JPH0752919B2 - Video signal contour correction device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an improvement in a contour correction device for a video signal.

[Prior Art] FIG. 1 shows a conventional contour correction apparatus for video signals. In the figure, the original video signal S1 from the video signal source 1 is applied to one input of the adder circuit 3 through the amplifier circuit 2 as required. This original video signal S1 is the contour correction signal generation circuit 6
Also given to. The contour correction signal generating circuit 6 is composed of two differentiating circuits 4 and 5 connected in series. Differentiator circuit 4
Differentiates the component of the original video signal S1 during the video period, and the differentiating circuit 5 again differentiates the output. Therefore, the contour correction signal E1, which is the output of the contour correction signal generation circuit 6, is the second derivative of the component of the original video signal S1 during the video period. The contour correction signal E1 is given to the other input of the adding circuit 3 and is combined with the original video signal S1 given from the one input. In this way, the adder circuit 3 outputs the contour-corrected video signal S2.

Next, the operation of the conventional apparatus shown in FIG. 1 will be described with reference to the waveform chart of FIG. Now, it is assumed that the original video signal S1 from the video signal source 1 is obtained as a pulse wave in each horizontal synchronization section, as shown in FIG. 2A, for example. In this case, the contour correction signal E1 obtained from the contour correction signal generation circuit 6 is obtained as a secondary differential wave at the rising and falling positions of the original video signal S1 which is a pulse wave, as shown in FIG. 2B. The original video signal S1 (waveform A) and the contour correction signal E1 (waveform B) are combined in the adder circuit 3 to obtain a contour-corrected video signal S2 having a waveform as shown in FIG. 2C. As is clear from FIG. 2C, the contour-corrected video signal S2 is a combination of the secondary differential waves at the rising and falling positions of the original video signal S1 which is a pulse wave. If an image is obtained on a display device (not shown) using the contour-corrected video signal S2 thus obtained, the contour of the image is obtained by using the original video signal S1 as it is. It becomes clearer than the case of

However, in such a conventional device, the original video signal S1
Depending on the contents of the above, the screen may become difficult to see if contour correction is performed. This is particularly remarkable when the number of positive or negative pulsed waves (hereinafter simply referred to as pulses) included in the second derivative wave per vertical synchronization section is relatively large. In that case, the screen on the display device obtained by using the contour-corrected video signal S2 becomes a so-called "dusty" image, which is difficult to see.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the drawbacks of the conventional device as described above, and to provide a contour correction apparatus for a video signal in which the contour is not made difficult to see. is there.

The present invention is a contour correction device for performing contour correction of a video signal, and contour correction signal generating means for receiving the video signal and generating a contour correction signal for the contour correction,
Means for receiving the contour correction signal and counting it from the vertical synchronizing signal to the next vertical synchronizing signal; and a sample for sampling the count output of the counting means and holding it from the vertical synchronizing signal to the next vertical synchronizing signal. Holding means; clipping means for receiving the contour correction signal and clipping the contour correction signal in response to the output of the sample holding means; and synthesizing means for synthesizing the output of the clipping means with the video signal. There is.

[Embodiment of the Invention] FIG. 3 is a block diagram showing a preferred embodiment of a contour correction apparatus for video signals according to the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. Unlike the conventional device shown in FIG. 1, the contour correction device for a video signal according to the present invention includes a contour correction signal generation circuit 6
And the adder circuit 3 between the clip width variable clip circuit 9
Have. The variable clip width clipping circuit 9 includes an input terminal 8a connected to the contour correction signal generating circuit 6 and an adding circuit 3
It has an output terminal 8b connected to and a control terminal 8c. A control signal generation circuit 10 which receives the contour correction signal E1 and provides an output signal V2 for controlling the clip width variable clip circuit 9 is connected between the contour correction signal generation circuit 6 and the control terminal 8c.

The control signal generation circuit 10 is configured as follows. That is, the contour correction signal which is the second derivative of the original video signal S1.
E1 is supplied to the detection circuit 11 and, for example, only the pulse of positive polarity is detected among the pulses included in the contour correction signal E1. Pulse P1 detected in the detection circuit 11
Is applied to the counting pulse generation circuit 12, shaped, and output as a counting pulse P2. The counting pulse P2 is counted by the counting circuit 15. The counting circuit 15 converts the N-bit binary numbers PC1, PC2, ... PCN into a D / A converter.
It is given to 16 as a count output. The counting circuit 15 is reset to zero by the reset pulse P3 from the reset pulse generating circuit 13. The digital values of the binary numbers PC1, PC2, ... PCN are given to the D / A converter 16 and the analog value V
Converted to 1. The analog value V1 is given to the sample hold circuit 18. The sample and hold circuit 18 uses the sampling pulse from the sampling pulse generation circuit 17.
The analog value V1 is sampled at the input time of P5,
The value V2 is continuously output until the next sample pulse P5 is input. The reset pulse generating circuit 13 and the sampling pulse generating circuit 17 receive the vertical synchronizing pulse P4,
As a result, reset pulse P3 and sampling pulse
P5 is synchronized with the vertical synchronization pulse P4.
The vertical synchronizing pulse P4 is given from a vertical synchronizing pulse generating circuit 14 provided separately from the control signal generating circuit 10. The vertical sync pulse generation circuit 14 is adapted to give a vertical sync pulse P4 which is synchronized with the vertical sync of the original video signal S1. Output of sample hold circuit 18 (that is, control signal generation circuit
The output 10) V2 is given to the control terminal 8c of the clip width variable clip circuit 9.

