JPH0358694A - Color signal processing unit - Google Patents

Abstract

PURPOSE:To prevent decoloring by checking the correlation between an actual signal component and a crosstalk component received from an adjacent track and selecting a comb-line filter using a component of one preceding horizontal period or a comb-line filter using component of one succeeding horizontal period depending on the state of the correlation. CONSTITUTION:The unit is provided with 1st averaging circuits 8, 9 averaging input and output color signals of a 1st delay circuit 6, 2nd averaging circuits 10, 11 averaging input and output color signals of a 2nd delay circuit 7, a conversion circuit 15 converting an output of a 3rd subtraction circuit 14 into a correlation value and a 3rd delay circuit 16 retarding the correlation value. Then a selection circuit 17 decides whether a comb line filter comprising the 1st averaging circuits 8, 9 or a comb line filter comprising the 2nd averaging circuits 10, 11 is to be used depending on an output of the 1st subtractor circuit 12, an output of a 2nd subtractor circuit 13 and an output of the 3rd delay circuit 16 to control a changeover circuit 18. Thus, a comb line filter output in response to the content of the signal is obtained, then decoloring is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a color signal processing device used in a video tape recorder.

2. Description of the Related Art In recent years, there has been an increasing demand for higher image quality in consumer video tape recorders, and deterioration in image quality due to dubbing during editing has become a particular problem.

An example of conventional color signal reproduction processing will be described below with reference to the drawings.

FIG. 2 shows a part of conventional color signal reproduction processing. In Fig. 2, ``-'' is the head, 2 is the amplifier, 2
1 is a low-pass filter, 22 is a frequency conversion circuit, 23 is a delay circuit, 24 is a subtraction circuit, and 25 is a band-pass filter.

The operation of the color signal processing device constructed as described above will be described below with reference to FIG. 2.

A reproduced signal output from the head 1 is amplified by an amplifier 2, and a color signal portion is extracted by a low-pass filter 21. The color signal output from the low-pass filter 21 is frequency-converted by a frequency conversion circuit 22. At the same time, the phase for each horizontal period is restored. The frequency-converted color signal is input to the delay circuit 23. Subtraction circuit 24
Then, the signal output obtained by subtracting the color signal output from the delay circuit 23 from the frequency-converted color signal passes through the band-pass filter 25 and becomes a reproduced color signal output. In the above description of the color signal reproduction processing, parts such as ACC and APC that are not directly related to the present invention are omitted.

Problems to be Solved by the Invention However, in the above structure, the comb filter for removing crosstalk consisting of the delay circuit 23 and the subtraction circuit 24 is always operating, so that the signal input to the delay circuit 23 When there is no correlation between the output signal and the output signal, color distortion occurs. By repeating dubbing, this color discoloration will spread by the number of times of dubbing.

In view of the above problems, the present invention provides a color signal processing device that does not cause color fading and does not significantly increase the circuit scale.

Means for Solving the Problems In order to solve the above-mentioned problems, the color signal processing device of the present invention is a helical scan type having a plurality of heads that frequency modulates the luminance signal and converts the color signal into low 5 ranges for recording. In a video tape recorder, the playback signal output from the head passes through a low-pass filter,
After the phase of the color signal separated from the reproduced signal is restored for each horizontal period, the color signal is divided into n(n
is an integer) A first delay circuit that delays the color signal by a horizontal period, a second delay circuit that delays the color signal output from the first delay circuit by n horizontal periods, and an input color signal and an output color of the first delay circuit. a first averaging circuit that averages the input and output signals of the second delay circuit; a second averaging circuit that averages the input and output color signals of the second delay circuit; and the input and output signals of the first delay circuit. A first subtraction circuit that takes the difference between the input signal and the output signal of the second delay circuit, and a second subtraction circuit that takes the difference between the input signal of the second delay circuit and the second delay circuit. a third subtraction circuit that calculates the difference between the output signal of m (m6 is an integer) horizontal period delay circuit, a switching circuit that outputs either the output of the first averaging circuit or the output of the second averaging circuit, and the first subtraction circuit. The switching circuit includes a selection circuit that determines which output is to be output from the switching circuit based on the output of the switching circuit, the output of the second subtraction circuit, and the output of the third delay circuit.

