JP2602392B2 - Image signal processing circuit for liquid crystal projection type video display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A liquid crystal projection type image display device has been developed due to advantages such as a smaller volume as compared with a CRT projection type display device, particularly, a rear type device having a shorter depth and a simple operation adjustment. Have been.

However, since a lamp is used as a light source to illuminate the liquid crystal panel, shading occurs in which the center of the screen is bright and the periphery is dark, and the image quality is inferior as it is to the conventional CRT type. Was.

Therefore, in order to obtain an image quality equivalent to that of a CRT, it is necessary to correct this shading. However, in this case, the only way to do this is to match the high-brightness part to the low-brightness part. is there.

[0005]

As described above, the liquid crystal projection type video display has the following various problems.

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

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

3) In a CRT, the peripheral circuit performance is insufficient for brightening the entire screen. Therefore, a method of brightening only a small portion locally and giving a gloss to an image has been adopted. However, since the liquid crystal does not emit light in a point-sequential manner unlike a CRT, this method cannot be adopted, and the image becomes flat as a whole, which has conventionally been a weak point of the liquid crystal projection display device. .

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an image signal processing circuit configured to prevent the overall brightness from being reduced due to shading correction and to obtain an image quality equivalent to that of a CRT. .

[0010]

In order to achieve the above object, the present invention relates to an image signal processing circuit of a liquid crystal projection type video display device provided with a shading correction circuit for correcting non-uniformity of luminance distribution on a screen. A differentiating means for inputting an image signal in a predetermined minute area and outputting each of a differential signal in a horizontal direction and a vertical direction, and controlling a logic level 1 when a sum of the two differential signals is equal to or more than a predetermined threshold value. Control means for outputting a signal and directly supplying the VT corrected component signal to the liquid crystal drive circuit without passing through the shading correction circuit when the control signal is at the logical level 1. is there. According to another aspect of the present invention, in an image signal processing circuit of a liquid crystal projection type video display device provided with a shading correction circuit for correcting non-uniformity of luminance distribution of a screen, an image signal in a predetermined minute area is input, And differentiating means for outputting each of the differential signals in the vertical direction, and determining whether or not the two differential signals each exceed a specific threshold value. When the results of the determination both exceed a specific threshold value, 1 is output, and when the control signal is at logic level 1,
VT without going through the shading correction circuit
Control means for directly supplying the corrected component signal to the liquid crystal drive circuit.

[0011]

In the above configuration of the present invention, the shading correction is performed on one screen as a whole, but in a local minute area, the shading correction is canceled according to the change in the video signal level (differential output). The luminance reproduction level is set to the maximum luminance before shading correction.

In other words, according to the present invention, in order to prevent a reduction in luminance due to shading correction, a correction signal is omitted based on information on the details of an image so that the original brightness can be reproduced and a local luminance can be reproduced. By preventing the small portions from becoming dark, the image can be made glossy.

[0013]

Embodiments of the present invention will be described below in detail.

In one embodiment of the present invention described here, the white light of the light source is spectrally decomposed into RGB primary colors, and light modulation corresponding to each primary color signal is performed for each color through a predetermined liquid crystal device. A method of forming and projecting primary color light rays is adopted. In this case, in order to adapt the input signal to the liquid crystal device, a circuit for performing signal processing such as gamma characteristic correction is provided.

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

Reference numeral 4 denotes a circuit for performing voltage-transmittance correction (VT correction), which restores the γ correction suitable for the CRT and at the same time, performs a correction matching the luminance characteristics of the liquid crystal.

Reference numeral 6 denotes a shading correction circuit. Although not shown in the drawing, the three primary colors RG of the display are set in advance.
The luminance distribution of the B screen is measured, and a correction signal based on a difference from the set luminance distribution is stored in a memory. Then, the 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 by the lowest luminance of the actual screen.

Numeral 8 denotes a differentiating circuit for differentiating an input image signal of a primary color 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. 3, the same processing is performed for each pixel to obtain a differentiated signal D _H. Further, in the vertical direction using a delay circuit of 1H as shown in FIG. 4, to create a signal taking the difference, the differential signal D _V from the difference signal and after the line of the previous line (scanning line).

The horizontal differentiating circuit and the vertical differentiating circuit shown in FIGS. 3 and 4 detect a change in the signal level in a 3 dot × 3 dot differential area. By adopting the circuit configuration shown in FIG. 6, it is also possible to perform differentiation on a small area of 5 dots × 5 dots.

Reference numeral 10 denotes a discriminating circuit, which detects two bright signals in the minute area by two differential signals D _H ,
When the sum of V _D is greater than or equal to a predetermined threshold value, it outputs a control signal of logic level "1".

[0021] As the determination circuit 10, as in the circuit shown in FIG. 2, whether horizontal differential signal D _H and the vertical differential signal D _V exceeds the threshold K ₁ and K ₂ each separate comparators The control signal “1” may be output only when the output of each comparator is “1”.

A switching circuit 12 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.

Numeral 14 denotes a liquid crystal driving circuit, which has 12 layers.
It has functions to perform scanning line interpolation for performing non-interlace 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 area, the VT-corrected component signal is output 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 in a large area of the image, and the screen is displayed with uniform brightness. However, in the local image, the shading correction is removed and the luminance returns to the original luminance. And the peak luminance is improved. As a result, the same performance as that of the CRT is secured, and one of the defects in the image quality of the liquid crystal projection display device is removed.

[0026]

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 in the past, and to obtain a high-quality image having brightness.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a specific configuration of a discrimination circuit shown in FIG.

FIG. 3 is a circuit diagram for performing horizontal differentiation by inputting pixel data of 3 × 3 dots;

FIG. 4 is a circuit diagram for performing vertical differentiation by inputting 3 × 3 dot pixel data;

FIG. 5 is a circuit diagram for performing horizontal differentiation by inputting 5 × 5 dot pixel data;

FIG. 6 is a circuit diagram for performing vertical differentiation by inputting pixel data of 5 × 5 dots.

[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 (2)

(57) [Claims] In the image signal processing circuit according to claim 1 The liquid crystal projection type image display device having a shading correction circuit for correcting the non-uniformity of the brightness distribution of the screen, enter the image signal in a predetermined small area, horizontal
And differentiating means for outputting each differential signal in the vertical direction, and when the sum of the two differential signals is equal to or greater than a predetermined threshold,
A control signal of logic level 1 is output, and the control signal is
In the case of Bell 1, the signal passes through the shading correction circuit.
VT-corrected component signal directly
An image signal processing circuit comprising: control means for directly supplying the liquid crystal drive circuit. 2. A system for correcting non-uniformity of luminance distribution on a screen.
Liquid crystal projection type video display device equipped with an edging correction circuit
In the image signal processing circuit, and the input image signal in a predetermined minute space, horizontal
And differentiating means for outputting each differential signal in the vertical and vertical directions, and each of the two differential signals exceeds a specific threshold value.
And whether the result of the determination exceeds a specific threshold value
Output a control signal of logic level 1 when the
When the control signal is at logic level 1, the shading
VT-corrected component without the use of a correction circuit
Control means for directly supplying a NENT signal to a liquid crystal drive circuit
Image signal processing circuit, characterized by comprising and.