JP2003150130A - Outline emphasizing circuit of liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an outline emphasizing circuit of a liquid crystal display device capable of solving the problem that noise components are made conspicuous in a portion expanded by gamma correction, due to the overemphasized outline correction and the effectiveness of the outline correction is reduced in a portion compressed by the gamma correction. SOLUTION: A means is provided to correct the degree of outline emphasis based on the signal levels of input video signals and the gamma characteristics of a liquid crystal panel, in the outline emphasizing circuit of a liquid crystal display device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour emphasizing circuit in a liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as a contour correction circuit, there has been known a contour correction circuit that secondarily differentiates an input luminance signal and superimposes it on an original signal to perform contour correction.

Assume that a liquid crystal projector outputs an image created by a PC. In a TV receiver or the like, the display area is narrower than the entire video area defined by the video signal, so that the edges of the entire video area are not displayed. On the other hand, in the liquid crystal projector, since the entire image area defined by the image signal is displayed, the edge of the entire image area is also displayed.

On the liquid crystal projector side, when contour correction is performed on a video signal input from a PC by a circuit similar to the conventional contour correction circuit, the contour at the end of the picture is emphasized and displayed. is there.

On the liquid crystal projector side, a PC
If contour correction is performed on a video signal input from the same circuit as a conventional contour correction circuit, the contour is emphasized even on a clear portion such as a contour of a character or the like in a video created by a PC. Therefore, there is a problem that an unnatural image is reproduced.

In the liquid crystal projector, gamma correction is performed on the signal after the contour correction. FIG. 1 shows the input-output characteristic of the gamma correction circuit. Also, FIG.
Shows the output signal for the input signal when the input level corresponds to the expanded portion of the gamma characteristic and the output signal for the input signal when the input level corresponds to the compressed portion of the gamma characteristic.

When the input level corresponds to the compressed part of the gamma characteristic as shown in FIG. 2 (a), the amplitude of the output signal is reduced by gamma correction, and the input level becomes gamma as shown in FIG. 3 (b). When it corresponds to the extended portion of the characteristic, the gamma correction increases the amplitude of the output signal. Therefore, if uniform contour correction is performed on the entire image area, the contour correction is too effective in the portion expanded by the gamma correction and a noise component is noticeable, and the effect of the contour correction is reduced in the portion compressed by the gamma correction. There is a problem.

[0008]

SUMMARY OF THE INVENTION The present invention has a problem that the contour correction is too effective in a portion expanded by gamma correction and a noise component is conspicuous, and the contour correction effect is reduced in a portion compressed by gamma correction. An object of the present invention is to provide a contour enhancement circuit in a liquid crystal display device that can be eliminated.

Further, the present invention provides a liquid crystal display device capable of preventing a contour from being emphasized on a clear portion such as a contour of a character or the like in a video image created by a PC and reproducing a natural image. An object is to provide a contour enhancement circuit.

[0010]

According to a first aspect of the present invention, there is provided means for correcting the degree of edge enhancement based on the signal level of the input video signal and the gamma characteristic of the liquid crystal panel. To do.

According to a second aspect of the invention, there is provided a means for correcting the degree of edge enhancement based on the amount of change in the input video signal.

According to a third aspect of the present invention, there is provided means for correcting the degree of edge enhancement based on the signal level of the input video signal, the gamma characteristic of the liquid crystal panel, and the amount of change in the input luminance signal. And

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, a means is provided for prohibiting contour enhancement from being performed on a peripheral portion of the image area. And

The invention described in claim 5 is the same as in claims 1, 2 and
In the invention described in 3 or 4, when the amount of change in the input video signal is smaller than a predetermined value, contour enhancement is not performed,
It is characterized in that it comprises means for subtracting the contour emphasis waveform from the input video signal.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention applied to a liquid crystal projector will be described below with reference to FIGS.

FIG. 3 shows the configuration of the contour correction circuit provided in the liquid crystal projector.

The RGB signals input from the PC are sent to the luminance signal conversion section 1 and the addition circuit 6.

The brightness signal converter 1 converts the RGB input signal into a brightness signal. The brightness signal obtained by the brightness signal conversion unit 1 is sent to the brightness level & change amount detection unit 2 and also to the secondary differentiation circuit 3.

The secondary differentiating circuit 3 secondarily differentiates the inputted luminance signal, and outputs a second differential waveform (edge emphasis waveform) to the multiplying circuit 5.

The brightness level & change amount detection unit 2 detects the input level and change amount (differential value) of the input brightness signal,
The detected input level and change amount are sent to the correction amount determination unit 4.

The correction amount determining unit 4 calculates a correction amount (multiplier circuit) based on a combination of the input level and the change amount detected by the brightness level & change amount detecting unit 2 and a LUT (look-up table) prepared in advance. 5 multiplication factor). The range of the correction amount is 0 to 2, for example.

This LUT has a small correction amount when the input level is the expanded portion of the gamma characteristic, and a large correction amount when the input level is the compressed portion of the gamma characteristic. Is large, the correction amount is small, and when the change amount is small, the correction amount is large.

When the input level is the expanded portion of the gamma characteristic, the correction amount is reduced, and when the input level is the compressed portion of the gamma characteristic, the correction amount is increased.
This is to solve the problem that the contour enhancement correction is excessively effective due to expansion by the gamma correction circuit, or the contour enhancement effect is reduced due to compression by the gamma correction circuit.

