JPH06274131A - Image signal processing circuit for liquid crystal projection type video display device - Google Patents

Abstract

PURPOSE:To make an image glossy similarly to a CRT by preventing a local decrease in luminance which is reduced by shading correction conventionally. CONSTITUTION:A horizontal differential signal DH and a vertical differential signal DV are obtained based on of luminance information on respective parts of a screen. Then a discriminating circuit 10 adds those differential signals DH and DV together, respective comparators discriminate whether the sum exceeds threshold values K1-K4 respectively, and on of three-bit control signals '000'-'100' is outputted according to the outputs of the respective comparators. Then four kind of video signals are supplied to a liquid crystal driving circuit 14 in response to the three-bit control signal ('000'-'100'). Namely, the signals from the signal A before the shading correction to the signal B after the shading correction are divided into four stages and selectively outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing circuit for driving a liquid crystal panel of a liquid crystal projection type image display device.

[0002]

2. Description of the Related Art A liquid crystal projection type image display device is being developed due to advantages such as a smaller volume than a CRT projection type display device, especially a rear type device having a short depth, and easy operation adjustment. Has been.

However, since a lamp is used as a light source for illuminating the liquid crystal panel, shading occurs in which the central part of the screen is bright and the peripheral part is dark, and the image quality is inferior to that of the conventional CRT type as it is. It was

Therefore, in order to obtain an image quality equivalent to that of a CRT, it was necessary to correct this shading. However, in that case, since there is no choice but to match the high-brightness part with the low-brightness part, the brightness will become darker overall, and it is difficult to actually perform this correction under the present circumstances. is there.

[0005]

As described above, the liquid crystal projection type image display device has various problems listed below.

1) Since the above-mentioned shading occurs, the peripheral portion of the screen becomes extremely dark, and the effect of the large screen is reduced.

2) In order to correct the shading, the brightness of the bright portion is reduced to make the brightness (luminance) levels uniform. As a result, the overall brightness is inevitable.

3) In the CRT, the peripheral circuit performance is insufficient to brighten the entire screen. Therefore, a method of brightening only a small local portion to make the image glossy is adopted. However, since the liquid crystal does not emit light in a dot-sequential manner like a CRT, this method cannot be adopted, and the overall image feels flat, which has been conventionally regarded as a weak point of the liquid crystal projection display device. .

Therefore, in view of the above points, it is an object of the present invention to provide an image signal processing circuit configured so as to prevent an overall reduction in luminance caused by shading correction and obtain an image quality equivalent to that of a CRT. .

[0010]

In order to achieve the above object, the present invention provides a liquid crystal projection type image display device equipped with a signal processing circuit for correcting non-uniformity of luminance distribution on a screen. The means for generating a correction signal for correcting the non-uniformity of the brightness distribution based on the information of 1. and the means for controlling the correction amount by the correction signal and reproducing the brightness of the details of the screen. is there.

[0011]

According to the above-mentioned structure of the present invention, shading is corrected as a whole in order to solve the above-mentioned problems.
Locally, the amount of correction is controlled according to the fineness of the video signal,
The brightness reproduction level can be controlled.

That is, by making the local small portion particularly bright, the image can be made glossy and the image quality equivalent to that of the CRT can be obtained.

[0013]

In the embodiments described in detail below, as a signal processing circuit for correcting shading, the brightness distribution on the screen of the display is measured in advance, and the correction signal based on the difference from the set brightness distribution is stored in the memory. It is assumed that a means for obtaining a predetermined luminance distribution characteristic by reading out this signal for each pixel, calculating the product and the sum with the input signal is taken. In this case, the reproducible luminance is limited to the lowest luminance of the actual screen.

On the other hand, in order to obtain information on a fine portion of the screen, a signal obtained by differentiating the input image signal in the horizontal and vertical directions is created. A signal obtained by extracting a signal having a predetermined level or higher is used as a control signal. The control signal controls the execution of the shading correction. As a result, the fine portion becomes a bright luminescent spot, and the brilliance of details can be reproduced.

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

In the embodiments of the present invention described here, white light from a light source is spectrally decomposed into RGB primary colors, and light is modulated in accordance with each primary color signal through a predetermined liquid crystal device for each color, and then each primary color is obtained. A method of constructing and projecting light rays is adopted. In this case, in order to adapt the input signal to the liquid crystal projection type image display device, it has a circuit for performing signal processing such as gamma characteristic correction.

Embodiment 1 FIG. 1 is a block diagram showing one channel in one embodiment of the present invention. In the figure, 2 is an A / D converter, which inputs RGB component signals and outputs an 8-bit serial signal.

Reference numeral 4 denotes a circuit for voltage-transmittance correction (VT correction), which restores the .gamma.-correction suitable for the CRT and, at the same time, corrects the brightness of the liquid crystal.

Reference numeral 6 is a shading correction circuit. Although not shown in the figure, the three primary colors RG of the display are previously set.
The brightness distribution of the B screen is measured, and the correction signal based on the difference from the set brightness distribution is stored in the memory. Then, this correction signal is read out for each pixel, and a product / sum operation is performed with the primary color input signal to obtain a predetermined luminance distribution characteristic. In this case, the reproducible luminance is limited to the lowest luminance of the actual screen.

