JPH0239793A - White balance control circuit - Google Patents

Abstract

PURPOSE:To moderate that influence caused by the lowering of saturation and the change of a hue to occur by the control of an inner measuring system appears as a bluish impression even in a receiver cathode ray tube having a high general color temperature by setting the origin of the white color temperature of the first color-difference signal to be used in an encoder to a position biased to an orange color dimension on a coordinate. CONSTITUTION:(R-Y) and (B-Y) signals as the first color-difference signals for using for the encoder are obtained from color information corresponding to plural types of the color light of a color video camera device. Further, control signals for controlling the color temperature are obtained using the color information, and the structure of the title circuit is made into the one to execute control so as to offset the origin of the white color temperature of a two-dimensional coordinate axis expressed with the (R-Y) and (B-Y) signals to the position biased to the orange color dimension on the coordinate compared with the position of the origin of the white color temperature of the two-dimensional coordinate axis when the control signals are obtained by directly using the (R-Y) and (B-Y) signals. Namely, the signals to be used in a control path is the signals obtained by adjusting the (R-Y) and (B-Y) signals as the color-difference signals to be used for the encoder, and a control loop operates so as to obtain a balance using the signals obtained by deforming the (R-Y) and (B-Y) signals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a white balance control circuit used in a color television camera.

(Prior Art) An automatic color temperature tracking system, so-called a fully automatic white balance control system, is one of the important features in home color video cameras.

A color television camera is provided with a white balance control system so that when a white subject is imaged, the color reproduction looks natural.

White balance control systems can be roughly divided into two types: one type with an external color temperature sensor, and one type with an internal color temperature sensor.Each type has advantages and disadvantages, but the present invention applies to the internal type. Therefore, the method will be explained below.

In the inner method, the white balance is determined using the captured video signal, a control signal is created, and the balance is adjusted. Compared to a single external color temperature sensor, this method can provide a more accurate white balance and is expected to improve stability, and there will be no difference in the image when replacing a zoom lens or the like.

Furthermore, since there is no need to provide a sensor, there are many advantages such as the ability to easily miniaturize the camera head. However, on the other hand, it also has the disadvantage that the white balance is easily changed depending on the content of the video signal itself.

Generally, in the inside method, it is desirable to extract only the signal of the portion corresponding to the white object from the video signal obtained by imaging, determine the white balance from this signal, and adjust the balance. However, it is a difficult technique to extract only the signal of a portion corresponding to a white object from a video signal that changes over time.

Also, because the color temperature cannot be determined directly, is the white subject part accompanied by a continuous color temperature change from orange to blue?
It is difficult to accurately determine and extract. For this reason, simple video cameras that use single-focal-length lenses without a zoom-up function have adopted the idea that if the entire screen is averaged, white will be dispersed. However, when a close-up image of a monochromatic light area is taken, the color changes are still severe, and to avoid this, an algorithm is required to determine the signal corresponding to the white object area.

As a method for this, a width detection fully automatic white balance control method has been proposed, which extracts only the signal of the part corresponding to the color temperature locus of the white subject part and uses that signal to control the white balance. (Tokuko Showa 60-2
(See Publication No. 2952).

This method is based on the idea that when only the brightness of an object of the same color changes, the color difference signal as the video camera's color information and the luminance signal that distinguishes brightness and darkness are almost proportional to each other, so the color difference signal level The value obtained by dividing the value by the luminance signal level can be used as a measure of color regardless of brightness, so a method is used to control white balance by extracting a signal corresponding to the change in color temperature of a white subject from this measure of color. be.

However, since the detected color range has a wide range, it is inevitable that the color change exceeds the permissible range of the human eye. In general, the color temperature range that humans perceive as white is from 3DOOk to 600 [
If the color is less than 1, the color will appear orange, and if it is more than that, the color will appear blue.

For this reason, on the side that controls the white balance, it is necessary to devise a control means and to limit the color temperature.

FIG. 5 shows a circuit that compares the (RY) and (B-Y) signals with a reference voltage and controls the white balance so that the signals become R-Y and B-Y independently.

