JPH02174376A - Picture quality correction circuit - Google Patents

Abstract

PURPOSE:To ensure the correction of picture quality with a fixed pre-overshoot amount by switching the delay times of the 1st and 2nd delay lines with each other to increase each delay time in case the rise time of a luminance input signal is long. CONSTITUTION:A switch means 10 switches the delay times of the 1st and 2nd delay lines 1 and 8 in response to the rise time of a luminance input signal with input of a different luminance input signal. For instance, the delay times of both lines 1 and 8 are increased when the input signal has a long rise time. Thus the amplitude of a primary differential signal obtained from subtractions carried out between the luminance input signal and the delay signal passed through the line 1 via a subtraction circuit 3 is not reduced to prevent the reduction of the pre-overshoot amount of a luminance correction signal. Thus it is possible to ensure the correction of picture quality with a fixed pre- overshoot amount.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image quality correction circuit that provides a thin pre-overshoot.

2. Description of the Related Art In a conventional image quality correction circuit, as shown in FIG. 3, a delay line 1, a delay line 2, etc. are used to form a first-order differential signal and a second-order refined signal from a luminance input signal.
A correction signal is formed by calculating these signals,
Image quality is corrected by adding this to the luminance signal.

A conventional image quality correction circuit will be described below with reference to the drawings.

The configuration of a conventional image quality correction circuit is shown in Fig. 3, and the waveform diagram of each part in Fig. 3 is shown in Fig. 4 (aHb). The luminance input signal passes through delay line 1, and at point (a),
A luminance signal B delayed from the luminance input signal A is obtained at point (a), and this is subtracted from the luminance input signal A by the subtraction circuit 3 to obtain 1.
A second differential signal C is obtained at (two) points. Furthermore, the multiplication circuit 4 multiplies the first-order differential signal C by the signal at point (1), which is obtained by delaying this one-component signal C by the delay line 2, and produces a narrow signal at point (e). Get E. By differentiating the one-component signal C, a second-order differential signal F is obtained at the (force) point. This differentiation circuit 5 may be formed using a high-pass filter, or may be formed by subtracting the signals before and after the delay line 2. By multiplying the signal F by the multiplication circuit 6, a correction signal G with a very narrow width is obtained at point (g). By adding this correction signal G to the luminance signal B after passing through the delay line 1 in the addition circuit 7, a luminance correction signal H with a very narrow pre-overshoot width is obtained at point (i), and as a result, Image quality correction is being performed.

Problems to be Solved by the Invention However, in such a conventional image quality correction circuit, when the brightness No. 18 with different rise speeds is input, the amplitude of the brightness correction signal differs, and the amount of pre-overshoot differs. This state is shown in the waveform diagram of FIG. 4 1b).

Waveforms at points (A) to (R) in Figure 3 when the rise time of the luminance input signal A' in Figure 4(b) is 1.5 times longer than A in Figure 4(a). It shows. Figure 4 (aHb)
Comparing the first-order differential signals C and C' at this point, the amplitude of the one-component signal C in FIG. 4(a) is 1, whereas the amplitude is 1 in FIG. 4(b). Order differential signal C'
The amplitude in the case of 0.67 is small. therefore,
Each point (1) to (
The signals in (a) are all 0.6 of the amplitude of the signal in Fig. 4(a).
7 times, and the pre-overshoot amount is also 0.67 times, which is a problem.

The present invention solves the above-mentioned conventional problems, and aims to provide an image quality correction circuit that can make the amount of pre-overshoot constant even for luminance input signals having different rise times.

Means for Solving the Problems In order to solve the above problems, an image quality correction circuit of the present invention includes a first delay line, a subtraction circuit for subtracting signals before and after the first delay line, and a subtraction circuit for subtracting signals before and after the first delay line. a second delay line connected later, the subtraction circuit and the second delay line connected later;
a first multiplier circuit that multiplies the output of the delay line;
a second multiplication circuit that multiplies a signal obtained by differentiating the output of the subtraction circuit by the output of the first multiplication circuit, and adds the output of the second multiplication circuit and the luminance signal that has passed through the first delay line. an image quality correction circuit comprising: an adding circuit; the image quality correction circuit has means for switching the delay times of the first delay line and the second delay line so that when the rise time of the luminance input signal is long, the delay time of each of the first delay lines is also lengthened; It is prepared.

Effect With the above configuration, when different luminance input signals are input, the switching means selects the following according to the rise time of the luminance input signal:
Since the delay times of the first delay line and the second delay line are switched, for example, when the rise time of the luminance input signal is long, the first and second delay lines are switched to a delay time with a long delay time. Then, the amplitude of the first component signal obtained by subtracting the luminance input signal and the delayed signal passed through the first delay line by the subtraction circuit does not become as small as in the conventional case, and therefore the pre-overshoot amount of the luminance correction signal decreases. This will prevent it from becoming smaller. In this way, even for luminance input signals with different rise times, the amplitude of the luminance correction signal is constant, and image quality correction with a constant pre-overshoot amount can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. It should be noted that the same reference numerals are given to parts that have the same functions and effects as those of the conventional example, and the explanation thereof will be omitted.

