U.S. patent application number 09/173001 was filed with the patent office on 2002-01-10 for method and apparatus for displaying moving images while correcting false moving image contours.
Invention is credited to TANAKA, AKIRA, WATANABE, TAKUYA, YAMADA, HACHIRO.
Application Number | 20020003542 09/173001 |
Document ID | / |
Family ID | 17669594 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003542 |
Kind Code |
A1 |
TANAKA, AKIRA ; et
al. |
January 10, 2002 |
METHOD AND APPARATUS FOR DISPLAYING MOVING IMAGES WHILE CORRECTING
FALSE MOVING IMAGE CONTOURS
Abstract
When gradation data of a present frame is corrected in
combination with gradation data of a preceding frame for each
display pixel, the level of correction is controlled according to a
predetermined dispersion pattern corresponding to a matrix of
pixels on a plasma display panel. The display pixels where the
gradation level varies in the same way are not corrected uniformly,
but some are excessively corrected and some are uncorrected such
that they are mixed in a two-dimensional pattern. Moving images
displayed on the plasma display panel with gradations expressed
according to the subfield process for pixels are prevented from
suffering false moving image contours.
Inventors: |
TANAKA, AKIRA; (TOKYO,
JP) ; WATANABE, TAKUYA; (TOKYO, JP) ; YAMADA,
HACHIRO; (TOKYO, JP) |
Correspondence
Address: |
SUGHRUE MION ZINN MACPEAK & SEAS
2100 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
200373202
|
Family ID: |
17669594 |
Appl. No.: |
09/173001 |
Filed: |
October 15, 1998 |
Current U.S.
Class: |
345/581 |
Current CPC
Class: |
G09G 2320/0285 20130101;
G09G 2320/0266 20130101; G09G 2340/16 20130101; G09G 3/2033
20130101; G09G 2310/0286 20130101; G09G 3/296 20130101; G09G
2320/0261 20130101 |
Class at
Publication: |
345/581 |
International
Class: |
G09G 005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 16, 1997 |
JP |
283747/1997 |
Claims
What is claimed is:
1. A method of displaying a moving image by dividing a frame into a
plurality of subfields having different relative luminance ratios
and displaying a moving image of multiple gradations on a display
panel having a matrix of display pixels, comprising the steps of:
producing new n (n is a natural number) corrected video gradation
data from video gradation data of a preceding frame and video
gradation data of a present frame for each of the display pixels;
selecting at least two of said video gradation data of the
preceding frame, said video gradation data of the present frame,
and said n corrected video gradation data; and displaying the
selected video gradation data at display pixels of a predetermined
selection pattern.
2. A method of displaying a moving image by dividing a frame into a
plurality of subfields having different relative luminance ratios
and displaying a moving image of multiple gradations on a display
panel having a matrix of display pixels, comprising the steps of:
producing new n (n is a natural number) corrected video gradation
data from video gradation data of a preceding frame and video
gradation data of a present frame for each of the display pixels;
selecting at least two of said video gradation data of the
preceding frame, said video gradation data of the present frame,
and said n corrected video gradation data; and combining the
selected video gradation data with each other and dispersing the
combined video gradation data in a pixel plane of the display
pixels according to a predetermined selection pattern.
3. A method of displaying a moving image by dividing a frame into a
plurality of subfields having different relative luminance ratios
and displaying a moving image of multiple gradations on a display
panel having a matrix of display pixels, comprising the steps of:
producing new n (n is a natural number) corrected video gradation
data from video gradation data of a preceding frame and video
gradation data of a present frame for each of the display pixels;
selecting at least two of said video gradation data of the
preceding frame, said video gradation data of the present frame,
and said n corrected video gradation data; and combining at least
one of the selected video gradation data with said video gradation
data of the present frame and dispersing the combined video
gradation data in a pixel plane of the display pixels according to
a predetermined selection pattern.
4. A method of displaying a moving image by dividing a frame into a
plurality of subfields having different relative luminance ratios
and displaying a moving image of multiple gradations on a display
panel having a matrix of display pixels, comprising the steps of:
producing new n (n is a natural number) corrected video gradation
data from video gradation data of a preceding frame and video
gradation data of a present frame for each of the display pixels;
selecting at least two of said video gradation data of the
preceding frame, said video gradation data of the present frame,
and said n corrected video gradation data; and combining at least
one of the selected video gradation data with said video gradation
data of the preceding frame and dispersing the combined video
gradation data in a pixel plane of the display pixels according to
a predetermined selection pattern.
5. A method of displaying a moving image by dividing a frame into a
plurality of subfields having different relative luminance ratios
and displaying a moving image of multiple gradations on a display
panel having a matrix of display pixels, comprising the steps of:
producing new n (n is a natural number) corrected video gradation
data from video gradation data of a preceding frame and video
gradation data of a present frame for each of the display pixels;
selecting at least two of said video gradation data of the
preceding frame, said video gradation data of the present frame,
and said n corrected video gradation data; and combining the
selected video gradation data of the preceding frame with said
video gradation data of the present frame and dispersing the
combined video gradation data in a pixel plane of the display
pixels according to a predetermined selection pattern.
6. A method of displaying a moving image by dividing a frame into a
plurality of subfields having different relative luminance ratios
and displaying a moving image of multiple gradations on a display
panel having a matrix of display pixels, comprising the steps of:
producing new n (n is a natural number) corrected video gradation
data from video gradation data of a preceding frame and video
gradation data of a present frame for each of the display pixels;
selecting at least two of said video gradation data of the
preceding frame, said video gradation data of the present frame,
and said n corrected video gradation data; displaying the selected
video gradation data at display pixels of a predetermined selection
pattern; and if there is generated a gradation transition between
said video gradation data of the preceding frame and said video
gradation data of the present frame, combining said video gradation
data of the preceding frame and said video gradation data of the
present frame with each other and dispersing the combined video
gradation data in a pixel plane of the display pixels according to
a predetermined selection pattern.
