JPH0134518B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for processing color video signals that can be used in video tape recorders and the like.

Conventional configurations and their problems In consumer color video tape recorders (VTRs) that are currently widely used,
The luminance signal occupies the recordable high band side.
The carrier color signal is converted into an FM signal, and the carrier color signal is frequency-converted to the lower frequency side of the FM luminance signal, and a frequency multiplexed signal of these FM luminance signals and the carrier color signal that has been low-frequency converted is recorded on a magnetic tape. . During playback, the FM luminance signal and the low-frequency converted carrier color signal are separated from the reproduced multiplexed signal, and the original luminance signal is demodulated from the FM luminance signal, and the low-frequency converted carrier color signal is demodulated from the FM luminance signal. The color signal is frequency converted to the original frequency band. Color signal processing in such a recording method is quite complex, and this has been a problem in simplifying the VTR circuit. In addition, especially for recent consumer
VTRs use guard bandless azimuth recording to achieve high recording density, but in this case, the phase of the carrier color signal is changed for each horizontal line to prevent crosstalk between adjacent tracks to the color signal. The system is configured so that the phase is returned for each line during playback, and a 1H comb filter is placed on the playback output side. Such processing not only complicates the circuit, but also
A glass delay line is required to construct the comb filter, which poses a problem in terms of miniaturization.

Purpose of the Invention The purpose of the present invention is to simplify the color signal processing circuit of a VTR and to make it possible to implement it on an LSI by using a configuration that does not use a glass delay line, thereby reducing the size and cost of the circuit. The object of the present invention is to provide a processing method.

Structure of the Invention The color video signal processing method of the present invention adds a phase change to the reproduced low-frequency conversion carrier color signal, which is opposite to the phase change in units of fields and lines received on the recording side, and then combs the reproduced low-frequency conversion carrier color signal. As a result, the comb filter can process the frequency band of the low-frequency conversion carrier color signal, making it possible to use semiconductors using CCDs (charge-coupled devices) and digital memories. This makes it possible to miniaturize the circuit and reduce costs.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in comparison with conventional examples.

Figure 1 shows a typical consumer azimuth recording VTR.
FIG. 2 is a schematic configuration diagram of a reproduction side color signal processing system. (Actually, a circuit for eliminating time axis fluctuations is involved, but it is omitted to avoid complicating the explanation.) The color video signal reproduced by the magnetic tape and rotating head is processed by a low-pass filter to convert the reproduced low-thorn conversion carrier color signal A. separated and applied to frequency converter 1. A head switching signal B from the rotating cylinder and a horizontal synchronizing signal C extracted from the reproduced color video signal are applied to a phase converter 2. The phase converter 2 generates a local oscillation frequency for frequency conversion with the reproduced low frequency conversion carrier color signal A, and changes the phase of each line by a head switching signal and a horizontal synchronizing signal.
The phase change for each line is controlled so that the phase change is in the opposite direction to the phase change made to the conveyed color signal during recording. Frequency converter 1 and phase converter 2
The reproduced low frequency conversion carrier color signal A is returned to the high frequency range by the band pass filter (BPF) 3, and the NTSC
In this method, the color signal is centered around 3.58MHz.
The color signal returned to 3.58MHz has crosstalk components from adjacent tracks removed by a comb filter, and a carrier color signal D is output. In this way, the conventional reproduction side color signal processing system changes the phase of the low-pass converted carrier color signal during frequency conversion, returns it to the carrier color signal, and then passes it through a comb filter.

FIG. 2 is a schematic diagram of a reproduction side color signal processing system showing an embodiment of the present invention. The reproduced low-pass converted carrier color signal A passes in this order through a phase converter 5, a comb filter 6, a frequency converter 7 to which a local oscillator 8 is coupled, and a bandpass filter 9, and is converted into a carrier color signal D. The difference from the conventional example shown in FIG. 1 is that before frequency conversion, a phase change is applied and the signal is passed through a comb filter. The phase converter 5 applies a predetermined phase change to the inputted low-pass conversion carrier color signal A in a direction opposite to that during recording for each line using a head switching signal B and a horizontal synchronizing signal C. The comb filter 6 functions to remove crosstalk components from adjacent tracks from the phase-changed low-pass converted carrier color signal. The principle by which adjacent crosstalk components are removed by the comb filter 6 while maintaining the low-pass conversion carrier color signal will be explained with reference to FIGS. 3 and 4.

