
Is performed (S34, S35, S36).
Thereafter, the process is advanced by one pixel in the horizontal direction (S37), and the same processing is repeated until the number of pixels in the horizontal direction is reached (S38). When the processing of the i-th row is completed (Y in S38), the pixel in the vertical direction is advanced by one pixel (S39), and the horizontal pixel is set to an initial value i = 0 (S41) until the number of pixels in the vertical direction is reached. The same processing is repeated (S40).

Next, an example of the configuration of the luminance judgment circuit 6 and the achromatic color range setting circuit 8 and their operations will be described. FIG. 7 is a block diagram showing a configuration example of the luminance determination circuit 6 and the achromatic color range setting circuit 8. The luminance determination circuit 6 includes a matrix circuit 16 and adders / register pairs 17a for the number of divided areas.
To 17e and a counter 18 for counting the pixel clock CLK
And a selector 19 for selecting an adder based on the count value of the counter 18, and a comparator & selector 20 for the outputs of the adder / register pairs 17a to 17e. In the matrix circuit 16, the RG from the color interpolation circuit 4
A matrix conversion is performed on the B data to obtain a luminance signal Y for each pixel. This luminance signal Y is supplied to the pixel clock CL
The luminance signal Y is integrated for each of the areas A to E by counting K by the counter 18 and integrating it by the adder / register pair 17a to 17e selected by the selector 19. Based on these integration results, the comparator & selector 20 compares the luminance for each area, and the luminance range setting circuit 21 constituting the achromatic color range setting circuit 8 sets the luminance range (Y range) to the achromatic color detection circuit. 9

FIG. 8 shows a flowchart of an example of setting the luminance range by the luminance range setting circuit 21. In the flowchart, max is the maximum value of the average luminance, the minimum value of min is the luminance average, N is the number of divided areas, Ev ₀ ~Ev _n is the average luminance value for each area, YH brightness upper limit value for the achromatic detection, YL indicates the lower limit of luminance when achromatic color is detected, YHC indicates the upper limit of the default luminance, and YLC indicates the lower limit of the default luminance.

First, the maximum value of the average luminance is set to 0, and the minimum value of the average luminance is set to 255 (S51, S52).
After n indicating the target area is set to N−1 (S5
3) Compares the luminance average value Ev _n in the area is larger than the maximum value max of the average luminance (S54), greater if the maximum value max of the luminance average luminance average value Ev _n in the area
Is updated (S55). Similarly, update set Compares the luminance average value Ev _n in the area is smaller than the minimum value min of the luminance average (S56), the luminance average value Ev _n of the area smaller as the minimum value min of the luminance average (S57). Such maximum value / minimum value setting processing is similarly repeated for each area until n becomes 0 (S5).
8, S59).

After the maximum value and the minimum value are set based on the luminance information of each area in the current imaging frame, n indicating the target area is set to N-1 again (S60), and the luminance average of the area is set. the comparison of whether or not the value Ev _n is within a range ΔC allowed for the variation range is performed for each area (S61, S62, S63). If there is no area exceeding the fixed range ΔC (N in S61, Y in S62),
The luminance upper limit value YH at the time of achromatic color detection is set to the initial value YHC (S64). On the other hand, if there is an area exceeding the fixed range ΔC (Y in S61), the luminance upper limit value YH at the time of achromatic color detection is set to a changed value calculated by the calculation of (max + min) / 2 (S65).

Further, an example of the configuration of the achromatic color determination circuit 9 and its operation will be described. FIG. 9 is a block diagram illustrating a configuration example of the achromatic color determination circuit 9. First, the buffer memory 7
From the R, G, B data obtained from
Color difference data generating circuits 22a and 22 for calculating BG
b is provided. Further, the color difference data RG, B-B obtained from these color difference data generation circuits 22a, 22b.
G is an achromatic color extraction color difference range data set in advance from outside or a luminance range (Y
A comparator 23 is provided for comparing and determining whether the image is an achromatic color based on the range. An adder / register pair 24 that performs an addition process on the R, G, B data obtained from the buffer memory 7 based on the determination result of the comparator 23.
r, 24g, and 24b are provided for each color data.
Further, a counter 25 for counting the number of pixels determined by the comparator 23 is also provided. This allows
Basically, color difference data RG,
B-G is created, and R, which is determined to be an achromatic color from the preset achromatic color extraction color difference range data and the luminance range data,
Only the G and B data values are integrated.