7. A method according to claim 1, wherein said predetermined
selection pattern comprises a pattern of horizontally adjacent
display pixels among said display pixels.
8. A method according to claim 1, wherein said predetermined
selection pattern comprises a pattern of vertically adjacent lines
across said display pixels.
9. A method according to claim 1, wherein said predetermined
selection pattern comprises a checkerboard pattern of horizontally
and vertically arranged display pixels among said display
pixels.
10. A method according to any of claim 7, wherein said
predetermined selection pattern comprises a combination of frames
successively arranged in time.
11. A method according to any of claim 8, wherein said
predetermined selection pattern comprises a combination of frames
successively arranged in time.
12. A method according to any of claim 9, wherein said
predetermined selection pattern comprises a combination of frames
successively arranged in time.
13. A method according to claim 1, wherein said predetermined
selection pattern comprises a randomly dispersed pattern.
14. An apparatus for displaying a moving image by dividing a frame
into a plurality of subfields having different relative luminance
ratios and displaying a moving image of multiple gradations on a
display panel having a matrix of display pixels, comprising: data
input means for entering data; data storage means for storing video
gradation data of a preceding frame corresponding to unit pixels of
the display pixels; data correcting means for producing new n (n is
a natural number) corrected video gradation data from the video
gradation data of the preceding frame stored in aid data storage
means and video gradation data of a present frame from said data
input means; and correction control means for combining a plurality
of video gradation data including at least two of said video
gradation data of the preceding frame, said video gradation data of
the present frame, and said n corrected video gradation data, and
dispersing the combined video gradation data in a pixel plane of
the display pixels according to a predetermined selection
pattern.
15. An apparatus according to claim 14, wherein said correction
control means comprises means for combining at least two of said n
corrected video gradation data from said data correcting means with
each other, and dispersing the combined video gradation data in the
pixel plane of the display pixels according to said predetermined
selection pattern.
16. An apparatus according to claim 14, wherein said correction
control means comprises means for combining at least one of said n
corrected video gradation data from said data correcting means with
said video gradation data of the present frame from said data input
means, and dispersing the combined video gradation data in the
pixel plane of the display pixels according to said predetermined
selection pattern.
17. An apparatus according to claim 14, wherein said correction
control means comprises means for combining at least one of said n
corrected video gradation data from said data correcting means with
said video gradation data of the preceding frame from said data
storage means, and dispersing the combined video gradation data in
the pixel plane of the display pixels according to said
predetermined selection pattern.
18. An apparatus according to claim 14, wherein said correction
control means comprises means for combining said video gradation
data of the preceding frame from said correcting means with said
video gradation data of the present frame from said data input
means, and dispersing the combined video gradation data in the
pixel plane of the display pixels according to said predetermined
selection pattern.
19. An apparatus according to claim 14, wherein said correction
control means comprises means for combining said video gradation
data of the preceding frame and said video gradation data of the
present frame with each other, and dispersing the combined video
gradation data in the pixel plane of the display pixels according
to said predetermined selection pattern, if there is generated a
gradation transition between said video gradation data of the
preceding frame from said data correcting means and said video
gradation data of the present frame from said data input means.
20. An apparatus according to claim 14, wherein said predetermined
selection pattern comprises a pattern of horizontally adjacent
display pixels among said display pixels.
21. An apparatus according to claim 14, wherein said predetermined
selection pattern comprises a pattern of vertically adjacent lines
across said display pixels.
22. An apparatus according to claim 14, wherein said predetermined
selection pattern comprises a checkerboard pattern of horizontally
and vertically arranged display pixels among said display
pixels.
23. An apparatus according to claim 20, wherein said predetermined
selection pattern comprises a combination of frames successively
arranged in time.
24. An apparatus according to claim 21, wherein said predetermined
selection pattern comprises a combination of frames successively
arranged in time.
25. An apparatus according to claim 22, wherein said predetermined
selection pattern comprises a combination of frames successively
arranged in time.
26. An apparatus according to claim 14, wherein said predetermined
selection pattern comprises a randomly dispersed pattern.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] 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.
[0003] 2. Description of the Related Art
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] One conventional AC plasma display panel will be described
below with reference to FIG. 1 of the accompanying drawings.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] A dielectric layer 111 is positioned in facing relation to
the surface discharge electrodes 101.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] A process of displaying an image on the plasma display panel
100 shown in FIG. 1 will be described below.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] For example, if a video signal is to be represented in 256
8-bit binary gradation levels, then, as shown in FIG. 2a 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".
[0027] 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.
[0028] For example, if the gradation level of a certain display
pixel is "127", then, as shown in a left-hand side of FIG. 2b 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.
[0029] If the gradation level of a certain display pixel is 128,
then, as shown in a right-hand side of FIG. 2b, sustaining pulses
of one subfield which is weighted by "128" are applied to the
display pixel in the period of one frame.
[0030] 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.
[0031] However, some moving images displayed according to the
subfield process tend to suffer interferences.
[0032] 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.
[0033] When a color image is displayed, it may suffer a
color-shifted contour or a reduction in resolution.
[0034] Such interferences are referred to as false moving image
contours.
[0035] 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.
[0036] While these interferences may be referred to as false color
contours, they are essentially generated by a combination of false
moving image contours for the respective colors in a displayed
color image.
