JPS62137994A - Video signal processor - Google Patents

Abstract

PURPOSE:To reduce noises to improve the picture quality by emphasizing a time base-compressed luminance signal and chrominance signal by different extents of emphasis. CONSTITUTION:A nonlinear emphasis circuit 7NC of the C signal and a nonlinear emphasis circuit 7NY of the luminance Y signal are provided, and outputs of these circuits are taken out in a prescribed period by a switch 30 and are supplied to a common linear emphasis circuit 7L. The extent of emphasis of the circuit 7NC is made smaller than that of the circuit 7NY. Therefore, the limiter level of the circuit 7NC is made higher, and the time constant of a high-pass filter is made smaller. In the reproducing circuit side, a reproduced TCI signal is supplied to a common linear deemphasis circuit 16L, and a switch 31 is switched to supply the output to a non-linear deemphasis circuit 16NC of the C signal and a non-linear deemphasis circuit 16NY of the Y signal.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a video signal processing device that can be applied to VTRs, television receivers, etc., and particularly relates to a video signal emphasis circuit using the 'T' (1 system). .

[Requirement of the invention]

The present invention aims to reduce noise and improve image quality by applying emphasis using different amounts of emphasis to each time-axis compressed luminance signal and color signal. be.

[Conventional technology]

Conventionally, a luminance signal Y and a color signal C as shown in FIG. 6A have been used.
Y/C separation is performed on the video signal S9 containing the signal C.
For example, the time axis is compressed to 1/4, and the time axis of the signal Y is compressed to 3/4, for example, and these time axis compressed signals C and Y are transferred to IH (horizontal scanning period) as shown in Figure B. TCI (T
ime Compressed In tegra t
A video signal transmission method using the ed) method is known. In addition, in FIGS. 6A and 6B, HP is the horizontal synchronization signal, and S
, indicates a color burst signal.

Further, the signal shown in FIG. B will be hereinafter referred to as a TCI signal.

FIG. 7 shows a recording circuit of a VTR that receives the TCI signal, and FIG. 8 shows a reproducing circuit.

In FIG. 7, the video signal sv and Y/C are each
A separation circuit 1 separates the carrier color signals C and Y into carrier color signals. The signal C is demodulated by the demodulation circuit 2 to become the signal C. This signal C is compressed to 1/4 by the time axis compression circuit 3 and then applied to the contact C side of the switch 5. Further, the signal Y is compressed to 3/4 by the time axis compression circuit 4 and then applied to the contact Y of the switch 5. Based on the synchronization signal of the signal sv, the control circuit 6 controls the time axis compression circuit 3 according to the period of the signal C and the period of the signal Y in FIG. 6B.
．． 4 and switch 5.

Therefore, the TCI signal shown in FIG. 6B is obtained from the switch 5. After this T(l signal is corrected to emphasize the high frequency range in an emphasis circuit 7, it is FM modulated by an FM modulation circuit 8, and this FM-TCI signal is applied to a recording/reproducing head 10 through a recording amplifier 9. , are recorded on the tape 11.

During playback, in FIG. 8, the head 10 is moved from the tape 11
The FM-TCl signal reproduced by the reproduction amplifier 12,
The TCI signal is demodulated by being applied to the demodulation circuit 15 through the equalizer circuit 13 and limiter 14. This TCI signal is sent to the de-emphasis circuit 16.
After the inverse characteristics are corrected during recording, the time-axis compressed signal C and signal Y are separately taken out by a switch 17 controlled by the control circuit 6. and signal C
The time axis of signal Y is expanded by a factor of 4 by the time axis expansion circuit 18, and the time axis of signal Y is expanded by a factor of 4/:3 by the time axis expansion circuit 19. The signals c and Y, which have been expanded in time and restored to their original form, are applied to the matrix circuit 20, whereby the R, G, and B signals are rotated once again.

FIG. 9 shows the emphasis circuit 7 in the recording circuit, and FIG. 10 shows the de-emphasis circuit 16 in the reproducing circuit. Note that linear correction and non-linear correction are generally performed in the emphasis circuit 7 and de-emphasis circuit 16, and FIGS. 9 and 10 show circuit examples for performing non-linear correction.

In FIG. 9, it is assumed that a TCI signal forming a rectangular wave as shown in FIG. 11 is manually input.

This TCI signal includes noise N as shown. By passing this TC signal to the bypass filter 21, a signal in which noise N is superimposed on the differential waveform as shown in FIG. 11 is obtained from the bypass filter 2I. This signal is then limited to a predetermined level by a limiter 22 and then added to the original TCI signal in an adder 23, whereby the signal shown in the figure is obtained from the adder 23.

Next, in the de-emphasis circuit 16 of FIG.
The signal is input to adder 24.

