JPH0693784B2 - Y / C separation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a Y / C separation device, and is particularly suitable for application to a digital television receiver.

[Prior Art] In recent years, in order to improve image quality, a composite video signal is once converted into a digital signal through an analog / digital conversion circuit, Y / C separation, demodulation of three primary color signals R, G, B, etc. 2. Description of the Related Art A digital television receiver that executes processing and then returns to an analog signal for display operation has been realized.

In such a television receiver, the sampling clock signal in the analog / digital conversion is phase-locked to the color burst signal and is formed so as to have a frequency that is four times the color subcarrier frequency (hereinafter,
Such a clock signal forming method is called a burst lock method).

Good processing can be performed in the case of performing signal processing by sampling with a sampling clock signal by the burst lock method for a video signal without temporal fluctuation (jitter) such as television broadcasting.

By the way, in recent years, there has been proposed a television receiver which can be used not only for receiving a television broadcast but also as a display device of a video tape recorder or a display device of a computer game machine. The video signal reproduced by the video tape recorder has jitter. In addition, since the video signal output from the computer game machine adopts the non-interlaced scanning system, the luminance signal and the chrominance signal are not interleaved. When a video signal that has such jitter and / or is not interleaved (hereinafter referred to as a non-standard video signal) is sampled by a sampling clock signal by the burst lock method, Y / C separation according to the so-called comb filter method is performed. The following inconveniences occur.

Since the sampling points in the upper and lower horizontal scanning lines are out of phase and the data do not correspond to each other, accurate calculation cannot be performed, resolution cannot be sufficiently obtained, and inconveniences such as double imaging occur. Also, in the case of so-called double speed scanning, the time point of the 1/2 horizontal scanning period and the time point when the clock signal is generated become irrelevant, and the positions of the upper and lower horizontal scanning lines cannot be aligned, which lowers the resolution.

Therefore, there has been proposed a method (hereinafter, referred to as an H-lock method) of forming a sampling clock signal by dividing a horizontal synchronizing signal, instead of creating a clock signal in phase with a color burst signal.

[Problems to be Solved by the Invention] When the clock signal is formed by the H-lock method, the clock signal is formed from the horizontal synchronizing signal, so that the luminance signal is appropriately calculated above and below the horizontal scanning line. Can be obtained.

However, when the H-lock method is adopted, the chroma signal in the non-standard video signal is not defined in the phase above and below the horizontal scanning line, so that the separation is insufficient even if it is separated according to the comb filter separation method. There are cases. Also, when the chroma signal is separated and then demodulated to a color signal, the color subcarrier signal, which is the reference for demodulation, is formed in a circuit separate from the clock signal. In some cases, the demodulation operation was not performed well.

The present invention has been made in consideration of the above points, and even when the H-lock method is adopted as the method of generating the sampling clock signal, it is possible to obtain a good chroma signal for various video signals. An object of the present invention is to provide a Y / C separation device that can demodulate a signal well.

[Means for Solving Problems] In order to solve such problems, in the present invention, a Y / C separation device for separating a luminance signal and a chroma signal after converting a composite video signal into digital data is provided. An optimum one of the separated chroma signals is determined on the basis of a plurality of separating means having different separation methods for separating the luminance signal and the chroma signal and the color burst signal of the chroma signals separated by the respective separating means. , Or the selection control means for determining the combined ratio of the separated chroma signals, and select one of the chroma signals according to the command signal from the selection control means, or a plurality of chroma signals in the command ratio. And a chroma signal output means for synthesizing to form an output chroma signal.

[Operation] When a clock signal generation method that is determined irrespective of the phase of the chroma signal is adopted, the level and phase of the color burst signal of the separated chroma signal fluctuate according to jitter and the like. Moreover, the amount of fluctuation varies depending on the separation method. Therefore, the selection control means determines the optimum chroma signal based on the color burst signal of the chroma signals from the plurality of separation means, or determines the combination ratio of the chroma signals,
The chroma signal output means forms and outputs the chroma signal based on this determination.

As a result, even if the clock signal is formed regardless of the phase of the chroma signal, a good chroma signal can be separated and output.

[Embodiment] An embodiment in which the present invention is applied to a video tape recorder will be described in detail below with reference to the drawings.

In FIG. 1, a composite video signal COMP sampled by a clock signal formed according to the H-lock system is supplied to the Y / C separation device 1.

This separation device 1 includes a comb filter separation circuit 2 that separates a chroma signal CC according to a comb filter separation system, and a frequency separation circuit (bandpass filter) 3 that separates a chroma signal CF along a frequency axis of a video signal according to a frequency separation system. And the chroma signal CC separated by each separation circuit 2 and 3 and
CF is given to the separation method selection control circuit 4.

