JPH06245224A - White balance correction device - Google Patents

Abstract

PURPOSE:To change the white balance of the white signal portion of a color video signal in the white balance for a color television receiver or the like. CONSTITUTION:The device is provided with a white signal detection circuit 4 detecting a white level signal from a chroma signal from a luminance signal (Y)/chrominance signal (C) separator circuit 1 and a correction circuit 5 correcting a level of either red, green or blue signal only for a period for the white level signal detected by the white signal detection circuit 4, and the white balance of a white level signal portion of a color video signal is changed from a standard white balance by emphasizing a level of any of primary color signal outputs (R, G, B) of a matrix circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white balance correction device for changing the white balance of only a white signal portion of a color video signal in the white balance of a color television receiver or a color display monitor.

[0002]

2. Description of the Related Art In color television receivers and the like, a method of setting a color temperature of an image higher than a standard value has been often adopted in order to increase apparent sharpness and brightness of the image. Various methods are used to increase the color temperature, and an example thereof is the method shown in FIG. As shown in FIG. 3A, a correction circuit including a diode D31 and a resistor R32 is provided in parallel with the resistor R31 at the emitter of the amplifying transistor TR31. With this correction circuit, the base input V31 has a higher amplification degree as the amplitude becomes larger due to the non-linearity of D31, and the collector output V32, as shown in FIG. , The amplitude increases by e1. For example, when only the blue signal is amplified by the circuit of FIG. 9B, only the blue signal is emphasized relative to the other red and green signals, so that the white balance is closer to the blue side than the standard. However, if the above correction is excessively performed, the reproducibility of the skin color will be impaired. Further, in the case of FIG. 3B, it is effective for a portion having a large amplitude, that is, a white peak, but is less effective in the vicinity of the middle because of the characteristics of the circuit.

[0003]

SUMMARY OF THE INVENTION In view of the drawbacks of the conventional methods described above, the present invention provides a white balance correction device for detecting a white signal portion of a video signal and changing the white balance of only that portion. The purpose is to

[0004]

According to the present invention, there is provided means for detecting a white signal within a scanning period of a color image signal, and either red, green or blue only during the period of the white signal detected by the white signal detecting means. And means for correcting the level of one signal,
It is an object of the present invention to provide a white balance correction device that changes the white balance of only the white signal portion of a color video signal.

[0005]

The white signal portion is detected from the chroma signal after separation of the luminance (Y) / chroma (C) signal or the color difference signal such as (RY). Further, a correction circuit is provided so as to correct the level of only a specific color of the primary color signals (R, G, B). This correction circuit is operated to amplify only the detected white signal portion.
As a result, the white balance of the white signal portion is such that the color provided with the correction circuit is emphasized.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A white balance correction device according to the present invention will be described below with reference to the drawings. 1 is a block diagram of essential parts showing an embodiment of a white balance correction apparatus according to the present invention, and FIG.
5 is a video signal waveform diagram for explaining FIG. In FIG. 1, 1 is a Y / C separation circuit that separates a color video signal S1 into a luminance (Y) signal and a chroma (C) signal, and 2 is a chroma (C) signal from R (red) -Y, B (blue). ) -Y color demodulation circuit for demodulating color difference signals, 3 is a matrix circuit for extracting R, B, G (green) primary color signals from a luminance signal and color difference signals, 4 is Y / C separation circuit 1 or color demodulation A white signal detection circuit 5 for detecting a white signal from the circuit 2 is a correction circuit for correcting the level of a specific color.

Next, the operation of the present invention will be described. Y
The chroma signal separated from the video signal S1 by the / C separation circuit 1 is input to the color demodulation circuit 2 and also to the white signal detection circuit 4. Now, it is assumed that the video signal S1 having one horizontal period is as shown in FIG. The symbol a indicates color sub-conveyance. That is,
The portions of the periods T1, T3, and T5 are signals with some color, and the other periods T2, T4, and T6 are white signals without color sub-carrier. White signal detection circuit 4 from Y / C separation circuit 1
The chroma signal input to is also a signal similar to the above, with a portion having a color subcarrier and a portion having no color subcarrier (white signal). Therefore,
The white signal detection circuit 4 detects a white signal portion depending on the presence or absence of this subcarrier.

