JPH02246582A - Outline correcting circuit for video signal - Google Patents

Abstract

PURPOSE:To variously control the outline emphasis effect by setting respective gains of two outline correction signals to different values and setting extents of preshoot and overshoot to arbitrary different values. CONSTITUTION:An original signal A and respective output signals B and C of first and second delay means 2A and 2B are added and subtracted to generate first to third outline correction signals B-A, B-C, and 2B-(A+C) which are changed only in the vicinity of the change part of the original signal A. Values of a coefficient (gain) K2 by which the signal B-A is multiplied and a gain K3 by which the signal B-C is multiplied are adjusted independently of each other to obtain a preshoot and overshoot generating signal A, and this signal Z is added to an intermediate signal Y to adjust extents of preshoot and overshoot independently of each other. Thus, an optimum picture quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video signal contour correction circuit suitable for use in, for example, a television receiver to emphasize the contours of a color image.

[Summary of the invention]

The present invention provides a video signal contour correction circuit suitable for use in, for example, a television receiver to emphasize the contours of a color image, including a first delay means for delaying an original signal; a second delaying the output signal of the means;
, the original signal, and the respective output signals of the first and second delay means are added and subtracted to obtain the first . An addition/subtraction circuit for forming second and third contour correction signals, and a logic operation circuit for forming a fourth contour correction signal from the first, second and third contour correction signals are provided. A signal obtained by adjusting the gain of each of the second contour correction signals is added to generate a preshoot and overshoot generation signal, and a signal obtained by adjusting the gain of the fourth contour correction signal and its preshoot are added. By adding the shoot and overshoot generation signals to the output signal of the first delay means, the rising and falling edges of both the luminance signal and the chrominance signal are well sharpened, which impairs the image quality. This makes it possible to enhance the outline of an image without any distortion, and also to add an arbitrary amount of preshoot or overshoot.

[Conventional technology]

Conventionally, in the composite color video signal of the NTSC system, the signal bandwidth of the color difference signal (0.5 MHz>) was set narrower than the signal bandwidth (4.2 MHz) of the luminance signal. In the contour part of the image, which corresponds to an area where the video signal changes rapidly, the color change cannot follow the change in brightness, causing the contour to become unclear and the image quality to deteriorate.For this reason, contour enhancement It was thought that contour enhancement could be performed using a circuit.

[Problem to be solved by the invention]

However, the conventional contour enhancement circuit disclosed in, for example, Japanese Patent Laid-Open No. 61-224783 always applies a certain amount of preshoot and/or overshoot before and after the contour in order to make the level difference between the contours clear. In the case of a luminance signal, the contours stand out and a certain degree of effect can be obtained, but in the case of a color difference signal, the hue of the contours shifts, resulting in an unnatural image, and the image quality deteriorates. There were cases where it was put away.

Further, in the conventional edge enhancement circuit, the amount of preshoot and the amount of overshoot can only be set to be the same, so there is an inconvenience that the effect of edge enhancement cannot be adjusted in various ways.

In view of these points, the present invention sharpens the rising and falling edges of both the luminance signal and the color signal, enhances the outline of the image without degrading the image quality, and reduces the amount of preshoot and overshoot. The purpose of the present invention is to propose a video signal contour correction circuit that can independently change the amount of image signal.

[Means to solve the problem]

The video signal contour correction circuit according to the present invention includes a first delay means (2) for delaying the original signal A, as shown in FIG.
A), a second delay means (2B) for delaying the output signal B of the first delay means (2^), and the original signal A and the respective output signals of the first and second delay means. Add and subtract B and C to obtain the first result. second and third contour correction signals, (
Addition/subtraction circuit (3) forming, for example, B-A, B-C and 2B-(A+C)).

(4), (5) and the first one. A logic operation circuit (6) that forms a fourth contour correction signal W from the second and third contour correction signals is provided, and the gain of each of the first and second contour correction signals is adjusted. is added to generate the preshoot and overshoot generation signal Z (for example, 2x (
B−A)+, x(B−C)) is generated, and the signal KIXW obtained by adjusting the gain of the fourth contour correction signal W and its preshoot and overshoot generation signal Z are added to the fourth contour correction signal W. This signal is added to the output signal of the first delay means (2A).

