FIELD OF THE INVENTION
[0001] The present invention relates to plasma display panels and more particularly to a
compensation method for improving color saturation and image quality of plasma display
panel by adjusting the strength of input image signals.
BACKGROUND OF THE INVENTION
[0002] A manufacturing process of a conventional alternating current discharge type plasma
display panel (PDP) 10 is shown in FIG. 1. First, two different activation layers
are formed on glass substrates 11 and 12 respectively. Then seal the peripheries of
glass substrates 11 and 12 together. A mixed gas consisting of helium (He), neon (Ne),
and xenon (Xe) (or argon (Ar)) having a predetermined mixing volume ratio is stored
in a discharge space formed in between the glass substrates 11 and 12. A front plate
11 is defined as one of the glass substrates 11 and 12that facing viewers. A plurality
of parallel spaced transparent electrodes 111, a plurality of parallel spaced bus
electrodes 112, a dielectric layer 113, and a protection layer 114 are formed from
the front plate 11 inwardly. Correspondingly, from rear plate 12 inwardly, a plurality
of parallel spaced data electrodes 121, a dielectric layer 124, a plurality of parallel
spaced ribs 122, and a uniform phosphor layer 123 are formed. When a voltage is applied
on electrodes 111, 112, and 121, dielectric layers 113 and 124 will discharge in discharge
cell 13 formed by adjacent spaced ribs 122. As a result, a ray having a desired color
is emitted from phosphor layer 123.
[0003] Since the plurality of parallel spaced ribs 122 and a uniform phosphor layer 123
are formed on rear plate 12 when a ray from environment is lit on the PDP 10, it is
possible for light diffused from spaced ribs 122 and uniform phosphor layer 123 on
rear plate 12. As a result, the color saturation and image quality of PDP is degraded
significantly when PDP 10 is exposed to a bright environment.
[0004] Conventionally, a number of improvements have been proposed to mitigate above problems.
For example, NEC (Japan) implements a capsulated color filter technique. A filter
20 on front plate 11 is formed on each of corresponding red, green, and blue discharge
cells 13 as shown in FIG. 2. With this, it is possible to filter out reflected light
from discharge cells 13 caused by bright environment, thereby increasing color saturation
of PDP. However, the manufacturing cost is increased significantly because the manufacturing
process of filters 20 is complex. Another improvement technique is proposed by Plasmaco
(Japan) in which circular polarizing filters are used for eliminating the adverse
influence of bright environment. However, the brightness of PDP may be adversely affected
since the transmissibility of such circular polarizing filters is low. Thus, such
technique is undesirable.
[0005] In view of the above, such conventional improvements are disadvantageous since only
filters are employed for eliminating reflection from discharge cells 13 caused by
bright environment. Thus, it is desirable to provide a novel method for improving
color saturation and image quality of PDP in order to overcome the above drawbacks
of prior art
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to provide a compensation process for improving
color saturation and image quality of a plasma display panel (PDP), the process comprising
the steps of: a) calculating the brightness of a visible light generated by environment
light on PDP through performing a numeric operation according to color mixing theory,
and the corresponding light ought to be generated by each of red, green, and blue
discharge cells of each of a plurality of pixels on the PDP to exclude the visible
light generated by environment light; b) increasing or decreasing strength of input
image signals of each of the red, green, and blue discharge cells in accordance with
the result of calculation; and c) generating light from each of the red, green, and
blue discharge cells to eliminate the visible light from causing an adverse effect
on the PDP
[0007] It is another object of the present invention to provide a number of environment
light modes (e.g., strong light mode, room light mode, exhibition light mode, etc.)
preset in control circuit of PDP for user to select an appropriate light mode depending
on the real environment of PDP and to perform a compensation on color saturation of
PDP effectively excluding the visible light generated by environment light from the
generated light of each of the red, green, and blue discharge cells, thereby eliminating
an adverse effect of the environment light on the PDP.
[0008] The above and other objects, features and advantages of the present invention will
become apparent from the following detailed description taken with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009]
FIG. 1 is a sectional view of a conventional alternating current discharge type plasma
display panel (PDP);
FIG. 2 is a sectional view of another conventional technique utilized by NEC (Japan)
illustrating the implementation of capsulated color filters;
FIG. 3 is a block diagram illustrating the processes of a first preferred embodiment
of compensation method according to the invention;
FIG. 4 is a graph illustrating the effect before and after implementing the compensation
of the invention on color saturation of PDP, while first 128 gray scales of respective
color of input image are sampled and the threshold value of respective color is set
as 20 in a bright environment.
FIG. 5 is a block diagram illustrating the processes of a second preferred embodiment
of compensation method according to the invention; and
FIG. 6 is a block diagram illustrating the processes of a third preferred embodiment
of compensation method according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] Typically, an image shown on a well known PDP consists of a plurality of pixels.