Effects The present invention uses the above-described structure to eliminate crosstalk from adjacent tracks by the effects described below. From the output of the first subtraction circuit, the output of the second subtraction circuit, and the output of the third delay circuit, a comb filter by the first averaging circuit or a comb filter by the second averaging circuit is used. By determining whether to use a comb filter using a selection circuit and controlling a switching circuit, a comb filter output can be obtained in accordance with the content of the signal.

Example Below, regarding a color signal processing device which is an example of the present invention,
This will be explained with reference to the drawings. FIG. 1 shows a color signal processing device according to an embodiment of the present invention.

In Figure 1, "C11- is the bottom, 2 is the amplifier, and 3 is the A.
/D converter, 4 is a low-pass filter, 5 is a demodulation circuit, 6
is a first delay circuit, 7 is a second delay circuit, 8 is a first addition circuit, 9 is a first multiplication circuit, 10 is a second addition circuit,
11 is a second multiplication circuit, 12 is a first subtraction circuit, 13 is a second subtraction circuit, 1-4 is a third subtraction circuit, 15 is a conversion circuit, 16 is a third delay circuit, 17 is a selection circuit, 18 is a switching circuit, 19 is a modulation circuit, and 20 is a D/A converter.

The operation of the color signal processing device configured as described above will be explained below with reference to FIG.

A reproduced signal output from the head 1 is input to an amplifier 2. The output of the amplifier 2 is input to the A/D converter 3,
converted into a digital signal.

The reproduced signal converted into a digital signal is input to a low-pass filter 4, and color signal components are separated. The separated color signals are input to the demodulation circuit 5 and demodulated into two color difference signals. At the same time, the phase for each horizontal period is restored. The color difference signal output from the demodulation circuit 5 is the first
The signal is input to the delay circuit 6 and delayed by one horizontal period. The output of the first delay circuit 6 is input to the second delay circuit 7 and delayed by one horizontal period. The input and output of the first delay circuit 6 are added together in the first adder circuit 8, and the output of the first adder circuit 8 is set to 172 in the first multiplier circuit 9 to obtain the output of the first comb filter. obtain. The input and output of the second delay circuit 7 are added together in a second addition circuit 10, and the output of the second addition circuit 10 is made 172 in a second multiplication circuit 11 to obtain a second comb filter output. . Further, the input from the output of the first delay circuit 6 is subtracted by the first subtraction circuit 12. The input is subtracted from the output of the second delay circuit 7 by a second subtraction circuit 13. The input of the first delay circuit 6 is subtracted from the output of the second delay circuit 7 by a third subtraction circuit 14.

The output of the subtraction circuit 14 is converted by a conversion circuit 15 into two types of correlation information (correlated and non-correlated). If the absolute value of the output of the subtraction circuit l4 is greater than a predetermined constant value (denoted as K l ), no correlation is output, and if it is smaller than K1, a correlation is output. The output (■ bit) of the conversion circuit 15 is input to the third delay circuit 16 and delayed by the aqua regia early period. Switching circuit 1
8 switches between the first comb filter output and the second comb filter output in accordance with the control signal output from the selection circuit 17, and the selected output is modulated by the modulation circuit 19, and the D/ The A converter 20 converts the signal into an analog signal and outputs it as a reproduced color signal. In the selection circuit 17, the output of the first subtraction circuit 12, the output of the second subtraction circuit 13,
The output of the third delay circuit 16 is input, and based on these values, the output of the switching circuit 18 is selected and a control signal is output.

The selection circuit 17 is configured such that at least one of the absolute value of the output of the first subtraction circuit 12 and the absolute value of the second subtraction circuit 13 is smaller than a predetermined constant value (denoted as K 2 ). Sometimes, the absolute value of the output of the first subtraction circuit 12 and the absolute value of the output of the second subtraction circuit 13 are compared, and the absolute value of the l-th subtraction circuit 12 is the same as that of the second subtraction circuit 10. If it is smaller than the absolute values of paths 1 and 3, the first comb filter output is set as the output of the switching circuit 18, and the second subtraction circuit 13
If the absolute value of The absolute value of the arithmetic circuit 13 is the predetermined constant value (K
2), if the output of the third delay circuit 16 is uncorrelated, the output of the king comb filter is used as the output of the switching circuit, and if the output of the third delay circuit 16 is correlated, In this case, the output of the second comb filter is configured to be the output of the switching circuit.

