CA2017757C - Method for driving display device - Google Patents
Method for driving display deviceInfo
- Publication number
- CA2017757C CA2017757C CA002017757A CA2017757A CA2017757C CA 2017757 C CA2017757 C CA 2017757C CA 002017757 A CA002017757 A CA 002017757A CA 2017757 A CA2017757 A CA 2017757A CA 2017757 C CA2017757 C CA 2017757C
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
- H04N3/10—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical
- H04N3/12—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by switched stationary formation of lamps, photocells or light relays
- H04N3/127—Scanning details of television systems; Combination thereof with generation of supply voltages by means not exclusively optical-mechanical by switched stationary formation of lamps, photocells or light relays using liquid crystals
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2044—Display of intermediate tones using dithering
- G09G3/2051—Display of intermediate tones using dithering with use of a spatial dither pattern
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
- G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
- G09G3/3611—Control of matrices with row and column drivers
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/2007—Display of intermediate tones
- G09G3/2044—Display of intermediate tones using dithering
- G09G3/2051—Display of intermediate tones using dithering with use of a spatial dither pattern
- G09G3/2055—Display of intermediate tones using dithering with use of a spatial dither pattern the pattern being varied in time
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- Engineering & Computer Science (AREA)
- Crystallography & Structural Chemistry (AREA)
- Computer Hardware Design (AREA)
- General Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Physics & Mathematics (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Liquid Crystal Display Device Control (AREA)
- Liquid Crystal (AREA)
- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
- Transforming Electric Information Into Light Information (AREA)
Abstract
A frame thinning out system has been used as a display driving method for making a gradational display with several brightness levels on the screen of a liquid crystal display device and the like. A display driving method of the present invention, sets a plurality of frame time periods, during which each of pixels on the screen is controlled to display an image, as one integration time period. Pixels are turned on only for a number of specified frame time periods corresponding to the desired brightness level. In this driving method the pixels of the display device are grouped into groups of a plurality of pixels contiguous to each other, the number of pixels to be turned on in each frame time period is selected corresponding to specified gradation data within the same group, so that the number of pixels to be turned on for one frame time period may be equal between subgroups in the scanning lines within the same group, and the frame time period is set to a period so short that a human does not feel flicker. In this way, a group of pixels as a unit image area, a gradational display without noticeable flicker can be obtained. Since no delicate shades of brightness occur among pixels to the same gradation level, the quality of the display is improved.
Description
20 ~ 7757 The present invention relates to a method for driving a display device, such as a liquid crystal display device or a thin film EL display device.
In a liquid crystal display device and the like, a frame thinn;ng out system is well-known as a driving system for enabling a display panel to display a gradationally toned image with several brightness levels on its screen.
The frame th; nn; ng out system turns on pixels only in the number of frames corresponding to a level of brightness to be displayed out of all frames within an integration time period consisting of a plurality of frame time periods so as to visually obtain a medium level of brightness in each integration time period.
The applicant of the present invention has already proposed a driving method to reduce flicker on a screen by grouping pixels of the display device into groups, each of which is composed of a plurality of pixels contiguous to each other, and limiting the total number of pixels to be turned on for each frame time period within the same group according to the display data as a display driving method improving the conventional frame thinning out system.
Table 1 shows gradation rules (rules for turning pixels ON or OFF for a specific frame time period) for a gradational display by setting eight frame time periods as one integration time period by means of this driving method.
In this case, all pixels on the screen are grouped into groups of four pixels contiguous to each other as shown by arrow II on the display panel composed of a plurality of pixels arranged in the form of a matrix, as shown schematically in Figure 1.
Frame Gradation Pixel Level 1 2 3 4 5 6 7 8 A 0 o 0 0 0 0 0 0 0 / 8 B 0 o 0 0 0 0 0 0 C O o o O O O O O
1 / 8 B 0 0 1 o o o o 0 2 / 8 B o 1 0 0 0 1 0 0 A
C 1 1 1 1 1 1' D
In Table 1, numeral "1" indicates turning a pixel ON and numeral "0" indicates turning a pixel OFF.
Figure 2 is a magnification of one group of pixels shown by arrow II in the display panel of Figure 1. In the group of pixels, when setting the pixel in the upper left hand corner of the screen of the display panel 1 as a pixel in the 0th row and 0th column, the pixel arrangement is set so that in Figure 2 the two upper pixels A and B are in an even-numbered row, the two lower pixels C and D are in an odd-numbered row, the two left pixels A and C are in an even-numbered column, and the two right pixels B and D are in an odd-numbered column.
Figure 3 is a schematic diagram showing a gradation rule for each of pixels A through D in displaying a 6/8 gradation level all over the screen of the display panel 1.
As shown in Figure 3, in displaying the 6/8 gradation level, three pixels B, C and D are turned ON
(pixels A is turned OFF) for the first frame time period, three pixels A, C and D are turned ON (pixel B is OFF) for the second frame time period, three pixels A, B and D are turned ON (pixel C is OFF) for the third frame time period, and three pixels A, B and C are turned ON (pixel D is OFF) for the fourth frame time period. The rule for the first through fourth frame time periods is also applied to the fifth through eighth frame time periods, and this cycle of eight frame time periods as an integration time period is then repeated. Namely, in displaying the 6/8 gradation level, three pixels are always turned ON for each frame time period and each of pixels A through D are turned ON equally six times for eight frame time periods.
In this case the brightness level as a whole of a unit image area of one group of pixels A through D is as shown in Figure 4.
Since three pixels are turned ON throughout all frame time periods, the brightness level is always "3/4".
