JPH04326284A - White balance adjusting device - Google Patents

Abstract

PURPOSE:To reduce the deviation of white balance by shortening an integration circuit or the time constant of gain control when the change direction of gain is close to the optimum gain in the case of fine weather outdoors and prolonging the time constant when the direction is away from the optimum gain. CONSTITUTION:Integration circuits 27 and 28 integrate color difference signals by variable time constants and supply the results to gain control circuits 13 and 14 as color evaluation value. The gain control circuit 13 supplies a B gain control signal to a B amplifier circuit 5, and the gain control circuit 14 supplies an R gain control signal to an R amplifier circuit 4. The both gain control signals are inputted to a time constant calculation circuit 23 as current gain valued. The color difference signal of a picture obtained by executing the gain control as mentioned above is integrated again, and the color evaluation value obtained by the integration is inputted to the time constant calculation circuit 23. The time constant calculation circuit 23 changes the time constant of the gain according to the change direction of the gain to the prescribed gain. In this case, the optimum gain in the case of fine weather outdoors most frequently using a camera is used as the prescribed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic white balance adjustment device for a color video camera that controls white balance based on a captured video signal obtained from an image sensor.

0002

2. Description of the Related Art In a color video camera, it is necessary to control the white balance in order to correct differences in the wavelength distribution of light depending on the light source. This control is for red (hereinafter referred to as R),
The ratio of the three primary color signals of blue (hereinafter referred to as B) and green (hereinafter referred to as G) is 1:1.
:1 by adjusting the gain of each color signal. Generally, a method is used in which the gain is adjusted so that the integral value of the screen color difference signals R-Y and B-Y becomes zero, as shown in, for example, Japanese Patent Application Laid-Open No. 62-35792 (H04N9/73). It is being

FIG. 2 is a block diagram of a white balance adjustment circuit using this method. The light that has passed through the lens 1 is photoelectrically converted by an image sensor (CCD) 2 and then sent to a color separation circuit 3.
Then, the three primary color signals of R, G, and B are taken out, and the G color signal is directly output, and the R and B color signals are output through the R amplification circuit 4 and the B amplification circuit 5, and then to the camera process and matrix circuit 6.
A luminance signal Y and red and blue color difference signals R-Y and B-Y are generated and sent to the video circuit 7.

At the same time, the two color difference signals are integrated for a sufficiently long time by integrating circuits 17 and 18, respectively, and gain control circuits 13 and 14 control the R and B amplifier circuits 4 and 14 so that the result becomes zero. Adjust the gain of 5.

[0005]

[Problem to be Solved by the Invention] The above method is based on the empirical rule that when photographing a general subject, the value obtained by averaging the color difference signals of the entire screen is equivalent to that when photographing a completely white surface. Therefore, the photographic screen must contain each color on average.

However, with this method, when the color of the subject itself is uneven, such as when taking a close-up of a person wearing a red or blue sweater, it is difficult to average the color distribution across the screen. If you perform the white balance adjustment as described above for such a subject, the gain will change in the direction of canceling out the biased color, the white balance will shift to the complementary color side, and the correct color will be displayed. It has the disadvantage that it cannot be reproduced.

[0007] In order to alleviate this drawback, attempts have been made to lengthen the control time constant so that the white balance does not shift when photographing a colored subject for a short period of time, but at the same time, with this method, Recovery is also delayed, and overall performance does not improve.

[0008]

[Means for Solving the Problems] The present invention performs white balance adjustment based on a color information signal in a captured video signal, and changes the time constant of an integrating circuit or a gain control circuit depending on the direction of gain change. More specifically, the time constant is shortened in the direction approaching a predetermined gain, and the time constant is lengthened in the direction away from the predetermined gain.

[0009]

[Operation] Since the present invention is constructed as described above, if a gain that is likely to be used during normal shooting is used as the predetermined gain, the time constant is lengthened in the direction that the white balance shifts when shooting a colored subject. The time constant can be shortened in the direction of recovery,
There is almost no negative effect due to the long time constant.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of an automatic white balance adjustment circuit according to this embodiment. Note that the same parts as those in FIG. 2 are given the same reference numerals, and the description thereof will be omitted.

Integrating circuits 27 and 28 receive color difference signals B-Y and R.
-Y is integrated with a variable time constant T, and the respective integration results are supplied to the subsequent gain control circuits 13 and 14 as color evaluation values b and r. The gain control circuit 13 supplies the B gain control signal to the B amplifier circuit 5 for controlling the gain of the B amplifier circuit 5 so that the color evaluation value b becomes zero. Similarly, the gain control circuit 14 supplies the R amplifier circuit 4 with an R gain control signal for controlling the gain of the R amplifier circuit 4 so that the color evaluation value r becomes zero. Furthermore, both gain control signals are input to the time constant calculation circuit 23 as current gain values. Further, the color evaluation values b and r obtained by re-integrating the screen color difference signal obtained by applying these gain controls are similarly input to the time constant calculation circuit 23.

