JPH0514468B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a contour correction device for improving the sharpness and definition of video signals in color television receivers, video tape recorders, and the like.

[Prior art] Figure 3 shows the journal of the Institute of Electronics and Communication Engineers (July 1983 issue Vol.
66-B No. 7), ``A method for calculating sharpness in television images'', is a diagram showing how the rising edge of a step waveform is improved by conventional edge enhancement.

It is well known that emphasizing the edges of a television image improves its sharpness.
It is often applied to luminance signals that determine the shape of objects.

As shown in Figure 3, the conventional correction means for emphasizing the contour is configured to obtain a second-order differential signal of the original signal waveform, multiply this signal by a certain coefficient, and then add it to the original signal waveform. be.

To explain with a diagram, the second differential waveform Q″(x) of the step waveform I ₂ (=Q(x)), which is the original signal that has been band-limited in the transmission path, is found, and it is multiplied by a certain coefficient −a. The waveform Id is added to the original signal waveform I ₂ to obtain the contour correction signal waveform I ₂ +Id.

If the amount of improvement in the rise time by this contour correction means is expressed in terms of time relative to amplitude change, the original signal waveform
As for I ₂ , it is V ₁ /X ₁ , whereas the contour correction signal waveform I ₂ +Id is V ₂ /X ₂ , indicating that the rise time is considerably improved.

The sharpness of the image is improved by improving the rise of the signal corresponding to the contour portion of the television image, that is, by emphasizing the contour portion.

[Problems to be Solved by the Invention] The conventional contour correction means calculates the second derivative of the original signal waveform, multiplies this signal waveform by a certain coefficient, and then adds it to the original signal waveform. As shown in the shaded area, the level exceeds the level of the original signal waveform, which causes a problem of waveform saturation when the original signal waveform has the maximum amplitude of the transmission system's dynamic range.

This invention was made to solve the above-mentioned problems, and provides a contour correction device that can enhance the contour and improve the sharpness of an image without causing saturation of the original signal waveform. With the goal.

[Means for Solving the Problems] The contour correction means according to the present invention includes a first delay means for delaying an input signal by a predetermined time, and a second delay means for delaying the input signal by a time longer than the first delay means. delay means; means for calculating the absolute value A of the amplitude difference between the output signal of the first delay means and the input signal; and means for calculating the absolute value A of the amplitude difference between the output signal of the first delay means and the second
means for calculating the absolute value B of the amplitude difference with the output signal of the second delay means, and compares the magnitude of these two absolute values A and B, and calculates the output signal of the second delay means during the period where A<B. and selects the input signal when A=B, and selects and outputs the output signal of the first delay means during the period of A>B.

[Operation] The means for selecting and outputting three signals is A=B.
, the rising part of the signal is switched from a low-level signal with a large amount of delay to a high-level undelayed signal, so the rise time is shortened, and the falling part of the signal is switched ,
A similar choice can be made to shorten the fall time. Therefore, a signal with an enhanced contour without exceeding the amplitude of the input signal can be obtained.

[Embodiment of the Invention] FIG. 1 is a block circuit diagram of an embodiment of the invention. In the figure, 1 is an input terminal into which a luminance signal is input, 2 and 3 are delay circuits that delay the input signal by time D, and 4 is a subtracter that calculates the amplitude difference between the output signal of delay circuit 2 and the input signal every time. , 5 is a subtracter that calculates the amplitude difference between the output signal of delay circuit 2 and the output signal of delay circuit 3, 6 is an absolute value circuit that outputs the absolute value A of the output of subtracter 4, and 7 is the output of subtracter 5. 8 is a comparator that compares the magnitude of outputs A and B of absolute value circuits 6 and 7 and outputs a switching signal based on the result; 9 is a comparator that outputs a switching signal based on this switching signal. This is a changeover switch that switches between the input signal and the output signals of the delay circuits 2 and 3 and outputs the same to the output terminal 10.

Next, the operation will be explained.

An input signal input from the input terminal 1 is delayed by a time D in a delay circuit 2, and then delayed by a time D in a delay circuit 3. Therefore, the changeover switch 9-3
Three signals, ie, an input signal at the current time, and input signals at time D and time 2D before, are simultaneously input to the three input terminals a, b, and c. Now, if the output signal of delay circuit 2 is f(t), the current input signal is f
(t+D), and the output signal of the delay circuit 3 is f
(t-D). FIG. 2 shows the positional relationship of these three signals. The subtracter 4 every time,
(amplitude of signal f(t)) - (amplitude of signal f(t+D))
(hereinafter written as "f(t)-f(t+D)"), and the absolute value circuit 6 outputs the absolute value A of the subtraction result. Similarly, the subtractor 5 calculates f(t)−f
(t-D), and the absolute value circuit 7 outputs the absolute value B of the subtraction result. The comparator 8 compares the absolute values A and B, and during the period when A<B, the changeover switch 9 is switched to the terminal a to output the signal f(t+D), and A=
When B, switch to terminal b and output signal f(t),
During the period A>B, switch to terminal c and send signal f(t-D).
The changeover switch 9 is changed over by outputting a changeover control signal that outputs the changeover control signal. As a result, from the output terminal 10,
A signal g(t) shown by a thick solid line in FIG. 2 is output. The waveform of this output signal g(t) is a signal obtained by correcting the input signal f(t) with a slow rise time to a signal waveform with a fast rise time, and does not exceed the amplitude of the original signal, so saturation is low. This phenomenon does not occur.

In addition, when the calculation in the above example is expressed by the formula, A=|f(t)-f(t+D)|...(1) B=|f(t)-f(t-D)|...(2) Become. Furthermore, the output signal g(t) is as follows: g(t)=f(t+D)...(period of A<B) f(t)...(when A=B) f(t-D)...(A>B period).

Note that in the above embodiment, the application is applied to a time-continuous signal, that is, an analog signal waveform, but
Similar effects can be obtained when applied to discrete signals, that is, digital signal waveforms.

In the above embodiment, two delay circuits 2 and 3 with delay time D were used to create three signals delayed by time D, but the first delay circuit with delay time D and the second delay circuit with delay time 2D were created. Three signals may be created using two delay circuits.

Further, in the above embodiment, the three signals are separated by the delay time D, but the delay time intervals do not necessarily have to be the same.

[Effects of the Invention] As described above, according to the present invention, the amplitude difference absolute values A and B between an input signal, a signal obtained by delaying the input signal by a predetermined time, and a signal further delayed than the delayed signal are compared. Based on the results these 3
Since two signals are switched and output, the sharpness and definition of the input video signal are improved, and
This has the effect of providing a contour correction device that can perform contour correction of a video signal without saturation even if the input signal has a large amplitude.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a signal waveform diagram of each part to explain the operation of this embodiment, and Fig. 3 is a signal waveform by a conventional contour correction means. FIG. 3 is a waveform diagram for explaining the processing of FIG. 2, 3... Delay circuit, 4, 5... Subtractor, 6,
7... Absolute value circuit, 8... Comparator, 9... Changeover switch. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first delay means for delaying the input video signal for a predetermined time, a second delay means for delaying the input video signal for a time longer than the first delay time, and an output signal of the first delay means and the input video. means for calculating the absolute value A of the amplitude difference between the first delay means and the second delay means; means for calculating the absolute value B of the amplitude difference between the output signal of the first delay means and the output signal of the second delay means; By comparing the magnitudes of the absolute values A and B, the input video signal is selected for the period when A<B, the output signal of the first delay means is selected when A=B, and the output signal from the first delay means is selected for the period when A>B. and means for selecting and outputting the output signal of the second delay means.