Accordingly, the 6/8 brightness level is displayed on the average during one integration time period consisting of - ~
eight frame time periods and brightness level of the group does not vary as a whole of the unit image area, so flicker is reduced.
In the above-mentioned driving method previously proposed, however, as shown in Figure 3, in the 6/8 brightness level the number of pixels turned ON in a subgroup of pixels A and B in the upper even-numbered row of pixels A through D is different from the number of pixels turned ON in a subgroup of pixels C and D in the lower odd-numbered row. As a result, the quality of the display isdeteriorated depending on the viewing angle when the above-mentioned driving method is applied to a capacitive display device such as a liquid crystal display device.
Since a capacitive display device, such as a liquid crystal display device, shows a phenomenon wherein the rightness of the pixel turned ON at that time varies according to the number of pixels turned ON out of the pixels arranged in one row (common line) on the screen of the display panel 1, the difference between the number of pixels turned ON in a subgroup of pixels A and B in the upper even-numbered row and the number of pixels turned ON
in a subgroup of pixels C and D in the lower odd-numbered row causes such deterioration of quality of the display that the brightness of the pixels varies for each frame time period and the bright points seem to be vibrating.
This problem occurs also in displaying the other gradation levels.
An object of the present invention is to provide a display driving method which makes it possible to display a high quality image with no noticeable flicker and no delicate shades of brightness among pixels of the same gradation level even in a capacitive display device such as a liquid crystal display device.
According to the present invention, there is provided a method for driving a display device having a plurality of scanning lines to make a gradationally toned display with several brightness levels by setting a plurality of frame time periods, during which each of pixels on a screen is controlled for displaying an image, as one integration time period and by turning on pixels for a number of specified frame time periods corresponding to display data of the image within the integration time period, comprising the steps of grouping the pixels of the display device into groups, each of which is composed of a plurality of pixels contiguous to each other; selecting the number of pixels to be turned on for each of the frame time periods within one integration time period corresponding to specified gradation data of each group of pixels, so that the number of pixels to be turned on for one frame time period may be equal between subgroups of pixels in the scanning lines within the same group of pixels; and setting the frame time period during the number of pixels to be turned on is kept constant to a period shorter than a predetermined period.
The invention provides a display driving method which makes a gradationally toned display by using multiple gradation data for each frame time period on the basis of a plurality of gradation data which are apart by a nearly equal level from the specified gradation data in directions opposite to each other.
Further, the invention provides a display device driving method which makes a gradationally toned display by turning on a number of pixels corresponding to the specified gradation data for each frame time period.
Still further, the invention provides a display driving method in which each pixel to be turned on is selected from pixels in different positions within each of the groups of pixels for each frame time period.
Furthermore, the invention provides a display driving method in which the difference between the plurality of gradation data is selected so as to be the minimum unit of gradation data.
Still furthermore, the invention provides a display driving method in which a period of variation among the plurality of gradation data is selected so as to be the same period as the frame time period.
According to the invention, all pixels of a display device are grouped into a plurality of groups, each of which is composed of a plurality of pixels contiguous to each other, and the number of pixels to be turned on for each frame time period within one integration time period is selected corresponding to specified gradation data, so that the number of pixels to be turned on for one frame time period may be equal between subgroups in the scanning lines within the same group. The frame time period during which the number of pixels to be turned on is kept constant is selected so as to be shorter than a predetermined period, namely, the minimum period for which a human feels flicker.
Accordingly, in viewing a plurality of pixels over one group of pixels as a unit image area, a high quality gradational display without noticeable flicker can be obtained. Since no delicate shades of brightness occur among pixels to display the same gradation level, the quality of the display is improved.
As mentioned above, according to a display device driving method of the present invention, selecting the number of pixels to be turned on out of a plurality of pixels contiguous to each other forming one group of pixels for each frame time period corresponding to its display data reduces variation of brightness as a whole of the group of pixels and makes it possible to obtain a gradationally toned display without noticeable flicker.
Since the number of pixels to be turned on for each frame time period is equal to each other among the subgroups respectively arranged in the scanning line within the same group, no delicate shades of brightness occur among pixels to display the same gradation level even in case of applying this driving method to a capacitive display device such as a liquid crystal display device. As a result, the quality of the display is improved significantly.
In the accompanying drawings which illustrate embodiments of the present invention:
Figure 1 is a plan view of a display panel illustrating a group of pixels for a previously proposed driving method as an example of the prior art;
Figure 2 is a plan view of a magnification of a group of pixels of the display panel of Figure l;
Figure 3 is a schematic diagram illustrating a gradation rule for displaying a 6/8 gradation level in the driving method of Figure 1;
Figure 4 is a schematic diagram showing the variation of brightness in a group of pixels controlled by the gradation rule of Figure 3;
Figure 5 is a block diagram of a configuration of a liquid crystal display device driving method to which a driving method of an embodiment of the present invention is applied;
Figure 6 is a schematic plan view of the display panel of the liquid crystal display device of Figure 5;
Figure 7 is a magnification of one group of pixels of the display panel of Figure 6;
Figure 8 is a schematic diagram showing gradation rules applied to the liquid crystal display device driving method;
Figures 9(a), 9(b), 9(c), 9(d), 9(e), 9(f), 9(g) and 9(h) are schematic diagrams showing the variation of brightness in one group of pixels controlled on the basis of the gradation rules of Figure 8;
Figure 10 is a schematic diagram showing gradation rules for displaying a checker pattern;
Figures ll(a), ll(b), ll(c), ll(d), ll(e), ll(f), ll(g) and ll(h) are schematic diagrams showing the variation of brightness in one group of pixels controlled on the basis of the gradation rules of Figure 10;
Figure 12 is a plan view schematically showing a display screen of the checker pattern;
' r . ~
-Figure 13 is a schematic diagram showing a gradation rule for a 6/8 gradation level for displaying a checker pattern of Figure 12 on the basis of the gradation rule in the driving method previously proposed as an example; and Figure 14 is a schematic diagram showing the variation of brightness in one group of pixels controlled on the basis of the gradation rule of Figure 13.