The R and B signals obtained from the color video camera are respectively supplied to subtracters 13.14 via gain control amplifiers 11.12. The subtracters 13 and 14 are supplied with a Y signal obtained by a color video camera. Therefore, the subtracters 13 and 14 provide color difference signal information (R-Y
), (B-Y) signals are obtained. (RY), (B-Y
) signals are respectively fed to clamp circuits 16,18.

The clamp circuit 17 outputs a reference level signal. The outputs of the clamp circuits 16, 17, and 18 are respectively supplied to low pass filters (LPF) 19, 20° 21 and smoothed.

The outputs of the low-pass filters 19 and 20 are compared in a comparator 22, and the outputs of the low-pass filters 20 and 21 are compared in a comparator 23.
are compared. The outputs of the comparators 22.23 are supplied to the control terminals of the corresponding gain control amplifiers 11.12 via limiters 24.25 and amplifiers 26.27, respectively.

As a result, the control signal for the R and B signals is reduced to 3000.
By limiting the control range from k to BOOOk, the sixth
The white balance control operation is limited to the shaded area in the figure.

FIG. 6 shows the balance adjustment area on two-dimensional coordinates, with (RY) on the vertical axis and (B-Y) on the horizontal axis. The curve in the figure shows the white color temperature locus in blackbody radiation.

In the above white balance control method, as shown by the diagonal lines in Figure 6, there is a control area for light sources that do not have a deviation from the white color temperature trajectory and for light sources such as fluorescent lights that have deviations from the trajectory. . Furthermore, since the system obtains white balance by independently controlling the R and B signals, white balance control is also performed for the line system and magenta system in the same way. As a result, all colors are
As shown by the arrow in the figure, the color saturation converges toward the origin of RBY.

In images captured using this control method, the green grass became pale and the magenta color of flowers was not well reproduced, resulting in an overall image with poor color tone, even though it was a color camera.

A circuit as shown in FIG. 7 is conceivable as a circuit to solve this problem.

This circuit is a circuit that restricts the line system and magenta system from converging to white. Generally, the gain control directions of the R and B signals are in opposite directions on the white blackbody radiation locus. This blackbody radiation locus is in a direction substantially perpendicular to the axis (R-B) indicated by a dotted line in FIG.

Therefore, in order to limit the convergence to the line system and magenta system, the outputs of the low-pass filters 19 and 21 are compared with one comparator 30, and the difference outputs are sent to the limiters 24 and 24, respectively.
25 and correspondingly via amplifiers 26, 27. As a result, for line systems and magenta systems,
It does not converge to the origin, but only converges to the axis indicated by the dotted line in FIG. Therefore, convergence to the origin is not performed except for those on the color temperature locus, and the saturation of green and magenta does not decrease.

(Problem to be solved by the invention) However, although this is good for white balance control when imaging a white wave object, when evaluated from an overall perspective, when imaging a radio wave object, the arrow R-B shown
A change in hue and a decrease in saturation occur by the amount of control indicated by the hatched area toward the convergence axis R and R.

When viewing images captured using this control method on a general receiver, the color temperature of the CRT is extremely high (approximately 1000), so the impression of bluishness of the CRT increases as the saturation decreases. , the overall bluish impression increases. In addition, since general television receivers do not have a margin for reproducibility of green rather than blue, this control method (B-Y)
The result is that the young leaf color near the axis is drawn toward the R-8 convergence axis direction, resulting in a color reproducibility with a stronger bluish tinge, which gives a very strange feeling.

Therefore, the present invention is capable of alleviating the effect of the decrease in saturation and change in hue caused by the control of the 11P1 method, which appears as a bluish impression even in a common cathode ray tube receiver with a high color temperature. The purpose of this invention is to provide a white balance control circuit that can

[Structure of the Invention] (Means for Solving the Problems) The present invention obtains a control signal for color temperature control using color information corresponding to multiple types of colored lights of a color video camera device,
In a white balance control circuit that obtains white balance adjustment by controlling the gain of color information of the color video camera device using the control signal, a first color difference signal (RY) for use in an encoder is generated from the color information. ) and (B-Y) signals are obtained. Further, the (RY) and (B-Y) signals and the luminance signal (
Y) or obtain the control signal using the color information and (
The origin of the white color temperature on the two-dimensional coordinate axis represented by the (RY) and (B-Y) signals is the dimension when the above control signal is obtained directly using the (R-Y) and (B-Y) signals. The configuration is such that control is performed so as to offset the origin of the white color temperature on the coordinate axes to a position biased towards the orange dimension on the coordinates.