[0037] Such a phenomenon is responsible for color shifts or
reductions in resolution in the display of moving images.
[0038] FIG. 2b illustrates a situation in which the gradation level
of a certain display pixel varies from "127" to "128". In the
gradation level of "127", sustaining pulses are concentrated in the
first half of the frame. In the gradation level of "127",
sustaining pulses are concentrated in the second half of the frame.
Therefore, a blank period free of sustained emission is present
between frames across a transition from the gradation level of
"127" to the gradation level of "128". Because the display pixel
does not emit light for a period of time longer than the preceding
and following frames, the gradation level of the display pixel
which is actually visually perceived by the human eye is lower than
the gradation level that is to be displayed.
[0039] Conversely, when the gradation level of a certain display
pixel varies from "128" to "127", as shown in FIG. 3 of the
accompanying drawings, the gradation level of the display pixel is
actually visually perceived as being lower than the gradation level
that is to be displayed because the light emission in subfields is
concentrated in a short period of time.
[0040] For varying the gradation level of a display pixel on a CRT
(Cathode-Ray Tube) display unit, the intensity of the electron beam
may be modulated to adjust the luminance of the display pixel in an
analog fashion. A number of display pixels on the CRT display unit
are successively scanned in order to display an image on the CRT
display unit. Since the successive scanning of the display pixels
is completed in an instantaneous period of time, the CRT display
unit does not suffer false moving image contours.
[0041] In apparatus for displaying moving images according to the
subfield process, such as plasma display panels, each gradation bit
is displayed in a time-division multiplex fashion at a low speed in
a period of time close to the duration of one field, and the
observer visually combines displayed gradation bits as one image
based on the spatial integration performed by the human eye.
[0042] If a visually combined image is a moving image, then a clear
bright-line interference or dark-line interference occurs when the
moving image is followed by the eye. Specifically, when pixels
visually perceived as bright or dark pixels are followed by the
eye, they are combined as a bright or dark line fixedly on the
retina.
[0043] The principles of generation of false moving image contours
have been described above.
[0044] Processes for eliminating false moving image contours have
been disclosed in Japanese Patent Laid-Open Publication No.
271325/95, Japanese Patent Laid-Open Publication No. 54852/96, and
Japanese Patent Laid-Open Publication No. 234694/96, for
example.
[0045] According to the processes disclosed, combinations of
gradation data which make actually displayed gradations
inappropriate are registered in advance. If gradation data of a
preceding frame and gradation data of a present frame match any of
the registered combinations, then sustaining pulses to be outputted
for the gradation data of the present frame are corrected to a
predetermined form.
[0046] Therefore, display pixels whose gradation levels vary
according to any of the registered combinations of gradation data
are supplied with sustaining pulses that have been corrected to
make displayed gradations appropriate. As a result, a moving image
is prevented from suffering a false contour such as a bright line
or a dark line.
[0047] Moving image display apparatus revealed in the above
publications register combinations of gradation data which make
actually displayed gradations inappropriate in advance, and correct
sustaining pulses to prevent the gradations of display pixels from
being inappropriate when any of the registered combinations is
detected.
[0048] Actually, however, it is difficult to optimally correct the
displayed levels of multiple gradations. Particularly, it is
difficult to thoroughly eliminate inadequately colored lines from
fully colored images. For example, while it is possible to produce
corrective settings for sufficiently eliminating false contours
from images which are moving at a certain speed, the levels of such
corrective settings will be improper, tending to generate bright
and dark lines adjacent to each other, when images are moving at
speeds higher and lower than the expected speed.
SUMMARY OF THE INVENTION
[0049] It is therefore an object of the present invention to
provide a method and an apparatus for displaying moving images
while appropriately correcting false contours of the moving
images.
[0050] A method according to the present invention displays a
moving image by dividing a frame into a plurality of subfields
having different relative luminance ratios and displaying a moving
image of multiple gradations on a display panel having a matrix of
display pixels.
[0051] The method comprises the steps of producing new n (n is a
natural number) corrected video gradation data from video gradation
data of a preceding frame and video gradation data of a present
frame for each of the display pixels, selecting at least two of the
video gradation data of the preceding frame, the video gradation
data of the present frame, and the n corrected video gradation
data, and displaying the selected video gradation data at display
pixels of a predetermined selection pattern.
[0052] According to this method, the gradation levels of display
pixels in a region where a false moving image contour occurs are
not corrected uniformly, but excessively corrected display pixels
and uncorrected display pixels are mixed together in a
two-dimensional pattern. Therefore, the false moving image contour
is effectively prevented from occurring.
[0053] An apparatus for displaying a moving image according to the
present invention includes data input means, data storage means,
and data correcting means. The data input means enters data, and
the data storage means stores video gradation data of a preceding
frame corresponding to unit pixels of the display pixels. The data
correcting means produces new n (n is a natural number) corrected
video gradation data from the video gradation data of the preceding
frame stored in aid data storage means and video gradation data of
a present frame from the data input means. The apparatus divides a
frame into a plurality of subfields having different relative
luminance ratios and displays a moving image of multiple
gradations.
[0054] The apparatus also has correction control means. The
correction control means combines a plurality of video gradation
data including at least two of the video gradation data of the
preceding frame, the video gradation data of the present frame, and
the n corrected video gradation data, and disperses the combined
video gradation data in a pixel plane of the display pixels
according to a predetermined selection pattern.
[0055] The display pixels arranged in a matrix normally display
images at gradation levels corresponding to video gradation data.
If a combination of gradation data of a preceding frame and
gradation data of a present frame is such that it generates a false
moving image contour, then the gradation data is corrected to
prevent the false moving image contour from occurring.