Referring now to Figure 5, a controller 2, for controlling the driving of a liquid crystal display device 3, has a random access memory 4 (hereinafter referred as to RAM) which stores display data including gradation data thereof, a switch group 5 which sets gradation rules for a frame thinning out system, and a timing signal generating circuit 6 which generates timing signals necessary for making the liquid crystal display device 3 display an image.
A host computer 7 controls the timing signal generating circuit 6.
Figure 6 is a plan view schematically showing a display panel 8 of the liquid crystal display device 3 in which a plurality of pixels are arranged in the form of a matrix, and Figure 7 is a plan view schematically showing a magnification of one group of pixels shown by arrow VII in the display panel 8 of Figure 6.
Referring now to Figures 8 and 9, operation of a liquid crystal display device driving method of the present invention is described as follows. The gradation rules applied to the liquid crystal display device driving method for displaying a uniform gradation over the screen of the display panel 8 is shown schematically in Figure 8.
Assuming that a gradationally toned display with 9 gradation levels, including 0/8 ("0" level), 1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7/8 and 8/8 ("1" level) gradation levels, is performed by setting eight frame time periods as one integration time period, a case is described wherein a unit image area with the 0/8, 1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7/8, '`~; lS~, or 8/8 gradation level in brightness is displayed with a group of pixels A, B, C, D, E, F, G and H shown in Figure 7.
When setting the pixel in the upper left hand corner of the screen of the display panel 8 shown in Figure 6 as a pixel in the 0th row and 0th column, all pixels on the display panel 8 are grouped into a plurality of groups, each of which is composed of the pixels shown in Figure 7, so that the upper pixels A, B, G, and H may be in the (2m)th row on the screen, the lower pixels C, D, E, and F may be in the (2m+1)th row on the screen, pixels A and C in the leftmost column may be in the (4n)th column, pixels B and D
in the 2nd column from the left may be in the (4n+1)th column on the screen, pixels G and E in the 3rd column from the left may be in the (4n+2)th column on the screen, and pixels H and F in the rightmost column may be in the (4n+3)th column on the screen (where m and n are integers which are equal to or greater than 0 and independent from each other).
In the switch group 5 shown in Figure 5, the gradation rules shown in Figure 8 are applied to the pixels A through H. Namely, in this case, the gradation rules applied to the pixels A through D are exactly the same as the gradation rules applied to pixels A through D in case of the proposed example shown in Table 1. When setting the driving data for turning ON or OFF the pixels A, B, C, D, E, F, G and H, respectively, as a, b, c, d, e, f, g and h, the gradation rules shown in Figure 8 sets a=e, b=f, c=g and d=h. Thus, for the pixels in Figure 7, the ON/OFF state of the lower pixels E and F is set to the same as the ON/OFF
state of the upper pixels A and B in each frame, and the ON/OFF state of the upper pixels G and H is set to the same as the ON/OFF state of the lower pixels C and D.
In displaying the 0/8 gradation level, the OFF (no lighting) state is always selected for all of the eight pixels A through H for all eight frame time periods, and this cycle is then repeated.
~' -- lO 20 1 7757 In displaying the 1/8 gradation level, the ON
(lighting) state is selected for pixels A and E in the first of eight frames, the OFF state is selected for all eight pixels A through H in the second frame, the ON state is selected for pixels B and F in the third frame, the OFF
state is selected for all eight pixels A through H in the fourth frame, the ON state is selected for pixels C and G in the fifth frame, the OFF state is selected for all eight pixels A through H in the sixth frame, the ON state is selected for pixels D and H in the seventh frame, and the OFF state is selected for all eight pixels A through H in the eighth frame. This cycle is then repeated. Thus, in displaying the 1/8 gradation level, a frame in which two pixels are turned ON and another frame in which all eight pixels are turned OFF are alternately displayed. In this case, each of pixels A through H is turned ON equally once (in one frame) during the eight frame time periods.
In displaying the 2/8 gradation level, the ON state is selected for pixels A and E in the first frame, for pixels B and F in the second frame, for pixels C and G in the third frame, for pixels D and H in the fourth frame, and the pixel control rules for the first through fourth frames are repeated in the fifth through eighth frames. This cycle is then repeated. Thus, in displaying the 2/8 gradation level, two pixels are turned ON in all frames and each of pixels A through H is turned ON equally twice during the eight frame time periods.
In displaying the 3/8 gradation level, the ON state is selected for pixels A and E in the first frame, for pixels B, C, F and G in the second frame, for pixels C and G in the third frame, for pixels A, D, E and H in the fourth frame, for pixels D and H in the fifth frame, for pixels B, C, F and G in the sixth frame, for pixels B and F in the seventh frame, and for pixels A, D, E and H in the eighth frame. This cycle is then repeated. Thus, in displaying the 3/8 gradation level, a frame in which two pixels are turned ON and another frame in which four pixels are turned ~,~
ON are alternately displayed, and each of pixels A through H is turned ON equally three times during the eight frame time periods.