Separation method selection control circuit 4 controls incoming chroma signal CC and
Based on CF, coefficient signals K and (1-K) that indicate which chroma signal CC or CF to control, or that indicate the superimposition ratio of chroma signal CC or CF, are formed to form multiplication circuit 5 respectively. And 6 are given.

The multiplying circuit 5, to which the chroma signal CC is given from the separating circuit 2, multiplies the chroma signal CC by the coefficient designated by the incoming coefficient signal K and gives it to the adding circuit 7. In addition, the multiplication circuit 6
Is supplied with the chroma signal CF from the separation circuit 3 and multiplies the chroma signal CF by the coefficient designated by the incoming coefficient signal (1-K) to the adder circuit 7. The adder circuit 7 adds the coefficient-multiplied chroma signals to obtain and output the output chroma signal C, and at the same time, supplies it to the subtractor circuit 8.

Further, the subtraction circuit 8 is supplied with the composite video signal COMP through the delay circuit 9 for phase synchronization with the chroma signal C, and the luminance signal Y is obtained by subtracting the chroma signal C from the composite video signal COMP. It is designed to output.

The separation method selection control circuit 4 has a configuration described below in detail.

Chroma signals CC and CF output from each separation circuit 2 and 3
Is given to the subtraction circuit 10, and after the mutual difference is obtained in the subtraction circuit 10, it is given to the burst gate circuit 11. The burst gate circuit 11 is provided with a burst flag BF that takes a logic "H" during the period of the color burst signal, and the burst gate circuit 11 extracts only the color burst period of the incoming differential signal based on the burst flag BF. . In this way, the extracted difference signal is converted into an absolute value via the absolute value circuit 12, integrated by the integration circuit 13, and given to the coefficient generation circuit 14. Coefficient generation circuit 14
In accordance with the conversion curve CUP shown in FIG. 2, the multiplication circuits 5 and 6 described above use the coefficients K and (1-K) corresponding to the value of the integrated signal.
Output to.

Here, since the frequency separation circuit 3 separates the chroma signal CF on the frequency axis regardless of the information of the upper and lower horizontal scanning lines,
The color burst signal in the chroma signal CF separated by the separation circuit 3 has a predetermined level even if the composite video signal COMP has jitter and the phases of the upper and lower horizontal scanning lines do not correspond.

On the other hand, the comb filter separation circuit 2 uses the correlation between the upper and lower horizontal scanning lines to subtract the data of the upper and lower lines to cancel the luminance signal component and obtain the chroma signal CC. If COMP has jitter and the data phases do not correspond between the upper and lower horizontal scanning lines, the color burst signal is added even if the subtraction operation is performed and the color burst signal is not doubled and is smaller than the predetermined level. .
Since the color burst signal is inverted for each horizontal scanning line, when the subtraction operation is performed, the color burst signal is an addition operation.

Therefore, while the frequency separation circuit 3 outputs the chroma signal CF whose level in the color burst period is substantially constant regardless of the jitter, the comb filter separation circuit 2 increases the jitter according to the jitter. Chroma signal CC including color burst signal with low average level
Is output.

Therefore, in the separation method selection control circuit 4, the difference between both CC and CF during the color burst period is extracted through the subtraction circuit 10 and the burst gate circuit 11 and converted into DC through the absolute value circuit 12 and the integration circuit 13. The selection ratio is given to the coefficient generation circuit 14 according to the quality of both chroma signals CC and CF.

When the chroma signal CC from the comb filter separation circuit 2 is good, the differential DC signal DC becomes almost 0 level. In such a case, the coefficient generation circuit 14 outputs "1" as the coefficient K as shown in FIG. 2 so that the chroma signal CC is selected as the output chroma signal C. This is because the chroma signal CC according to the comb filter separation method is generally better than the chroma signal CF according to the frequency separation method in consideration of image quality deterioration such as cross color. Similarly, in the range in which the level of the color burst signal of the chroma signal CC from the comb filter separation circuit 2 is slightly lower than the level of the color burst signal of the chroma signal CF from the frequency separation circuit 3, that is, the DC signal DC is Predetermined value DC1
In the smaller range, the output chroma signal C is the chroma signal CC that follows the comb filter separation method that is generally good.

When the chroma signal CC becomes worse due to jitter etc. and the direct current signal DC becomes larger than the predetermined value DC1, the chroma signals CC and CF are weighted and superimposed according to the degree of exceeding the predetermined value DC1 to form the output chroma signal C. The coefficient generation circuit 14 generates a coefficient so that the coefficient is generated.

