JPH0326071A - Contour correction circuit - Google Patents

Abstract

PURPOSE:To obtain a sharp picture without intrusion of a black thin line to a black contour by not applying contour correction by scanning speed modulation to a low brightness part of a luminance signal but applying it only to a high brightness part. CONSTITUTION:A limiter circuit 5 clips a low brightness part because a diode D is put on when an inputted negative polarity luminance signal Y reaches a prescribed level or over. The signal is differentiated by a 1st order differentiating circuit 6, supplies the result to a speed modulation coil 8 to apply the horizontal deflection, then the speed of the low luminance component of the 1st half of the leading part and the latter half of the trailing part of the luminance signal is not quickened and no speed modulation is implemented. Thus, no contour correction by the speed modulation is applied to the 1st half of the leading part and the latter half of the trailing part of the low luminance signal on the screen but applies to the latter half of the leading and the first half of the trailing part of the high luminance signal. Then clear picture quality without intrusion of a black thin line to the contour of the black level is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a contour correction circuit for a television receiver, and more particularly to a contour correction circuit using a scanning speed modulation circuit.

(b) Technique of Jubei It has been well known to use a scanning speed modulation circuit in order to improve the sharpness of an image. has been done.

The principle of scanning speed modulation will be explained according to Figure 5. The same figure (a
) by first-order differentiating the luminance signal shown in ( ).
Obtain a first-order differential signal such as b → and supply it to a speed modulation coil installed separately from the horizontal and vertical change coils to perform horizontal deflection according to the waveform shown in Figure (b). Added to the deflection magnetic field, this is equivalent to a horizontal magnetic field acting on the electron beam as shown in FIG. 3(c). Therefore, the same figure (
As shown in d), in the first half of the rising portion of the luminance signal, the scanning speed of the electron beam is fast, so the brightness on the screen is suppressed, and in the second half of the rising portion, the scanning speed is slow, so the brightness on the screen is high. Further, since a similar effect occurs at the falling portion of the luminance signal, the luminance on the screen becomes as shown in FIG.

However, in areas with high brightness, the electron beam works far away, making the image thinner than the actual image, while in areas with low brightness, the electron beam moves slowly, making the image thicker than the actual image, resulting in image distortion.

Particularly in low-brightness areas, a thick black line appears on the outline of the black area, so when a person's face is displayed, the nostrils become black and large, making it unsightly.

(c) Problems to be Solved by the Invention The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to obtain clear image quality in low-luminance areas where the disadvantages caused by speed modulation occur even when contour correction is performed by speed modulation. purpose.

(2) Means for Solving the Problems In the present invention, a limiter for clipping the low-luminance portion of the video signal is disposed before the first-order differentiator circuit.

(E) Operation The above-described means works so that contour correction by speed modulation is not performed on the low-luminance portion of the video signal.

(f) Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the circuit of this embodiment, in which (1) is a YC separation circuit that separates a composite video signal into a luminance signal (Y) and a color signal (C), and (2) is a YC separation circuit that separates a luminance signal (Y) from a composite video signal. An edge enhancement circuit that adds the correction signal obtained by the two-time differentiation to the luminance signal (Y) to enhance the edge. (3) outputs the edge-enhanced video signal to the CRT (4). This is a video output circuit.

On the other hand, (5) is a feature of this embodiment, and the luminance signal (Y)
(6) is a first-order differentiation circuit that first-order differentiates this output; (7) amplifies this first-order differential output and sends it to the speed modulation coil (8) of the CRT (4). This is an output circuit that supplies

FIG. 2 is a specific circuit diagram of the limiter circuit, which is composed of a diode (D), a capacitor (C), and bias resistors (Rl) and (R.) connected in series. This limiter circuit (5) has a negative polarity luminance signal (Y
) is above a predetermined level, the diode (D) turns on, thereby clipping the low brightness portion.

Furthermore, a diode-connected transistor (T) as shown in FIG. 3 may be used instead of the diode (D).

Next, the operation of the circuit of this embodiment will be explained with reference to FIG.

The luminance signal shown in FIG. 4(a) is clipped at a low luminance portion by the limiter circuit (5) and becomes as shown in FIG. 4(b).

Then, when this signal is differentiated by the first-order differentiator circuit (6), the width of the differentiated pulse is narrower than in the conventional example, as shown in FIG.

Therefore, when this waveform is supplied to the velocity modulation coil (8) and horizontally deflected, the electron beam becomes equivalent to the horizontal magnetic field acting on it as shown in 11ffi(d).

Therefore, the speed of the low-luminance portion in the first half of the rising portion and the latter half of the falling portion of the luminance signal does not become faster as shown in FIG. 2(e), and no speed modulation is performed.

Therefore, as shown in FIG. 5(f), the brightness signal on the screen is not subjected to contour correction by speed modulation for the low-luminance parts in the first half of the rising part and the latter half of the falling part; Contour correction by velocity modulation is performed only on the high-brightness portions of the image.

(g) Effects of the Invention As described above, according to the present invention, contour correction by scanning speed modulation is not performed in the low brightness portion of the brightness signal, but only in the high brightness portion, so that an even thicker black line is added to the contour of the black portion. Clear images can be obtained without any interference.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a contour correction circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific embodiment of the limiter, FIG. 3 is a diagram showing another embodiment of the limiter, and FIG. 4 is a diagram showing a specific embodiment of the limiter. FIG. 5 is a waveform diagram illustrating the operation of the circuit of this embodiment, and FIG. 5 is a waveform diagram illustrating the conventional contour correction operation. (2)...Contour emphasis circuit, (5)...Limiter, (
6)...first-order differentiation circuit, (8)...speed modulation circuit.

Claims (1)

[Claims] (1) In a contour correction circuit comprising a first-order differentiating circuit for first-order differentiating a video signal and a speed modulation coil that receives the output of the first-order differentiating circuit as an input, a low-luminance portion of the video signal is clipped at a stage before the first-order differentiating circuit. A contour correction circuit characterized in that a limiter is arranged.