JP3158768B2 - Color signal amplitude limiter for video signals - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display apparatus such as a television receiver and the like, in which the saturation of a color signal of an input signal is larger than a standard value, the overdrive or dynamic range of those display elements is exceeded. The present invention relates to a color signal amplitude limiting device for a video signal capable of automatically preventing loss of display capability and maintaining color tone and gradation of a color signal.

[0002]

2. Description of the Related Art In recent years, as the number of media for supplying video signals increases, the number of signals input to an image display device such as a television receiver often exceeds an original standard level. The color signal amplitude limiting device for a video signal automatically adjusts the amplitude of the color signal even when such a non-standard signal is input, keeps the amplitude within the dynamic range of the video display element, and stores the original information. It is considered important because of its ability to communicate.

Hereinafter, an example of the above-described conventional color signal amplitude limiting device for a video signal will be described with reference to the drawings.

FIG. 5 is a block diagram of a conventional color signal amplitude limiting device for a video signal, and FIG. 6 is a waveform diagram of each part. This will be described below with reference to FIGS. In FIG. 5, reference numeral 1 denotes a chrominance signal demodulation circuit which demodulates a chrominance signal modulated on a chrominance subcarrier, and performs RY, BY, G
-Output Y or any two color difference signals. A color saturation adjustment circuit 2 adjusts an input color difference signal to an appropriate color saturation (amplitude) by a color control signal and outputs a color difference signal. At the same time, in order to keep the ratio between the luminance signal and the chrominance signal constant, the contrast control signal is also adjusted so that the chrominance signal has an amplitude corresponding to the amplitude of the luminance signal. Reference numeral 3 denotes a luminance signal amplitude adjustment circuit that adjusts the amplitude of the input luminance signal according to the contrast control signal and outputs the adjusted signal. Reference numeral 4 denotes a brightness adjustment circuit which clamps the pedestal level of the appropriate signal to a constant potential and outputs the signal in accordance with the brightness control signal. Reference numeral 5 denotes a luminance signal amplitude limiting circuit which prevents overdrive when the input level of the luminance signal or the like becomes large,
This is performed by an amplitude limiting circuit or a gamma correction circuit. 6
Is a matrix circuit that adds the luminance signal and the color difference signal to generate color signals R, G, and B and outputs the signals to a CRT or a display device. Reference numeral 7 denotes a Zener diode, which limits the amplitude of the output signals R, G, and B of the matrix circuit when the display device is overdriven so as to prevent overdrive.

The operation of the color signal amplitude limiting device for a video signal configured as described above will be described below.

First, a color signal a modulated on a color subcarrier is input to a color demodulation circuit 1 and demodulated into color difference signals c and d.
In this embodiment, c is RY and d is BY. After this,
The color difference signals are output as color difference signals f and g after the color saturation is adjusted by the color saturation adjustment circuit 2. On the other hand, the luminance signal is first subjected to amplitude adjustment by the luminance signal amplitude adjustment circuit 3 and then output as the luminance signal b after the pedestal level is fixed by the brightness adjustment circuit 4. The luminance signal b is input to a luminance signal amplitude limiting circuit 5 for preventing overdriving of the luminance signal, and overdrive is prevented by processing such as gamma correction and amplitude limitation. The luminance signal and the chrominance signal that have passed through the above circuit system are input to the matrix circuit 6, converted into chrominance signals R, G, and B and output to the display element. At this time, the luminance signal is amplitude-restricted, but there is no color-amplitude restriction of the color difference signal, so that a non-standard input signal whose color saturation is increased is input, or the color saturation is excessively increased by the adjustment circuit 2. The color signal R,
Since G and B are overdriven, the amplitude is limited by the Zener diode 7 and output to the display element.

[0007]

However, in the above-described configuration, the color signal output j is amplitude-limited by the Zener diode as shown in FIG. There is a problem that the tonality is deleted and the original color cannot be sufficiently expressed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an apparatus for limiting the amplitude of a color signal capable of expressing the original color tone and hue even when the amplitude is limited.

[0009]

In order to solve the above-mentioned problems, a color signal amplitude limiting device for a video signal according to the present invention comprises a first maximum value detection circuit, a second maximum value detection circuit, and a first maximum value detection circuit. , A second addition circuit, a switch circuit, a peak value detection circuit, a first comparison circuit, a second comparison circuit,
The configuration includes a clamp circuit, an average luminance level detection circuit, and a clip circuit.