Further, when the chroma signal CC deteriorates due to jitter or the like and the DC signal DC exceeds the second predetermined value DC2 which is larger than the first predetermined value DC1, the chroma signal CC by the comb filter separation method cannot be used. Since it has deteriorated to some extent, the coefficient generation circuit 14 outputs the chroma signal CF from the frequency separation circuit 3 as the output chroma signal C by the coefficient K.
Is set to "0".

Thus, according to the embodiment described above, the chroma signal CC and
Since CF is weighted and selected according to the jitter component, etc., when the composite video signal COMP is sampled by the clock signal according to the H-lock method, even if a video signal COMP having jitter etc. arrives, a good output chroma is obtained. The signal C can be obtained.

FIG. 3 shows a second embodiment of the present invention in which parts corresponding to those in FIG. 1 are designated by the same reference numerals. In this embodiment, as a separation circuit, the comb-shaped filter separation in the above-mentioned embodiments is performed. In addition to the circuit 2 and the frequency separation circuit 3, the interframes that separate the chroma signal CR by using the correlation between the frames
A Y / C separation circuit 20 is provided.

The chroma signals CC, CF and CR from the separation circuits 2, 3 and 20 are
It is given to the corresponding multiplication circuits 5, 6, 21 and the separation method selection control circuit 22. The separation method selection control circuit 22 includes two difference signal detection units 23, each of which is formed by sequentially connecting a subtraction circuit, a burst gate circuit, an absolute value circuit, and an integration circuit similarly to the difference signal detection unit in the embodiment shown in FIG.
And 24. The first difference signal detection unit 23 uses the chroma signal CC
And CF are input, and a DC signal DC11 indicating the level difference in the color burst period of the chroma signal CC with respect to the chroma signal CF is applied to the coefficient generation circuit 25. The second difference signal detector 24 receives the chroma signals CF and CR, and outputs the DC signal DC indicating the level difference between the chroma signal CF and the chroma signal CR in the color burst period.
12 is supplied to the coefficient generation circuit 25.

The coefficient generation circuit 25 uses the incoming detection DC signals DC11 and DC12.
The weighting factors a, b, c (0 ≦ a, b, c ≦ 1, a + b + c = 1) for the chroma signals CC, CF, CR are generated based on the , CF,
Multiply CR by a factor. The chroma signal thus multiplied by the coefficient is added in the adding circuit 7 to obtain the output chroma signal C, which is subtracted from the composite video signal COMP in the subtracting circuit 8 to obtain the luminance signal Y.

Also in this embodiment, it is possible to output a good chroma signal even if the video signal analog-to-digital converted by the H-lock method has jitter.

It should be noted that in the above-described embodiment, the number of separation circuits is two and three.
However, the present invention is not limited to this, but can be applied to those having a plurality of separation circuits, and the separation method of the separation circuit is not limited to that of the above-described embodiment. .

Further, in the above-described embodiment, the chroma signals from the respective separation circuits are weighted and combined to obtain the output chroma signal. However, the chroma signals may always be selectively output from a plurality of chroma signals. . The point is that the output chroma signal may be determined based on the level of the color burst period of the separated chroma signal.

[Effects of the Invention] As described above, according to the present invention, when a composite video signal is analog-to-digital converted using a clock signal of the H-lock system, it is satisfactory even if the video signal is a non-standard video signal. It is possible to obtain a Y / C separation device that can separate clock signals.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a Y / C separation device according to the present invention, FIG. 2 is a schematic diagram showing the input / output of a coefficient generating circuit thereof, and FIG. 3 is a second embodiment of the present invention. It is a block diagram showing. 2 ... Comb filter separation circuit, 3 ... Frequency separation circuit, 4 ...
Separation method selection control circuit 5, 6 ... Multiplication circuit, 7 ... Addition circuit, 8 ... Subtraction circuit, 11 ... Burst gate circuit, 14 ... Coefficient generation circuit.

Claims (1)

[Claims] 1. A Y / C for separating a luminance signal and a chroma signal after converting a composite video signal into digital data.
In the separating device, a plurality of separating means having different separating methods for separating the luminance signal and the chroma signal and a color burst signal of the chroma signal separated by each separating means are used to select the most suitable one of the separated chroma signals. Selection control means for deciding one or a combination ratio of each of the separated chroma signals, and selecting one of the chroma signals according to a command signal from the selection control means, or A Y / C separation device comprising: a chroma signal output means for synthesizing the chroma signals at a command ratio to form an output chroma signal.