JPH02125587A - Recording and reproducing system for video signal - Google Patents

Abstract

PURPOSE:To improve the S/N of a video information part and to express video information in detail by providing a circuit compressing a synchronizing signal component in an input video signal and a circuit expanding the synchronizing signal so as to expand the relative dynamic range of a video information signal part. CONSTITUTION:A composite video signal inputted to an input terminal 1 at recording is separated into a luminance signal and a chrominance signal. Only the synchronizing signal component of the luminance signal is compressed by a synchronizing signal compression circuit 3. Then a video signal picked up from a tape by a video head 7 is separated into an FM modulation luminance signal and a low frequency conversion chrominance signal. The FM modulation luminance signal is demodulated by a luminance signal demodulation circuit 9 and the synchronizing signal is decoded to a proper level by a synchronizing signal expansion circuit 10. The relative dynamic range of the video signal part by the compression of the synchronizing signal is expanded to improve the S/N of the video information part at reproduction thereby expressing the video information in more detail.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for recording and reproducing video signals, and more particularly to a method for recording and reproducing video signals that records and reproduces luminance signals.

[Conventional technology]

Conventionally, video tape recorders, electronic still cameras, etc. have been used as recording and reproducing devices for this type of video signal, but these devices separate the input composite video signal into a color signal and a luminance signal. is FM modulated and recorded on a recording medium. In addition, in these devices, the S/N
As a means of improvement, emphasis is carried out by emphasizing the high frequency components of the input signal and then subjecting it to FM modulation and compressing the high frequencies during playback.

[Problem to be solved by the invention]

Emphasis in the conventional video signal recording and reproducing system described above is applied only to the input signal itself. However, the part that you actually want to increase the S/N is the actual video information part of the input video signal, and for simple pulse signals such as synchronization signals, there is no need to increase the S/N, and the S/N does not need to be increased. Even if the deterioration of N is large, it is possible to reproduce a stable waveform by using a pulse shaping circuit or the like. On the contrary, by treating these synchronization signals exactly the same as video information components, the dynamic range of the video information components is suppressed.

The object of the present invention is to
An object of the present invention is to provide a video signal recording and reproducing method that can improve the /N ratio and express video information in detail in an apparatus that records and reproduces video signals as digital.

[Means to solve the problem]

The video signal recording and reproducing method of the present invention includes a circuit that compresses the synchronization signal component in the input video signal by performing nonlinear operations, and a circuit that demodulates the luminance signal in the video signal read by the video head and expands the synchronization signal. and is configured to expand the relative dynamic range of the video information signal section.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a video signal recording and reproducing circuit for explaining one embodiment of the present invention, and is an embodiment in which the present invention is applied to a color under one-type VTR.

As shown in FIG. 1, during recording, a composite video signal input to an input terminal 1 is separated into a luminance signal and a color signal by a Y/C+ separating circuit 2 at the next stage. Of these, only the synchronization signal component of the luminance signal is compressed by the synchronization signal compression circuit 3, and FM modulated by the luminance signal FM modulation circuit 4.

On the other hand, the color signal is low-frequency converted by a low-frequency conversion circuit. These FM modulated fourth degree signals and low frequency converted color signals are mixed and then sent to the video head 7 by the recording amplifier 6.
recorded on tape.

Next, during playback, the video signal picked up from the tape by the video head 7 is transferred to the playback preamplifier 8.
After being amplified by FM, a filter (not shown)
It is separated into a modulated luminance signal and a low frequency converted color signal. This F
The M modulated luminance signal is demodulated by a luminance signal demodulation circuit 9,
A synchronization signal expansion circuit 10 restores the synchronization signal to an appropriate level. On the other hand, the low frequency converted color signal is restored to its original frequency by the high frequency conversion circuit 11. The restored luminance signal and color signal are mixed and output to the output terminal 12 as a composite video signal.

FIG. 2 is an input/output voltage characteristic diagram of the synchronization signal compression circuit shown in FIG. 1.

