JPH0712195B2 - Contour correction device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour correction device for improving the sharpness and definition of a video signal in a color television receiver, a video tape recorder or the like.

[Conventional technology]

 FIG. 3 shows a block circuit diagram of a conventional example.

In the figure, (1) is an input terminal to which a luminance signal is input,
(2) and (3) are delay circuits for delaying the input signal by time D, (4) is every time, a subtracter for calculating the amplitude difference between the output signal of the delay circuit (2) and the input signal, and (5) is A subtractor for calculating the amplitude difference between the output signal of the delay circuit (2) and the output signal of the delay circuit (3), (6) an absolute value circuit for outputting the absolute value | A | of the output of the subtractor (4), (7) is an absolute value circuit that outputs the absolute value | B | of the output of the subtractor (5), and (8) is the absolute value circuit (6), (7) output | A |, | B | Compare
A comparator that outputs a switching signal based on the result,
(9) switches the input signal and the output signals of the delay circuits (2) and (3) on the basis of this switching signal to output terminal (10).
It is a switching switch that outputs to.

Next, the operation will be described.

The input signal output from the input terminal (1) is delayed by time D in the delay circuit (2), and then delayed in time D by the delay circuit (3). Therefore, the three input terminals a, b, and c of the switching switch (9) are simultaneously input with the input signal at the current time and the input signal at time D and time 2D before. Now, assuming that the output signal of the 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. 4 shows the positional relationship of these three signals. Subtractor (4)
Is (amplitude of signal f (t))-(signal f (t +
The amplitude of (D)) (hereinafter referred to as “f (t) −f (t + D)”) is calculated, and the absolute value circuit (6) outputs the absolute value | A | of the subtraction result. Similarly, the subtractor (5)
(T) -f (t-D) is calculated, and the absolute value circuit (7) outputs the absolute value | B | of the subtraction result. Comparator (8) is absolute value |
A |, | B | is compared, and during the period of | A | <| B |, the switching switch (9) is switched to the terminal a to output the signal f (t + D),
When | A | = | B |, it is switched to the terminal b and outputs the element f (t). During the period | A |> | B |, it is switched to the terminal c and the signal f (t−
A switching control signal for outputting D) is output to switch the switching switch (9). As a result, from the output terminal (10),
A signal g (t) indicated by a thick solid line in FIG. 4 is output.
The waveform of the output signal g (t) is a signal obtained by correcting the input signal f (t) having a slow rise time into a signal waveform having a fast rise time, and does not exceed the amplitude of the original signal. Does not occur.

The operation in the above embodiment is expressed by an equation: | A | = | f (t) -f (t + D) | | B | = | f (t) -f (t-D) |. The output signal g (t) is Is represented as

[Problems to be solved by the invention]

Since the conventional contour correction device is configured as described above, when the change of the input signal is fast with respect to the delay time D of the signal, the switch circuit output g (t) is output as shown in FIG.
Has a problem that the signal waveform has poor reproducibility compared with the input signal f (t).

The present invention has been made in order to solve the above problems, and improves the reproducibility of the signal output from the switch circuit so that the contour can be changed without impairing the reproducibility even for a rapidly changing input signal. An object of the present invention is to obtain a contour correction device that can enhance the sharpness of an image.

[Means for solving problems]

The contour correction device according to the present invention includes a circuit for generating a second signal delayed by a fixed time with respect to the first input video signal and a circuit for generating a third signal delayed by a fixed time with respect to the second signal; First
A switch circuit for switching the first, second, and third signals and a condition setting circuit for switching the switch circuit are provided. As a first condition for switching the output signal in the switch circuit, When the sign of the amplitude difference is equal to the sign of the amplitude difference between the second and third signals, the second signal is selected. The second condition is the condition of the conventional method.

[Operation] When the sign of the amplitude difference between the second signal and the first signal is equal to the sign of the amplitude difference between the second signal and the third signal, the second signal is selected, so that the waveform Contour correction with improved reproducibility is performed.

Example of Invention

 Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, (1) to (10) show the same components as those having the same reference numerals in FIG. 3 of the conventional example.
1) is a circuit for discriminating between positive and negative signs of the outputs of the subtractors (4) and (5), and (12) is a switch control circuit for switching the first switch which is the output of the sign discrimination circuit (11). The switch circuit (9) is switched using the condition signal and the second switch switching condition signal output from the comparator (8).