According to the present invention, the change in the original signal A is achieved by adding and subtracting the original signal A and the respective output signals B and C of the first and second delay means (2) and (2B). The first, second and third contour correction signals vary only in the vicinity of the portion (e.g. B-A).

B-C and 2B-(A+C)) are generated. and,
By further calculating these first to third contour correction signals, a fourth contour correction signal W for correcting the state of the changing portion of the original signal A is easily generated.

Furthermore, since the gain of the fourth contour correction signal W is adjusted and added to the output signal of the first delay means (two people), the amount of correction for the changing portion of the original signal A can be easily adjusted. can be increased or decreased.

Furthermore, the amounts of preshoot and overshoot are set to different values by setting the respective gains of the first and second contour correction signals to different values to generate the preshoot and overshoot generation signals. be able to.

[Effect]

[Embodiment] Hereinafter, an embodiment of the video signal contour correction circuit of the present invention will be described with reference to the drawings. Although this example is configured using a digital circuit, for convenience of explanation, the customer digital signal is shown as an analog signal after digital/analog conversion.

FIG. 1 shows the contour correction circuit of this example. In this FIG. Input the digitized original signal. This original signal is supplied to the first delay circuits (2) and the first subtraction circuit (3) each consisting of a shift register or the like, and the delayed signal B ( B indicating green light
) are supplied to the second delay circuit (2B), the first subtraction circuit (3), and the second subtraction circuit (4), respectively. Further, the delay signal C output from the second delay circuit (2B) is supplied to the second subtraction circuit (4). These first and second delay circuits (2A) and (2B) each set a delay time T to, for example, 140 nS when the original signal A is the luminance signal Y, and when the original signal A is the color difference signal R-
When Y or B-Y, set the delay time T to 560 nS, for example.
Set respectively.

The N10 subtraction circuit (3) adds the difference signal B-A between the original signal and the delayed signal B to the addition circuit (5) and the logic operation circuit (6).
The second subtraction circuit (4) supplies the difference signal B−C between the delayed signal B and the delayed signal C to the addition circuit (5) and the logic operation circuit (6). ) is a signal 2B-(
A+C) is supplied to the logic operation circuit (6).

Assuming that the original signal A is a trapezoidal wave with a rising period T and a falling period T2 as shown in the second prisoner, the delayed signal B~
Signals 2B-(A+C) are as shown in FIGS. 2B to 2F, respectively. In this case, the logic operation circuit (6) generates a contour correction signal W as shown in FIG. ＞ Supply.

This contour correction signal W has a rising period T of the delayed signal B.

), it changes as "0 → negative → 0 → positive → O" centering on the O level, and during the falling period T2 of the delayed signal B, it changes as "0 → negative → 0 → positive → O".
-+Positive → 0 → Negative → 0''. Further, for example, the absolute value of the falling slope angle of the signal W during the period T, is equal to or smaller than the absolute value of the rising slope angle of the delayed signal B (as appropriate).

The first multiplication circuit (14A) multiplies the contour correction signal W by a predetermined coefficient (0≦1≦1), and then adds 1 to the signal obtained by multiplying the contour correction signal W by a predetermined coefficient.
×W is supplied to one input terminal of the first adder circuit (15A), and the delay signal B output from the first delay circuit (2A) is supplied to the other input terminal of this adder circuit (15^).
supply. This adder circuit (15A) uses the signal K l
x W and the delayed signal B are added to form an intermediate signal Y;
This intermediate signal Y is supplied to one input terminal of the second adder circuit (15B). That is, Y = B + (K+ x W)”
” ”(1) holds true.

2 A and G as the original signal A and the contour correction signal W, respectively.
Assuming a signal as shown in FIG. 2 and setting the values of rQJ, rl/2J and "1" to the coefficients in the multiplication circuit (14^), the intermediate signal Y becomes the function Y3 shown in FIG. 2H, respectively.
．． Y2 and Yl, and compared to the original signal, Kl=
It can be seen that except for the case of 0, the rising and falling edges are sharpened and the outline is emphasized without any preshoot or overshoot.

