JPS61148679A - Recording device of digital video signal - Google Patents

Abstract

PURPOSE:To perform reproduction of recording with narrower band of transmission by skipping the digital video signal data to be sampled at a prescribed sampling cycle at a rate one sample per N samples, and recording the skipped data. CONSTITUTION:The titled system is composed of a means 4 which skipps the data at every prescribed sampling cycle of the input digital video signal, and a means 5 which convert the skipped signal to be of the regular time sequence as the input digital video signal. The input video signal is skipped by the skipping circuit 4 at every prescribed sampling cycle. The band able to be demodulated by the sampling frequency of this input digital video signal is amply higher than the video signal band. Therefore, even after such skipping is executed, the original data can be completely reexpressed. The data lacking the part that is skipped is converted by the time base converting circuit 5 to be of an regular time sequence.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital video signal recording apparatus for recording a digital color video signal on, for example, a magnetic tape.

[Conventional technology]

When the composite color video signal 1 is digitized and recorded, its sampling frequency fs is set to the color subcarrier frequency fs of the carrier color signal for convenience in signal processing.
It is often taken as an integer multiple of c.

For example, the sampling frequency f3 of a composite color video signal of the NTSC system is the color subcarrier frequency (f5
c = 3.58FvHIz) four times the frequency (3,58X
4 = 14.32) MHz is often used.

The conventional digital video signal recording apparatus digitizes and records, for example, an NTSC system composite color video signal as it is, using a sampling frequency that is an integral multiple of the color subcarrier frequency fsc.

[Problem that the invention seeks to solve]

According to the sampling theorem, if sampling is performed at a sampling frequency twice the highest frequency, the original signal can be completely restored. Therefore, the frequency 4fsc (=14.32 MHz
), the frequency 2 f sc (
= 7.16MHz) can be restored. On the other hand, the highest frequency band of the NTSC composite color video signal is 4.5 MHz.

Therefore, the frequency of the NTSC color video signal is 4f.
When sampling is performed at the sc sampling frequency, the highest frequency that can be restored is up to 7.16 MHz, whereas the video signal band is 4.5 MHz, and 4.
The band from 5 Mllz to 7.16 MHz is a wasted band.

A conventional digital video signal recording apparatus digitizes and records an NTSC system composite color video signal as it is at a sampling frequency of, for example, 4 fsc. For this reason, the recorded signal includes a useless band. If the sampling frequency is determined so as not to create a wasted band, the problem arises that the correspondence between the sampling frequency fs and the color subcarrier frequency fsc disappears, making signal processing difficult.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a digital video signal recording apparatus that can reduce the amount of recorded information without causing difficulties in signal processing or deteriorating image quality.

The color subcarrier frequency of a PAL color video signal is 4.43M1(z), and the sampling frequency four times this color subcarrier frequency is approximately 1
The frequency becomes 7.7MHz. Therefore, in order to record a PAL system composite digital color video signal using a tape head transmission system for an NTSC system composite digital color video signal, the transmission band of the tape head transmission system is rather narrow.

Therefore, another object of the present invention is to produce a PAL system composite color video signal with a sampling frequency of 17.7 MHz by using the tape head system of a digital VTR for an NTSC system composite color video signal with a sampling frequency of 14.32 MHz. An object of the present invention is to provide a digital video signal recording device capable of recording video signals.

Furthermore, as recording methods for digital color video signals, there are two methods: digitizing and recording a composite color video signal, and digitizing each component (Y: luminance signal, U, V'? color difference signal) of the color video signal. There is a recording method. In the case of the component method, 13.5 MHz is recommended as the sampling frequency. In order to record a digital composite color video signal with a sampling frequency of 4 fsc using the tape head transmission system of such a component type digital VTR, the transmission band of the tape head transmission system is rather narrow.

Therefore, it is still another object of the present invention to record 14.32 MHz by using a component digital VTR tape head system with a sampling frequency of 13.5 MHz.
An object of the present invention is to provide a digital video signal recording device capable of recording a digital composite color video signal having a sampling frequency of Hz.