[0010]

According to the present invention, a switch circuit for inputting a luminance signal passed only through a luminance signal amplitude adjustment circuit and a brightness adjustment circuit, or a clamp circuit, according to the above configuration,
The first maximum value detection circuit and the first comparison circuit detect the high color saturation portion of the demodulated color difference signal before performing the saturation adjustment, and close the switch at that portion. The output signal of the switch circuit and the maximum value of the color difference signal subjected to the color saturation adjustment are added by the first addition circuit to the signal detected by the second maximum value detection circuit, and the color signal of the portion with high color saturation is added. The components corresponding to the signal amplitudes of the outputs R, G and B are obtained, and the peak value of the signal after the addition for a certain period is detected by a peak value detection circuit.
The comparison circuit compares the peak value with an amplitude limiting voltage corresponding to the maximum amplitude determined by a preset display element, and if the peak value exceeds the amplitude limiting voltage, controls the color saturation. By performing feedback control so that the voltage is reduced by the second adder circuit, the amplitude of the color signal can be limited without impairing the amplitude or gradation of a portion having high color saturation. .

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an apparatus for limiting a color signal amplitude of a video signal according to an embodiment of the present invention.

FIG. 1 is a block diagram showing a color signal amplitude limiting device for a video signal according to a first embodiment of the present invention. FIG. 2 is a waveform diagram showing waveforms at various parts in FIG.

In FIG. 1, 1 is a color demodulation circuit, 2 is a color saturation adjusting circuit, 3 is a luminance signal amplitude adjusting circuit, 4 is a brightness adjusting circuit, 5 is a luminance signal amplitude limiting circuit, and 6 is a matrix circuit. This configuration is the same as in the conventional embodiment. A first maximum value detection circuit 8 detects the maximum value (larger amplitude) of the color difference signals RY and BY color-demodulated. Reference numeral 15 denotes a first comparison circuit, which is connected to the output of the first maximum value detection circuit, and turns on the switch circuit 10 when the maximum value is close to or exceeds 100% at a standard level. Operate. Reference numeral 10 denotes a switch circuit, which receives a luminance signal from the brightness adjustment circuit and, when turned on, inputs the signal to the first addition circuit. 9 is
The second maximum value detection circuit detects a maximum value of a color difference signal output from the color saturation adjustment circuit. Reference numeral 11 denotes a first addition circuit which adds the maximum value detected at 9 to the output of the switch circuit 10. Reference numeral 12 denotes a peak detection circuit which detects and outputs a peak value of an output signal of the first addition circuit over several fields. Reference numeral 13 denotes a second comparison circuit which compares the detection result of the peak detection circuit with an amplitude limit voltage indicating a maximum amplitude level determined by a preset display element, and determines that the peak detection result exceeds the amplitude limit voltage. In this case, the second adder circuit 14 operates to lower the color control signal and lower the color saturation. Reference numeral 14 denotes a second addition circuit for this purpose.

The operation of the apparatus for limiting the amplitude of a color signal of a video signal constructed as described above will be described below with reference to FIGS.

First, the maximum value of the color-demodulated color difference signals c and d (c is RY and d is BY) is detected by a first maximum value detection circuit 8 to obtain a signal e. The signal e is supplied to the first comparison circuit 15
Is compared with the reference voltage o representing near 100% in the standard amplitude level, and when the signal e exceeds o, the switch circuit 10 is turned on. The output luminance signal b of the brightness adjustment circuit 4 is connected to the switch circuit 10, and this signal b is sent to the first addition circuit when the switch is turned on. The other input of the first adder circuit 11 receives the maximum value h of the color difference signal after passing through the color saturation adjustment circuit 2. By adding h and b, the saturation value of the saturation is calculated. A detection signal i equal to the output signal of the actual matrix circuit 6 in the high part is obtained. The peak level of the detection signal i is detected by the peak detection circuit 12 over several fields, and a peak detection voltage k is obtained. Next, the peak detection voltage k and the amplitude limiting voltage 1 are compared by the second comparison circuit 13,
When the peak detection voltage k exceeds the amplitude limit voltage l, the color control signal for adjusting the saturation of the color saturation adjustment circuit 2 is reduced by the second addition circuit 14, so that the color saturation is reduced. Operate. The circuits from the second maximum value detection circuit to the second addition circuit constitute a feedback loop. When the peak detection voltage k exceeds the amplitude limit voltage 1 by the above operation, as a result,
The amplification degree of the color saturation adjustment circuit decreases until the two become equal, and the feedback operation ends.

