JPS62155678A - Contour correction circuit - Google Patents

Abstract

PURPOSE:To emphasize the contour of a bright part without increasing noise in a dark part by forming a contour signal by using a clip circuit for outputting a signal part of a white peak level side above a clip voltage. CONSTITUTION:When a clamp pulse of one horizontal scanning period (1H) comes to an input terminal 9, a transistor Q1 performs an on and off operation according to the clamp pulse. To a contour forming circuit 2, a video signal (c) obtained by slicing a video signal (b) by a voltage E1' is supplied. An adder 3 adds a video signal (a) and a contour signal (d) respectively to form a video signal (e) emphasizing the contour part and outputs to an output terminal 10. This video signal (e) has the dark part in which the contour is not emphasized and the noise is not increased, so that the S/N of the dark part is improved in comparison with the conventional one.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a contour correction circuit, and more particularly to a 12-contour compensation IF circuit that emphasizes the contour portion of a video signal.

BACKGROUND OF THE INVENTION FIG. 4 shows a block diagram of an example of a conventional contour correction circuit. In the figure, a video signal as shown in FIG. 5(A), which has entered the input terminal 1, is supplied to a contour creation circuit 2 and a q adder 3, respectively. The contour creation circuit 2 is based on a well-known principle.
Incoming video! j A ring A (signal (or
A second-order differential signal) is generated and output to the adder 3.

+t>Z3 converts the incoming video signal and contour signal into I! ? A: A video signal as shown in FIG. 5(C) is output to the output terminal 4. In this way, Figure 5 (Δ)
As shown in (C), in the video input to the input terminal 1, the outline portion of the video signal that transitions from the black level to the white level or from the white level to the fidelity level is emphasized. As a result,
When the video signal output to the output terminal 4 is reproduced, an image with clear outlines can be obtained.

Problems to be Solved by the Invention However, in the conventional contour part i [circuit shown in FIG.
As shown in ) to (C), there is a drawback that noise in high frequency components increases in both bright and dark areas of the video signal. In this case, the signal level in the dark area is the signal level J in the bright area,
Because the rim is small, the ratio of the signal level to the noise level in the dark area, that is, the S/N in the dark area, is worse than the S/N in the bright area, and the dark area becomes visually noticeable due to noise. There was a problem with it being put away.

Therefore, the present invention provides a contour correction circuit 11 that solves the problem described in F by reducing the contour enhancement of dark areas compared to bright areas of a video signal. The purpose is to provide

A one-stage contour correction circuit according to the present invention for solving the problem includes a clamp circuit that clamps the base level of the video signal to a preset clamp voltage and outputs the result, and a clamp circuit that clamps the base level of the video signal to a preset clamp voltage and outputs the result, and a and a clip circuit that outputs a signal portion on the white peak level side that is higher than the clip voltage in the output video signal of the clamp circuit, and generates a contour signal based on the output signal of the clip circuit. configured to do so.

Effect: By the above-mentioned clamp circuit and clip circuit, the waveform of the video signal is converted into a <r waveform such that the portion between the clamp voltage and the clip voltage, that is, the portion corresponding to the dark portion of the video signal is sliced. . When the outline of a video signal is enhanced using a contour signal generated based on the output signal of a clipping circuit having such a waveform, the amount of outline emphasis in dark areas of the video signal is reduced compared to the bright areas of the video signal compared to the conventional method. It will be done.

Next, an embodiment of the circuit of the present invention will be described with reference to FIGS. 1 to 3.

Embodiment FIG. 1 shows a circuit diagram of an embodiment of the contour correction circuit according to the present invention. In the figure, the same components as in FIG. 4 are given the same reference numerals. In this example, condenser C+
, a clamp circuit 6 consisting of an NPNt transistor Q1 and a reference voltage source 5 that generates and outputs a reference voltage Eo (Eo>O). and capacitor C2, die A-de D+,
A clip circuit 7 consisting of a resistor R2 and a variable resistor R3 is provided, and this clamp circuit 6. Clip circuit 7. NPN transistor Q2. The feature lies in that the contour creation circuit 8 is constituted by the resistor R+ and the contour creation circuit 2.

Here, the video signal input terminal 1 is /Jll g-)
It is connected to one input terminal of the transistor Q1, and is also connected to the collector of the transistor Q1 and the base of the I transistor Q2 via the terminal C1. transistor Q
1 is connected to the clamp pulse input terminal 9 and grounded via its F-mitter (or reference voltage) source 5. On the other hand, the collector of transistor Q2 is connected to the commercial voltage VCC.
is connected to the power supply line supplied with resistor R2.
and are grounded via capacitor C2 and variable resistor R3J, respectively, and other parallel circuits. This capacitor C2, resistor R2, variable resistor [73 connection points G, L, guide wire D
1 is connected in the forward direction to the emitter of the transistor Q2 and the connection point of the resistor R1, and is also connected to the other input terminal of the adder 3 via the diode D1 and the contour creation circuit 2. . The output terminal of this adder 3 is connected to an output terminal 10.

