JPS58104587A - Color video camera - Google Patents

Abstract

PURPOSE:To stabilize the picture quality of skin color, by controlling that colors within a range regarded as skin color substantially are closed to ideal skin color. CONSTITUTION:A luminance signal (Y signal) 1, the 1st color difference signal (R-Y signal) 2, and the 2nd color diference signal (B-Y signal) 3 are applied to a skin color detection circuit 4. The detection circuit 4 detects a range having the possibility of skin color from the signals 3, 2 and 1 to produce a red color control signal 28 and a blue color control signal 29. The signals 2 and 28 are applied to the 1st mixing circuit 30 and the signals 3 and 29 are applied to the 2nd mixing circuit 31. The signals in circuits 30 and 31 are applied to a modulation circuit 32, where the 1st and the 2nd chrominance subcarrier waves 33 and 34 are amplitude-modulated to generate a chrominance carrier signal 35.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses one or more image pickup tubes or solid-state image pickup devices to convert the three primary colors of an object into electrical signals. and a first and second color difference signal, and amplitude modulates the color difference signal using the first and second color subcarriers to create a carrier color signal,
The present invention relates to a color video camera that obtains a desired video signal output by adding the luminance signal and the carrier color signal.

An object of the present invention is to automatically correct unnatural skin tones that occur when the white balance adjustment provided in a color camera is incomplete or under constantly changing lighting conditions during shooting. The aim is to eliminate the hassle of adjusting the camera, improve operability, and improve image quality.

Conventionally, various skin color correction devices have been developed as a method for correcting skin color distortion caused by a camera side or a signal transmission line in a television receiver.

A correction device in a television receiver mainly compares the phase or amplitude value of the received carrier color signal with the phase or width value of a reference signal corresponding to skin color, and when the difference is small, the correction device adjusts the phase or amplitude value of the received carrier color signal to the carrier color signal. Assuming that the corresponding color is close to skin color, the reproduced skin color is corrected by changing the carrier color signal itself or the phase or demodulation gain of the color demodulation axis of the color demodulation circuit. The above correction method works effectively when the carrier color signal produced by the color camera has a phase or amplitude value close to the reference signal with respect to the skin color of the subject.

However, if a carrier color signal far removed from the reference signal is transmitted as a skin color due to maladjustment of the color camera, etc., there is a drawback that the skin color cannot be corrected.

The present invention provides a skin color correction function, which has conventionally been provided mainly on the television receiver side, on the color camera side, thereby making it possible to perform correction even in cases where it could not be corrected on the conventional television receiver side. This stabilizes the quality of the skin color image reproduced in the John receiver. Alternatively, the present invention makes it possible to reduce errors in the skin color signal sent from the camera and reproduce a stable skin color image without requiring any correction device on the television receiver side. The above functions are especially necessary when using a simple color camera for home use where photographing conditions frequently change.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is a block diagram of essential parts showing an embodiment of the present invention.

The three primary color signals obtained from an imaging device such as an image pickup tube are
The color difference signal is converted into a brightness signal indicating the brightness of the subject and two color difference signals, and this color difference signal is amplitude-modulated by a color subcarrier and then added to the brightness signal above. It is output from

The skin color stabilizing device, which is the main part of the present invention, is provided in a color difference signal processing circuit that modulates the amplitude of the two color difference signals using a color subcarrier. Usually, red, green, and blue are selected as the three primary color signals due to color reproduction and restrictions from the picture tube. In the following, these will be referred to as an R signal, a G signal, and a B signal. The luminance signal (hereinafter referred to as Y signal) is created by mixing R, G, and B signals in consideration of the visual sensitivity of the eye.

On the other hand, the color difference signal is more Y than the R signal or the B signal.
Created by subtracting signals. Below, R-Y signal, B-
It is written as Y signal.

Y signal 1. RY signal 2. The BY signal 3 is supplied to a skin color detection circuit 4. As shown in FIG. 2, this skin color detection circuit 4 includes level detection circuits 5, 6.
．． Addition circuit 10. It is configured including gate circuits 11 and 12. An example of the configuration of the level detection circuits 5, 6.7 is shown in FIG. In the same figure, the input signal 13 is supplied to two comparators 14.15 whose outputs have two states: high level or low level, and is compared with reference voltages vl, +vH of a reference voltage source 16.17. . The comparator 16 is configured to output a high level when the input signal level is higher than vL, and the comparator 14 is configured to output a high level when the input signal level is lower than vH. The adder circuit 18, which performs high-level and low-level binary signal processing, is supplied with the outputs of the comparators 14 and 15, and is configured to output a high level only when both input levels are high.