Figure 3 shows the phase relationship of the low-pass conversion carrier color signal.
FIG. 3 is a diagram showing the case of VHS system. During recording, the phase of the A track is shifted in the direction of advancing by 90 degrees line by line, changing as shown by the arrow a. In other words, if it is 0 degrees on line 1, it will advance 90 degrees on line 2, 180 degrees on line 3, 270 degrees on line 4, return to the same state as line 1 on line 5, and repeat the same changes thereafter. In the B track, the phase is shifted in the direction of delay by 90 for each line, and changes as shown by the arrow b. During playback, the phase shifter 5 applies a phase shift in the opposite direction to that during recording, so that the playback output of track A, for example, has its phase returned to its original state, as shown in c. Generally, when reproducing the A track, a portion of the B track signal is also picked up as adjacent crosstalk, and this is indicated by a broken arrow. The phase b of the adjacent crosstalk component is phase-shifted by 90 degrees in the lag direction. d represents a signal delayed by one line (usually called 1H) from c. e is the playback output c of A track.
It is the sum of the signal d delayed by 1H,
As a result, the adjacent crosstalk components indicated by the broken lines have opposite phases and cancel each other out, so that only the A-track signal is extracted. Here, the signal of c and d
Adding means passing through a comb filter. In other words, when the A-track output c is expressed as a spectrum, it is shown in FIG. 4a. The low frequency conversion carrier color signal in the VHS system has a band of approximately ±500KHz centered around _40H ( _H is the line frequency) _,
The distribution has a peak at each point. On the other hand,
Since the phase of the crosstalk component is reversed line by line as shown by the broken line in Figure 3c, its spectrum falls into the _H interval. Therefore, by passing the signal through a Y-shaped comb filter having the characteristics shown in FIG. 4b, the main signal for each _H is extracted and the crosstalk component is removed. As described above, adjacent crosstalk can be removed by returning the phase shift and then passing the low frequency conversion carrier color signal as it is through the Y-shaped comb filter.

The low frequency converted carrier color signal from which adjacent crosstalk has been removed by the comb filter 6 is sent to a frequency converter 7;
The frequency is converted to a predetermined band (3.58 MHz in the case of NTSC system) by a local oscillator 8 and a bandpass filter 9, and a carrier color signal D is obtained.

In the configuration shown in Fig. 2, the band used by the comb filter 6 is the low frequency conversion carrier color signal (629KHz± in the VHS system).
500KHz) band is sufficient. Therefore, it is easy to use a semiconductor analog delay circuit such as a CCD for the 1H delay circuit that is a component of the comb filter. In other words, if a CCD were to be used for the 1H delay when returning to 3.58MHz as in the conventional example, a high clock frequency would be required and the number of CCD stages would increase, making it difficult to implement in terms of performance and cost. On the other hand, a 1H delay at 629KHz requires a lower clock frequency and fewer stages, which is advantageous in terms of performance and cost. As described above, in the embodiment shown in FIG. 2, the comb filter can be easily constructed from a semiconductor such as a CCD, and the circuit can be easily miniaturized.