Note that the number of pixels is determined by the resolution of PDP. A pixel consists
of three discharge cells capable of emitting red, green, and blue lights respectively.
Hence, the color of a pixel of image shown on PDP is a mixture of red, green and blue
lights emitted by respective discharge cell. For example, a, b, and c are gray scales
of red, green and blue lights emitted by respective discharge cell of each pixel of
PDP. R
cell, G
cell, and B
cell are brightness of respective gray scale in phosphor layer of discharge cells corresponding
to each pixel. In a dark environment (i.e., not influenced by light), the brightness
of respective red, green, and blue discharge cell may be expressed by equations (1),
(2) and (3) below:
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0001)
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0002)
and
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0003)
[0011] Hence, lmage
Dark of each pixel observed in the dark environment is expressed by equation (4) below:
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0004)
[0012] Since a plurality of parallel spaced ribs and a uniform phosphor layer are formed
on rear plate when a visible light from environment is lit on the PDP, a diffused
light is thus generated. Hence, an additional visible light W is generated on PDP.
One aspect of the invention is to eliminate the adverse effect of such visible light
W on color saturation and image quality of PDP. Thus, laws of color matching proposed
by Grassman is adopted in which the additional visible light W, which can be generated
by red, green and blue discharge cells, may be expressed by the following equation
(5)
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0005)
Wherein R
cell, G
cell, and B
cell are brightness of gray scale of red, green and blue discharge cells respectively
and α, β and γ are the number of gray scales of red, green and blue discharge cells
respectively.
[0013] Since the visible light W diffused from spaced ribs and phosphor layer may degrade
significantly the color saturation and image quality of PDP when PDP is exposed to
a bright environment. The invention utilizes the control circuit of PDP for increasing
or decreasing the strength of input image signals (or input voltage) of each discharge
cell to exclude the effect of the additional visible light W from the color generated
by red, green and blue discharge cells while showing image on PDP. As a result, the
adverse effect of the visible light W on PDP is completely eliminated, thereby improving
the color saturation and image quality of PDP.
[0014] In the first embodiment of the invention, the additional visible light W on PDP generated
by environment light may be prepared by a predetermined mixing ratio of red, green
and blue lights. In a bright environment, the visible light W diffused from PDP may
be expressed by above equation (5). The Image
Bright observed in the bright environment is expressed by equation (6) below which is an
addition of equations (4) and (5):
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0006)
wherein α R
cell + β G
cell + γ B
cell is the adverse effect of the additional visible light W on PDP, i.e. the main factor
of the degradation of color saturation and image quality of PDP.
[0015] In the embodiment shown in FIG. 3, it is required to first calculate the affecting
degree of the environment light (i.e., the additional visible light W) in compensating
color saturation of PDP in a bright environment. As such, prior to image output it
is possible to adjust the strength of input image signals of each discharge cell by
the control circuit. Thus, the brightness of the generated color may be expressed
by equations (7), (8) and (9) with the exclusion of visible light W:
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0007)
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0008)
and
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0009)
[0016] For avoiding a negative value from generating by each discharge cell when an operation
is performed on each of above equations (7) to (9), a threshold value of respective
color (e.g., threshold value of red = Th
Red, threshold value of green = Th
Green, or threshold value of blue = Th
Blue) is selected. Hence, it is possible to determine whether the gray scale of respective
color of input image (e.g., red gray scale is a, green gray scale is b, or blue gray
scale is c) is larger than, equal to, or smaller than the threshold value of the corresponding
color. Thereafter, prior to outputting image on PDP the invention can activate the
control circuit to perform an operation on each of above equations (7) to (9), thereby
adjusting the strength of input image signals of each discharge cell. Hence, after
the compensation on image of PDP by the invention, the brightness of pixel may be
expressed by equation (10) below:
brightness of pixel after compensation = brightness of red discharge cell after
compensation + brightness of green discharge cell after compensation + brightness
of blue discharge cell after compensation + W
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0010)
As stated above, since the brightness of the visible light W may be expressed
as the addition of the brightness of color generated by red, green, and blue discharge
cells R
cell, G
cell and B
cell, i.e., W = α R
cell + β G
cell + γ B
cell. It is apparent from equation (10) that the adverse effect of the visible light W
on PDP is completely eliminated.
