Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-12-05
2004-02-17
Mengistu, Amare (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
Reexamination Certificate
active
06693609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a driving method and apparatus for a plasma display panel, and more particularly to a method of generating an optimal light-emission pattern for a plasma display panel in order to select a light-emission pattern where a moving picture pseudo contour noise is minimized. Also it relates to a method of measuring a contour noise for a plasma display panel in order to rapidly calculate a contour noise degree and a method of selecting a gray scale in order to select a sub-field array and a gray scale with which the contour noise is minimized.
2. Description of the Related Art
Generally, a plasma display panel (PDP) makes a fluorescent body radiate by using an ultraviolet with a wavelength of 147 nm generated upon discharge of an inactive mixture gas such as He+Xe, Ne+Xe or He+Ne+Xe gas, to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development.
Referring to
FIG. 1
, a discharge cell of a three-electrode, AC surface-discharge PDP includes a scanning/sustaining electrode Y and a common sustaining electrode Z provided on an upper substrate
1
, and an address electrode X provided on a lower substrate
4
.
The address electrode X perpendicularly cross a sustaining electrode pair including one scanning/sustaining electrode Y and one common sustaining electrode Z. On the upper substrate
1
, a dielectric layer
2
and a protective film
3
are disposed in such a manner to cover the scanning/sustaining electrode Y and the common sustaining electrode Z. A dielectric layer
5
is entirely deposited onto the lower substrate
4
in such a manner to cover the address electrode X, a barrier rib
6
is provided thereon in a direction parallel to the address electrode X. A discharge such as an inactive mixture gas is injected into a discharge space defined between the upper/lower substrate
1
and
4
and the barrier rib
6
.
In such a PDP, for implementing a gray level of a picture, one frame is divided into a plurality of sub-fields, each of which a brightness weighting value is given to, so as to be driven in a manner of time division. A sub-field array is defined as a set of a plurality of sub-fields which are included within one frame interval. Each sub-field included in the sub-field array is again divided into a reset interval or setup interval for initializing cells of the entire screen, an address interval for selecting cells and a sustaining interval determined in proportion to the brightness weighting value where a discharge frequency is set in advance.
FIG. 2
represents an eight bit default code including 8 sub-fields corresponding to each bit of eight bits in a sub-field array. In the eight bit default code, eight sub-fields each has the brightness weighting value increased in the order from a least significant bit to a most significant bit by 2
n
(wherein n=0, 1, 2, 3, 4, 5, 6 and 7) to be capable of expressing 256 gray levels.
The PDP may generate a pseudo contour noise from a moving picture because of its characteristic of implementing a gray scale of a picture by a combination of sub-fields. Hereinafter, such a moving picture pseudo contour noise is referred briefly to as a ‘contour noise’. If the contour noise is generated, then a pseudo contour emerges on the screen to deteriorate a display quality of moving picture. For instance, when the screen is moved to the right at a speed of 1 pixel/frame after the left half of the screen was displayed by a gray level value ‘127’ and the right half of the screen was displayed by a gray level value ‘128’ as shown in FIG.
3
and
FIG. 4
, an eye of an observer follows such a motion of the screen to simultaneously view lights irradiated from the adjacent two pixels. Since light-emissions from the two pixels each displaying gray levels ‘127’ and ‘128’ are accumulated at an interface between gray levels, the eye views the two pixels more brightly rather than recognizing a real brightness of the two pixels respectively. In other words, the eye views a peak white, that is, a white band emitted more brightly than the other area from the two pixels emitted by the gray levels of ‘127’ and ‘128’. On the contrary, if the screen, the left half of which is displayed by the gray level value ‘128’ and the right half of which is displayed by the gray level value ‘127’, is moved to the right, then a black band emerges from a boundary portion between gray level values ‘127’ and ‘128’.
Strategies for eliminating such a contour noise include a scheme of dividing one sub-field to add 1 or 2 sub-fields for increasing the total number of sub-fields, a scheme of re-arranging a sequence of sub-fields, a scheme of adding sub-fields and re-arranging a sequence of sub-fields, and etc. Further, they include a scheme of carrying out an error diffusion method together with any one of the above-mentioned schemes. However, since said addition of sub-fields causes a lack of an address interval or a sustaining interval, there is raised a problem that a screen becomes dark.
An example of said scheme of re-arranging sub-fields is a scheme of arranging sub-fields at a sequence of brightness weighting values ‘1, 2, 4, 8, 16, 64, 32, 64, which was suggested in U.S. Pat. No. 6,100,939. Other example is a scheme of randomly arranging a sequence of sub-fields for each frame in accordance with an input image signal, which was suggested in Japanese Laid-open Gazette No. Pyung 7-27135. Such schemes of re-arranging a sequence of sub-fields are capable of reducing the contour noise to a certain degree. However, since it is virtually impossible for such schemes to meet all events at which any contour noise is generated because the contour noise appears in various types in accordance with an input image signal, such schemes have a limit that a contour noise reduction effect fails to reach to a desired level.
Recently, in order to eliminate a moving picture pseudo contour noise, there has been suggested a code (hereinafter ‘contour noise free code’) that allows all sub-fields from a sub-field arranged at an initial time of the frame until sub-fields arranged thereafter to be continuously turned on in response to an enlargement of a gray level value as shown in FIG.
4
. In the contour noise free code, a brightness weighting value of each sub-field is determined in order that an emission of a light can be linearly increased, when viewed at the time axis, to thereby prevent a generation of the contour noise as shown in FIG.
5
.
As can be seen from
FIG. 6
, the contour noise free code has a disadvantage that an expressible gray level value is limited to ‘the number of sub-fields plus 1’. For example, in the contour noise free code as shown in
FIG. 5
, a brightness weighting value of each sub-field is set to 1, 2, 4, 8, 16, 24, 32, 40, 56 and 72 to thereby limit the gray level value into 11 gray levels of 0, 1, 3, 7, 15, 31, 55, 87, 127, 183 and 255 corresponding thereto.
For this reason, a use of the contour noise free code raises a problem that though no contour noise is generated, the number of expressible gray levels becomes insufficient to deteriorate a picture quality. In order to compensate for such a reduction in total number of gray levels from the contour noise free code, a multi-toning technique using an error diffusion method, which permits to visually recognize a larger number of gray levels than the number of real gray levels, may be applied. However, the multi-toning technique brings about a deterioration of picture quality caused by an error diffusion artifact or a dithering pattern, etc.
In the mean time, a light-emission pattern determined by a combination of sub-fields is selected from a considerably large number of events. For this reason, it is virtually impossible to find out an optimal light-emission pattern capable of minimizing the contour noise from all possible light-emission pat
Hong Ki Sang
Kang Seong Ho
Kim Jae Woo
Kim Yong Duek
Koo Bon Cheol
Fleshner & Kim LLP
LG Electronics Inc.
Mengistu Amare
LandOfFree
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