As described above, according to the first embodiment of the present invention, when a signal having a very high color saturation is input, the signal itself is not limited and gradation is lost. By lowering the degree, the amplitude of the color signal can be limited while maintaining the original gradation and hue of the color.

Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a block diagram showing a color signal amplitude limiting device for a video signal according to a second embodiment of the present invention. In FIG. 3, components other than 16 to 19 are exactly the same as in the first embodiment. 16
Is a clamp circuit for clamping the pedestal level of the luminance signal or the tip of the synchronization signal to a constant potential. 17
Is an average luminance level detection circuit for detecting an average luminance level (APL) of a luminance signal. Reference numeral 18 denotes a clip circuit which clips and flattens a detection signal of a portion having a low average luminance level among the average luminance levels. Reference numeral 19 denotes a third adding circuit that adds the clipped average luminance level and the amplitude limiting voltage of the chrominance signal and outputs an amplitude limiting voltage according to the APL.

The operation of the apparatus for limiting the amplitude of a color signal of a video signal configured as described above will be described below with reference to FIGS.

FIG. 4 is a diagram showing the operations of the present embodiment in which 16 to 14 are newly added.
19 illustrates the operation of 19 blocks. The operation of the other blocks in the second embodiment is the same as that in the first embodiment, and thus the description is omitted. The difference between the second embodiment and the first embodiment lies in that the amplitude limiting voltage of the color signal is changed according to the APL using the third adder circuit.
According to the embodiment, even if there is no signal that has passed through the luminance signal amplitude adjusting circuit 3 or the brightness adjusting circuit 4, the present luminance signal amplitude limiting device can be realized by the input luminance signal.

First, the input luminance signal is input to the clamp circuit 16 and clamped. One of the output signals is guided to the switch circuit 10 and performs the same operation as that of the first embodiment, and the other output is the average luminance level detection circuit 17.
And an average luminance level is detected. This detection characteristic is shown in FIG. Here, originally CRT (cathode ray tube)
Paying attention to the fact that the condition of the overdrive is only the portion where the APL is low, the clip circuit 18 flattens the portion where the average luminance level is low to a constant value.
This state is shown in FIG. Next, the clipped average luminance level and the amplitude limiting voltage 1 used in the first embodiment are added by a third adding circuit, and a new amplitude limiting voltage s is obtained.
Get. FIG. 4C shows a state of the change of the amplitude limiting voltage s depending on the average luminance level. By applying the amplitude limiting voltage s to the second comparison circuit, the amplitude limitation is stronger when the average luminance level is low, and the amplitude limitation is weakened when the average luminance level is high. Amplitude limitation can be effectively applied to a video having a low luminance level.

As described above, according to the second embodiment, the luminance signal amplitude adjusting circuit 3 is provided by providing the clamp circuit, the average luminance level detecting circuit, the clipping circuit, and the third adding circuit for the luminance signal. Signal amplitude limiting device that can realize a color signal amplitude limiting device without a signal having passed through the brightness adjustment circuit 4 and a color amplitude limiting device that can eliminate lack of gradation and change in hue in a portion where the amplitude is limited. Is provided.

In the first embodiment, the output color difference signals of the color demodulation circuit are RY and BY.
Any one or two of -Y, BY, GY,
Or all. In one case, the first and second maximum value detection circuits can be eliminated.

[0023]

As described above, according to the present invention, it is possible to limit the amplitude of a color signal without deteriorating the gradation of a portion having a high color saturation and without changing the hue.

[Brief description of the drawings]

FIG. 1 is a block diagram of a color signal amplitude limiting device for a video signal according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of the color signal amplitude limiting device for the video signal.

FIG. 3 is a block diagram of a color signal amplitude limiting device for a video signal according to a second embodiment of the present invention;

FIG. 4 is an explanatory diagram of the operation of the color signal amplitude limiting device for the video signal.

FIG. 5 is a block diagram of a conventional video signal color signal amplitude limiting device.