FIG. 10 shows a flowchart of an example of the achromatic color determination process. First, the luminance Y of the target pixel data is calculated (S
71) The luminance Y is the luminance upper limit value YH for achromatic color detection
It is determined whether the value is larger than the lower limit value YL (S72, S73). If it is larger than the luminance upper limit YH or smaller than the luminance lower limit YL, it is excluded from the target of the achromatic color determination. If the luminance is equal to or less than the luminance upper limit YH and is equal to or greater than the luminance lower limit YL, color difference data RG and BG are calculated (S74). Next, the calculated color difference data RG
Achromatic color extraction color difference ranges RGL to R
It is determined whether it is within the range of GH (S75, S7)
6). If it is not within the achromatic color extraction color difference range RGL to RGH, it is excluded from the target of the achromatic color determination. Similarly, it is determined whether or not the calculated color difference data BG is within a preset achromatic color extraction color difference range BGL to BGH (S77, S78). Achromatic color extraction color difference range BGL ~
If it is not within the BGH, it is excluded from the target of the achromatic color determination. After such determination, the achromatic color extraction color difference range RGL
To RGH, BGL to BGL are sequentially counted (S79), and the respective integrated values Rsum, Gsum,
The value of Bsum is added one by one (S80). At the same time, the count value of the counter 25 is also incremented by one (S81). Such processing is repeated similarly until the count value of the counter 25 reaches the total number of pixels (S82).

Further, an example of the configuration of the gain control circuit 10 and its operation will be described. FIG. 11 shows a gain control circuit 1.
FIG. 4 is a block diagram showing an example of the configuration of 0. This gain control circuit 10 calculates each integrated value R obtained from the achromatic color judgment circuit 9.
A gain calculation circuit 26 for calculating gain control amounts Rgain and Bgain for R and B based on sum, Gsum and Bsum, and a gain control amount Rga calculated by the gain calculation circuit 26
It comprises multipliers 27a and 27b for multiplying R data and B data by in and Bgain.

FIG. 12 shows a flowchart of an example of gain calculation by the gain calculation circuit 26. That is, the integrated value Rsum,
The gain control amount Rgain is calculated based on Gsum (S9).
1), gain control amount Bgai based on integrated values Gsum and Bsum
n is calculated (S92).

Next, a second embodiment of the present invention will be described with reference to FIG. 1 to FIG. 12 are denoted by the same reference numerals, and description thereof will be omitted. This embodiment differs from the first embodiment only in the setting process of the luminance range for performing achromatic color extraction in the achromatic color range setting circuit 8.
The rest is basically the same as the first embodiment.

Therefore, the achromatic color range in the present embodiment
A processing example of the setting circuit 8 will be described. Here, the brightness
Example of average brightness value and constant value for each area from determination circuit 6
For example, the set value AE used for exposure control_VAL Use
This sets the luminance range. For example, in FIG.
Average brightness value EV for each of areas A to E shown_A , EV
_B , EV_C , EV_D , EV_E Is EV_A = 120 EV_B = 120 EV_C = 80 EV_D = 80 EV_E = 120 and the set value AE_VAL RANGE =
In the case of 20, the average brightness of the areas A, B and E is AE
_VALWithin the range of ± RANGE, average luminance value of areas C and D
Is AE_VALOut of range of ± RANGE. At this time, the area
If there is a high possibility of a different light source near the average luminance indicated by C and D
Then, the luminance range is changed and set from the initial value of 255> Y> 32 to 255> Y> (120 + 80) / 2, that is, 255> Y> 100.

For other areas, suppose that AE _VAL
When a high luminance average value exceeding + RANGE is indicated, the same processing as in the first embodiment (excluding the luminance range from being set) is performed.

