JPH09200576A - Clip compensation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide excellent images without tailing by more appropriately performing clip compensation. SOLUTION: Reproducing luminance signals (a) inputted to this clip compensation circuit 1 are inputted to a high-pass filter 2 and a detection circuit 6. In the high-pass filter 2, the edge part of the reproducing luminance signals (a) is extracted and the output signals (b) are inputted to a gain control amplifier 7. In the GCA 7, prescribed gain control is performed corresponding to luminance level detection signals from the detection circuit 6 and signals (c) in which amplitude becomes larger at the edge part where a luminance level is higher are outputted. The signals (c) are branched into two, one is added to the reproducing luminance signals (a) by an adder 3 and turned to the signals (d) and the other is inputted to a limiter 4. The signals (e) limited to a prescribed level are outputted in the limiter 4, the signals (e) are subtracted from the signals (d) by a subtractor 5, the edge part lower than a prescribed amplitude level is offset, only the edge part higher, than the prescribed amplitude level is clip-compensated and the result is outputted as output signals (f) from the clip compensation circuit 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clip compensating circuit for shaping a waveform of an edge portion of a video signal.

[0002]

2. Description of the Related Art A luminance signal processing circuit of a magnetic recording / reproducing apparatus is constructed, for example, as shown in FIG. An edge of the input luminance signal is emphasized by the emphasis circuit 101, and F
If the data is modulated by the M modulator 103 and recorded on the magnetic recording medium as it is, white and black noise called inversion occurs, so that white / dark clip (W / D CLI)
P) The circuit 102 limits the recording frequency as shown in FIG. Since the edge portion emphasized by the emphasis circuit 101 is missing due to the white / dark clip at the time of recording, the edge portion is compensated at the time of reproduction. The clip compensating circuit 106 performs this compensation.

A conventional clip compensation circuit 106 is constructed as shown in FIG. 13, for example. Then, FIG. 14 is a diagram showing signal waveforms of respective portions of FIG. The reproduction luminance signal m input to the clip compensation circuit 106 is input to the high pass filter (HPF) 2. The output signal n whose edge portion is extracted by the high-pass filter 2 is branched into two, one of which is added to the input signal m by the adder 3 to be a signal o, and the other is input to the limiter 4. The limiter 4 outputs the signal p limited to a predetermined level and outputs the signal p.
Is subtracted from the signal o by the subtractor 5, and the edge portion below the predetermined amplitude level is canceled. Therefore, the clip compensation is performed only for the edge portion having the predetermined amplitude level or higher, and the clip compensation circuit 106 outputs the output signal q.

In this way, the clip compensation amount is determined according to the amplitude level of the edge portion.

[0005]

However, in the above-mentioned conventional clip circuit, since the compensation amount is determined only according to the amplitude level of the edge portion, as shown in FIG. In different cases (edge portions A and A'in FIG. 14A, and edge portions B and B'in FIG. 14B), the same compensation amount is obtained, resulting in insufficient compensation or overcompensation as shown by the waveform of the signal q in FIG. As a result, white or black tailing was generated on the right side of the edge portion, and the image quality was deteriorated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a clip compensation circuit that more appropriately performs clip compensation and provides a good image without tailing.

[0007]

To achieve the above object, the present invention provides a clip compensation circuit for compensating for an edge portion of a clipped video input signal, the compensation amount being changed according to the luminance level of the video input signal. It has a compensation amount changing means for performing.

Further, in the clip compensating circuit for compensating for the edge portion of the clipped video input signal, it is characterized in that it has a compensation amount changing means for changing the compensation amount according to the direction of the edge of the video input signal.

Further, in the clip compensating circuit for compensating the edge portion of the clipped video input signal, there is provided a compensation amount changing means for changing the compensation amount according to the luminance level of the video input signal and the edge direction. And

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a clip compensation circuit 1 according to a first embodiment of the present invention,
The components corresponding to those in FIG. 13 are designated by the same reference numerals. In FIG. 1, a clip compensating circuit 1 is a high-pass filter (H which extracts an edge portion of an input luminance signal a).
PF) 2 and a limiter (LI) that limits the level to be compensated.
M) 4 and a detection circuit (Y
DET) 6, a gain control amplifier (hereinafter abbreviated as “GCA”) 7 whose gain is controlled according to a detection signal from the detection circuit 6, a luminance signal a and a GCA
The output signal c from the adder 3 is added, and the subtracter 5 from the output signal d from the adder 3 is subtracted from the output signal e from the limiter 4.