FIG. 6 is a waveform diagram of the color signal amplitude limiting device for the video signal.

[Explanation of symbols]

 Reference Signs List 8 first maximum value detection circuit 9 second maximum value detection circuit 10 switch circuit 11 first addition circuit 12 peak value detection circuit 13 second comparison circuit 14 second addition circuit 15 first comparison circuit 16 clamp Circuit 17 Average luminance level detection circuit 18 Clip circuit 19 Third addition circuit

Continuation of the front page (56) References JP-A-2-145084 (JP, A) JP-A-5-30525 (JP, A) JP-A-3-201697 (JP, A) JP-A-49-57724 (JP) , A) Japanese Utility Model Showa 58-66779 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 9/44-9/78

Claims (2)

(57) [Claims] 1. A contrast control circuit for adjusting the amplitude of a luminance signal of a video signal, a brightness control circuit disposed before or after the contrast control circuit for adjusting the brightness of the luminance signal, and a color signal for the video signal. Demodulated color difference signals RY, BY, G-
A first maximum value detection circuit for detecting the maximum value of Y or any two of them, and a first maximum value detection circuit connected to the output of the first maximum value detection circuit; To detect when the amplitude of the maximum value is large.
And the first comparison circuit is turned on when the comparison result of the first comparison circuit has a large maximum value, and the input is connected to the luminance signal after the amplitude adjustment and the brightness adjustment. A second circuit for detecting the maximum value of RY, BY, GY of the color difference signal after adjusting the color saturation of the color difference signal after demodulation, or any two of them; A maximum value detection circuit, a first addition circuit connected to the output of the second maximum value detection circuit, for adding the maximum value to the output of the switch circuit, and a first addition circuit connected to the output of the first addition circuit A peak detection circuit for detecting a peak value of the output signal of the addition circuit for a certain period of time, and comparing the output signal of the peak detection circuit connected to the output of the peak detection circuit with a preset amplitude limiting voltage to detect the peak value. Output when the voltage is larger than the amplitude limit voltage. A second comparison circuit configured to output a signal, a second addition circuit for adding the color control voltage and the output of the second comparison circuit, and demodulation according to the output voltage of the second addition circuit. A color saturation adjustment circuit that adjusts the amplitude of the color difference signal, thereby limiting the overdrive of the display element without changing the hue even when a signal whose saturation exceeds the standard level is input. And a color signal amplitude limiting device for a video signal. 2. A clamp circuit for clamping a luminance signal of a video signal, an average luminance level detection circuit for calculating an average luminance level of the luminance signal, a clip circuit for clipping a detection signal of a portion having a low average luminance level, A third adding circuit for adding the output signal of the clipping circuit to a preset amplitude limiting voltage of the color signal; and a color difference signal RY, BY, GY, GY, Alternatively, a first maximum value detection circuit for detecting the maximum value of any two of these signals is connected to an output of the first maximum value detection circuit, and the amplitude of this maximum value is compared with a preset voltage. A first comparison circuit for detecting the case where the amplitude of the maximum value is large; and a first comparison circuit connected to the first comparison circuit. The first comparison circuit is turned on when the comparison result of the first comparison circuit is large. Output of clamp circuit The switch circuit connected to the input and output of the color difference signal after adjusting the color saturation of the color difference signal after demodulation.
A second maximum value detection circuit for detecting the maximum value of the signals Y, BY, GY, or any two of them; and a second maximum value detection circuit connected to the output of the second maximum value detection circuit. A first adder circuit for adding the value and the output of the switch circuit, a peak detection circuit connected to the output of the first adder circuit for detecting a peak value of an output signal of the adder circuit for a certain period, Comparing the output signal of the third addition circuit with the output signal of the peak detection circuit, which is connected to the output of the peak detection circuit,
A second comparison circuit configured to output an output signal when the peak detection voltage is higher than the output voltage of the third addition circuit; and a second comparison circuit that adds the color control voltage and the output of the second comparison circuit. An adder circuit, and a color saturation adjustment circuit for adjusting the amplitude of the demodulated color difference signal in accordance with the output voltage of the second addition circuit, wherein a signal whose saturation exceeds the standard level is output. A color signal amplitude limiting device for a video signal, which is capable of limiting overdrive of a display element without changing a color tone even when input.