With the above configuration, the level detection circuits 5, 6.7 have a function of having a high level output when the voltage level of the input signal is between the reference voltages vL and vB. The adder circuit 10 performs high-level and low-level binary signal processing.
The outputs of the level detection circuits 5, 6 and 7 are supplied, and a high level signal is output only when all of the outputs are at high level.

The Y signal is supplied to a level detection circuit 6, the RY signal is supplied to a level detection circuit 6, and the BY signal is supplied to a level detection circuit 7, each of which has a predetermined voltage range. When the signal is within the range, the adder circuit 10 outputs a high level signal. Output.

On the other hand, the RY signal and the BY signal are supplied to subtraction circuits 8 and 9, respectively, and output a difference signal from the reference voltage vR9VB. The gate circuits 11 and 12 are supplied with the difference signal and the output signal of the adder circuit 1o, and are configured to pass the difference signal when the adder circuit output is at a high level, and use it as the output signal of the skin color detection circuit 4. .

FIG. 4 is a diagram showing the skin color detection range of the skin color detection circuit 4. In the figure, the level detection circuit 60 reference voltage is set to vR.
H9vRL, level detection circuit 70 reference voltage vBll,
If vBL is set, the area within the shaded area is considered to be the skin color. In addition, with regard to brightness, there is usually little possibility that high-brightness and low-brightness skin tones will occur, so if the reference voltages vYHl and vYL of the level detection circuit 6 are set to exclude these, skin tones can be detected more accurately. becomes. Fourth
Point Q in the figure is the center value for skin color detection, and is set to the center value of the appearance range of the RY signal and BY signal when the skin color is photographed. vR2VB is the RY signal at point Q and B
- This is the voltage level of the Y signal, and corresponds to each reference voltage level to the subtracting circuits 8 and 9.

FIG. 6 shows an example of signal waveforms of each part of the skin color detection circuit based on the above configuration. body) is the luminance signal, (
C) is the RY signal, (E) is the B-Y signal, (B).

(D) and (F) are the output signals of the level detection circuits 5 and 6.7, respectively, (G) is the output signal of the adder circuit 10, (H)
, (I) are the output signals of the gate circuits 11 and 12.

Hereinafter, the output signals of the gate circuits 11 and 12 will be referred to as a red control signal 28 and a pre-control signal 29, respectively.

Next, skin color correction using the red control signal and blue control signal generated by the skin color detection circuit 4 will be explained.

The R-Y signal 2 and the red control signal 28 are supplied to a first mixing circuit 30, and the BY signal 3 and the pre-control signal 29 are supplied to a second mixing circuit 31.

The output signals of the first and second mixing circuits 30.31 are fed to a modulation circuit 32, where the first. second color subcarrier 33
．． 34 is amplitude modulated to produce a carrier color signal 35.

FIG. 6 is a block diagram showing an example of the configuration of the first mixing circuit 3o. In the figure, the red control signal 28 is supplied to a variable gain amplifier circuit 38 via an amplitude detection circuit 36 and, if necessary, a delay circuit 37 for time adjustment. FIG. 7 shows the characteristics of the amplitude detection circuit 36, which outputs a signal responsive to the amplitude value regardless of whether the red control signal (horizontal axis) is positive or negative.

The variable gain amplifier circuit 38 has a gain responsive to the output signal 39 of the amplitude detection circuit 3-6, and has a gain of zero when the output signal 39 is zero, and has a larger gain as the level of the output signal 39 increases. Configure it as follows.

The subtraction circuit 4o is configured to subtract the output signal of the variable gain amplifier circuit 38 from the RY signal 2.

Regarding the second mixing circuit 31, the first mixing circuit 31 uses the pre-control signal 29 and the B-Y signal 3 as input signals.
It has the same configuration as .

FIG. 8 shows the above-mentioned 1. FIG. 3 is a vector diagram showing the operation of the second mixing circuit 30, 31 and the color correction operation in the present invention. In the figure, it is assumed that the vector when a certain subject is photographed is 41. If the vector 41 is a color within the skin color area indicated by diagonal lines in FIG. 4, the skin color detection circuit 4 outputs a red control signal, ie, vector 42, and a blue control signal, ie, vector 43. Subtraction circuit 4 in the first mixing circuit 3o
44, the R-Y signal or vector 44 and the first
Subtraction is performed with the output signal of the variable gain amplifier circuit 38 in the mixing circuit 3o, that is, the vector 45, and the result is output. Similarly, in the second mixing circuit 31, the BY signal, that is, the vector 46 and the vector 470 are subtracted and output. Therefore, the combined vector of the output signals of the first and second mixing circuits 30 and 31 is the vector 48. vector 49
indicates the amount of color correction that is substantially reproduced by the television receiver. Regarding other colors, if the colors are within the shaded area in FIG. 4, correction as shown by vector 60 is performed.

