JPH0683465B2 - White balance adjustment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white balance adjusting device for a color video camera, and in particular, can provide control characteristics suitable for a so-called full-auto white balance system in which the adjusting operation is continuously performed during shooting. The present invention relates to a white balance adjusting device.

(Background of the Invention) As a conventional method for automatically adjusting the white balance according to a change in a state during shooting (for example, a change in color temperature due to a change in lighting), for example, National Technical Report, Volume 31, Number. January-February, 1985 (Nationa
l Technical Report Vol.31 No.1 Feb.1985) "Simple automatic tracking white balance system" is mentioned. This method detects the color temperature of the illumination light from the signal obtained from the image pickup tube (specifically, R
-Y, B-Y color difference signals are sent to the automatic white balance control circuit (A
utomatic White-Balance Control, abbreviated as AWC hereinafter)), and A to the gain control circuit placed in the R, B color signal path.
This is a method for performing white balance correction by feeding back the WC output.

In the simplified automatic white balance control method using this analog circuit, a negative feedback system having a relatively low gain is used to adjust the color difference signal (for example, RY, BY) level of the image in the direction of being suppressed to zero. It is a thing. This is because both of the color difference signal levels are 0 in an achromatic color screen whose white balance is properly adjusted, and even in a general image in which various chromatic colors are mixed, the color difference signal levels are averaged over the entire screen. It is based on what can be regarded as equivalent to the achromatic screen. (However, this does not apply to cases where a chromatic color alone exists on the screen and occupies a large area.) Control by the simplified automatic white balance control method when the subject is achromatic The characteristics are shown in FIG. Fifth
In FIG. (A) and FIG. 5 (b), the vertical axis represents
The carrier leak and the color difference signal level (for example, RY or BY) in the NTSC signal are shown, and the horizontal axis shows the color temperature. The carrier leak is an achromatic color, and is almost zero when the white balance is ideal.

As is clear from the figure, even when the white balance correction is performed, an error occurs to some extent because the lube gain is reduced as described above except at the adjustment reference point (color temperature with the best white balance). It is of course easy to add more powerful correction by taking the control gain of the feedback system high, but if the subject is the above theory, that is, if the average of the entire screen is taken, the color difference signal can be treated in the same way as an achromatic screen. In other words, when a single chromatic color occupies a large area on the screen, it causes deterioration of color reproduction.

As described above, the above-described conventional method allows full-automization at all times by allowing the correction error after the automatic white balance control, can be realized with a simple circuit configuration, and is excellent in terms of operability and price. There is. However, even when the white balance correction is performed, there is a considerable error other than the adjustment reference point, that is, the allowable correction error is large.

(Object of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to use various imaging conditions (for example, color) in an inexpensive circuit without using a complicated control system, that is, without increasing the circuit scale. It is to provide a white balance adjusting device capable of improving white balance accuracy by following changes in temperature, etc.). Further, this is to provide a low-priced video camera with a high-quality image (for example, regarding color reproducibility).

(Summary of the Invention) A feature of the present invention is that the color temperature of a subject is detected by using the level of a color difference signal and the gain of a chromaticity signal is controlled according to the level so that the white balance is constantly adjusted. In the white balance adjustment apparatus described above, the white balance adjustment is improved by appropriately moving the white balance adjustment center color temperature (the color temperature at which the white balance is most adjusted).

(Embodiment of the Invention) First, the principle of the present invention will be described.

In FIG. 5, it is considered that the range in which the white balance in the vicinity of the adjustment reference point is relatively good or the adjustment reference point itself is laterally stretched. This is a step forward from the theory that when the absolute value of the color difference signal level (that is, the deviation from the reference value) is small, it is due to the change in color temperature, and when it is large, it is due to the saturation of the subject. , It is equivalent to assuming that even if the very thin coloring is converged to white, it does not seem that visually inconvenient. This assumption is valid because a certain amount of color shift occurs in the human eye and depending on the type of illumination.

According to the present invention, the control characteristic such as the above-mentioned white balance adjustment reference point or the vicinity thereof in which the range where the white balance is relatively good is laterally extended is realized by continuously or stepwise shifting the adjustment reference value. It was made based on the idea that it could be done.

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 1 is a color separation circuit, 2 and 3 are gain control circuits,
Reference numeral 4 is a matrix circuit, 5 is an encoder, 6 and 7 are sub-auto white balance circuits according to the present invention, and 8 and 9 are conventional analog auto white balance circuits.

The configuration of the sub auto white balance circuits 6 and 7 is equivalent to that of the auto white balance circuits 8 and 9. That is, the deviation of the white balance from the ideal state is detected by the difference between the color difference signal level and the reference voltage determined by each constant in the white balance control system, and an appropriate amount of control voltage is supplied to the auto white balance circuit. .

