JPH0250577A - Image quality improvement circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention sharpens a portion of a video signal corresponding to the contour of an image (hereinafter referred to as the contour of the video signal) to improve the sharpness of a reproduced image. This invention relates to an image quality improvement circuit that improves image quality.

[Conventional technology]

A well-known method for improving image UJ sharpness is to perform second-order differentiation of a video signal, invert and amplify it, and add it to the original video signal. However, there is an upper limit to the transmission band of video signals in television receivers, etc., and high-frequency components are attenuated, so in the above method, preshoots and overshoots with a wide width UJ occur in the contours of the video signal. A proposal has been made to make the contour of the video signal steeper without adding a chute, which would otherwise degrade the image quality. An example of this is shown in FIG.

For example, as a device for CIJ a,
Publication No. 55315 and TV Technology/October 1985 issue p.
Examples include the time compression shadow contour correction circuit shown in pages 22-264.

The /igs diagram will be briefly explained below.

In FIG. 5, 1 is an input terminal, 2.3 is a delay circuit that sequentially delays the video signal input from input terminal 1, and 4
, 5.6 is a subtraction circuit, 7 is controlled by the output signal of the subtraction circuit 6, and selectively processes the video signal ξ inputted from the input terminal 1 and the output signal of the delay circuit 2.5, which sequentially delays the video signal ξ. This is a contour forming circuit that outputs a video signal with steep contours.

Next, the operation will be explained using FIG. 6.

Figures 5g and 6 show the signal waveforms at each part of a to e shown in the wJS diagram.The video signal input from input terminal 1 is delayed by a certain period of time in delay circuit 2.5.
．． Assuming that the delay times of 3 are equal and τ, the result will be as shown in a to C shown in Figure @6.

The subtracting circuits 4, 5.6 constitute a contour signal generation circuit which extracts a contour signal d8 indicating the contour portion of the video signal from the three signals a to C described above, and the contour signal d is expressed by the following formula.

d = (b-c) - (a-b)
...(The contour signal d is supplied as a control signal to the contour forming circuit 7, and the contour forming circuit 7 is controlled by the contour signal d and performs selection processing of the a to c% signals, as shown in FIG. 6e. Outputs a video signal with sharp edges.

[Problem to be solved by the invention]

In the conventional circuit shown in FIG. 5 above, the frequency characteristics of the contour signal d output from the subtraction circuit 6 are as shown in FIG. This results in a comb-shaped characteristic.

In FIG. 7, the frequency fp at which the signal level reaches its maximum is τ, which is equal to the delay time of the delay circuit 2.3 shown in FIG. 5, fp=□ (2) 2 τ It is expressed as The frequency fp at which the contour signal d is maximum is generally set to approximately 2 to 5 MHz, which is visually noticeable.

Then, as shown in Fig. 7, the point where the frequency becomes 2fp,
``In other words, the contour signal d becomes zero near 4 to 6 MHz,
Video signals in this frequency band have the disadvantage that contours cannot be sharpened.

In particular, in recent years, as the screens of television receivers have become larger, it has become necessary to sharpen the contour UJ over a wider band (this problem is becoming more serious).

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image quality improvement circuit that solves the problems of the prior art described above and can sharpen contours over a wide band.

[Means to solve the problem]

The above purpose is to provide first... Second. Third. a fourth delay circuit, the video signal and the second . The output signal of the 44th IJ delay circuit generates the first (/1 contour signal); a second contour signal generation circuit that generates a second contour signal; an addition circuit that adds the first contour signal and the second contour signal; and a second contour signal generation circuit that adds the first contour signal and the second contour signal; a contour forming circuit which receives the output signal of the fourth UJ delay circuit and is controlled by the output signal of the adder circuit to form and output a video signal with a steep contour;
This is achieved by having the following.

[Effect]

Said 1st. The second contour signal generation circuit has a comb-shaped characteristic in which the output signal has alternately maximum and minimum points of the signal level with respect to the frequency, and the frequency at which the signal level is the minimum is Said 1st. 41.42, the third . The delay time of the fourth delay circuit is set in advance. As a result, the first
．． Even if one output signal of the second contour signal generation circuit becomes the minimum (signal level is zero), it is compensated by the output signal of the other, so that the output signal of the adder circuit that becomes the control signal of the contour forming circuit is Therefore, the image quality of the video signal output from the contour forming circuit is improved over a wide band.