The time constant calculating circuit 23 determines the time constants of the integrating circuits 17 and 18 based on a value indicating a predetermined gain that is preset by the above-mentioned four inputs and external volumes 24 and 25. Here, as the predetermined gain, the optimal gain (reference gain K) when the camera is used outdoors under clear weather is used most often.

Next, the time constant calculation operation in the time constant calculation circuit 23 will be explained using FIGS. 4 and 5. In addition, in FIGS. 4 and 5, in order to make the explanation easier to understand, the difference between the color evaluation value and the gain of each of the R and B amplifier circuits 4 and 5 from the reference gain K (correction amount of R gain and B gain) is shown. They are shown on the same coordinate axes, with the horizontal axis representing the B gain correction amount for the color evaluation values b and K, and the vertical axis representing the R gain correction amount for the color evaluation values r and K. At the origin in the figure, that is, when the amount of correction is zero, each amplifier circuit is set to the optimum gain for outdoor sunny weather.

First, the current gain correction value is plotted as a point P on a graph, and the color evaluation values r and b are further plotted as a point Q on the same graph. Here, in order to perform optimal white balance adjustment on the screen at point Q, it is necessary to change the gain so that point Q moves toward the origin, and at this time, the direction of shift of point P should be in the direction closer to the origin. In this case, the time constant T of the integrating circuit is set short, and conversely, in the case of moving away from the origin, the time constant T is set long.

For example, when point P and point Q are at positions as shown in FIG. Therefore, the gain correction amount is also at a point P that is slightly positive with respect to the origin.
It is in. If white balance adjustment is performed from this state, it is necessary to bring point Q to the origin. The direction of transition is toward the origin. Therefore, the time constant calculation circuit 23 shortens the time constants T of the integrating circuits 27 and 28, assuming that the white balance is in the recovery state from the state where the white balance is shifted due to the shooting of a colored subject with biased colors. Works to quickly influence coordination.

Furthermore, when point P and point Q are located at the positions shown in FIG. Even if there is a point P at a slightly negative position, it is necessary to bring the point Q to the origin by adjusting the white balance. must be decreased, and the direction of transition of point P is further away from the origin. Therefore, the time constant calculation circuit 23 assumes that the white balance is shifting due to the shooting of a colored subject with a biased color, and increases the time constant T so that the current screen evaluation is less likely to affect the white balance adjustment. Function. In the examples of FIGS. 4 and 5, in order to make the explanation easier to understand, points P and Q are plotted on the vertical axis focusing on the color difference signal RY.
We considered only the case where the color difference signal B-Y is located, but in reality, we also consider the color difference signal B-Y, and when it is necessary to control so that either the R or B gain moves away from the origin, it is necessary to lengthen the time constant T. The time constant calculation circuit 23 functions.

As another method, when it is necessary to control one of them so that it approaches the origin, the time constant may be shortened.

FIG. 3 is a circuit block diagram of another embodiment, in which the output of the time constant calculation circuit 23 is transmitted to the gain control circuits 13 and 14.
and changes the gain control time constants of these gain control circuits 13 and 14. That is, when the time constant T is short, the gain is changed so that the color evaluation values r and b instantly become zero, and when the time constant T is long, the gain is changed so that the color evaluation values r and b become zero. By reducing the rate and taking time to change the gain, it essentially functions to intentionally suppress white balance adjustment. In this case, select whether to shorten or lengthen the time constant by
A judgment is made for each color of blue, and the time constant of each gain control circuit is changed independently.

It goes without saying that the operations of each of the circuits described above can also be processed by software using a microcomputer.

[0020]

Since the present invention is constructed as described above, deviations in white balance due to colored subjects can be reduced, and even if deviations occur, they can be quickly restored.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.

FIG. 2 is a circuit block diagram of a conventional example.

FIG. 3 is a circuit block diagram of another embodiment of the present invention.

FIG. 4 is an explanatory diagram for determining a time constant.

FIG. 5 is an explanatory diagram for determining a time constant.

[Explanation of symbols]

4 R amplifier circuit 5　B amplifier circuit 27, 28 Integral circuit 13, 14 Gain control circuit 23 Time constant calculation circuit

Claims (2)

[Claims] [Claim 1] Based on the color information signal in the captured video signal,
A white balance adjustment device for changing the gain of each color signal, characterized in that the time constant of the gain is changed depending on the direction of gain change with respect to a predetermined gain. 2. In a white balance adjustment device that changes the gain of each color signal based on a value obtained by integrating a color information signal in a captured video signal by an integrator, the integrator A white balance adjustment device characterized by changing a time constant of.