[0056] Since the degrees of data conversion for the respective
display pixels are dispersed according to a selection pattern, the
gradation levels of display pixels in a region where a false moving
image contour occurs are not corrected uniformly, but excessively
corrected display pixels and uncorrected display pixels are mixed
together in a two-dimensional pattern.
[0057] With the above apparatus, because the gradation levels of
display pixels in a region where a false moving image contour
occurs are not corrected uniformly, but are corrected such that
excessively corrected display pixels and uncorrected display pixels
are mixed together in a two-dimensional pattern. Consequently, it
is possible to effectively prevent a false moving image contour
from occurring.
[0058] The apparatus for displaying moving images according to the
present invention has a matrix of display pixels on a display panel
for displaying gradations according to the subfield process. The
apparatus may comprise a plasma display apparatus or a DMD, for
example, as long as it can display moving images on its display
panel.
[0059] The means referred above may be arranged in any way that
allows them to perform their functions, and may be a dedicated
hardware arrangement, a computer programmed to perform the
functions, functions implemented in a computer by an arbitrary
program, or any of combinations thereof.
[0060] The above and other objects, features, and advantages of the
present invention will become apparent from the following
description with reference to the accompanying drawings which
illustrate examples of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] FIG. 1 is a fragmentary exploded perspective view of a
conventional plasma display panel;
[0062] FIG. 2a is a diagram showing an arrangement of subfields in
one frame according to a subfield process used with respect to the
conventional plasma display panel;
[0063] FIG. 2b is a timing chart of drive pulses which are
generated when the gradation level of gradation data varies in a
pattern;
[0064] FIG. 3 is a timing chart of drive pulses which are generated
when the gradation level of gradation data varies in another
pattern;
[0065] FIG. 4 is a block diagram of a plasma display apparatus as a
moving image display apparatus according to a first embodiment of
the present invention;
[0066] FIG. 5 is a block diagram of a pattern generator of the
plasma display apparatus shown in FIG. 4;
[0067] FIG. 6 is a diagram showing a selection pattern of dots on a
display panel screen;
[0068] FIG. 7a is a timing chart of drive pulses which are
uncorrected when the gradation level of gradation data varies;
[0069] FIG. 7b is a timing chart of a luminance level that is
visually perceived when the drive pulses shown in FIG. 7a are
applied;
[0070] FIG. 7c is a timing chart of drive pulses which are
optimally corrected according to a conventional process when the
gradation level of gradation data varies;
[0071] FIG. 7d is a timing chart of a luminance level that is
visually perceived when the drive pulses shown in FIG. 7c are
applied;
[0072] FIG. 7e is a timing chart of drive pulses which are
excessively corrected according to the first embodiment of the
present invention when the gradation level of gradation data
varies;
[0073] FIG. 7f is a timing chart of a luminance level that is
visually perceived when the drive pulses shown in FIG. 7g are
applied;
[0074] FIG. 7g is a timing chart of a luminance level that is
visually perceived according to the first embodiment of the present
invention, the luminance level corresponding to the average of the
luminance levels shown in FIGS. 7d and 7f;
[0075] FIG. 8 is a diagram showing an arrangement of subfields in
one frame in a plasma display apparatus as a moving image display
apparatus according to a second embodiment of the present
invention;
[0076] FIG. 9a is a timing chart of drive pulses which are
uncorrected when the gradation level of gradation data varies;
[0077] FIG. 9b is a timing chart of a luminance level that is
visually perceived when the drive pulses shown in FIG. 9a are
applied;
[0078] FIG. 9c is a timing chart of drive pulses which are
excessively corrected according to the second embodiment of the
present invention when the gradation level of gradation data
varies;
[0079] FIG. 9d is a timing chart of a luminance level that is
visually perceived when the drive pulses shown in FIG. 9c are
applied;
[0080] FIG. 9e is a timing chart of a luminance level that is
visually perceived according to the second embodiment of the
present invention, the luminance level corresponding to the average
of the luminance levels shown in FIGS. 9b and 9d; and
[0081] FIG. 10 is a diagram showing an arrangement of subfields in
one frame in a plasma display apparatus as a moving image display
apparatus according to a third embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0082] A plasma display apparatus 1 as a moving image display
apparatus according to a first embodiment of the present invention
will be described below with reference to FIGS. 4, 5, 6, and 7a
through 7g.
[0083] As shown in FIG. 4, the plasma display apparatus 1, which is
an AC plasma display apparatus, generally comprises a plasma
display panel 2 and a drive circuit 3.
[0084] As shown in FIG. 6, the plasma display panel 2 comprises a
plurality of surface discharge electrodes 11 extending parallel to
rows and spaced successively along columns. Each of the surface
discharge electrodes 11 comprises a scanning electrode 12 and a
sustaining electrode 13 which are disposed parallel to each
other.
[0085] A plurality of data electrodes 14 extending parallel to the
columns are disposed in opposed relation to the surface discharge
electrodes 11. The data electrodes 14 are spaced successively along
the rows.
[0086] Discharge spaces (not shown) filled with a discharge gas
such as of helium, neon, xenon, or the like are provided between
the electrodes 11, 14, forming display pixels capable of
individually emitting light at the points of intersection between
the surface discharge electrodes 11 and the data electrodes 14.
[0087] The plasma display apparatus 1 is capable of displaying
fully colored images. As shown in FIG. 6, the plasma display panel
2 comprises a two-dimensional matrix of square tricolor pixels 24
each comprising three vertically elongate display pixels which are
coated respectively with R, G, B phosphors (red, green, and blue
phosphors).