〔Example〕

Examples of the present invention will be described below.

The first reason is a block diagram showing one embodiment of the image quality improvement circuit according to the present invention, and the same reference numerals are used for the conventional example shown in FIG. The detailed explanation will be omitted.

In FIG. 1, 9, 10, 11, and 12 are delay circuits.

13, 14, and 15 are subtraction circuits, and 16 is an addition circuit.

It is assumed that the delay times of delay circuits 9.12 and 10.12 are equal to τ, and that the delay times of delay circuits 10.11 are also equal to τ. Furthermore, the sum of the delay times of delay circuits 9 and 10 is set equal to the delay time of delay circuit 2 explained in FIG.

That is, τ=τ, +τ. Subtraction circuit 15
゜14 and 15 are delay circuits 9 similar to subtraction circuits 4 and 5.6.
A second contour signal generating circuit is constructed which extracts a contour signal hz oil from the output signals f, b, and g of 10 and 11, and the contour signal is expressed by the following formula.

h=(b-g)-(f-b)...(3
) The contour signals d and h output from the subtraction circuits 6 and 14 are added in an adder circuit 16, and the output thereof is supplied as a combined contour signal to the contour forming circuit 7 as a control signal.

Now, the delay time τ7. Assuming that the ratio of τ is set to τ:τ = 1:2, the contour signals d and h have the frequency characteristics shown in FIG. In FIG. 2, the frequency fp at which the signal level of the contour signal d is maximum is expressed by the equation (2) mentioned above, and the frequency fp' at which the contour signal bUJ (!!) level is maximum is similarly fp ′=j core ゛Direct5) Furthermore, the frequencies at which the contour signals d and h are minimum are frequencies that are even multiples of the values shown in equations (4) and (5) above, respectively. Therefore, the delay time τ1. When the ratio of τ is 1=2, the frequency fo at which both contour signals d and h are minimum is fo=6 fp=4
fp'-(6). This is the frequency at which the contour signal kpm obtained by adding the contour signals d and h is small, and by using this contour signal as the control signal for the 8 contour forming ports 7, it is possible to solve the problem in contrast to the conventional example 1 explained in the fifth factor. The frequency band in which image quality can be improved can be expanded six times.

In this embodiment, the video signal a input from the input terminal 1 and the delay circuit ? , 10.11.12 are supplied to a contour forming circuit 7, and a specific circuit example of this contour forming circuit 7 is shown in FIG.

In the third v4, T, -'-T are the video signal a and the delay circuit 9, 10.11. shown in the first factor, respectively.
12 output signals f+k)+g*(! are input to the input terminal.

T6 is a control signal input terminal to which the contour signal k in FIG. 1 is input, and T? is an output terminal for outputting a video apex e with sharp contours and improved image quality. + Qt to Q+ y are transistors, 1 to I4 are current sources, and VB is a voltage source.

Vcc is the circuit power supply.

The T channel shown in Fig. 3 is almost the same as the circuit shown as "1-hour compression type new contour correction channel" in the above-mentioned TV Gijutsu October issue, p. 25, and its detailed explanation is as follows. is omitted.

In the circuit shown in FIG. 5, the video signal a shown in FIG. 1 and each output signal f of delay circuits 9, 10, 11, and 12.

Since b, g, and c are each input, #! The delay time interval between each signal can be narrowed compared to the conventional example shown in FIG. This has the effect of reducing unevenness in the peak direction.

FIG. 4 is a block diagram showing another embodiment of the image quality improvement circuit according to the present invention, and parts that are the same as those explained in FIGS. 1 and 5 or have the same functions are designated by the same reference numerals. The detailed explanation will be omitted.