FIG. 13 is a flowchart showing this embodiment in addition to the flowchart shown in FIG. The processing up to step S64 is performed in the same manner as in FIG. In the determination result of step S61, the fixed range ΔC
If the area exceeds the present judges whether lower be outside the range of (S61 of Y), a preset constant value _{Hlim (= AE VAL ± RANGE)} (S66). If it is smaller than the fixed value Hlim (Y in S66), the lower luminance limit YL at the time of achromatic color detection is set to a changed value calculated by the calculation of (max + min) / 2 (S67), and the upper luminance limit YH is initialized. The value YHC is set (S64). on the other hand,
If it is larger than the fixed value Hlim (N in S66), the luminance upper limit YH at the time of achromatic color detection is set to a changed value calculated by the calculation of (max + min) / 2 according to the first embodiment (S65). ), The lower luminance limit YL is the initial value Y
The LC is set (S68).

By setting the luminance range using the exposure control set value as in the present embodiment, the achromatic judgment of the luminance greatly deviating from the luminance of the subject can be prevented.
High-accuracy white balance processing without color shift of the subject can be performed.

A third embodiment of the present invention will be described with reference to FIGS. 1 to FIG. 12 are denoted by the same reference numerals, and description thereof will be omitted. This embodiment is different from the first embodiment in the configuration of the luminance range setting processing for performing achromatic color extraction in the achromatic color range setting circuit 8 and the configuration and processing of the gain control circuit 10. It is.

Thus, an example of processing of the achromatic color range setting circuit 8 in the present embodiment will be described. Here, based on the average luminance value of each area from the luminance determination circuit 6, a plurality of luminance ranges for performing achromatic color determination are set, here, two levels. For example, the average brightness values EV _A , EV _B , EV for each of the areas A to E shown in FIG.
_C, EV _D, when EV _E were _{EV A = 120 EV B = 120} EV C = 80 EV D = 80 EV E = 120, that the luminance distribution around the 120 and 8
It is divided into two stages, one centered on 0, and the brightness range is set as follows: 255>Y> (120 + 80) / 2, (120 + 80) for the initial value 255>Y> 32.
/ 2>Y> 32 That is, two luminance ranges are set as follows: 255>Y> 100, 100>Y> 32.

FIG. 14 is a flowchart showing this embodiment in addition to the flowchart shown in FIG. In the drawing, YH1 and YH2 are upper limit values of luminance when the achromatic color is extracted by dividing the luminance range into two, and YL1 and YL2 are respective luminance values when the achromatic color is extracted by dividing the luminance range into two. Indicates the lower limit. The processing up to step S63 is shown in FIG.
Is performed in the same manner as As a result of the determination in step S61, when there is an area exceeding the fixed range ΔC (Y in S61), one of the luminance upper limit values YH1 is set to the initial value YHC (S101) and the luminance lower limit value YL is set.
1 is set to the changed value calculated by the calculation of (max + min) / 2 (S102). Further, the other luminance upper limit value Y
H2 is set to a changed value calculated by the calculation of (max + min) / 2 (S103), and the lower luminance limit YL2 is set to an initial value YLC (S104). This gives 2
A step luminance range is set. On the other hand, when there is no area exceeding the fixed range ΔC (N in S61, S62
Y), the luminance upper limit YH1 is set to the initial value YHC (S105), and the luminance lower limit YL1 is also set to the initial value YLC.
(S106), and 0 is set for both the luminance upper limit YH2 and the luminance lower limit YL2 (S107, S1).
08). That is, as in the case of the above-described embodiment, only one luminance range is set by the initial value.

The achromatic determination circuit 9 performs achromatic determination for each pixel for each luminance range.

The gain control circuit 10 calculates the amount of gain control in each luminance range and compares the amounts of gain control. If the two gain control amounts differ according to the comparison result, for example, the gain control amount based on the achromatic color determination result of the luminance range including the average luminance value of the area C having a high probability of containing the subject is used. To work.