The feature of the color correction according to the present invention is that, as shown in FIG.
This is an operation that brings the user closer to the target. Therefore, with respect to changes in color difference signals due to fluctuations in illumination conditions during shooting, changes in skin color reproduced on a television receiver are reduced, thereby achieving stabilization of skin color image quality. In addition, by prohibiting correction for colors that are far away from the ideal skin color point, and by designing a circuit as shown in Figure 7 for colors that are slightly far away, the amount of correction can be reduced and the entire screen can be adjusted. The composition is such that the colors are harmonious and do not mix.

In addition, in the above description, the RY signal is used.

Although we have explained the case where the B-Y signal is a color difference signal,
The present invention can be similarly implemented in the case where color difference signals are synthesized using other primary color signals.

Furthermore, although the present invention has been described with a focus on stabilizing skin color image quality, it is also possible to focus on and similarly stabilize any other color.

[Brief explanation of drawings]

FIG. 1 is a block diagram of main parts showing one embodiment of the present invention, and FIG.
The figure is a Zoroku diagram showing an example of the configuration of a skin color detection circuit used in the present invention, FIG. 3 is a block diagram showing an example of the configuration of a level detection circuit, FIG. 4 is a diagram showing a skin color detection range, and FIG.
, (B), (C), (D), (IC)
, (F) t(G)(H), CI) are signal waveform diagrams of each part of the skin color detection circuit, FIG. 6 is a block diagram showing an example of the configuration of the mixing circuit, and FIG. 7 is a characteristic diagram of the amplitude detection circuit. , FIG. 8 is a vector diagram for explaining the skin color correction operation according to the present invention. 1... Luminance signal, 2... First color difference signal, 3... Second color difference signal, 4... Flesh color detection circuit, 5.6.7 ...Level detection circuit, 8,
9...subtraction circuit, 10...addition circuit,
11.12...Gate circuit, 14°16...
... Comparator, 18 ... Addition circuit, 28
...Red control signal (first control signal), 29...
...Blue control signal (second control signal), 3Q, 31...
. . . 1st and 2nd mixing circuits, 32 . . . modulation circuits, 33. 34 . . . 1st. Second color subcarrier, 35.
... Carrier color signal, 36 ... Amplitude detection circuit, 38 ... Variable gain amplifier circuit, 4o ...
・Subtraction circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2-1 L
JFigure 3L
JFigure 4Figure 5 (1)
ρFigure 6

Claims (1)

[Claims] (1) Using the three primary color signals obtained from the imaging device,
is configured to generate a luminance signal and first and second color difference signals, amplitude modulate a color subcarrier by the first and second color difference signals to generate a carrier color signal; a skin color detection circuit that is supplied with the first and second color difference signals and outputs the first and second control signals during a period corresponding to a skin color portion of the subject; a first mixing circuit that is supplied with the second color difference signal and the second control signal and performs mixing processing of both signals; a second mixing circuit that is supplied with the second color difference signal and the second control signal and performs mixing processing of both signals; output signals of first and second mixing circuits and first and second color subcarriers are provided, and the output signals of said first and second mixing circuits amplitude modulate said first and second color subcarriers. 1. A color video camera comprising a modulation circuit configured to obtain a carrier color signal from an output of said modulation circuit. (2. In the description of claim (1), the skin color detection circuit outputs a high level signal when a luminance signal is supplied and the luminance signal is within a predetermined voltage level, and when the luminance signal is within a predetermined voltage level, a first level detection circuit that outputs a low level signal when the signal is outside the level; and second and third level detection circuits that are supplied with the first and second color difference signals and output high level or low level signals; , an adder circuit to which the output signals of the first, second and third level detection circuits are supplied, and outputs a high level signal only when all inputs are at high level;
a first subtraction circuit to which the first color difference signal is supplied and outputs a difference signal from a predetermined reference voltage level; a second subtraction circuit to which the second color difference signal is supplied; Second
The circuit includes first and second gate circuits configured to be supplied with the output signal of the subtraction circuit and whose gates are configured to open only during a period when the output value of the addition circuit is at a high level; A color video camera characterized in that the first and second control signals are obtained from the output of the second gate circuit.