The present embodiment is characterized in that the reference voltages of the auto white balance circuits 8 and 9 are controlled by the sub auto white balance circuits 6 and 7.

Next, the operation of this embodiment having the above configuration will be described.

A signal output from an image pickup tube (not shown) by photographing a subject is input to the color separation circuit 1 after being amplified by a preamplifier (not shown). The color separation circuit 1 separates the color signals into chromaticity signals of R and B signals. The separated R and B signals are gain controlled by gain control circuits 2 and 3, respectively. Thereafter, the R and B signals are input to the matrix circuit 4, and the matrix circuit 4 outputs the color difference signals (R−Y _L ) and (B−Y _L ). The color difference signals ( _RYL ) and ( _BYL ) are sent to the encoder 5, the sub-auto white balance circuits 6 and 7, and the auto white balance circuits 8 and 9.

The sub-auto white balance circuits 6 and 7 and the auto white balance circuits 8 and 9 have a function of performing auto white balance correction. By controlling the gains of the gain control circuits 2 and 3 with the output signals of the automatic white balance circuits 8 and 9, the white balance is automatically corrected.

Next, the operations of the sub-auto white balance circuits 6 and 7 and the auto white balance correction circuits 8 and 9, which are characteristic parts of this embodiment, will be described in detail.

The sub-auto white balance circuits 6 and 7 and the auto white balance correction circuits 8 and 9 operate by two inputs of a color difference signal and a reference voltage. A representative example showing the input / output relationship is shown in FIG.

As is apparent from FIG. 6, the outputs of the sub-auto white balance circuits 6 and 7 and the auto white balance correction circuits 8 and 9 are predetermined on both sides of the reference voltage according to the magnitude of the input color difference signal. It has the characteristic of changing linearly within the range.

In addition, the reference voltage is set in the positive (+) direction or the negative (-) direction.
When adjusted in the direction, the characteristic of FIG. 6 can be shifted to the left or right.

Therefore, the color difference signal (R-
If the magnitudes of Y _L ) and (B−Y _L ) change, the output values of the sub-auto white balance circuits 6 and 7, that is, the reference voltages of the auto white balance circuits 8 and 9 change. Therefore, the input / output characteristics of the automatic white balance circuits 8 and 9 are shifted to the left and right according to the magnitude of the input color difference signal.

As a result, the waveforms shown in FIGS. 5 (a) and 5 (b) are also shifted to the left and right, and as a result, as shown by the dotted curves in FIGS. 7 (a) and 7 (b), It is possible to realize the control characteristic expanded in the axial direction, that is, the characteristic in which the white balance characteristic is improved.

In the first embodiment, the color difference signal (RY,
The sub-auto white balance circuits 6 and 7 are used for each of B-Y), but I) only one of the color difference signals is used, and II) the sub auto white balance is performed by comparing or difference of each color difference signal. The circuit can be omitted as one by driving the circuit or the like. However, since the reference voltages of the automatic white balance circuits 8 and 9 do not always match, it is natural that this point needs to be dealt with.

Next, a circuit diagram of the second embodiment of the present invention is shown in FIG.
In this embodiment, automatic white balance circuits 8 and 9 are used.
It is characterized in that the white balance correction signal output from is corrected by the signal output from the sub auto white balance circuit 6. This correction is made by the output from the sub auto white balance circuit 6
Since the output voltage of 10 is shifted, the shift direction of the waveform in FIG. 6 is up and down, but if the control amount is limited, the operation near the output intermediate value is regarded as the same as that of the first embodiment. be able to.

As a result, even if the gain control amount of the entire auto white balance system is reduced, the control ability in the vicinity of the adjustment reference color temperature point is maintained, so that the control can be performed more strongly against the color temperature fluctuation in the vicinity of the reference point. Can suppress the color collapse of the chromatic screen.

The effects of the first and second embodiments described above will be explained with reference to FIG. FIG. 8 shows white balance correction when there is no white balance control (dotted line), when it is controlled by the conventional white balance control method (dashed line), and when it is controlled by the white balance control method of this embodiment (solid line). The characteristics are shown comparatively, where the horizontal axis represents color temperature and the vertical axis represents carrier leak.

From FIG. 8, it is apparent that the method of the present embodiment improves the white balance with respect to the color temperature fluctuation near the reference point.

Next, a third embodiment of the present invention is shown in FIG. Compared to the first embodiment, this embodiment is characterized in that the reference voltage of the automatic white balance circuits 8 and 9 is switched by the manual switch 11 to simplify the circuit configuration. A fourth embodiment of the present invention is shown in FIG. This embodiment is different from the second embodiment in that the output signals of the automatic white balance circuits 8 and 9 are switched and corrected by the manual switch 11. It goes without saying that a variable resistor may be used instead of the manual switch of the third and fourth embodiments.

