Method of and apparatus for displaying halftone images

A method displays a halftone image on a display unit by using a frame division technique that divides each frame of the halftone image into subframes each having a specific sustain discharge period to provide a specific intensity level. The method differs the position of the halftone image on the display unit from subframe to subframe in each frame. The method is capable of displaying dynamic halftone images without intensity level disturbance, smears, or false color contours.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of and an apparatus for 
displaying dynamic halftone images on, for example, a gas discharge panel 
according to a frame division technique without intensity level 
disturbance or false color contours. 
2. Description of the Related Art 
To meet a demand for large thin display units, there have been proposed 
plasma display panels, gas discharge panels, DMDs (digital micromirror 
devices), EL (electric luminescence) display panels, fluorescent display 
panels, liquid crystal display panels, etc. 
Among them, the gas discharge panels are considered to be most advantageous 
for direct-view large HDTV display units because they are simple to form a 
large unit, emit light by themselves, provide high display quality, and 
achieve high response speed. The gas discharge panels display static 
halftone images without problem. They, however, frequently cause 
disturbance and deteriorate display quality when displaying dynamic 
halftone images. It is required, therefore, to provide a method of 
displaying dynamic halftone images without disturbance. 
The details of the prior arts and their problems will be explained later 
with reference to drawings. 
SUMMARY OF THE INVENTION 
An object of the present invention is to display dynamic halftone images 
without intensity level disturbance, smears, or false color contours. 
According to the present invention, there is provided a method of 
displaying a halftone image on a display unit by using a frame division 
technique that divides each frame of the halftone image into subframes 
each having a specific sustain discharge period to provide a specific 
intensity level, comprising the step of differing a displayed position of 
the halftone image on the display unit from subframe to subframe in each 
frame. 
The displayed position in each subframe may be successively advanced 
between a first position determined by display data provided for a first 
frame and a second position determined by display data provided for a 
second frame next to the first frame. The displayed position in each 
subframe may be determined according to a motion vector set between the 
first position and the second position. The displayed position in each 
subframe may be determined according to control data determined by a 
function that is set according to characteristic values of the subframes 
constituting the frame and the position of the halftone image in a 
specific subframe. 
The method may further comprise the steps of displaying the halftone image 
at the first position in one of the subframes having a highest intensity 
level; finding a delay time between the highest intensity subframe and 
each of the other subframes; dividing each of the delay times by a frame 
period; multiplying each of the quotients by the motion vector, to provide 
each subframe vector; calculating positions according to the subframe 
vectors; and displaying the halftone image at the calculated positions in 
the corresponding subframes. 
The method may further comprise the steps of selecting one of the subframes 
as a vector origin; displaying the halftone image in the selected 
subframe; finding a delay time between the selected subframe and each of 
the other subframes; dividing each of the delay times by a frame period; 
multiplying each of the quotients by the motion vector, to provide each 
subframe vector; calculating positions according to the subframe vectors; 
and displaying the halftone image at the calculated positions in the 
corresponding subframes. 
An origin of the motion vector may be determined at a start position of a 
sustain discharge period of the subframes, and the delay time of each 
subframe may be determined at a start position of a sustain discharge 
period of a corresponding subframe. An origin of the motion vector may be 
determined at a center position of a sustain discharge period of the 
subframes, and the delay time of each subframe may be determined at a 
center position of a sustain discharge period of a corresponding subframe. 
When the number of subframes to be turned ON in the frame is smaller than a 
predetermined number, the method may further comprise the steps of forming 
at least one subframe groups; selecting one of the subframe groups as a 
vector origin; displaying the halftone image in the selected subframe 
group; finding a delay time between the intensity level center of the 
selected subframe group and the intensity level center of each of the 
other subframe groups; dividing each of the delay times by a frame period; 
multiplying each of the quotients by the motion vector, to provide each 
subframe group vector; calculating positions according to the subframe 
group vectors; and displaying the halftone image at the calculated 
positions in the corresponding subframe groups. 
According to the present invention, there is also provided a method of 
displaying a halftone image on a display unit by using a frame division 
technique that divides each frame of the halftone image into subframes 
each having a specific sustain discharge period to provide a specific 
intensity level, comprising the step of turning OFF at least one of 
subframes that are coupled together when displaying the halftone image 
with different intensity levels, thereby suppressing a bright part to be 
produced by the coupled specific subframes. 
The number of subframes to be additionally turned OFF or ON may be 
determined according to a scroll speed of the halftone image or the 
intensity levels. The subframes adjacent to the specific subframes may be 
turned OFF or ON, when the scroll speed of the halftone image is high. 
Further, according to the present invention, there is provided a method of 
displaying a halftone image on a display unit by using a frame division 
technique that divides each frame of the halftone image into subframes 
each having a specific sustain discharge period to provide a specific 
intensity level, comprising the step of turning ON at least one of 
subframes that are OFF when displaying the halftone image with different 
intensity levels, thereby suppressing a dark part that are produced by the 
specific subframes. 
The number of subframes to be additionally turned OFF or ON may be 
determined according to a scroll speed of the halftone image or the 
intensity levels. The subframes adjacent to the specific subframes may be 
turned OFF or ON, when the scroll speed of the halftone image is high. 
In addition, according to the present invention, there is also provided an 
apparatus for displaying a halftone image on a display unit by using a 
frame division technique that divides each frame of the halftone image 
into subframes each having a specific sustain discharge period to provide 
a specific intensity level, comprising a motion vector detection unit for 
detecting a motion vector that indicates a moving direction of the 
halftone image, by comparing display data for a first frame of the 
halftone image with display data for a second frame next to the first 
frame; and a differing unit for differing the display position of the 
halftone image from subframe to subframe in the first frame according to 
the motion vector. 
The apparatus may further comprise a dividing unit for dividing each delay 
time, which is found between the first subframe and each of the other 
subframes in the given frame, by a frame period and providing each 
correction value; and a frame interpolator for multiplying the display 
data for the given frame by each of the correction values, to generate 
display data for each of the subframes of the given frame, so that the 
halftone image is displayed according to the display data of the 
subframes. 
According to the present invention, there is provided a method of 
displaying a halftone image on a display unit by using a frame division 
technique that divides each frame of the halftone image into subframes 
each having a specific sustain discharge period to provide a specific 
intensity level, comprising the steps of comparing an intensity level of a 
given pixel between consecutive frames when the intensity level of the 
pixel changes between the consecutive frames; and enabling or disabling at 
least one intensity level adjusting subframe in the subframes of the frame 
of the pixel in accordance with the result of the comparing step. 
The step of enabling or disabling the intensity level adjusting subframe 
may comprise the step of enabling an intensity level adjusting subframe in 
the subframes of one of consecutive frames that cause a change in 
intensity level between them, to substantially satisfy the following 
expressions: S1.ltoreq.S2+.DELTA.S.ltoreq.S3 or 
S1.gtoreq.S2+.DELTA.S.gtoreq.S3 where S1 is an average of B(t), which is a 
temporal change in a stimulus on a human eye, before the change of 
intensity level, S2 is an average of B(t) during the change of intensity 
level, S3 is an average of B(t) after the change of intensity level, and 
.DELTA.S is an average of a temporal change in a stimulus on a human eye 
due to the intensity level adjusting subframe. 
The step of enabling or disabling the intensity level adjusting subframe 
may comprise the step of enabling an intensity level adjusting subframe to 
substantially satisfy the following expressions: 
0.ltoreq..DELTA.S.ltoreq.2(S1-S2) or 0.ltoreq..DELTA.S.ltoreq.2(S3-S2) 
where S1 is an average of B(t), which is a temporal change in a stimulus 
on a human eye, before the change of intensity level, S2 is an average of 
B(t) during the change of intensity level, S3 is an average of B(t) after 
the change of intensity level, and .DELTA.S is an average of a temporal 
change in a stimulus on a human eye due to the intensity level adjusting 
subframe. 
The step of enabling or disabling the intensity level adjusting subframe 
may comprise the step of disabling an intensity level adjusting subframe 
in the subframes of one of consecutive frames that cause a change in 
intensity level between them, to substantially satisfy the following 
expressions: S1.ltoreq.S2-.DELTA.S.ltoreq.S3 or 
S1.gtoreq.S2-.DELTA.S.gtoreq.S3 where S1 is an average of B(t), which is a 
temporal change in a stimulus on a human eye, before the change of 
intensity level, S2 is an average of B(t) during the change of intensity 
level, S3 is an average of B(t) after the change of intensity level, and 
.DELTA.S is an average of a temporal change in a stimulus on a human eye 
due to the intensity level adjusting subframe. 
The step of enabling or disabling the intensity level adjusting subframe 
may comprise the step of enabling an intensity level adjusting subframe to 
substantially satisfy the following expressions: 
0.ltoreq..DELTA.S.ltoreq.2(S2-S1) or 0.ltoreq..DELTA.S.ltoreq.2(S2-S3) 
where S1 is an average of B(t), which is a temporal change in a stimulus 
on a human eye, before the change of intensity level, S2 is an average of 
B(t) during the change of intensity level, S3 is an average of B(t) after 
the change of intensity level, and .DELTA.S is an average of a temporal 
change in a stimulus on a human eye due to the intensity level adjusting 
subframe. 
The intensity level adjusting subframe may be enabled or disabled at or 
around the center of original subframes that are enabled to provide 
different intensity levels between consecutive frames. The subframes may 
be arranged in order to enable or disable the intensity level adjusting 
subframe at or around the center of original subframes that are enabled to 
provide different intensity levels between consecutive frames. The 
subframes of each frame may be arranged such that one having the highest 
intensity level and one having the second highest intensity level are not 
adjacent to each other. 
According to the present invention, there is also provided a method of 
displaying a halftone image on a display unit by using a frame division 
technique that divides each frame of the halftone image into subframes 
each having a specific sustain discharge period to provide a specific 
intensity level, comprising the steps of comparing display signals 
provided for consecutive frames with each other; and enabling or disabling 
a predetermined bit of the display signals according to a result of the 
comparison. 