[0088] As shown in FIG. 4, the plasma display apparatus 1 has a
data input unit 31 for being supplied with a video signal, an A/D
(analog-to-digital) converter 32 connected to the data input unit
31, and a gamma (.gamma.) corrector 33 connected to the A/D
converter 32.
[0089] The data input unit 31 is supplied with a video signal
composed of many gradation data. The A/D converter 32 quantizes
analog gradation data of a video signal from the data input unit 31
into digital gradation data. The gamma corrector 33 corrects the
gradations of digital gradation data from the A/D converter 32.
[0090] The plasma display apparatus 1 also has signal input units
34a-34c for being supplied with a vertical synchronizing signal, a
horizontal synchronizing signal, and a mode setting signal,
respectively. The signal input unit 34a and the gamma corrector 33
are connected to a data correcting circuit 35.
[0091] The data correcting circuit 35 has a frame memory 36
inserted in one of two signal lines from the gamma corrector 33.
The two signal lines from the gamma corrector 33 are connected to a
processing circuit 37 of the data correcting circuit 35.
[0092] The signal input units 34a-34c are connected to a pattern
generator 38 of the data correcting circuit 35. The pattern
generator 38 is connected to the processing circuit 37.
[0093] The signal input unit 34b is connected to a dot clock
generator 39 which is connected to the pattern generator 38.
[0094] The frame memory 36 temporarily stores one frame, at a time,
of gradation data and outputs the stored frame after having delayed
same for a period of time which corresponds to the duration of one
frame.
[0095] The processing circuit 37 has a LUT (Look-Up Table) 40 which
stores corrective data that can be addressed by gradation data of a
preceding frame and gradation data of a present frame. The
processing circuit 37 also has a data reading circuit 49 and a
correction executing circuit 50. The data reading circuit 49 reads
corrective data from the LUT 40 which have been addressed by
gradation data of a present frame directly supplied from the gamma
corrector 33 and gradation data temporarily stored in the frame
memory 36.
[0096] Since gradation data comprise numerical values representing
gradation levels, for example, the corrective data are established
as numerical values for increasing and reducing the numerical
values representing gradation levels.
[0097] The correction executing circuit 50 adds positive or
negative numerical values of the corrective data read from the LUT
40 to the numerical values representing gradation levels of the
gradation data of the present frame, for thereby correcting the
gradation data with the corrective data.
[0098] The pattern generator 38 which is connected to the
correction executing circuit 50 generates a selection pattern for
controlling the level of correction by the correction executing
circuit 50.
[0099] More specifically, as shown in FIG. 5, the pattern generator
38 comprises a first D-type flip-flop 41 having a data input
terminal for being supplied with a dot clock signal and a reset
input terminal for being supplied with the horizontal synchronizing
signal, a second D-type flip-flop 43 having a data input terminal
for being supplied with the horizontal synchronizing signal through
an inverter 42 and a reset input terminal for being supplied with
the vertical synchronizing signal, and a third D-type flip-flop 45
having a data input terminal for being supplied with the vertical
synchronizing signal through an inverter 44 and a reset input
terminal for being supplied with the mode setting signal.
[0100] The first and second flip-flops 41, 43 are connected to
respective input terminals of a first exclusive-OR gate 46. The
output terminal of the first exclusive-OR gate 46 and the third
flip-flop 45 are connected to respective input terminals of a
second exclusive-OR gate 47. The second exclusive-OR gate 47 has an
output terminal connected to a data input terminal of a fourth
D-type flip-flop 48, which has a reset input terminal for being
supplied with the dot clock signal. The fourth flip-flop 48 is
connected to the correction executing circuit 50 of the processing
circuit 37.
[0101] The pattern generator 38 outputs a signal for controlling
the level of correction by the correction executing circuit 50
depending on the dot clock signal, the horizontal synchronizing
signal, the vertical synchronizing signal, and the mode setting
signal. As shown in FIG. 6, the selection pattern generated by the
pattern generator 38 has the level of correction reversed for every
tricolor pixel 24 and also for every scanning line, and is reversed
for every frame.
[0102] The data correcting circuit 35 is connected to the drive
circuit 3, which is connected to the plasma display panel 2.
[0103] The drive circuit 3 includes a first data arranging circuit
52 connected to the processing circuit 37, a memory input/output
control circuit 53 connected to the first data arranging circuit
52, and a frame buffer memory 54 connected to the memory
input/output control circuit 53.
[0104] The signal input unit 34b and the dot clock generator 39 are
connected to the first data arranging circuit 52.
[0105] The first data arranging circuit 52 mixes R, G, B gradation
data supplied from the processing circuit 37 and arranges the
gradation data such that their addresses differ for respective
gradation bits.
[0106] The memory input/output control circuit 53 controls storing
of the mixed R, G, B gradation data into and reading of the mixed
R, G, B gradation data from the frame buffer memory 54. The frame
buffer memory 54 temporarily stores the mixed R, G, B gradation
data.
[0107] The drive circuit 3 also has a subfield generator 56
connected to the signal input unit 34a, a system clock generator
55, and a timing generator 57 which is connected to the memory
input/output control circuit 53.
[0108] The memory input/output control circuit 53 is connected
through a second data arranging circuit 58 to upper and lower data
drivers 59, 60, which are connected to the data electrodes 14 of
the plasma display panel 2.
[0109] The timing generator 57 is connected to a scan driver 61 and
a sustain driver 62. The scan driver 61 is connected to the
scanning electrodes 12, and the sustain driver 62 is connected to
the sustaining electrodes 13.
[0110] The system clock generator 55 generates a system clock
signal. The subfield generator 56 generates subfields of various
intervals at various times in one frame in synchronism with the
system clock signal that is generated by the system clock generator
55 based on the vertical synchronizing signal from the signal input
unit 34a.
