JP2626746B2 - Color video signal processing circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color video signal processing circuit, and more particularly to a color video signal of a frequency interleaving system, which separates a luminance signal and a carrier chrominance signal from each other. And a color video signal processing circuit that generates a color difference signal by demodulating the color difference signal.

FIG. 4 is a block diagram showing an example of a conventional color video signal processing circuit. In the figure, a color video signal of a frequency interleaving system of, for example, an NTSC system which enters an input terminal 1 is separated into a carrier chrominance signal and a luminance signal by a Y / C separation circuit 2a. The output carrier color signal of the Y / C separation circuit 2a is supplied to a color signal processing circuit 3a.

The color signal processing circuit 3a includes, for example, a bandpass filter for a carrier color signal wave, a color signal demodulation circuit and a necessary burst gate circuit, an automatic color saturation control circuit (ACC circuit), a killer circuit, and a color signal demodulation auxiliary circuit. And a carrier recovery circuit (generally composed of a phase locked loop (PLL)). The color signal processing circuit 3a outputs a color difference signal (for example, RY and BY) obtained by demodulating the input carrier chrominance signal to the matrix circuit 4a.

On the other hand, the output luminance signal Y of the Y / C separation circuit 2a is supplied to the matrix circuit 4a via a luminance signal processing circuit 5a having a built-in horizontal or vertical beaking correction circuit, contrast control circuit, and the like. Matrix circuit 4a
Generates three primary color signals R, G, B based on the incoming color difference signal and luminance signal Y and outputs them to the CRT 6.

The above is the configuration of the conventional color video signal processing circuit using analog processing. On the other hand, a conventional color video signal processing circuit based on digital processing has a configuration in which an A / D converter 7 and a D / A converter 8 are added as shown in FIG. Here, the Y / C separation circuit 2b, the color signal processing circuit 3b, the matrix circuit 4b, and the luminance signal processing circuit 5b are obtained by digitizing each circuit in FIG.

In FIG. 5, a color video signal coming from an input terminal 1 is converted from analog to digital by an A / D converter 7 and supplied to a Y / C separation circuit 2b. Then, after the same signal processing as in FIG. 4 is performed digitally, the digital three primary color signals R, G, B output from the matrix circuit 4b are converted to D / A
The data is converted from digital to analog by the converter 8 and supplied to the CRT 6.

By the way, as the Y / C separation circuit 2a or 2b, a line correlation type separation circuit (a so-called comb filter) using one horizontal scanning period (1H) delay line or 2H delay line is conventionally used. FIG. 6 is a block diagram showing an example of the Y / C separation circuits 2a and 2b. Here, the color video signal coming into the input terminal 9 is delayed by 1H in the 1H delay line 10. Subtracter 11 performs a subtraction between the color video signal of 1H before the line to be outputted through the color video signal and the 1H delay line 10 of the current line, as is well known, f _H / 2 (where, f _H is A signal having an odd multiple of the horizontal scanning frequency is waved, and a carrier color signal is output to an output terminal 13 via a bandpass filter (BPF) 12.

On the other hand, the adder 14 adds the color video signal of the current line to the current line.
By adding the 1H color video signal of the preceding line, as well known, take out the luminance signal of the even multiple of a frequency of f _H / 2. The adder 15 adds the output luminance signal of the adder 14 and the luminance signal that has passed through the low-pass filter 16 and outputs the result to the output terminal 17.

However, in the conventional color video signal processing circuit, the Y / C separation is simply performed by the Y / C separation circuits 2a and 2b formed by the comb filters. There is a problem that it is not possible to avoid cross color interference from a signal to a carrier color signal and dot interference from a carrier color signal to a luminance signal. Among them, particularly, dot disturbance has a remarkable effect on image quality, and is a major factor in image quality deterioration.

The modes of occurrence of the dot disturbance include, first, when the hue of the carrier chrominance signal sharply changes in the vertical direction, and second, when the hue of the carrier chrominance signal sharply changes in the horizontal direction.

The former generation mode always occurs in a Y / C separation circuit using a horizontal delay line.Conventionally, a trap circuit for level attenuating the color subcarrier frequency component of, for example, 3.58 MHz is inserted on the luminance signal output side. By doing so, dot interference was reduced. However, in this case, there is a problem that the horizontal resolution particularly at a frequency around 3.58 MHz is deteriorated.

On the other hand, the latter mode occurs because the cutoff frequency of the LPF 16 is high, and can be improved by sufficiently reducing the cutoff frequency, but the resolution in the oblique direction on the screen deteriorates.

Accordingly, an object of the present invention is to provide a color video signal processing circuit which solves the above-mentioned problem by selectively performing level attenuation of a color subcarrier frequency component in a luminance signal adapted to line correlation. I do.

Means for Solving the Problems The color video signal processing circuit according to the present invention generates and outputs a detection signal according to the absolute value of the level difference between the color difference signals between the current line and the line one horizontal scanning period before. And level attenuating means.