By applying a part of the output of this adder 24 to a bypass filter 25, a signal having a waveform shown in FIG. 11 is obtained from this bypass filter 25, and this signal is level limited by a limiter 26 and then 24 and subtracted from the input TCI signal. As a result, an output signal having a noise-free waveform as shown in FIG. 11 is obtained from the de-emphasis circuit 16.

[Problem that the invention seeks to solve]

The aforementioned emphasis circuit 7 and de-emphasis circuit 1
6, as is clear from FIG. 11, the noise N remains in the output waveform of the de-emphasis circuit 16 during the period indicated by to. This residual noise N1
is generated by limiting the level of the output waveform of the bypass filter 25 in FIG. 1O using the limiter 26.

That is, since the output waveform of the bypass filter 25 is cut at the liminter level and added to the adder 24, this cut is not performed. Negative feedback is not applied to the part between jj and J1.
Therefore, the noise N in said part of the TCt signal.

will remain without being subtracted.

If this residual noise N, occurs in the signal C, when this signal C is extended to 4 times by the time 1 extension circuit 18, the noise N1 is also extended at the same time to 4t.

This noise N1 appears on the screen because it is expanded to the length of . Since the signal C has a higher expansion rate and a higher degree of saturation than the signal Y, it may be particularly noticeable depending on the content of the screen. For example, when there are consecutive parts of the same brightness but different hues, there may be noticeable noise, and when the same screen is consecutive, vertical band noise may appear.

Means for Solving Problem C] In the present invention, emphasis circuits having different emphasis amounts for the signal C and the signal Y are provided.

[For production]

By reducing the time constant of the emphasis circuit for the signal with a higher compression ratio, for example, the signal C, and/or increasing the limiter level, the amount of emphasis is made smaller than that for the signal Y, and the residual noise N1 is reduced. period t. can be shortened.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, in which the emphasis circuit 7 is improved.

In this embodiment, a non-linear emphasis circuit 7NC for a C signal and a non-linear emphasis circuit 7 for a Y signal are used.
In addition, the outputs of these nonlinear emphasis circuits 7N, 7Hf are taken out at predetermined intervals by switches 30 and supplied to a common linear emphasis circuit 7L. Further, the amount of emphasis of the non-linear emphasis circuit 7NC is selected to be smaller than the amount of emphasis of the non-linear emphasis circuit 7NY.

For this purpose, the limiter level of the nonlinear emphasis circuit 7 NC (limiter level of limiter 22 in FIG. 9)
is selected to be high, and the time constant of the bypass filter (bypass filter 21 in FIG. 10) is selected to be small.

Furthermore, de-emphasis characteristics are determined for the reproduction circuit in accordance with the emphasis characteristics of the recording circuit. That is, the second
As shown in the figure, by supplying the reproduced TCT signal to a common linear emphasis circuit 16L and switching the switch 31, the output is sent to a non-linear de-emphasis circuit 16NC for signal C and a non-linear de-emphasis circuit 16sy for signal Y. It is designed to supply each.

According to the above configuration, as shown in FIG.
When the signal C of the r signal is input, the differential waveform obtained from the nonlinear emphasis circuit 7 NC bypass filter (bypass filter 21 in FIG. 9) is smaller than that in FIG. 11, and the limiter level is also higher. So,
The output waveform of the nonlinear emphasis circuit 7NC (the output waveform of the adder 23 in FIG. 9) is as shown in the figure. By applying this output waveform to the de-emphasis circuit lPt16 in FIG.
The output waveform of the bypass filter (bypass filter 25 in Fig. 10) of G, , , : has a small differential waveform as shown in Fig. 3, and the part cut by the limiter (t
o period) is narrower than the 10 periods in FIG. Therefore, the t0 period in the output waveform of the de-emphasis circuit 16Ne also becomes sufficiently short, and the time axis modulation circuit 18 in the subsequent stage
Even if the image is expanded by a factor of 4, for example, it will not be noticeable on the screen.

FIG. 4 shows a second embodiment, and parts corresponding to those in FIG. 1 are given the same reference numerals.

In this embodiment, the emphasis circuit 7 is provided with a linear emphasis circuit 741.7LY having different emphasis characteristics for the signal C and the signal Y, respectively. It goes without saying that the reproduction circuit side also includes a de-emphasis circuit 16 having characteristics corresponding to the emphasis circuit 7.

FIG. 5 shows an example of a specific circuit configuration of the emphasis circuit 7 shown in FIG. 4 above.

