JPH03274884A - White balance control circuit - Google Patents

Abstract

PURPOSE:To execute the white balance control with high accuracy by detecting whether a picture element is near white or not at every picture element in an image pickup screen, integrating only the picture element being near white, and controlling the gain of each chrominance signal so that this integral value becomes white. CONSTITUTION:When it is detected that an input picture element is near white by a white detecting circuit 7, gate circuits 6A, 6B and 6C are opened, and a digital luminance signal Y, and a digital color difference signal (R-Y) and (B-Y) from a camera signal processing circuit 5 are supplied to integration circuits 8A, 8B and 8C through gate circuits 6A, 6B and 6C, respectively. By the integration circuits 8A, 8B and 8C, the digital luminance signal Y, and the digital color difference signal (R-Y) and (B-Y) of the picture element being near white are integrated, respectively. Outputs of these integration circuits 8A, 8B and 8C are supplied to a controller 9 and the gain setting quantity of chrominance signals R, G and B is derived, and the white balance adjustment is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to automatic white balance control of a video camera.

[Summary of the invention]

In automatic white balance control of a video camera, this invention detects pixels that are closer to a black body radiation curve than a predetermined threshold level from among each pixel in an image capturing screen, and uses pixels that are close to this black body radiation curve. By performing white balance control, highly accurate auto white balance control can be performed.

In this invention, in the first half of control, the threshold level for detecting whether a pixel is near the black body radiation curve is set in a wide range, and as the control progresses, this threshold level is set in a narrow range. This makes it possible to perform highly accurate white balance control even under different light sources.

[Conventional technology]

In a video camera, it is necessary to perform white balance adjustment according to the color temperature of the light source. Traditionally, manual white balance adjustment was performed using, for example, a white cap.
This is done by setting the gain of each color signal so that the ratio of each color signal becomes a predetermined ratio. Manual white balance adjustment requires readjusting the white balance every time the light source changes, which is not easy to use. For this reason, recent video cameras are equipped with an automatic white balance control circuit. In the auto white balance control circuit, the gain of each color signal is automatically set according to the color temperature of the light source, so there is no need to readjust the white balance even if the light source is changed, resulting in good operability.

[Means to solve the problem]

Conventional auto white balance control circuits assume that if the colors on the screen are uniformly distributed, then adding all the colors on the screen will result in white. I am trying to set the signal gain. However, in an actual image capture screen, each color signal is not uniformly distributed, and the value obtained by adding the color signals does not necessarily result in white. For this reason, the conventional auto white balance control circuit has a problem in that highly accurate white balance adjustment cannot be performed depending on the image capture screen.

Therefore, an object of the present invention is to provide an auto white balance control circuit that can perform highly accurate white balance adjustment.

[Means for Solving the Problems] The present invention detects pixels that are closer to a black body radiation curve than a predetermined threshold level from among each pixel in an imaging screen, and uses pixels that are close to the black body radiation curve to This is a white balance control circuit that performs white balance control.

In this invention, the threshold level is set in a wide range in the first half of the control, and as the control progresses, the threshold level is set in a narrow range.

[Effect]

It is detected whether each pixel in the imaged screen is close to white. Then, only pixels close to white are integrated, and the gain of each color signal is controlled so that this integrated value becomes white.
White balance control is performed. Since white balance control is performed using only pixels that are close to white, highly accurate white balance control can be performed regardless of the imaging screen.

In the first half of the control, the threshold level for detecting whether a pixel is close to white is set in a wide range, and as the control progresses, this threshold level is set in a narrow range. Therefore, the accuracy is high and white balance control can be performed based on any light source.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. 1st
In the figure, the output of a CCD image sensor 1 is supplied to a sample and hold circuit 2. In sample hold circuit 2, C
The output of the CD image sensor 1 is sampled and held. The output of the sample hold circuit 2 passes through the AGC circuit 3 to the A/
The signal is supplied to the D converter 4.

The A/D converter 4 digitizes the CCD image sensor element image signal for each pixel. The output of the A/D converter 4 is supplied to a camera signal processing circuit 5. The camera signal processing circuit 5 generates a digital luminance signal Y and digital color difference signals (RY) and (B-Y).

This digital luminance signal Y, digital color difference signal (R-
Y) and (B-Y) are supplied to gate circuits 6A, 6B and 6C, respectively, and also to white detection circuit 7. The white detection circuit 7 detects whether each input pixel is in the vicinity of white from the digital luminance signal Y and the digital color difference signals (RY) and (BY).

That is, as shown in FIG. 2, an area A surrounded by a broken line is set on the color difference vector. In the first half of the control, this area A is set to a wide range, and as the control progresses, the area A is set to a narrow range. Further, B is a blackbody radiation curve. If it is on this black body radiation curve B, no color will appear.

W is a white dot. It is determined whether the input pixel is within this area A. If the input pixel is within this area A, it is determined that the color is close to white. Based on this, the white detection circuit 7 outputs a gate control signal.

This gate control signal is supplied to gate circuits 6A, 6B, and 6C. When the white color detection circuit 7 detects that the input pixel is close to white, the gate circuits 6A, 6B, and 6C are opened. Then, digital luminance signal Y, digital color difference signal (R-Y) and (B-
Y) is supplied to integrating circuits 8A, 8B and 8C via gate circuits 6A, 6B and 6C, respectively. Integrating circuit 8
A, 8B and 8C, digital luminance signal Y of pixels close to white, digital color difference signals (R-Y) and (B-Y)
are respectively integrated.

The outputs of the integrating circuits 8A, 8B, and 8C are supplied to the controller 9. The controller 9 outputs the integral value of the digital luminance signal Y, the digital color difference signals (RY) and (B
-Y), the gain setting amounts of the color signals R, G, and B are determined. Based on this gain setting amount, the gains of the red signal R and the blue signal B are controlled with the green signal G as a reference so that the integral value of a pixel close to white becomes white.

As a result, white balance adjustment is performed.

As described above, area A is narrowed as the control progresses. Therefore, in the latter half of the control, white balance control is performed so that the integral value of a pixel that is very close to white becomes white.

〔Effect of the invention〕

According to this invention, it is detected whether each pixel in the image capture screen is close to white, and only the pixels close to white are integrated.
The gain of each color signal is controlled and white balance control is performed so that this integral value becomes white. In this way, since only pixels close to white are used, highly accurate white balance control can be performed regardless of the imaging screen.

Further, in the first half of the control, the threshold level for detecting whether a pixel is close to white is set in a wide range, and as the control progresses, this threshold level is set in a narrow range. Therefore, highly accurate white balance control can be performed regardless of the light source.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a vector diagram used to explain the embodiment of the invention. Explanation of main symbols in the drawings 7: white detection circuit, 6A to 6C: gate circuit. 8A to 8C: Integrating circuit, 9: Controller.

Claims (2)

[Claims] (1) White balance control is performed by detecting pixels that are closer to the black body radiation curve than a predetermined threshold level from among each pixel in the image capture screen, and using the pixels that are close to the black body radiation curve. Balance control circuit. (2) The white balance control circuit according to claim 1, wherein the threshold level is set in a wide range in the first half of the control, and the threshold level is set in a narrow range as the control progresses.