JPS6364486A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To record/reproduce a video signal with excellent picture quality by extracting a video signal by two kinds of band pass filters having a different filter characteristic and adding and combining video signals in response to the signal level so as to obtain an output video signal whose signal band is changed in response to the signal level. CONSTITUTION:An input video signal Sin is fed to a coefficient generating circuit 2, an LPF 3 having a conventional reinging characteristic and an LPF 4 having a filter characteristic without rining to be caused. The circuit 2 generates coefficients X1, X2 changed relatively within a prescribed range in response to a mean picture level of the signal Sin and adds the result to multipliers 6, 7 of a signal synthesizing circuit 5. Moreover, the output Y1 subjected to band limit by the LPF 3 is fed to the multiplier 6 and the output Y2 being subjected to band limit by the LPF 4 is fed to the multipler 7. Then video signals from the multipliers 6, 7 are added by an adder 8 in a ratio in response to the signal level to output an output signal Sout whose signal band is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal processing circuit for band-limiting a video signal, and is applied to, for example, a recording system in a video tape recorder.

[Summary of the invention]

The present invention provides two types of band-limiting filters with different filter characteristics in a video signal processing circuit that limits the band of a video signal transmitted via a video signal transmission system such as a video tape recorder that performs magnetic recording and reproduction of video signals. By limiting the band of the video signal at , and adding and combining the outputs of each filter at a ratio according to the signal level of the input video signal, an output video signal whose signal band changes according to the input signal level is formed. This is how it was done.

[Conventional technology]

Traditionally, video tape recorders (VTRs) that magnetically record and reproduce video signals have FM-modulated the input video signal and recorded it on magnetic tape, and because the transmission band is narrow, the input stage of the modulator is A low-pass filter is provided to limit the band of the video signal. Also, generally V T
R is set so that it is 100% manually input when using a signal generator, and when a video camera etc. is connected, the input becomes 120% to 140%, which tends to cause overmodulation, so the input video White at traffic lights
Signal processing such as crimp and dark clip is applied.

[Problem that the invention seeks to solve]

By the way, a low-pass filter does not cause any change in the signal level of the output signal if the input signal is a single frequency signal, but for square wave signals, it causes ringing in the output by attenuating harmonics. It has the characteristic of generating pre-shoot. Conventionally, video signal processing circuits have used low-pass filters that have a ringing characteristic of about 5% to 10%, and when the signal level of the input video signal is large, the ringing causes the image quality to deteriorate. . Furthermore, even if the input video signal is subjected to signal processing such as white clipping or dark clipping, it is not possible to sufficiently prevent the occurrence of overmodulation due to the ringing caused by the above-mentioned low-pass filter. , the video signal itself is changed by the clip processing described above. Problems such as the generation of new distortions occurred due to the loss of parts.

Therefore, in view of the above-mentioned conventional problems, the present invention provides V
The object of the present invention is to provide a video signal processing circuit with a new configuration that suppresses ringing of video signals with high signal levels in video signal transmission systems such as TRs, and effectively prevents overmodulation from occurring. It is.

Means for Solving Problems c] In order to solve the conventional problems as described above, the video signal processing circuit according to the present invention includes a first band-limiting filter and a second band-limiting filter that does not cause ringing. filter, and a signal synthesis circuit that adds and synthesizes the outputs of each of the band-limiting filters at a ratio according to the signal level of the input video signal, and divides the input video signal into bands using two types of band-limiting filters with different filter characteristics. It is characterized in that it is limited and supplied to the signal synthesis circuit.

[Effect]

A video signal processing circuit according to the present invention forms an output video signal whose signal band changes depending on the signal level of an input video signal.

〔Example〕

Hereinafter, one embodiment of the video signal processing circuit according to the present invention will be described in detail with reference to the drawings.

In the block diagram of FIG. 1, an input video signal (S in
) is supplied from the signal input terminal 1 to the coefficient generation circuit 2, and also includes a first low-pass filter (LPF+) 3 having a ringing characteristic of about 5% to 10% of normal and a so-called T filter characteristic that does not cause ringing. The signal is supplied to the signal synthesis circuit 5 via a second low-pass filter (LPF2) 4 having the following characteristics.

The coefficient forming circuit 2 calculates the average image level (A P L ) of the input video signal (Sin).
For example, the APL is 10 depending on the
coefficients (XI) that vary complementary in the range from % to 100%;
(X2) to each multiplier 6 of the signal synthesis circuit 5.
It is designed to be given to 7. Further, the first low-pass filter 3 limits the band of the input video signal (S in ) and supplies its output (Yl) to the multiplier 6 . Further, the second low-pass filter 4 limits the band of the input video signal (Sin) and supplies its output (Y2) to the multiplier 7.

Further, the signal synthesis circuit 5 includes each of the multipliers 6°7,
It is composed of an adder 8 that adds and synthesizes the outputs, and each output (Yl) from each of the above-mentioned low-pass filters 3.4.
, (Y2) are subjected to additive synthesis at the synthesis ratio shown in Figure 2, and the additive synthesis output is output as the video signal (Sout).
The signal is outputted from the signal output terminal 9 as a signal.

In the embodiment with the above-described configuration, for example, as shown in FIG. 3, the signals (Sa), A, P L,
No. 48 (Sb) with 100% or more and A F” I, is 1
When an input video signal (S in) containing Q in the range 0% to 100% (S() and 4) is supplied, the band is limited as follows for each signal. The output video signal (Sout) is outputted from the signal output terminal ().