[Means for solving problems]

The present invention comprises a means 4 for thinning data of an input digital video signal at each predetermined sampling period, and a means 5 for converting the thinned digital video signal into the same time sequence as the input digital video signal. This is a digital video signal recording device characterized by:

[Effect]

The input digital video signal is thinned out by a thinning circuit 4 at every predetermined sampling period. The band that can be restored using the sampling frequency of this input digital video signal is sufficiently higher than the band of the video signal, so even if data is thinned out in this way, the original data can be completely reproduced. The thinned out data is converted into the same time sequence by the time axis conversion circuit 5 and recorded.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is an input terminal. An NTSC color video signal is supplied from an input terminal 1 to an A/D converter 3 via a low pass filter 2. The A/D converter 3 converts this color video signal to a frequency of 4f.
It is digitized using a sampling clock of sc (fsc: color subcarrier frequency). The output of the A/D converter 3 is supplied to a thinning circuit 4.

The thinning circuit 4 cuts off one sample of the input digital signal into six samples, for example, and sends out a thinned out output. That is, as shown in FIG. 2A, the A/D converter 3 outputs sampling data St , St ,
Syu,... is output, and this A/D converter 3
For the output of , data Sb, “S l
l+ S lll+ . . . are thinned out as shown in FIG. 2B.

The output of the thinning circuit 4 is supplied to the time axis conversion circuit 5. The time axis conversion circuit 5 is constituted by a memory, and the thinning circuit 4
By writing the output of once to the memory and reading the data written to the memory using a read clock with a frequency 5/6 times that of the sampling clock fs, the sampling period becomes uneven due to the thinned out data. The data shown in FIG. 2B forms continuous data having the same time sequence as the input digital color video signal in the sense that it has the same sampling period.

The output of the time axis conversion circuit 5 is supplied to an encoder 6, where it undergoes processing such as error correction code encoding.

The encoder 6 is supplied with sync data from a terminal 7, and the sync data is inserted every predetermined amount of digital data. The output of the encoder 6 is supplied to the rotary head 8,
A digital video signal is recorded on a magnetic tape 9 by a rotary disc 8.

In an NTSC color video signal, for example, frequency 4
The number of samples in one horizontal section when digitized using the fsc sampling pulse is 9, as shown in Figure 3A.
There are 10 samples. As shown in one example above, 6
One sample data is thinned out for each sample (and the number of samples becomes (910x5/6=758.3) samples.

These 759 samples are processed by the time axis conversion circuit 5, thereby reducing the sampling frequency. Therefore,
The data rate of digital signals recorded on the magnetic tape 9 is lowered, and recording and reproduction can be performed in a narrower transmission band.

FIG. 4 shows an example of a reproducing apparatus for reproducing a digital video signal recorded by a recording apparatus to which the present invention is applied.

A digital video signal recorded on a magnetic tape 10 is supplied from a rotary disk 11 to a decoder 12. The decoder 12 subjects the input data to processing such as decoding of an error correction code. The output of the decoder 12 is the time axis conversion circuit 13
supplied to The time axis conversion circuit 13 includes sampling data S thinned out in the recording device shown in FIG.
Data missing sections are provided at positions corresponding to S, z, 5Iff+....

The output data of the time axis conversion circuit 13 corresponds to the output of the thinning circuit 4 (FIG. 2B) in the recording apparatus shown in FIG. At the same time, an interpolation flag indicating that data is missing is generated corresponding to the portion where the data missing section has been inserted.

The output of the time axis conversion circuit 13 is supplied to an interpolation circuit 14. The data supplied to the interpolation circuit 14 lacks data Sh, Stz, Sts, . . . every six samples. These missing data S by the interpolation circuit 14
i, Sl! , St. , ... are interpolated.

The output of the interpolation circuit 14 is supplied to the D/A converter 15 and converted from a digital signal to an analog signal. D/
The output of the A converter 15 is supplied to an output terminal 16, from which a reproduced analog video signal is taken out.

The interpolation circuit 14 can be realized, for example, by the configuration of an FIR digital filter shown in FIG.

In FIG. 5, ten delay circuits 21 are connected in cascade.
A terminal 19 is derived from one end of .about.30, and an interpolation flag indicating that data is missing is supplied from the terminal 19. The output from the other end of the cascaded delay circuits 21 to 30 is supplied to the switch circuit 51 as a switch control signal.

