JPH09307922A - Color signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the color signal processing circuit in which control with high accuracy is conducted against a color temperature change in an object (or light source) while relieving the load of both the hardware and the software. SOLUTION: Integration value data of R-G, B-G obtained by integrating color difference signals R-G, B-G for each field are added by an adder 82 in a controller 8 to convert the data R-G, B-G into R+B-2G and subtracted by a subtractor 83 to convert the data R-G, B-G into R-B 2G in the color signal processing circuit provided with a white balance function of the feedback control system, then a gain setting circuit, 84 sets R and B gains so as to take white balance based on the gain information.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color signal processing circuit, and more particularly to a color signal processing circuit having an automatic white balance function for automatically performing white balance by feedback control in a solid-state image sensor system using a CCD or the like. .

[0002]

2. Description of the Related Art White balance means, for example, in a solid-state image sensor system, when the color temperature of a light source changes, as shown in FIG. This is to match a white color that moves along a locus) and appears colored (for example, becomes reddish at a low color temperature and bluish at a high color temperature) with an achromatic white color. Here, the color temperature means the temperature (° K) of a black body having the same chromaticity as the test light source. Also,
In FIG. 10, the origin is achromatic white.

In this white balance operation, integration is performed on color signals from the idea that when all the colors on the screen are added together, white is obtained. In a conventional color signal processing circuit, R (red), G (green), and B (blue) primary color signals are integrated (detected), and white balance is adjusted based on the integrated value data, or RY (Red-luminance), BY
The operation of integrating each color difference signal of (blue-luminance) and adjusting the white balance based on the integrated value data has been performed.

[0004]

However, R,
In the case of the former color signal processing circuit that uses the G and B primary color signals as the integrated value data, although it is easy to convert to various data formats, the processing for that increases the software capacity and the integrated value data. Since there are 3 sets, there is a large amount of data, and accordingly three integration circuits are required,
There was a problem that the burden on the hardware also increased.
On the other hand, in the case of the latter color signal processing circuit that uses the RY and BY color difference signals as the integrated value data, the white locus (blackbody radiation curve in FIG. 8) due to the change in color temperature cannot be taken into consideration. There is a problem that it is not possible to perform highly accurate control.

Further, in the white balance function of the feedforward control system, Y (luminance signal) and C
There is also known a color signal processing circuit that integrates r and Cb (color difference signals) and adjusts white balance based on the integrated value data. However, in this case also, since the integrated value data is three sets, the data amount is large. Moreover, there is a problem that the number of integrating circuits increases. In addition, there is a problem that the load of software for data conversion processing from the integrated value data is heavy.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the burden on both hardware and software, and to achieve accuracy with respect to changes in the color temperature of a subject (or a light source). It is to provide a color signal processing circuit capable of performing high control.

[0007]

A color signal processing circuit according to the present invention adopts a feedback control system, and R, G, B
White balance amplifier for performing gain adjustment between the primary color signals, an integrating circuit for obtaining the integrated value of each color difference signal of R-G and B-G for each field, and the integrated value of each color difference signal by addition and subtraction processing. Converted to RB and R + B-2G signals,
A controller for controlling the gain of the white balance amplifier based on the signals of RB and R + B-2G is provided.

In the color signal processing circuit having the above structure, R-
The integrated value data for each field of the G and B-G color difference signals are obtained, and these integrated value data are converted into signals of RB and R + B-2G. Then, white balance is achieved by feedback control for the two axes R-B and R + B-2G. RB is close to a locus (black body radiation curve) in which white changes with respect to the color temperature change of the subject (or the light source). R + B-2G is the direction in which the white color changes when the subject is under a fluorescent lamp (or when the light source is a fluorescent lamp).

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a solid-state imaging device system to which the present invention is applied.

In FIG. 1, a lens 1 projects an image of a subject (not shown) on an image pickup surface of a solid-state image pickup device 2. The solid-state image sensor 2 is composed of, for example, a CCD, converts an image passing through the lens 1 into an electric signal, and supplies the electric signal to the preamplifier 3. The preamplifier 3 samples and holds the output signal of the solid-state image sensor 2 to take out necessary data, and also performs gain control in order to adjust to an appropriate level. The output signal of the preamplifier 3 is supplied to the A / D conversion circuit 4
After being converted from an analog signal to a digital signal in the above, it is supplied to the digital signal processing circuit 5.

