JPS61121683A - Skin-color correcting circuit - Google Patents

Abstract

PURPOSE:To correct with a simple constitution and with a high accuracy by detecting a hue of two demodulated digial color difference signals and selecting the corrected quantity in the skin-color direction accumulated in accordance with the hue. CONSTITUTION:A demodulated digital B-Y color difference signal 21 and a digital R-Y color difference signal 22 are supplied to a hue detecting circuit 3. The hue detecting circuit 23 derivates the ratio of two digital color difference signals, and by obtaining a reverse tangent function of the ratio, the hue of the two above-mentioned digital color difference signal is detected. A signal 234 showing a hue detected at the hue detecting circuit 23 is supplied to a reading exclusive-use memory 25 as an address signal to control the reading exclusive-use memory 25. The reading exclusive-use memory 25 is programmed so as to generate a corrected quantity in the skin-color direction in correspondence to a phase difference with an I shaft coincident with the hue of two inputted digital color difference signals and the vector of the ideal skin-colored color tone, as a control signal to adjust a hue of two inputted digital color difference signals.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital NTSC color television receiver in which a demodulated color signal is corrected in the direction of skin color according to deviation from a reference value corresponding to skin color. Related to automatic skin color correction circuit 0 Conventional technology The colors reproduced in an NTSC color television receiver are not originally reproduced due to factors such as distortion of the transmission line, differential gain and differential phase of the broadcast equipment repeater and the receiver. It is reproduced with a different hue from the color of the image.

In particular, the human eye is extremely sensitive to distortion of skin color, and faithful reproduction of skin color is considered to be the most important problem from the viewpoint of visual psychology. In order to solve such problems, I
There is a skin color correction circuit that reproduces surrounding colors around the axis in colors close to skin tones within an appropriate range and amount of pull.

An example of the conventional skin color correction circuit described above will be described below with reference to the drawings.

FIG. 4 is a block diagram of a conventional skin color correction circuit.
The figure is a vector diagram showing the principle of correction.

In FIG. 4, a phase detector 2 generates a reference subcarrier locked to the burst phase of the input carrier color signal. 4
tfi amplitude limiting amplifier, 6 a single-axis detector, 8 a variable gain amplifier, 1o an adder, and 12 a color demodulator.

The operation of the skin color correction circuit configured as described above will be explained below.

First, the input carrier color signal 1 is supplied to the phase detector 2,
A reference subcarrier 3 locked to the burst phase of the input carrier color signal 1 is obtained. On the other hand, the input carrier color signal 1 is also supplied to the amplitude limiting amplifier 4, and its output signal, the carrier color signal 6 whose amplitude is kept constant, is supplied together with the reference subcarrier 3 to the uniaxial detector 6. A signal T corresponding to the difference between the carrier color signal 6 whose amplitude is kept constant and "one axis" is detected. The output signal T of the single-axis detector e is supplied to a variable gain amplifier 8, and the smaller the difference between the constant amplitude carrier color signal 6 and the I-axis, the greater the amplification factor for the constant amplitude carrier color signal 6. is controlled so that it becomes large. The output signal 9 of the variable gain amplifier 8 is added to the reference subcarrier 3 by an adder 10 to obtain a demodulation subcarrier 11, in which the carrier color signal 1 is added to the color demodulator 1.
Color signal 1 demodulated in 2 and corrected for skin color
3 is obtained. That is, as shown in Fig. 5, a carrier color signal whose phase is shifted by α from the 1st axis is demodulated as a signal whose phase is shifted by α - β with the demodulation subcarrier shifted by β from the reference subcarrier. is corrected so that it approaches the skin color by β (for example, rxxxic Tr
＆ng＆OtiOng OnConsumer Kle
QtOniC5, 1976, ppl 11-117).

Problems to be Solved by the Invention However, the conventional device with the above configuration is suitable for an NTSC color television receiver configured with an analog signal processing circuit, and a circuit that processes a video signal with a digital signal. In digital color television receivers with This has had problems such as difficulty in arbitrarily setting the correction characteristics.

