JPS6115472A - Profile correcting circuit of video signal - Google Patents

Abstract

PURPOSE:To suppress the deterioration of the S/N to a low value by an aperture correction signal by adjusting the gain of an aperture correction signal in response to an input level of the video signal so as to adjust the mixing ratio with the video signal. CONSTITUTION:An output of an aperture correction signal generator 10 is given to a gain controller 13 of an aperture correction signal regulator 12, the gain is adjusted and the result is given to a mixer 8. Then the profile correction mixed with the video signal by the mixer 8 is outputted to an output terminal 9 via an AGC circuit 14. The input and output signal of the AGC circuit 14 is given respectively to clamp circuits 15, 16 and integrated by integration circuits 17, 18 and then given to a comparator 19. When the gain of the AGC circuit 14 is large, that is, when the input level of the video signal is low, a signal decreasing the gain from the comparator 19 to the gain controller 13 is given.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a video signal contour that improves 8/N by controlling the magnitude of an aperture correction signal according to the input level of the video signal. This invention relates to a correction circuit.

[Description of prior art]

As a conventional image signal contour correction circuit, there is one shown in FIG. 1, for example. The video signal contour correction circuit shown in FIG. 2 will be explained with reference to the waveform diagram shown in FIG. A video signal a applied to an input terminal 1 is applied to a mixer 2 and a delay element 3.

The output of this delay element 3 is given to yet another delay element 4, and the output C of this delay element 4 is given to a mixer 2. The output a from the mixer 2 is given to another mixer 6 via a -1/2 amplifier 5, where it is mixed with the output of the delay element 3, and then a low-pass filter 7 removes high-frequency components and outputs an aperture signal. A correction signal e is output. This aperture correction signal e is the output b (video signal) of the delay element 2.
The signals are further mixed in a mixer 8 and outputted to an output terminal 9 as a contour correction signal f. In this way, the video signal contour correction circuit sharpens the edge portions of the video signal. By sharpening the etch portion of the Eirin signal, the apparent resolution and sharpness of the above image can be increased.

By the way, this contour correction of the video signal is similar to raising the frequency characteristics of the high-frequency components of the video signal. The mixing ratio of the video signal b (luminance signal) and the aperture correction signal e to be mixed is always constant. Therefore, if an aperture correction signal is mixed at a certain mixing ratio with a video signal whose input level is low and the 8/N is poor,
This has the disadvantage that it increases the noise component contained in the video signal, making 87N even worse.

[Summary of the invention]

The present invention has been made to further improve the above-mentioned video signal contour correction circuit, and adjusts the gain of the aperture correction signal according to the input level of the video signal to adjust the mixing ratio with the video signal. Therefore, when a low-level video signal is input, a video signal contour correction circuit is provided which controls the amount of the aperture correction signal added to the video signal to suppress the 8/N deterioration caused by the aperture correction signal to a low level. The purpose is to provide.

[Explanation of Embodiments] The third embodiment will be described below regarding the video signal contour correction circuit of the present invention.
This will be explained with reference to FIGS. 8 through 5. FIG. 3 is a block circuit diagram of an embodiment of the video signal contour correction circuit of the present invention, FIG. 4 is a specific circuit diagram of the block circuit diagram shown in FIG. 3, and FIG. FIG. 4 is a diagram showing the relationship between the aperture correction signal gain-controlled by the aperture correction signal adjuster of FIG. 3 and the input level of the video signal.

In FIGS. 3 and 4, circuits having the same functions as those in FIG. 1 are denoted by the same reference numerals, and redundant explanation will be omitted.

10 is an aperture correction signal generator, which, like the one shown in FIG.
/2 asip 5 and a slicer 11. Note that although a slicer 11 is used in FIG. 3 in place of the low-pass filter 7 in FIG. 1, any device may be used as long as it can remove pulse-like high frequency components generated by signal mixing.