(Operation) With the above means, the signals used in the control path are color difference signals used in the encoder (R-Y), (B-Y)
The signal is an adjusted signal, and the control loop is (RY)
, the (B-Y) signal is used to maintain balance, so the two-dimensional dust J represented by the (R-Y) and (B-Y) signals, and 2 represented by i Idl.
The origin (W) of the white color temperature on the dimensional coordinate axis is offset from the origin (W) of the white color temperature obtained by directly using the (RY) and (BY) signals.

As a result, the origin of the white color temperature of the first color difference signal used in the encoder can be set at a position biased toward the orange dimension on the coordinates, and the bluish impression on the receiver side can be alleviated.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. The circuit of FIG. 1 differs from conventional circuits in the following points.

That is, the outputs of gain control amplifiers 11 and 12 are supplied to subtracters 13 and 14 via amplifiers 41 and 42, respectively. The outputs of the low-pass filters 19 and 20 are compared by a comparator 22, and the output images of the low-pass filters 19 and 21 are compared by a comparator 23. Further, the output of the comparator 22 and the output of the comparator 23 are added by an adder 43 and the result is supplied to the limiter 24.

The outputs of the gain control amplifiers 11.12 are also output from the subtracters 51.12.
52 performs subtraction processing with the luminance signal Y, and subtracters 51 and 52 convert the color difference signal for the encoder, that is, (R
-Y) and (B-Y) signals are created.

Other parts are the same as those in FIG. 5, and therefore are given the same reference numerals as in FIG.

According to the above circuit, apart from the first color difference signal input to the encoder, the R and B signals are gain-controlled and supplied to the control signal generator for controlling the gain control amplifiers 11 and 12. There is. Assuming that the gains of the amplifiers 41 and 42 are α and β, the second color difference signals obtained from the subtracters 13 and 14 are (R-Y) −Signal −R−−Y (B−Y) −Signal −B− -Y R''-αR, B--βB. Therefore, the white balance control circuit that obtains the control signal to the gain control amplifiers 11 and 12 is as follows: R--Y, , R--B-. As a result, when looking at the signal input to the encoder, αR-Y, αR
−βB. Rewriting both equations, it becomes (RY)-1(1-α)/α)IY (B-Y)-1(1-β)/β)IY.

If α×1 and β〉1, then it is proportional to the luminance signal Y. (RY)>0, (BY)<0.

From the above equation, the two-dimensional coordinates represented by the (R-Y) and (B-Y) signals are the two-dimensional coordinates represented by the (R-Y) and (B-Y) signals by the conventional white balance control circuit.
Comparing the dimensional coordinates, it becomes as shown in Fig. 2. In other words, the color difference signal used on the encoder side is offset toward orange. W and W′ are the origins of the white color temperature of the two-dimensional color temperature coordinate axis represented by the color difference signal.

In this embodiment, the comparator 22 has a reference signal and (RY)=
It provides the average level output of the signal. This strain is α
Obtain a control operation that becomes RY.

In addition, the average level output of the (RY)'' signal and the average level output of the (B-Y) signal are input to the comparator 23. Therefore, the control loop according to this system is
Obtain the control operation as follows. Therefore, as a whole, Y−αR−
It will operate so that βB is achieved.

According to the above-described embodiment, the first color difference signal input to the encoder has an offset in the orange color system, so that the first color difference signal input to the encoder has an offset in the orange color system, so that the first color difference signal input to the encoder has an offset in the orange color system. It is possible to reduce the bluish impression of Furthermore, since the axis of convergence in the bluish direction of the line system can be corrected to orange, it is possible to suppress the unnatural reproducibility of blue-green.

This invention is not limited to the embodiments described above, and various embodiments are possible.

FIG. 3 shows another embodiment of the present invention, which differs from the previous embodiment in the means for generating the (RY) (BY)-signal, which is the second color difference signal. In this embodiment, subtractor 13.
14, which are the first color difference signals (RY) and (B-
Y) The signal is input directly. The other parts are
This is the same as the previous embodiment. According to this example, (RY)''-RY- (B-Y)--B-Y- is obtained.