FIG. 5 is a block diagram of a reproduction side signal processing system showing another embodiment of the present invention. The reproduction low-pass conversion carrier color signal A is converted into a digital color signal E by the AD converter 10, and a phase change is applied to the phase converter 11.
Passes through digital comb filter 12 to DA converter 1
3 returns it to an analog signal and local oscillator 1
5 is restored to a carrier color signal by a frequency converter 14 and a bandpass filter (BPF) 16 coupled thereto. The difference from the embodiment of FIG. 2 is that the phase conversion and comb filter are performed on the digital signal of the low-pass conversion carrier color signal. Phase converter 11
This applies a phase change to the digital signal as it is, and an example of its operation is shown in FIG. In the VHS system, it is necessary to realize advances and delays in 90° increments. 6A is an input analog signal, which can be considered as part of the low frequency conversion carrier color signal. A is for a phase shift of 0°, and each sample value of the input signal is
S ₁ , S ₂ , S ₃ , S ₄ , S ₅ , S ₆ . . . are, for example, 6-bit digital values. (The figure shows the state converted to analog.) The signal A is delayed by 90° (270°
The advanced) signal is C, and this is achieved by delaying each sample value obtained in A by one sample period (in this case, the sample frequency is four times the frequency of the low-pass conversion carrier color signal). The 90° lead (270° lag) signal is obtained by delaying each sample value of A by one sample period and further reversing its analog polarity (eg, taking the complement for digital values). Although not shown, a 180° lead or lag can be easily realized by making each sample value in A reverse polarity in an analog manner. in this way,
By delaying and inverting the sampled digital signal, the phase of the digital signal can be shifted.
The configuration of a digital comb filter can be realized using a 1H digital memory and an adder. FIG. 7 shows an example of the configuration of a digital comb filter. Input F is a digital value obtained by phase shifting the low-pass conversion carrier color signal, and this signal is applied to 1H memory unit 17 and adder 18. A digital signal delayed by 1H is also applied to the adder 18, and its output becomes a digital signal passed through a Y-shaped comb filter. In this way, a comb filter can be easily realized using digital signals. In the embodiment shown in FIG. 5, since phase conversion and comb filtering are performed using digital signals, it is possible to realize a predetermined operation with higher precision and without performance deterioration compared to conventional analog processing. In particular, conventional comb filters use glass delay lines, and it has been difficult to obtain ideal comb characteristics due to various reasons such as variations in the delay time, spurious waves due to reflection, and fluctuations in frequency characteristics in the pass band. On the other hand, with a digital comb filter, an ideal comb filter can be easily obtained.
Further, the AD converter 10 and the DA converter 13 are
It is sufficient to cover the band of the low-pass conversion carrier color signal,
For example, compared to processing in the 3.58MHz band, it can be done on an extremely small scale.

Although the above embodiment mainly describes color signal processing of the VHS system, it goes without saying that it can be implemented in exactly the same way for a system such as the β system, which processes only by a 180° relationship without using 90° for phase shift. .

Effects of the Invention As is clear from the above description, the present invention applies a phase change to the reproduced low-frequency conversion carrier color signal, which is opposite to the phase change in units of fields and lines received on the recording side. Since the signal is passed through a comb-shaped filter, the phase shift required in the reproduction side color signal processing system and the comb-shaped filter can be realized in the low-frequency conversion carrier color signal band.
The above-mentioned functions can be implemented as a semiconductor using a CCD or the like, and it is also easy to convert them into digital signals and process them. Therefore, the signal processing system on the playback side can be implemented as a single-chip LSI, and extremely useful effects such as cost reduction and space occupancy can be achieved by reducing the number of parts and adjustment processes.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a conventional reproduction side color signal processing system in a VTR, FIG. 2 is a schematic block diagram of a reproduction side color signal processing system according to an embodiment of the present invention, and FIGS. The figure is a principle diagram for explaining the principle of the present invention, FIG. 5 is a schematic block diagram of a reproduction side color signal processing system according to another embodiment of the present invention, and FIG. 6 is an explanation of the operation of the phase converter. FIG. 7 is a block diagram showing an example of the configuration of a digital comb filter. 5... Phase converter, 6... Comb filter, 7... Frequency converter, 8... Local oscillator, 9... Bandpass filter, 10... AD converter, 11... Phase converter, 12... Digital comb filter, 13... D.A.
Converter, 14... Frequency converter, 15... Local oscillator, 16... Band pass filter.

Claims (1)

[Scope of Claims] 1. Converting the reproduced low frequency conversion carrier color signal into a digital signal and digitally processing it to give a phase change that is opposite to the phase change processed for each field and line during recording, A color video signal processing method characterized in that the signal is then passed through a digital comb filter. 2. The color video signal processing method according to claim 1, wherein the phase change due to digital processing is constructed by delaying and inverting the digital signal. 3. The color video signal processing method according to claim 1, wherein the digital comb filter includes a one-horizontal scanning period delay circuit using a digital memory and an adder.