JP3214517B2 - Gamma correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction circuit used for a liquid crystal projector or the like.

[0002]

2. Description of the Related Art Conventionally, this kind of gamma correction circuit has, for example, the configuration shown in FIG. 4, and has an A / D conversion circuit 1 for digitally converting an input video signal and a gamma characteristic of a liquid crystal display device in advance. A gamma correction ROM (hereinafter referred to as ROM) 2 which stores data for gamma correction and uses a digital signal from the A / D conversion circuit 1 as an address;
A D / A converter 3 for converting the data read from the ROM 2 into an analog signal; the analog-converted signal is used as a gamma correction output of the liquid crystal display device. As described above, by using the ROM 2 as a table, a control signal for correcting the gradation characteristics of the liquid crystal display can be obtained by the input signal.

[0003]

When the gamma correction circuit performs 2.2 gamma correction, for example, as shown in the graph of FIG. 5, the luminance difference level of the display image due to the input video signal is large. By the way, since the gamma correction value greatly changes, vertical stripes are generated on the screen, and for example, in the case of a color image, there is a disadvantage that the luminance difference appears green.

[0004] To solve this, the A / D conversion circuit 1
Can be increased, but A /
The D conversion circuit is expensive, which increases the cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to increase the number of bits of data for obtaining a gamma-corrected output, to obtain a smooth gamma-corrected output, and to provide a large luminance difference. An object of the present invention is to provide a gamma correction circuit capable of smoothing an image and smoothing a gradation.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for converting a video (image) based on an input video signal into a liquid.
When displaying the LCDs, using the ROM as a table, the gamma correction circuit for a data read from the ROM are D / A converted and gamma correction signal, you digital converting the input video signal A / D conversion means previously stores a predetermined gamma correction data, the upper SL a /
A storage unit that is to be read the gamma correction data corresponding to the input video signal data obtained by the D converting means as an address, your horizontal of said input video signal
And a dither matrix means for outputting a threshold value of the dither matrix to the vertical synchronization signal, data read from the storage means as upper bits, data obtained by the dither matrix means as lower bits,
D / A conversion means for converting the data constituted by the upper bits and the lower bits into analog signals and converting the data into a control signal for gamma correction is provided.

[0007]

With the above configuration, the above dither matrix
Although corresponding to each pixel of the unit or al screen data (threshold) is read, the data is a low-order bit data for the original gamma correction read from the storage means (gamma correction ROM), By adding the lower bit data, the number of data bits for obtaining a gamma correction output is increased.

As a result, the gamma correction output obtained by the D / A conversion means is made smooth,
Even where the luminance difference of the video is large, the gamma correction value does not change drastically, and no vertical stripes appear on the screen at the boundary of the luminance difference.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a gamma correction circuit using a ROM as a table in order to obtain a gamma correction output based on an input video signal. Upper bits, a threshold value of an organized dither matrix is called out to the upper bit data and added as lower bit data, and the added upper bit and lower bit data are converted into analog signals, that is, the effective D / A conversion is performed. Gamma correction output for smoothing a sudden change in the level of a video (image).

Therefore, as shown in FIG. 1, the gamma correction circuit according to the present invention includes a horizontal synchronizing signal of an input video signal and a synchronizing / separating circuit 4 for separating the horizontal synchronizing signal, and a synchronizing circuit for synchronizing with the separated horizontal synchronizing signal. A dot clock reproducing circuit 5 that reproduces a dot clock of a predetermined frequency (a sample clock used in a driver of a liquid crystal display), and a first counter (which uses this dot clock as a count and is cleared by the separated horizontal synchronization signal). A horizontal counter) 6, a second counter (vertical counter) 7 that counts the separated horizontal synchronization signals and is cleared by the separated vertical synchronization signals, and the first and second counters 6, 7 The count value of the data is an address (for example, 2 bits each), and the data from the gamma correction ROM (hereinafter referred to as ROM) 2 A dither ROM8 to enable reading the lower bit data (e.g. 4 bits data),
Data composed of upper bits and lower bits read from ROM 2 and dither ROM 8 (12 bits)
And a D / A conversion circuit (e.g., 12 bits) 9 for converting the analog signal into a gamma correction output.

A / D conversion circuit 1 and gamma correction
ROM 2 is the same as that described in FIG.
It may be. Further, since the systematic dither method uniquely determines a threshold (threshold) in the case of binarization according to a position, for example, a Bayer type shown in FIG.
The lower 4-bit data is obtained.