FIG. 2 is a diagram showing the waveforms of the signals a to f of the respective parts of FIG.

The reproduced luminance signal a input to the clip compensation circuit 1 is input to the high pass filter 2 and the detection circuit 6. The high-pass filter 2 extracts the edge portion of the reproduction luminance signal a and outputs its output signal b to the GCA 7. In the GCA 7, the brightness level detection signal from the detection circuit 6 is used to perform gain control as shown in FIG. 3,
A signal c having a larger amplitude at an edge portion having a higher brightness level
Is output. This signal c is split into two, one of which
The adder 3 adds the reproduced luminance signal a to form a signal d, and the other is input to the limiter 4. The limiter 4 outputs the signal e limited to a predetermined level, the signal e is subtracted from the signal d by the subtractor 5, the edge portions below the predetermined amplitude level are canceled, and only the edge portions above the predetermined amplitude level are clip-compensated. The output signal f is output from the clip compensation circuit 1.

As shown in FIG. 15, the higher the brightness level of the input signal a, the greater the amount of edge loss.
The GCA 7 increases the gain in the edge portion having the higher brightness level, and the compensation amount increases as the brightness level becomes higher, so that it is possible to perform the appropriate clip compensation like the output signal f.

FIG. 4 is a block diagram showing a schematic configuration of the clip compensation circuit 11 according to the second embodiment of the present invention. The clip compensating circuit 11 of the present embodiment is the same as that shown in FIG.
The configuration of the limiter is different from that of the conventional clip compensation circuit 106 of FIG. 3, and therefore, in FIG. 4, the same components as those of FIG. In FIG. 4, the limiter 12 is a vertically asymmetric limiter in which the upper limiter level to be limited is smaller than the lower limiter level.

FIG. 5 is a diagram showing the waveforms of the signals m to q of the respective parts of FIG.

The reproduced luminance signal g input to the clip compensation circuit 11 is input to the high pass filter 2. The output signal h whose edge is extracted by the high-pass filter 2 is 2
The input signal g is added by the adder 3 into the signal i, and the other is input to the limiter 12. The limiter 12 outputs the signal j limited to a predetermined level.
Is output, the signal j is subtracted from the signal i by the subtracter 5, the edge portion below the predetermined amplitude level is canceled, the clip compensation is performed only on the edge portion above the predetermined amplitude level, and the output signal k from the clip compensation circuit 11 is output. Is output as.
Here, as described above, since the upper limiter level of the limiter 12 is smaller than the lower limiter level, the signal j
Is smaller in the rising edge part than in the falling edge part, and the clip compensation amount is larger in the rising edge part than in the falling edge part.

As shown in FIG. 15, the input signal g has a larger amount of missing edges at the rising edge portion than at the falling edge portion, but the limiter 12 is vertically asymmetrical and the upper limiter level is lower than the lower limiter level. Because it's small
The amount of clipping compensation in the rising edge portion is larger than that in the falling edge portion, and appropriate clipping compensation can be performed like the output signal k.

FIG. 6 is a block diagram showing a schematic configuration of the clip compensation circuit 21 according to the third embodiment of the present invention. The clip compensating circuit 21 of the present embodiment is different from the clip compensating circuit 1 of the first embodiment described above only in that the limiter is replaced by the limiter 12 of the second embodiment described above, and therefore the configuration thereof is different. The description of the operation will be omitted.

In the present embodiment, the clip compensation amount can be controlled by the brightness level and the edge direction, so that more appropriate clip compensation can be performed.