Reference numeral 8 is a differentiating circuit, which differentiates the input image signals of the primary colors in the horizontal and vertical directions in order to obtain information on a fine portion of the screen. In the horizontal direction, as shown in FIG. 4, the same processing is performed pixel by pixel to obtain a differential signal D _H. Further, in the vertical direction, a delay circuit of 1H is used as shown in FIG. 5, and a differential signal D _V is created from a signal obtained by taking the difference between the preceding line (scanning line) and the following line.

The horizontal differentiating circuit and the vertical differentiating circuit shown in FIGS. 4 and 5 detect the change in the signal level in the 3 dot × 3 dot differentiating area. By adopting the circuit configuration as shown in FIG. 7, it is possible to perform differentiation on a minute area of 5 dots × 5 dots.

Numeral 10 is a discriminating circuit, which detects two differential signals D _H ,
When the sum of V _D exceeds a predetermined threshold value, a 1-bit control signal a (a = 0 or a = 1) is output.

Reference numeral 12 denotes a switching circuit, which switches to the A side when the control signal is "1" and to the B side when the control signal is "0" for each pixel.

Reference numeral 14 is a liquid crystal driving circuit, which is developed in 12 layers.
It has the functions of scanning line interpolation for non-interlaced conversion and line / field inversion for inverting the DC level applied to the liquid crystal.

According to the configuration shown in FIG. 1, when the control signal becomes "1" in response to the differential signal of the minute region, the component signal which has undergone the VT correction without passing through the shading correction circuit 6. Is directly input to the liquid crystal drive circuit 14.

As a result, shading correction is performed on a large area of the image and the screen is displayed with uniform brightness, but in the local image, the shading correction is removed and the original light emission brightness is restored. And the peak brightness is improved. As a result, performance equivalent to that of a CRT is secured, and one of the defects in image quality of the liquid crystal projection display device is removed.

Embodiment 2 FIG. 2 shows a second embodiment of the discrimination circuit 10 shown in FIG. In the discrimination circuit 10 shown in the figure, the horizontal differential signal D _H and the vertical differential signal D _V are added, and the value is the threshold value K _{1 to} K _1.
Whether it exceeds ₄ is determined by a separate comparator,
Depending on the output of each comparator, any of the 3-bit control signals “000” to “100” is output.

FIG. 3 shows a switching circuit 1 used in this embodiment.
2 shows the configuration. As shown in the figure, four types of video signals are supplied to the liquid crystal drive circuit 14 (see FIG. 1) in response to the 3-bit control signals (“000” to “100”).
That is, the signal A, which has not been subjected to the shading correction, to the signal B, which has been subjected to the shading correction, is selectively output in four stages.

Next, the overall operation of the image signal processing circuit constructed by FIGS. 1 to 3 will be outlined.

In the circuit shown in FIG. 1, as already described, the luminance distribution of the three primary color RGB screens of the display is measured in advance, and the correction signal based on the difference from the set luminance distribution is stored in the memory. The signal processing circuit for each primary color reads out this signal for each pixel, calculates the product and sum with the primary color input signal, and obtains a predetermined luminance distribution characteristic. In this case, the reproducible luminance is limited to the lowest luminance of the actual screen.

The differentiating circuit 8 shown in FIG. 1 differentiates the input image signals of the primary colors in the horizontal and vertical directions in order to obtain the information of the fine portion of the screen. A 1H delay circuit is used in the vertical direction, and a differential signal is created from a signal obtained by taking a difference from the previous line (scanning line) and a signal obtained after the difference. However,
Since the bright part is targeted, the subtraction is performed from the line, and thereafter, the signals of both are added to obtain a differential signal.
In the horizontal direction, the same processing is performed for each pixel to obtain a differential signal. A signal of a predetermined level or more is extracted from the sum of the horizontal and vertical directions and used as a control signal.

The execution of the shading correction is controlled by this signal. As a result, shading correction is performed on a large area of the image, and the screen is displayed with uniform brightness.However, in the local image, the shading correction is reduced, and the value returns to a value close to the original emission brightness. The peak brightness is improved. As a result, performance equivalent to that of a CRT is secured, and one of the defects in image quality of the liquid crystal projection display device is removed.

[0033]

As described above, according to the present invention, it is possible to prevent a local decrease in luminance which has been reduced by performing shading correction, and to make an image glossy like a CRT.

[Brief description of drawings]

FIG. 1 is a block diagram showing an entire embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the discrimination circuit 10 shown in FIG.

FIG. 3 is a circuit diagram showing another embodiment of the switching circuit 12 shown in FIG.

FIG. 4 is a circuit diagram in which pixel data of 3 × 3 dots is input to perform horizontal differentiation.

FIG. 5 is a circuit diagram for inputting pixel data of 3 × 3 dots to perform vertical differentiation.

FIG. 6 is a circuit diagram for inputting 5 × 5 dot pixel data to perform horizontal differentiation.

FIG. 7 is a circuit diagram for inputting pixel data of 5 × 5 dots to perform vertical differentiation.

[Explanation of symbols]

 2 A / D converter 4 VT correction circuit 6 Shading correction circuit 8 Differentiation circuit 10 Discrimination circuit 12 Switching circuit 14 Liquid crystal drive circuit

Claims (1)

[Claims] 1. A liquid crystal projection type image display device equipped with a signal processing circuit for correcting non-uniformity of brightness distribution on a screen, for correcting non-uniformity of brightness distribution based on information of image details. An image signal processing circuit comprising: a unit for generating a correction signal; and a unit for controlling a correction amount by the correction signal to reproduce the brightness of a detail of a screen.