The step of enabling or disabling the predetermined bit of the display 
signals may comprise the step of enabling or disabling a predetermined bit 
of a display signal provided for a given pixel when the intensity level of 
the pixel is changed temporally, thereby enabling or disabling an 
intensity level adjusting subframe of the pixel. The step of enabling or 
disabling the predetermined bit of the display signals may comprise the 
step of enabling or disabling a predetermined bit of a display signal 
provided for a given pixel when the intensity level of the pixel is 
changed temporally, thereby enabling or disabling an intensity level 
adjusting subframe of the pixel and smoothing a change in the intensity 
level of the pixel between consecutive frames. 
The step of enabling or disabling the predetermined bit of the display 
signals may comprise the steps of comparing display signals provided for 
consecutive frames with each other; and enabling or disabling a 
predetermined intensity level adjusting subframe in at least one of the 
frames when enabled bits of the display signals change between the frames. 
The step of enabling or disabling the predetermined bit of the display 
signals may comprise the step of enabling or disabling a predetermined 
intensity level adjusting subframe in one of consecutive frames "n" and 
"n+1" when the state of the most significant bit of each display signal 
provided for the frames changes between the frames. The step of enabling 
or disabling the predetermined bit of the display signals may comprise the 
step of enabling or disabling a predetermined intensity level adjusting 
subframe in one of consecutive frames "n" and "n+1" when the state of a 
highest bit of each display signal provided for the frames changes between 
the frames. 
The subframes in each frame may be arranged in ascending order of the 
intensity levels thereof, and the step of enabling or disabling the 
predetermined bit of the display signals may comprise the step of enabling 
a predetermined intensity level adjusting bit of a display signal provided 
for a frame "n+1" when the highest intensity subframe of a frame "n" is 
disabled and when the highest intensity subframe of the frame "n+1" is 
enabled. The subframes in each frame may be arranged in ascending order of 
the intensity levels thereof, and the step of enabling or disabling the 
predetermined bit of the display signals may comprise the step of 
disabling a predetermined intensity level adjusting bit of a display 
signal provided for a frame "n+1" when the highest intensity subframe of a 
frame "n" is enabled and when the highest intensity subframe of the frame 
"n+1" is disabled. 
The subframes in each frame may be arranged in descending order of the 
intensity levels thereof, and the step of enabling or disabling the 
predetermined bit of the display signals may comprise the step of 
disabling a predetermined intensity level adjusting bit of a display 
signal provided for a frame "n" when the highest intensity subframe of the 
frame "n" is disabled and when the highest intensity subframe of a frame 
"n+1" is enabled. The subframes in each frame may be arranged in ascending 
order of the intensity levels thereof, and the step of enabling or 
disabling the predetermined bit of the display signals may comprise the 
step of enabling a predetermined intensity level adjusting bit of a 
display signal provided for a frame "n" when the highest intensity 
subframe of the frame "n" is enabled and when the highest intensity 
subframe of a frame "n+1" is disabled. 
The subframes in each frame may be arranged with one having the second 
highest intensity level at the top and one having the highest intensity 
level at the end, and the step of enabling or disabling the predetermined 
bit of the display signals may comprise the step of enabling a 
predetermined intensity level adjusting bit of a display signal provided 
for a frame "n+1" when the highest intensity subframe of a frame "n" is 
disabled and when the highest intensity subframe of the frame "n+1" is 
enabled. The subframes in each frame may be arranged with one having the 
second highest intensity level at the top and one having the highest 
intensity level at the end, and the step of enabling or disabling the 
predetermined bit of the display signals may comprise the step of 
disabling a predetermined intensity level adjusting bit of a display 
signal provided for a frame "n+1" when the highest intensity subframe of a 
frame "n" is enabled and when the highest intensity subframe of the frame 
"n+1" is disabled. 
The subframes in each frame may be arranged with one having the highest 
intensity level at the top and one having the second highest intensity 
level at the end, and the step of enabling or disabling the predetermined 
bit of the display signals may comprise the step of disabling a 
predetermined intensity level adjusting bit of a display signal provided 
for a frame "n+1" when the highest intensity subframe of a frame "n" is 
disabled and when the highest intensity subframe of the frame "n+1" is 
enabled. The subframes in each frame may be arranged with one having the 
highest intensity level at the top and one having the second highest 
intensity level at the end, and the step of enabling or disabling the 
predetermined bit of the display signals may comprise the step of enabling 
a predetermined intensity level adjusting bit of a display signal provided 
for a frame "n+1" when the highest intensity subframe of a frame "n" is 
enabled and when the highest intensity subframe of the frame "n+1" is 
disabled. 
Further, according to the present invention, there is also provided an 
apparatus for displaying a halftone image on a display unit by using a 
frame division technique that divides each frame of the halftone image 
into subframes each having a specific sustain discharge period to provide 
a specific intensity level, comprising a frame memory for storing display 
data of a given frame; a comparator for comparing the display data stored 
in the frame memory with display data of the next frame; and a data 
addition unit for adding data from the comparator to the display data of 
one of the frames.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
For a better understanding of the preferred embodiments of the present 
invention, the problem in the prior art will be explained. 
A conventional memory-type gas discharge panel displays halftone images 
according to a frame division technique that divides each frame of an 
image into N subframes each providing a specific intensity level. The 
subframes are SF0, SF1, SF2, . . . , SF(N-1) that provide intensity levels 
of 2.sup.0, 2.sup.1, 2.sup.2, . . . , 2.sup.N-1, respectively. Each frame 
displays a given intensity level by enabling and disabling the subframes 
thereof, and the human eye sees the sum of the intensity levels of enabled 
subframes of the frame due to the persistence characteristic of the human 
eye. The number of intensity levels realized in each frame by combinations 
of subframes is 2.sup.N. 
FIG. 1 shows eight subframes (N=8) SF0 to SF7 contained in a frame. The 
subframe SF0 represents a lowest intensity level and corresponds to a 
least significant bit b0 of display data. The subframe SF7 represents a 
highest intensity level and corresponds to a most significant bit b7 of 
display data. 
If frames that represent similar intensity levels with quite different 
combinations of subframes alternate, flicker will occur to deteriorate 
display quality. 
FIG. 2 shows the statuses of subframes of frames that display intensity 
levels 127 and 128. As shown in FIG. 2, in the intensity level 127, the 
subframes SF0 to SF6 are enabled (turning ON) and the subframe SF7 is 
disabled (turning OFF); on the other hand, in the intensity level 128, the 
subframes SF0 to SF6 are disabled (OFF) and the subframe SF7 is enabled 
(ON). 
When these frames are alternated, there will be a frame period containing 
only OFF subframes and a frame period containing only ON subframes. 
These ON and OFF frames are alternated to cause flicker. This phenomenon 
frequently occurs due to conversion errors or noise when converting an 
analog image involving smoothly changing intensity levels into a digital 
image. The conversion errors or noise are amplified into flicker to 
deteriorate display quality. 
To suppress flicker, Japanese Unexamined Patent Publication No. 3-145691 
arranges the subframes of each frame in order of SF0, SF2, SF4, SF6, SF7, 
SF5, SF3, and SF1. 
Flicker occurs when frames that display similar intensity levels with quite 
different combinations of subframes are alternated. The flicker becomes 
stronger as intensity levels increase. To solve flicker, Japanese 
Unexamined Patent Publication No. 4-127194 halves the highest intensity 
level subframe and inserts a subframe having a lower intensity level 
between them. 
Japanese Unexamined Patent Publication No. 5-127612 reports that the frame 
division technique sometimes provides rough, low-quality dynamic images, 
and proposes a method of improving the frame division technique. 
The proposal employs a unit for doubling a frame frequency of less than 70 
Hz in a display unit. Each frame of the doubled frame frequency has at 
least one normal-bit subframe including a highest-intensity-level subframe 
and at least one under-bit subframe. The disclosure displays a static 
image with every two frames representing an intensity level, and a dynamic 
image with every frame representing an intensity level. This technique 
creates display data for the doubled frames according to input display 
data. 
FIG. 3 shows a first frame displaying intensity level 31 and a second frame 
displaying intensity level 32. The first and second frames are doubled 
frames. In the first and second frames, subframes 31a and 32a provide an 
identical intensity level, and subframes 31b and 32b provide another 
identical intensity level. These subframes are normal-bit subframes. The 
other subframes are under-bit subframes. 
The prior art may cause no intensity level disturbance when displaying 
static images or slow dynamic images. It, however, causes intensity level 
disturbance when displaying fast dynamic images. The intensity level 
disturbance will be explained with reference to FIGS. 4 to 7 in which each 
frame consists of six subframes that are arranged in order of SF5, SF4, 
SF3, SF2, SF1, and SF0. 
FIGS. 4 to 6 show different types of intensity level disturbance according 
to a prior art and FIG. 7 shows a dark part formed between intensity 
levels 31 and 32 during a right scroll. 
A vertical blue line is displayed with the subframe SF5 being enabled 
(turned ON) and is scrolled from the right to the left. When the blue line 
is scrolled at a speed of a pixel per frame, the human eye sees as if it 
is smoothly moving even over red and green subpixels that are not turned 
ON actually. The smooth movement is visible even when the blue line is 
moved at a speed of several pixels per frame. This phenomenon occurring on 
the human eye is called an "apparent motion" or ".beta. motion" in 
psychology. 
In FIG. 4, a vertical blue line is displayed with the subframes SF5 and SF4 
being enabled and is scrolled from the right to the left at a speed of a 
pixel per frame. In this case, the human eye sees the subframes SF5 and 
SF4 being spatially separated from each other. Although the subframe SF5 
of a blue subpixel is enabled in FIG. 4, the human eye sees as if it is 
moving over red and green subpixels. 
When the subframe SF4 is turned ON after a write period of about 2 msec 
after turning ON the subframe SF5, the human eye sees as if the subframe 
SF4 follows the subframe SF5 in the scrolling direction. If all subframes 
of each frame are enabled and scrolled as shown in FIG. 5, they are viewed 
as if they are spatially separated from one another. 