FIG. 15 is a block diagram showing a configuration example of the gain control circuit 10 for this purpose. In the present embodiment, each integrated value Rsum, Gsu obtained from the achromatic color determination circuit 9 is used.
a gain calculation circuit 28 for calculating gain control amounts Rgain1, Rgain2, Bgain1, Bgain2 for R and B for each luminance range based on m and Bsum, and gain control amounts Rgain1, Rgai
selectors 30a and 30b for selecting any one of n2, Bgain1, and Bgain2 at a pixel position corresponding to the luminance signal Y and the number of clocks counted by the counter 29, and R data by a gain control amount Rgain1 or Rgain2 selected by the selector 30a. A multiplier 27a that performs gain control on
Gain control amount Bgain1 selected by selector 30b
Or, a multiplier 27b for performing gain control for white balance for B data by Bgain2.

However, as the gain control, the setting and selection of the gain control amounts Rgain and Bgain may be performed by selecting the smaller gain control amount. Alternatively, the present invention is not limited to the selection of either one of the gain control amounts, and the weighting may be performed based on the integrated data and the like, and the weighted gain control amount may be used.

According to the present embodiment, even when a luminance distribution appears, a large number of achromatic color determination data can be sampled, white balance control capable of suppressing color shift can be performed, and gain control can be performed. The degree of freedom in white balance processing can be increased by the method of determining the amount.

In these embodiments, the above-described processing is executed by the circuit configuration including the color interpolation circuit 4, the luminance determination circuit 6, the achromatic color range setting circuit 8, the achromatic color determination circuit 9, and the gain control circuit 10. However, the processing may be controlled by software using a processor or the like.

[0056]

According to the white balance control method of the present invention, the achromatic color determination is performed by changing and setting the luminance range for performing the achromatic color determination based on the luminance information of the luminance distribution in the unit of area. Therefore, the white balance processing can be performed with high accuracy even during imaging in which a different light source is included in the imaging frame.

According to the second aspect of the present invention, in the white balance control method according to the first aspect, since the achromatic color detection on the high luminance side is not performed based on the luminance information, an outdoor scene is photographed indoors. Even in such a case, white balance control without a sense of incongruity can be performed except for the influence of outdoor data having a high luminance value.

According to the third aspect of the present invention, in the white balance control method according to the first or second aspect, the achromatic color detection is performed by using luminance information and a fixed value, for example, an exposure control value, in the imaged frame. Since the setting of the luminance range is performed, achromatic color detection in the luminance range near the subject is performed, and white balance processing that suppresses color shift of the subject can be performed.

According to the white balance control method of the present invention, the gain control amount is obtained for each luminance range based on the luminance information, and the control is performed by appropriately setting the gain control amount based on the result. Therefore, more flexible and accurate white balance control becomes possible.

According to the white balance control apparatus of the present invention, the achromatic color range is set by the achromatic color range setting means to change and set the luminance range for performing the achromatic color determination based on the luminance information of the luminance distribution in the unit of area. Since the achromatic color determination is performed by the means, the white balance processing can be performed with high accuracy even during shooting in which a different light source is included in the imaging frame.

According to the sixth aspect of the present invention, the achromatic color detection on the high luminance side is not performed based on the luminance information. Therefore, even when an outdoor scene is photographed indoors, an outdoor scene having a high luminance value can be obtained. Except for the influence of data, white balance control without a sense of incongruity becomes possible.

According to the seventh aspect of the present invention, in the white balance control apparatus according to the fifth or sixth aspect, the achromatic color range setting means uses the luminance information and a fixed value, for example, an exposure control value, in the imaging frame. Since the luminance range for achromatic color detection is set, achromatic color detection in the luminance range near the subject is performed, and white balance processing that suppresses color shift of the subject can be performed.

According to the eighth aspect of the present invention, a luminance range for achromatic color detection is set by using luminance information and a constant value, for example, an exposure control value, in an imaging frame. Achromatic color detection in the luminance range of
White balance processing that suppresses color shift of the subject can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a color imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating an example of an imaging frame.

FIG. 3 is a flowchart illustrating an example of a basic process.

FIG. 4 is a schematic diagram showing an example of the arrangement of CCD filters.

FIG. 5 is a block diagram illustrating a configuration example of a color interpolation circuit.

FIG. 6 is a flowchart showing an example of the color interpolation processing.

FIG. 7 is a block diagram illustrating a configuration example of a luminance determination circuit and an achromatic color range setting circuit.

FIG. 8 is a flowchart illustrating an example of a luminance range setting process.

