KR0183134B1 - Contour compensation circuit of image signal - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction circuit of a video signal for sharpening the contour of an output image output on a CRT (Cathode-ray Tube) in a television receiver, the first integration integrating a luminance signal detected from the video signal. Means for differentiating the signal integrated by the first integrating means, and the contour of the video signal adapted to perform contour correction on the video signal based on the differential signal by the differentiating means and the luminance signal. The correction circuit is characterized in that it comprises a second integrating means coupled in parallel to the first integrating means, and a switching means for selectively operating the second integrating means in accordance with the RF / AV mode.

Description

Image Correction Circuit

1 is a block diagram showing a contour correction circuit of a video signal according to the prior art.

FIG. 2 is a signal waveform diagram for explaining the operation of the contour correction circuit shown in FIG.

3 is a circuit diagram showing the detailed configuration of the contour correction circuit shown in FIG.

4 is a block diagram showing a contour correction circuit of an image signal according to an embodiment of the present invention.

* Brief description of the main parts of the drawing

1: main IC 2: first integrating circuit

3: first differential circuit 41: second integrating circuit

42: second differential circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction circuit of a video signal for sharpening the contour of an output image output on a CRT (Cathode-ray Tube) in a television receiver.

In general, in the television receiver, outline correction is performed to improve the sharpness of the image output to the CRT. This outline correction is to emphasize the outline between the image output on the CRT by generating a pre shoot and an over shoot for the luminance signal separated from the composite video signal.

FIG. 1 is a configuration diagram showing a contour correction circuit which is generally used. In the drawing, reference numeral 1 denotes a predetermined level for the luminance signal Y separated from the Y / C separation circuit (luminance / color signal separation circuit: not shown). Is an adder circuit for adding a sharpness signal, 2 is an integrator circuit for integrating the output signal of this adder circuit 1 with a predetermined integration time constant, and 3 is a predetermined Differential circuit that differentiates by the derivative time constant.

Further, reference numeral 4 generates and outputs a predetermined R (Red), G (Green), B (Blue) signal and a luminance signal (-Y) based on the luminance signal (Y) and the color signal. Although not, the main IC executes tone control on the video signal based on the sharpness signal Sha, the color, tint, brightness and contrast control signals. In particular, when the output signal from the differential circuit 4 is input to the sharpness signal input terminal Sha, the main IC 4 internally integrates the signal and executes color tone control corresponding to the level of the integrated signal. In addition, after the second derivative is further differentiated to generate the contour correction signal, contour correction is performed by overlapping the differential signal with the luminance signal input through the luminance signal input terminal (Yin).

That is, in the configuration of FIG. 1, when the luminance signal output from the addition circuit 1 is a square wave as shown in FIG. 2a, the output of the integrating circuit 2 becomes as shown in FIG. 2b, and the integrated signal becomes a differential circuit ( Through 3), the signal of FIG. 3c is input to the sharpness signal input terminal Sha of the main IC 4. In the main IC 4, the first differential signal input to the sharpness signal input Sha is low-pass filtered to generate a tone control signal, while the second differential signal is second-differentiated again. The same signal is generated and then overlapped with the luminance signal input to the luminance signal input terminal (Yin) to generate the luminance signal whose contour is corrected as shown in FIG.

The luminance signal of FIG. 2d becomes a signal whose boundary portion is highlighted. Therefore, when the projection sign is scanned on the CRT based on the luminance signal, the difference between adjacent luminance signals having different luminance levels is very large due to the second derivative signal superimposed on the luminance signal. The outline of the video signal is very clear.

FIG. 3 is a block diagram showing the actual circuit configuration of the contour correction circuit shown in FIG. 1, wherein in FIG. 3, reference numeral VRI denotes a variable resistor for adjusting the sharpness signal level, C1 denotes a high frequency filter, C2 is a coupling capacitor.

As shown in FIG. 3, the sharpness signal line and the luminance signal line are coupled by the capacitors C2 and C3 and the capacitor C4 in series connection, and between the connection point of the capacitors C2 and C3 and ground, an inductor ( L1 and a resistor R2 are coupled, and a resistor R1 is coupled in series between a connection point of the sharpness signal line and the capacitor C2 and the variable resistor VR1.

Here, the resistor R1 and the capacitors C2 and C3 constitute the differential circuit 3, and the capacitor C3, the inductor L1, and the resistor R2 constitute the integrating circuit 2. The differential time constant and integral time constant determined by each element determine the magnitude of the preshoot and overshoot of the luminance signal output from the main IC 4, respectively.

That is, Fig. 2f shows a case where the luminance signal output from the main IC 4 is viewed on a mono scope screen. Here, if the integral time constant of the integrating circuit 2 is increased, the preshoot On the other hand, while the overshoot increases and the value of the differential time constant of the differential circuit 3 is increased, the preshoot increases while the overshoot decreases. In the case of manufacturing, as shown in Fig. 2f, the preshoot and overshoot are set by appropriately setting the integral time constant and the derivative time constant so that the magnitude of the preshoot and the overshoot of the luminance signal output from the main IC 4 are the same. It is to prevent the deterioration of the image quality due to the difference.

However, the above-described contour correction circuit has the following problem.

That is, in general, in case of a broadcast signal (RF signal) received through an antenna, the signal modulation rate is set to about 70%, whereas in the case of a signal reproduced and output from an AV (Audio Video) device such as a video device, etc. The signal modulation rate is set to approximately 100%. Nevertheless, in the case of a general television receiver, the integral time constant and the differential time constant of the contour correction circuit are set so that the preshoot and the overshoot are the same size based on the broadcast signal (RF signal) received through the antenna. In the case of a video signal input from a video device or the like, the luminance signal output from the main IC 4 becomes a signal in which overshoot is emphasized as shown in FIG.

