Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-10-15
2002-01-22
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C084S088000, C084S089000, C084S090000, C084S690000
Reexamination Certificate
active
06340961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for displaying moving images by controlling the levels of gradations of a matrix of display pixels on a display panel with drive pulses, and more particularly to such a method and an apparatus for displaying moving images while correcting false moving image contours.
2. Description of the Related Art
One of various display units capable of displaying moving images is a plasma display panel. The plasma display panel displays images through emission of light from phosphors based on electric discharges, and is expected to attract much attention as a panel-type display unit which emits light on its own with high luminance.
There are basically two types of plasma display panels, i.e., a DC (Direct Current) plasma display panel and an AC (Alternating Current) plasma display panel. Since the AC plasma display panel has electrodes not exposed in a discharge space, the AC plasma display panel is said to be more durable than the DC plasma display panel where electrodes are exposed in a discharge space.
AC plasma display panels are classified into opposed discharge design and surface discharge design. The opposed discharge structure has vertical and horizontal electrodes facing each other across a discharge space. The surface discharge structure has pairs of surface discharge electrodes comprising scanning and sustaining electrodes, which are disposed on a flat surface.
AC plasma display panels are promising as large-size full-color flat display panels because they provide a large memory margin and have good light emission efficiency.
One conventional AC plasma display panel will be described below with reference to
FIG. 1
of the accompanying drawings.
As shown in
FIG. 1
, a plasma display panel
100
comprises a plurality of surface discharge electrodes
101
extending parallel to rows and spaced successively along columns. Each of the surface discharge electrodes
101
comprises a scanning electrode
102
and a sustaining electrode
103
which are disposed parallel to each other.
A plurality of data electrodes
104
extending parallel to the columns are disposed in opposed relation to the surface discharge electrodes
101
. The data electrodes
104
are spaced successively along the rows.
Discharge spaces
105
filled with a discharge gas such as of helium, neon, xenon, or the like are provided between the electrodes
101
,
104
, forming display cells capable of individually emitting light at the points of intersection between the surface discharge electrodes
101
and the data electrodes
104
.
The scanning and sustaining electrodes
102
,
103
are disposed as electrical conductive thin films on a glass substrate
106
. The data electrodes
104
are printed as electrical conductors on another glass substrate
107
.
A white glazed layer
108
is deposited on the data electrodes
104
and positioned underneath a plurality of partitions
109
extending parallel to the columns and spaced successively along the rows.
Gaps defined between the partitions
109
are disposed as the discharge spaces
105
in opposed relation to the data electrodes
104
. Phosphor layers
110
are coated on surfaces which define the discharge spaces
105
.
A dielectric layer
111
is positioned in facing relation to the surface discharge electrodes
101
.
A plurality of data drivers are connected respectively to the data electrodes
104
, and a plurality of scan drivers are connected respectively to the scanning electrodes
102
.
One or more sustain drivers are connected to the sustaining electrodes
103
. These drivers jointly make up a driver circuit (not shown) for the plasma display panel
100
.
The display pixels arranged in a two-dimensional matrix on the screen of the display panel are individually controlled for light emission to display desired images in dot matrix patterns.
A process of displaying an image on the plasma display panel
100
shown in
FIG. 1
will be described below.
In a preparatory mode, preliminary discharge pulses are applied between the scanning electrodes
102
and the sustaining electrodes
103
of the plasma display panel
100
to produce preliminary discharges between those electrodes. With the preliminary discharges thus produced, discharges will stably be developed in the plasma display panel
100
for displaying images.
Then, the scan drivers apply progressively shifted scanning pulses respectively to the scanning electrodes
102
, and the data drivers apply data pulses to certain data electrodes
104
which correspond to an image to be displayed, in synchronism with the scan drivers. The positions of all display pixels are progressively scanned to write wall charges in those display pixels which correspond to the image to be displayed.
Then, sustaining pulses are applied as drive pulses to all the scanning electrodes
102
and all the data electrodes
104
. Then, only the phosphor layers
110
of the display pixels in which the wall charges have been written emit light, displaying a dot matrix of image with binary values on the plasma display panel
100
.
There has been a demand for the display of images in multiple gradations on the plasma display panel
100
. One process for meeting such a demand is a subfield process.
The subfield process will be described below. The display pixels which correspond to the image to be displayed emit light when sustaining pulses are applied with the wall charges being written in those display pixels. Therefore, the luminance of emitted light can be adjusted when the number of applied sustaining pulses is controlled.
One frame which represents a unit of time for displaying images is divided into a plurality of subfields, and sustaining pulses are established in advance as drive pulses of various durations for those subfields.
For example, if a video signal is to be represented in 256 8-bit binary gradation levels, then, as shown in
FIG. 2
a
of the accompanying drawings, there are established subfields in one frame which serve as sustained emission periods for applying sustaining pulses at the ratio of “1, 2, 4, . . . , 128”.
By appropriately combining the sustaining pulses in those subfields, it is possible to change the number of sustaining pulses in one frame within the range of 256 pulses. Therefore, the matrix of display pixels on the plasma display panel
100
can be energized in a time-division multiplex fashion.
For example, if the gradation level of a certain display pixel is “127”, then, as shown in a left-hand side of
FIG. 2
b
of the accompanying drawings, trains of sustaining pulses in
7
subfields that are weighted respectively by “1, 2, . . . , 64” are applied to the display pixel. Consequently, 7 trains of sustaining pulses which are weighted by “127” are applied to the display pixel in the period of one frame.
If the gradation level of a certain display pixel is 128, then, as shown in a right-hand side of
FIG. 2
b
, sustaining pulses of one subfield which is weighted by “128” are applied to the display pixel in the period of one frame.
When the plasma display panel
100
is energized according to the subfield process, since the number of sustaining pulses applied in one frame to display pixels on the plasma display panel
100
can be adjusted, displayed images can be expressed in gradations.
However, some moving images displayed according to the subfield process tend to suffer interferences.
For example, when an image whose lightness varies smoothly, e.g., an image of a cheek of a human's face, moves on the display screen, a dark or bright contour may appear in an image region which should be smooth.
When a color image is displayed, it may suffer a color-shifted contour or a reduction in resolution.
Such interferences are referred to as false moving image contours.
In a displayed color image, since bit carry points for the respective colors are spatially different from each other, interferences occur at different positions with respect to the respective colors.
While these interferences may be refer
Tanaka Akira
Watanabe Takuya
Yamada Hachiro
Kovalick Vincent E.
NEC Corporation
Shalwala Bipin
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