In the fourth □□□, 17 is a variable gain amplifier to which the contour signal output from the subtraction circuit 6 is input, adjusts and outputs the magnitude of this signal, and 18 is a control 1 voltage that controls the gain of the variable gain amplifier 17. 19 is an addition circuit that adds the output signal of the contour forming circuit 7 and the contour signal whose size has been adjusted to v4 in the variable gain amplification circuit 17;
0.21 is 7111:J! A delay circuit that delays the output signal of the circuit 19 by a certain period of time; 22, 23, and 24 a subtraction circuit; 25 a variable gain amplifier that receives the output signal of the subtraction circuit 24, adjusts the magnitude of this signal OJ, and outputs it; 26 27 is an input terminal to which a control voltage for controlling the gain of the variable gain amplifier 25 is supplied, and 27 is an adder circuit that adds the output signal of the delay circuit 20 and the output signal of the variable gain amplifier 25 and outputs the result to the output terminal 8. be.

The image quality improvement circuit shown in FIG. 4 not only makes the contour of the video signal steep, but also converts the relatively low frequency (2 to 5 MHz) contour signal output from the subtraction circuit 6 into a variable gain amplifier. 17, adjust its size, and add it to the output of the contour forming circuit 7, thereby emphasizing visually noticeable frequencies and creating an image with a sense of depth. Further, the delay circuits 20, 21 . Subtraction circuit 22.2
5.24. Variable gain amplifier 25. The circuit composed of the adder circuit 27 is an image quality adjustment circuit using a generally well-known delay circuit, and the delay time of the delay circuits 20 and 21 is reduced to increase the frequency at which the outline is emphasized (6 to 8 MHz).
By doing so, a thinner chute can be added to the sharply contoured contour in the contour forming circuit 7, and the sharpness can be improved.

〔Effect of the invention〕

According to the present invention, the zero frequency of the contour signal used to sharpen the contour can be made higher than in the past, so there is an effect that the contour of the video signal can be sharpened over a wide band. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the image quality improvement circuit according to the present invention, FIG. The figure is a circuit diagram showing a specific example of the contour forming circuit in Fig. 1, Fig. 4 is a block diagram showing another embodiment of the image quality improvement circuit according to the present invention, and Fig. 5 shows an example of the conventional image quality improvement circuit. A block diagram, and FIG. 6 is a waveform diagram showing the signal waveforms of each part of the conventional example shown in FIG. 5. FIG. 7 is a characteristic diagram showing the frequency characteristics of the output signal of the subtracter 6 in FIG. 1... Input terminal 9, 10.11.12... Delay circuit 4, 5.6.1
5.14.15...Subtraction circuit 16...Addition circuit 7...Contour forming circuit 8...Output terminal 1 Figure 42 Figure 5 Punishment 6 Figure 7

Claims (1)

[Scope of Claims] 1. First, second, third, and fourth delay circuits connected in series to sequentially delay an input video signal; a first contour signal generation circuit that generates a first contour signal from the output signal of the delay circuit; and a second contour signal generation circuit that generates a second contour signal from the output signals of the first, second, and third delay circuits. an adding circuit that adds the first contour signal and the second contour signal to output a third contour signal; and an adder circuit that adds the first contour signal and the second contour signal to output a third contour signal; an output signal of the delay circuit, and is controlled by the third contour signal to form and output a video signal in which a portion corresponding to the contour of the image is steeper than the input video signal; An image quality improvement circuit characterized by being equipped with. 2. The image quality improvement circuit according to claim 1, wherein the first
The contour signal generating circuit generates the second contour signal from the input video signal.
a first subtraction circuit that subtracts the output signal of the fourth delay circuit from the output signal of the second delay circuit; and a second subtraction circuit that subtracts the output signal of the fourth delay circuit from the output signal of the second delay circuit. An image quality improvement circuit comprising: a third subtraction circuit that subtracts the output signal of the first subtraction circuit from the output signal of the circuit and outputs this as the first contour signal. 3. The image quality improvement circuit according to claim 1, wherein the second
The contour signal generation circuit includes a fourth subtraction circuit that subtracts the output signal of the second delay circuit from the output signal of the first delay circuit, and a fourth subtraction circuit that subtracts the output signal of the second delay circuit from the output signal of the second delay circuit.
a fifth subtraction circuit that subtracts the output signal of the delay circuit, and subtracts the output signal of the fourth subtraction circuit from the output signal of the fifth subtraction circuit, and outputs this as the second contour signal. An image quality improvement circuit comprising: a sixth subtraction circuit. 4. The image quality improvement circuit according to claim 1, wherein the first
and a fourth delay circuit having equal delay times, and the second and third delay circuits having equal delay times.