JPH03229592A - Picture quality adjustment circuit - Google Patents

Abstract

PURPOSE:To prevent the level of a luminance high band signal from being over enhanced at the outline part of a luminance signal by supplying it to an adding means after limiting the level of the luminance high band component outputted from an amplifying means on the basis of the level of the extracted luminance high band component. CONSTITUTION:The level of the luminance high band signal YH' outputted from a VCA 13 can be controlled so that it is prevented from being over enhance at the outline part of the luminance signal Yin by switching adaptively the luminance high band component YH' outputted from the VCA 13 so as to be added to the luminance signal Yin either as it is or after limiting its level according to the level of the luminance high band component YH outputted from a YH extraction circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an improvement of an image quality adjustment circuit used for compensating for resolution deterioration in an image reproduction device such as a television receiver.

(Prior Art) As is well known, image reproduction equipment in the current NTSC system includes measures to compensate for resolution deterioration of high-chroma images.
Color difference signal (R-
By performing predetermined calculations on (Y, B-Y, etc.),
An image quality adjusting means is provided which generates a control signal corresponding to a change in saturation and adjusts the level of a high frequency component of an input luminance signal based on this control signal.

FIG. 7 shows such a conventional image quality adjustment circuit. That is, the luminance signal Yin supplied to the input terminal ]1
is supplied to the Yl+extraction circuit 12 and the luminance high-frequency component Yl
After the voltage + is extracted, it is supplied to a voltage control amplifier circuit (hereinafter referred to as VCA) 13, where it is amplified with a gain corresponding to a gain control voltage VCTL, which will be described later. and,
The level-adjusted brightness high frequency No. 13 Yl+ output from this VCA 13 and the brightness signal Yln supplied to the input terminal 11 are added in the adder circuit 14, thereby producing the level-adjusted brightness of the high frequency component. A signal is obtained and taken out at output terminal 15.

Further, the gain control voltage V CTL is generated as follows. That is, the color signal C1n supplied to the input terminal 16 is supplied to the decoder 17, where it is orthogonally biaxially demodulated and converted into two color difference signals RY and BY. These color difference signals R-Y and B-Y have a gain kl,
2. After being amplified by three amplifier circuits 18, 19, and 20, the signals are supplied to clampers 21, 22, and 23, and the horizontal synchronization portions are clamped to the same potential. The output of each clamper 21, 22.2.3 is output to a selector 24, respectively.
The one with the highest voltage level is selected and output. Thereafter, the output selected by the selector 24 is sliced by a slicer 25 at a preset slice level, and the output level of the slicer 25 is set by a clamper 26.
By clamping at , the gain control voltage V CTL is generated.

Here, for example, each gain k of the amplifier circuits 18, 19.20
l, to 2. 3, kl-1, 14, 2--1.14/2, and 3-2.03, respectively, and when the slice level of the slicer 25 is 100% and the brightness level is 1, the level is 0.1. When set in this way, the gain control voltage VCTL has a correlation with the saturation, that is, it corresponds to the saturation level. In the high chroma part, the gain control voltage V
As the CTL becomes weaker, the gain of the VCA 13 becomes larger, and the level of the brightness high-frequency signal Y11', which is its output, is adjusted to be larger.

Note that the gain of the VCA 13 changes colors depending on the eye even when the saturation is the same, and in the above setting example, the gain of the VCA13 adaptively changes for each hue and saturation, and the frequency characteristics of the high saturation part in the NTSC system can be approximated by black and white. The brightness of the achromatic portion of the signal can be corrected to a level equivalent to the transmission level of the high frequency signal.

However, in the conventional image quality adjustment circuit as mentioned above,
Color difference signal R- obtained by orthogonal two-axis demodulation of color signal Cin
Since the cane control voltage V CTL of VCA 13 is generated using Y and B-Y, the luminance signal Y
The level of the brightness high-frequency signal YH' outputted from the VCA 13 is excessively emphasized at the contour portion of "in", resulting in a problem that the image becomes unnatural.