In displaying the 4/8 gradation level, the ON state is selected for pixels A, C, E and G in the first frame and for pixels B, D, F and H in the second frame. The gradation rules for the first and second frames are repeated in the third through eighth frames. This cycle is then repeated.
Thus, in displaying the 4/8 gradation level, four pixels are turned ON in all eight frames and each of pixels A through H is turned ON equally four times during the eight frames.
In displaying the 6/8 gradation level, the ON state is selected for pixels B, C, D, F, G and H in the first frame, for pixels A, C, D, E, G and H in the second frame, for pixels A, B, D, E, F and H in the third frame, for pixels A, B, C, E, F and G in the fourth frame, and the gradation rules for the first through fourth frames are repeated in the fifth through eighth frames. This cycle is then repeated. Thus, in displaying the 6/8 gradation level, six pixels are turned ON in all frames and each of pixels A
through H is turned ON equally six times during the eight frame time periods.
In displaying the 7/8 gradation level, the ON state is selected for pixels B, C, D, F, G and H in the first frame, for all pixels A through H in the second frame, for pixels A, C, D, E, G and H in the third frame, for all pixels A through H in the fourth frame, for pixels A, B, D, E, F and H in the fifth frame, for all pixels A through H in the sixth frame, for pixels A, B, C, E, F and G in the seventh frame, and for all pixels A through H in the eighth frame. This cycle is then repeated. Thus, in displaying the 7/8 gradation level, a frame in which six pixels are turned ON and another frame in which eight pixels are turned ON are alternately displayed and each of pixels A through H
is turned ON equally seven times during the eight frame time periods.
. . .
~i~
~12 201 7757 In displaying the 8/8 gradation level, the ON state is always selected for all eight pixels A through H during the eight frame time periods, and this cycle is then repeated.
5According to these gradation rules, the controller 2 drives eight pixels A through H forming one group in the display panel 8 of the liquid crystal display device 3. In these cases, the brightness levels as a whole of one group of eight pixels in the display panel 8 are as shown in 10Figures 9(a), 9(b), 9(c), 9(d), 9(e), 9(f), 9(g) and 9(h).
That is to say, in displaying the 0/8 gradation level, since all eight pixels A through H are turned OFF
throughout all frame time periods, the brightness level is always "0", as shown in Figure 9(a). Accordingly, the average brightness level is also "0" during one integration time period consisting of eight frame time periods. In this case, since the brightness level does not vary, there is no flicker.
In displaying the 1/8 gradation level, as shown in Figure 9(b), since two pixels are turned ON in the first frame, the brightness level is "2/8" and since all eight pixels are turned OFF in the second frame the brightness level becomes "0", and this cycle is repeated. As a result, the 1/8 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "2/8" and "0" brightness levels is half the frame frequency and (quadruple) greater than the frequency having eight frame periods as one integration period, flicker is reduced significantly.
In displaying the 2/8 gradation level, as shown in Figure 9(c), since two pixels are always turned ON
throughout all frame time periods, the brightness level is always "2/8". Accordingly, the average brightness level is also "2/8" during one integration time period consisting of eight frame time periods. In this case, since the brightness level does not vary, there is no flicker.
In displaying the 3/8 gradation level, as shown in Figure 9(d), since two pixels are turned ON in the first frame the brightness level is "2/8" and since four pixels are turned ON in the second frame the brightness level becomes "4/8", and this cycle is repeated. As a result, the 3/8 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "2/8" and "4/8" brightness levels is half the frame frequency and (quadruple) greater than the frequency having eight frame periods as one integration period, flicker is reduced significantly.
In displaying the 4/8 gradation level, as shown in Figure 9(e), since four pixels are always turned ON
throughout all frame time periods, the brightness level is always "4/8". Accordingly, the average brightness level is also "4/8" during one integration time period consisting of eight frame time periods. In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 6/8 gradation level also, as shown in Figure 9(f), since six pixels are always turned ON
throughout all frame time periods, the brightness level is always "6/8". In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 7/8 gradation level, as shown in Figure 9(g), since six pixels are turned ON in the first frame, the brightness level is "6/8" and since all eight pixels are turned ON in the second frame, the brightness level becomes "8/8", and this cycle is repeated. As a result, the 7/8 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since a frequency of alternating the "6/8"
and "8/8" brightness levels is half the frame frequency and greater than the frequency of one integration time period, flicker is reduced significantly.
In displaying the 8/8 gradation level, as shown in Figure 9(h), since all eight pixels are always turned ON
throughout all frame time periods, the brightness level is always "8/8". Accordingly, the average brightness level is also "8/8" during one integration time period consisting of 8 frame time periods. In this case, since the brightness level does not vary, there is no flicker.
As mentioned above, since the ON/OFF state of pixels A and B in the upper row of pixels A through H of one group is the same as the ON/OFF state of pixels E and F in the lower row and the ON/OFF state of pixels C and D in the lower row is the same as the ON/OFF state of pixels G and H
in the upper row, the number of pixels turned ON of pixels A, B, G and H in the upper row and the number of pixels turned ON of pixels C, D, E and F in the lower row are always equal to each other. Accordingly, when the same brightness level is displayed all over the screen, the number of pixels turned ON out of the pixels arranged in one scanning line in a frame is always the same as that in any other frame. As a result, the brightness of the pixels turned ON does not vary in each frame and any delicate shades of brightness do not occur among pixels.
Referring now to Figures 10, 11 and 12 for displaying a checker pattern as shown in Figure 12 on the basis of the gradation rules shown in Figure 8, Figures ll(a) through ll(h) are schematic diagrams showing the variation of brightness level in a gradational display obtained by the gradation rules of Figure 10.