FIG. 6 shows a vertical blue line displayed with the subframes SF5 to SF0 
being enabled and scrolled from the right to the left at a speed of two 
pixels per frame. Due to the extended intervals to two pixels, the human 
eye sees faster movements of the subframes. When the subframe SF4 is 
turned ON, the subframe SF5 is ahead thereof. Namely, the human eye sees 
the subframes spreading for a distance corresponding to a frame period. 
Although the subframes of each frame actually emit light in the same pixel, 
the human eye sees as if they emit light in different pixels when a 
dynamic image is displayed. In this case, an intensity level assigned to a 
given frame is not displayed as the sum of the subframes of the frame, 
thereby causing intensity level disturbance. 
FIGS. 7 and 8 show dark and bright parts that appear between specific 
intensity levels when displaying a halftone image of a single color and 
scrolling the image. 
In the figures, each frame consists of six subframes SF5 to SF0 that are 
arranged in descending order of the intensity levels thereof. A halftone 
image is displayed with blue whose intensity level is gradually increased 
from the left to the right, and the image is scrolled to the right. A dark 
part appears between specific intensity levels that involve quite 
different numbers of ON subframes. 
Such dark part is produced between, for example, intensity levels 31 and 
32, 15 and 16, or 7 and 8. In FIG. 7, the image is moved at a speed of two 
pixels per frame, and a dark part appears between intensity level 31, 
which is realized by enabling (turning ON) the subframes SF4 to SF0, and 
intensity level 32, which is realized by enabling the subframe SF5 alone. 
The dark part occurs because the subframes are spatially separated from one 
another when displaying dynamic images. The dark part of FIG. 7 extends 
for one pixel, i.e., three red (R), green (G), and blue (B) subpixels. 
When the image is scrolled to the left, a bright part occurs between 
intensity levels 31 and 32 as shown in FIG. 9. 
When displaying a dynamic image with single color or with the same 
subframes being enabled in each subpixel of a given pixel, the image may 
involve a dark or bright part. When displaying a dynamic image with 
different subframes being enabled in the subpixels of a given pixel, the 
image may involve unwanted colors. 
For example, false color contours of amaranthine and green appear along the 
flesh-colored cheek of an image of a person displayed, when the person 
displayed looks back. 
Next, preferred embodiments of the present invention will be explained with 
reference to the drawings. 
A first aspect of the present invention provides a method of displaying a 
halftone image on a display unit according to a frame division technique 
that divides each frame of the halftone image into subframes each having 
an addressing period and a specific sustain discharge period to provide a 
specific intensity level. When displaying dynamic halftone images, the 
method differs the position of each frame of image on the display unit 
from subframe to subframe. More precisely, the method successively 
advances the position of each dynamic image on the display unit from 
subframe to subframe between a first position determined by display data 
provided for a given frame and a second position determined by display 
data provided for the next frame. The method determines the position of 
the dynamic image in each subframe according to a motion vector set 
between the first and second positions. 
FIG. 10 is a block diagram showing a display unit employing a halftone 
image displaying method according to a first embodiment of the first 
aspect of the present invention. The display unit 1 has a display panel 2, 
an X-decoder 3-1, an X-driver 3-2, a Y-decoder 4-1, a Y-driver 4-2, and a 
controller 5. The controller 5 controls the decoders and drivers, which 
drive the panel 2. 
A frame of an image to be displayed on the panel 2 consists of subframes 
that are combined to display a required intensity level. The controller 5 
divides each subframe into an addressing period and a sustain discharge 
period. The sustain discharge period of each subframe is set to provide an 
intensity level specific to the subframe. A vector detector 6 detects a 
motion vector indicating the moving direction of an image according to 
display data provided for a given frame and display data provided for the 
next frame. A display instruction unit 9 determines display positions for 
the subframes according to the motion vector. 
The panel 2 may be a memory-type gas discharge panel, an EL panel, or a 
liquid crystal panel, capable of displaying halftone images with the use 
of subframes. 
A movement calculator 7 has a divider and a multiplier. The movement 
calculator 7 finds, in each frame, a delay time between a given subframe 
and the first subframe, divides the delay time by a frame period, 
multiplies the quotient by the motion vector detected by the vector 
detector 6, and calculates a movement for the subframe. A positioner 8 
determines the position of an image to be displayed in a given subframe. 
The display instruction unit 9 provides an instruction to display the 
image according to the position determined by the positioner 8. These 
units 6 to 9 form a frame interpolator 10. 
More precisely, the vector detector 6 compares display data for a given 
frame with display data for the next frame and detects a motion vector 
that indicates the moving direction of a dynamic halftone image 
represented with the display data. The movement calculator 7 finds a delay 
time between a given subframe and the first subframe, divides the delay 
time by a frame period, to provide a correction value, multiplies the 
motion vector by the correction value, and calculates a movement for the 
subframe. The positioner 8 determines the position of an image to be 
displayed in the subframe according to the movement calculated by the 
movement calculator 7. The display instruction unit 9 provides an 
instruction to display the image according to the position determined by 
the positioner 8. Then, the halftone image is displayed on the display 
panel 2. 
FIGS. 11A to 11D show the display positions of a halftone image according 
to a prior art. The halftone image is displayed in frames n and n+1 
according to display data D1. In FIG. 11A, the image is displayed at a 
position P1 having coordinates (X1, Y1) in the frame n. In FIG. 11B, the 
image is displayed at a position P2 having coordinates (X2, Y2) in the 
frame n+1. FIG. 11C shows a motion vector A oriented from the first 
position P1 in the frame n toward the second position P2 in the frame n+1. 
FIG. 11D shows spatially separated subframes between the positions P1 and 
P2 although the last one of the subframes actually emits light at the 
position P1. 
FIG. 12A shows the positions of the same halftone image in the subframes of 
a given frame according to the first aspect of the present invention, and 
FIG. 12B shows the timing of enabling the subframes. 
Due to the apparent motion of the human eye, the display positions of the 
subframes SF5 to SF0 are P15 to P10, respectively, as shown in FIG. 11D. 
These display positions are expressed as follows: 
##EQU1## 
where 
EQU a.sub.0 =(t.sub.5 -t.sub.5)/t.sub.F 
EQU a.sub.1 =(t.sub.5 -t.sub.4)/t.sub.F 
EQU a.sub.2 =(t.sub.5 -t.sub.3)/t.sub.F 
EQU a.sub.3 =(t.sub.5 -t.sub.2)/t.sub.F 
EQU a.sub.4 =(t.sub.5 -t.sub.1)/t.sub.F 
EQU a.sub.5 =t.sub.5 /t.sub.F 
EQU P1=(X1, Y1) 
EQU A=(X2-X1, Y2-Y1) 
As shown in FIG. 11D, the image is seen at different positions in the 
subframes, respectively, according to the prior art, to provide unwanted 
intensity levels or colors and cause intensity level disturbance or false 
color contours. On the other hand, the first aspect of the present 
invention compares display data provides for consecutive frames with each 
other, detects a motion vector, finds in each frame a delay time between a 
given subframe and the first subframe, divides the delay time by a frame 
period, to provide a coefficient, multiplies the motion vector by the 
coefficient, and calculates a display position for each subframe, thereby 
suppressing intensity level disturbance or false color contours and 
improving display quality. 
As shown in (1) to (6) of FIG. 12A, the first aspect of the present 
invention gradually moves the image from the first display position P1 to 
the second display position P2 according to calculated data. 
The first aspect of the present invention determines a motion vector 
according to a first position of display data provided for a given frame 
and a second position of display data provided for the next frame. 
FIG. 12B shows a frame consisting of six subframes SF5 to SF0 that are 
arranged in this order. The subframe SF5 provides the highest intensity 
level and the subframe SF0 provides the lowest intensity level. 
FIG. 12A(1) shows that the first subframe SF5 of the frame n is carrying 
out sustain discharge. The subframe SF5 displays an image according to the 
display data D1 at the first position P1 (Q10). 
The second display position P2 indicated with a dotted line is a position 
where the frame n+1 displays the image. 
The motion vector A indicates display coordinates or the moving state of a 
display block (Xij) between the frames n and n+1. 
FIG. 12A(2) shows that the second subframe SF4 of the frame n is carrying 
out sustain discharge to display the image at a position Q11 between the 
positions P1 and P2. 
The present invention uses a delay time t1 between the sustain discharge of 
the subframe SF4 and the sustain discharge of the subframe SF5 as a 
control factor. The delay time t1 is divided by a frame period t.sub.F, 
and the quotient is multiplied by the motion vector A, to calculate the 
position Q11. 
In FIG. 12A(2), the quotient t1/t.sub.F is multiplied by the motion vector 
A, to provide an individual vector A1 according to which the display 
position Q11 for the subframe SF4 is determined. 
Similarly, FIGS. 12A(3) to 12A(6) show display positions Q12 to Q15 for the 
subframes SF3 to SF0, respectively. These positions are calculated 
according to individual motion vectors A2 to A5 found for the subframes 
SF3 to SF0, respectively. The vectors A0 to A5 are obtained as follows: 
EQU A0=0.times.A (1) 
EQU A1=(t1/tF).times.A (2) 
EQU A2=(t2/tF).times.A (3) 
EQU A3=(t3/tF).times.A (4) 
EQU A4=(t4/tF).times.A (5) 
EQU A5=(t5/tF).times.A (6) 
The display positions Q10 to Q15 are expressed as follows: 
##EQU2## 
where Ax and Ay are the X and Y components of the motion vector A. 
EQU Ax=X2-X1 
EQU Ay=Y2-Y1 
In this way, the first aspect of the present invention divides each frame 
into at least two subframes that provide each a specific intensity level. 
The moving direction and size of a display image of each frame are 
detected pixel by pixel, or pixel block by pixel block. The first subframe 
of the frame displays the image as it is, and the next subframe displays 
the image at a position shifted from the first position in the moving 
direction. 
According to the first aspect, it is preferable to make the subframe that 
provides the highest intensity level as a vector origin. The subframe 
serving as the vector origin displays an image without moving it. 