In view of the above-mentioned problems, the present invention provides an all-digital skin color correction circuit that is suitable for an NTSO television receiver equipped with a digital signal processing circuit and can perform accurate correction with a simple configuration.

Means for Solving the Problems In order to solve the above problems, the skin color correction circuit of the present invention has the following features:
Means for detecting the hue of the two demodulated digital color difference signals, and a control signal for selecting the accumulated correction amount in the skin color direction according to the hue of the two detected digital color difference signals and adjusting the hue. a programmable read-only memory that outputs the amount of correction in the selected skin tone direction;
A configuration comprising means for adjusting the hue of the two digital color difference signals delayed in order to match the timing with the control signal for adjusting the hue, using the control signal for adjusting the hue, and outputting two digital color difference signals corrected for skin color. It is equipped with the following.

According to the above-described configuration, the present invention detects the hue from the two digital color difference signals after demodulation, and adjusts the hue of the two digital color difference signals to the skin color using a control signal that indicates the amount of correction in the skin color direction according to the detected hue. In order to adjust the amount of correction in the skin tone direction, in an NTSC television receiver equipped with a digital signal processing circuit, correction can be performed with a simple configuration and with high precision, and a control signal indicating the amount of correction in the skin tone direction can be programmed using a read-only memory. Since the correction characteristics are generated, it is possible to arbitrarily set the correction characteristics.

Embodiment Below, a skin color correction circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a block diagram of a skin color correction circuit according to an embodiment of the present invention. In FIG. 1, 23 is a hue detection circuit, 25 is a read-only memory, 29 is a delay device, 3
2 is a hue adjustment circuit.

The operation of the skin color correction circuit of the present invention configured as described above will be explained below with reference to FIGS. 1, 2, and 3.

First, the demodulated digital B-Y color difference signal 21 and digital R-Y color difference signal 22 are supplied to the hue detection circuit 23. The hue detection circuit 23 derives the ratio of the two digital color difference signals, and detects the hue of the two digital color difference signals by taking the arctangent function of the ratio. That is, a signal 24 indicating a phase difference (hereinafter referred to as hue) from the BY axis is generated according to the well-known formula shown below.

A signal 24 indicating the hue detected by the hue detection circuit 23 is supplied to the read-only memory 25 as an address signal for controlling the read-only memory 25.

The read-only memory 25 stores the amount of correction in the skin color direction in response to the phase difference between the hue of the two input digital color difference signals and the I-axis that matches the ideal skin color tone vector.
That is, it is programmed to generate the amount of hue rotation in one axis direction as a control signal for adjusting the hue of the two input digital color difference signals.

FIG. 2 is a characteristic diagram showing a preferred embodiment of the relationship between the hue of two input digital color difference signals stored in the read-only memory 26 and the amount of correction in the skin color direction. Since the amount of correction is derived using a programmable read-only memory, the skin color correction characteristics of the NTSC television receiver can be freely set in advance, including the range and magnitude of correction. In addition, read-only memory 2
5 is equipped with a control input section that can control on/off switching of correction in the direction of skin color using a switching signal 26.
In a television receiver that can simultaneously receive systems other than the NTSC system by setting the amount of correction in the skin color direction to zero, this is preferable since it does not affect reception of systems other than the NTSC system. .

On the other hand, the two demodulated digital color difference signals 21 and 22
are supplied to the delay device 29 and delayed to match the time and timing required for processing in the hue detection circuit 23 and read-only memory 25, resulting in two digital color difference signals 30.
．． 31 is output. The two delayed digital color difference signals 30.31, which are the output signals of the delay device 29, are supplied to the hue adjustment circuit 32 together with the control signal 27.28 for adjusting the hue, which is the output signal of the read-only memory 25, to adjust the skin tone. The hue is adjusted in the direction.

The hue adjustment circuit 32 adjusts the hue by performing a matrix operation that performs coordinate axis conversion as shown in the following equation, and outputs a skin color corrected digital (B-Y) signal 33 and a skin color corrected digital (R-Y) signal. 34 is output.

In the above equation, θ indicates the rotation amount of the hue, and the control signal for adjusting the hue corresponds to a signal indicating cos θ and sin θ, which are matrix elements in the above equation.