In Figure 12, a pixel to be turned ON is indicated as a blank box and a pixel to be turned OFF is indicated as a hatched box. The pixel in the upper left hand corner of the screen and the pixels alternately disposed thereafter are turned ON. Accordingly, the gradation rules shown in Figure 10 are equivalent to those according to which pixels B, C, E and H controlled according to the gradation rules shown in Figure 8 are turned OFF throughout all frame time periods.
As mentioned above, since the gradation rules shown in Figure 8 are set so that the ON/OFF state of pixels A and ~f~
B of the group of pixels shown in Figure 7 may be equal to the ON/OFF state of pixels E and F and the ON/OFF state of pixels C and D may be equal to the ON/OFF state of pixels G
and H. Pixels F and G to be set in the same ON/OFF state as pixels B and C are not changed to be turned OFF among the pixels E, F, G and H in order to display a checker pattern, even in case wherein pixels B and C to be originally turned ON are changed to be turned OFF in order to display a checker pattern among pixels A, B, C and D. In other words, it is pixels E and H that are changed to be turned OFF among pixels E, F, G and H in order to display a checker pattern in spite of being originally turned ON.
On the other hand, even when pixels E and H of the group of pixels E, F, G and H are changed to be turned OFF
lS in order to display a checker pattern in spite of being originally turned ON, pixels A and D of the group of pixels A, B, C and D to be set in the same ON/OFF state as pixels E and H are not changed to be turned OFF in order to display a checker pattern. Accordingly, the number of pixels turned ON in each frame according to the gradation rules for displaying a checker pattern is reduced to one half as compared with that according to the gradation rules shown in Figure 8. However, the corresponding relation between the number of pixels turned ON and the gradation levels is kept equal in both cases.
Thus, in Figure 10, in displaying the 0/8 gradation level, the ON/OFF state of the pixels is the same as that in Figure 8. However, in displaying the 1/8 gradation level, pixel A is turned ON in the first frame, all pixels are turned OFF in the second frame, pixel F is turned ON in the third frame, all pixels are turned OFF in the fourth frame, pixel G is turned ON in the fifth frame, all pixels are turned OFF in the sixth frame, pixel D is turned ON in the seventh frame, and all pixels are turned OFF in the eighth 3S frame. Thus, in displaying the 1/8 gradation level, a frame in which one pixel is turned ON and another frame in which all eight pixels A through H are turned OFF are alternately displayed.
In displaying the 2/8 gradation level, the ON state is selected for pixel A in the first frame, for pixel F in the second frame, for pixel G in the third frame, for pixel D in the fourth frame, and the same gradation rules as applied in the first through fourth frames are applied to the fifth through eighth frames. Thus, in displaying the 2/8 gradation level, one pixel is turned ON in all frames.
In displaying the 3/8 gradation level, the ON state is selected for pixel A in the first frame, for pixels F and G in the second frame, for pixel G in the third frame, for pixels A and D in the fourth frame, for pixel D in the fifth frame, for pixels F and G in the sixth frame, for pixel F in the seventh frame, and for pixels A and D in the eight frame. Thus, in displaying the 3/8 gradation level, a frame in which one pixel is turned ON and another frame in which two pixels are turned ON are alternately displayed.
In displaying the 4/8 gradation level, the ON state is selected for pixels A and G in the first frame, for pixels D and F in the second frame, and this cycle is then repeated. Thus, in displaying the 4/8 gradation level, two pixels are turned ON in all frames.
In displaying the 6/8 gradation level, the ON state is selected for pixels D, F and G in the first frame, for pixels A, D and G in the second frame, for pixels A, D and F in the third frame, and for pixels A, F and G in the fourth frame. The same gradation rules as applied in first through fourth frames are applied in the fifth through eighth frames. Thus, in displaying the 6/8 gradation level, three pixels are turned on in all frames.
In displaying the 7/8 gradation level, the ON state is selected for pixels D, F and G in the first frame, for pixels A, D, F and G in the second frame, for pixels A, D
and G in the third frame, for pixels A, D, F and G in the fourth frame, for pixels A, D and F in the fifth frame, for pixels A, D, F and G in the sixth frame, for pixels A, F and '~ 17 20 1 7757 G in the seventh frame, and for pixels A, D, F and G in the eighth frame. Thus, in displaying the 7/8 gradation level, a frame in which three pixels are turned ON and another frame in which four pixels are turned ON are alternately displayed.
In displaying the 8/8 gradation level, the ON state is selected for pixels A, D, F and G in all frames. Thus, in displaying the 8/8 gradation level, four pixels are turned ON in all frames.
In these cases, the brightness levels as a whole of one group of eight pixels A through H in the display panel 8 are as shown in Figures ll(a), ll(b), ll(c), ll(d), ll(e), ll(f), ll(g) and ll(h).
That is to say, in displaying the 0/8 gradation level, since all pixels A through H are turned OFF
throughout all frame time periods, the brightness level is always "0" as shown in Figure ll(a).
In displaying the 1/8 gradation level, as shown in Figure ll(b), since one pixel is turned ON in the first frame, the brightness level is "1/8" and since all eight pixels are turned OFF in the second frame the brightness level becomes "0". This cycle is then repeated. As a result the 1/16 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "1/8"
and "0" brightness levels is half the frame frequency and (quadruple) greater than the frequency having eight frame periods as one integration period, flicker is reduced significantly.