In this way, according to this example, the changing part of the original signal is sharpened without causing any preshoot or overshoot at the intermediate signal Y stage, so the outline of the image corresponding to the original signal is in a natural shape. There are benefits to be emphasized. Furthermore, when configured with a digital circuit, the circuit scale can be made relatively small, and there is an advantage that there are no problems such as deterioration of characteristics or errors due to variations in characteristics of components.

In addition, in FIG. 1, the difference signal B-A is supplied to the second multiplier circuit (14B), and the second multiplier circuit (14B)
) is a signal obtained by multiplying the difference signal B-A by a predetermined coefficient by 2, and adds X(B-A) to the third addition circuit (15C).
is supplied to one input terminal of the Similarly, the difference signal B-C is supplied to a third multiplier circuit (14C), and this third multiplier circuit (14C) multiplies the difference signal B-C by a predetermined coefficient to obtain a signal KtX. (B c) is supplied to the other input terminal of the third adder circuit (15C), and the preshoot and overshoot generation signal Z, which is the output signal of the third adder circuit (15C), is added to the second adder. It is supplied to the other input terminal of the circuit (15B>).

Therefore, the following equation holds.

Z = K2 × (B A) + Kz x (B
C)...(2) The second addition circuit (15B)
adds the intermediate signal Y and the preshoot and overshoot generation signal Z to obtain an output signal OUT as a video output signal, and sends this output signal OUT to the output terminal (16).
supply to. Therefore, the output signal OUT is expressed by the following equation.

0UT = Y + Z = B + K + X W + K 2 × (B
A ) + K s X (B C) (3) Assuming the function Y1 of FIG. Assuming that the coefficients in the circuit (14B) and the third multiplication circuit (14C) are 2 and 3, respectively, and K2=1 and K2=0.5, the signal is 2X(B-A), K.

x(B-C), the preshoot and overshoot generation signals Z, and the output signal OUT are shown in FIGS. 2I to 2rI!, respectively.
It becomes as shown in JL. In this example, since the value of coefficient 2 and the value of coefficient 2 are different, as is clear from FIG.
The shape of is the preshoot part PRE and the overshoot part OV.
It is different from E. Therefore, the finally obtained output signal ○IJT also has different amounts of preshoot and overshoot.

In this way, according to this example, the coefficient (
By independently adjusting the value of K2 (a type of gain) and the value of K3, a coefficient (a type of gain) that multiplies the difference signal B-C,
Obtain the preshoot and overshoot generation signal Z,
Since this signal Z is added to the intermediate signal Y, there is an advantage that the amount of preshoot and the amount of overshoot can be adjusted independently to obtain the optimum image quality.

Note that, for example, if the input signal A supplied to the input terminal (1) is a color difference signal, it may be better not to have preshoot and overshoot. Therefore, in order to eliminate preshoot and overshoot, the second multiplier circuit (1
4B) and the third multiplication circuit (14C), the values of 2 and 2 may both be set to 0. Furthermore, by varying the values of 2 and 3, various image qualities can be easily obtained.

Although the logic operation circuit (6) in the example of FIG. 1 can be realized by, for example, software of a microcomputer, FIG. 3 shows an example of a hardware configuration. In this FIG. 3, (6) shows the logic operation circuit as a whole, and this logic operation circuit (6) includes a polarity inversion circuit (7),
(8), minimum value circuits (9A) to (9D), maximum value circuits (IOA) to (100), and addition circuits (11), (1
2), (13)jF) Configure. In this case, the minimum value circuits (9A) to (9D) are circuits that output the smaller of the two human input signals, and the maximum value circuits (IOA) to
(100) are circuits that each output the larger of the two human input signals.