Further, when the change amount is large, the correction amount is made small, and when the change amount is small, the correction amount is made large like the outline of characters or the like in the image created by the PC. This is because a more natural image is reproduced by not emphasizing the contour in a clear portion and emphasizing the contour in a picture with a fine content.

FIG. 4A shows a case where the contour correction is uniformly performed on the English character "H" as in the conventional example.
In (b), for the English character "H", the part where the amount of change is large as in the present embodiment shows the case where the edge enhancement degree is low. In FIG. 4 (a), the outline of the letter "H" is emphasized and the letter "H" is hard to see, whereas in Fig. 4 (b), the outline of the letter "H" is not emphasized. You can see that the English letter "H" is easier to see.

The correction amount determined by the correction amount determination unit 4 is sent to the multiplication circuit 5 as a multiplication coefficient. Multiplication circuit 5
Generates a final contour emphasis waveform by multiplying the secondary differential waveform sent from the secondary differential circuit 3 by the correction amount determined by the correction amount determination unit 4. Multiplication circuit 5
The contour emphasis waveform generated by is sent to the adder circuit 6. The adder circuit 6 superimposes the contour emphasis waveform generated by the multiplier circuit 5 on the RGB input signal and outputs it.

The valid period determining section 7 determines the upper, lower, left and right end portions of the entire video period defined by the RGB input signals.
It is provided in order to prevent the contour enhancement processing from being performed. The valid period determination unit 7 outputs a contour correction invalid signal to the correction amount determination unit 4 when signals for pixels at the upper, lower, left, and right ends are input in the entire video period defined by the RGB input signals. To do. When the contour correction invalid signal is input, the correction amount determination unit 4 outputs 0 as the correction amount. As a result, the contour correction is not performed on the top, bottom, left, and right ends of the entire video period defined by the RGB input signals. As a result, when displaying an image created by a PC on a liquid crystal projector, there is no unnaturalness in which the contour is emphasized at the edge of the displayed image.

FIG. 5A shows a case where contour correction is performed on the end of the video period as in the conventional example, and FIG. 5B shows this embodiment on the end of the video period. The case where the contour correction is not performed as shown in FIG. Figure 5 (a)
In contrast, while the end of the video period is emphasized, in FIG.
In (b), since the end of the video period is not emphasized, it can be seen that even if this part is displayed, there is no unnaturalness.

When the change amount detected by the brightness level & change amount detecting unit 2 is smaller than a predetermined value, the correction amount determining unit 4 sets "1" as the correction amount in order to obscure the noise component. ", And the addition circuit 6 outputs
RG the secondary differential waveform generated by the secondary differential circuit 3
You may make it subtract from a B input signal.

[0030]

According to the present invention, it is possible to solve the problem that the contour correction is too effective in the portion expanded by the gamma correction and the noise component is conspicuous, and the effect of the contour correction is reduced in the portion compressed by the gamma correction. Like

Further, according to the present invention, it is possible to prevent the contour from being emphasized with respect to a clear portion such as the contour of a character or the like in the image created by the PC, and a natural image can be reproduced. .

[Brief description of drawings]

FIG. 1 is a graph showing an example of gamma characteristics of a liquid crystal panel.

FIG. 2 is a schematic diagram showing an output signal for an input signal when the input level corresponds to an expanded part of the gamma characteristic and an output signal for an input signal when the input level corresponds to a compressed part of the gamma characteristic.

FIG. 3 is a block diagram showing a configuration of a contour correction circuit provided in the liquid crystal projector.

FIG. 4 shows a case in which contour correction is uniformly performed for the English character “H” as in the conventional example, and for the English character “H” where the amount of change is large as in the present embodiment, the contour emphasis degree is set. It is a schematic diagram which shows the case where it lowered.

FIG. 5 shows a case where contour correction is performed on the end of the video period as in the conventional example, and a case where contour correction is not performed on the end of the video period as in the present embodiment. It is a schematic diagram which shows.

[Explanation of symbols]

1 Luminance signal converter 2 Brightness level & change amount detector 3 2nd order differentiation circuit 4 Correction amount determination unit 5 Multiplier circuit 6 adder circuit 7 Effective period determination section

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Jun Mishima             2-5-3 Keihan Hondori, Moriguchi City, Osaka Prefecture             Within Yo Denki Co., Ltd. F term (reference) 5C006 AF50 BC16 EC11 FA31                 5C021 PA01 PA17 PA58 PA66 PA67                       PA75 XA34 XB03 XB04                 5C080 AA10 BB05 CC03 DD01 EE01                       EE17 JJ01 JJ02 JJ04 JJ05                       KK02

Claims (5)

[Claims] 1. An edge enhancement circuit in a liquid crystal display device, comprising means for correcting the degree of edge enhancement based on a signal level of an input video signal and a gamma characteristic of a liquid crystal panel. 2. An edge enhancement circuit in a liquid crystal display device, comprising means for correcting the degree of edge enhancement based on the amount of change of an input video signal. 3. An edge enhancement circuit in a liquid crystal display device, comprising means for correcting the degree of edge enhancement based on the signal level of an input video signal, the gamma characteristic of a liquid crystal panel, and the amount of change of an input luminance signal. 4. The contour enhancement circuit in a liquid crystal display device according to claim 1, further comprising means for prohibiting contour enhancement from being performed on a peripheral portion of a video area. 5. The apparatus according to claim 1, further comprising means for subtracting the contour emphasis waveform from the input video signal without performing the contour emphasis when the variation of the input video signal is smaller than a predetermined value.
5. An outline emphasis circuit in the liquid crystal display device according to any one of 2, 3 and 4.