That is, for a signal (Sa) in which A, P i, are io% or more -1, - the first low-pass filter 3
An output video signal (Sout) is obtained which has been subjected to normal band-limiting using filter characteristics. Also, AP L is 1
For a signal (sb) of 00% or more, an output video signal (Soot) is obtained which is band-limited without ringing due to the T filter characteristic of the second low-pass filter 4. Furthermore, the signal (Sc) whose APL is in the range of 10% to 100%? For this purpose, the output signal (y+) subjected to band limitation by the first low-pass filter 3 and the output signal (F2) subjected to band limitation by the second low-pass filter 4 are expressed as follows. , P1. , an output video signal (Sout) is obtained which is added and combined at a combination ratio (xl :xz) corresponding to
It is possible to obtain an output video signal (Sout) whose 11υ band changes without depending on the rail, and there is no ringing even in areas with high signal levels.
By applying it to the 'R' ↑, L reappointment system, the occurrence of Oher modulation 1 can be effectively prevented, resulting in good image quality of the image 1, 13υ 1i! .

You will be able to perform playback.

Here, the video signal processing circuit according to the embodiment shown in FIG. 1 can be embodied, for example, in the circuit configuration shown in FIG. Applies to etc.

That is, in the specific example shown in FIG.
in) is supplied from the signal input terminal 11 to the low-pass filter 13 via the Hanwha amplifier 12. This low-pass filter 13 is the first low-pass filter (
It is equivalent to LPFI) and performs normal band limiting with ringing of about 5% to 10%. The video signal band-limited by the low-pass filter 13 is supplied to a bypass filter 15 and a first delay circuit 16 via an amplifier 14.

The bypass filter 15 has a characteristic opposite to that of the second low-pass filter (I, pF2), which has a T-filter characteristic that does not generate double ringing.
The high-frequency component in the video signal output from the low-pass filter 13 is extracted and supplied to the multiplier 20 via the amplifier 16. Further, the first delay circuit 17 has a delay characteristic substantially equal to the delay characteristic of the bypass filter 15, and the first delay circuit 17 has a delay characteristic that is substantially equal to the delay characteristic of the bypass filter 15. is fed to the clamp amplifier 19 and the phase 2 delay circuit 21 via the amplifier 18.

The clamp amplifier 19 is connected to the first delay circuit 17 described in -.
APL of the video signal supplied from 1. O0% is clamped to 0■ potential, and the inverted amplified output of the video signal is supplied to the 1/2 multiplier 20. The multiplier 20 multiplies the high-frequency component signal obtained by the bypass filter 15 and the inverted amplified output signal from the clamp amplifier 19, and supplies the output to the adder 22. Further, the second delay circuit 1B21 has a delay of 1.1.times. that corresponds to the operating time of the multiplier 20.
The video signal obtained by delay matching with the multiplied output signal by 9 is supplied to the 1-j]l'l calculator 22.

Then, the adder 22 performs addition and subtraction synthesis of the multiplied output signal from the multiplier 29 and the delay-matched video signal with opposite polarities, and outputs the combined output as the output video signal (Soul) 7. It is output from the signal output terminal 23.

That is, in this specific example, the low-pass filter 13
The so-called aperture circuit (trowel) subtracts and synthesizes the high-frequency components obtained by the bypass filter 15 from the video signal band-limited by the above-mentioned second low-pass filter (
I, p F2) performs band control + R operation, and multiplies the above high-frequency component signal by using the inverted output AI) L as a coefficient, which is clamped to a predetermined potential by one clamp amplifier. :Input video signal (Sin)
The adder 22 forms an output video signal (Sout) whose signal band changes depending on the signal level of the output video signal (Sout). That is, when the signal level of the input video signal (S in) is low, the signal level of the multiplied output signal by the multiplier 20 is also low, and the video signal band-limited by the low-pass filter 13 is directly output as the output video signal (Sout). When the signal level becomes high, the multiplier 2
The signal level of the output signal multiplied by 0 increases, resulting in an output video signal (S
out) is output.

〔Effect of the invention〕

As is clear from the description of the embodiments above, in the video signal processing circuit according to the present invention, the video signal, which has been band-limited by two types of band-limiting filters with different filter characteristics, is converted into a ratio according to the signal level. By adding and synthesizing the signals, an output video signal whose signal band changes according to the signal level can be obtained.Moreover, since one of the filters is a band-limiting filter that does not cause ringing in areas where the signal level is high, ringing is eliminated. It is possible to form a video signal of extremely good quality without any distortion.

Therefore, according to the present invention, by applying it to the recording and reproducing system of a VTR, for example, it becomes possible to effectively prevent the occurrence of overmodulation and record and reproduce video signals with good image quality. The purpose can be fully achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a video signal processing circuit according to the present invention, and FIG. 2 is a diagram showing the relationship between coefficients multiplied by a video signal and the signal level of an input video signal in the embodiment. FIG. 3 is a schematic diagram showing the relationship; FIG. 3 is an input video signal field waveform diagram for explaining the operation of the above embodiment;
The figure is a block diagram showing a specific example of the configuration of a video signal processing circuit according to the present invention. 1...Signal input terminal 2...Coefficient forming circuit s, 4. i3...Low pass filter 5...Signal synthesis circuit 6.7.20...Multiplier 8.22...Adder

Claims (1)

[Claims] A first band-limiting filter, a second band-limiting filter that does not cause ringing, and a signal that adds and synthesizes the outputs of each of the band-limiting filters at a ratio corresponding to the signal level of the input video signal. A video signal processing circuit comprising: a synthesis circuit, wherein an input video signal is band-limited by two types of band-limiting filters having different filter characteristics and then supplied to the signal synthesis circuit.