FIG. 3 schematically shows the correction function of an embodiment of the present invention configured as described above.

As described above, according to this embodiment, there is a hue detection circuit that detects hue from two digital color difference signals, a read-only memory that derives a correction amount in the skin color direction corresponding to the hue, and two digital color difference signals. By providing a hue adjustment circuit that brings the hue closer to the skin color direction, skin color correction can be performed accurately with a simple configuration. Also, by using a programmable read-only memory in deriving the correction amount, the correction characteristics can be designed flexibly, and the color quality of a color television receiver can be significantly improved.

In this embodiment, the B-Y and R-Y signals are used as the two digital color difference signals, but by changing the contents of the programmable read-only memory, any color difference signal having an orthogonal relationship to each other can be used. Often, I,Q signals can also be used.

In addition, by adding a certain constant to the correction amount in the skin color direction and storing it in a programmable read-only memory, the B-Y and RY signals are supplied as input color difference signals, and the I, R-Y signals are supplied as output color difference signals. It is also possible to obtain a Q signal, supply I and Q signals as input color difference signals, and obtain B -Y and RY signals as output color difference signals.

Effects of the Invention As described above, the present invention includes a means for detecting the hue of two demodulated digital color difference signals, and a means for detecting the accumulated correction amount in the direction of skin color according to the hue of the two detected digital color difference signals. a programmable read-only memory for selecting and outputting a correction amount in the selected skin tone direction as a control signal for adjusting hue; and two digital color differences delayed to align with the control signal for adjusting said hue. Since it is constituted by a means for adjusting the hue of the signal by a control signal for adjusting the hue and outputting two digital color difference signals corrected for skin color, accurate skin color correction can be performed with a simple configuration. In addition, since it is constructed entirely of digital circuits, it is possible to obtain effects such as stability and high reliability, and it is also possible to obtain the effect of reducing costs because it is suitable for integration into integrated circuits.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a digital skin color correction circuit in an embodiment of the present invention, Fig. 2 is a skin color correction characteristic diagram in an embodiment of the present invention, and Fig. 3 is a schematic diagram of a correction function in an embodiment of the present invention. FIG. 4 is a block diagram of a conventional analog skin color correction circuit, and FIG. 5 is a vector diagram showing the principle of the correction shown in FIG. 2... Phase detector, 4... Amplitude limiting amplifier, 6... Single axis detector, 8... Variable gain amplifier, 1o...・Adder, 12...
Color demodulator, 23...hue detection circuit, 26...
・・Read-only memory, 29・・・・Delay device, 32・
...Hue adjustment circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3? −i

Claims (4)

[Claims] (1) An input section for receiving two demodulated digital color difference signals, a means connected to the input section for detecting the hue of the two digital color difference signals, and a memory having a correction amount in the skin color direction. , a program that selects the amount of correction in the skin color direction accumulated therein according to the hue of the two detected digital color difference signals, and outputs the selected correction amount in the skin color direction as a control signal for adjusting the hue; a read-only memory capable of being connected to said input and said second
delay means for delaying the two digital color difference signals in order to match the timings of the two digital color difference signals and the control signal for adjusting the hue; and the delay means for delaying the two digital color difference signals by the control signal for adjusting the hue. A skin color correction circuit comprising means for adjusting the hue of the skin color and outputting two skin color corrected digital color difference signals. (2) The means for detecting the hue of two digital color difference signals includes means for obtaining a signal indicating the ratio of the two digital color difference signals, and means for inputting the signal indicating the ratio and outputting a signal representing the arctangent function thereof. A skin color correction circuit according to claim 1, comprising: (3) The skin color correction circuit according to claim 1, wherein the programmable read-only memory includes a control input section that can control switching on and off of correction in the direction of skin color. (4) The hue of the two digital color difference signals delayed by the control signal that adjusts the hue is adjusted, and the skin color is corrected.
The means for outputting the two digital color difference signals includes means for inputting the delayed two digital color difference signals and the control signal for adjusting the hue, and rotating the color demodulation axis by performing a matrix operation for converting the coordinate axes. A skin color correction circuit according to claim 1.