As shown in FIG. 2, the input luminance signal 13 is clamped in advance so that the pedestal level is always at the potential at point A, and is input to this synchronizing signal compression circuit. On the other hand, the synchronizing signal output voltage of this circuit is compressed as shown in the output waveform 14.

FIG. 3 is an input/output voltage characteristic diagram of the synchronization signal expansion circuit shown in FIG. 1.

As shown in FIG. 3, this input/output characteristic is the inverse of the input/output characteristic shown in FIG. , and the sync signal is expanded. Finally,
The levels of the synchronization signals are equal upon input, such as signals 13.16.

The above-described synchronous signal compression circuit 3 and synchronous signal expansion circuit 1
The characteristic curve like 0 does not need to be a perfect polygonal line characteristic, and the same can be said of characteristic curves like the dotted lines shown in FIGS. 2 and 3. In this case, the current-voltage characteristic (I -V characteristics) etc., it can be realized relatively easily.

FIG. 4 is a characteristic diagram of analog input and digital output when the synchronization signal shown in FIG. 1 is corrected and expanded by a digital circuit.

As shown in FIG. 4, in such compression and expansion, the compression ratio is considered to be 1/2. First, the conversion characteristics of the AD converter for the input signal 17 are as shown in the figure. Here, N.

is the digital data obtained by A/D converting the pedestal level of the input signal, and when compressing the converted digital data, the data below No. is Y= (1/2)X,
For data above No, Y=X(], / 2 > No
By performing arithmetic processing such as this, the synchronization signal is compressed to 1/2 on the digital data. Also, if the digital data corresponding to the pedestal level after compression is Ns, then when decompressing, the data below N5 is Y=2X, N
, the synchronization signal is expanded twice by performing arithmetic processing such as Y-X + 2 N s on the above data.

In this example, compression and expansion can be made to have perfect polygonal characteristics as shown in the figure, and improvement in waveform reproducibility can be expected.

〔Effect of the invention〕

As described above, the video signal recording/reproducing method of the present invention increases the relative dynamic range of the video signal portion by compressing the synchronization signal. As a result, for example, if the compression ratio of the synchronization signal is set to 1/2 and the ratio of the video level of the input video signal to the synchronization signal level is 10 = 4, the ratio of the video level will be 10/14 = 5/7 due to compression. What was 10/
12=5/6, that is, about 1.16 times. This expansion rate can be further increased by reducing the compression ratio of the synchronization signal. This expansion of the relative dynamic range results in an expansion of the deviation of the video signal component during FM modulation, for example, and increases the deviation of the video signal component during playback.
This has the effect of improving N.

Furthermore, in an apparatus that records and reproduces video signals in digital form, the resolution of the video information section is relatively increased, and the video information can be expressed more precisely.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a video signal recording/reproducing circuit for explaining one embodiment of the present invention, FIG. 2 is an input/output voltage characteristic diagram of the synchronization signal compression circuit shown in FIG. 1, and FIG. FIG. 4 is a characteristic diagram of analog input and digital output when the synchronization signal shown in FIG. 1 is compressed and expanded by a digital circuit. 1...Input terminal, 2...Y/C separation circuit, 3...
Synchronous signal compression circuit, 4... Luminance signal FM modulation circuit, 5
. . . Low frequency conversion circuit, 6 . . . Recording amplifier, 7 .・
High frequency conversion circuit, 12... Output terminal, 13... Input waveform of the sync signal compression circuit, 14... Output waveform of the sync signal compression circuit, 15... Input waveform of the sync signal expansion circuit, 1
6...Output waveform of the synchronization signal expansion circuit, 17...AD
Converter input signal.

Claims (1)

[Claims] The video information signal section includes a circuit that compresses the synchronization signal component in the input video signal by performing nonlinear operations, and a circuit that demodulates the luminance signal in the video signal read by the video head and expands the synchronization signal. A video signal recording and reproducing method characterized by expanding the relative dynamic range of a video signal.