FIG. 7 is a block diagram showing a schematic configuration of the clip compensation circuit 31 according to the fourth embodiment of the present invention. The clip compensating circuit 31 of the present embodiment is different from the clip compensating circuit 1 of the first embodiment described above in that the configuration of the high-pass filter 32 and the GCA 7 are omitted. That is, the high-pass filter 32 of the present embodiment is a variable high-pass filter whose cutoff frequency changes according to the detection signal of the detection circuit 6, and thus the GCA 7
Is omitted.

As described above, in the first embodiment, instead of controlling the gain of the edge portion by the GCA 7 according to the brightness level, the cutoff frequency of the high-pass filter 32 is changed as shown in FIG. Controls the gain of the section.

Therefore, also in this embodiment, as in the first embodiment, appropriate clip compensation can be performed.

FIG. 9 is a block diagram showing a schematic configuration of a clip compensation circuit 41 according to the fifth embodiment of the present invention. The clip compensating circuit 41 of the present embodiment is different from the clip compensating circuit 21 of the third embodiment described above in that the configuration of the limiter 42 and the GCA 7 are omitted. The limiter 42 of the present embodiment is a variable limiter whose limiter level is variable by the detection signal of the detection circuit 6.

That is, instead of the fixed vertically asymmetrical limiter 12 of the third embodiment, a variable limiter 42 for varying the limiter level according to the brightness level is used, and the upper and lower limiter levels are used. , The clip compensation amount is changed.

As described above, in the present embodiment, the clip compensation amount can be controlled depending on the luminance level and the edge direction, so that more appropriate clip compensation can be performed.

[0027]

As described above, according to the invention of the present application, the compensation amount is changed according to the luminance level and / or the edge direction of the video input signal, so that the clip compensation can be performed more appropriately. It is possible to provide a good image without tailing.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a clip compensation circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing waveforms of signals a to f of respective portions of the clip compensation circuit of FIG.

FIG. 3 is a diagram showing a gain characteristic with respect to a luminance signal level of the gain control amplifier of FIG.

FIG. 4 is a block diagram showing a schematic configuration of a clip compensation circuit according to a second embodiment of the present invention.

5 is a diagram showing waveforms of signals m to q of respective parts of the clip compensation circuit of FIG.

FIG. 6 is a block diagram showing a schematic configuration of a clip compensation circuit according to a third embodiment of the present invention.

FIG. 7 is a block diagram showing a schematic configuration of a clip compensation circuit according to a fourth embodiment of the present invention.

8 is a diagram showing a cutoff frequency characteristic with respect to a luminance signal level of the high pass filter of FIG.

FIG. 9 is a block diagram showing a schematic configuration of a clip compensation circuit according to a fifth embodiment of the present invention.

10 is a diagram showing a limiter level characteristic with respect to a luminance signal level of the limiter of FIG.

FIG. 11 is a block diagram showing a general configuration of a luminance signal processing circuit of the magnetic recording / reproducing apparatus.

12 is a diagram showing an example of recording frequencies limited in the white / dark clip circuit of FIG.

13 is a block diagram showing a configuration of a conventional clip compensation circuit in FIG.

14 is a diagram showing a signal waveform of each part of the clip compensation circuit of FIG.

15 is a diagram showing an amplitude level of an edge portion of a reproduction luminance signal input to the clip compensation circuit of FIG.

[Explanation of symbols]

 6 Detection Circuit 7 Gain Control Amplifier 12 Vertically Asymmetric Limiter 32 High-pass Filter with Variable Cutoff Frequency 42 Limiter Variable Level Limiter

Claims (3)

[Claims] 1. A clip compensating circuit for compensating for an edge portion of a clipped video input signal, comprising a compensation amount changing means for changing a compensation amount according to a luminance level of the video input signal. circuit. 2. A clip compensating circuit for compensating for an edge portion of a clipped video input signal, comprising a compensation amount changing means for changing a compensation amount according to a direction of an edge of the video input signal. Compensation circuit. 3. A clip compensating circuit for compensating for an edge portion of a clipped video input signal, comprising a compensation amount changing means for changing a compensation amount according to a luminance level and an edge direction of the video input signal. Clip compensation circuit.