This circuit consists of linear emphasis circuit 7L7LY and non-linear emphasis circuit 7NC1? It is mainly composed of New York and New York. Linear emphasis circuit 71C
% 7 LY is configured as shown in the figure by an operational amplifier, a CR time constant circuit, etc., and is configured to receive a TCI signal. Nonlinear emphasis circuit 7N1
The bypass filter 21 consists of an operational amplifier, a CR time constant circuit, etc., a limiter 22 consisting of a transistor circuit (14), and an adder 23 consisting of an operational amplifier, etc. .

Linear emphasis J)', 1 +2871. C
27, A. The bypass filter 21 and the limiter 22 are provided with switches 32, 33, and 34, and the switches 32, 33, and 34 are connected to the control go
The contacts c and y can be switched according to the periods of the signals C and Y in FIG. Note that the switch 34 is configured to be ON during the period of the signal Y.

As described above, the time-axis compressed signals C and Y are expanded by 4 times and 4/3 times, respectively, in the reproduction circuit, and therefore the noise N in the C signal becomes noticeable. In this embodiment, the above-mentioned noise residual time t of the signal C1Y. are made approximately equal to make the noise less noticeable. For this reason, during the period of signal C, switch 3
3 to reduce the time constant of the bypass filter 21, and also turn off the switch 34 to reduce the time constant of the bypass filter 21.
I am trying to increase the limiter level.

In the bypass filter 21, the switch 33 is connected to the contact point C.
The time constant τ6 when the side is closed and signal C is applied is R,l+5cffR.

becomes. Furthermore, the time constant τ when the switch 33 is closed to the contact Y side and the signal Y is applied is R71+SC
It becomes 4R7. And in this example, ciR.

C4R7, i.e. τ. Each constant is selected so that τ7.

Also, the gain at the output of the bypass filter 21 is
By lowering the input level of the next-stage limiter 22 for signal C, the limiter level is equivalently increased. In this case, since the gain changes for a small signal, the switch 34 turns on the current source I,
Turn it off and match the gains of signal C and signal Y.

As mentioned above, nonlinear emphasis circuit 7 NC17
, 4Y, in order to improve the noise residual time t0 of signal C, the time constant and limiter level are switched.
'/, it is necessary to lower the turnover frequency by making the emphasis amount of signal C smaller than that of signal Y. This is because the amount of emphasis increases during large swings, and because the time axis of signal C is expanded three times as much as signal Y during reproduction, low-frequency noise becomes more noticeable.

For this reason, in this embodiment, the turnover frequency is changed in the following manner by switching the switch 32.

Emphasis 'Imc and turnover frequency f for signal C. C is 2π C+R+ Emphasis fi1my and turnover frequency [. 7 is C2R.

Therefore, C1R1>C2R2 and R++Rz/Rz<
By selecting R3+R4/Ra, fO
c<f. It can be set to V.

If the reproduction circuit is equipped with a known noise canceller circuit, the ring of residual noise N1 can be reduced by providing two noise canceller circuits with different characteristics for the signals Y and C only on the reproduction circuit side. Ru. However, if the emphasis circuit of the recording circuit is constructed as in the present invention, it can contribute to overall improvement in image quality in terms of waveform reproducibility including noise, distortion, etc.

〔Effect of the invention〕

When processing the T CI signal, it is possible to perform signal processing that reduces screen noise based on residual noise that occurs particularly in color signals and has excellent waveform reproducibility.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
The figure is a block diagram showing an embodiment of the de-emphasis circuit corresponding to Fig. 1, Fig. 3 is a waveform diagram for explaining the emphasis and de-emphasis of Figs. A block diagram showing the second embodiment, FIG. 5 is a circuit diagram showing an example of the specific circuit configuration of FIG. 4, FIG. 6 is a waveform diagram for explaining the TC■ signal, and FIG. A block diagram of a recording circuit of a VTR to which the present invention can be applied, FIG. 8 is a block diagram of a reproducing circuit of the VTR, FIG. 9 is a block diagram showing an embodiment of an emphasis circuit, and FIG. 1O is an implementation of a de-emphasis circuit. FIG. 11, a block diagram showing an example, is a waveform diagram for explaining conventional emphasis and de-emphasis. In addition, in the symbols used in the drawings, 3, 4-------------... 1 time axis compression circuit 7 N C+ 78 'l''''-'-'---
Non-linear emphasis circuit 7LC17Lv-----
---It is a one-linear emphasis circuit.

Claims (1)

[Scope of Claims] A video signal processing device to which a luminance signal and a chrominance signal, each of which has been time-axis compressed at a predetermined compression ratio, is input, a first high-frequency band to which the time-axis compressed luminance signal is supplied. An emphasis circuit, a second high-frequency emphasis circuit to which the time-axis compressed color signal is supplied and which has a correction amount different from the correction amount of the first high-frequency emphasis circuit. Video signal processing device.