The digital signal processing circuit 5 converts the digital input signal from the A / D conversion circuit 4 into R (red) and G.
White balance is achieved by adjusting the gain between the primary color separation circuit 51 for separating primary color signals of (green) and B (blue) (hereinafter referred to as R, G, B signals) and the R, G, B signals. White balance amplifiers 52R, 52G,
52B and a γ correction circuit 53 for performing a gamma (γ) correction for faithful color reproduction. Here, taking white balance (matching) means making the ratios of the R, G, and B signals equal. In this example, A
Although the / D conversion circuit 4 is arranged in the preceding stage of the digital signal processing circuit 5, it may be provided in the processing circuit 5.

In this digital signal processing circuit 5,
In adjusting the white balance, a relational expression of R × R gain = G × G gain = B × B gain, that is, R × R gain-G × G gain = B × B gain-G × G gain = 0 holds. As described above, the gains of the white balance amplifiers 52R, 52G, and 52B are operated. In this example, the white balance is adjusted by fixing the gain of the white balance amplifier 52G and controlling the gains of the other two white balance amplifiers 52R and 52B with the G signal as a reference. Therefore, the white balance amplifier 52G for the G signal can be omitted.

The R, G, B signals after the white balance adjustment are subjected to signal processing such as γ correction, and then combined with a luminance (Y) signal (not shown) to become a video signal, and further D / A.
The conversion circuit 6 converts the digital signal into an analog signal and outputs the analog signal. The D / A conversion circuit 6 is also
As in the case of the A / D conversion circuit 4, it may be arranged in the digital signal processing circuit 5. The R, G, B signals that have passed through the white balance amplifiers 52R, 52G, 52B are also supplied to the optical detector (OPD) 7.

FIG. 2 shows an example of the circuit configuration of the optical detector 7. In the figure, the optical detector 7 includes a subtracter 71 for subtracting the G signal from the R signal, and a B
A subtractor 72 for subtracting the G signal from the signal, a subtracter 71,
An integrator circuit 73 for integrating the color difference signals which are the output signals of 72, that is, the R-G signal and the B-G signal for each field.
It has a circuit configuration that includes and.

As shown in FIG. 3, the integrating circuit 73 has different integration ranges divided into a high-luminance portion and a normal-luminance portion according to the integral slice level based on the luminance level, and in the high-luminance portion, it is higher than the integral slice level. Only high-luminance data (R-G, B-G) is integrated, and in the normal-luminance part, luminance data lower than the integrated slice level (R-G, B-).
Integrate only G). However, when the brightness is extremely high, it is determined that the brightness is saturated, and the data above the high brightness limiter is not integrated. In addition, data whose brightness is too low is regarded as noise, and data below the low brightness limiter is not integrated.

As described above, the optical detector 7 is provided with various limiters and special processing so that the white balance processing does not malfunction under special conditions (for example, conditions such as full-color single color). Then, the integrated value data (RG, BG) obtained by integrating in different integration ranges of the high brightness part / normal brightness part for each field is supplied to the controller 8 of the next stage. In this example, R,
The color difference signals RG and BG are generated from the G and B signals, and then the color difference signals RG and BG are integrated.
It is also possible to integrate the R, G and B signals first and then generate the color difference signals RG and BG from the integrated R, G and B signals.

The controller 8 is composed of, for example, a microcomputer. An example of functional blocks of the controller 8 is shown in FIG. In the figure, the controller 8 stores the integrated value data (R-G, BG) of the high brightness part and the integrated value data (R-G, BG) of the normal brightness part, which are supplied from the optical detector 7. Compare and 0
To the comparator circuit 81 which outputs the integrated value data closer to the value of the R, and the adder 82 which adds the integrated value data of RG and BG selected by the comparator circuit 81 and outputs the data of R + B-2B. And a subtracter 83 for subtracting the BG integrated value data from the RG integrated value data and outputting the RB data.
And a gain setting circuit 84 for setting each gain of the R signal and the B signal based on each data of R + B-2B and RB.
Each of the functions is provided and these functions are executed by software.

The integrated value data obtained by integrating the R-G and B-G color difference signals in this manner is used as the controller 8
In the above, since the data can be converted only by simple arithmetic processing such as addition and subtraction by converting each data of R + B-2B and RB in the addition / subtraction processing, the load of software can be reduced. In this example, R +
Although the calculation of each data of B-2B and RB is performed by software in the controller 8 including a microcomputer, the comparison circuit 81, the adder 82, the subtractor 83, and the gain setting circuit 84 of the controller 8 are calculated. It is also possible to configure each function with hardware, and in this case, the load on the hardware can be reduced.