In the above configuration, the input terminal 9 is connected to the input terminal 9 for one horizontal scanning period (1H
) period, the transistor Q
1 performs on/off operations in response to clamp pulses.

In this case, during II when the clamp pulse is at a high level, the transistor Q1 is turned on, and the collector DC potential of the l-transistor Q1 is fixed to the reference voltage Eo, and the voltage is set to the reference voltage Eo. is charged, while
During the period when the clamp pulse is at low level, transistor 0
1 is off, but the charge on the capacitor C1 increases.
1-The collector DC potential of transistor Q1 is also the reference voltage E. Fixed.

As a result, the video signal a shown in FIG. 2 (△) that enters the input terminal 1 has a base level of 3. The quasi-voltage E
o, and the video signal b as shown in the same figure (B)
・and is supplied to the bases of transistors 1 to Q2.

On the other hand, the voltage across capacitor C2 is the power supply voltage V
The voltage is set to E1 obtained by dividing C by a resistor R2 and a variable resistor R3. Here, if the forward voltage drop of the diode D1 is Vo+, then the voltage E+' at the connection point of the cathode of the diode D+, the resistor R1, and the emitter of the transistor Q2 (however, if the white peak level of the movie signal a is Eo, then El )>E+'>Eo) is expressed as equation (1).

E+ '=E+ -Vo +
(1) For this reason, the transistor Q2 compares the level 1e of the electric current a (ii ?i E) input to its base with the voltage E+', and turns on when 1-e>E1'. It turns off when L e≦E+'.

Therefore, the contour generation circuit 2 is supplied with the video signal at a voltage E+'
A video signal C as shown in FIG. Compared to the video signal S, the dark portion 1 of this video signal C has been sliced by a clip circuit.

The contour generation circuit 2 generates a second contour based on the incoming video signal C.
A contour signal d as shown in FIG. 3(D) is generated and output to the adder 3. The adder 3 adds the video signal a and the contour signal d to generate a video signal C whose contour portion is emphasized as shown in FIG.
I'm leaving.

Compared to the video signal shown in FIG. 5(C), this video signal e does not have its dark areas emphasized for its outline, and therefore the noise does not increase in the dark areas as described above. The invention improves the S/N ratio in dark areas compared to the prior art.

In this way, the characteristics of the video signal level versus contour enhancement of the circuit of the present invention are non-linear, as shown in FIG. That is, when the video signal level V input to the input terminal 1 becomes O≦V<EO, a cloud appears between the edge enhancements, and the video signal level V becomes E. When ≦■≦E+',
The edge enhancement portion is approximately zero or changes depending on the characteristics of the diode D1, and when the video signal level V is V>E+', the edge enhancement period increases approximately in proportion to the increase in the video signal level (2).

Note that the configurations of the clamp circuit 6 and the clip circuit 7 are not limited to the configuration shown in FIG.
Other circuit configurations may also be used. Further, the characteristics of the above-mentioned video I & signal signal and contour enhancement are not limited to the characteristics shown in FIG. That's fine.

Effects of the Invention As described above, according to the present invention, the outline emphasis of the dark parts is reduced compared to the bright parts of the video signal, so that it is possible to increase the noise in the dark parts of the video signal. The S/N ratio in dark areas is improved, and therefore images with good and clear outlines can be obtained.

[Brief explanation of drawings]

FIG. 1 is a circuit system diagram showing an embodiment of the contour section 11-circuit according to the present invention, and FIGS. 2 and 3 are signal waveform diagrams and video signal level diagrams for explaining the operation of the circuit system shown in FIG. 1, respectively. The characteristic diagram of the contour emphasizing section, FIGS. 4 and 5, are a block system diagram and a signal waveform diagram for explaining the operation of an example of a conventional contour correction circuit, respectively. DESCRIPTION OF SYMBOLS 1... Video signal input terminal, 2.8... Contour creation circuit, 3... Shoreline device, 5... Reference voltage source, 6... Clamp circuit, 7... Clip circuit, 9... ...Clamp pulse input terminal, 10...Video signal output terminal, C+ r
C2... Capacitor j) 1D +... Diode, Q+, Q2... Transistor, R+, R2...
・Resistance, R3...variable resistance.

Claims (1)

[Claims] In a contour correction circuit that adds a video signal and a contour signal at a level corresponding to the level of the contour portion of the video signal to generate a video signal in which the contour portion is emphasized, the base value level of the video signal is determined. It has a clamp circuit that clamps to a preset clamp voltage and outputs it, and a clip voltage that is set between the clamp voltage and the white peak level of the video signal, and the clip voltage in the output video signal of the clamp circuit is higher than or equal to the clip voltage. 1. A contour correction circuit comprising: a clip circuit that outputs a signal portion on the white peak level side of the contour correction circuit, and is configured to generate the contour signal based on the output signal of the clip circuit.