Computer graphics processing and selective visual display system – Display driving control circuitry – Intensity or color driving control
Reexamination Certificate
2002-11-26
2004-11-16
Lee, Wilson (Department: 2821)
Computer graphics processing and selective visual display system
Display driving control circuitry
Intensity or color driving control
C345S089000, C349S017000
Reexamination Certificate
active
06819335
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gray scale reducing method, an image displaying method, and an image displaying apparatus. More specifically, it relates to a gray scale reducing method for favorably reducing the number of gray levels with no use of a gray scale conversion table and to a method and an apparatus for speciously reproducing a fine image of which the number of gray levels is greater than that of a display panel.
BACKGROUND OF THE INVENTION
FIG. 9
is a block diagram of a conventional liquid crystal display.
The liquid crystal display
500
comprises a 1024-to-1021 gray scale conversion table
51
for converting an image data A
(1024)
of 1024 gray levels (=10 bits) received from, e.g., a computer (not shown) into an image data Y
(1021)
of 1021 gray levels, a 256 gray scale image data sample storage
2
where image data samples of 256 gray levels are stored as sets of four different 256 gray scale images (=8 bits) for speciously reproducing an image of 1021 gray levels, a random number generator circuit
3
for generating a random number N to select and release a set of image data D
1
to D
4
of 256 gray levels at each four frames in response to the image data Y
(1021)
of 1021 gray levels received from the 256 gray scale image data sample storage
2
, and a 256 gray scale monochrome liquid crystal display panel
4
for displaying images of 256 gray levels determined by the 256 gray scale image data D
1
to D
4
. The image to be reproduced shall be a monochrome image.
FIG. 10
is a diagram showing an arrangement of the 1024-to-1021 gray scale conversion table
51
.
The image data A
(1024)
of 1024 gray levels stored at the (left) entry column consists of a binary 10-bit value ranging from “0000000000” and “0000000001”, to “1111111111” equivalent from 0 to 1023 (of the decimal notation).
The image data Y
(1021)
of 1021 gray levels at the (right) entry column consists of a binary 10-bit value which corresponds to a 1024 gray scale image ranging from 0 to 1020 (of the decimal notation). As the gray levels are reduced by three, three entries of the 10-bit value are overlapped in the storage.
FIG. 11
is an explanatory view showing the principle of speciously reproducing an image of 1021 gray levels with the use of four frames of 256 gray levels.
It is assumed that the frames F
1
, F
2
, F
3
, and F
4
are displayed at short intervals of {fraction (1/60)} the second and their gray level of 256 gray scale at a given pixel is varied from L
1
, L
2
, and L
3
to L
4
. The gray level at the pixel is apparently equal to a level (L
1
+L
2
+L
3
+L
4
) of the 1021 (=2255×4+1) gray scale. When L
1
=
63
, L
2
=
63
, L
3
=
63
, and L
4
=
64
, the level
253
of the 1021 gray scale can speciously be reproduced. This technique for reproducing an intermediate tone with the use of a series of frames is known as interframe error diffusion or Frame Rate Control.
Accordingly, as each set of the four different image data samples of 256 gray levels stored in the 256 gray scale image data sample storage
2
(
FIG. 4
) are equal to an image data Y
(1021)
of 1021 gray levels, they can speciously be reproduced as a 1021 gray scale mono chrome image.
The random number N provided for selection of a set of the 256 gray scale image data samples is intended to minimize the generation of “flicker” and stripe noises which are derived from the regularity of a change in the grays level at each frame.
The conventional liquid crystal display
500
requires a memory for storage of 10 kilobits (=1024×10 bits) as the 1024-to-1021 gray scale conversion table
51
and will thus be increased in the overall cost.
Also, if the random number N is low in the accuracy (i.e. a particular pattern appears at very short intervals and its value is repeated at high frequency), the effect of “flicker” and stripe noises may increase thus allowing an observer to have an abnormal impression.
It is hence a first object of the present invention to provide a gray scale reducing method for favorably reducing the number of gray levels with no use of a gray scale conversion table.
It is a second object of the present invention to provide a method and an apparatus for speciously reproducing a fine image of which the number of gray levels is greater than that of a display panel.
SUMMARY OF THE INVENTION
As a first aspect of the present invention, a gray scale reducing method is provided comprising a step of converting a bit stream input (a
&agr;−1
, a
&agr;−2
, a
&agr;−3
, . . . , a
0
) of 2
&agr;
gray levels expressed by A=
&agr;−1
×2
&agr;−1
+a
&agr;−2
2×2
&agr;−2
+a
&agr;−3
×2
&agr;−3
+ . . . +a
0
×2
0
[&agr;≧2] into a bit stream output of (2
&agr;
−2
&agr;−&bgr;
+1) gray levels expressed by Y=a
&agr;−1
×2
&agr;−1
+a
&agr;−2
×2
&agr;−2
+a
&agr;−3
×2
&agr;−3
+ . . . +a
0
×2
0
−(a
&agr;−1
×2
&agr;−&bgr;−1
+a
&agr;−2
×2
&agr;−&bgr;−2
+ . . . +a
&bgr;
×2
0
)[&agr;>&bgr;≧1].
The gray scale reducing method of the first aspect enables a simple arithmetic operation of subtracting the upper (&agr;−&bgr;) bits from the input A of 2
&agr;
gray levels as a bit stream (a
&agr;−1
, a
&agr;−2
, a
&agr;−3
, . . . , a
0
) to determine a bit stream output Y of (2
&agr;
−2
&agr;−&bgr;
+1) gray levels with no use of any gray scale conversion table. Since the inputs A to be converted into the identical output Y are equally dispersed at 2
&agr;−&bgr;
−1 different locations, its conversion can be prevented from biasing and thus improved in the accuracy. More particularly, when &agr;=10 and &bgr;=8, a bit stream of 1024 (=2
10
) gray levels can accurately be converted into a bit stream of 1021 (=2
10
−2
10−8
+1) gray levels.
As a second aspect of the present invention, an image displaying method is provided comprising steps of converting an image data by the gray scale reducing method of the first aspect from a bit stream of 2
&agr;
gray levels to a bit stream of (2
&agr;
−2
&agr;−&bgr;
+1) gray levels, and speciously reproducing by interframe error diffusion a fine image of which the gray level is equal to that of the converted bit stream.
The image displaying method of the second aspect enables to speciously reproduce by interframe error diffusion an image of which the number of gray levels is favorably reduced by the gray scale reducing method of the first aspect.
As a third aspect of the present invention, an image displaying method is provided comprising a step of controlling the gray level in each of m segments (m≧2) of one pixel on the frame-by-frame basis to speciously reproduce with the use of plural frames an image of which the number of gray levels is greater than that of a display panel which is capable of varying the gray level in each segment.
The image displaying method of the third aspect enables to change the gray level at each segment of a single pixel for spatially modulating the luminance of the pixel in one frame, thus displaying the number of gray levels of the pixel which is greater than that of the segments. More particularly, when one pixel consists of three segments, the gray level in one or two of the three segments can be declined to be lower by one step than that of the other segments or segment to reproduce an intermediate tone at steps of ⅓ the gray level. Accordingly, during the process of interframe error diffusion to speciously reproduce an image of which the number of gray levels is increased, the gray level of each pixel can be minimized in the difference between frames hence significantly attenuating the generation of “flicker” and stripe noises in the image.
As a four
Jordan and Hamburg LLP
Lee Wilson
Totoku Electric Co., Ltd.
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