[0017] Referring to FIG. 4, first 128 gray scales of respective color of input image are
sampled and the threshold value of respective color is set as 20. In a bright environment,
a compensation on color saturation of PDP is performed by the invention. It is apparent
that in the low gray scale region, the negative values of equations (7) to (9) are
avoided. Most importantly, the adverse effect of the bright environment light on PDP
is completely eliminated. In the embodiment, if gray scale of each color of input
image (e.g., red gray scale is a, green gray scale is b, and blue gray scale is c)
is smaller than the threshold value of respective color, the brightness of pixel after
compensation may be expressed by equation (11) below:
brightness of pixel after compensation = brightness of red discharge cell after
compensation + brightness of green discharge cell after compensation + brightness
of blue discharge cell after compensation + W
![](https://data.epo.org/publication-server/image?imagePath=2002/45/DOC/EPNWA1/EP01110882NWA1/imgb0011)
Adjust the strength of input image signals of respective discharge cell based
on the ratio between gray scale of each color of input image and default threshold
gray scale. As a result, the negative values are avoided. Further, the adverse effect
of the bright environment light on PDP is completely eliminated.
[0018] Referring to FIG. 5, there is shown a second embodiment of the invention wherein
an active compensation on color saturation is performed in a bright environment. A
light sensor is used to detect environment light. The detected values are processed
in order to evaluate the effect of environment light on PDP. Finally, a compensation
on color saturation of PDP may be performed accordingly.
[0019] Referring to FIG. 6, there is shown a third embodiment of the invention wherein an
inactive compensation on color saturation is performed in a bright environment. A
number of environment light modes (e.g., strong light mode, room light mode, exhibition
light mode, etc.) are provided for user selection when control circuit of PDP is activated.
With this, user may select an appropriate light mode depending on the real environment
of PDP. Similarly, a compensation on color saturation of PDP may be performed accordingly.
[0020] In brief, the invention can adjust the brightness of the generated red, green, or
blue light by increasing or decreasing the strength of input image signals of respective
discharge cell of each pixel. Hence, the adverse effect of environment light on color
saturation of PDP is completely eliminated. Most importantly, there is no need to
modify the construction of PDP or perform an additional processing thereon. This is
simple, resulting in a reduction in the manufacturing cost.
[0021] While the invention has been described by means of specific embodiments, numerous
modifications and variations could be made thereto by those skilled in the art without
departing from the scope and spirit of the invention set forth in the claims.
1. A compensation process for improving color saturation and image quality of a plasma
display panel (PDP), said process comprising the steps of:
a) calculating the brightness of a visible light generated by environment light on
PDP through performing a numeric operation according to a color mixing theory, and
the corresponding light ought to be generated by each of red, green, and blue discharge
cells of each of a plurality of pixels on the PDP sufficient to exclude the visible
light generated by environment light on PDP;
b) increasing or decreasing strength of input image signals of each of said red, green,
and blue discharge cells in accordance with the result of calculation; and
c) generating light from each of said red, green, and blue discharge cells to eliminate
said visible light from causing an adverse effect on said PDP.
2. The compensation process of claim 1, wherein said visible light is expressed by an
addition of a value of said red light, a value of said green light, and a value of
said blue light respectively generated by each of red, green, and blue discharge cells
of each of a plurality of pixels on the PDP through said numeric operation according
to said color mixing theory.
3. The compensation process of claim 1, wherein said visible light is expressed by an
addition of two values of different color lights generated respectively by two different
discharge cells of each of a plurality of pixels on the PDP through said numeric operation
according to said color mixing theory.
4. The compensation process of claim 2 or 3, wherein said values are used for adjusting
strength of said input image signals of each of said red, green, and blue discharge
cells so that an adverse effect of said visible light on PDP is eliminated by said
generated light having said values.
5. The compensation process of claim 4, further comprising a light sensor for detecting
said environment light so as to calculate the brightness of light generated from each
of said red, green, and blue discharge cells of each pixel on said PDP through performing
said numeric operation.
6. The compensation process of claim 4, further comprising the step of providing a plurality
of user selectable environment light modes, which is selected to activate a control
circuit in said PDP corresponding to a real environment of said PDP, to eliminate
said visible light from causing an adverse effect on color saturation of said PDP.
7. The compensation process of claim 4, further comprising the steps of setting a threshold
gray scale of each of red, green, and blue lights generated from each of said red,
green, and blue discharge cells of each pixel on said PDP; and detecting and determining
whether said gray scale of each of red, green, and blue lights of an input image is
larger than or equal to said threshold gray scale of each of red, green, and blue
lights, whereby if said determination is positive a control circuit in said PDP is
operative to adjust said strength of said input image signals of each of said red,
green, and blue discharge cells so that said adverse effect of said visible light
on PDP is eliminated by said generated light.
8. The compensation process of claim 4, further comprising the steps of detecting and
determining whether said gray scale of each of red, green, and blue lights of an input
image is smaller than said threshold gray scale of each of red, green, and blue lights,
whereby if said determination is positive a control circuit in said PDP is operative
to adjust said strength of said input image signals of each of said red, green, and
blue discharge cells so that negative values are avoided from generating by each of
said red, green, and blue discharge cells.