FIG. 4 shows an example of the clip width variable clip circuit 9 shown in FIG. In FIG. 4, the input terminal 8a is
The output E1 of the contour correction signal generation circuit 6 of FIG. 3 is given. The output V2 of the control signal generating circuit 10 shown in FIG. 3 is applied to the control terminal 8c. The control terminal 8c is connected to the plus input of an operational amplifier 91 used as a non-inverting amplifier circuit. A pair of NPN transistors 93 and 94 for noise clipping and a pair of PNP transistors 95 and 96 for noise clipping are also connected between the power supply V _cc and ground.
Are connected respectively. The outputs of the operational amplifiers 91 and 92 are supplied to the base of the NPN transistor 94 and the base of the PNP transistor 96. The contour correction signal E1 from the input terminal 8a is given to the base of the NPN transistor 93 and the base of the PNP transistor 95, respectively. A pair of NPN transistors 93 for noise clipping
And 94 outputs, and also a pair of PNP transistors 9
The outputs of 5 and 96 are guided to the output terminal 8b via the emitter follower circuit including the NPN transistor 97, respectively.

If the clip width of this circuit is Ec, this clip width Ec
Is determined by the output potential difference of the operational amplifiers 91 and 92.

Ec = Ea−Eb (where Ea> Eb) (1) where Ea and Eb are operational amplifiers 91 and 92, respectively.
Is the output voltage of.

The output voltage Ea of the operational amplifier 91 is the input voltage V2 of the control terminal 8c.
Changes according to the value of. Further, the gain of the operational amplifier 91 is determined by appropriately selecting the resistor 98 having the resistance value R1 and the resistor 99 having the resistance value R2. That is, the output voltage Ea of the operational amplifier 91 is expressed by the following equation.

Ea = (1 + R2 / R1) V2 (2) Considering the equation (1), the clip width Ec is determined by the following equation.

Ec = (1 + R2 / R1) V2-Eb (3) Next, the operation of the clip width variable clip circuit shown in FIG. 4 will be described. The clip operation is achieved as follows. That is, the input signal (contour correction signal E1) from the input terminal 8a is given to the base of the NPN transistor 93. On the other hand, the base of the NPN transistor 94 is supplied with a DC voltage (reference voltage) that serves as a reference for the clip level. When the base voltage of the NPN transistor 93 is higher than that of the NPN transistor 94, the NPN transistor 94 is in the cutoff state, while the NPN transistor 93 is in the cutoff state.
Operates and its output is taken out from its emitter through the NPN transistor 97.

Next, conversely to the above case, consider a case where the base voltage of the NPN transistor 93 is lower than the base voltage of the NPN transistor 94. In this case, the NPN transistor 93
Is in a cut-off state, while the NPN transistor 94 is in an operating state, and the potential of the emitter becomes constant by the reference voltage applied to its base. This constant potential is
It is taken out from the output terminal 8b via the NPN transistor 97. In this way, a voltage below a certain level can be clipped to a constant potential.

Although the clip for the negative side of the reference voltage is explained above, the PNP transistors 95 and 96 are also used for the positive side.
It is clear that a similar operation can be achieved by using

FIG. 5 is a waveform diagram showing the relationship between the input signal and the output signal of the clip width variable clip circuit 9. The input signal (contour correction signal E1) of the clip width variable clipping circuit 9 shown in FIG. 5A is clipped by the clip width variable clipping circuit 9 by the clip width Ec shown in FIG. It is output as the output signal E2. Above (3)
As is clear from the equation, the clip width Ec is
It increases or decreases in proportion to the output V2 of the control signal generation circuit 10 given to the.

FIG. 6 is a waveform diagram for explaining the operation of the video signal contour correcting apparatus shown in FIG. 3 which is a preferred embodiment of the present invention. The operation of the embodiment shown in FIG. 3 will be described below with reference to FIG. For the sake of explanation, as shown in FIG. 6, attention is paid to one vertical sync section of the original video signal S1 obtained from the video signal source 1, and further to one horizontal sync section in this vertical sync section.

As shown in FIG. 6A, assuming that the original video signal S1 includes N pulses in one horizontal synchronization section, the contour correction signal E1 obtained by the contour correction signal generation circuit 6 is as shown in FIG. 6B. In addition, a set of 2N pulses of positive polarity and negative polarity is included in the horizontal synchronization section. This contour correction signal E1 is given to the detection circuit 11 in the control signal generation circuit 10, and from the detection circuit 11, as shown in FIG. 6C1, 2N positive polarity pulses P1 are generated in the horizontal synchronization section. Is output. this
2N positive-polarity pulses P1 are counted pulse generation circuit 12
Is shaped into a counting pulse 2 as shown in FIG. 6C2.

