JPS61220567A - Controller for profile correcting circuit - Google Patents

Abstract

PURPOSE:To adjust automatically picture quality in accordance with an S/N by providing an automatic gain adjusting circuit for adjusting gains of a profile correcting signal and adjusting them according to a noise level. CONSTITUTION:An input digital luminance signal is inputted to the 1st unit time delay element 31, the 1st adder 33 and an AND circuit 42. The adder 33 adds the output signal of the 2nd unit time delay element 32 to its input signal, and the output is inputted to the 2nd adder 36 through an automatic gain control circuit 34 and a multiplier 35. The 2nd adder 36 adds the output of the multiplier 35 to that of the 1st unit time delay element 31, thereby obtaining the output signal subjected to profile correction. Here gains of the automatic gain adjusting circuit 34 are made variable by a gain adjusting signal from a decoder 41, which is made variable by the S/N. Accordingly the appropriate profile correction can be automatically executed in accordance with the value of the S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a contour correction circuit for a television receiver.

[Technical background of the invention]

Current television receivers incorporate an image quality adjustment circuit (contour correction circuit) to compensate for the beam amortization characteristics of the picture tube (a phenomenon in which the resolution of the picture tube deteriorates as the frequency of the video signal increases). ing. This circuit uses preshoot and auto-auto on the contour part of the luminance signal.
By adding shoots, the image quality can be made sharper, or conversely, it can be made smoother to make the image softer. These contour correction circuits include one that performs contour correction in the horizontal direction (hereinafter referred to as "horizontal contour correction") and one that performs contour correction in the vertical direction (hereinafter referred to as "vertical correction"). In the so-called digital television system that processes video signals digitally, this circuit has the configuration 1 shown in Figure 4.
556...9° In FIG. 4, the digitally processed luminance signal is input to the first unit time delay element 11a and the adder I.
2 is input. The output of the first unit time delay element IIa is input to the second unit time delay element 11b. 1st
In the adder 12, the input signal and the output signal of the second unit time delay element IIb are added, and the added output is multiplied by 1 in the multiplier 13 and input to the second adder I4. The second adder I4 uses the output of the multiplier 13 and the first
The outputs of unit time delay element IIa are added to obtain an output signal.

Here, if the signals of each part are replaced with waveforms and expressed, the result will be as shown in FIG. Time t1. ．． t1 is the first . The delay time signal obtained by the second unit time delay elements 11a and llb is a contour correction signal.

The above unit time delay element is 0 in the case of horizontal contour correction.
It is a 1-bit delay circuit such as a 24179717071 circuit, and the clock is the sampling frequency. Further, in the case of vertical contour correction, a shift register or the like is used to obtain a delay amount of one horizontal period.

[Problems with background technology]

When contour enhancement is performed, the frequency response reaches a high level in the high range. Therefore, the high frequency noise component is large, which is particularly noticeable when the S/N is small. In such a case, by adjusting the value of α of the multiplier 13 in the bull diagram to a negative value, conversely, by smoothing the contour and lowering the high frequency response isometrically, Techniques are used to reduce high frequency noise. As described above, in the conventional circuit, the image quality has to be adjusted manually, which is cumbersome.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a contour correction circuit that can automatically adjust contour correction according to the S/N of an input signal.

[Summary of the invention]

In order to achieve the above object, the present invention provides an automatic gain adjustment circuit 34 that adjusts the gain of the contour correction signal, for example as shown in FIG. 1, so that the gain is adjusted according to the noise level. , AND circuit 42, unit time delay element 3
7, adder 38, absolute value circuit 39, leakage integration circuit 40,
A noise detection and gain adjustment means using a decoder 4I is provided.

[Embodiments of the invention]

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

FIG. 1 shows one embodiment of the present invention, in which an input signal (digital luminance signal) is input to a first unit time delay element 31, a first adder 33, and an AND circuit . The output of the first unit time delay element 31 is input to the second adder 36 and also to the second unit time delay element 32.・=6− In the first adder 33, the output signal of the second unit time delay element 32 and the input signal are added, and the output is sent to the second unit time delay element 32 via the automatic gain adjustment circuit 34 and the multiplier 35. Adder 36
is input. The second adder 36 adds the output of the multiplier 35 and the output of the first unit time delay element 3I to obtain a contour-corrected output signal.

An external adjustment signal for contour correction is input to the multiplier 35 as a coefficient α. The delay amount of the first and second unit time delay elements 31 and 32 is set to be one clock of the sampling frequency in the case of horizontal contour correction, and one horizontal line in the case of vertical contour correction. . In the adder 33, the signal that has passed through the delay element twice, that is, in the case of horizontal contour correction, the signal of two samples before and the current signal is added, and in the case of vertical contour correction, the signal of two horizontal lines before and the current signal are added. signals are added.

