Television – Image signal processing circuitry specific to television – Chrominance signal amplitude control
Patent
1995-11-17
1997-04-15
Lee, Michael
Television
Image signal processing circuitry specific to television
Chrominance signal amplitude control
348791, 348647, H04N 968, H04N 930
Patent
active
056214790
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of driving a liquid crystal display device for performing color display, more particularly to a method of driving a liquid crystal display device for displaying information corresponding to a picture of a composite video signal in color.
2. Description of the Related Art
There has been widely used a liquid crystal display device capable of performing a color display as a display of various information from apparatuses and instruments such as a liquid crystal color TV, a personal computer, etc.
A prior art basic driving method of such a liquid crystal display device will be explained with reference to FIG. 16.
A composite video signal CV is converted into RGB analog signals by a chrominance circuit 50 which are inputted to a driving circuit 51. The driving circuit 51 actuates a liquid crystal panel 52 based on the voltage levels of the RGB analog video signals to control the transmittance of each pixel corresponding to each color of red, green and blue on a liquid crystal panel so as to perform color display.
The composite video signal may be of the NTSC system, the PAL system or the SECAM system. The NTSC system will be described hereinafter.
FIG. 17 shows an example of a composite video signal. This signal is converted into RGB analog video signals having red, green and blue colors respectively by the chrominance circuit 50.
FIG. 18(a)-18(c) show the converted RGB analog video signals. In the figure, denoted at An is the maximum amplitude of each of the RGB analog video signals.
The driving circuit 51 controls the transmittance of each pixel corresponding to each color of red, green and blue on a liquid crystal panel 52 in response to the voltage levels of the inputted RGB analog video signals to faithfully reproduce the image of the RGB analog video signals thereon.
FIG. 19 shows the relationship between the RGB analog video signals and the transmittance of the liquid crystal panel. In the figure, the lateral axis represents the voltage levels of the RGB analog video signals while the vertical axis represents the transmittance TLCD of the liquid crystal panel. A T-V curve c represents the transmittance characteristic.
When the voltage level of the RGB analog video signal is as large as the maximum amplitude An, the transmittance of the liquid crystal panel becomes 100%, and when the voltage level thereof is 0, the transmittance also becomes 0%. A color picture is displayed based on the transmittance characteristic.
As mentioned above, in the prior art liquid crystal display device, there is only one transmittance characteristic as shown in FIG. 19 so that an image represented by a composite video signal is represented based on the same transmittance characteristic irrespective whether color or monochrome. Accordingly, the color reproducibility of a color picture displayed on the prior art liquid crystal display device is determined by the color demodulation performance of a chrominance circuit 50 in FIG. 16, and hence the demodulation performance of the chrominance circuit is regarded as important.
Whereupon, even if the chrominance circuit 50 having a high demodulation performance is employed, a picture actually displayed on the liquid crystal display device appears inferior to that displayed on a color CRT in color reproducibility. This is mainly caused by the NTSC broadcasting system. The NTSC system is conceived on the premise of employment of a CRT as an image receiver, and it skillfully employs many techniques utilizing characteristics of the CRT and of human visual processing and interpretation.
However, the CRT is different from the liquid crystal display device in a method of display. The NTSC system sometimes causes inconvenience in color reproducibility on the liquid crystal display device, which is different from the CRT in the method of display.
The CRT performs color display when an electronic gun emits an electronic beam to a fluorescent body to make the same emit light. Contrary to this, the l
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patent: 4633299 (1986-12-01), Tanaka
patent: 4942458 (1990-07-01), Miyajima et al.
patent: 5257108 (1993-10-01), Muraoka
patent: 5404165 (1995-04-01), Ohtsubo et al.
Citizen Watch Co. Ltd.
Lee Michael
LandOfFree
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