In displaying the 2/8 gradation level, as shown in Figure ll(c), since one pixel is always turned ON throughout all frame time periods, the brightness level is always "1/8". Accordingly, the average brightness level is also "1/8" during one integration time period consisting of 8 frame time periods. In this case, since the brightness level does not vary, there is no flicker.
In displaying the 3/8 gradation level, as shown in Figure ll(d), since one pixel is turned ON in the first frame the brightness level is "1/8" and since two pixels are turned ON in the second frame the brightness level becomes "2/8", and this cycle is repeated. As a result, the 3/16 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "1/8" and "2/8" brightness levels is half the frame frequency and greater than the frequency of an integration period having eight frame time periods, flicker is reduced significantly.
In displaying the 4/8 gradation level, as shown in Figure ll(e), since two pixels are always turned ON
throughout all frame time periods, the brightness level is always "2/8". Accordingly, the average brightness level is also "2/8" during one integration time period consisting of eight frame time periods. In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 6/8 gradation level, as shown in Figure ll(f), since three pixels are always turned ON
throughout all frame time periods, the brightness level is always "3/8". In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 7/8 gradation level, as shown in Figure ll(g), since three pixels are turned ON in the first frame the brightness level is "3/8" and since four pixels are turned ON in the second frame, the brightness level becomes "4/8". This cycle is then repeated. As a result, the 7/16 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "3/8" and "4/8" brightness levels is half the frame frequency and greater than the frequency of one integration period, flicker is reduced significantly.
In displaying the 8/8 gradation level, as shown in Figure ll(h), since four pixels are always turned ON
throughout all frame time periods, the brightness level is ~ 19 2~ 1 7757 always "4/8". Accordingly, the average brightness level is also "4/8" during one integration time period consisting of 8 frame time periods. In this case also, since the brightness level does not vary, there is no flicker.
In displaying the checker pattern shown in Figure 12 according to the gradation rules of the previously proposed example shown in Table 1, flicker is noticeable on the screen. This is described below using the 6/8 gradation level of display as an example.
Figure 3 is a schematic diagram showing the gradation rule for the 6/8 gradation level in Table 1. The gradation rule for displaying a checker pattern as shown in Figure 12 is indicated by a schematic diagram shown in Figure 13.
The schematic diagram shown in Figure 13 is equivalent to the case of turning OFF pixels B and C in all frames in the schematic diagram shown in Figure 3.
Accordingly, the brightness as a whole of the unit image area of one group of four pixels A through D is as shown in Figure 14. In Figure 14, pixel D is turned ON in the first frame and the brightness level is "1/4", pixels A and D are turned ON in the second frame and the brightness level is "2/4", pixels A and D are turned ON in the third frame and the brightness level is "2/4", pixel A is turned ON in the fourth frame and the brightness level is "1/4", and the gradation rules applied in the first through fourth frames are repeated in the fifth through eighth frames. Thus, in displaying a checker pattern according to the gradation rule for the 6/8 gradation level, the brightness level is "2/4"
in two consecutive frames and "1/4" in the following two consecutive frames. This cycle is repeated. Accordingly, the frequency of alternating the "1/4" and "2/4" brightness levels is one quarter the frame frequency, and is less than the frequency for the same 6/8 brightness level in the above-mentioned embodiment. Thus, when the frame frequency is about 80 Hz, the frequency of alternating becomes about 20 Hz, and, as a result, flicker is very noticeable and causes a deterioration of the quality of the display.
In contrast, in an embodiment of the present invention, the frequency of alternating the variation of brightness level is at least about half the frame frequency, so flicker is not as noticeable as mentioned above.
In a liquid crystal display device and the like, a frame thinn;ng out system is well-known as a driving system for enabling a display panel to display a gradationally toned image with several brightness levels on its screen.
The frame th; nn; ng out system turns on pixels only in the number of frames corresponding to a level of brightness to be displayed out of all frames within an integration time period consisting of a plurality of frame time periods so as to visually obtain a medium level of brightness in each integration time period.
The applicant of the present invention has already proposed a driving method to reduce flicker on a screen by grouping pixels of the display device into groups, each of which is composed of a plurality of pixels contiguous to each other, and limiting the total number of pixels to be turned on for each frame time period within the same group according to the display data as a display driving method improving the conventional frame thinning out system.
Table 1 shows gradation rules (rules for turning pixels ON or OFF for a specific frame time period) for a gradational display by setting eight frame time periods as one integration time period by means of this driving method.
In this case, all pixels on the screen are grouped into groups of four pixels contiguous to each other as shown by arrow II on the display panel composed of a plurality of pixels arranged in the form of a matrix, as shown schematically in Figure 1.
Frame Gradation Pixel Level 1 2 3 4 5 6 7 8 A 0 o 0 0 0 0 0 0 0 / 8 B 0 o 0 0 0 0 0 0 C O o o O O O O O
1 / 8 B 0 0 1 o o o o 0 2 / 8 B o 1 0 0 0 1 0 0 A
C 1 1 1 1 1 1' D
In Table 1, numeral "1" indicates turning a pixel ON and numeral "0" indicates turning a pixel OFF.
Figure 2 is a magnification of one group of pixels shown by arrow II in the display panel of Figure 1. In the group of pixels, when setting the pixel in the upper left hand corner of the screen of the display panel 1 as a pixel in the 0th row and 0th column, the pixel arrangement is set so that in Figure 2 the two upper pixels A and B are in an even-numbered row, the two lower pixels C and D are in an odd-numbered row, the two left pixels A and C are in an even-numbered column, and the two right pixels B and D are in an odd-numbered column.