In FIG. 3, the difference signal B-8 output from the first subtraction circuit (3) is sent to one of the minimum value circuit (9A) and maximum value circuit (10B) via the polarity inverting circuit [7]. The difference signal B-C supplied to the input terminal and output from the second subtraction circuit (4) is sent to one of the maximum value circuit (IOA) and the minimum value circuit (9B) via the polarity inversion circuit (8). The signal 2B-(A+C) supplied to the input terminal and output from the adder circuit (5) is sent to the minimum value circuit (9^), (9B)
and the other input terminal of the maximum value circuit (IOA>, (10B)).
A>, (10B) and minimum value circuit (9A), (
9B), P, M, and N are respectively connected to the minimum value circuit (9C), <90) and maximum value circuit (IOC).
.

(100), and a signal with a value of 0 is commonly supplied to the other input terminal of each of the minimum value circuit (9C), (90) and maximum value circuit (IOc), (100). do.

Furthermore, the output signal Q of the minimum value circuit (9C) and the output signal R of the maximum value circuit (10(')) are added to an adder circuit (11).
The output signal S of the maximum value circuit (100) and the output signal T of the minimum value circuit (9D) are respectively added to the adder circuit (12).
The output signal U of the adder circuit (11) and the output signal V of the adder circuit (12) are respectively supplied to the adder circuit (13). Then, the output signal of this adder circuit (13) is made into a contour correction signal W, and this contour correction signal W is supplied to a multiplication circuit (14A). The configuration other than this is the same as the example shown in FIG. The relational expressions for each output signal described above are summarized below.

L=MAX[C-8,2B-(Arc)], M=M
IN [A-8, 2B-(Arc) ] ” = (4
) N=M I N [C-8,2B-(Arc) ],
P=MAX [A-8, 2B-(Arc)]...
= (5) Q=MIN[L, OF, R=MAX[M
, OF ----(6) S=MAX[
N, 0], T-)4IN[P, OF
・-・(7) tl=Q+R, V=S+T, W
=tl+V-
--- (8) To explain the operation of the example in Figure 3, assume that the original signal is a trapezoidal wave that rises from time t to time t and falls from time t to time t7 as shown in Figure 4A. hand,
The interval between time to and t2 and the interval between time t5 and t are each 2T, which is twice the delay time T in the delay circuit (2A). In this case, the delayed signal B becomes a trapezoidal wave that rises from time t to time t3 and falls from time t6 to time t, as shown in FIG. 〜As shown in FIG. 4Q. The contour correction signal W is "〇-" from time 1+ to time t3.
Negative -0 → Positive → 0'' from time t6 to time 1. It will change as "0 → positive → 0 → negative → 0".

Also, since the intermediate signal Y is a signal obtained by multiplying the contour correction signal W in Fig. 4 Q by a coefficient, +xW and the delayed signal B in Fig. 4 B, if the coefficient = 1 There is a fourth
The signal is shown by the solid line Y1 in Figure R. And the coefficient is +
When =1/2 or 1=0, the intermediate signal Y becomes the signal shown by the broken line Y2 or the dashed-dotted line Y3 in FIG. 4R, respectively. From FIG. 4R, it can be seen that as the value of 1 in the coefficient increases from 0 to 1, the rise and fall of the intermediate signal Y gradually becomes sharper. Therefore, when the first multiplier circuit (14A) is provided as in this example to perform a kind of gain adjustment on the contour correction signal W, the first multiplier circuit (14A)
^) There is an advantage in that the degree of enhancement of the outline of the image corresponding to the original signal can be easily adjusted by simply changing the value of the coefficient.

Next, an application example of the video signal contour correction circuit of the present invention will be explained with reference to FIGS. 5 and 6.

FIG. 5 shows a digital color receiver incorporating the contour correction circuit of the present invention, and in this FIG.
The input terminal (18) to which the SC system composite color television signal is supplied is an analog Y/C separation circuit, and this analog Y/C separation circuit (18) converts the supplied composite color television signal into a luminance signal Y. and a color signal C, and demodulates the color signal C to generate color difference signals R-Y and BY. The obtained luminance signal Y and color difference signals R-Y and BY are respectively ^/D Converter (19A), (19B), (19c
). In addition, the A/D converter (19^) ~ (19
The digital signals outputted from C) are respectively supplied to the contour correction circuits (208) to (20C) of the example shown in FIG. 1 according to the present invention to increase the sharpness of the rising edge and falling edge of the signal. In this case, the contour correction circuit (2OA>).