In the controller 8, R + B-2B,
The R gain information and the B gain information set based on each data of RB are fed back to the white balance amplifiers 52R and 52B of the digital signal processing circuit 5. That is, the controller 8 is R + B-2B, R
Based on each data of −B, the white balance is adjusted by software, and from the evaluation value data from the white balance gain and the optical detector 7, the color temperature in a state where the white balance is matched and how it is changed after that. It is determined whether or not the size of the pull-in limit frame that limits the range of white balance is changed in accordance with the change in the color temperature of the light source.

To adjust the white balance, first,
The integrated value data of each of the high-luminance portion and the normal-luminance portion are compared, and the one closer to the origin (RG = 0, BG = 0), that is, 0 is adopted. In the case of the example shown in FIG. 5, since the integrated value data of the high brightness portion is closer to 0 than the integrated value data of the normal brightness portion, the integrated value data of the high brightness portion is used. Then, the coordinate position of the evaluation value data is determined, and if it is within the pull-in limit frame, the coordinate position (quadrant or on the axis)
To operate the white balance gain, and set the origin (R-G
= 0, BG = 0).

In the case of this example, the R gain is lowered and the B gain is raised. Then, the obtained R gain and B gain are reflected in the white balance balance amplifiers 52R and 52B in the digital signal processing circuit 5. If the evaluation value data is outside the pull-in limit frame, the white balance adjustment operation is not performed. Note that the pull-in restriction frame is set in order to prevent an erroneous operation in which even an originally non-white object is pulled in.

Thereafter, in the controller 8, R + B-
A procedure of a specific operation for adjusting the white balance executed based on each data of 2G and RB will be described with reference to the flowchart of FIG.

First, an optical detector (OPD)
7. Evaluation value data, that is, each of the R-G and B-G integrated value data is loaded from step 7 (step S1), and the loaded integrated value data is data with a low brightness level (for example, all-blue,
It is determined whether or not the subject is a red subject (step S)
2). Then, if the evaluation value data is data having a low brightness level, this processing is ended. If the evaluation value data is not data with a low brightness level, it is determined whether the data is outside the appropriate range, that is, the integrated value data is too low or too high (step S3).

If the evaluation value data is out of the proper range, this process ends. If the evaluation value data is within the proper range, RG and B-integrated in the high luminance part and the normal luminance part, respectively.
The integrated value data of G are compared, and the data closer to 0 is adopted (step S4). Then, by adding and subtracting using the integrated value data of the adopted one, RG, B
The -G integrated value data is converted into R + B-2G and RB data (step S5). Next, the code of R + B-2G is determined (step S6), and then the code of RB is determined (step S7). By this sign determination, RB,
In the coordinate axis of R + B-2G, it is determined where the data is.

Next, it is judged whether or not the data is within the pull-in restriction frame (step S8). If the data is out of the pull-in restriction frame, this processing is ended. On the other hand, if the data is within the pull-in limit frame, the pull-in operation for white balance is performed by controlling the gains of the white balance amplifiers 52R and 52B in the digital signal processing circuit 5 (step S9). Then, the white balance gain and the integration range are returned to the digital signal processing circuit 5, and a series of processing is ended.

Here, the pull-in limit frame, the dead zone, the convergence point and the gain operation for pull-in will be described with reference to FIG. The dead zone is provided in order to prevent oscillation when it does not completely become 0 (it does not converge to the origin). In FIG. 7, the data is first
When it is in the quadrant, the gain (R gain) of the white balance amplifier 52R is lowered, when it is in the second quadrant, the gain (B gain) of the white balance amplifier 52B is raised, and when it is in the third quadrant, the R gain is raised, If it is in the fourth quadrant, the B gain is lowered.

If the data is on the R-B and R + B-2G axes, the R gain and the B gain are operated simultaneously. That is, the data is R + B-2G> 0 and R
When it is on the + B-2G axis, both the R gain and the B gain are lowered. Data is R + B-2G <0 and R + B-2
If it is on the G axis, increase both R gain and B gain. If the data is RB> 0 and is on the RB axis, the R gain is decreased and the B gain is increased. Data is R
When -B <0 and on the RB axis, the R gain is increased and the B gain is decreased.

Next, an example of reduction / enlargement of the pull-in limit frame according to the change in color temperature will be described with reference to FIG. In FIG. 8, the broken line frame represents the default reference pull-in limit frame, the thin solid line frame represents the post-convergence pull-in limit frame, and the thick solid line represents the reduced / enlarged pull-in limit frame.