The Y / C separation circuit constituted by the comb filter separates the color video signal of the frequency interleaving system from the color video signal and generates the detection signal from the demodulated color difference signal. Based on this detection signal, level attenuation suitable for line correlation is selectively performed on the color subcarrier frequency component included in the luminance signal separated from the color video signal by the Y / C separation circuit.

Embodiments The present invention is intended to remove a color subcarrier frequency component in a luminance signal separated by a Y / C separation circuit using a horizontal delay line without particularly deteriorating resolution among image quality. , Without changing the existing Y / C separation circuit, etc.
The purpose is supplementarily achieved by adding a circuit or the like.

FIG. 1 is a block diagram showing an embodiment of a color video signal processing circuit according to the present invention. 4 and 5 in FIG.
The same components as those in the drawings are denoted by the same reference numerals, and description thereof will be omitted. This embodiment is characterized in that a detection circuit 21 and an adaptive processing circuit 22 are provided for the conventional color video signal processing circuit shown in FIG.

The detection circuit 21 outputs to the adaptive processing circuit 22 a detection signal corresponding to the amount of line correlation of the color difference signals, that is, the amount of change in hue between the lines. The adaptive processing circuit 22 performs optimal luminance signal processing as described later according to the input detection signal.

By the way, for example, when the hue of the n-th line (where n is a natural number) and the (n + 1) -th line change greatly, or the n-th line has a certain hue, the (n + 1) -th line When a line is a so-called achromatic color without a color subcarrier, dot interference occurs in a luminance signal.

As described above, the dot disturbance has a luminance signal of 3.58 MHz.
In this embodiment, the detection circuit 21 detects and detects that there is no line correlation due to a sudden change in the hue between the lines because the color subcarrier frequency component is reduced by applying a trap for reducing the level of the color subcarrier frequency component. Only when a signal is generated, a 3.58 MHz trap is turned on for the luminance signal in the adaptive processing circuit 22.

In this way, if the hue hardly changes between lines or if the change is gradual, 3.58 MHz
Since the trap is not turned on, it is possible to prevent the horizontal resolution of most parts of the screen from deteriorating.

Next, referring to FIG. 1, the output color difference signal of the color signal processing circuit 3a is supplied to the matrix circuit 4a and also to the detection circuit 21. The detection circuit 21
As shown in FIG. 2, a line correlation detecting circuit 26 comprising a 1H delay line 23, a subtractor 24 and an absolute value circuit 25, a comparator 27 and a reference value generating circuit 28.

The color difference signal input to the input terminal 29 is supplied directly to the subtractor 24, and is also delayed by 1H via the 1H delay line 23 and supplied to the subtractor 24. The subtractor 24 calculates the current line and 1H
The color difference signals of the previous line are subtracted from each other, and a signal corresponding to the level difference between the two signals is output to the absolute value circuit 25. Here, when the hue does not change between the current line and the line before 1H, that is, when there is a line correlation between the two lines, the output subtraction signal level of the subtractor 24 is zero. When there is no line correlation between the two lines, an output subtraction signal having a positive or negative value having a level proportional to the amount of change in the hue is obtained.

The absolute value circuit 25 generates an absolute value signal having a level corresponding to the absolute value level of the output subtraction signal of the subtractor 24,
Output to the comparator 27. This absolute value indicates the weakness of the line correlation.

The comparator 27 compares the level of the input absolute value signal with the output signal of the reference value generating circuit. Here, the reference value is set so that the resolution degradation is practically minimized at the stage of designing and manufacturing.

Here, the comparator 27 generates a detection signal which becomes, for example, a high level when the absolute value is larger than the reference value, and becomes a low level when the absolute value is smaller than the reference value, and outputs the detection signal to the output terminal 30. I do. That is, the detection signal is at a high level when the line correlation is weak, and is at a low level when the line correlation is strong.

FIG. 3 is a circuit diagram of an embodiment of the adaptive processing circuit 22. In the figure, the detection signal input terminal 31 is grounded through a resistor R ₁ and R _2. Connection point of the resistors R ₁ and R _2, NPN
Connected to the base of transistor T. Transistor T
Is connected to a connection point A between a luminance signal input terminal 33 and a luminance signal output terminal 34 via a trap element 32 including a capacitor C and a coil L. The trap element 32 has a resonance frequency of 3.58 MHz.

In the above configuration, during the period in which the detection signal is at the high level, the transistor T is turned on.
Is grounded via the trap element and the collector-emitter of the transistor T. This allows the adaptive processing circuit
22 operates as the trap circuit, and the input terminal 33 is connected to 3.58 of the incoming luminance signal processing circuit 5a in the output luminance signal.
The color subcarrier frequency component of MHz is trapped, and the luminance signal of the other frequency components is output to the matrix circuit 4a via the output terminal.

On the other hand, during the period in which the detection signal is at the low level, the transistor T is turned off, so that the luminance signal entering the input terminal 33 is not trapped as described above, and the matrix circuit 4a is directly passed through the output terminal 34. Output to

In this way, when the line correlation is weak such that the hue changes greatly between the lines, trapping is performed on the luminance signal. On the other hand, when the line correlation such that the hue hardly changes is strong, the trap is performed. No trap is performed on the luminance signal.