The first aspect of the present invention forms a motion vector for a given 
frame according to display data provided for the frame and display data 
provided for the next frame, and prepares display data for each subframe 
of the frame in question according to the motion vector. This technique 
displays dynamic images without spatially dispersing the subframes of each 
frame, thereby preventing intensity level disturbance and false color 
contours. 
The first aspect employs the frame interpolator 10 (FIG. 10) to create 
display data for each subframe. 
FIG. 13 shows an example of the frame interpolator 10 according to the 
first aspect of the present invention. 
The frame interpolator 10 has a vector detector 6, which consists of a 
frame memory 61 for storing display data for a frame "n" and a detector 
62. The detector 62 receives the display data for the frame n from the 
frame memory 61 as well as display data for the next frame "n+1," and 
according to these pieces of data, provides a motion vector A for the 
display data for the frame n. A movement calculator 7 finds a delay time 
tn between the light emission timing of a given subframe SFn and the light 
emission timing of the first subframe, divides the delay time by a frame 
period tF, for example, 16.7 msec, to provide a control function tn/tF, 
multiplies the control function tn/tF by the motion vector A, and 
calculates an individual motion vector An for the subframe SFn. 
A positioner 8 determines the position of an image to be displayed in the 
subframe SFn according to the individual motion vector An. The positional 
data is supplied to the controller 5 of the display unit 1 through a 
display instruction unit 9. 
FIG. 14 is a flowchart showing the steps of the method according to the 
first aspect of the present invention. 
Step S1 reads a display position of an image in a first frame n. The 
display position P1 is equal to a position where the image is displayed in 
the subframe SF5. 
Step S2 reads a second display position P2 of the image in a second frame 
n+1. 
Step S3 calculates a motion vector A according to the first and second 
display positions P1 and P2. Step S4 selects a subframe SFn in the frame 
n. 
Step S5 finds a delay time tn between the light emission timing of the 
subframe SFn and that of the first subframe SF5. Step S6 divides the delay 
time tn by a frame period tF and provides a control function tn/tF. Step 
S7 multiplies the control function tn/tF by the motion vector A and 
calculates an individual motion vector An for the subframe SFn. 
Step S8 moves the image to a calculated display position. Step S9 checks to 
see if the subframe SFn is the last subframe. If it is not the last 
subframe, step S10 increments n by one, and step S4 is again carried out. 
If the subframe SFn is the last subframe in step S9, step S11 increments 
the frame number n by one, and step S1 is again carried out. These steps 
are repeated until all frames are displayed. 
FIG. 15 shows an example of determining the delay time of each subframe, 
and FIG. 16 shows another example of determining the same. 
The technique of FIG. 15 sets a delay time start point at the center of the 
light emission period of a subframe that serves as the origin of a motion 
vector. The delay time of a given subframe is measured between the start 
point and the center of the light emission period of the given subframe. 
The technique of FIG. 16 is employed when the number of subframes to be 
turned ON (enabled) is smaller than the total number of subframes. In this 
case, the subframes are grouped so that the number of groups is equal to 
the number of subframes to be enabled. The center of each group is used to 
calculate a delay time. 
In FIG. 16, the number of subframes contained in each frame is six, and the 
number of subframes to be enabled is three. The origin of a motion vector 
is set at the temporal center of the light emission periods of the first 
two subframes SF5 and SF4, i.e., at a position corresponding to a 
reciprocal of the ratio of intensity levels of the subframes SF5 and SF4. 
A point for measuring the delay time of a given subframe group is set at 
the center of the intensity levels of the subframe group. 
Another embodiment of the first aspect of the present invention will be 
explained. 
As explained above, the conventional frame division technique causes the 
apparent motion when displaying dynamic images so that the human eye sees 
the subframes of each frame spatially separated from one another. The 
following embodiment solves this problem. 
FIG. 17 shows a frame consisting of six subframes SF5 to SF0. The intensity 
levels provided by the subframes gradually increase from SF0 to SF5. 
Returning to FIG. 7, there is an image consisting of four pixels among 
which three display intensity level 31 and one displays intensity level 
32. The image is scrolled to the right at a speed of two pixels per frame. 
The scroll speed is slow, and only a blue subpixel is enabled (turned ON) 
in each pixel, i.e., red and green subpixels in each pixel are disabled 
(turned OFF). A time point for enabling the subframe SF5 is a reference 
time point. 
According to FIGS. 7 and 17, it is understood that a three-subpixel 
interval between pixels 31(3) and 32(1) involves no light emission, to 
produce a dark part S. The present invention forcibly emits light during 
the three-pixel interval, to suppress the dark part S. In FIG. 7, an 
additional subframe will be enabled in the pixel 32(1), to increase the 
intensity level of the pixel 32(1) higher than 32. 
Returning to FIG. 8, there is an image consisting of four pixels among 
which two display intensity level 32 and two display intensity level 31. 
The image is scrolled to the right. 
A three-subpixel interval between pixels 32(2) and 31(1) involves much 
light emission, to produce a bright part M. The present invention forcibly 
turns OFF some subframes, to suppress the bright part M. In FIG. 7, some 
subframes in one of the pixels 31(1) and 31(2) are turned OFF, to drop the 
intensity level of the pixel in question below 31. 
Any image scrolled leftwards, rightwards, or vertically is handled in the 
same manner. 
FIG. 9 shows the same image as FIG. 7 but scrolled to the left. FIG. 9 
produces a bright part M instead of the dark part S of FIG. 7. Namely, 
dark and bright parts appear oppositely when the horizontal scrolling 
direction is reversed. 
Vertical scrolling causes no false color contours because each vertical 
stripe made of the same kind of subpixels involves a single color. The 
vertical scrolling, however, causes dark and bright parts, which may be 
removed by the same processes as for the horizontal scrolling. 
FIG. 18 shows a method of solving the dark part S of FIG. 7 encircled with 
a dotted line. The subframe SF2 of the pixel 32(1) is additionally enabled 
(turned ON), to increase the intensity level of the pixel 32(1) from 32 to 
36, thereby suppressing the dark part S. 
Turning ON the subframe SF2 is effective to suppress the dark part S only 
when the scroll speed is slow. If the scroll speed is fast, the subframes 
SF2 and SF3 will be turned ON to suppress the dark part S. 
As a scroll speed increases, the number of subframes to be additionally 
turned ON must be increased. 
FIG. 19 shows a method of solving the bright part M of FIG. 8 encircled 
with a dotted line. The subframes SF0 to SF2 of the pixel 31(1) are turned 
OFF (disabled), to decrease the intensity level of the pixel, thereby 
suppressing the bright part M. 
Turning OFF the subframes SF0 to SF2 is effective to suppress the bright 
part M only when the scroll speed is slow. If the scroll speed is fast, 
the subframes SF0 to SF3 will be disabled to suppress the bright part M. 
FIG. 20 shows an image consisting of six pixels with four displaying 
intensity level 31 and two displaying intensity level 32. The image is 
scrolled to the right at a speed of four pixels per frame. A dark part S 
of FIG. 20 is wider than that of FIG. 7 scrolling at a speed of two pixels 
per frame. To suppress the wide dark part S of FIG. 20, not only the 
subframes SF2 and SF3 of the pixel 32(1) but also the subframe SF2 of the 
pixel 32(2) must be additionally turned ON as shown in FIG. 22. According 
to psychological tests, only turning ON the subframes SF2 and SF3 of the 
pixel 32(1) was insufficient to suppress the dark part S, and additionally 
turning ON the subframe SF2 of the pixel 32(2) was effective to cancel the 
same. 
Namely, changing the intensity levels of the pixels 31(4), 32(1), and 32(2) 
to 31, 44, and 36, respectively suppresses the dark part S as well as 
false color contours. 
FIG. 21 shows an image consisting of five pixels with three displaying 
intensity level 32 and two displaying intensity level 31. The image is 
scrolled to the right at a speed of four pixels per frame. A bright part M 
of FIG. 21 is wider and brighter than that of FIG. 8 scrolling at a speed 
of two pixels per frame. 
To suppress the bright part M of FIG. 21, not only the subframes SF2 and 
SF3 of the pixel 31(1) but also the subframes SF1 and SF2 of the pixel 
31(2) must be turned OFF (disabled) as shown in FIG. 23. 
Namely, the intensity levels of the pixels 31(1) and 31(2) are changed to 
19 and 25, respectively, to suppress the bright part M as well as false 
color contours. 
As explained above, the second embodiment of the first aspect of the 
present invention provides a method of displaying a halftone image on a 
display unit according to a frame division technique that divides each 
frame of the halftone image into subframes each having an addressing 
period and a specific sustain discharge period to provide a specific 
intensity level. If combinations of subframes to realize different 
intensity levels between frames of a dynamic halftone image produce a 
bright part, the second embodiment disables some of the subframes, thereby 
canceling the bright part, and if they produce a dark part, the second 
embodiment additionally enables some subframes, thereby canceling the dark 
part. 
The number of subframes to be additionally enabled or disabled is 
determined according to the scroll speed or intensity levels of the 
dynamic image. If the scroll speed is high or if the intensity levels are 
high, the number of subframes to be additionally turned OFF or ON is 
increased, and in the opposite case, the number is decreased. 
To select subframes to be additionally turned OFF or ON, the second 
embodiment employs a table 11 shown in FIGS. 10 and 24 stored in a memory. 
The second embodiment of the first aspect of the present invention may turn 
OFF or ON subframes in the next frame, if the scroll speed is high. 
The first embodiment of the first aspect of the present invention detects a 
motion vector for each pixel or pixel block (for example, 16.times.16 
pixels) according to display data provided for consecutive frames. The 
first subframe in a given frame displays display data provided for the 
frame as it is. A delay time is found between the first subframe and a 
given one of the other subframes. The delay time is divided by a frame 
period. The quotient is multiplied by the motion vector, to calculate a 
display position for the given subframe. 
This method solves the problem of the apparent motion that the subframes of 
a frame of a dynamic image are spatially separated from one another, 
prevents intensity level disturbance, and improves display quality. 
The second embodiment of the first aspect of the present invention cancels 
a dark or bright part caused between specific intensity levels due to the 
spatial separation of the subframes of a frame of a dynamic image, by 
turning ON or OFF subframes between the intensity levels. 