Figure 3 is a schematic diagram showing a gradation rule for each of pixels A through D in displaying a 6/8 gradation level all over the screen of the display panel 1.
As shown in Figure 3, in displaying the 6/8 gradation level, three pixels B, C and D are turned ON
(pixels A is turned OFF) for the first frame time period, three pixels A, C and D are turned ON (pixel B is OFF) for the second frame time period, three pixels A, B and D are turned ON (pixel C is OFF) for the third frame time period, and three pixels A, B and C are turned ON (pixel D is OFF) for the fourth frame time period. The rule for the first through fourth frame time periods is also applied to the fifth through eighth frame time periods, and this cycle of eight frame time periods as an integration time period is then repeated. Namely, in displaying the 6/8 gradation level, three pixels are always turned ON for each frame time period and each of pixels A through D are turned ON equally six times for eight frame time periods.
In this case the brightness level as a whole of a unit image area of one group of pixels A through D is as shown in Figure 4.
Since three pixels are turned ON throughout all frame time periods, the brightness level is always "3/4".
Accordingly, the 6/8 brightness level is displayed on the average during one integration time period consisting of - ~
eight frame time periods and brightness level of the group does not vary as a whole of the unit image area, so flicker is reduced.
In the above-mentioned driving method previously proposed, however, as shown in Figure 3, in the 6/8 brightness level the number of pixels turned ON in a subgroup of pixels A and B in the upper even-numbered row of pixels A through D is different from the number of pixels turned ON in a subgroup of pixels C and D in the lower odd-numbered row. As a result, the quality of the display isdeteriorated depending on the viewing angle when the above-mentioned driving method is applied to a capacitive display device such as a liquid crystal display device.
Since a capacitive display device, such as a liquid crystal display device, shows a phenomenon wherein the rightness of the pixel turned ON at that time varies according to the number of pixels turned ON out of the pixels arranged in one row (common line) on the screen of the display panel 1, the difference between the number of pixels turned ON in a subgroup of pixels A and B in the upper even-numbered row and the number of pixels turned ON
in a subgroup of pixels C and D in the lower odd-numbered row causes such deterioration of quality of the display that the brightness of the pixels varies for each frame time period and the bright points seem to be vibrating.
This problem occurs also in displaying the other gradation levels.
An object of the present invention is to provide a display driving method which makes it possible to display a high quality image with no noticeable flicker and no delicate shades of brightness among pixels of the same gradation level even in a capacitive display device such as a liquid crystal display device.
According to the present invention, there is provided a method for driving a display device having a plurality of scanning lines to make a gradationally toned display with several brightness levels by setting a plurality of frame time periods, during which each of pixels on a screen is controlled for displaying an image, as one integration time period and by turning on pixels for a number of specified frame time periods corresponding to display data of the image within the integration time period, comprising the steps of grouping the pixels of the display device into groups, each of which is composed of a plurality of pixels contiguous to each other; selecting the number of pixels to be turned on for each of the frame time periods within one integration time period corresponding to specified gradation data of each group of pixels, so that the number of pixels to be turned on for one frame time period may be equal between subgroups of pixels in the scanning lines within the same group of pixels; and setting the frame time period during the number of pixels to be turned on is kept constant to a period shorter than a predetermined period.
The invention provides a display driving method which makes a gradationally toned display by using multiple gradation data for each frame time period on the basis of a plurality of gradation data which are apart by a nearly equal level from the specified gradation data in directions opposite to each other.
Further, the invention provides a display device driving method which makes a gradationally toned display by turning on a number of pixels corresponding to the specified gradation data for each frame time period.
Still further, the invention provides a display driving method in which each pixel to be turned on is selected from pixels in different positions within each of the groups of pixels for each frame time period.
Furthermore, the invention provides a display driving method in which the difference between the plurality of gradation data is selected so as to be the minimum unit of gradation data.
Still furthermore, the invention provides a display driving method in which a period of variation among the plurality of gradation data is selected so as to be the same period as the frame time period.
According to the invention, all pixels of a display device are grouped into a plurality of groups, each of which is composed of a plurality of pixels contiguous to each other, and the number of pixels to be turned on for each frame time period within one integration time period is selected corresponding to specified gradation data, so that the number of pixels to be turned on for one frame time period may be equal between subgroups in the scanning lines within the same group. The frame time period during which the number of pixels to be turned on is kept constant is selected so as to be shorter than a predetermined period, namely, the minimum period for which a human feels flicker.
Accordingly, in viewing a plurality of pixels over one group of pixels as a unit image area, a high quality gradational display without noticeable flicker can be obtained. Since no delicate shades of brightness occur among pixels to display the same gradation level, the quality of the display is improved.
As mentioned above, according to a display device driving method of the present invention, selecting the number of pixels to be turned on out of a plurality of pixels contiguous to each other forming one group of pixels for each frame time period corresponding to its display data reduces variation of brightness as a whole of the group of pixels and makes it possible to obtain a gradationally toned display without noticeable flicker.
Since the number of pixels to be turned on for each frame time period is equal to each other among the subgroups respectively arranged in the scanning line within the same group, no delicate shades of brightness occur among pixels to display the same gradation level even in case of applying this driving method to a capacitive display device such as a liquid crystal display device. As a result, the quality of the display is improved significantly.
