JPS61216587A - Digital processing circuit for color video signal in recording and reproducing system - Google Patents

Abstract

PURPOSE:To eliminate the deterioration in S/N by providing a Y/C separating circuit for separating a digitized color video signal into a brightness signal and a color signal, an automatic color control (ACC) circuit for adjusting a level of the separated color signal to a predetermined level, and a synthesizing circuit for synthesizing the color signal outputted from this ACC circuit with the brightness signal again in a processing circuit. CONSTITUTION:When a color signal passes through a band pass filter 7, if the band pass filter 7 is constituted of a delay circuit 7a of 2tau and an adder 7b, a color signal of N bit is increased to N+1, and if there is further subse quent band pass filter, the number of the bits of the outputted color signal is increased. From a Q characteristic of the band pass filter 7, a signal informa tion lost on digitizing can be restored. The number of bits of the color signal increased by the band pass filter 7 is rised in level, for instance, based on a burst signal, in the next ACC circuit to have a predetermined level of the color signal. The color signal rised in level is synthesized with a Y signal again in an adder 10 to be supplied to a recording and reproducing device 12, for instance, of a VTR, etc.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a digital processing circuit for a composite color video signal suitable for converting a composite color video signal into a digital signal, and recording and reproducing the signal. be. .

[Summary of the invention]

Converts the composite power radio signal into a digital signal
A digital signal circuit that converts the signal back into an analog signal after playback; the color signal is extracted from the converted composite color video signal into a digital signal, the extracted color signal is adjusted to a predetermined level, and then the luminance signal is converted into a digital signal. Combined with digital composite color video transmission again! Therefore, the quantization noise of the color signal is reduced, and the deterioration of the video signal due to dubbing can be alleviated.

[Conventional technology]

Generally, when a composite color television signal (hereinafter simply referred to as a color video signal) is repeatedly recorded and reproduced, the signal quality deteriorates each time.

One method for solving this problem is to record color video signals as digital signals, but in this case as well, quantization noise is generated during the analog-to-digital conversion process.

By the way, the width of the IVp-p color video signal is usually 0.7Vp-p for the luminance signal (hereinafter referred to as the Y signal), while the width of the color burst signal is 0.3■p-p'.
For example, if such a color video signal is converted to an 8-bit foot degree, a simple calculation of lζ will result in quantization noise t, so the S/N of the Y signal is approximately 4.
5da, whereas the color burst signal S/
N is approximately 37°3 dB, and the S/N of the color signal is generally poor.

Therefore, even when using the digital reproduction method, if taching is repeated, quantization noise will cause the S of the color signal to change.
/N becomes markedly degraded, and this tendency is especially noticeable when the color signal level decreases in the transmission system.
/N becomes worse, resulting in deterioration of image quality.

[Problem that the invention seeks to solve]

Therefore, A/D is used to alleviate such problems.

Either increase the conversion bit number of the D/A converter, or separate the color video signal into the Y signal and color signal before converting it to a digital signal, raise the rail of only the color signal, and combine it with the Y signal again. It is conceivable that the signal is then converted into a digital signal, but the former method has the disadvantage that the A/D-D/A converter becomes expensive, increasing the cost of the entire recording/reproducing system. In addition, the latter method has the disadvantage that the Y signal and the color signal are separated in an analog manner and then combined again, so signal deterioration is likely to occur, and it is difficult to integrate the circuit into an IC.

This invention was made to solve this problem. After converting a color video signal to a digital signal, the rail of the color signal is adjusted before recording and playback, thereby reducing the S/N. The present invention provides a digital processing circuit for color video signals in a recording/reproducing system that reduces the amount of noise.

[Means for solving problems]

After the color video signal is converted into a digital signal by an A/D converter, the color signal is separated by an IH delay circuit, a band 9-pass filter, etc. Then, the separated color signals are converted to an ACC (Automatic Color Control).
rol) After the color signal is railed up to an appropriate level by the circuit, it is combined with the Y signal again to form a digital color video signal, which is then used for recording and playback.

[Effect]

The separated digital color signal has a smaller dynamic range than the Y signal, and has a higher attenuation in the transmission path, so the S/N is generally poorer, but the digitized color signal is processed using a digital bandpass filter. Since the number of bits increases due to the arithmetic operation, the rail of the color signal can be easily increased by shifting the increased number of bits in the ACC circuit.

As a result, quantization noise generated during recording and reproduction can be reduced.

〔Example〕

FIG. 1 shows a digital processing circuit for color video signals in the recording/reproducing system of the present invention, where l is an A/D converter that converts the color video signal into a digital signal, for example 4fsc (fsc is the color The sample time is the period of the subcarrier frequency). 11 indicates a digital processing circuit for digitized color video signals, 2 is an IH delay circuit, 3 is an adder, 4 is a subtracter, 5 is a delay circuit for phase adjustment, and 6 is a 3.58 MHz±500K
A trap circuit that traps the range of H and z, 7 is a punt 5Z filter for extracting color signals, and 8 is an AC
C circuit, 9. is an adder.