Accordingly, the second embodiment prevents false color contours and 
improves the display quality of matrix display panels such as plasma 
display panels that display digital signals. 
As explained above in detail, the first aspect of the present invention 
detects a motion vector between consecutive frames according to display 
data of a dynamic image provided for the frames, finds in each frame a 
delay time between the first subframe and a given subframe, divides the 
delay time by a frame period, and multiplies the quotient by the motion 
vector, to calculate an individual motion vector for the given subframe. 
The given subframe displays an image according to the individual motion 
vector. The first aspect of the present invention prevents false color 
contours and intensity level disturbance, thereby improving the display 
quality of dynamic images. 
False color contours appearing on a dynamic image displayed according to 
the prior art will be explained with reference to FIGS. 25A to 27C. In the 
figures, each frame consists of subframes SF0 to SF7 with the subframe SF0 
providing the lowest intensity level and the subframe SF7 providing the 
highest intensity level. 
FIG. 25A shows a dynamic image scrolled from the left to the right at a 
speed of a pixel per frame, and FIG. 25B shows a dynamic image scrolled 
from the right to the left at a speed of a pixel per frame. In FIGS. 25A 
and 25B, an ordinate indicates time t, and an abscissa indicates a spatial 
position x. Reference marks 1F to 4F indicate frames. 
FIGS. 26A to 26C correspond to FIG. 25A and show a problem occurring when 
an image is scrolled from the left to the right. FIGS. 27A to 27C 
correspond to FIG. 25B and show a problem occurring when an image is 
scrolled from the right to the left. 
The image of FIG. 25A includes adjacent pixels that display intensity 
levels 128 and 127 and is scrolled from the left to the right at a speed 
of a pixel per frame. Due to the apparent motion, a coordinate origin on 
the retina of the human eye moves along a dotted line ROR. The image of 
FIG. 25A is seen as shown in FIG. 26A when coordinates on the retina are 
fixed. In FIG. 25A, the scale of the ordinate indicates the position on 
the retina, and one unit of the scale corresponds to a distance (or 
length) determined by moving the image in one frame period. 
The image of FIG. 25B includes adjacent pixels that display intensity 
levels 128 and 127 and is scrolled from the right to the left at a speed 
of a pixel per frame. A coordinate origin on the retina moves along a 
dotted line ROL. The image of FIG. 25B is seen as shown in FIG. 27A when 
coordinates on the retina are fixed. In FIG. 25B, the scale of the 
ordinate is the same as that shown in FIG. 25A. 
Intensity level 127 is realized by enabling (turning ON) the subframes SF0 
to SF6 and disabling (turning OFF) the subframe SF7. Intensity level 128 
is realized by turning OFF the subframes SF0 to SF6 and turning ON the 
subframe SF7. For the sake of simplicity, each pixel has no area in FIGS. 
26A and 27A. 
When the image having intensity levels 128 and 127 is scrolled from the 
left to the right, an intensity level K(x) at a position x on the retina 
forms a gap between the pixels that display intensity levels 128 and 127 
as shown in FIG. 26B. As a result, a stimulus L(x) on the retina drops to 
form a valley between intensity levels 128 and 127 as shown in FIG. 26C. 
Integrated stimuli for x=2.5 to 3.5, x=3.5 to 4.5, and x=4.5 to 5.5 are 
L(1), L(2), and L(3), respectively, and are expressed as follows: 
EQU L(1).about.L(3)&gt;&gt;L(2) 
Due to this, a dark line DL appears between the pixels that display 
intensity levels 128 and 127. This is the intensity level disturbance. 
The stimulus L(x) on the retina is expressed as follows: 
##EQU3## 
Where, .lambda. denotes an optional integer. Note that, in the above 
equation, the integral area is determined from .lambda.-0.5 to 
.lambda.+0.5, but the integral area can be variously determined. 
Nevertheless, this integral area is preferably determined to coincide with 
the area where the intensity level disturbance is caused. 
When the image having intensity levels 128 and 127 is scrolled from the 
right to the left, an intensity level K(x) at a position x on the retina 
is continuous between the pixels that display intensity levels 128 and 127 
as shown in FIG. 27B. As a result, stimulus L(x) on the retina reaches a 
peak between intensity levels 128 and 127 as shown in FIG. 27C. 
Integrated stimuli for x=2.5 to 3.5, x=3.5 to 4.5, and x=4.5 to 5.5 are 
L(1), L(2), and L(3), respectively, and are expressed as follows: 
EQU L(1).about.L(3)&lt;&lt;L(2) 
Due to this, a bright line BL appears between the pixels that display 
intensity levels 128 and 127. 
When an image consisting of green subpixels displaying intensity levels 128 
and 127, respectively, and a red subpixel displaying intensity level 64 is 
moved from the right to the left, a dark line appears between the green 
subpixels that display intensity levels 128 and 127. At this time, the red 
subpixel keeps intensity level 64 because it has no intensity level 
boundary. The human eye combines the subpixels and sees a red color in the 
green dark line, to thereby cause a false color contour. 
This phenomenon frequently occurs in a flesh-colored part where intensity 
levels smoothly change. For example, false color contours of red and green 
appear along the flesh-colored cheek of an image of a person displayed, 
when the person displayed looks back. 
FIGS. 28A and 28B show image displaying techniques to which the present 
invention is applied. The technique of FIG. 28A corresponds to that of 
FIG. 1. 
The technique of FIG. 28A divides each frame into subframes each having 
separate addressing and sustain discharge (light emission) periods. The 
technique of FIG. 28B distributes an addressing period into sustain 
discharge periods. 
FIGS. 29A to 29C show a principle of displaying halftone images according 
to the second aspect of the present invention. These drawings correspond 
to FIGS. 26A to 26C, respectively. 
When L(1).about.L(3)&gt;&gt;L(2) to form a dark line DL between the pixels that 
display intensity levels 128 and 127, an equivalent pulse (subframe, or 
light emission block) is enabled to apply a stimulus .DELTA.L(4) as 
follows: 
EQU if L(1)&gt;L(3) then L(1).gtoreq.L(2)+.DELTA.L(4).gtoreq.L(3) 
EQU if L(1)&lt;L(3) then L(1).ltoreq.L(2)+.DELTA.L(4).ltoreq.L(3) 
In FIGS. 29A and 29B, an equivalent pulse EPA is enabled with respect to a 
dark line caused between intensity levels 128 and 127 that are scrolled 
from the left to the right. As a result, the stimulus L(2) at an interface 
between intensity levels 128 and 127 is increased by .DELTA.L(4) as shown 
in FIG. 29C, thereby preventing smears or false color contours. 
The first principle of the second aspect of the present invention provides 
a method of displaying a halftone image on a display unit with each frame 
of the halftone image having subframes that have individual intensity 
levels and are combined to provide a required intensity level. The method 
includes the step of enabling an intensity level adjusting subframe in the 
subframes of one of consecutive frames that involve a change in intensity 
level between them, to substantially satisfy an expression of 
S1.ltoreq.S2+.DELTA.S.ltoreq.S3, or S1.gtoreq.S2+.DELTA.S.gtoreq.S3, where 
S1 is an average of B(t), which is a temporal change in a stimulus on the 
human eye, before the change of intensity level, S2 is an average of B(t) 
during the change of intensity level, S3 is an average of B(t) after the 
change of intensity level, and .DELTA.S is an average of a temporal change 
in a stimulus on the human eye due to the intensity level adjusting 
subframe. 
.DELTA.S is determined to substantially satisfy 
0.ltoreq..DELTA.S.ltoreq.2(S1-S2), or 0.ltoreq..DELTA.S.ltoreq.2(S3-S2). 
FIGS. 30A and 30B show an effect of inserting an equivalent pulse to turn 
ON a subframe. In FIG. 30A, an ordinate represents light emission 
intensity I(t), and an abscissa represents time t. In FIG. 30B, an 
ordinate represents stimulus B(t) on the human eye, and an abscissa 
represents time t. Reference marks 1F to 4F represent frames. 
When the equivalent pulse EPA of FIG. 30A is enabled, .DELTA.S is added to 
an average S2 of the stimulus B(t) between intensity levels 127 and 128, 
to increase the stimulus B(t) up to S2+.DELTA.S. It is ideal to make 
.DELTA.S to be S1.ltoreq.S2+.DELTA.S.ltoreq.S3. However, the effect of 
preventing false color contours is provided even if .DELTA.S slightly 
fluctuates. 
FIGS. 31A and 31B show the conditions of .DELTA.S produced by an equivalent 
pulse, in which FIG. 31A shows an ideal form of .DELTA.S and FIG. 31B 
shows a maximum value of .DELTA.S. 
As indicated with a dotted line in FIG. 31A, it is ideal that 
.DELTA.S=S1-S2, or .DELTA.S=S3-S2. It is, however, difficult to secure the 
ideal value, and therefore, .DELTA.S is set in a given range in practice. 
As indicated with a dotted line in FIG. 31B, the maximum value of .DELTA.S 
is 2(S1-S2) or 2(S3-S2). If .DELTA.S exceeds the maximum value, false 
color contours worsen. It is understood that .DELTA.S provides some effect 
if it is greater than zero. Accordingly, .DELTA.S may be determined as 
0.ltoreq..DELTA.S.ltoreq.2(S1-S2), or 0.ltoreq..DELTA.S.ltoreq.2(S3-S2). 
FIGS. 32A to 32F show the area of each pixel based on FIGS. 29A to 29C. For 
the sake of simplicity, FIGS. 26A to 26C and 29A to 29C show each pixel 
without area. In practice, each pixel has a predetermined area, and 
therefore, the images of FIGS. 26A to 26C and 29A to 29C will be those 
shown in FIGS. 32A to 32F in practice. In FIGS. 32A to 32F, a scroll speed 
is determined one pixel per frame. 
FIG. 32A corresponds to a frame 1F of FIG. 26A, FIG. 32B to FIG. 26B, FIG. 
32C to FIG. 26C, FIG. 32D to a frame 1F of FIG. 29A, FIG. 32E to FIG. 29B, 
and FIG. 32F to FIG. 29C. 