First, a case (a) in which the R gain is small, the B gain is large, the evaluation value data (RB) is negative and is outside the pull-in limit frame will be described. At a certain reference color temperature, when the white balance is changed to a low color temperature within the reference pull-in limit frame (broken line frame),
The white of the origin of the coordinates indicated by the broken line converges on the origin of the coordinates indicated by the solid line. From this state, when the color temperature is changed to the next higher color and the outside of the pull-in restriction frame (thin solid line frame) after convergence, the white balance cannot be maintained as it is.

However, this evaluation value data (RB)
Is outside the pull-in restriction frame (frame with a thin solid line) after convergence, but is within the reference pull-in restriction frame (frame with a broken line), so white balance should be taken. Therefore, as shown by the thick solid line frame, the pull-in restriction frame after convergence is expanded to the high color temperature side to the range in which the current evaluation value data (RB) is fetched. As a result, even if it converges at the low color temperature last time, changes to the high color temperature side this time, and is outside the pull-in restriction frame (thin solid line frame) after convergence, the reference pull-in restriction frame (broken line frame)
As long as it is within the range, the white balance operation is performed.

Next, a case (b) in which the R gain is large, the B gain is small, the evaluation value data (RB) is negative and is within the pull-in limit frame will be described. At a certain reference color temperature, when the white balance is changed to a higher color temperature within the reference pull-in limit frame (broken line frame),
The white of the origin of the coordinates indicated by the broken line converges on the origin of the coordinates indicated by the solid line. When the color temperature is changed from this state to a higher color temperature, the white balance is maintained as it is within the pull-in restriction frame (thin solid line frame) after convergence.

However, this evaluation value data (RB)
Is within the pull-in restriction frame (thin solid line frame) after convergence, but is outside the reference pull-in restriction frame (broken line frame), and therefore white balance should not be taken. Therefore, as shown by the thick solid line frame, the pull-in restriction frame after convergence (thin solid line frame) is reduced to the low color temperature side to the range in which the current evaluation value data (RB) is not captured. . As a result, even if it converges at the previous high color temperature, changes to a higher color temperature side, and falls within the post-convergence pull-in limit frame (thin solid line frame), the reference pull-in limit frame (broken line As long as it is outside the frame, the white balance operation is not performed.

Next, a case (c) in which the R gain is small, the B gain is large, the evaluation value data (RB) is positive and is within the pull-in limit frame will be described. At a certain standard color temperature,
When the white balance is changed to a low color temperature within the reference pull-in limit frame (broken line frame), the white of the origin of the coordinates shown by the broken line converges on the origin of the coordinates shown by the solid line. If the color temperature changes further from this state,
If it is within the pull-in restriction frame (frame with thin solid line) after convergence,
The white balance will be taken as it is.

However, this evaluation value data (RB)
Is within the pull-in restriction frame (thin solid line frame) after convergence, but is outside the reference pull-in restriction frame (broken line frame), and therefore white balance should not be taken. Therefore, as shown by the thick solid line frame, the pull-in restriction frame after convergence (thin solid line frame) is reduced to the high color temperature side to the range where the current evaluation value data (RB) is not captured. . As a result, even when it converges at the low color temperature last time, it further changes to the color temperature side and becomes within the pull-in restriction frame (thin solid line frame) after convergence, the reference pull-in restriction frame (broken line As long as it is outside the frame, the white balance operation is not performed.

Next, a case (d) in which the R gain is large, the B gain is small, the evaluation value data (RB) is positive and is outside the pull-in limit frame will be described. At a certain standard color temperature,
When the white balance is changed to a high color temperature within the reference pull-in restriction frame (broken line frame), white at the origin of the coordinates indicated by the broken line converges on the origin of the coordinates indicated by the solid line. From this state, when the color temperature next changes to the low color temperature, and when it goes out of the pull-in restriction frame (thin solid line frame) after the convergence, the white balance cannot be maintained as it is.

However, this evaluation value data (RB)
Is outside the pull-in restriction frame (frame with a thin solid line) after convergence, but is within the reference pull-in restriction frame (frame with a broken line), so white balance should be taken. Therefore, as shown by the thick solid line frame, the pull-in restriction frame after convergence is expanded to the low color temperature side to the range in which the current evaluation value data (RB) is fetched. As a result, even if it converges at the previous high color temperature, changes to the low color temperature this time, and is outside the pull-in limit frame (thin solid line frame) after convergence, the reference pull-in limit frame (broken line frame)
As long as it is within the range, the white balance operation is performed.