An input terminal 20 is led out from one end of ten delay circuits 31 to 40 connected in cascade, and thinned data in which one sample is missing every six samples is supplied from the terminal 20. Outputs from the other ends of the cascaded delay circuits 31 to 40 are supplied to an input terminal 51A of the switch circuit 51. Outputs from the connection point between the input terminal 20 and the delay circuit 31 and the connection points of the delay circuits 31 to 35 are supplied to multiplication circuits 41 to 45, respectively. Connection points of delay circuits 36 to 40 and delay circuit 4
The outputs of 0 are supplied to multiplication circuits 46-50, respectively. The multiplication circuits 41 to 45 have coefficients of -5, -4, -3, and -.
This is a multiplication circuit that multiplies 2 and -1, respectively. Multiplication circuit 46
~50 is a coefficient of 1°k2. This is a multiplication circuit that multiplies , , , and , respectively. The outputs of the multiplication circuits 41 to 50 are supplied to the addition circuit 52.

Five delay circuits 5 in which the outputs of the adder circuit 52 are connected in cascade.
3 to 57. The outputs of the delay circuits 53 to 57 connected to the I line are input to the input terminal 51B of the switch circuit 51.
supplied to The output of the output terminal 51C of the switch circuit 51 is supplied to the output terminal 58 and taken out from the output terminal 58.

While no data is missing, the input terminal 51A and the output terminal 51C of the switch circuit 51 are connected, and the input terminal 2
Data from 0 is taken out from output terminal 58 via delay circuits 31-40. When missing data is supplied from the input terminal 20, a flag indicating data missing is supplied from the terminal 19. When the flag supplied from the terminal 19 is supplied to the switch circuit 51 via the delay circuits 21 to 30, the input terminal 51B and the output terminal 51C of the switch circuit 51 are connected. Therefore, the output of the adder circuit 52 is taken out from the output terminal 58 via the delay circuits 53 to 57. The flag supplied to the switch circuit 51 is supplied via ten delay circuits 21-30. The output of the adder circuit 52 is sent to five delay circuits 53 to 57.
The signal is supplied to the input terminal 51B of the switch circuit 51 via. Therefore, when the flag is supplied to the switch circuit 51 via the delay circuits 21 to 30, the interpolated data obtained from the five samples before and after the missing data is sent to the delay circuit 51.
Obtained from 7. This interpolated data perfectly reproduces the missing data, assuming that the characteristics of this filter are completely flat within the band of the video signal and there is no phase delay.

This interpolated data is taken out from output terminal 58.

Note that the present invention is applicable not only to NTSC color video signals but also to PAL color video signals. Further, it is also applicable in the same way when, for example, a frequency of 3fscO is used as the sampling frequency fs.

〔Effect of the invention〕

According to this invention, digital video signal data at each predetermined sampling period is thinned out by one sample to N samples,
Since thinned data is recorded, the data rate of the recorded digital signal is lowered, and recording and reproduction can be performed in a narrower transmission band. However, the sampling frequency is an integral multiple of the color subcarrier frequency f's, for example 4fsc, and the band that can be restored by this sampling frequency is sufficiently wider than the band of the video signal. Therefore, the thinned out data can be completely reproduced by interpolation, and there will be no difficulty in signal processing or deterioration of image quality.

In addition, since recording and playback can be performed in a narrower transmission band, it is possible to record and reproduce 17.7M by using the tape head system of a digital VTR for an NTSC system composite color video signal with a sampling frequency of 14.32MHz.
It is possible to record PAL composite color video signals with a sampling frequency of Hz or component digital VT with a sampling frequency of 13.5MHz.
Using the R tape head system, it is possible to record a digital composite color video signal with a sampling frequency of 14.32 MHz.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a route map used to explain an embodiment of the present invention, FIG. 3 is a route map used to explain digital data to be recorded, and FIG.
The figure is a block diagram of an example of a reproducing apparatus for reproducing a digital video signal recorded by a recording apparatus to which the present invention is applied, and FIG. 5 is a block diagram of an example of an interpolation circuit in the reproducing apparatus. 1: input terminal, 3: A/D converter, 4: thinning circuit, 58 time axis conversion circuit.

Claims (1)

[Claims] means for thinning out data for each predetermined sampling period of the input digital video signal; time axis conversion means for converting the thinned out digital video signal into the same time sequence as the input digital video signal; 1. A digital video signal recording device comprising: means for recording the output signal of the time axis conversion means on a recording medium.