Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-10-13
2004-03-02
Awad, Amr (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S600000, C345S601000, C345S690000
Reexamination Certificate
active
06700559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display unit that is used as a monitor for a personal computer (hereinafter to be referred to as a PC), a word processor, etc., and further as a display for a television receiver, and a projector. More specifically, the present invention relates to a liquid crystal display unit that carries out a control for matching an image to be displayed with the characteristics of a liquid crystal panel in order to obtain an image of a satisfactory color balance.
2. Description of the Prior Art
In recent years, along with the development of a liquid crystal panel having higher resolution and fuller color range, there has been an increase in demand for liquid crystal display units that have features such as low voltage driven, thin and light weight, in the information equipment field including personal computers as main products, and in the image equipment field including television receivers and projectors as main products.
Two widely used liquid crystal display units include a twisted nematic (TN) liquid crystal and a super twisted nematic (STN) liquid crystal. The super twisted neumatic liquid crystal has a transmission characteristic of improved sharpness due to its large twist angle. A driving system for the liquid crystal display units has shifted from a segment driving type, initially introduced, to a matrix driving type in order to realize a higher resolution. The matrix driving type has a pair of transparent electrodes divided into two and disposed to be mutually orthogonal with each other, each having a belt shape, with one transparent electrode working as a scanning electrode and the other as a signal electrode. Points of intersection between these electrodes form pixels, and they are selectively applied with voltages to display optional image information. This matrix driving type is broadly divided into a simple matrix type and an active matrix type that uses switching elements. Particularly, an active matrix driving type liquid crystal display that uses a thin-film transistor (TFT) can obtain a high resolution and a high contrast, and therefore, has been widely distributed.
The TFT active matrix liquid crystal will be explained in detail.
FIG. 1
is a functional block diagram for explaining a liquid crystal driving system. As shown in
FIG. 1
, a reference number
51
denotes a signal electrode drive circuit,
52
denotes a scanning electrode drive circuit, and
5
denotes a liquid crystal display panel. The scanning electrode drive circuit
52
is constructed of a shift register circuit. The output of the scanning electrode drive circuit
52
is produced from a lateral line transparent electrode
54
and is applied to a gate of a TFT that is connected in parallel in a horizontal direction on the liquid crystal panel
5
. The signal electrode drive circuit
51
is constructed of a shift register and a sample holding circuit. The output of the signal electrode drive circuit
51
is produced from a vertical line transparent electrode
53
and is applied to a drain or a source of a TFT that is arrayed in a perpendicular direction on the liquid crystal panel
5
. When a scanning signal is added to the gates of these TFT's, a current is conducted between the source and the drain. When an image signal is added to the source or the drain, the liquid crystal layer is charged and is applied with an electric charge. The applied electric charge is held until the next scanning signal is given. The volume of light that passes through the liquid crystal layer changes according to the voltage applied to the liquid crystal layer. Therefore, it is possible to control the optical transmission volume by the image signal voltage. In other words, the scanning electrode drive circuit
52
turns ON the TFT in the horizontal direction together, and during this period, the signal electrode drive circuit
51
writes image information of one line component into pixels of each intersection point. This is sequentially scanned in the vertical direction to thereby display the image information.
The development of color display technology for the liquid crystal display panel is also progressing with the development of the high-resolution technology. As general methods of color display, there are a color filtering method that has RGB filters corresponding to each pixel disposed on the surface of the liquid crystal, and a three-panel method that provides a liquid crystal panel to each RGB image and supplies a back light or a front light of RGB to each liquid crystal panel. Both methods form a display of a color image for each of the RGB components, and adds and mixes these color components to display the color image. The color filtering method has features of compactness and lightweight, and has been widely distributed in PC monitors and liquid crystal TVs. The three-panel method has a large device scale but can obtain an image of a high resolution and a high luminance. Therefore, this method has been applied to liquid crystal projectors and the like.
Two input types of liquid crystal display units have been widely used. One is an analog interface liquid crystal display unit that inputs conventional video signals of conventional TV's and videos, and the other is a digital interface liquid crystal display unit that is capable of directly inputting digital video data of PC's. In recent years, digitization of video data has progressed rapidly along with the development of digital technology, due to increasing memory capacities as well as increasing processing capacity. Digital data can be more easily processed for the editing of videos like a non-linear editing than analog data. Further, digital data has no deterioration in image quality, and can be compressed at a high compression rate. Therefore, it is considered that the digitization of images will be further promoted in future. For the image digital data, various formats have been proposed because of a difference between a moving image and a still image, and a difference in compression methods. At present, digital data generally has eight bits (256 gradations) for each of R, G and B, and the data can be used to display full colors of about 1.63 million colors based on additive mixture of color stimuli.
Liquid crystal display panels as the display element have unique optical rotary dispersion characteristics. Optical rotary dispersion characteristics are a phenomenon where the optical transmittance changes depending on the wavelength of light and depending on the voltage. More specifically, a red color component (a long-wavelength area) becomes large and a blue color component (a short-wavelength area) becomes small in the optical transmittance during an application of a low voltage. Therefore, even when a gray scale is displayed, the white balance in each gradation is disturbed, and a coloring occurs according to the voltage applied. This not only causes an inconvenience in the gray scale display, but also interferes with color display performance. Particularly, there is a problem that when a gray portion such as a shade exists in the image, a color appears in this portion.
Further, in the color image display according to this color filtering method, a light from the pixel does not enter the corresponding RGB filter in an ideal manner, and the light leaks to another filter, which causes RGB crosstalk. This RGB crosstalk disturbs the color balance, and makes it impossible to reproduce a desired color.
Optical Compensation Technique
A double-layer STN liquid crystal (DSTN) method is an example that solves the problem of the coloring attributable to the optical rotary dispersion characteristics. According to this method, two liquid crystal panels having optical rotary dispersion characteristics in opposite directions are superimposed with each other, and a coloring generated by a first-layer liquid crystal panel is canceled by a second-layer optical compensation liquid crystal panel, thereby achieving non-coloring. This method can substantially
Nakajima Takayuki
Shimizu Hajime
Tanaka Seiichi
Awad Amr
Birch & Stewart Kolasch & Birch, LLP
Sharp Kabushiki Kaisha
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