The above description is of the case where the present invention is applied to an analog color video signal processing circuit as shown in FIG. 4, but the present invention is not limited to analog circuits as shown in FIG. Of course, it can be applied to digital circuits. When the present invention is applied to a digital circuit, there are the following advantages.

(1) The 1H delay line 23 in the detection circuit 21 can be easily obtained.

(2) Various arithmetic circuits such as the subtractor 24 and the absolute value circuit 25 in the detection circuit 21 can be easily obtained.

(3) The processing filter in the adaptive processing circuit 22 (that is,
The trap element 32) can be freely formed, and the high-speed switching of the processing filter on / off according to the detection signal can be easily performed.

Note that the output detection signal of the detection circuit 21 is not limited to a signal that changes in a binary manner as in the present embodiment, but may be any number of detection signals depending on the type of processing mode of the adaptive processing circuit 22. To perform optimal luminance signal processing.

Further, the adaptive processing circuit 22 is not a digital detection signal but, for example, a detection signal whose level changes in an analog manner according to the level difference of the color difference signal between the current line and the line 1H before. The color subcarrier frequency component in the luminance signal may be attenuated in proportion to the level. In this case, for example, the detection circuit 21 outputs the line correlation detection value (that is, the output absolute value signal of the absolute value circuit 25) to the adaptive processing circuit 22 as a detection signal without passing through the comparator 27.

Although the detection circuit 21 detects the line correlation based on the color difference signal, the detection circuit 21 may detect the line correlation based on the luminance signal. However, the luminance signal is subjected to processing such as peaking correction in the horizontal and vertical directions and contrast control by the luminance signal processing circuit 5a, and the processing is performed according to the user's intention, so that the luminance signal is unstable. Therefore, it is not preferable to detect the line correlation based on the luminance signal.

The signal processed by the circuit of the present invention is not limited to the NTSC color video signal, but may be a PAL color video signal. Further, the configuration of the adaptive processing circuit 22 is not limited to the configuration of turning on / off the trap circuit, and may be any configuration as long as the level of the chrominance subcarrier frequency component in the luminance signal is attenuated according to the detection signal. Of course.

Effect of the Invention As described above, according to the present invention, the level attenuation of the chrominance subcarrier frequency component in the luminance signal adapted to the line correlation is selectively performed, so that the Y / C separation function of the Y / C separation circuit is improved. Even if it is insufficient, dot interference to the luminance signal due to the carrier chrominance signal can be prevented at the output side of the Y / C separation circuit, making it possible to compensate for the insufficient Y / C separation function. In addition, even if, for example, the Y / C separation circuit built in a large-scale integrated circuit (LSI) has to be improved to compensate for the insufficiency of the Y / C separation function, the present invention can be applied to improve the performance. Therefore, it is possible to obtain an image having a good resolution from which dot interference has been eliminated only by adding a simple configuration to an existing Y / C separation circuit having an insufficient Y / C separation function. It has such features as possible.

Further, since the color video signal processing circuit of the present invention obtains the line correlation detection signal from the color difference signal obtained by demodulating the carrier color signal, not the carrier color signal, the color video signal processing circuit detects when the detection signal is obtained from the carrier color signal. 3.58 needed for signal lines
No need for a MHz bandpass filter or envelope detection circuit (because the demodulation step to color difference signals (that is, in the color signal processing circuit) is equivalent to a 3.58 MHz bandpass filter and envelope detection circuit), and Cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a color video signal processing circuit according to the present invention, and FIGS.
FIG. 4 is a block diagram showing one example of a conventional color video signal processing circuit, and FIG. 5 is a block diagram showing another example of a circuit diagram showing another example of a circuit diagram. FIG. 6 is a block diagram showing an example of a conventional Y / C separation circuit. 1 ... Color video signal input terminal, 2a ... Y / C separation circuit, 3
a ... Color signal processing circuit, 4a ... Matrix circuit, 5a ...
Luminance signal processing circuit, 6 CRT, 21 detection circuit, 22
... Adaptive processing circuit, 23 ... 1H delay line, 24 ... Subtractor, 25
... Absolute value circuit, 26 ... Line correlation detection circuit, 27 ... Comparator, 28 ... Reference value generation circuit, 29 ... Color difference signal input terminal, 30 ... Detection signal output terminal, 31 ... Detection signal input Terminal, 32: trap element, 33: luminance signal input terminal, 34
… Luminance signal output terminal, C… capacitor, L… coil, R ₁ , R ₂ … resistance, T… transistor.

Claims (1)

(57) [Claims] 1. A luminance signal and a carrier chrominance signal are separated from a frequency interleaving color video signal by a Y / C separation circuit constituted by a comb filter, and the carrier chrominance signal is demodulated by a chrominance signal processing circuit. A line correlation detection circuit for generating and outputting a detection signal corresponding to an absolute value of a level difference between the current line and a line one horizontal scanning period before the current line and a line before the horizontal scanning period. Means for selectively performing level attenuation adapted to line correlation based on the detection signal with respect to a color subcarrier frequency component included in the luminance signal. .