FIGS. 33A to 33C show another principle of displaying halftone images 
according to the second aspect of the present invention and correspond to 
FIGS. 27A to 27C. 
When L(1).about.L(3)&lt;&lt;L(2) to form a bright line BL between the pixels that 
display intensity levels 128 and 127, an equivalent pulse (subframe, or 
light emission block) is disabled (turned OFF) to remove a stimulus 
.DELTA.L(4) as follows: 
EQU if L(1)&gt;L(3) then L(1).gtoreq.L(2)-.DELTA.L(4).gtoreq.L(3) 
EQU if L(1)&lt;L(3) then L(1).ltoreq.L(2)-.DELTA.L(4).ltoreq.L(3) 
In FIGS. 33A and 33B, an equivalent pulse EPA is disabled with respect to a 
bright line caused between intensity levels 128 and 127 that are scrolled 
from the right to the left. As a result, the stimulus L(2) at an interface 
between intensity levels 128 and 127 is decreased by .DELTA.L(4) as shown 
in FIG. 33C, thereby preventing false color contours. 
As explained above, the second principle of the second aspect of the 
present invention provides a method of displaying a halftone image on a 
display unit with each frame of the halftone image having subframes that 
have individual intensity levels and are combined to provide a required 
intensity level. The method includes the step of disabling an intensity 
level adjusting subframe in the subframes of one of consecutive frames 
that display different intensity levels, to substantially satisfy an 
expression of S1.ltoreq.S2-.DELTA.S.ltoreq.S3 or 
S1.gtoreq.S2-.DELTA.S.gtoreq.S3, where S1 is an average of B(t), which is 
a temporal change in a stimulus on the human eye, before the change of 
intensity level, S2 is an average of B(t) during the change of intensity 
level, S3 is an average of B(t) after the change of intensity level, and 
.DELTA.S is an average of a temporal change in a stimulus on the human eye 
due to the intensity level adjusting subframe. 
.DELTA.S is determined to substantially satisfy 
0.ltoreq..DELTA.S.ltoreq.2(S2-S1), or 0.ltoreq..DELTA.S.ltoreq.2(S2-S3). 
FIGS. 34A and 34B show an arrangement of bits corresponding to subframes 
according to the second aspect of the present invention. 
In FIG. 34A, intensity level 127 realized by enabling bits b0 to b6 for the 
subframes SF0 to SF6 (FIG. 1) is changed to intensity level 128 realized 
by enabling a bit b7 for the subframe SF7. A dark part appearing at this 
time is canceled by enabling equivalent pulses to provide intensity level 
63 at a position A. The same is carried out when intensity level is 
changed from 127 to 130 in a period T. Then, it is difficult to precisely 
express the intensity level change. 
When the subframes of each frame are arranged in order of SF0 to SF7 as 
shown in FIG. 1, the same intensity level 63 corresponding to the 
subframes SF0 to SF6 is enabled when intensity level changes from 127 to 
128 and from 127 to 130. As a result, it is difficult to finely display 
the changing intensity levels. 
To solve this problem, the subframes (light emission blocks) are arranged 
in order of SF6, SF0, SF1, SF2, SF3, SF4, SF5, and SF7. Namely, the 
subframe SF6 corresponding to a bit b6 for providing intensity level 64 is 
set at the top of each frame. The subframe SF6 is enabled when the 
intensity level changes from 127 to 130, and the subframes SF0 to SF5 are 
used to display fine intensity level changes. 
FIGS. 35A to 35C show another arrangement of bits that represent subframes 
according to the present invention. 
According to the arrangements of FIGS. 1 and 34B, it is impossible to 
disable an equivalent pulse at position B of FIG. 35A when intensity level 
changes from 63 (subframes SF0 to SF5) to 64 (subframe SF6). Accordingly, 
the bit arrangement must be changed. 
As shown in FIGS. 35B and 35C, the subframes are arranged in order of SF6, 
SF5, SF0, SF1, SF2, SF3, SF4, and SF7. In this case, intensity level 64 
instead of 63 is used to adjust intensity level. As a result, an 
equivalent pulse for intensity level 16 may be disabled at the position B 
of FIG. 35A when the intensity level changes from 63 to 64. 
FIGS. 36A to 38B show simulation results carried out at three different 
scroll speeds according to the second aspect of the present invention. In 
each simulation, the width of a light emission band is equal to 40 pixels 
containing 120 subpixels with 20 left pixels displaying intensity level 
127 and 20 right pixels displaying intensity level 128. Light emission 
duty is 100%. Each pixel consists of red (R), green (G), and blue (B) 
subpixels. 
The scroll speed of the simulation of FIGS. 36A and 36B is a pixel (three 
subpixels) per frame, that of FIGS. 37A and 37B is three pixel (nine 
subpixels) per frame, and that of FIGS. 38A and 38B is five pixels (15 
subpixels) per frame. In each drawing, an ordinate represents intensity 
level, and an abscissa represents subpixels. 
In FIGS. 36A, 37A, and 38A, adjacent intensity levels 127 and 128 are 
scrolled from the left to the right, and an equivalent pulse EPS 
corresponding to intensity level 64 (subframe SF6, i.e., bit b6) is 
disabled. Intensity levels 127 and 128 of these drawings are opposite to 
those of FIGS. 25A and 25B. 
In FIGS. 36B, 37B, and 38B, adjacent intensity levels 127 and 128 are 
scrolled from the right to the left, and an equivalent pulse EPA 
corresponding to intensity level 64 (subframe SF6, i.e., bit b6) is 
enabled. Intensity levels 127 and 128 of these drawings are opposite to 
those of FIGS. 25A and 25B. 
In FIGS. 36A to 38B, a continuous line indicates a waveform of intensity 
levels the human eye senses before enabling/disabling the equivalent 
pulses EPA and EPS, and a dotted line indicates a waveform after the 
application of the equivalent pulses according to the second aspect of the 
present invention. 
The equivalent pulses EPA and EPS are effective to relax a peak or valley, 
to suppress a bright or dark line. In FIGS. 36A, 37A, and 38A, a bright 
line appearing between intensity levels 127 and 128 is canceled by 
disabling the subframe SF6 (bit b6) that provides intensity level 64, 
thereby dropping the peak of the waveform and preventing false color 
contours. In FIGS. 36B, 37B, and 38B, a dark line appearing between 
intensity levels 127 and 128 is canceled by enabling the subframe SF6 (bit 
b6), thereby increasing the valley of the waveform and preventing false 
color contours. 
FIGS. 39A to 39D show the effect of the second aspect of the present 
invention with an image being moved horizontally with no false pixels 
being seen. False pixels are seen when dynamic images are displayed on a 
matrix display unit. For example, a red subpixel is seen at the positions 
of green and blue subpixels. 
In FIG. 39A, adjacent intensity levels 128 and 127 are scrolled 
horizontally from the left to the right without an equivalent pulse EPA 
that enables an intensity level adjusting subframe. FIG. 39B shows the 
same scrolling situation as FIG. 39A but with the equivalent pulse. FIG. 
39C shows the sum of stimuli for five frames without the equivalent pulse, 
and FIG. 39D shows the same but with the equivalent pulse. 
When no equivalent pulse is applied, a large valley between intensity 
levels 128 and 127 of FIG. 39C produces a dark line. This valley is 
canceled by the equivalent pulse EPA as shown in FIG. 39D. 
FIGS. 40A and 40B show the effect of the second aspect of the present 
invention with an image being moved diagonally from the lower left to the 
upper right. 
A dark line appearing between adjacent intensity levels 128 and 127 
diagonally moved is canceled by the equivalent pulse EPA similar to the 
case of horizontally moving the images. 
FIGS. 39A to 40B show the effect of the second aspect of the present 
invention on dynamic images. The effect of the same on static images will 
be explained with reference to FIGS. 41A to 44D. 
FIG. 41A shows a temporal change between intensity levels 127 and 128, and 
FIG. 41B shows a temporal change in stimuli on the retina with respect to 
the change of FIG. 41A. 
Even in a still image, there will be a valley VP in stimuli on the retina 
when display intensity level changes from 127 to 128 as shown in FIG. 41B. 
In this case, an equivalent pulse EPA for enabling, for example, the 
subframe for intensity level 64 is applied when the intensity level 
changes from 127 to 128 as shown in FIG. 41C, thereby reducing a change in 
the stimuli on the retina as shown in FIG. 41D. 
Even in a still image, there will be a peak PP in stimuli on the retina as 
shown in FIG. 42B when display intensity level changes from 128 to 127 as 
shown in FIG. 42A. In this case, an equivalent pulse EPA for disabling, 
for example, the subframe for intensity level 64 is applied when the 
intensity level changes from 128 to 127 as shown in FIG. 42C, thereby 
reducing a change in the stimuli on the retina as shown in FIG. 42D. 
FIGS. 43A to 43D apply an equivalent pulse EPA for enabling the subframe 
for intensity level 16 when the intensity level of a static image changes 
from 63 to 64. FIGS. 44A to 44D apply an equivalent pulse EPS for 
disabling the subframe for intensity level 16 when the intensity level of 
a static image changes from 64 to 63. 
In this way, the second aspect of the present invention prevents intensity 
level disturbance and false color contours on images, in particular, 
dynamic images. 
Display units that achieves the method of the second aspect of the present 
invention will be explained. 
FIG. 45 is a block diagram showing a display unit according to the present 
invention. The display unit 100 is connected to a unit 200 for 
enabling/disabling intensity level adjusting subframes (light emission 
blocks). The unit 200 receives display data 210 and provides adjusted 
display data 220. 
The display unit 100 has a display panel 102, an X-decoder 131, an X-driver 
132, a Y-decoder 141, a Y-driver 142, and a controller 5. The controller 5 
controls the decoders and drivers, which drive the display panel 102. 
Each frame of an image is divided into subframes (light emission blocks) 
that display individual intensity levels on the display panel 102. Each 
subframe consists of an addressing period and a sustain discharge period. 
