JP2004064586A - White balance adjustment circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white balance adjustment circuit by which the dynamic range of a white balance-adjusted color information signal is prevented from reducing. <P>SOLUTION: In adjusting the white balance of a photographed object image, amplifiers 24a-24c individually provide Rgain, Ggain, and Bgain being white balance grains to R data, G data, B data corresponding to the object image. A CPU (Central Processing Unit) 22 evaluates the color of the object image and sets the white balance adjustment gain provided to color data corresponding to the maximum color evaluation value to the standard value (=1.0). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a white balance adjustment circuit, and more particularly to a white balance adjustment circuit that is applied to, for example, a video camera and adjusts the white balance of a captured subject image.
[0002]
[Prior art]
In this type of conventional video camera, a color evaluation value is obtained for each of a plurality of regions forming a subject image, and a color evaluation value included in the pull-in range shown in FIG. The average value was calculated, and the white balance was adjusted so that the average value converged at the intersection of the RG axis and the BG axis.
[0003]
Specifically, among the R data, G data, and B data corresponding to the subject image, a gain corresponding to the average value of the color evaluation values is given to the R data and B data, thereby adjusting the white balance of the subject image. It had been.
[0004]
[Problems to be solved by the invention]
However, in the related art, since the color data to which the reference gain is applied is always the G data, there is a problem that the dynamic range of the RGB data in which the white balance is adjusted is reduced depending on the subject. That is, when the subject exists under natural light, the level of the G data becomes maximum as shown in FIG. For this reason, even if gains larger than 1.0 (for example, 1.3 and 1.2) are given to the R data and the B data at the time of white balance adjustment, the dynamic range is not reduced. However, when the subject is under a light source with a low color temperature, the level of the R data becomes maximum as shown in FIG. Therefore, when a gain smaller than 1.0 (for example, 0.7 and 0.9) is given to the R data and the B data at the time of white balance adjustment, the dynamic range of the RGB data subjected to the white balance adjustment is reduced. I will.
[0005]
Therefore, a main object of the present invention is to provide a white balance adjustment circuit that can prevent a dynamic range of a color information signal subjected to white balance adjustment from being reduced.
[0006]
[Means for Solving the Problems]
The present invention is a white balance adjustment circuit that adjusts a white balance of a captured subject image, wherein a plurality of white balance adjustment gains including a reference gain are individually applied to a plurality of color information signals corresponding to the subject image, A white balance adjustment circuit comprising: an evaluation unit that evaluates a color of a subject image; and a changing unit that changes a color information signal to which a reference gain is applied based on an evaluation result of the evaluation unit.
[0007]
[Action]
When adjusting the white balance of the captured subject image, the assigning unit individually assigns a plurality of white balance adjustment gains including a reference gain to a plurality of color information signals corresponding to the subject image. Here, the color of the subject image is evaluated by the evaluation unit, and the color information signal for giving the reference gain is changed by the changing unit based on the evaluation result of the evaluation unit.
[0008]
Preferably, the evaluation means individually integrates the plurality of color information signals, and specifies a maximum integrated value from among the plurality of integrated values obtained thereby. The changing means sets the color information signal corresponding to the maximum integrated value as a color information signal to which a reference gain is applied.
[0009]
【The invention's effect】
According to the present invention, since the color information signal to which the reference gain is applied is changed based on the evaluation result of the color of the subject, the dynamic range of the color information signal subjected to the white balance adjustment is prevented from being reduced. be able to.
[0010]
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.
[0011]
【Example】
Referring to FIG. 1, a digital video camera 10 of this embodiment includes a lens 12. The optical image of the subject enters the light receiving surface of the image sensor 16 via the lens 12 and the primary color filter 14 mounted on the front of the image sensor 16. The primary color filter 14 has R, G, and B filter elements corresponding to each pixel, as shown in FIG. Therefore, the amount of charge generated by each light receiving element formed on the light receiving surface reflects the amount of R, G, or B light.