That is, at the point of change from the highly saturated portion to the achromatic portion, the luminance signal Yln has many high-frequency components. on the other hand,
The gain control voltage V CTL should originally be 0 in the achromatic color part, but because the band of the color difference signals R-Y and B-Y is narrow, it cannot follow the change in the luminance signal Yin.
In other words, he hasn't been able to get down to O level. Therefore, in the contour part of the luminance signal Yin, the gain control voltage V
Since the CTL is not O, the VCA 13 has a gain, and since there is a large amount of high-luminance component Yl+, the level of the high-luminance signal YH' output from the VCA 13 is overemphasized.

(Problem to be Solved by the Invention) As described above, the conventional image quality adjustment circuit has the problem that the level of the luminance high-frequency signal is overemphasized in the contour part of the luminance signal, making the image unnatural. are doing.

This invention was made in consideration of the above circumstances, and is an extremely good method that prevents the level of the brightness high frequency signal from being overemphasized in the contour part of the brightness signal and makes it possible to obtain a natural image. The purpose is to provide an image quality adjustment circuit.

[Configuration of the Invention (Means for Solving the Problems) The picture quality adjustment circuit according to the present invention includes an extraction means for extracting a high frequency component from a brightness signal of a television signal, and a brightness high-frequency component extracted by the extraction means. an amplification means for amplifying the high frequency range component with a gain corresponding to a control signal given from the outside; an addition means for adding the luminance high frequency component outputted from the amplification means to the luminance signal; The present invention is directed to a device having a generation means for generating a control signal to be supplied to an amplification means based on a plurality of color difference signals obtained by two-axis demodulation.

Based on the level of the brightness high frequency component extracted by the extraction means, the level of the brightness high frequency component outputted from the amplification means is limited and supplied to the addition means.

Further, the image quality adjustment circuit according to the present invention has the following features:
The control signal is configured to limit the level of the control signal generated by the generation means based on the level of the brightness high frequency component extracted by the extraction means and to supply the control signal to the amplification means.

(Function) According to the above configuration, the level of the luminance high frequency component added to the luminance signal is controlled based on the level of the luminance high frequency component extracted by the extraction means, so the luminance signal This prevents the level of the brightness high-frequency signal from being overemphasized in the contour portion of the image, making it possible to obtain a natural image.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In FIG. 1, the same parts as in FIG. 7 are shown with the same symbols, and only the different parts will be described here. That is, the luminance high-frequency component YH output from the Y11 extraction circuit 12 is amplified by an amplifier circuit 27, double-wave rectified by an absolute value circuit (hereinafter referred to as ABS) 28, and then
It is supplied to one input terminal of the comparator 29. The comparator 29 has the reference level V rer applied to its other input terminal, and outputs a signal that is L level when the output level of the ABS 28 is higher than the reference level V rer, and is H level when it is lower.

On the other hand, the luminance high-frequency component Yl+' output from the VCA 13
is supplied to one input terminal of the adder circuit 31 via the gate circuit 30, and after being level-limited by the limiter 32, is supplied to the other input terminal of the adder circuit 31 via the gate circuit 33.

Here, the gate circuit 30 is non-conductive when the output of the comparator 29 is at L level, and is conductive when the output is at H level. Further, the gate circuit 33 becomes conductive when the output of the comparator 29 is at the L level, and the gate circuit 33 becomes conductive when the output of the comparator 29 is at the L level
When it is at level, it becomes non-conductive. The output of the adder circuit 31 is supplied to the adder circuit 14 and added to the luminance signal Yln.

According to the configuration of the above embodiment, the YH extraction circuit 12
When the level of the luminance high-frequency component Yl+ output from the gate circuit 30.3 is lower than the reference level V ref, the gate circuit 30.3
3 becomes conductive and non-conductive, respectively, so VC
The same operation as in the prior art is performed in that the brightness high frequency component Y'' output from A13 is directly added to the brightness signal Yln by the adder circuit 14 via the adder circuit 31.