In the third and fourth embodiments, the control voltage applied to the gain control circuits 2 and 3 is constant irrespective of the photographing conditions, so the switching is left to the user's judgment, but instead. A bold shift is possible. For example, if the manual switch is changed over in three steps, it has three independently fixed white balance adjustment reference color temperatures.
These three points are preferably set for indoor use, outdoor fine weather, and outdoor cloudy weather, respectively.

According to this embodiment, since there is a sufficient margin for color temperature fluctuations, the gain control amount of the entire auto white balance system is reduced to perform white balance correction on the chromatic color screen, as in the first and second embodiments. Color crush can be suppressed.

FIG. 9 shows control characteristic diagrams according to the third and fourth embodiments,
The horizontal axis represents color temperature and the vertical axis represents carrier leak.

In FIG. 9, the characteristics written with thick solid lines show the characteristics when an appropriate switching operation is performed. From this characteristic,
It can be seen that the region with good accuracy is greatly expanded when the appropriate switching operation is performed.

The third and fourth embodiments differ from the first and second embodiments in the following effects.

I) The adaptive color temperature range can be widened.

II) White balance adjustment Small changes near the reference color temperature tend to be ignored.

As another modified example of the present invention, a microcomputer type, a digital counter type, or the like may be used in place of the switching method using the manual switch, so that a white balance can be set accurately.

The above embodiments are premised on that the gain control circuits 2 and 3 have sufficient control capability with respect to the respective embodiments. When actually configuring the system based on the embodiment, it is desirable to use a method of connecting the gain control circuits 2 and 3 in a plurality of stages according to the required control capability.

(Effect of the Invention) According to the present invention, since the white balance is adjusted by the white balance method composed of a plurality of control systems, a novel control characteristic which has never existed can be realized and a simple circuit configuration can be realized. There is an effect that the white balance adjustment error can be reduced and the color reproducibility can be improved.

In addition, the price can be reduced and the operation can be simplified.

[Brief description of drawings]

FIGS. 1, 2, 3, and 4 are block diagrams showing the first, second, third, and fourth embodiments of the present invention, respectively.
FIG. 5 is a diagram showing a white balance control characteristic according to a conventional method, FIG. 6 is a diagram showing an input / output relationship of an automatic white balance circuit, FIG. 7 is a diagram showing a white balance control characteristic according to the present invention, and FIG. FIG. 9 and FIG. 9 are diagrams showing white balance control characteristics for explaining the effects of the first and second embodiments and the third and fourth embodiments, respectively. 1 ... Color separation circuit, 2.3 ... Gain control circuit, 4 ... Matrix circuit, 5 ... Encoder, 6.7 ... Sub auto white balance circuit, 8.9 ... (Main) auto white balance circuit , 10 …… Variable power supply, 11 …… Manual switch

Claims (6)

[Claims] 1. A means for controlling a gain of a chromaticity signal corresponding to a color temperature of a copy, a means for outputting a color difference signal from a color signal whose gain is controlled by the means, and a white balance according to a level of the color difference signal. Having a means for outputting a correction signal,
In a white balance adjusting device configured to control the gain of the chromaticity signal by the white balance correction signal, the means for outputting the white balance correction signal outputs a white balance correction signal according to the level of the color difference signal. A white balance adjusting device, comprising: an automatic white balance circuit for performing a white balance adjustment; and a correction unit that moves a reference point that is a central color temperature of the white balance adjustment of the automatic white balance circuit. 2. The white balance adjusting apparatus according to claim 1, wherein the means for moving the reference point is a sub-auto white balance circuit having the same configuration as the auto white balance circuit. 3. The device according to claim 1, wherein the means for moving the reference point includes a means for generating a plurality of reference point voltages and a selection means for selecting any one of the reference voltages. The white balance adjusting device according to the first section. 4. A means for controlling a gain of a chromaticity signal corresponding to a color temperature of an object, a means for outputting a color difference signal from a color signal whose gain is controlled by the means, and a white balance correction according to a level of the color difference signal. Having means for outputting a signal,
In a white balance adjusting device configured to control the gain of the chromaticity signal by the white balance correction signal, the means for outputting the white balance correction signal outputs a white balance correction signal according to the level of the color difference signal. A white balance adjusting device, comprising: an automatic white balance circuit that performs the above operation; and a correction unit that changes the bias voltage of the output of the automatic white balance circuit. 5. The sub-auto white balance circuit having the same configuration as the auto white balance circuit, wherein the correction means comprises:
5. The white balance adjusting device according to claim 4, wherein the white balance adjusting device comprises a variable power source controlled by an output signal of the circuit. 6. The correction means according to claim 4, wherein the correction means comprises a means for generating a plurality of bias voltages and a means for selecting any one of the bias voltages. The described white balance adjustment device.