[0012]
The timing generator (TG) 34 reads out charges (pixel signals) generated by the image sensor 16 by a raster scan method. The read pixel signal is converted into a digital signal, that is, pixel data by the A / D converter 18, and the converted pixel data is input to the first signal processing circuit 20. The first signal processing circuit 20 performs signal processing such as CDS or AGC on the input pixel data, and performs color separation on the pixel data on which such processing has been performed. As a result, each pixel has all the color information of R, G, and B, and the R data, G data, and B data of the same pixel are simultaneously output from the first signal processing circuit 20 to the white balance adjustment circuit 22. Is done.
[0013]
R data is given Rgain by the amplifier 24a, G data is given Ggain by the amplifier 24b, and B data is given Bgain by the amplifier 24c. The R data, G data, and B data to which gains have been applied by the amplifiers 24a to 24c are subjected to a matrix operation in a matrix circuit 26. As a result, Y data, U data, and V data are generated.
[0014]
The R data, G data and B data are also input to the integrating circuit 28. The screen is divided into eight in the horizontal and vertical directions as shown in FIG. 5, and 64 divided areas are formed on the screen. The integrating circuit 28 integrates the R data, G data, and B data for each color information and for each divided area. Thus, the integrated values Rij, Gij, and Bij of each divided area are generated over one frame period. Note that i and j indicate the positions of the divided areas in the horizontal direction and the vertical direction, respectively, and are assigned one of values “1” to “8”.
[0015]
When the shutter button 32 is operated, the CPU 30 performs pre-exposure on the image sensor 16 and adjusts the white balance based on the integrated values Rij, Gij and Bij output from the integrating circuit 28 based on the pre-exposure, After the white balance adjustment is completed, the main exposure is performed on the image sensor 16. The Y data, U data, and V data based on the pixel signals obtained by the main exposure are recorded on the recording medium 40 through compression processing by the second signal processing circuit 38.
[0016]
When performing white balance adjustment in response to the operation of the shutter button 32, the CPU 30 processes the flowcharts shown in FIGS. Note that a control program corresponding to this flowchart is stored in the ROM 42.
[0017]
First, in step S1, the counters 30i and 30j and the registers 30r, 30g and 30b are initialized. The count i of the counter 30i, the count i of the counter 30i, the register value ΣR of the register 30r, the register value ΣG of the register 30g, and the register value ΣB of the register 30b are all set to “0”.
[0018]
When the shutter button 32 is operated, first, pre-exposure is executed, and R data, G data, and B data obtained by the pre-exposure are white balance adjustments according to the initial values of Rgain, Ggain, and Bgain. Is given. The integrated circuit 28 obtains integrated values Rij, Gij, and Bij of the R data, G data, and B data that have been subjected to the white balance adjustment.
[0019]
The initial values of Rgain, Ggain, and Bgain are values at which the white balance is appropriately adjusted when a subject having a color temperature of 5100K (reference color temperature) is photographed. Since there is an error in the characteristics of each manufactured image sensor, initial values of Rgain, Ggain, and Bgain are individually calculated when each digital camera is manufactured. When the same object is photographed by setting the initial values of Rgain, Ggain and Bgain in the amplifiers 24a, 24b and 24c, the R data, G data and B data output from the amplifiers 24a, 24b and 24c are transmitted between the digital cameras. Will match each other.
[0020]
In step S3, the divided areas specified by the count values i and j of the integrated values Rij, Gij, and Bij of the R data, G data, and B data subjected to white balance adjustment according to the initial values of Rgain, Ggain, and Bgain. , Gij, and Bij. In step S5, Yij, (RG) ij and (BG) ij are calculated based on the acquired integrated values Rij, Gij and Bij. Yij indicates an integrated value of the Y signal detected from the divided area (i, j), and can be defined as a luminance evaluation value. On the other hand, (RG) ij indicates a difference between integrated values of the R signal and the G signal detected from the divided area (i, j), and (BG) ij is detected from the divided area (i, j). 4 shows the difference between the integrated values of the B signal and the G signal.
[0021]
In a succeeding step S7, fy (RG) ij and fy (BG) ij are obtained according to Expression 1.