On the other hand, when the level of the luminance high frequency component YH output from the YH extraction circuit 12 is higher than the reference level Vrer, the gate circuits 30 and 33 are in a non-conducting state and a conducting state, respectively, so that the output from the VCA 13 is After the brightness high-frequency component YF is level-limited by the limiter 32, it is added to the brightness signal YNn by the adder circuit 14 via the adder circuit 31.

Therefore, depending on the level of the brightness high-frequency component Y11 output from the Yl extraction circuit 12, the brightness high-frequency component Y" output from the VCA 13 is adapted to be added to the brightness signal Yin either as is or with the level limited. Since the switching is done according to the outline of the luminance signal Yln, VCA1
The level of the brightness high-frequency signal Y11' output from 3 can be controlled to prevent it from being overemphasized,
This makes it possible to obtain natural images.

Here, FIG. 2 shows a modification of the above embodiment. That is, numeral 34 in the figure is an input terminal to which the output of the ABS 28 is supplied. The signal supplied to this input terminal 34 is supplied to one input terminal of a comparator 35. This comparator 35 has the reference level V rer applied to its other input terminal, and generates an output k (0<k<1) corresponding to how far the output level of the ABS 28 is from the reference level V rer. It is something to do.

The output of the comparator 35 is multiplied by the luminance high-frequency signal Yll' output from the VCA 13, which is supplied to the input terminal 37, by the multiplier circuit 36, and is then supplied to one input terminal of the adder circuit 38. ing. In addition, the output of the comparator 35 is provided with a reference value of 1 by three subtraction circuits.
The subtracted value (1-k) and the input terminal 37
A multiplier circuit 41 multiplies the brightness high-frequency signal Yl+' supplied to the multiplier circuit 41 with a signal whose level is limited by a limiter 40, and the multiplier is supplied to the other input terminal of the adder circuit 38. The output of the adder circuit 38 is added to the luminance signal Yen in the adder circuit 14 via the output terminal 42.

According to the configuration shown in FIG.
The brightness high-frequency signal YH' supplied to the input terminal 37 and the brightness high-frequency signal Yl+' whose level has been limited by the limiter 40 are added at different addition ratios according to the output k of the luminance signal Yln. Since the signals are added, more precise control can be performed than in the circuit shown in FIG.

Next, FIG. 3 shows another embodiment of this invention.

In FIG. 3, the same parts as in FIG. 7 are indicated by the same symbols, and will be explained with reference to FIG. 4. That is, the luminance signal Yln supplied to the input terminal 11 is converted into a luminance high frequency component Y by the YH extraction circuit 43 as shown in FIG. 4(a).
The old is extracted. This brightness high-frequency component Y old has a gain of 4
After being amplified by the amplifier circuit 44 as shown in FIG. 4(b), the ABS 45 performs double-wave rectification as shown in FIG. 4(c). The output of the ABS 45 is then sliced by a slicer 46 at a predetermined slice level S1, as shown in FIG. 4(d). This slice level S
1 is set so that only the relatively high-level brightness high-frequency component YH in the contour portion of the brightness signal Yjn is obtained.

The signal level-sliced by the slicer 46 is
After being amplified by the amplifier circuit 47 with a gain of 5 as shown in FIG. 4(e), it is subtracted by the subtracting circuit 48 from the output of the selector 24 shown in FIG. ) is obtained. Thereafter, this signal is level-sliced by the slicer 25 at a predetermined slice level (for example, 0 level), as shown in FIG. 4(h).
As shown in , the luminance high frequency component Y is 0 in the high level part of 11.
A gain control voltage V CTL that corresponds to the level is obtained.

Therefore, since the gain control voltage VCTL is set to 0 level in the high level portion of the brightness high frequency component Yl+ in the contour portion of the brightness signal Yln, the VCA
The gain of VCA 13 becomes 0, and the level of the brightness high-frequency signal Yl+' output from VCA 13 can be controlled to prevent it from being overemphasized, making it possible to obtain a natural image. .

Here, FIGS. 5 and 6 respectively represent the above-mentioned Y)I
A specific example of the extraction circuit 12.43 is shown.