Further, 12 is a recording/reproducing device for recording a digitally processed color video signal, such as a magnetic tape (VTR),
This applies to recording/playback devices using disks, memories, etc.

Furthermore, 13 is a D/A converter which converts the color video signal reproduced as a digital signal into an analog signal.

In this invention, the color video signal converted into a digital signal as described above is processed by an IH delay circuit which is constructed of a digital circuit as is well known. , an adder 3, and a subtracter 4 into a Y signal component and a color signal component, and a complete Y signal is formed via a trap 6 and an adder 9.

On the other hand, the color signal extracted by the band nine-pass filter configured with digital circuits is sent to the next ACC circuit 8.
After being adjusted to a predetermined standard, the adder 10 synthesizes it with the Y signal again to produce a J-digitized color video signal. By the way, the A/D converter 1 Generally, as mentioned above, the color signal properties of digital color television signals converted by the digital color TV signal are significantly reduced in the transmission system. , the dynamic range of the converted color signal is 1/
lO, that is, 2 for the number of conversion bits of the regular color signal.
~3 bits smaller, increasing quantization noise. Therefore, each time such a signal is recorded or reproduced, the color signal deteriorates significantly.

Therefore, in the case of the present invention, a color signal digitized by Y/C separation is extracted, added to the ACC circuit 8, and uploaded to a predetermined rail.

In this case, when the color signal passes through the band 9 pass filter 7, for example, as shown in FIG.
If a band 9 filter is configured with adder 7b, the N-bit color signal will increase to N+1 bits, and if there is a subsequent band 9 filter, the number of bits of the output color signal will be To increase. Then, signal information lost during digitization can be recovered from the Q characteristic of the bandpass filter 7. Note that although the color signal is averaged over time, the band of the color signal is at most f me±500 KHz, so this does not pose much of a problem.

The number of bits of the chrominance signal increased by the 9-pass filter '7 is properly looped up in the next ACC circuit 8, for example, using the burst signal as a reference, and is set to a predetermined chrominance signal level.

This rail-up is an increased color signal digital coat 9
This can be easily done by shifting the signal.

Then, the properly Lubricated color signal is again sent to the adder 10 and combined with the Y signal, and is supplied to a recording/reproducing device 12 such as a VTR.

However, according to this method, it is possible to record and re-record without significantly increasing the quantization noise of color signals whose level tends to drop due to transmission lines and other factors, so even when dubbing is repeated, S /N can be reduced.

FIG. 3 shows a block diagram in which the i-digital processing circuit 11 is provided on the playback side of the recording/playback device 12, and the same parts as in FIG. 1 are given the same reference numerals. In this embodiment as well, the quality of the color video signal converted into an analog signal by the D/A converter 13 can maintain the same S/N ratio as in FIG.

FIG. 4 shows still another embodiment of the invention,
The color signal railed up by the digital processing circuit 11 is Y
The recorded voice is also ρ, which is recorded on the two-channel recording/playback device full 2' without being combined with the signal. After reproduction, the adder 10 converts the signal into a color video signal, and the D/A converter 13 converts the signal into an analog signal.

[Invention effect]

□ As explained above, the digital processing of the color video signal in the recording/reproduction system □ of the present invention involves converting it into a digital signal, performing Y/C separation, and extracting the color signal through a pan-P nose filter. Later, in addition to the ACC circuit, the signal is adjusted to a predetermined level, so that it is possible to reduce the decrease in the S/N ratio of the color signal, which tends to deteriorate due to repeated dubbing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a digital processing circuit for color video signals according to the present invention, FIG. 2 is an explanatory diagram of a digital low-pass filter, and FIG. FIG. 4 is a block diagram showing another embodiment of the invention. In the figure, 1 is an A/D converter, 2 is an IH delay circuit, 3.9.
10 is an adder, 4 is a subtracter, 5 is a delay circuit, 6 is a trap circuit, 7 is a band 9 filter, 8 is an ACC circuit, 12 is a recording/reproducing device, and 13 is a D/A converter. ;, −, I, j

Claims (1)

[Claims] Converts composite color video signals to digital signals and records/records them.
In a recording/playback system that converts the composite color video signal into an analog signal after playback, between an A/D converter that converts the composite color video signal into a digital signal and a D/A converter that converts the digital signal into an analog signal, A Y/C separation circuit that separates a digitized color video signal into a luminance signal and a color signal, an ACC circuit that adjusts the level of the separated color signal to a predetermined level, and a color signal output from the ACC circuit. 1. A digital processing circuit for a color video signal in a recording/reproducing system, characterized in that a synthesis circuit for synthesizing the luminance signal and the luminance signal again is provided.