FIG. 4 shows yet another embodiment. In this embodiment, the amplifiers 41, 42 and subtracters 13 and 14 in FIG. 1 are omitted, and the outputs of subtracters 51 and 52 are input to clamp circuits 16 and 18, respectively. As it is, it is not possible to have an offset, so for example, the voltage E is applied to the (RY) signal input to the comparator 22.
supply, shifting the balance. The other parts are
This is the same as the embodiment shown in FIG.

[Effects of the Invention] As explained above, according to the present invention, the influence of the decrease in saturation and the change in hue caused by the control of the inner method is reduced.
Even in a typical cathode ray tube receiver having a high color temperature, the appearance of a bluish impression can be alleviated, contributing to good color reproduction.

[Brief explanation of the drawing]

FIG. 1 is a configuration explanatory diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing color temperature coordinates shown to explain the operation of the circuit of this invention, and FIGS. 3 and 4 are respectively diagrams of the invention. FIG. 5 is a configuration explanatory diagram showing a conventional white balance control circuit, and FIG. 6 shows color temperature coordinates shown to explain the operation of the circuit in FIG. 5. figure,
FIG. 7 is a diagram for explaining the configuration of a conventional white balance control circuit, and FIG. 8 is a diagram showing color temperature coordinates for explaining the operation of the circuit in FIG. 11.12...gain control amplifier, 13.14°51.
52...Subtractor, 16.17.18...Clamp circuit, 19,20.21...Low pass filter, 22.23
...Comparator, 43...Adder, 24.25...Limiter, 26, 27, 41.42...Amplifier.

Claims (3)

[Claims] (1) Obtain a control signal for color temperature control using color information corresponding to multiple types of colored lights of a color video camera device, and use the control signal to control the gain of color information of the color video camera device to achieve white balance. In the white balance control circuit that obtains the adjustment, from the color information, first color difference signals (R-Y) and (B-
Y) a first means for obtaining a signal; and further using the color information, a second color difference signal (R
-Y)' and (B-Y)' signals, the (RY)' and (B-Y)' signals are used to obtain the control signal; The above (R-Y)' and (B-Y)'
1. A white balance control circuit comprising: third means for controlling Y, R, and B information, which are constituent elements of a signal, to be equal. (2) Obtain a control signal for color temperature control using color information corresponding to multiple types of colored lights of a color video camera device, and use the control signal to control the gain of color information of the color video camera device to achieve white balance. In the white balance control circuit that obtains the adjustment, from the color information, first color difference signals (R-Y) and (B-
(R-Y)' and (R-Y)' signals, which are second color difference signals, by using the first means for obtaining the (R-Y) and (B-Y) signals and the luminance signal (Y). a second means for obtaining the (R-Y)'signal; and a second means for obtaining the control signal using the (R-Y)' and (B-Y)'signals;(R-Y)' and (B-Y) so that the origin of the white color temperature obtained by white balance control obtained when the control signal is obtained directly by using the signal is offset to a position biased toward the orange color system. ′
1. A white balance control circuit comprising: third means for controlling Y, R, and B information, which are constituent elements of a signal, to be equal. (3) Obtain a control signal for color temperature control using color information corresponding to multiple types of colored lights of a color video camera device, and use the control signal to control the gain of color information of the color video camera device to achieve white balance. In the white balance control circuit that obtains the adjustment, from the color information, first color difference signals (R-Y) and (B-
a first means for obtaining a (RY) signal, and a level-controlled signal obtained by smoothing the (RY) or (B-Y) signal;
)' signal, one of the (R-Y)' or (B-Y)' signals, and the (B-Y) or (R- Y) signal and a reference signal corresponding to the luminance signal (Y) to obtain the control signal;
The origin of the white color temperature on the two-dimensional coordinate axis represented by the (RY) and (B-Y) signals is the two-dimensional value obtained when the control signal is obtained directly using the (R-Y) and (B-Y) signals. A white balance control circuit comprising: third means for controlling each color information so as to be offset to a position biased toward the orange dimension on the coordinates from the origin of the white color temperature on the coordinate axes.