As described above, in the color signal processing circuit in the solid-state image pickup device system, it is determined how the color temperature of the light source changes when the white balance is automatically adjusted by the feedback control. By changing the size of the pull-in limit frame according to the color temperature of the light source at the time of convergence and the color temperature of the light source after the change, it is possible to perform control so as not to deviate from the originally set reference pull-in limit frame.

That is, after the white balance is taken under a light source of a certain color temperature and then the color temperature is changed next, if the color temperature is within the standard pull-in limit frame and the color temperature is adjusted to white, the white balance is taken. , It is possible to perform the white balance operation without malfunction so that the other ones are not taken.

Further, from the idea that when all the colors of an image including various colors are added up, it becomes white, RG, B-
The G color difference signal is integrated, and the integration range is set in two ways, a high-luminance part and a normal-luminance part, and it is determined, depending on the condition of the subject, which one has higher brightness or normal brightness, which is closer to white. , By controlling the gain of the white balance based on the integrated value data that is closer to white, more accurate auto white balance can be realized.

In particular, when deciding which of the high-luminance part and the normal-luminance part of the integration for each luminance is to be adopted, R-
Since each data of G and B-G is used as a parameter, it is not necessary to carry out arithmetic processing of multiplication and division, so that the load of hardware and software can be reduced.
In this example, the RG and BG color difference signals are integrated, but it is also possible to integrate the RY and BY color difference signals and use the integrated value data.

When adjusting the white balance,
By using the respective data of RB and R + B-2G, RB is close to the locus (black body radiation curve) in which white changes with respect to the color temperature of the subject (or the light source), so that the accuracy is improved. Good control can be performed, and since white is a direction in which R + B-2G changes when the subject is under a fluorescent lamp (or when the light source is a fluorescent lamp), accurate control can be performed as in RB. . Moreover, since the gain information is obtained using the R, G, B signals before passing through the γ correction circuit 53 which is a non-linear circuit, there is no fear of color misregistration.

FIG. 9 shows RB, on the RY and BY axes.
It is a coordinate system showing R + B-2G and a black body radiation curve (simulation). As is clear from the figure, it can be seen that the black-body radiation curve shown by the thick solid line and RB almost match. Therefore, if the pull-in limit frame is set by the value of R-B and control is performed so as to move the pull-in limit frame along the axis, it is possible to easily match the white due to the color temperature change with the achromatic white.

[0043]

As described above, according to the present invention,
In the color signal processing circuit having the white balance function of the feedback control system, the integrated value data for each field of the R-G and B-G color difference signals is obtained, and the integrated value data is added / subtracted to obtain the RB signal. And R + B-2G
By converting to signals and taking white balance based on these signals, simple addition and subtraction processing is sufficient, and since division and multiplication processing is unnecessary, hardware,
It is possible to perform the control with high accuracy with respect to the color temperature change of the subject (or the light source) with less load on the software. Therefore, when it is applied to a consumer-use camera, a commercial-use camera, or an industrial-use camera having an auto white balance, the image quality can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a solid-state imaging device system to which the present invention is applied.

FIG. 2 is a circuit block diagram of an example of an optical detector.

FIG. 3 is a diagram showing an integration range in an integration circuit.

FIG. 4 is a functional block diagram of an example of a controller.

FIG. 5 is a conceptual diagram showing an example of a white balance operation.

FIG. 6 is a flowchart showing a white balance processing procedure.

FIG. 7 is a conceptual diagram of a gain operation for pulling in.

[FIG. 8] Reduction of the pull-in limit frame according to the change in color temperature
It is a figure which shows the example of expansion.

FIG. 9 is a diagram showing an RY and BY coordinate system.

FIG. 10 is a diagram showing a pull-in restriction frame.

[Explanation of symbols]

2 solid-state image sensor 4 A / D conversion circuit 5 digital signal processing circuit 6 D / A conversion circuit 7 optical detector
8 controller 51 primary color separation circuit 52R, 52G, 52B white balance amplifier 53 γ (gamma) correction circuit 71, 72, 83 subtractor 73 integration circuit 81 comparison circuit 82 adder 84 gain setting circuit

Claims (1)

[Claims] 1. A color signal processing circuit for automatically performing white balance processing by feedback control, wherein gain adjustment between mutual primary color signals of R (red), G (green) and B (blue) is performed. A white balance amplifier for performing, an integrating circuit for obtaining the integrated value of each color difference signal of RG and BG for each field, and an integrated value of each color difference signal obtained by the integrating circuit is added / subtracted by RB. , R + B-2G signal, and this R-
A color signal processing circuit, comprising: a controller that controls the gain of the white balance amplifier based on B, R + B-2G signals.