The display panel 102 may be a gas discharge panel such as a plasma 
display panel, a panel employing DMDs (digital micromieror devices), an EL 
panel, etc., that employ the frame division technique to display intensity 
levels. 
The display unit 100 of FIG. 45 may employ any kind of display panel that 
realizes intensity levels with the use of subframes. The unit 200 
according to the present invention enables or disables intensity level 
adjusting subframes (equivalent pulses, or light emission blocks) 
according to the display data 210 and provides the adjusted display data 
220. 
FIG. 46 is a block diagram showing an example of the unit 200. 
The unit 200 has a delay unit 310 for delaying the display data 210 by a 
frame and a unit 400 for enabling or disabling intensity level adjusting 
subframes. The unit 400 receives the display data 210 for a given frame 
and display data 230 for the preceding frame. The unit 400 enables or 
disables the intensity level adjusting subframes in the display data 210 
and provides adjusted display data 220. 
FIG. 47 is a block diagram showing an example of the unit 400 of FIG. 46, 
according to a first embodiment of the second aspect of the present 
invention. 
The unit 400 has a unit 410 that receives display data 210 for a present 
frame and display data 230 for the preceding frame, to check equivalent 
pulses, and a unit 420 for enabling or disabling equivalent pulses, which 
enable or disable the intensity level adjusting subframes, according to 
the preceding display data 230 and the output of the unit 410. 
FIG. 48 is a block diagram showing an example of the unit 400 of FIG. 47. 
Display data 210 shown in FIG. 47 for a frame "n+1" consists of bits 
b0.sub.n+1 to b7.sub.n+1 indicated with reference numerals 211 to 218. 
Adjusted display data 220 shown in FIG. 47 for the frame n+1 consists of 
bits b0.sub.n+1 ' to b7.sub.n+1 ' indicated with reference numerals 221 to 
228. Display data 230 shown in FIG. 47 for a frame "n" includes second and 
first highest bits b6.sub.n and b7.sub.n indicated with reference numerals 
237 and 238, respectively. 
In FIG. 48, the unit 410 for checking equivalent pulses consists of two 
equivalent pulse testers 411 and 412. The unit 420 for enabling or 
disabling the equivalent pulses has units 421 and 422 for receiving output 
signals 431 and 433 and polarity signals 432 and 434 from the testers 411 
and 412. The unit 400 provides the adjusted display data 220 according to 
the display data 210 for the frame n+1 and display data 230 for the frame 
n. 
The tester 411 determines whether or not the most significant bits b7.sub.n 
and b7.sub.n+1 of the frames n and n+1 are enabled. The tester 412 
determines whether or not the second most significant bits b6.sub.n and 
b6.sub.n+1 of the frames n and n+1 are enabled. The testers 411 and 412 
determine the polarity of equivalent pulses, i.e., whether the equivalent 
pulses must be enabled or disabled to turn ON or OFF the intensity level 
adjusting subframes (light emission blocks). 
The output Y1 of the tester 411 indicates whether or not the b7.sub.n and 
b7.sub.n+1 differ from each other. If the output Y1 is at high level, the 
bits b7.sub.n and b7.sub.n+1 differ from each other, and if it is at low 
level, the bits are equal to each other. The output Y0 of the tester 411 
indicates the polarity of the equivalent pulse. If the output Y0 is at 
high level, the polarity is positive to enable the equivalent pulse to 
turn ON the intensity level adjusting subframe. If the output Y0 is at low 
level, the polarity is negative to disable the equivalent pulse to turn 
OFF the intensity level adjusting subframe. 
FIG. 49 is a logic circuit diagram showing an example of the tester 411 
(412) for testing an equivalent pulse. 
The tester 411 (412) consists of an exclusive OR gate, which provides the 
outputs Y0 and Y1 according to inputs A and B. Each of the testers 411, 
412, 511, and 512 has the same arrangement as the tester 411 of FIG. 49. 
Table 1 shows truth values of the tester. 
TABLE 1 
______________________________________ 
Input Output 
B A Y1 Y0 Conditions 
______________________________________ 
L L L X No change 
L H H H Apply positive equivalent pulse 
H L H L Apply negative equivalent pulse 
H H L X No change 
______________________________________ 
FIG. 50 is a logic circuit diagram showing the unit 421 (422) for enabling 
or disabling the equivalent pulse. The unit 421 consists of two AND gates 
AND1 and AND2, an OR gate OR, and an inverter INV. The unit 421 provides 
an output Y according to inputs A, B, and S. Each of the units 421, 422, 
521, and 522 has the same structure as the unit 421 of FIG. 50. Table 2 
shows truth values of the unit 421. 
TABLE 2 
______________________________________ 
Input Output 
A B S Y Conditions 
______________________________________ 
X L L L No change 
X H L H No change 
L X H L Negative equivalent pulse 
H X H H Positive equivalent pulse 
______________________________________ 
As shown in Table 1 and FIGS. 48 and 49, for example, in the tester 
(equivalent pulse tester) 411, the most significant bit (first highest 
bit) b7.sub.n+1 of the frame "n+1" (next frame of the frame "n") is 
supplied to the input A, and the most significant bit b7.sub.n of the 
frame "n" (optional frame) is supplied to the input B. When the signal 
levels of the inputs A and B are not changed, the equivalent pulse is not 
added or subtracted by bringing the output Y1 at low level "L", on the 
other hand, when the signal levels of the inputs A and B are changed, the 
equivalent pulse is added or subtracted by bringing the output Y1 at high 
level "H". As clearly shown in FIG. 49, the signal level of the output Y0 
is the same as that of the input A. 
As shown in Table 2 and FIGS. 48 and 50, for example, in the unit 
(equivalent pulse enabling or disabling unit) 421, the output Y1 (output 
signal of the XOR gate) of the tester 411 is supplied to the input S, the 
output Y0 (b7.sub.n+1) of the tester 411 is supplied to the input A of the 
unit 421, and the second highest bit (b6.sub.n+1) of the frame "n+1" is 
supplied to the input B of the unit 421. 
Therefore, when the most significant bits b7.sub.n and b7.sub.n+1 of the 
frames n and n+1 are different from each other, the input S of the unit 
421 is at high level "H", and the output of the AND gate (AND2) is 
appeared as the output Y of the unit 421 through the OR gate. Concretely, 
when the most significant bit b7 of the frame n is disabled (low level 
"L": for example, intensity level 127) and the most significant bit 
b7.sub.n+1 of the frame n+1 is enabled (high level "H": for example, 
intensity level 128), both of the inputs S and A of the unit 421 are at 
high level "H", so that a positive equivalent pulse (for example, 
intensity level 64) is added to the original signal (display data 210), or 
an equivalent pulse is enabled. On the other hand, when the most 
significant bit b7 of the frame n is enabled ("H") and the most 
significant bit b7.sub.n+1 of the frame n+1 is disabled ("L"), the input S 
of the unit 421 is at high level "H" and the input A of the unit 421 is at 
low level "L", so that a negative equivalent pulse is added to (equivalent 
pulse is subtracted from) the original signal, or an equivalent pulse is 
disabled. 
In FIG. 48, the equivalent pulse tester 412 and equivalent pulse enabling 
or disabling unit 422 receive the bit signals b6.sub.n+1, b6.sub.n, and 
b5.sub.n+1 which are lower by one bit rank than the bit signals 
(b7.sub.n+1, b7.sub.n, and b6.sub.n+1) for the tester 411 and unit 421, 
and carry out the same processes of tester 411 and unit 421 for the one 
bit lower signals. Note that the operations (output levels against input 
levels) of each equivalent pulse tester and each equivalent pulse enabling 
or disabling unit shown in FIGS. 51, 53, 54, and 57 to 69 are the same as 
the above embodiments. 
FIG. 51 is a block diagram showing another example of the unit 400 of FIG. 
47. The unit 400 consists of two equivalent pulse testers 411 and 412, 
units 421 and 422 each for enabling or disabling an equivalent pulse, and 
nine delay units 490 to 498. The unit 421 provides an output signal 435 
that is formed by enabling or disabling a signal 217, i.e., bit 
b6.sub.n+1. The delay units 496 and 495 provide output signals 436 and 437 
by delaying signals 237 (b6.sub.n) and 216 (b5.sub.n+1) by one pixel. 
The unit 400 of FIG. 51 relates the status of the higher equivalent pulse 
to the status of the lower equivalent pulse. 
If the equivalent pulse for the second highest bit for the subframe SF6 is 
enabled or disabled, the equivalent pulse for the third highest bit for 
the subframe SF5 is determined accordingly. Namely, signals 218 and 238 to 
the unit 411 correspond to signals 227 and 436 to the unit 412. Signals 
431, 432, and 217 to the unit 421 correspond to signals 433, 434, and 437 
to the unit 422. The unit 421 determines whether the equivalent pulse for 
the second highest bit must be enabled or disabled, and the unit 422 
determines whether the equivalent pulse for the third highest bit must be 
enabled or disabled. 
FIG. 52 is a block diagram showing another example of the unit 400 of FIG. 
46, according to a second embodiment of the second aspect of the present 
invention. 
In FIGS. 52 and 47, the display data 210 and 230 are supplied oppositely. 
The unit 400 of FIG. 52 has an equivalent pulse tester 410 for receiving 
display data 210 for a given frame and display data 230 for the preceding 
frame, and an equivalent pulse disabling/enabling unit 420 for receiving 
the display data 210 and the output of the unit 410. 
The unit 400 of FIG. 47 handles frames each having subframes (light 
emission blocks) that are arranged in ascending order of the intensity 
levels thereof. The unit 400 of FIG. 52 handles frames each having 
subframes (light emission blocks) that are arranged in descending order of 
the intensity levels thereof. 
FIG. 53 is a block diagram showing an example of the unit 400 of FIG. 52, 
and FIG. 54 is a block diagram showing another example of the unit 400 of 
FIG. 52. 
