Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-08-08
2004-10-26
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S591000, C345S593000, C345S603000, C348S179000
Reexamination Certificate
active
06809714
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a color image processing art for a color output device, particularly to a method and an apparatus for more-accurately adjusting a white point.
2. Prior Art
In recent years, a liquid-crystal display (LCD) have been widely used as a display device for displaying images of a personal computer or television or for various monitors in addition to a CRT. In case of a color display system using the CRT or LCD, it is considered to be ideal to approach colors which can be displayed by the system as, close to natural colors as possible (this is referred to as display color fidelity). Moreover, it is requested for an apparatus using a CRT or LCD to automatically adjust a color or an operator (user) to manually adjust the color in accordance with the state of the apparatus, that is, the environment of the system such as illumination so that an optimum color can be displayed in accordance with each environment (this is referred to as color calibration). Furthermore, it is eagerly requested that the same color can be outputted independently of the type of output device (this is referred to as device transfer characteristic or color matching). These arts are generally referred to as color management. For a color display system that is a high-performance model from the next generation downward, various researches and developments are performed as indispensable technical matters. Particularly, the white point adjustment for adjusting an achromatic color tone in display is very important, which has been realized so far for a color monitor and the like.
In this case, an xy chromaticity diagram shown in
FIG. 15
is used to quantitatively handle all natural colors. The diagram expresses the color tone and saturation of a color in accordance with the position of chromaticity coordinates, showing chromaticity coordinates expressed by a horizontal axis x=X.(X+Y+Z) and a vertical axis y=Y.(X+Y+Z), where X, Y, and Z are the three stimulus values of the XYZ color system. All colors sensed by eyes of a person are shown on and inside of the horseshoe-shaped closed curve c. Points R, G, and B in
FIG. 15
are points expressing only primary display colors of R (red), G (green), and B (blue) in a specific color display system and thereby, it is possible to express all colors on sides and the inside of a triangle RGB by properly mixing R, G, and B. Moreover, maximum-luminance white can be generally obtained as a mixed color W when bringing R, G, and B into the maximum luminance, which is normally located nearby the intersection of median lines of the triangle RGB.
To design a color display system, a better white point is determined by adjusting the value of the maximum luminance at points R, G, and B or changing positions of the points R, G, and B in FIG.
15
. For example, in case of a color display system using an LCD module, it is necessary to consider the spectral radiation of a backlight and a light transmittance through a color filter.
On the other hand, even in case of determining an optimum white point correspondingly to a color display system as described above, several problems occur depending on various conditions including an environmental condition because the determined value is a fixed value. Firstly, there is a problem that the color tone of white differs depending on the environmental illumination where a display is set. For example, when designing a white point at a point having a color temperature of 7000K, the point is felt bluish under an incandescent-lamp illumination at approx. 2800K or yellowish under daylight at 6500K. Secondly, there is a problem that preferable white points are changed depending on the content of a display image. For example, a desired white color differs between an application on MS-Windows and a photograph or dynamic image. Particularly, in case of a photograph image, the desired white color is influenced by the situation when the photograph was taken. Thirdly, there is a problem that the individual difference between users is large for the taste of a white color. For example, Japanese people generally tend to like bluish white. These tendencies are also influenced by an individual difference of ocular function such as an ocular disease. Fourthly, there is a problem on production. For example, in case of an LCD module, white-point producing fluctuation occurs up to approx. ±0.03 on xy chromaticity coordinates.
Therefore, it is very significant as a method for solving the above problems to configure a color display system so that a user can adjust the white point at the maximum-gray-scale achromatic color (so-called the full level white) by any method.
Moreover, as an intrinsic problem on a TFTLCD monitor, there is a phenomenon of blue shift in intermediate-gray-scale achromatic colors particularly in a low gray scale. This is a phenomenon that, when making a TFTLCD device display an achromatic color (color in which R, G, and B have the same gray scale), the color becomes more bluish as lowering the gray scale value (that is, chromaticity coordinates shift in the blue-color direction). This phenomenon becomes considerably remarkable depending on the type x of LCD panel. Though it is requested to secure a large angle of visibility for recent LCDs, the phenomenon becomes more remarkable as an angle for a user to view a display (angle of visibility) tilts from the head-on position of the display. When the phenomenon occurs, an achromatic color at an intermediate gray scale is deviated from the setting at the maximum gray scale, no matter how much the white point at the maximum gray scale can be adjusted to desirable chromaticity coordinates (color temperature). Therefore, this causes a new problem.
Though not directly related to the present invention, a prior art for white balance compensation is disclosed in Japanese Published Unexamined Patent Application No. 9-147098 and 7-336700. Japanese published Unexamined Patent Application No. 9-147098 discloses an art for applying LUT conversion to input RGB signals in accordance with the reference white value and reference black value designated by an operator. Moreover, Japanese Published Unexamined Patent Application No. 7-336700 discloses an art for A/D-converting input RGB signals into analog signals and uniforming luminances by an inverse gamma compensation circuit and a white balance compensation circuit.
A display system performing full digital processing has recently become a main stream. For example, in case of LCD display systems except some products, an LCD module uses digital data before the data is inputted to source drivers. Also, an LCD monitor having a built-in LCD module had been provided with an analog interface, performed A/D conversion inside, and transmitted a digital video signal to the LCD module. In recent years, however, some LCD monitors have appeared which are provided with a digital video interface using a low-voltage-differential-type digital data transmission system such as LVDS or TMDS {PanelLink (trademark of Silicon Image Inc.), in which a video signal uses digital data until it is inputted to source drivers after it is outputted from the graphics controller of a system unit. Moreover, in the field of notebook-type PCs, only digital data has been used so far.
When considering the above situation, a technique is required in which the processing for the above white point adjustment can be digitally performed by an efficient circuit.
Under the above background, the present applicant previously proposed an art for adjusting the maximum-gray-scale achromatic color (full white) W and the minimum-gray-scale achromatic color (full black) O to target chromaticity coordinates (W′ and O′) as a technique for efficiently performing white point adjustment in digital processing (Japanese Patent Application No. 97183/1999). The art is very superior in performing white point adjustment without increasing a circuit in size. However, when using only the above art, each col
Sohda Masayuki
Yamauchi Kazushi
Chow Dennis-Doon
Trepp, Esq. Robert M.
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