Accordingly, an object of the present invention is to provide a contour correction circuit for a video signal, which has been created to solve the above-described problems, so that good contour correction can be performed for both an RF signal and an AV signal.

The contour correction circuit of a video signal according to the present invention for realizing the above object comprises first integrating means for integrating a luminance signal detected from the video signal, and differentiating means for differentiating a signal integrated by the first integrating means. In the contour correction circuit of the video signal configured to perform contour correction on the video signal on the basis of the differential signal by the differential means and the luminance signal, second integration means coupled in parallel to the first integration means. And switching means for selectively operating the second integrating means in accordance with the RF / AV mode.

Further, the differential means is characterized in that it comprises a first differential means for switching operation at the time of the operation of the first integration means, and a second differential means for switching operation at the time of the operation of the second integration means.

According to the present invention having the above-described configuration, in the AV mode, the second integrating means is combined in parallel with the first integrating means, so that the integral time constant is set small.

Therefore, the excessive overshoot in the AV mode is improved by the integral time constant reduced in this way, so that the degradation of the output image quality caused by the contour correction can be prevented.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

4 is a block diagram showing a contour correction circuit of an image signal according to an embodiment of the present invention. In the drawing, reference numeral 41 denotes a second integrating circuit provided in parallel with respect to the first integrating circuit 2, The capacitor C6, the inductor L2 and the resistor R3 together with the capacitor C3 of the first integrating circuit 2 form an integral circuit.

Further, reference numeral 42 denotes a second differential circuit provided in parallel with respect to the above-described first differential circuit 3, which is a capacitor C8 provided in parallel with the capacitor C7 of the first differential circuit 3. ) Together with the capacitors C2, C3 and C9 form a differential circuit. In the first differential circuit 3_, the capacitors C8 and C9 correspond to the capacitor C4 in FIG.

Also, in FIG. 4, the second integrating circuit 41 is grounded through the current path of the transistor Q1 to the switching means, and the transistor Q1 has its base end output via the resistor R4. Is coupled to Here, although the configuration is not shown in detail in the drawing, the microprocessor outputs a high level switching signal when the viewer selects the AV mode, and outputs a low level switching signal when the viewer selects the RF mode. Done. That is, the second integrating circuit 41 is in a parallel coupling state with respect to the first integrating circuit 2 in the AV mode in which the transistor Q1 is on, and in the RF mode in which the transistor Q1 is off. In this case, the contour correction circuit is composed of only the first integrating circuit 2.

In the first and second differential circuits 3 and 42, unlike the integrated circuits, the first or second differential circuits 3 and 42 selectively function by transistors Q2 and Q3 as switching means. It is configured to. The transistors Q2 and Q3 are selectively turned on by the switching signal output from the microprocessor described above. That is, the differential circuits 3 and 42 operate the first differential circuit 3 in the AV mode and the second differential circuit 42 in the RF mode.

The most characteristic part of the above-described configuration is that the integral time constant of the integrating circuit varies depending on the AV / RF mode. That is, in general, when the integration circuits are combined in parallel, the integration time constant becomes small. If the integral time constant is reduced in this manner, the overshoot of the luminance signal is reduced as described in FIG. Therefore, as shown in FIG. 4, in the AV mode, the transistor Q1 is turned on to operate the second integrating circuit 41 to prevent excessive overshoot generated in the AV mode.

On the other hand, in FIG. 4, the first and second differential circuits 3 and 42 are for appropriately setting the levels of the preshoot and overshoot according to the operation state of the second integrating circuit 41 described above.

In the above configuration, in the RF mode, the transistor Q1 is turned off by the low level switching signal output from the microprocessor, the transistor Q2 is turned off, and the transistor Q3 is turned on. Thus, in this case, the first integrating circuit 2 and the second differential circuit 42 are turned on. At this time, the first integral circuit 2 and the second differential circuit 42 have their integral time constants and differential time constants set so that their preshoot and overshoot levels are the same for the RF signal.

In the AV mode, the transistor Q1 is turned on by the high level switching signal output from the microprocessor, the transistor Q2 is turned on, and the transistor Q3 is turned off. In this case, therefore, the first integrating circuit 2 and the second integrating circuit 41 are turned on, and the first integrating circuit 3 is turned on. Therefore, in this case, excessive overshoot in the AV mode is suppressed in accordance with the reduction of the integral time constant as described above. In this case, the first differential circuit 3 is configured such that the level of the overshoot and the preshoot has an appropriate value. The derivative time constant is set.

Therefore, in the above embodiment, since the preshoot and the overshoot of constant size are always obtained in the RF mode and the AV mode, it is possible to provide good contour correction for the video signal output on the CRT.

In addition, this invention is not limited to the said Example, It can implement in a various deformation | transformation in the range which does not deviate from the technical summary of this invention.

As described above, according to the present invention, it is possible to realize a contour correction circuit of a video signal that enables good contour correction for both the RF signal and the AV signal.

Claims (2)

A first integrating means for integrating the luminance signal detected from the video signal, and a differentiating means for differentiating the signal integrated by the first integrating means, and based on the differential signal by the differentiating means and the luminance signal. A contour correction circuit of an image signal adapted to perform contour correction on a signal, the second integration means coupled in parallel with the first integration means and selectively operating the second integration means in accordance with the RF / AV mode. Contour correction circuit of a video signal comprising a switching means for. The method of claim 1, wherein the differentiating means comprises a first differentiating means for switching operation when the first integrating means is operated, and a second differentiating means for switching operation during the operation of the second integrating means. A contour correction circuit for a video signal.