The output of this aperture correction signal generator 10 is given to the gain controller 13 of the aperture correction signal adjuster 12,
The gain is adjusted and applied to the mixer 8. Then, the contour correction signal mixed with the video signal by the mixer 8 is outputted to the output terminal 9 via the AGC circuit 14.

Here, to explain the aperture correction signal adjuster, the input and output signals of the AGC circuit 14 are given to clampers 15 and 16, respectively, predetermined DC voltages are added to each, and further, integrators 17 and 18 are respectively added. It is integrated by , and is provided to the comparator 19 . The time constants of the integrators 17 and 18 are larger than the time constant of the AGC circuit 14, so that the aperture correction signal adjuster 12 does not malfunction in response to sudden signal changes in the video signal. and,
The outputs of integrators 17 and 18 are compared in comparator 19 and A
When the gain of the GC circuit 14 is large, that is, when the input level of the video signal is low, a signal for lowering the gain is given from the comparator 19 to the gain controller 13.

Thus, the relationship between the input level of the video signal and the amount of the aperture correction signal is as shown in FIG.

If the input level of the video signal is low, the amount of the aperture correction signal added is reduced, and if the input level of the video signal is high, the amount of the aperture correction signal added is increased. Note that the inflection point P of the change in the aperture correction signal with respect to the input level of the video signal may be adjusted by changing the DC voltage of either one of the lamp units 15 and 16.

6 and 7 show other embodiments of the video signal contour correction circuit of the present invention, FIG. 6 is a block circuit diagram of the other embodiment, and FIG. 7 is shown in FIG. FIG. 2 is a specific circuit diagram of a block circuit diagram.

In FIGS. 6 and 7, the video signal applied to the input terminal 1 is first gain-adjusted by the AGC circuit 14, and then
As applied to the aperture correction signal generator 10, the configuration is different from the video signal contour correction circuit shown in FIGS. 3 and 4. However, the input and output signals of the AGC circuit 14 are given to the aperture correction signal adjuster 12 to control the gain of the aperture correction signal output from the aperture correction signal generator 10, and the gain-controlled aperture correction signal and the image The mixing of the signals with the mixer 8 is similar to that shown in FIGS. 3 and 4. [Effects of the Invention] As explained above, according to the video signal contour correction circuit of the present invention, the mixing ratio of the video signal and the aperture correction signal can be adjusted according to the input level of the video signal. Therefore, when the input level of the video signal is low, the amount of the aperture correction signal to be mixed is small, and even if a low input level video signal with a poor S/N is corrected for contour, the S/N will not deteriorate. Further, in the case of a high input level video signal with a good 8/N ratio, contour correction is performed even more strongly, and the apparent resolution of the upper image can be increased, which is an excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram of a conventional video signal contour correction circuit, FIG. 2 is a waveform diagram explaining the operation of the block circuit shown in FIG. 1, and FIG. 3 is a video signal contour correction circuit according to the present invention. FIG. 4 is a block circuit diagram of one embodiment of the correction circuit, and FIG. 5 is a specific circuit diagram of the block circuit diagram shown in FIG. 3.
A diagram showing the relationship between the aperture correction signal gain-controlled by the aperture correction signal adjuster shown in the figure and the input level of the video signal, and FIG. 6 is a block circuit of another embodiment of the video signal contour correction circuit of the present invention 7 are specific circuit diagrams of the block circuit diagram shown in FIG. 6. In the figure, 2.6.8... mixer, 10... aperture correction signal generator, 12... aperture correction signal adjuster, 14... AGC circuit.

Claims (1)

[Claims] an AGC circuit for a video signal, an aperture correction signal generator, and an aperture correction signal adjuster that controls the gain of the aperture correction signal from the aperture correction signal generator in accordance with the gain control of the video signal by the AGC circuit; A video signal contour correction circuit comprising a mixer that mixes the aperture correction signal whose gain is controlled by the aperture correction signal adjuster and the video signal.