[0111] The timing generator 57 supplies a subfield timing signal to
the memory input/output control circuit 53, the scan driver 61, and
the sustain driver 62.
[0112] The second data arranging circuit 58 converts the
arrangement of gradation data into a form corresponding to an
actual displayed image. The data drivers 59, 60 output data pulses
to the data electrodes 14 of the plasma display panel 2 depending
on gradation data.
[0113] The scan driver 61 outputs scanning pulses as drive pulses
to the scanning electrodes 12 of the plasma display panel 2
depending on the subfield timing signal from the timing generator
57. The sustain driver 62 outputs sustaining pulses as drive pulses
to the sustaining electrodes 13 of the plasma display panel 2
depending on the subfield timing signal from the timing generator
57.
[0114] When a video signal composed of many gradation data
individually set to respective gradation levels is supplied from an
external source to the plasma display apparatus 1, the display
pixels of the tricolor pixels 24 of the plasma display panel 2 are
individually energized for displaying a color image whose colors
are expressed by the pixels for desired gradations.
[0115] When a video signal representing a moving image is supplied
frame by frame to the plasma display apparatus 1, if the gradation
data of a preceding frame and the gradation data of a present frame
match a predetermined combination of gradation data, then the
gradation level of the gradation data of the present frame is
corrected to prevent false moving image contours from being
generated.
[0116] At this time, the level of correction of the gradation data
for preventing false moving image contours from being generated is
controlled depending the matrix arrangement of the pixels of the
plasma display panel 2 and the frames according to the selection
pattern.
[0117] A method of displaying moving images on the plasma display
panel 2 according to the first embodiment of the present invention
will be described below.
[0118] When a video signal composed of many gradation data
individually set to respective gradation levels is supplied frame
by frame to the signal input unit 31, the supplied analog R, G, B
gradation data are converted by the A/D converter 32 into digital
gradation data, whose gradations are inversely gamma-corrected by
the gamma corrector 33.
[0119] The corrected gradation data are supplied frame by frame to
the data correcting circuit 35, in which the gradation data are
temporarily stored frame by frame in the frame memory 36. The
processing circuit 37 reads corrective data from the LUT 40 which
are addressed by the temporarily stored gradation data of a
preceding frame and newly supplied gradation data, and adds the
corrective data to the gradation data to be displayed, for thereby
correcting the gradation data.
[0120] Depending on a vertical synchronizing signal, a horizontal
synchronizing signal, and a mode setting signal that are supplied
frame by frame to the signal input units 34a-34c, the pattern
generator 38 controls the level of data correction by the
processing circuit 37 with a selection pattern.
[0121] Specifically, in the processing circuit 37, the first
flip-flop 41 frequency-divides the frequency of the dot clock
signal from the dot clock generator 39 to half, and is reset by the
horizontal synchronizing signal to output a low level at the time
of starting a main scanning cycle.
[0122] The horizontal synchronizing signal from the signal input
unit 34b has positive-going edges made effective by the inverter
42, and is frequency-divided as a clock signal to half by the
second flip-flop 43. Output signals from the first and second
flip-flops 41, 43 are converted by the exclusive-OR gate 46 into a
checkerboard-like selection pattern which has the level of
correction reversed for every tricolor pixel and every scanning
line.
[0123] The vertical synchronizing signal from the signal input unit
34a has positive-going edges made effective by the inverter 44, and
is frequency-divided as a clock signal to half by the third
flip-flop 45. Output signals from the third flip-flop 45 and the
exclusive-OR gate 46 are converted into a selection pattern which
is reversed for every frame. The resultant selection pattern is
outputted from the fourth flip-flop 48 to the processing circuit 37
in synchronism with the mode setting signal.
[0124] In the plasma display apparatus 1 according to the first
embodiment, the processing circuit 37 is arranged to correct false
moving image contours excessively and to decimate such excessive
correction events based on the selection pattern.
[0125] For example, as shown in FIGS. 7a through 7g and the Table
shown below, when the gradation level of gradation data which is
expressed in one of 64 6-bit gradation levels changes from "32" to
"31", the gradation data typically suffers a false moving image
contour.
1 TABLE 1 Data Pixel data of Pixel data of Pixel data of Signal
(n-1)th frame nth frame (n+1)th frame Input 100000 011111 011111
Uncorrected 100000 011111 011111 output Optimally 100000 101010
011111 corrected output Excessively 100000 110100 011111 corrected
output
[0126] According to a conventional process for correcting all the
gradation data, corrective data of "11", for example, is added to
the gradation data, so that the gradation level of the gradation
data in the present frame is "42".
[0127] With the plasma display apparatus 1 according to the first
embodiment, since the gradation level of only half of the gradation
data is corrected, corrective data of "21", for example, is added
to the gradation data, so that the gradation level of the gradation
data in the present frame is "52".
[0128] Of display pixels at positions where false moving image
contours occur, one half positioned in a checkerboard pattern as
shown in FIG. 6 is excessively corrected, and the remaining half is
not corrected.
[0129] R, G, B gradation data which have been corrected for false
moving image contours and outputted frame by frame from the data
correcting circuit 35 are mixed and arranged such that their
addresses differ for respective gradation bits. The arranged
gradation data are then temporarily stored in the frame buffer
memory 54 by the memory input/output control circuit 53.
[0130] The subfield generator 56 which is supplied with a system
clock signal from the system clock generator 55 generates subfields
in synchronism with the system clock signal based on the vertical
synchronizing signal The subfield generator 56 outputs a subfield
timing signal to the timing generator 57, from which the subfield
timing signal is supplied to the memory input/output control
circuit 53, the scan driver 61, and the sustain driver 62.