First, what is shown in FIG. 5 is a so-called second-order differential method, in which the luminance signal Yln supplied to the input terminal 49 is amplified by an amplifier circuit 50 and then transmitted to two delay circuits 51 and 52, respectively. Coefficient multiplication circuits 53 and 54 are applied to each output of the amplifier circuit 50 and delay circuit 51 and 52 by a certain amount.
．． 55, coefficients -1/2, 1. By multiplying by -1/2 and adding the respective multiplication results in an adder circuit 56, the brightness high frequency component YH is taken out from an output terminal 57.

The one shown in FIG. 6 is called a first-order differential method, in which the luminance signal Yln supplied to the input terminal 58 is amplified by an amplifier circuit 59 and then delayed by a delay circuit 60. The outputs of the five circuits and the delay circuit 60 are each multiplied by a coefficient 1 in the coefficient multiplication circuits 61 and 62, and then the subtraction circuit 6
3 from the output of the coefficient multiplier circuit 61 to the coefficient multiplier circuit 6
By subtracting the output of 2, the brightness high frequency component YH is taken out from the output terminal 64.

It should be noted that the present invention is not limited to the above-described embodiments, and can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to prevent the level of the brightness high-frequency signal from being overemphasized in the contour portion of the brightness signal, and to obtain a natural image. An image quality adjustment circuit can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the image quality adjustment circuit according to the present invention, FIG. 2 is a block diagram showing a modification of the same embodiment, and FIG. 3 is a block diagram showing another embodiment of the invention. 4 is a waveform diagram for explaining the operation of the embodiment of the same location, FIGS. 5 and 6 are block diagrams showing specific examples of the Y11 extraction circuit, and FIG. 7 is a conventional FIG. 2 is a block configuration diagram showing an image quality adjustment circuit of FIG. 11...Input terminal, 12...Y I+ extraction circuit, 1
3... VCA, 14... Adder circuit, 15... Output terminal, 16... Input terminal, 17... Decoder, 18
~20... Amplifier circuit, 21-23... Clamper, 2
4... Selector, 25... Slicer, 26... Clamper, 27... Amplifier circuit, 28... ABS, 29
...Comparator, 30...Gate circuit, 31...
-Addition circuit, 32...Limiter, 33...Gate circuit, 34...Input terminal, 35...Comparator, 3
6...Multiplication circuit, 37...Input terminal, 38...Addition circuit, 39...Subtraction circuit, 40...Limiter, 41
...Multiplication circuit, 42...Output terminal, 43...Y
I+ extraction circuit, 44...amplification circuit, 45...ABS
, 46... Slicer, 47... Amplifier circuit, 48...
・Subtraction circuit, 49...Input terminal, 50...Amplification circuit, 51.52...Delay circuit, 53-55...Coefficient multiplication circuit, 56...Addition circuit, 57...Output terminal, 58・
Input terminal, 59... amplifier circuit, 60... delay circuit,
61.62... Coefficient multiplication circuit, 63... Subtraction circuit,
64...Output terminal.

Claims (2)

[Claims] (1) extraction means for extracting a high-frequency component from a luminance signal of a television signal; and amplification means for amplifying the luminance high-frequency component extracted by the extraction means with a gain corresponding to a control signal applied from the outside; Adding means for adding the luminance high-frequency component outputted from the amplifying means to the luminance signal; and generating means for generating a control signal to be supplied, the image quality adjustment circuit limiting the level of the brightness high-frequency component output from the amplification means based on the level of the brightness high-frequency component extracted by the extraction means. 1. An image quality adjustment circuit comprising: a limiting means for supplying the sum to the adding means. (2) extraction means for extracting a high frequency component from the luminance signal of a television signal; and amplification means for amplifying the luminance high frequency component extracted by the extraction means with a gain corresponding to a control signal applied from the outside; Adding means for adding the luminance high-frequency component outputted from the amplifying means to the luminance signal; and generating means for generating a control signal to be supplied, wherein the level of the control signal generated by the generating means is limited based on the level of the luminance high frequency component extracted by the extracting means, and the control signal generated by the generating means is limited. An image quality adjustment circuit characterized by comprising a limiting means for supplying a supply to an amplifying means.