Computer graphics processing and selective visual display system – Display peripheral interface input device – Light pen for fluid matrix display panel
Reexamination Certificate
2000-01-06
2002-07-09
Mengistu, Amare (Department: 2672)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Light pen for fluid matrix display panel
C345S063000
Reexamination Certificate
active
06417835
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to display driving methods and apparatuses, and more particularly to a display driving method and apparatus suited to drive a plasma display panel (hereinafter simply referred to as a PDP).
The PDP is expected to become one of the display devices of the next generation and to replace the conventional cathode ray tube (CRT), because the PDP can easily realize reduction in the thickness of the panel, reduction in the weight of the panel, flat screen shape and large screen.
A PDP which makes a surface discharge has been proposed, and according to such a PDP, all pixels on the screen simultaneously emit light depending on display data. In the PDP which makes the surface discharge, a pair of electrodes are formed on an inner surface of a front glass substrate and a rare gas is filled within the panel. When a voltage is applied across the electrodes, a surface discharge occurs at the surface of a protection layer and a dielectric layer formed on the electrode surface, thereby generating ultraviolet rays. Fluorescent materials of the three primary colors red (R), green (G) and blue (B) are coated on an inner surface of a back glass substrate, and a color display is made by exciting the light emission from the fluorescent materials responsive to the ultraviolet rays. In other words, fluorescent materials of R, G and B are provided with respect to each pixel forming the screen.
FIG. 1
is a diagram showing an example of a gradation driving sequence of the PDP which makes the surface discharge as described above. As shown in
FIG. 1
, 1 field which is the time in which 1 image is displayed, is divided into a plurality of sub fields, and the gradation display of the image is made by controlling a light emission time (hereinafter referred to as a sustain time) in each sub field. 1 sub field is made up of an address display-time in which a wall charge is formed with respect to all of the pixels which are to make the light emission within the sub field, and the sustain time in which a luminance level is determined. In this specification, the “wall charge” refers to the charge induced at the dielectric layer and the protection layer on the electrodes and at the surface of the fluorescent materials. For this reason, if the number of sub fields within 1 field increases, the number of address display-times increases depending on the increase of the sub fields, thereby reducing the relative sustain times that may be provided for the light emission and deteriorating the luminance of the screen.
Accordingly, in order to increase the number of displayable gradation levels of the PDP using the limited number of sub fields, the PDP is generally driven with the sustain time proportional to the bit weighting as shown in FIG.
1
. In the case shown in
FIG. 1
, 1 field is made up of 6 sub fields SF
1
through SF
6
, and the display is made with 64 gradation levels based on 6-bit image data corresponding to each of the sub fields SF
1
through SF
6
. For the sake of convenience, the sustain times within the sub fields SF
1
through SF
6
are indicated by the hatching to indicate the ON state, that is, the light emission state. The duration ratios or length ratios of the sub fields SF
1
through SF
6
are set to satisfy a relation SF
1
:SF
2
:SF
3
:SF
4
:SF
5
:SF
6
=1:2:4:8:16:32. In this particular case, 1 field is approximately 16.7 ms.
When displaying a moving image on the PDP using the above described gradation driving sequence, a contour of an unnatural color which originally does not exist is generated at the surface of the moving object in the image due to the residual image effect and the like of the human eyes. In this specification, such a contour of the unnatural color caused by the residual image effect and the like will be referred to a “pseudo contour”. The pseudo contour becomes particularly conspicuous when a person on the screen moves. The pseudo contour appears to the human eyes as a band of green or red color at the skin-colored portion such as the face of the person, and the pseudo contour greatly deteriorates the image quality.
A description will be given of the mechanism by which the pseudo contour is generated in conjunction with
FIGS. 2 through 7
, by referring to phenomenons (1) through (3). For the sake of convenience,
FIGS. 2 through 7
show a case where 1 field is made up of 4 sub fields. In addition, in
FIGS. 2 through 5
, the length ratios the sustain times in the 4 sub fields are set to 1:2:4:8 in the sequence in which the light emission state is determined. In
FIGS. 6 and 7
, the length ratios of the sustain times in the 4 sub fields are set to 1:4:8:2 in the sequence in which the light emission state is determined. In
FIGS. 2 through 7
, those sustain times which assume the light emission state, that is, the light emission state, are indicated by the hatching. In this case, it is possible to display 16 gradation levels from a level 0 to a level 15. In
FIGS. 2 through 7
, the abscissa indicates the time, and the ordinate towards the upward direction indicates the left side of the screen and the ordinate towards the downward direction indicates the right side of the screen. In addition, the numerals indicated along the ordinate indicate the luminance level. The illustration of the address display-times with the sub fields, that is, the non-light emission times, is omitted in
FIGS. 2 through 7
.
Phenomenon (1)
In a first case, it is assumed for the sake of convenience that a Gray scale image which becomes brighter from the left towards the right of the image, that is, an image in which the luminance increases from the left to right of the image, is displayed on the PDP. If this image continuously moves towards the left of the screen by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes sparse appears to the human eyes. On the other hand, if this image continuously moves towards the right of the screen by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes dense appears to the human eyes. These sparse and dense portions where the light appears sparse and dense, respectively, occur when the human eyes focus on the moving object displayed on the screen, because the human eyes follow the moving direction and moving speed of the moving object and the visual point moves along loci indicated by bold arrows in
FIGS. 2 and 3
.
FIG. 2
is a diagram showing a locus of a visual field of human eyes in a case where a Gray scale image in which the luminance increases from the left to right of the image is displayed on a PDP and this image continuously moves towards the left of the screen by an amount corresponding to 1 pixel for every 1 field.
FIG. 3
is a diagram showing a locus of the visual field of the human eyes in a case where a Gray scale image in which the luminance increases from the left to right of the image is displayed on a PDP and this image continuously moves towards the right of the screen by an amount corresponding to 1 pixel for every 1 field.
Phenomenon (2)
In a second case, it is assumed for the sake of convenience that a Gray scale image which gradually becomes brighter from the left towards the right of the image, that is, an image in which the luminance gradually increases from the left to right of the image, is displayed on the PDP. If this image moves towards the left of the screen at a constant speed by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes sparse appears to the human eyes. On the other hand, if this image moves towards the right of the screen at a constant speed by an amount corresponding to 1 pixel for every 1 field, a portion where the light becomes dense appears to the human eyes. These sparse and dense portions where the light appears sparse and dense, respectively, occur when the human eyes focus on the moving object displayed on the screen, because the human eyes follow the moving direction and moving speed of the moving object and the visual point moves
Ishida Katsuhiro
Ogawa Kiyotaka
Otaka Nobuaki
Otobe Yukio
Tajima Masaya
Fujitsu Limited
Mengistu Amare
Staas & Halsey , LLP
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