The units of FIGS. 53 and 54 handle signals 231 to 238 (b0.sub.n to 
b7.sub.n) instead of the signals 211 to 218 (b0.sub.n+1 to b7.sub.n+1) of 
FIGS. 47 and 51, as well as signals 217 and 218 (b6.sub.n+1 and 
b7.sub.n+1) instead of the signals 237 and 238 (b6.sub.n and b7.sub.n) of 
FIGS. 47 and 51. The other parts of the circuits of FIGS. 53 and 54 are 
the same as those of FIGS. 47 and 51. 
FIG. 55 is a block diagram showing another example of the unit 200 of FIG. 
45 according to the second aspect of the present invention. 
The unit 200 has delay units 310 and 320 each for providing a delay of a 
frame and a unit 500 for enabling or disabling intensity level adjusting 
subframes (light emission blocks). The unit 500 receives display data 210 
for a given frame, display data 230 for the preceding frame, and display 
data 240 for two frames back, and provides display data 220 with enabled 
or disabled intensity level adjusting subframes. 
FIG. 56 is a block diagram showing an example of the unit 500 of FIG. 55, 
according to third and fourth embodiments of the second aspect of the 
present invention. 
The unit 500 has an equivalent pulse tester 510 for receiving display data 
210 for a given frame, display data 230 for the preceding frame, and 
display data 240 for two frames back, and a unit 520 for enabling or 
disabling equivalent pulses. The unit 520 receives the display data 230 
and the output of the tester 510. 
FIG. 57 is a block diagram showing an example of the unit 500 of FIG. 56 
according to the third embodiment. A signal 217 represents the second 
highest bit b6.sub.n+1 of the display data 210. Signals 221 to 228 
represent bits b0.sub.n+1 to b7.sub.n+1 that are formed by enabling or 
disabling the bits of the display data 210. Signals 231 to 238 represent 
the bits b0.sub.n to b7.sub.n of the display data 230. A signal 248 
represents the most significant bit b7.sub.n-1 of the display data 240. 
The unit 510 has two equivalent pulse testers 511 and 512. The unit 520 
consists of two units 521 and 522 for receiving output signals 531 and 533 
and polarity signals 532 and 534 from the testers 511 and 512. The unit 
500 receives the display data 230 (signals 231 to 238) and display data 
240 (signal 248) and provides display data 220 (signals 221 to 228) in 
which intensity level adjusting subframes are enabled or disabled. 
The tester 511 determines whether or not the most significant bits b7.sub.n 
and b7.sub.n-1 differ from each other. The tester 512 determines whether 
or not the second highest bits b6.sub.n and b6.sub.n+1 differ from each 
other. The testers 511 and 512 also determine the polarities of equivalent 
pulses to enable or disable bits corresponding to the intensity level 
adjusting subframes (light emission blocks). 
If the output Y1 of the tester 511 is at high level, the bits b7.sub.n and 
b7.sub.n-1 differ from each other, and if it is at low level, they are 
equal to each other. If the output Y0 of the tester 511 is at high level, 
the polarity of the equivalent pulse is positive to enable the intensity 
level adjusting subframe, and if it is at low level, the same is negative 
to disable the subframe. 
FIG. 58 is a block diagram showing another example of the unit 500 of FIG. 
56 according to the third embodiment. The unit 500 has delay units 590 to 
598 each providing a delay of a pixel. 
The unit 500 of FIG. 58 relates the status of a higher equivalent pulse to 
the status of a lower equivalent pulse. 
The third embodiment arranges, in each frame, subframes in order of SF5, 
SF4, SF0, SF1, SF2, SF3, and SF7. The fourth embodiment mentioned below 
arranges, in each frame, subframes in order of SF7, SF4, SF3, SF2, SF1, 
SF0, and SF5. Namely, the arrangement of subframes of the fourth 
embodiment of FIGS. 59 and 60 is opposite to that of the third embodiment 
of FIGS. 57 and 58. 
FIG. 59 is a block diagram showing an example of the unit 500 of FIG. 56, 
according to the fourth embodiment, and FIG. 60 is a block diagram showing 
another example of the unit 500 of FIG. 56, according to the fourth 
embodiment. 
The units of FIGS. 59 and 60 handle signals 247 (b6.sub.n-1) and 218 
(b7.sub.n+1) instead of the signals 217 (b6.sub.n+1) and 248 (b7.sub.n-1) 
of FIGS. 57 and 58. The other parts thereof are the same as those of FIGS. 
57 and 58. 
The units 400 and 500 for enabling/disabling intensity level adjusting 
subframes (light emission blocks) may be lookup tables stored in a RAM or 
ROM. 
FIG. 61 shows a modification of the unit for inserting the light emission 
block of FIG. 46. In FIG. 46, reference numeral 310 denotes a frame memory 
(delay unit) for delaying original signal (display data) by one vertical 
synchronizing period (1V), 400 denotes a unit for adding intensity level 
adjusting light emission block, 410 denotes a unit for testing equivalent 
pulse, and 420 denotes a unit for adding equivalent pulse. 
As shown in FIG. 61, in the present modification, the unit for testing 
equivalent pulse 410 comprises a comparator 410a and LUT (look up table: 
ROM) 410b, and the unit for adding equivalent pulse 420 is constituted as 
an adder. The comparator 410a compares the bit data of the frames n and 
n+1, when specific bit data is changed from an enabling state (ON) to a 
disabling state (OFF), then the LUT 410b outputs "+1"; when specific bit 
data is changed from the disabling state to the enabling state, then the 
LUT 410b outputs "-1"; and when specific bit data is not changed between 
both frames n and n+1, then the LUT 410b outputs "0". 
The LUT 410b is, for example, constituted as a ROM where predetermined data 
are written, and a predetermined equivalent pulse is output from the LUT 
410b in accordance with the output of the comparator 410a. Note that the 
equivalent pulse output from the LUT 410b has a positive or negative 
symbol. The adder 420 adds (adds or subtracts) the equivalent pulse to the 
display data 210, and output an adjusted display data 220. 
FIG. 62 shows another modification of the unit for inserting the light 
emission block of FIG. 46. 
In the unit for inserting the light emission block of FIG. 62, the unit for 
adding intensity level adjusting light emission block 400 is constituted 
as a ROM, the bit data of the frame n (delayed signal 230 by 1V) output 
from the frame memory 310 and the bit data of the frame n+1 display data 
210) are input to the ROM 400, and adjusted display data 220 corresponding 
to the bit data of the frames n and n+1 is directly output. The signals 
supplied to the input A* of the unit 400 are changed in accordance with 
the number of compared bit signals. For example, when the number of 
compared bit signals is two (b7 and b6), the input A* of the unit 400 
receives two bit signals. 
FIG. 63 is a flowchart showing an operation of the display unit according 
to the second aspect of the present invention. This operation employs a 
frame having separate addressing periods and sustain discharge periods 
(light emission periods). 
Step S31 produces red (R), green (G), and blue (B) signals. Step S32 stores 
signals of a frame "n" in a frame memory. Step S33 stores signals of a 
frame "n+1" in a frame memory. 
Step S34 checks the most significant bit b7 of each pixel in the signals of 
frames n and n+1. Step S35 carries out a process according to the most 
significant bits b7 of the frames n and n+1. 
More precisely, step S35 carries out nothing if the bits b7 of the frames n 
and n+1 are both enabled or disabled. If the bit b7 of the frame n is 
disabled and the bit b7 of the frame n+1 is enabled, step S35 enables a 
positive equivalent pulse EPA for enabling, for example, the bit b6 for 
intensity level 64 in the frame n+1. If the bit b7 of the frame n is 
enabled and the bit b7 of the frame n+1 is disabled, step S35 enables a 
negative equivalent pulse EPS for disabling the bit b6 for intensity level 
64 in the frame n+1. 
Step S36 checks the second highest bit b6 of each pixel in the frames n and 
n+1. Step S37 carries out a process according to the bits b6 of the frames 
n and n+1. 
More precisely, step S35 carries out nothing if the bits b6 of the frames n 
and n+1 are both enabled or disabled. If the bit b6 of the frame n is 
disabled and that of the frame n+1 is enabled, step S37 enables a negative 
equivalent pulse EPS for disabling, for example, the bit b4 for intensity 
level 16 in the frame n. If the bit b6 of the frame n is enabled and that 
of the frame n+1 is disabled, step S37 enables a positive equivalent pulse 
EPA for enabling the bit b4 for intensity level 16 in the frame n. Step 
S38 displays an image on the display panel such as a plasma display panel 
according to the display data thus prepared. 
FIG. 64 is a flowchart showing another operation of the display unit 
according to the second aspect of the present invention. This operation 
employs a frame that distributes an addressing period into sustain 
discharge periods as shown in FIG. 28B. Alternatively, each frame may 
consists of subframes (light emission blocks) that provide individual 
intensity levels. Steps S41 to S46 of FIG. 64 are equal to steps S31 to 
S36 of FIG. 63. 
Step S46 checks the second highest bit b6 of each pixel in the frames n and 
n+1. Step S47 carries out a process according to the bits b6 of the frames 
n and n+1. 
More precisely, step S47 carries out nothing if the bits b6 of the frames n 
and n+1 are both enabled or disabled. If the bit b6 of the frame n is 
disabled and that of the frame n+1 is enabled, step S47 enables a positive 
equivalent pulse EPA for enabling, for example, the bit b4 for intensity 
level 16 in the frame n+1. If the bit b6 of the frame n is enabled and 
that of the frame n+1 is disabled, step S47 enables a negative equivalent 
pulse EPS for disabling the bit b4 for intensity level 16 in the frame 
n+1. Step S48 displays an image on the display panel such as a plasma 
display panel according to the display data thus prepared. 
The present invention is applicable not only to gas discharge panels such 
as plasma display panels but also to other frame-division display panels 
such as panels employing DMDs (digital micromirror devices) and EL panels. 
As explained above, the second aspect of the present invention enables or 
disables intensity level adjusting subframes among the subframes of 
consecutive frames that display different intensity levels, thereby 
preventing intensity level disturbance, smears, and false color contours 
in displayed images, in particular, dynamic images. 
Many different embodiments of the present invention may be constructed 
without departing from the spirit and scope of the present invention, and 
it should be understood that the present invention is not limited to the 
specific embodiments described in this specification, except as defined in 
the appended claims.