JPH043586A - Vertical contour correction circuit - Google Patents

Abstract

PURPOSE:To control a correction quantity at a weak electric field and to prevent the deterioration in the S/N by providing an adder means adding a video signal and a vertical contour correction signal corrected by an addition quantity control circuit. CONSTITUTION:A vertical contour correction signal generating circuit 1 correcting a vertical change only from a video signal A is provided and a VIFAGC voltage detection means and an addition quantity control circuit 3 are provided. Then the vertical contour correction signal B1 is corrected by a prescribed correction quantity based on the detection output of the VIFAGC voltage detection means 2 when the signal is a prescribed strength or over. Moreover, the vertical contour correction signal is controlled to be reduced corresponding to the electric field strength when the electric field is a weak electric field of a prescribed value or below. Then a luminance signal Y obtained by a Y/C separation circuit 5 and the vertical contour correction signal B1 corrected by the addition quantity control circuit 3 are added by an adder means 4. Thus, the addition at weak electric field is reduced to prevent the deterioration in the S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vertical contour correction circuit used to improve the image quality of television receivers and the like.

[Conventional technology]

In recent years, as the image quality of television receivers has become higher, there has been significant progress in improving the image quality in the horizontal direction due to wider video signal bands, sharper horizontal contour correction, etc. Further, along with this improvement in image quality in the horizontal direction, vertical contour correction circuits that improve image quality in the vertical direction have been gradually introduced in order to obtain balanced image quality.

FIG. 6 shows an example of a conventional vertical contour correction circuit.

In this figure, (21) is a vertical contour correction signal generation circuit that generates a signal (B) that corrects only the vertical change portion from the video signal (A), and (22) is the video signal (A) and the vertical contour correction circuit. Adder (addition means) that adds signal (B)
It is.

Further, (23) is a Y/C separation circuit, which is a video signal (
A delay circuit unit (2) outputs a video signal (AI) obtained by delaying A) by IH (H: horizontal scanning period) and a video signal (A2) obtained by further delaying this video signal (A, ) by IH.
4), a video signal amplifier (25) that amplifies the IH delayed video signal (A1), a video signal (A) and an IH delayed video signal (A1);
+) and the 2H delayed video signal (A2) to the chroma signal (
C), and a subtraction circuit section (27) that subtracts the chroma signal (C) from the IH delayed video signal (A1) and outputs the luminance signal (Y).
It is composed of.

The vertical contour correction signal generation circuit (21) includes an amplifier (28) with an amplification factor of A, an inverter (29) that inverts the output of the amplifier (28), and amplifiers (30) and (3) with an amplification factor of A/2.
1), and an adder circuit section (32) that adds the outputs of these amplifiers. In Figure 7, (
a) is the output signal waveform of the inverter (29), (b) is A
/2x amplifier (30) output signal waveform, (c) is A/2
The output signal waveforms of the doubler amplifier (31) are shown, and the vertical contour correction signal (B) having a waveform as shown in FIG.

Then, an adder (22) adds this vertical contour correction signal (B) and the luminance signal (Y) obtained by the Y/C separation circuit (23), and the corrected luminance signal (
Y') is obtained.

Now, assuming that the waveform of the video signal (A) input to the vertical contour correction circuit shown in FIG. 6 is as shown in FIG. 8(a), the vertical contour correction signal generation circuit (21) As shown in FIG. 8(b), a correction signal (B) is generated by detecting only the portion where there is a change in the vertical direction. This vertical contour correction signal (B) is added to the luminance signal (Y) by an adder (22) so that only the portions that change in the vertical direction become sharp, as shown in FIG. 8(c). A corrected luminance signal (Y') is obtained, and the image quality in the vertical direction is improved. Note that each signal waveform shown in FIGS. 8(a) to (C) omits horizontal period signal components.

In addition to the above configuration, the conventional vertical contour correction circuit also receives a video signal (A) and an IH delayed video signal (A1) output from a Y/C separation circuit (23'), as shown in FIG.
and a vertical contour correction signal generation circuit using an LC filter (
21') to obtain the vertical contour correction signal (B), this case also has the same vertical image quality reoccupation function as the conventional example described above.

[Problem to be solved by the invention]

However, according to the conventional configuration as described above, the vertical contour correction signal generating circuit (2I) or (21")
Since it has the frequency characteristics shown in the figure, when the electric field is weak, noise of 2 to 3 MHz is also added at the same time, causing S
There was a problem that the N ratio deteriorated.

In particular, since the above-mentioned frequency band of 2 to 3 Mflz is a band to which the viewer's eyes are highly sensitive, the deterioration of the SN ratio is emphasized and the image quality is greatly affected.

In view of the above-mentioned problems, the present invention improves the image quality in the vertical direction by performing a predetermined correction according to the electric field strength when the electric field is strong or medium, while controlling the amount of correction when the electric field is weak. It is an object of the present invention to provide a vertical contour correction circuit that can prevent a decrease in the signal-to-noise ratio.

[Means to solve the problem]

In order to achieve the above object, the vertical contour correction circuit of the present invention includes a vertical contour correction signal generation circuit that generates a signal for correcting only the vertical change portion from a video signal, and a VIFAG
C voltage detection means, and the vertical contour correction signal is detected by the VIF.
Based on the detection output of the AGC voltage detection means, if the received electric field has a strength above a certain level, it is corrected with a predetermined correction amount, and if the received electric field has a strength below a certain level, the correction amount is adjusted as the electric field strength becomes weaker. an addition amount control circuit that controls to decrease the amount of addition;
The apparatus further includes an adding means for adding the video signal and the vertical contour correction signal corrected by the addition amount control circuit.

