Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-09
2002-05-28
Wu, Xiao (Department: 2774)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S691000, C345S600000, C345S089000
Reexamination Certificate
active
06396465
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gray shade displaying device and a method for displaying gray shades being suitable for use in an LCD (liquid crystal display) to display a color image in multiple shades of gray on a display of a computer, TV or the like.
2. Description of the Related Art
The LCD is now in increasing demand and further being developed rapidly, instead of a CRT (Cathode Ray Tube), for reasons that it does not occupy a large area for its installation, consumes power little and has little adverse effect on a human body.
In particular, a DSTN (Dual Supper Twisted Nematic)-type or STN (Super Twisted Nematic)-type LCD (hereinafter referred to simply as an “STN-LCD”) is increasing popular, among manufacturers, as a means of displaying images which can be designed or manufactured at a low cost.
Paralleling the widespread use of the LCD, the need for displaying a variety of varicolored images using gray-scale colors is increasing in the field of display technology for a computer or the like.
One pixel (color element) forming the LCD screen is represented by two values, one for a “light state” and the other for a “dark state” and, therefore, the gray-scale color can not be displayed by one pixel. To solve this problem, in a TFT (Thin Film Transistor)-type LCD which reacts quickly to a signal, by changing a ratio of time (i.e., duty ratio) between the light and dark states taken by one pixel, images can be displayed in multiple shades of gray.
However, such a method as used in the TFT-type LCD cannot be applied to the STN-LCD due to its slow reaction to a signal. In general, therefore, a method is adopted where one dot forming an image is composed of two or more pixels. For example, to display an image in 4 shades of gray, one dot is composed of 4 pixels and the number of pixels for the “light” state is changed depending on shades of gray to be displayed.
Conventionally, the STN-LCD for displaying images in multiple shades of gray is provided with a LCD controller to perform the processing described above.
FIG. 10
is a block diagram showing configurations of a conventional LCD controller used to display an image on an STN-type or DSTN-type color LCD panel. As shown in
FIG. 10
, the conventional LCD controller is comprised of an image memory interface
101
, a color data determining section
102
, a frame rate controlling section
103
, a display control signal outputting section
104
and a pattern recognizing section
105
. The image memory interface
101
is adapted to derive an image signal from the image memory. The color data determining section is used to produce color data for each of RGB (Red, Green and Blue colors, three primaries) colors using the image signal derived through the image memory interface. The frame rate controlling section is used to display data for an LCD panel based on color data outputted from the color data determining section
102
. The frame rate controlling section is also used to output display data for displaying gray shades and is provided with two or more gray shade registers (not shown) into which gray shade data corresponding to each color data is stored. The display control signal outputting section
104
is used to generate timing signals to display an image on the LCD panel in accordance with the display data. The pattern recognizing section
105
is used to output a pattern recognizing signal to indicate a position of a display pixel on the LCD panel.
The LCD panel has only a capability of displaying 2 values, one for a state of lighting and the other for a state of going off, in terms of its principles. To display an image in a shade of gray on the STN-type or DSTN-type color LCD panel, a method is available where one dot forming an image is composed of two or more pixels.
FIGS. 11A
to
11
C are explanatory views showing one example of methods for displaying gray shades on the LCD panel.
In
FIGS. 11A
to
11
C, one dot is composed of 4 pixels and the gray shade is expressed by changing the number of pixels being in a state of lighting (a diagonally shaped area shows that the pixel is in a state of going off and a hollow portion showing that the pixel is in a state of lighting). That is,
FIG. 11A
shows that one dot is turned off or is in a state of going off while
FIG. 11C
showing that one dot is turned on or in a state of lighting.
FIG. 11B
is an example of displaying of a gray-scale color.
Hereinafter, by taking the case of displaying 4 shades of gray as an example, operations of a conventional gray shade display using the LCD controller shown in
FIG. 10
are described.
FIG. 12
is a flowchart indicating one example of flows of processing by the LCD controller used in the conventional gray shade displaying device.
First, the frame rate controlling section
103
selects a gray shade register corresponding to color data for each of R, G and B colors outputted from the color data determining section.
FIG. 13
is an explanatory diagram showing a gray shade register selected in accordance with each color data. The gray shade register is provided to correspond to color data. In the case of displaying 4 shades of gray, for example, as shown in
FIG. 13
, 2 bits of data is required for the color data and one gray shade register corresponding to color data is selected out of 4 (2
2
) gray shade registers.
The gray shade register for each of the RGB colors may be provided independently or one gray shade register may be used in common for the RGB colors.
Next, the frame rate controlling section
103
selects a specified frame rate controlling pattern in accordance with the pattern recognizing signal indicating a position of the display pixel on the LCD panel (Step St
2
). The pattern recognizing signal outputted from the pattern recognizing section
105
is a signal indicating the position of the display pixel, which is represented by pixel values (x, y). The pattern recognizing signal outputted from the pattern recognizing section
5
is a signal indicating a position of a display pixel, which is represented by pixel values (x, y).
FIG. 14
is an explanatory view showing a relationship between each color element (dot) forming an image and the pixel values, which presents an image being 640 dots wide and 480 dots long.
As shown in
FIG. 14
, assuming that values existing at the upper-left portion on the image are (0, 0), values (1, 0) . . . (638, 0) and (639, 0) are disposed toward the right portion on the image and values (0, 1) . . . (0, 478) and (0, 479) are disposed downward on the image.
At this point, the frame rate controlling section
103
is adapted to select either of a frame rate controlling pattern A or B in accordance with low order 1 bit of the values x and y described above.
FIG. 15
is an explanatory view showing which frame rate controlling pattern, A or B, is selected by the frame rate controlling section
103
in accordance with values x and y (low order 1 bit).
FIGS. 16A and 16B
are explanatory views showing contents of the frame rate controlling pattern A and B to be selected by the frame rate controlling section
103
respectively. In the case of the frame rate controlling pattern A, if the frame function is zero (0), the 0-th bit of the gray shade register is used for displaying and, similarly, if the frame function is 1, 2, or 3, the 1-st, 2-nd or 3-rd bit of the gray shade register are used for displaying. On the other hand, in the case of the frame rate controlling pattern B, if the frame function is zero (0), the 1-st bit of the gray shade register is used for displaying and similarly if the frame function is 1, 2 or 3, the 2-nd, 3-rd or 0-th bit are used for displaying as well.
Next, the frame rate controlling section
103
is adapted to set data which corresponds to a value of a frame function, selected out of data stored in the gray shade register selected by Step St
1
in accordance with the frame rate controlling pattern selected by Step St
2
.
The frame function represents a function to be added each time one piece of a screen (i.e., one
Hutchins, Wheeler & Dittmar
NEC Corporation
Wu Xiao
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