Next, the operation will be described.

The signal input from the input terminal (1) is supplied to the delay circuit (2).
Is delayed by time D and then delayed by time by delay circuit (3). Therefore, the input terminal a of the switching switch (9),
Three signals, that is, the input signal at the current time and the input signals at time D and time 2D before are input to b and c at the same time.
If the output signal of the 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). These three are shown in FIG.
The positional relationship of two signals is shown. The subtractor (4) is f (t)-
f (t + D) (this is A) is calculated, the subtracter (5) calculates f (t) -f (t-D) (this is B), and the result is output. The sign discrimination circuit (11)
It is determined whether the positive and negative signs of A and B are the same, and the result is output as the first switch switching condition. On the other hand, the outputs A and B of the subtracters (4) and (5) are absolute value circuits (6) and (7).
Is input to and the absolute values | A | and | B | are output. Then, the comparator (8) compares the absolute values | A | and | B |. The output of the comparator (8) is the second switch switching condition. The first and second switch switching condition signals are input to the switch control circuit (12) to switch the switch circuit (9) according to the following conditions.

That is, when the signs of A and B are the same or when | A | = | B |, the signal is switched to the terminal b to output the signal f (t), the signs of A and B are not the same, and | A | < During the period of | B |, the signal f (t + D) is output by switching to the terminal a, and the symbols of A and B are not equal, and during the period of | A |> | B |, the signal is switched to the signal f (t
-D) is output. Such a control signal is output from the switch control circuit (11) and is output from the switch circuit (9) to the second circuit.
An output signal g (t) indicated by a thick solid line in the figure is obtained at the terminal (10).

If the above operation is expressed by an equation, Is represented.

The waveform g (t) obtained in FIGS. 2 and 5 is
It is obtained by switching three signals f (t + D), f (t) and f (t-D) at discrete time points.

〔The invention's effect〕

As described above, according to the present invention, the second signal obtained by delaying the input signal, which is the first signal, by the predetermined time and the third signal obtained by delaying the second signal by the predetermined time are created. First
Amplitude value A of the second signal and the second signal and the third signal
Means for calculating whether or not the positive and negative signs of the two amplitude differences A and B are the same, and the absolute value of this amplitude difference | A |, | B And the sign of A and B are not equal and the period of | A | <| B | selects the first signal, and the signs of A and B are equal or | A | = | In the period of B |, the second signal is selected, the signs of A and B are not equal,
Moreover, since the third signal is selected and output during the period of | A |> | B |, a contour correction device with good waveform reproducibility can be provided even for an input signal that changes rapidly. There is an effect to be obtained.

[Brief description of drawings]

1 is a block circuit diagram of an embodiment of the present invention, FIG. 2 is a waveform diagram of an output signal of this embodiment, FIG. 3 is a block circuit diagram of a conventional contour correcting device, and FIG. 4 is a conventional device. FIG. 5 is a waveform diagram of the output signal of FIG. 5, and FIG. 5 is an output waveform diagram of the conventional device in the case of a signal which changes rapidly. (2), (3) ... delay circuit, (4), (5) ... subtractor, (6), (7) ... absolute value circuit, (8) ... comparator, (9) ... Switch, (11) ... Sign discrimination circuit,
(12) …… Switch control circuit. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A means for generating a second signal by delaying an input video signal which is a first signal for a predetermined time, and a means for generating a third signal by delaying the second signal for a predetermined time. ,
Means for calculating a value A by subtracting the amplitude value of the first signal from the amplitude value of the second signal; and a value B by subtracting the amplitude value of the third signal from the amplitude value of the second signal And a means for determining whether or not the positive and negative signs of the two subtraction values A and B are the same, and outputting the determination signal, and an absolute value of the two subtraction values A and B. Compare the values | A |, | B | Means for outputting a signal indicating the comparison result of which is, and a period in which the signs of the subtraction values A and B are not the same and | A | <| B | based on the discrimination signal and the comparison result signal. Selects the first signal and selects the second signal while the subtraction values A and B have the same sign or | A | = | B | A contour correcting device comprising means for selecting and outputting the third signal during a period when the values are not the same and | A |> | B |.