Next, the operation of the gamma correction circuit having the above configuration will be described with reference to the schematic diagram of the dither ROM of FIG. 2 and the display screen diagram of FIG. 3. When displaying an image based on an input video signal on a liquid crystal display, The input video signal is A /
The data is converted into a digital signal by the D conversion circuit 1, and gamma correction data is read from a gamma correction ROM (hereinafter referred to as a ROM) 2 by the digital signal. At this time, the horizontal and vertical synchronizing signals of the input video signal are separated by the synchronizing separation circuit 4, and the horizontal dots of the screen 10 are counted by the first counter 6 based on the horizontal synchronizing signal. The horizontal counter on the screen 10 is counted by the second counter 7 based on the sync signal.

The data (threshold) of the dither ROM 8 is read out based on the count values of the first and second counters 6 and 7. In this case, as shown in FIG. 2 , the elements of the Bayer matrix are from 0 to 15, which are assigned from (0000) to (1111).

Therefore, the D / A conversion circuit 9 includes:
As in the conventional case, 8-bit data read from the ROM 2 is input as upper bits, and 4-bit data read from the dither ROM 8 is input as lower bits.
The bit data is converted into an analog signal to obtain a gamma correction control signal.

The above-mentioned Bayer type matrix is 16
Dither RO to apply to screen 10
The data of M8 is repeatedly read out to the entire screen 10 (shown by a broken line in FIG. 3).

As described above, the original gamma correction data of the ROM 2 used as the gamma correction table is set as the upper bit, and the number of bits is determined by using the data (threshold) of the dither ROM 8 as the lower bit of the upper bit data. Since the data with the increased number of bits is converted to analog and output as a gamma correction output, a smooth correction output can be obtained even in a place where the luminance difference is large. This does not occur, and in the case of a color image, the boundary of luminance does not appear as green. That is, the luminance difference of the display image becomes difficult to understand, that is, the gradation of the display image at that location becomes smooth. Further, since it is not necessary to use an A / D conversion circuit having a large number of bits, the cost can be reduced.

[0017]

As described above, according to the present invention, an input video signal is digitally converted to an address of a gamma correction ROM as a gamma correction table, and the data read from the gamma correction ROM is read. A gamma correction circuit that converts the analog signal to an analog signal and outputs a gamma correction control signal counts the dot clock of the screen based on the horizontal synchronization signal of the input video signal, and counts the horizontal synchronization signal based on the vertical synchronization signal of the input video signal The data (threshold) of the dither ROM is read using these count values as the address of the dither ROM, and the read data is used as the lower bits of the data read from the ROM, and Increase the number of bits,
Since the data with the increased number of bits is converted to analog and output as a gamma correction output, a smooth gamma correction output can be obtained, and no vertical stripes appear in places where the level difference of the displayed image is large. in, it is also not name the boundary of the brightness can be seen as green. Also , A /
There is no need to use a D conversion circuit, a relatively simple circuit
Done.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a gamma correction circuit showing one embodiment of the present invention.

FIG. 2 is a schematic diagram of a dither ROM used in the gamma correction circuit shown in FIG.

FIG. 3 is a schematic partial screen diagram for explaining the operation of the gamma correction circuit shown in FIG.

FIG. 4 is a schematic block diagram of a conventional gamma correction circuit.

5 is a schematic graph illustrating the operation of the gamma correction circuit shown in FIG.

[Explanation of symbols]

 Reference Signs List 1 A / D conversion circuit (8 bits) 2 Gamma correction ROM (storage means) 4 Synchronization separation circuit 5 Dot clock reproduction circuit 6 First counter 7 Second counter 8 Dither ROM (4 bits) 9 D / A conversion Circuit (12 bits)

Claims (1)

(57) [Claims] 1. A when displaying an image according to the input video signal to the liquid crystal Disupu <br/> ray, the gamma correction circuit for obtaining a gamma corrected output based on the input video signal into digital converted data, the input video signal a / D converting means you digital conversion beforehand predetermined gamma storing correction data, before SL a / D gamma correction de corresponding to the input video signal as an address the data obtained by the conversion means Data can be read
And Do storage means, a dither matrix unit for outputting a threshold value of the dither matrix on the basis of the horizontal and vertical synchronizing signals of the input video signal, the data read from said memory means and higher bits, the dither matrix means Gamma correction for a liquid crystal display, comprising D / A conversion means for converting the data obtained by the above-mentioned operations into lower bits and converting the data constituted by these upper bits and lower bits into an analog output by gamma correction. circuit.