Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2002-01-22
2004-08-03
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S099000, C345S690000
Reexamination Certificate
active
06771243
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a video display device. More particularly, the present invention relates to a display device and a method for driving the same with which image degradation can be reduced that would occur in producing animated images on the display device.
2. Description of the Related Art
Video display devices may generally be categorized as the “hold” type that allows continuous display of a same video image for a single frame period, or the “impulse” type that allows the video images to be displayed momentarily within a single frame period. Examples of the hold display devices include active matrix liquid crystal displays and organic electroluminescence devices. Examples of the impulse display devices include cathode-ray tubes.
FIGS. 14A and 14B
are graphical representations of luminance profiles for a given pixel of the hold and impulse display devices, respectively, plotted against a frame period. As shown in
FIG. 14A
, the hold display device keeps a constant luminance level over each of the individual frame periods. On the other hand, as shown in
FIG. 14B
, a peak luminance appears at the beginning of each frame period and the luminance drops down suddenly in the impulse display device.
As apparent from the above, the hold and impulse display devices have different display characteristics. The impulse display devices are said to be superior to the hold display devices in terms of showing animated images. This is described below.
FIGS. 15A and 15B
are explanation views showing display characteristics of a hold display device in conjunction with the case where white patterns travel on a black background, in which
FIG. 15A
shows the displacement of the pattern while
FIG. 15B
shows a luminance distribution thereof. In
FIG. 15A
, the ordinate stands for the time; the abscissa stands for the horizontal positions on the display screen; Pn (n is a natural number) represents pixels; and W represents a white pattern of five-pixel wide in the horizontal direction.
With the pattern W moved horizontally by one pixel per a given period of time, a viewer's eyes follows the pattern W along a line period (from the broken lines V
1
to V
4
) connecting the edges of the pattern W due to a large difference in luminance between the adjacent pixels at each edge of the pattern W.
In
FIG. 15A
, the broken lines V
1
and V
2
correspond to a displacement of the viewer's eyes gazing at the pixel having the smallest value n of the pixels Pn that make up the pattern W. More specifically, the broken lines V
1
and V
2
correspond to the displacement of the viewer's eyes at the end and beginning of a given frame period T, respectively, for the pixel in question.
The broken lines V
3
and V
4
correspond to a displacement of the viewer's eyes gazing at the pixel having the largest value n of the pixels Pn that make up the pattern W. More specifically, the broken lines V
3
and V
4
correspond to the displacement of the viewer's eyes at the end and beginning of a given frame period T, respectively, for the pixel in question.
Thus, the viewer's eyes gazing at the pattern W moves along the path from the broken line V
1
to the broken line V
4
. However, the video appears as blurred at the regions between the broken lines V
1
and V
2
as well as between the broken lines V
3
and V
4
due to the inherent display characteristic of the hold display device that shows the same video image for one frame period as described above with reference to FIG.
14
A. The cause of this blurring is described more in detail with reference to FIG.
15
B.
In
FIG. 15B
, portions of the black background are seen in the region left from the broken line V
1
and the region right from the broken line V
4
, and thus the luminance for these regions have the luminance value of zero (0).
There are both light emitting portions and non-light emitting portions in the regions between the broken lines V
1
and V
2
as well as between the broken lines V
3
and V
4
. The proportion of the light emitting portions becomes larger from the broken line V
1
to the broken line V
2
. The luminance increases accordingly at a constant rate until the luminance reaches the luminance B of the pattern W. Likewise, the proportion of the non-light emitting portions becomes smaller from the broken line V
3
to the broken line V
4
. The luminance decreases accordingly at a constant rate. The luminance B of the pattern W is kept at the region between the broken lines V
2
and V
3
.
As apparent from the above, the edges of the pattern W contains the regions of which luminance changes at a constant rate (between the broken lines V
1
and V
2
as well as between the broken lines V
3
and V
4
), that is, the regions having the gradient of the luminance curve. This gradient produces the blurry images around the edges. The viewer's perception of the pattern W is influenced as the pattern W having the five-pixel width L0 is identified to have a larger width L1.
Thus, the hold display device is suffered from significant degradation for animated images. On the contrary, the impulse display device has much less degradation. As described above with reference to
FIG. 14B
, the luminance drops down suddenly just after the beginning of each frame period. This causes shorter distances between the broken lines V
1
and V
2
as well as between V
3
and V
4
(
FIG. 15B
) as compared with those obtained in the hold display device, resulting in smaller blurry regions. Accordingly, the current accepted theory is that the impulse display devices are superior to the hold display devices in displaying animated images.
Attempts have been made to improve performance of the display for animations by means of making the display characteristics of the hold display devices much closer to those of the impulse display devices. A technique has been proposed as one approach that involves in inserting a black signal (hereinafter, referred to as a “black period”) into one frame period.
FIG. 16
is a graphical representation of a luminance profile for a given pixel obtained when a black period is inserted into one frame period. As shown in
FIG. 16
, one frame period is divided into a video display period and the black period. The black periods contribute to making the luminance profiles of the hold display device closer to those of the impulse display device as shown in FIG.
14
B.
FIGS. 17A and 17B
are explanation views showing display characteristics of a hold display device when a black period is inserted into one frame period, in conjunction with the case where white patterns travel on a black background, in which
FIG. 17A
shows the displacement of the pattern while
FIG. 17B
shows a luminance distribution thereof.
In
FIG. 17A
, the broken lines V
1
and V
2
correspond to a displacement of the viewer's eyes gazing at the pixel having the smallest value n of the pixels Pn that make up the pattern W. More specifically, the broken lines V
1
and V
2
correspond to the displacement of the viewer's eyes at the beginning of the black period Tb and the video display period Ta, respectively, for the pixel in question. The broken lines V
3
and V
4
correspond to a displacement of the viewer's eyes gazing at the pixel having the largest value n of the pixels Pn that make up the pattern W. More specifically, the broken lines V
3
and V
4
correspond to the displacement of the viewer's eyes at the beginning of the black period Tb and the video display period Ta, respectively, for the pixel in question.
Comparison between
FIGS. 17B and 15B
shows that the black periods Tb make it possible to reduce the distance between the broken lines V
1
and V
2
as well as the distance between the broken lines V
3
and V
4
. The smaller distances result in reduction of size of the regions having the gradient of the luminance curve, which in turn reduces the size of the blurry regions around the edges of the pattern W.
While the video display periods in the frame periods
Liang Regina
McDermott Will & Emery LLP
Nguyen Jennifer T.
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