[0131] The memory input/output control circuit 53 reads the frame
of gradation data temporarily stored in the frame buffer 54 in
synchronism with the subfield timing signal. The frame of gradation
data is converted into a form corresponding to an actual displayed
image by the second data arranging circuit 58, and then outputted
as data pulses from the data drivers 61, 62 to the data electrodes
14 of the plasma display panel 2.
[0132] At the same time, the scan driver 61 outputs scanning pulses
as drive pulses in response to the subfield timing signal to the
scanning electrodes 12 of the plasma display panel 2 for thereby
writing wall charges in display pixels which are to emit light, in
each subfield.
[0133] When wall charges are written in all the display pixels, the
sustain driver 62 outputs sustaining pulses as drive pulses to the
sustaining electrodes 13 to cause the display pixels in which the
wall charges have been written to emit light.
[0134] Since the wall charges are written according to the data
pulses and the scanning pulses and the sustaining pulses are
outputted in each subfield of one frame, the display pixels of the
plasma display panel 2 display respective gradations.
[0135] Three R, G, B display pixels are combined into a single
tricolor pixel 24, and a plurality of tricolor pixels 24 are
arranged in a two-dimensional matrix. Therefore, a fully colored
image whose colors are rendered by the respective tricolor pixels
24 is displayed on the plasma display panel 2.
[0136] The plasma display apparatus 1 displays successive frames of
a fully colored image, and hence displays a fully colored moving
image whose colors are rendered by the respective tricolor pixels
24.
[0137] Because gradations are expressed according to the subfield
process, when the displayed image moves on the plasma display panel
2, the displayed image tends to suffer a false moving image
contour. The plasma display apparatus 1 corrects the gradation
levels of those display pixels which are expected to suffer a false
moving image contour.
[0138] The gradation levels of display panels are excessively
corrected as is the case with the conventional process, and the
excessive correction is carried out for only half of the display
pixels which are dispersed two-dimensionally according to the
selection pattern.
[0139] Stated otherwise, a region where a false moving image
contour occurs contains excessively corrected display pixels and
uncorrected display pixels which are mixed together in a
two-dimensional pattern at a ratio of 1:1. Therefore, the display
pixels are visually perceived as being adequately corrected as a
whole.
[0140] As shown in FIGS. 7a and 7b, when the gradation level of
gradation data which is expressed in one of 64 6-bit gradation
levels changes from "32" to "31", the gradation data suffers a
false moving image contour.
[0141] According to the conventional process for uniformly
correcting all the gradation data at a position where a false
moving image contour is generated, corrective data of "11" is added
to the gradation data, so that the gradation level of the gradation
data in the present frame is "42", as shown in FIGS. 7c and 7d.
[0142] If the gradation level of "31" follows subsequently, then
when the corrected gradation level of "42" changes to "31", a false
moving image contour occurs.
[0143] With the plasma display apparatus 1 according to the first
embodiment, as shown in FIGS. 7e and 7f, since corrective data of
"21" is added to one half of the gradation data at the position
where a false moving image contour is generated, so that the
gradation level of the gradation data in the present frame is "52".
However, the gradation level of the remaining half of the gradation
data remains to be "31" and is not corrected.
[0144] The excessively corrected gradation level and the
uncorrected gradation level are visually perceived as being
averaged as a whole. Therefore, as shown in FIG. 7g, a false moving
image contour is effectively prevented from happening as a
whole.
[0145] Consequently, the plasma display apparatus 1 according to
the first embodiment is capable of correcting false moving image
contours well when the display pixels arranged in a matrix are
energized to express gradations according to the subfield process
to display moving images on the plasma display panel 2.
[0146] Inasmuch as the plasma display panel 2 has a matrix of
tricolor pixels 24 each comprising three R, G, B display pixels,
the plasma display apparatus 1 can display colored moving images of
good quality whose colors are rendered by the pixels.
[0147] Furthermore, the pattern generator 38 generates a selection
pattern on a real-time basis with a hardware arrangement from
various signals that have been extracted from a video signal.
Therefore, it is not necessary to register in advance a selection
pattern as image data in a memory.
[0148] The selection pattern has the level of correction reversed
for every square tricolor pixel 24, composed of R, G, B display
pixels, and also for every scanning line. Therefore, the level of
correction is dispersed uniformly in a pattern of minute units for
effectively preventing visually perceived false moving image
contours from being generated.
[0149] The selection pattern which corresponds to the matrix of
tricolor pixels 24 of the plasma display panel 2 is reversed every
frame. Therefore, excessively corrected positions and uncorrected
positions on the plasma display panel 2 are also dispersed in time
for effectively preventing visually perceived false moving image
contours from being generated.
[0150] The LUT 40 of the processing circuit 37 stores corrective
data that can be addressed by gradation data of a preceding frame
and gradation data of a present frame. Therefore, the gradation
data of the present frame can be corrected at a desired gradation
level depending on its combination with the gradation data of the
preceding frame.
[0151] In the above embodiment, the plasma display apparatus 1 as
the moving image display apparatus is a full color plasma display
apparatus. However, the present invention is applicable to various
image display apparatus in which the subfield process can be
employed for displaying gradations at respective pixels.
[0152] In the above embodiment, the pattern generator 38 generates
a selection pattern on a real-time basis with a hardware
arrangement from various signals that have been extracted from a
video signal. However, it is possible to read a selection pattern
which has been stored in advance as image data in a memory, and use
the selection pattern for the control of the level of
correction.