When the amount of crosstalk received from adjacent tracks is small, the correlation between before and after one horizontal period can be determined by the first subtraction circuit 12 and the second subtraction circuit 13. In this case, Select the output that is more correlated with the one that forms a comb filter. When there is a large amount of crosstalk received from adjacent tracks, the third delay circuit 16 calculates the correlation by looking at the difference between the crosstalk and the portion two horizontal periods apart where the relationships between the signal components are in phase. The presence or absence is determined and the output of the comb filter is selected.

Effects of the Invention As described above, according to the present invention, by having a memory for two horizontal periods, it is possible to simultaneously check the correlation between a certain amount of the actual signal and the crosstalk components from adjacent tracks, and to calculate the correlation. By converting information into 1 bit and using this information with a 1-horizontal delay delay, it is possible to accurately detect the presence or absence of correlation without increasing the amount of memory, even when the amount of stalking is large. , due to the state of this correlation, 1
The output of a comb filter consisting of the horizontal period before the horizontal period, or
Color fading can be prevented by selecting a comb-shaped filter that is compatible with the interval after one horizontal period.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a color signal processing device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional color signal processing device. 1...Head, 2...Amplifier, 3...
...A. / D converter, 4...LPF,
5... Demodulation circuit, 6... First delay circuit, 7... Second delay circuit, 8... First addition circuit, 9 ......first multiplication circuit, 10.
... second addition circuit, 11 ... second multiplication circuit, ``-2 ... first subtraction circuit, l3 ...
... second subtraction circuit, 14 ... third subtraction circuit, 15 ... conversion circuit, 16 ... third delay circuit, 17. ...Selection circuit, 18...
...Switching circuit, 19...Modulation circuit, 20...
...D/A converter, 21...LPF, 22
...Frequency conversion circuit, 23...Delay circuit, 24...Subtraction circuit, 25...BP
F0

Claims (2)

[Claims] (1) A helical scan type video tape recorder that has multiple heads that frequency-modulates the luminance signal and converts the color signal to low-pass for recording.The playback signal output from the heads is passed through a low-pass filter. After the phase of the color signal separated from the reproduced signal is restored for each horizontal period, the color signal is divided into n horizontal periods (n is an integer) as a means of removing crosstalk received from adjacent tracks. A first delay circuit that delays the color signal output from the first delay circuit, a second delay circuit that delays the color signal output from the first delay circuit for n horizontal periods, and an average of the input color signal and output color signal of the first delay circuit. A first averaging circuit takes the average of the input color signal and the output color signal of the second delay circuit, and a second averaging circuit takes the difference between the input signal and the output signal of the first delay circuit. 1 subtraction circuit, a second subtraction circuit that takes the difference between the input signal and the output signal of the second delay circuit, and the difference between the input signal of the first delay circuit and the output signal of the second delay circuit. a third subtraction circuit that takes the difference; a conversion circuit that converts the output of the third subtraction circuit into a certain type of correlation value; and a conversion circuit that converts the output of the third subtraction circuit into correlation values of a certain type; ) a third delay circuit that delays the horizontal period; a switching circuit that outputs either the output of the first averaging circuit or the output of the second averaging circuit; the output of the first subtraction circuit; A color signal processing device comprising: a selection circuit that determines which of the outputs of the first-stage switching circuit should be output from the output of the subtraction circuit and the output of the third delay circuit. (2) The delay amount of the first delay circuit, the second delay circuit, and the third delay circuit is one horizontal period, and the correlation value output from the conversion circuit is a binary value of correlation and non-correlation, When the content of the selection circuit is that at least one of the absolute value of the output of the first subtraction circuit and the absolute value of the second subtraction circuit is smaller than a predetermined constant value, the selection circuit selects the first subtraction circuit. The absolute value of the output of the second subtraction circuit is compared with the absolute value of the output of the second subtraction circuit, and if the absolute value of the first subtraction circuit is smaller than the absolute value of the second subtraction circuit, the first averaging circuit The output is set as the output of the switching circuit, and if the absolute value of the second subtraction circuit is smaller than the absolute value of the first subtraction circuit, the second average circuit output is set as the output of the switching circuit, and the output of the first subtraction circuit is set as the output of the switching circuit. and the absolute value of the second subtraction circuit are both larger than the predetermined constant value, and if the output of the third delay circuit has no correlation, the output of the first average circuit is switched. The output of the switching circuit is set as the output of the switching circuit, and if the output of the third delay circuit has a correlation, the output of the second average circuit is set as the output of the switching circuit. color signal processing device.