The output of the adder 33 is input to an automatic gain adjustment circuit 34 which determines the amplitude of the contour preroot and overshoot. This circuit multiplies the output of the adder 33 by X and outputs it. The value of this X is automatically changed by a control signal that changes depending on the S/N.

The variable means for X described above will be explained. First, variable X is obtained by bit-shifting the output digital signal of the adder 33 and inverting the sign bit in the automatic gain control circuit 34.

Next, the AND circuit 42 responds to the gate and pulse of the vertical erase period and outputs an input signal only during this period. The output of the AND circuit 42 is output from the unit time delay element 37.
is input to the adder 38. In the adder 38, the output of the unit time delay element 37 and the output of the AND circuit 42 are added, and the addition result is input to the absolute value circuit 39.

The above calculation involves subtracting the sample before the ① clock from the current sample (in the case of horizontal contour correction), thereby obtaining a random noise component. The absolute value of the noise component is taken by the absolute value circuit 39 and integrated by the integrating circuit 4o. As this integration circuit 40, a leaky integrator is used to prevent saturation. The output of the integrating circuit 40 is
It is converted into a signal for automatic adjustment by the decoder 41, and the previous X is varied.

As shown in FIG. 2, X is varied depending on the s/N. That is, when the S/N ratio is good, X is 1, and as the S/N ratio becomes worse, the focus of the output of the adder 33 is shifted to the right. That is, X is varied to 1°4'8. Tore is
Bit shifting may be performed by a decoder 4I that responds to the output of the integrating circuit 4o. Also, when the S/N gradually decreases and falls below a certain threshold, the sign of χ is changed, and as it decreases further, it is shifted to the left, i.e. -8'4'2' The values of -1 and X are controlled.

Accordingly, appropriate contour correction can be automatically obtained according to the S/N value.

The gain X variable means described above may be configured as shown in FIG. Parts corresponding to those in FIG. 1 will be described with the same reference numerals. In this embodiment, an automatic gain control (AGC) voltage at the analog signal stage is used for signal-to-noise ratio detection. That is, the AGC voltage (“AG
c) is converted into digital data by the analog-to-digital converter 5I.

This digital data is input to the decoder 52, converted into an appropriate format, and given to the automatic gain adjustment circuit 34 as a control signal. Depending on the frequency of the clock used in the analog-to-digital converter 51, the ability to resolve changes in the AGC voltage can be set.

〔Effect of the invention〕

As explained above, according to the present invention, when the SN ratio is large, the contour is strongly emphasized, and when the SN ratio is small, the contour is conversely smoothed. In other words, when the S/N ratio is high, higher resolution can be obtained by sacrificing a little S/N, and when the S/N ratio is small, the system has the effect of suppressing high frequency components and reducing noise in high frequency components. , this may be done dynamically.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing gain change characteristics of the adjustment circuit of FIG. 1, kf, and FIG. 3 is a circuit diagram showing another embodiment of the invention. FIG. 4 is a diagram showing a conventional contour correction circuit, and FIG. 5 is a signal waveform diagram of each part of the circuit shown in FIG. 37, s 2.37... unit time delay element, 34.
・・Automatic gain adjustment circuit, 39・Absolute value circuit, 40・
...Leakage integration circuit, 4I...decoder, 42...AND circuit.

Claims (5)

[Claims] (1) Create a first contour correction signal using the brightness signal of the television signal, adjust the gain of this first contour correction signal in a gain adjustment section to create a second contour correction signal, and use this to adjust the brightness. A control device for a contour correction circuit, comprising: contour correction means for adding to a signal; and means for detecting noise in the television signal and controlling the adjustment amount of the gain adjustment section according to the detected signal. . (2) The contour correction means includes two series-connected first and second delay means that delay the input luminance signal, and the gain adjustment section that adjusts the gain of the output of the second delay means;
addition means for subtracting the output of the gain adjustment section from the first delay means; the means for controlling the amount of adjustment of the gain adjustment section increases the gain of the gain adjustment section as the detection signal increases; is set to be negative and large, and as the detection signal becomes smaller, the gain of the gain adjustment section is made smaller, and when the detection signal falls below a certain value, the sign is positive and the gain is made larger. A control device for a contour correction circuit according to claim 1. (3) The means for controlling the adjustment amount of the gain adjustment section includes a gate means for extracting the noise during the vertical blanking period of the television signal, and an absolute value of an output component of the gate means to detect the noise. 2. A control device for a contour correction circuit according to claim 1, further comprising means for obtaining said detection signal by integrating said detection signal. (4) A patent characterized in that the means for controlling the adjustment amount of the gain adjustment section includes an analog-to-digital conversion means for converting an automatic gain control voltage from an automatic gain control circuit of a television receiver into digital data. A control device for a contour correction circuit according to claim 1. (5) The control device for a contour correction circuit according to claim 1, wherein the gain adjustment section is a means for obtaining a bit shift of input data according to a control signal.