(20B) and (20C) may be made common by dividing and using one contour correction circuit in a time-sharing manner.

The output signals of these contour correction circuits (2OA) to (20(:) are respectively supplied to a signal processing circuit (21), and the signal processing circuit (21) performs processing such as noise reduction and generation of an interpolation signal. The obtained luminance signal Y and color difference signals R-Y, B-Y are respectively sent to a D/^ converter (22A),
(22B) and (22C) to the RGB matrix (23). Three primary color signals R, G, and B are supplied from this RGB matrix (23) to a color picture tube (24).

According to the example in FIG. 5, it is possible to apply appropriate preshoot and overshoot to the luminance signal Y, and the rise and fall of the color difference signals R-Y and B-Y are improved, so that the chrominance signal is pre-shot. Since the sharpness can be increased without causing shoots or overshoots, there is the advantage that the contours of the color image are emphasized in a natural manner. Furthermore, by sharing the contour correction circuits (20^) to (20C) and using them in a time-sharing manner, there is an advantage that the circuit scale can be reduced.

Further, by performing interpolation or the like in the signal processing circuit (21), it is possible to easily emphasize the outline of a color image and realize high-resolution television (IOTV, εDTV, etc.).

Furthermore, according to the example in FIG. 5, since the amount of preshoot and overshoot can be adjusted arbitrarily, the
) to (22C) It is possible to compensate for the deterioration of the frequency characteristics caused by the aperture effect that causes the rise and fall of the signal to become blunt.

In the example in Fig. 5, the analog Y/C separation circuit (18
), but as shown in Figure 6, digital Y/C
A separation circuit (26) may also be used. In the example in FIG. 6, a synthetic color television signal input to the input terminal (17) is supplied to the digital Y/C separation circuit (26) via the A/D converter (25), and the digital Y/C The luminance signal Y and color difference signals RY, B-Y obtained by the separation circuit are sent to contour correction circuits (2OA), (20B), (20C), respectively.
). The other configurations are the same as the example shown in FIG.

As described above, the present invention is not limited to the above-described embodiments, and it goes without saying that changes can be made without departing from the gist of the present invention. For example, the present invention may be configured with an analog circuit.

〔Effect of the invention〕

According to the video signal contour correction circuit of the present invention, regardless of whether the original signal is a luminance signal or a color difference signal, the contour enhancement of the original signal corresponding to the contour portion can improve the image quality with a simple configuration using two delay means. There are benefits that can be done well without compromising.

Furthermore, by setting the respective gains of the first and second contour correction signals to different values, there is an advantage that the amount of preshoot and the amount of oversineat can be set to arbitrary different values.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the video signal contour correction circuit of the present invention, FIG. 2 is a timing chart diagram of the example shown in FIG.
FIG. 3 is a configuration diagram showing an example of the logical operation circuit of the example shown in FIG.
FIG. 4 is a timing chart diagram of the example shown in FIG. 3, and FIGS. 5 and 6 are configuration diagrams showing applied examples of the present invention, respectively. (2A), (2B> are respectively delay circuits, (3),
(4) is a subtraction circuit, (5) is an addition circuit, (6) is a logic operation circuit, (14A) is a first multiplication circuit, and (15A) is a subtraction circuit.
) is the first addition circuit, and (15B) is the second addition circuit. Mut! s z '1. Ir i f'l /1 th. t S t# tfut# 31! 】Smell 1 no F ξ no γ 1000+-) Figure 4

Claims (1)

[Scope of Claims] A first delay means for delaying an original signal, a second delay means for delaying an output signal of the first delay means, and the original signal and the first and second delay means. an addition/subtraction circuit that adds and subtracts the respective output signals to form first, second, and third contour correction signals; and a fourth contour correction signal that is formed from the first, second, and third contour correction signals. a logical operation circuit for generating a preshoot and overshoot generation signal by adding signals obtained by adjusting the gains of the first and second contour correction signals, and performing the fourth contour correction. A contour correction circuit for a video signal, characterized in that a signal obtained by adjusting the gain of the signal and the preshoot and overshoot generation signals are added to the output signal of the first delay means.