FIG. 9 is a block diagram illustrating a configuration example of an achromatic color determination circuit.

FIG. 10 is a block diagram showing an example of an achromatic color detection process.

FIG. 11 is a block diagram illustrating a configuration example of a gain control circuit.

FIG. 12 is a flowchart showing an example of the gain calculation.

FIG. 13 is a flowchart illustrating an example of a luminance range setting process according to the second embodiment of this invention.

FIG. 14 is a flowchart illustrating an example of a luminance range setting process according to the third embodiment of the present invention.

FIG. 15 is a block diagram showing a configuration example of the gain control circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 6 Luminance determination means 8 Achromatic color range setting means 9 Achromatic color determination means 10 Gain control means 11 Imaging frame

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Claims (8)

[Claims] 1. A luminance distribution is obtained based on image data of each predetermined area divided for an imaging frame, and the luminance distribution of each area is compared, and a luminance range in which achromatic color is extracted is determined in accordance with the comparison result. Set to an initial value or a calculated change value, perform achromatic determination on the image data within the set luminance range, and set a gain control amount for the image data based on the integrated data of the pixels determined to be achromatic. A white balance control method that achieves a white balance by using 2. The method according to claim 1, wherein when the luminance distribution of each area is different in two or more steps, the luminance range for performing achromatic color extraction based on the luminance distribution on the low luminance side is set to the calculated change value. White balance control method. 3. A luminance range in which achromatic color extraction is performed based on a luminance distribution on a high luminance side when a luminance distribution of each area is different in two or more steps in a range where a maximum luminance average value is equal to or less than a predetermined value. 3. The method according to claim 1, wherein the change value is set.
The white balance control method described in the above. 4. A luminance distribution is obtained based on image data of each predetermined area divided for an imaging frame, and the luminance distributions of the respective areas are compared. As a result of the comparison, the luminance distribution of each area has two levels. In the case of the above difference, the brightness range for performing achromatic color extraction is set to the calculated change value for each different brightness distribution according to the brightness distribution, and the image data is set within the brightness range for each brightness distribution set. A white balance control method which performs achromatic color determination and sets a gain control amount for the image data in accordance with the achromatic color determination result for each of the luminance distributions to obtain a white balance. 5. A luminance determining means for obtaining a luminance distribution based on image data for each of predetermined areas obtained by dividing an imaging frame imaged by an imaging device and comparing the luminance distribution for each area; Achromatic color range setting means for setting a luminance range for performing achromatic color extraction according to the comparison result to an initial value or a calculated change value; and achromatic color for the image data within the luminance range set by the achromatic color range setting means. Achromatic color determining means for performing determination, and gain control means for setting a gain control amount for the image data so as to obtain a white balance based on integrated data of pixels determined to be achromatic by the achromatic color determining means. White balance control device. 6. The achromatic color range setting means performs achromatic color extraction based on the luminance distribution on the low luminance side when the luminance distribution of each area is different by two or more levels as a result of the comparison by the luminance determining means. The white balance control device according to claim 5, wherein the brightness range is set to the calculated change value. 7. The achromatic color range setting means, as a result of the comparison by the luminance judging means, when the luminance distribution of each area is different in two or more steps in a range where the maximum luminance average value is equal to or less than a fixed value, 7. A modified value for calculating a luminance range in which achromatic color extraction is performed based on a luminance distribution on the luminance side.
The white balance control device as described in the above. 8. A luminance determining means for obtaining a luminance distribution based on image data for each of predetermined areas obtained by dividing an imaging frame imaged by an imaging element and comparing the luminance distribution for each area; According to the comparison result, the brightness range in which achromatic color extraction is performed is set to an initial value or a changed value. If the brightness distribution of each area is different in two or more stages as a result of the comparison, the brightness is different for each brightness distribution. An achromatic color range setting means for setting a luminance range for performing achromatic color extraction in accordance with the distribution to a calculated change value; and an achromatic color determination section for performing achromatic determination on the image data within the luminance range set by the achromatic color range setting means. A chromatic determination unit; and a gain control unit for setting a gain control amount for obtaining a white balance according to an achromatic determination result by the achromatic determination unit. White balance control device.