On the other hand, regarding the primary color signals (R, G, B) separated by the matrix circuit 3, blue is emphasized,
Therefore, the correction circuit 5 is inserted in the blue (B) output line. This is a case where the white balance is set closer to blue. The substantial operation of the correction circuit 5 is amplification, but the amplification action is performed only in the white signal portion (period) of the video signal. Specifically, the amplification operation is turned on / off. The configuration of the correction circuit 5 may be an analog amplifier or a digital processing method. However, in the case of digital processing, it has a configuration of A / D conversion processing for once converting into a digital signal, level shift (amplification) processing, and D / A conversion processing for returning to analog after processing. If the amplification operation of the correction circuit 5 is turned on / off corresponding to the white signal detection of the white signal detection circuit 4, the blue signal can be emphasized in comparison with the other signals (red and green) only in the white signal portion. Due to the emphasis of the blue signal, the white balance becomes closer to blue.

FIG. 2 conceptually shows the above operation.
(B). It is shown that the above-described emphasis (dotted line is solid line) is performed during the period of T2, T4, and T6 in the same figure.
Although the correction circuit 5 is provided in the blue signal line in FIG. 1, it may be inserted in another red or green line. The white balance in this case is closer to red in the former and closer to green in the latter.
Furthermore, there is also a method of inserting into two lines of red, blue, and green, in which case the white balance is closer to the combined color of the two colors. Although the white signal is detected from the chroma signal from the Y / C separation circuit 1 in the above, it can be detected from the presence or absence of the color difference signal output from the color demodulation circuit 2. That is, in FIG. 1, instead of the chroma signal from the Y / C separation circuit 1, the color difference signal S2 from the color demodulation circuit 2 is input to the white signal detection circuit 4. Since the zero potential (or operation reference potential) portion of all the color difference signals is the white signal portion, the white signal detection circuit 4 turns on the amplification operation of the correction circuit 5 when the white signal portion is detected as described above. , Turns off in other periods. As a result, the same effect as when the chroma signal is used can be obtained.

[0010]

As described above, according to the present invention, the white balance of only the white portion of a color image can be shifted to an arbitrary color, and other hues are changed at the same time as in the conventional case. There is no. Therefore, for example, it is possible to increase the apparent sharpness and brightness by adding the white balance of the white portion to the bluish color without changing the flesh color, and it is possible to improve the image quality.

[Brief description of drawings]

FIG. 1 is a principal block diagram showing an embodiment of a white balance correction device according to the present invention.

FIG. 2 is a video signal waveform diagram for explaining FIG.

FIG. 3 is a circuit diagram for explaining conventional white balance.

[Explanation of symbols]

 1 Y / C separation circuit 2 Color demodulation circuit 3 Matrix circuit 4 White signal detection circuit 5 Correction circuit S1 color video signal

Claims (4)

[Claims] 1. A means for detecting a white signal from within a scanning period of a color video signal, and a level of any one of red, green and blue signals is corrected only during a period of the white signal detected by the white signal detecting means. Means for changing the white balance of only the white signal portion of the color video signal. 2. The white signal detecting means is adapted to detect from the presence or absence of a color subcarrier in the chroma signal after separating the color video signal into a luminance signal and a chroma signal. 1. The white balance correction device according to 1. 3. The white balance correction apparatus according to claim 1, wherein the white signal detecting means detects the chroma signal from a color difference signal after color demodulating the chroma signal. 4. The white balance correction apparatus according to claim 1, wherein the signal to be corrected by the correction means is an arbitrary plurality of signals from red, green or blue.