[0153] In the above embodiment, the level of excessive correction
on gradation data in a region where a false moving image contour is
controlled by a selection pattern. However, for such correction
level control, it is possible to combine slightly excessive
correction and insufficient correction, combine highly excessive
correction and opposite correction, and combine a plurality of
stages of correction.
[0154] According to an experiment conducted by the inventors, the
best results were obtained with a combination in which bit status
changes responsible for a false moving image contour in a
particular luminance transition were shifted one frame in time.
[0155] With the plasma display apparatus 1, since the level of
excessive correction is controlled, one half of gradation data may
be corrected at an excessive level that is established in advance,
as with the conventional process, and the remaining half of
gradation data may not be corrected at all. The overall processing
operation of the plasma display apparatus 1 is thus simple and
preferable.
[0156] In the above embodiment, the level of excessive correction
is controlled in a rectangular range comprising a pixel for
preventing false moving image contours in a pattern of minute
units. However, the above range for correcting the level of
correction may comprise a plurality of pixels for lessening the
burden on the processing operation of the apparatus.
[0157] In the above embodiment, the two-dimensional selection
pattern corresponding to the matrix of the plasma display panel 2
is switched in time. However, the two-dimensional selection pattern
may be used as a fixed pattern without being switched in time.
[0158] In the above embodiment, because gradation data of a present
frame is corrected in combination with gradation data of a
preceding frame, the LUT 40 stores corrective data in advance which
can be addressed by the gradation data of the preceding frame and
the gradation data of the present frame.
[0159] However, the LUT 40 need not be employed, but a processor
(not shown) may be employed to correct the gradation data of the
present frame using parameters representing the gradation data of
the preceding frame and the gradation data of the present
frame.
[0160] According to the process of registering the corrective data
in advance, the gradation data of the present frame can be
corrected at a desired gradation level in combination with the
gradation data of the preceding frame. However, if many gradation
levels are involved, then it is necessary to register a large
amount of corrective data.
[0161] According to the process of correcting the gradation data
based on real-time processing, however, it is not necessary to
register a large amount of corrective data, but there may be
instances where it is difficult to correct the gradation data
reliable at a desired gradation level.
[0162] Since these two processes have both advantages and
disadvantages, it is preferable to select one of the processes in
view of various conditions including apparatus performance levels
and specifications.
[0163] A second embodiment of the present invention will be
described below with reference to FIGS. 8 and 9a through 9e. Those
parts of the second embodiment which are identical to those of the
first embodiment are denoted by identical reference characters and
will not be described in detail below.
[0164] A plasma display apparatus (not shown) as a moving image
display apparatus according to the second embodiment has a hardware
arrangement which is identical to that of the plasma display
apparatus 1 according to the first embodiment, and differs from the
plasma display apparatus 1 with respect to how subfields are
established.
[0165] In the plasma display apparatus 1 according to the first
embodiment, subfields are simply arranged in the order of their
intervals within a frame. In the plasma display apparatus according
to the second embodiment, however, as shown in FIG. 8, those of
subfields "MSB" which have long intervals are divided into a
plurality of subfields, which are dispersed.
[0166] For example, if a video signal is to be represented in 256
8-bit binary gradation levels, then, each of a longest subfield
"MSB-0" and a second subfield "MSB-1" is divided into a plurality
of subfields, and those divided subfields are dispersed.
[0167] When the gradation level of a certain display pixel varies
from "127" to "128", as shown in FIG. 9a, since drive pulses are
dispersed, a false moving image contour is prevented from occurring
even without the correction level control according to the present
invention if the moving image moves at a low speed, as shown in
FIG. 9b.
[0168] With subfields divided as described above, it is difficult
to properly establish corrective data for excessively corrected
pixels for visually eliminating a false moving image contour in
combination with uncorrected pixels.
[0169] According to the second embodiment, gradation data of a
preceding frame is simply regarded as corrected gradation data, and
the corrected gradation data and uncorrected gradation data are
disposed according to a selection pattern.
[0170] In the plasma display apparatus according to the second
embodiment, subfields having long intervals are divided into a
plurality of subfields, and gradation data of a preceding frame is
regarded as corrected gradation data, and the corrected gradation
data and uncorrected gradation data are disposed according to a
selection pattern.
[0171] Since a false moving image contour is dispersed in a wide
range, the false moving image contour is increased in area and
averaged as a whole, thus improving the quality of a moving image
which is visually perceived by the human eye.
[0172] Those gradation data of low gradations for which no
subfields are divided and which are arranged in the order of their
time intervals are preferably corrected in the same manner as with
the first embodiment, and dispersed according to a selection
pattern.
[0173] A third embodiment of the present invention will be
described below with reference to FIG. 10.
[0174] In the plasma display apparatus (not shown) used as a moving
image display apparatus according to the third embodiment, a
longest subfield "MSB-0" is divided into a subfield which is 1/2 of
the subfield "MSB-0" and two subfields each of which is 1/4 of the
subfield "MSB-0". Furthermore, gradation data of a preceding frame
is regarded as corrected gradation data, and the corrected
gradation data and uncorrected gradation data are disposed
according to a selection pattern.
[0175] In the plasma display apparatus according to the third
embodiment, subfields having long intervals are divided into a
plurality of subfields, and gradation data of a preceding frame are
regarded as corrected gradation data, and the corrected gradation
data and uncorrected gradation data are disposed according to a
selection pattern. Therefore, a false moving image contour is
dispersed in a wide range, thus improving the quality of a moving
image which is visually perceived by the human eye.
[0176] While preferred embodiments of the present invention have
been described using specific terms, such description is for
illustrative purposes only, and it is to be understood that changes
and variations may be made without departing from the spirit or
scope of the following claims.
* * * * *