Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-06-28
2004-06-22
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S068000
Reexamination Certificate
active
06753832
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for controlling light emission of a matrix display in a display period and an apparatus for carrying out the method.
More specifically the invention is closely related to a new addressing concept for matrix displays in which different grey levels for pixels are generated by controlling light emission/reflection/transmission with small pulses in a pulse width modulation form. Such a concept is e.g. used in plasma display panels (PDP) or other display devices where the pixel values control the generation of a corresponding number of small lighting pulses on the display.
The Plasma technology now makes it possible to achieve flat colour panels of large size (out of the CRT limitations) and with very limited depth without any viewing angle constraints.
Referring to the last generation of European TV, a lot of work has been made to improve its picture quality. Consequently, a new technology like the Plasma one has to provide a picture quality as good or better than standard TV technology. This picture quality can be decomposed in different parameters:
good response fidelity of the panel: A panel having a good response fidelity ensures that only one pixel could be ON in the middle of a black screen and in addition, this panel has to perform a good homogeneity. In order to improve that, a so-called “priming” is used which aims to excite the whole cells of the panel regularly but only during a short time. Nevertheless, since an excitation of a cell is characterized by an emission of light, the priming will modify the level of black. Therefore, this solution has to be used parsimoniously.
good brightness of the screen: This is limited by the dead time of the panel, a time in which no light is produced, comprising mostly the addressing time, and the erase time.
good contrast ratio even in a dark room: This is limited by the brightness of the panel combined with the black level
(
ratio
Brightness
blacklevel
)
.
In order to improve the response fidelity, the use of “priming” will, at the same time, reduce the contrast ratio.
All these parameters are also completely linked together and an optimal compromise has to be chosen to provide the best picture quality at the end.
Moreover, the success of such a new emerging technology is also dependent on its price. Furthermore, the power consumption of such a product should be as low as possible to ensure a consumer success.
A Plasma Display Panel (PDP) utilizes a matrix array of discharge cells which could only be “ON” or “OFF”. Also unlike a CRT or LCD in which grey levels are expressed by analogue control of the light emission, a PDP controls the grey level by modulating the number of light pulses per frame (sustain pulses). This time-modulation will be integrated by the eye over a period corresponding to the eye time response.
Since the video amplitude determines the number of light pulses, occurring at a given frequency, more amplitude means more light pulses and thus more “ON” time. For this reason, this kind of modulation is also known as PWM, pulse width modulation. To establish a concept for this PWM, each frame will be decomposed in sub-periods called “sub-fields”.
For producing the small light pulses, an electrical discharge will appear in a gas filled cell, called plasma and the produced UV radiation will excite a colored phosphor which emits the light.
In order to select which cell should be lighted, a first selective operation called addressing will create a charge in the cell to be lighted. Each plasma cell can be considered as a capacitor which keeps the charge for a long time. Afterwards, a general operation called “sustain” applied during the lighting period will add charges in the cell. In the cell addressed during the first selective operation, the two charges together will build up between two electrodes of the cell a firing voltage. UV radiation is generated which excites the phosphor for light emission. The discharge of the cell is made in a very short period and there remains some charge in the cell. With the next sustain pulse, this charge is increased again up to the firing voltage so that the next discharge will happen and the next light pulse will produced. During the whole sustain period of each specific sub-field, the cell will be lighted in small pulses. At the end, an erase operation will remove all the charges to prepare a new cycle.
The principle structure of a plasma cell in matrix plasma display technologie is shown in FIG.
1
. Reference number
10
denotes the face plate made of glass. With reference number
11
a transparent line electrode is denoted. The back plate of the panel is referenced with reference number
12
. There are two dielectric layers
13
for isolating face and back plate against each other. In the back plate are integrated column electrodes
14
being perpendicular to the line electrodes
11
. The inner part of the cells consists of the luminous substance
15
(phosphor) and separators
16
for separating the different coloured phosphors (green
15
a
), (blue
15
b
), (red
15
c
). The UV radiation caused by the discharge is denoted with reference number
17
. The light emitted from the green phosphor
15
a
is indicated with arrows having the reference number
18
. From this structure of a PDP it is clear, that there are three plasma cells necessary, corresponding to the three colour components R,G,B, to produce the colour of a picture element of the displayed picture.
The gray level of each R,G,B component of a pixel is controlled in a PDP by modulating the number of light pulses per frame period. This time modulation will be integrated by the eye over a period corresponding to the human eye time—response.
This principle will now be explained. But those skilled in the art will known the principle from the literature. In video technology an 8 bit representation of each colour component R,G,B is common. In that case each level of the luminance for each colour component will be represented by a combination of the 8 following bits:
1 -2 -4 -8 -16 -32 -64 -128
To realize such a coding with the PDP technology, the frame period will be divided in 8 lighting periods (called sub-fields), each one corresponding to a bit. The number of light pulses for the bit “2” is the double as for the bit “1”, and so forth. With these 8 sub-periods, it is possible, through sub-field combination, to build the 256 gray levels. The standard principle used to generate this gray modulation is based on the ADS (Address/Display Separated) principle, in which all operations are performed at different time on the whole panel. This principle is illustrated in FIG.
2
.
FIG. 2
represents an example of ADS addressing scheme based on an 8-bit encoding with only one priming period at the beginning of the frame. This is only an example and there are very different sub-field organisations known from the literature with e.g. more sub-fields and different sub-field weights. Often, more sub-fields are used to reduce moving artifacts and priming could be used on more sub-fields to increase the response fidelity. Priming is a separate optional period, where the cells are charged. This charge can lead to a small discharge, i.e. can create background light, which is in principle unwanted. After the priming period an erase period follows for immediately quenching the charge. This is required for the following sub-field periods, where the cells need to be addressed again. So priming is a period which facilitates the following addressing periods, i.e. it improves the efficiency of the writing stage by regularly exciting all cells, simultaneously.
In the ADS addressing method all the basic cycles are made one after the other. At first, all cells of the panel will be written (addressed) in one period, afterwards all cells will be lighted (sustained) and at the end all cells will be erased together. In all these cases, since operations are made on the whole panel, the time required for the operation, is long. In other words, if we take the example of priming and writing,
Correa Carlos
Weitbruch Sébastien
Zwing Rainer
Fried Harvey D.
Henig Sammy S.
Liang Regina
Nguyen Jennifer T.
Thomson Licensing S.A.
LandOfFree
Method for controlling light emission of a matrix display in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for controlling light emission of a matrix display in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for controlling light emission of a matrix display in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3343612