As shown in FIG. 6D, the vertical sync pulse generation circuit 14 outputs a negative pulse P4 synchronized with the vertical sync of the original video signal S1 of FIG. 6A. This pulse P4 is given to the reset pulse generating circuit 13 and the sampling pulse generating circuit 17, and in response thereto, the reset pulse P3 and the sampling pulse P5 shown in FIGS. 6E and 6F.
Are output respectively. The timings of the three pulses P3, P4, and P5 are represented by using t1, t2, t3, t4, t5, and t6 in FIG. 6G, and their relationship is as follows.

t1 <t2 <t3 <t4 <t5 <t6 FIG. 6H shows the output V1 of the D / A converter 16. This output V1
Are reset to zero in response to the reset pulse P3 shown in FIG. 6E. FIG. 6I shows the output V2 of the sample and hold circuit 18. This output V2 is sent to the D / A converter 1 in response to the sampling pulse P5.
It can be seen that it is a sample of the output V1 of 6.

FIG. 6J shows the output signal of the clip width variable clip circuit 9.
Indicates E2. A signal E2 shown in FIG. 6J is obtained by clipping only the clip width Ec shown in FIG. 6 from the contour correction signal E1 shown in FIG. 6B. The clip width Ec is controlled by the output voltage V2 of the control signal generation circuit 10 as described above.

The signal E2 in FIG. 6J is the original video signal S1 in the adder circuit 3.
Then, the adder circuit 3 outputs the contour-corrected video signal S2 shown in FIG. 6K.

According to the above-mentioned operation, 1 of the pulse P1 shown in FIG.
As the number per vertical synchronization section increases, the clip width Ec also increases proportionally. On the contrary, if the number of the pulses P1 per one vertical synchronization section becomes smaller, the clip width Ec also becomes proportionally smaller. In this way, since the clip width Ec changes in proportion to the number of the pulse P1 per vertical synchronization section, the contour correction signal (signal
E2) is a substantially constant signal regardless of the contour correction signal E1 before clipping. Therefore, it will be understood that the contour-corrected video signal S2 shown in FIG. 6K is always properly contour-corrected.

In the above-described embodiment, the case where the clip width variable clip circuit shown in FIG. 4 is used has been described, but any clip circuit that can change (not limited to proportional) the clip width in response to the control voltage is used. Other types may be used, and the same effect as that of the above-described embodiment can be obtained.

Further, in the above-mentioned embodiment, the output of the contour correction signal generating circuit 6 is directly given to the detecting circuit 11, but a clipping circuit or an amplitude discriminating circuit is provided between them to detect only a pulse having a certain amplitude or more. May be given to 11. Also in this case, the same effect as that of the above-described embodiment is obtained.

Further, a delay circuit may be inserted between the amplifier circuit 2 and the adder circuit 3, which makes it possible to perform more appropriate contour correction. The delay may be, for example, one vertical sync period.

As described above, according to the present invention, the means for receiving the contour correction signal and counting it from the vertical synchronizing signal to the next vertical synchronizing signal, and the count output of this counting means for sampling the vertical synchronizing signal. Since it has a sample hold means for holding from the signal to the next vertical synchronizing signal, it is possible to guarantee the uniformity of the aperture correction signal in the screen,
There is an effect that the level of the aperture correction signal for the same picture on the screen can be made the same.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional video signal contour correcting apparatus, FIG. 2 is a waveform diagram for explaining the operation of the conventional apparatus shown in FIG. 1, and FIG. 3 is a preferred embodiment of the present invention. FIG. 4 is a block diagram showing an example of a video signal contour correction device;
The figure is a circuit diagram showing an example of a clip width variable clip circuit.
FIG. 5 is a waveform diagram for explaining the operation of the variable clip width clipping circuit of FIG. 4, and FIG. 6 is a waveform diagram for explaining the operation of the preferred embodiment of the present invention shown in FIG. Is. In the figure, 1 is a video signal source, 2 is an amplifying circuit, 3 is an adding circuit, 4 and 5 are differentiating circuits, 6 is a contour correction signal generating circuit, 9 is a clip width variable clipping circuit, 10 is a control signal generating circuit, and 14 Are vertical sync pulse generation circuits, respectively.

Claims (2)

[Claims] 1. A contour correction device for performing contour correction of a video signal, comprising contour correction signal generating means for receiving the video signal and generating a contour correction signal for the contour correction, and the contour correction signal. Receiving means for receiving and counting it from the vertical synchronizing signal to the next vertical synchronizing signal; and sample holding means for sampling the count output of the counting means and holding it from the vertical synchronizing signal to the next vertical synchronizing signal. A video signal including clip means for receiving the contour correction signal and clipping the contour correction signal in response to the output of the sample and hold means, and synthesizing means for synthesizing the output of the clipping means with the video signal Contour correction device. 2. The contour correction device for a video signal according to claim 1, wherein the clipping means clips the contour correction signal with a clipping width according to the output of the sample and hold means.