[0022]
(Equation 1)
fy (RG) ij = (RG) ij / c1 * Yij
fy (BG) ij = (BG) ij / c2 * Yij
c1, c2: The numerical values indicated by the constants (RG) ij and (BG) ij reflect the exposure amount during the pre-exposure. That is, the numerical value increases when the exposure amount is large, but decreases when the exposure amount is small. If (RG) ij and (BG) ij having such characteristics are defined as the color evaluation value of each divided area, the color evaluation value varies depending on the exposure amount. On the other hand, the color of the subject does not inherently depend on the exposure amount, and the color of the subject is always the same unless the subject and the light source change. Therefore, even if the exposure amount is changed, the color evaluation value should keep the same value. For this reason, each of (RG) ij and (BG) ij is divided by c1 * Yij and c2 * Yij related to the exposure amount according to Equation 1, and the divided values fy (RG) ij and fy ( BG) ij is defined as a color evaluation value. Thus, the color evaluation value does not depend on the exposure amount, and the color of each divided area can be accurately evaluated.
[0023]
In step S9, it is determined where the color evaluation values fy (RG) ij and fy (BG) ij are located in the color distribution diagram shown in FIG. 6B, and weighting corresponding to the determined positions is performed. The coefficient Wij is detected from the table 30t shown in FIG. The table 30t is formed in the CPU 30. In a succeeding step S11, the detected weighting coefficient Wij is multiplied by the integrated values Rij, Gij and Bij fetched in the step S3 to obtain multiplied values Rij * Wij, Gij * Wij and Bij * Wij.
[0024]
According to FIG. 6A, the weighting coefficient Wij indicates any one of “0”, “6”, “7”, and “8”. Of these, the areas to which "6", "7" and "8" are assigned define the pull-in range, and the divided areas whose color evaluation values fall outside the pull-in range are invalidated by the processing in step S11. When focusing on the subject image shown in FIG. 5, the 14 divided areas indicated by oblique lines are blue sky of the same color, and the color evaluation value is out of the pull-in range indicated by oblique lines in FIG. Therefore, the 14 divided areas are invalidated, and the remaining 50 divided areas are activated.
[0025]
In step S13, the weights Rij * Wij, Gij * Wij and Bij * Wij calculated in step S11 are integrated for each color information. Specifically, an operation according to Equation 2 is performed, and the weight values Rij * Wij, Gij * Wij, and Bij * Wij calculated this time are added to the current register values ΣR, ΣG, and ΣB.
[0026]
(Equation 2)
ΣR = ΣR + Rij * Wij
ΣG = ΣG + Gij * Wij
ΣB = ΣB + Bij * Wij
In step S15, it is determined whether the accumulation according to equation 2 has been repeated 64 times. If NO, the count value i or j is updated in step S17, and the process returns to step S3. As a result, the processes of steps S3 to S13 are executed for the integrated values Rij, Gij, and Bij obtained in each of the 64 divided areas shown in FIG. When YES is determined in step S15, the register values ΣR, ΣG, and ΣB indicate the integrated values of the weight values Rij * Wij, Gij * Wij, and Bij * Wij over one screen. Therefore, the register values $ R, $ G, and $ B can be defined as the color evaluation values of all the divided areas included in the pull-in range.
[0027]
In steps S19 and S23, it is determined which of the register values $ R, $ G, and $ B is the maximum value. When the register value ΣG is the maximum value, it is determined as YES in step S19, and the process proceeds to step S21. When the register value ΣR is the maximum value, YES is determined in the step S23, and the process proceeds to a step 25. When the register value ΣB is the maximum value, YES is determined in the step S23, and the process proceeds to a step 27. In step S21, Rgain, Ggain, and Bgain are calculated according to equation 3, in step S25, Rgain, Ggain, and Bgain are calculated according to equation 4, and in step S27, Rgain, Ggain, and Bgain are calculated according to equation 5.