[For production]

With the above-described configuration, the present invention can control the amount of addition of the vertical contour correction signal to the luminance signal by detecting the VIFAGC voltage depending on the strength of the electric field, thereby reducing the amount of addition when the electric field is weak and preventing a drop in the S/N ratio. becomes possible.

〔Example〕

Hereinafter, a vertical contour correction circuit according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the basic configuration of a vertical contour correction circuit according to the present invention, and FIG. 2 shows the configuration of a specific embodiment thereof. In these figures, (1) is a vertical contour correction signal generation circuit that corrects only the vertical change portion from the video signal (A), and has the same configuration as the conventional vertical contour correction signal generation circuit (21). have.

(2) is a VIFAGC voltage detection means, and (3) is an addition amount control circuit, which converts the vertical contour correction signal (Bo) to the VIFAGC voltage detection means.
Based on the detection output of the GC voltage detection means (2), if the electric field is above a certain level, that is, approximately strong or medium electric field, it will be corrected with a predetermined correction amount, and if the electric field is weak and below a certain level, the electric field strength will be adjusted. The correction amount is controlled to be decreased in accordance with the above. Further, (4) is an addition means for adding the luminance signal (Y) obtained by the Y/C separation circuit (5) and the vertical contour correction signal (B+) corrected by the addition amount control circuit (3). The Y/C separation circuit (5) has the same configuration as the conventional Y/C separation circuit (23).

FIG. 3 shows an example of a specific circuit configuration of the VIFAGC voltage detection means (2). VI F shown in this figure
In the AGC voltage detection means (2), the VIP signal is passed through the surface acoustic wave filter (6) to the first IF amplifier circuit section (
7) and the AGC circuit (3) for automatic gain control when amplifying by the second IF amplification circuit section (8).
It is configured to take out an AGC voltage signal (V).

The vertical contour correction circuit of this embodiment having such a configuration takes advantage of the fact that the VIFAGC voltage (v) changes depending on the strength of the electric field, and converts the detection output of the VIFAGC voltage detection means (2) into the addition amount control circuit ( 3) Enter. On the other hand, the addition amount control circuit (3) includes a vertical contour correction signal generation circuit (1).
The vertical contour correction signal (BO) generated in is input, and this vertical contour correction signal (Bo) is corrected based on the VIFAGC voltage (V).

As shown in Figure 4, the amount of correction for this vertical contour correction signal (B.) is normally set in case of strong or medium electric fields, but as the electric field becomes weaker, noise starts to become noticeable. gradually reduces the amount of addition in response to the strength of the electric field,
If the electric field is below a certain level, the image quality will be mostly noise, so
The addition amount is also set to zero.

As described above, according to this embodiment, the vertical contour correction signal (
The amount of addition of Bn) to the video signal (A) can be controlled by detecting the VIFAGC voltage m, and the amount of addition can be reduced when the electric field is weak to prevent deterioration of the SN ratio.

In addition, in the present invention, as shown in FIG. 5, the vertical contour correction signal generation circuit (l'') may be constructed in the same manner as the vertical contour correction signal generation circuit (21') in the conventional example shown in FIG. Note that (5') in FIG. 5 is a Y/C separation circuit.

〔Effect of the invention〕

According to the present invention, the amount of addition of the vertical contour correction signal to the video signal is controlled according to the strength of the electric field, and when the electric field is weak, the amount of addition is reduced according to the strength of the electric field. Without requiring any operations, it is possible to prevent image quality from deteriorating in weak electric field conditions, and to receive television signals in an optimal state at all times.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of a vertical contour correction circuit according to the present invention, FIG. 2 is a block diagram of a vertical contour correction circuit in an embodiment of the present invention, and FIG. 3 is a VIFAGC in the vertical contour correction circuit. FIG. 4 is a block diagram showing an example of the voltage detection means; FIG. 4 is a control characteristic diagram of the amount of addition of the VI PAGC voltage and the vertical contour correction signal to the video signal due to the electric field; and FIG.
The figure is a block diagram of a vertical contour correction circuit according to another embodiment of the present invention, FIG. 6 is a block diagram showing an example of a conventional vertical contour correction circuit, and FIG. 7 is a vertical contour correction signal generation shown in FIG. FIG. 8 is a waveform diagram for explaining the operation in the circuit; FIG. 8 is a waveform diagram for explaining the operation in the vertical contour correction circuit shown in FIG. 6; FIG. 9 is a block diagram showing another example of the conventional vertical contour correction circuit. 10 are frequency characteristic diagrams of the vertical contour correction signal generation circuit. (1), Vertical contour correction signal generation circuit, (2)...
VIFAGC voltage detection means, (3)...addition amount control circuit, (4)...addition means, (A)...video signal, (
Bo)... Vertical contour correction signal, (Bl)... Vertical contour correction signal after correction. Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] a vertical contour correction signal generation circuit that generates a signal for correcting only a vertical change portion from a video signal; a VIFAGC voltage detection means;
Based on the detection output of the C voltage detection means, if the electric field has a strength above a certain level, it is corrected by a predetermined correction amount, and if the electric field has a strength below a certain level, the correction amount is decreased as the electric field intensity becomes weaker. 1. A vertical contour correction circuit comprising: an addition amount control circuit for controlling the addition amount; and an addition means for adding the video signal and the vertical contour correction signal corrected by the addition amount control circuit.