JP2605665B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device having a false contour suppression function in a liquid crystal color television receiver or the like.

[Prior art and its problems] Conventionally, a liquid crystal display device used in a liquid crystal color television receiver has a low display capability of a liquid crystal, that is, a contrast ratio is lower than that of a CRT. The number of driving bits and the like are suppressed to a low value of about 4 bits. However, at present, when the display capability of the liquid crystal is gradually increased, the boundary of the gradation looks like a contour line, that is, a so-called false contour is easily generated. The occurrence of the false contour can be prevented by increasing the number of processing bits. However, increasing the number of processing bits increases the circuit scale. As a result, there is a disadvantage that the circuit scale is increased by 20%.

[Object of the Invention] The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal display device capable of suppressing the occurrence of false contours without significantly increasing the circuit scale and improving the display quality. With the goal.

[The gist of the invention] The present invention utilizes the property that false contours are conspicuous in low-luminance portions and become inconspicuous in high-luminance regions, and slightly increases the number of quantization bits during A / D conversion. Non-linear compression is performed during compression to reduce the output change at low input values where false contours are likely to occur, and to increase the output change with respect to high input values to prevent the occurrence of false contours. .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 10 denotes an input terminal to which a composite video signal including a synchronization signal and a color signal is input.
It is sent to the color decoder 11 and the sync separation circuit 12. The color decoder 11 decodes an input composite video signal, separates R, G, and B color signals, and
Output to A / D converter 13. On the other hand, the sync separation circuit 1
2 separates the horizontal synchronizing signal and the vertical synchronizing signal from the input composite video signal, and outputs the same to the timing signal generator 14. The timing signal generation section 14 generates various timing signals according to the synchronization signal given from the synchronization separation circuit 12, and outputs a sampling signal to the A / D converter 13. The A / D converter 13 A / D converts the R, G, and B color signals sent from the color decoder 11 into 6-bit signals in synchronization with the sampling signal, and outputs the signals to the non-linear compressor 15. I do. As shown in FIG. 2, for example, the non-linear compressor 15 includes a ²⁶ × 4 bit R ROM 15a and a G RO
It is composed of ROM 15c for M15b and B, and nonlinearly compresses 6-bit color signals R, G, and B into 4-bit color signals R, G, and B, and distributes the gradation to a low-luminance portion. . That is, in the ROMs 15a to 15c, the storage data is set such that the input / output ratio is small at a low input level, and is increased as the input is increased. The color signal nonlinearly compressed into a 4-bit signal by the nonlinear compressor 15 is sent to the segment driver 16. Then, based on the timing signal from the timing signal generator 14, the segment driver 16 and the common driver 17 use, for example, “160 lines × 300 dots ×
The display driving of the color liquid crystal display panel 18 of "three colors" is performed.

Next, the operation of the above embodiment will be described. The composite video signal input from the input terminal 10 is converted into R,
The signal is separated into G and B color signals and sent to the A / D converter 13. The A / D converter 13 converts the R, G, and B color signals sent from the color decoder 11 into 6-bit digital signals. In this case, the input / output relationship of the A / D converter 13 is linear as shown in FIG. 3, and a 6-bit color signal that is digitally converted is obtained substantially in proportion to the input signal. The 6-bit color signal output from the A / D converter 13 is sent to the non-linear compressor 15, and is non-linearly compressed into a 4-bit signal. In this case, the non-linear compression is
As shown in the figure, the change in output is suppressed at a small input value, that is, at a portion where the luminance is low, and the change of the output increases as the input value increases.

Thereafter, the R, G, B color signals nonlinearly compressed by the nonlinear compressor 15 are sent to the segment driver 17. On the other hand, the synchronization signal included in the composite video signal is
The signal is separated by the synchronization separation circuit 12 and sent to the timing signal generation unit 14. The timing signal generator 14 generates various timing signals from the input synchronization signal, and supplies a sampling signal to the A / D converter 13 and a liquid crystal drive timing signal to the segment driver 16 and the common driver 17. The segment driver 16 reads the signals R, G, and B from the non-linear compressor 15 in synchronization with the timing signal from the timing signal generator 14, and drives the segment electrodes of the color liquid crystal display panel 18 for display. Further, the common driver 17 synchronizes with the timing signal from the timing signal generation unit 14 to
Are sequentially driven for display. The color video signal is displayed on the color liquid crystal display panel 18 as described above.

When the non-linear compressor 15 is constituted by a ROM as in the above embodiment, the compression characteristics for the R, G, and B color signals can be set according to the color filters of the liquid crystal display panel 18. . The non-linear compressor 15 can be constituted by a ROM as shown in the embodiment or by a digital operation circuit.

[Effects of the Invention] As described above in detail, according to the present invention, the number of quantization bits at the time of A / D conversion is slightly increased, and then, when performing bit compression, nonlinear compression is performed so as to match each color filter. The output change at low input values where false contours are likely to occur, and the output change at high input values was increased.
The color balance can be maintained, and the occurrence of false contours can be suppressed, and an image with good display quality can be obtained.
In addition, in the case of the non-linear compression, since the color change of a portion having a high luminance can be increased, there is an effect of color emphasis, and the screen can be emphasized and sharpened. Furthermore, since the number of quantization bits is slightly increased in the A / D converter and then returned to the original number of bits by the non-linear compressor, the display driver can be kept at the conventional number of bits, and the circuit configuration becomes complicated. Can be prevented.

[Brief description of the drawings]

1 shows an embodiment of the present invention. FIG. 1 is a block diagram showing a circuit configuration, FIG. 2 is a block diagram showing details of a non-linear compressor in FIG. 1, and FIG. 3 is a block diagram in FIG.
FIG. 4 is a diagram showing input / output characteristics of the A / D converter, and FIG. 4 is a diagram showing input / output characteristics of the nonlinear compressor. 10 input terminal, 11 color decoder, 12 synchronization separation circuit, 13 A / D converter, 14 timing signal generator, 1
5 ... Non-linear compressor, 16 ... Segment driver, 17 ... Common driver, 18 ... Color LCD panel.

Claims (1)

(57) [Claims] 1. A liquid crystal display device for A / D converting video signals of RGB and driving a liquid crystal display unit having a color filter corresponding to each of RGB with a digital signal of a predetermined number of bits. Means for converting the video signal into a digital signal having a number of bits greater than the number of display drive bits of the liquid crystal display unit, and matching the digitally converted digital signal with the number of display drive bits of the liquid crystal display unit, Non-linear compression means for performing non-linear compression so as to conform to the display characteristics of the color filter and to reduce the output change in the low-luminance portion; A means for outputting a signal to the liquid crystal display unit.