[0028]
[Equation 3]
Rgain = k1 * ΣG / ΣR
Ggain = 1.0
Bgain = k2 * ΣG / ΣB
k1, k2: constants
(Equation 4)
Rgain = 1.0
Ggain = k3 * ΣR / ΣG
Bgain = k4 * ΣR / ΣB
k3, k4: constants
(Equation 5)
Rgain = k5 * ΣB / ΣR
Ggain = k6 * ΣB / ΣG
Bgain = 1.0
k5, k6: Ggain is the reference gain (= 1.0) according to the constant 3, Rgain is the reference gain (= 1.0) according to the equation 4, and Bgain is the reference gain (= 1.0).
[0031]
In step S33, Rgain, Ggain, and Bgain obtained by any one of Expressions 3 to 5 are set in the amplifiers 24a, 24b, and 24c shown in FIG. 1, respectively. When the process of step S21 is performed, the reference gain is given to the G data, and the gain based on the register values ΣR, ΣG, and ΣB is given to the R data and the B data. When the process of step S25 is performed, the reference gain is given to the R data, and the gain based on the register values ΣR, ΣG, and ΣB is given to the G data and the B data. When the process of step S27 is performed, the reference gain is given to the B data, and the gain based on the register values ΣR, ΣG, and ΣB is given to the R data and the G data. From the amplifiers 24a, 24b and 24c, R data, G data and B data whose white balance has been adjusted are output.
[0032]
As can be understood from the above description, the amplifiers 24a to 24c included in the white balance adjustment circuit 22 individually convert the gains Rgain, Ggain, and Bgain, which are the white balance adjustment gain, into R data, G data, and B data corresponding to the subject image. Give. Here, the CPU 22 calculates the color evaluation values ΣR, ΣG, and ΣB, specifies the maximum color evaluation value from the calculated color evaluation values ΣR, ΣG, and ΣB, and outputs the color data corresponding to the maximum color evaluation value. Is set to a reference value (= 1.0). Therefore, the color data to which the reference gain is given is changed according to the color of the subject. This can prevent the dynamic range of the RGB data on which the white balance adjustment has been performed from being reduced.
[0033]
Although the present embodiment has been described using a digital video camera, the present invention can also be applied to an analog video camera. In this embodiment, the primary color filter is mounted on the light receiving surface of the image sensor. However, a complementary color filter may be mounted instead of the primary color filter.
[Brief description of the drawings]
FIG. 1 is a block diagram showing one embodiment of the present invention.
FIG. 2 is an illustrative view showing a primary color filter;
FIG. 3 is a flowchart showing a part of the operation of the CPU;
FIG. 4 is a flowchart showing another portion of the operation of the CPU;
FIG. 5 is an illustrative view showing a divided area formed on a screen;
FIG. 6A is an illustrative view showing a weighting coefficient and a pull-in range, and FIG. 6B is an illustrative view showing a plane formed by a BG axis and an RG axis;
FIG. 7 is an illustrative view showing a drawing range formed on a plane formed by the BG axis and the RG axis;
FIG. 8 is an illustrative view showing one portion of an operation in the related art;
[Explanation of symbols]
10 Digital video camera 20 First signal processing circuit 22 White balance adjustment circuits 24a to 24c Amplifier 26 Matrix circuit 28 Integration circuit 30 CPU
38 second signal processing circuit 40 recording medium

Claims (4)

In a white balance adjustment circuit that adjusts the white balance of a captured subject image,
Providing means for individually providing a plurality of white balance adjustment gains including a reference gain to a plurality of color information signals corresponding to the subject image,
A white balance adjustment circuit, comprising: evaluation means for evaluating the color of the subject image; and changing means for changing a color information signal to which the reference gain is applied based on an evaluation result of the evaluation means. 2. The evaluation unit according to claim 1, wherein the evaluation unit includes an integrating unit that individually integrates the plurality of color information signals, and a specifying unit that specifies a maximum integrated value from among the plurality of integrated values obtained by the integrating unit. 3. White balance adjustment circuit. 3. The white balance adjustment circuit according to claim 2, wherein said changing means sets a color information signal corresponding to said maximum integrated value as a color information signal to which said reference gain is applied. A video camera comprising the white balance adjustment circuit according to claim 1.

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