FIG. 1 shows a block diagram of an image correction circuit according to an embodiment of the present invention, and FIG. 2 shows a waveform diagram at each point in FIG. 1 when a luminance input signal with a long rise time is input. . In Figures 1 and 2, 8.9 is a delay line, delay line 8 is arranged in parallel with delay line 1 and has a different delay time from delay line 1, and delay line 9 is a delay line. 2
The delay line 2 is arranged in parallel with the delay line 2 and has a different delay time. 10.11 is a switch as a switching means, and the switch 10 is configured to change the delay time of delay lines 1 and 8, and the switch 11 is configured to change the delay time of delay lines 2 and 9, depending on the rise time of the luminance input signal. . At this time, the delay times of delay lines 1 and 2 are configured to be equal, and the delay times of delay lines 8 and 9 are configured to be equal.

The operation of the above configuration will be explained below. First, the delay time (delay amount) of delay line 1 and delay line 2 is set to, for example, 50 nsec, and the delay time of delay line 8 and delay line 9 is set to, for example, 100 nSf3C. Here, for example,
When the luminance input signal has a short rise time of 100 nsec, switch 10 is connected to delay line 1.
When the switch 11 is switched to the delay line 2 side, the operation at this time is the same as that shown in the conventional example, and the waveforms at each point (a) to (ri) are shown in Figure 4 fa). It becomes like that.

Next, when a luminance input signal having a long rise time of 150 nsec is input, the switch 10 is switched to the delay line 8 side, and the switch 11 is switched to the delay line 9 side. The waveforms at each point (a) to (ri) at this time are shown in FIG.

In FIG. 2, the brightness human input signal A'' has the same rise time as the brightness input signal A' shown in FIG. 4(b) of the conventional example. Since the delay time is set as long as 100 nscc by switching the delay time using the switch 10, the conventional 1
While the amplitude of the component signal C' is 0.67, the amplitude of one component No. 18 C'' of this embodiment is 1. This is because the rise time of the conventional example shown in FIG. 4(a) is short. The amplitude l of the one-component signal C is equal to the amplitude l of the one-component signal C at point (1) in FIG. The amplitude is equivalent to the amplitude in Fig. 4 (a) at each point (1) to (ri) when the rise time to the signal is short. Therefore, even if a luminance input signal with a long rise time is input, the rise time By switching the delay time using switches 10 and 11 in accordance with the above, it is possible to obtain image quality correction in which the amount of overshoot of the brightness correction signal is constant.

In addition, in this embodiment, the delay time of each of delay lines 1, 8 and 2.9 is set to 50.
I have switched to +1 S e C and 100nscc,
This may be designed to an appropriate delay time value depending on the rise time of the luminance input signal.

Furthermore, in an actual circuit, the delay time of the delay line is switched when the luminance input signal switches between a television signal and a video signal.

Also, delay lines 1 and 8 and delay line 2.
9 is built into the semiconductor integrated circuit, and the delay line 1 and the delay line 8 and the delay line 2 and the delay line 9 are respectively arranged in parallel to switch between delay lines having different delay times.

Effects of the Invention As described above, according to the present invention, means is provided for switching the delay times of the first delay line and the second delay line so that when the rise time of the luminance input signal is long, the delay time of each of them is also increased. By preparing,
Unlike in the past, the pre-overshoot amount of the brightness correction signal does not become small even when the rise time of the brightness input signal is long, and the amplitude of the brightness correction signal does not decrease even for the brightness input signal with a long rise time. Therefore, it is possible to obtain image quality correction with a constant pre-overshoot amount, which is extremely useful in practice.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an image quality correction circuit showing an embodiment of the present invention, Fig. 2 is a waveform diagram when the rise time of luminance input is long at each point of the image quality correction circuit, and Fig. 3 is a waveform diagram of the conventional image quality correction circuit. The block diagrams of the correction circuit, FIGS. 4(a) and 4(b), are waveform diagrams showing waveforms at each point of the image quality correction circuit, and show cases where the rise time of the luminance input signal is short and long. 1, 2, 8.9...delay line, 3...subtraction circuit, 4,6...multiplication circuit, 5...differentiation circuit, 7...
-Addition circuit, 10.11...Switch. Agent Yoshihiro Morimoto Figure 2 Figure 6 (a) A Figure 4 (1)) 4'

Claims (1)

[Claims] 1. A first delay line, a subtraction circuit that subtracts luminance signals before and after the first delay line, a second delay line connected after the subtraction circuit, and a subtraction circuit and the second delay line. The first to multiply the output of the delay line
a second multiplication circuit that multiplies the output of the first multiplication circuit by a signal obtained by differentiating the output of the subtraction circuit;
an image quality correction circuit comprising an output of the second multiplication circuit and an addition circuit that adds the luminance signal passed through the first delay line;
An image quality correction circuit provided with means for switching the delay time of each of the delay lines so that when the rise time of the luminance input signal is long, the delay time of each of the delay lines is also increased.