In the accompanying drawings which illustrate embodiments of the present invention:
Figure 1 is a plan view of a display panel illustrating a group of pixels for a previously proposed driving method as an example of the prior art;
Figure 2 is a plan view of a magnification of a group of pixels of the display panel of Figure l;
Figure 3 is a schematic diagram illustrating a gradation rule for displaying a 6/8 gradation level in the driving method of Figure 1;
Figure 4 is a schematic diagram showing the variation of brightness in a group of pixels controlled by the gradation rule of Figure 3;
Figure 5 is a block diagram of a configuration of a liquid crystal display device driving method to which a driving method of an embodiment of the present invention is applied;
Figure 6 is a schematic plan view of the display panel of the liquid crystal display device of Figure 5;
Figure 7 is a magnification of one group of pixels of the display panel of Figure 6;
Figure 8 is a schematic diagram showing gradation rules applied to the liquid crystal display device driving method;
Figures 9(a), 9(b), 9(c), 9(d), 9(e), 9(f), 9(g) and 9(h) are schematic diagrams showing the variation of brightness in one group of pixels controlled on the basis of the gradation rules of Figure 8;
Figure 10 is a schematic diagram showing gradation rules for displaying a checker pattern;
Figures ll(a), ll(b), ll(c), ll(d), ll(e), ll(f), ll(g) and ll(h) are schematic diagrams showing the variation of brightness in one group of pixels controlled on the basis of the gradation rules of Figure 10;
Figure 12 is a plan view schematically showing a display screen of the checker pattern;
' r . ~
-Figure 13 is a schematic diagram showing a gradation rule for a 6/8 gradation level for displaying a checker pattern of Figure 12 on the basis of the gradation rule in the driving method previously proposed as an example; and Figure 14 is a schematic diagram showing the variation of brightness in one group of pixels controlled on the basis of the gradation rule of Figure 13.
Referring now to Figure 5, a controller 2, for controlling the driving of a liquid crystal display device 3, has a random access memory 4 (hereinafter referred as to RAM) which stores display data including gradation data thereof, a switch group 5 which sets gradation rules for a frame thinning out system, and a timing signal generating circuit 6 which generates timing signals necessary for making the liquid crystal display device 3 display an image.
A host computer 7 controls the timing signal generating circuit 6.
Figure 6 is a plan view schematically showing a display panel 8 of the liquid crystal display device 3 in which a plurality of pixels are arranged in the form of a matrix, and Figure 7 is a plan view schematically showing a magnification of one group of pixels shown by arrow VII in the display panel 8 of Figure 6.
Referring now to Figures 8 and 9, operation of a liquid crystal display device driving method of the present invention is described as follows. The gradation rules applied to the liquid crystal display device driving method for displaying a uniform gradation over the screen of the display panel 8 is shown schematically in Figure 8.
Assuming that a gradationally toned display with 9 gradation levels, including 0/8 ("0" level), 1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7/8 and 8/8 ("1" level) gradation levels, is performed by setting eight frame time periods as one integration time period, a case is described wherein a unit image area with the 0/8, 1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7/8, '`~; lS~, or 8/8 gradation level in brightness is displayed with a group of pixels A, B, C, D, E, F, G and H shown in Figure 7.
When setting the pixel in the upper left hand corner of the screen of the display panel 8 shown in Figure 6 as a pixel in the 0th row and 0th column, all pixels on the display panel 8 are grouped into a plurality of groups, each of which is composed of the pixels shown in Figure 7, so that the upper pixels A, B, G, and H may be in the (2m)th row on the screen, the lower pixels C, D, E, and F may be in the (2m+1)th row on the screen, pixels A and C in the leftmost column may be in the (4n)th column, pixels B and D
in the 2nd column from the left may be in the (4n+1)th column on the screen, pixels G and E in the 3rd column from the left may be in the (4n+2)th column on the screen, and pixels H and F in the rightmost column may be in the (4n+3)th column on the screen (where m and n are integers which are equal to or greater than 0 and independent from each other).
In the switch group 5 shown in Figure 5, the gradation rules shown in Figure 8 are applied to the pixels A through H. Namely, in this case, the gradation rules applied to the pixels A through D are exactly the same as the gradation rules applied to pixels A through D in case of the proposed example shown in Table 1. When setting the driving data for turning ON or OFF the pixels A, B, C, D, E, F, G and H, respectively, as a, b, c, d, e, f, g and h, the gradation rules shown in Figure 8 sets a=e, b=f, c=g and d=h. Thus, for the pixels in Figure 7, the ON/OFF state of the lower pixels E and F is set to the same as the ON/OFF
state of the upper pixels A and B in each frame, and the ON/OFF state of the upper pixels G and H is set to the same as the ON/OFF state of the lower pixels C and D.
In displaying the 0/8 gradation level, the OFF (no lighting) state is always selected for all of the eight pixels A through H for all eight frame time periods, and this cycle is then repeated.
~' -- lO 20 1 7757 In displaying the 1/8 gradation level, the ON
(lighting) state is selected for pixels A and E in the first of eight frames, the OFF state is selected for all eight pixels A through H in the second frame, the ON state is selected for pixels B and F in the third frame, the OFF
state is selected for all eight pixels A through H in the fourth frame, the ON state is selected for pixels C and G in the fifth frame, the OFF state is selected for all eight pixels A through H in the sixth frame, the ON state is selected for pixels D and H in the seventh frame, and the OFF state is selected for all eight pixels A through H in the eighth frame. This cycle is then repeated. Thus, in displaying the 1/8 gradation level, a frame in which two pixels are turned ON and another frame in which all eight pixels are turned OFF are alternately displayed. In this case, each of pixels A through H is turned ON equally once (in one frame) during the eight frame time periods.
In displaying the 2/8 gradation level, the ON state is selected for pixels A and E in the first frame, for pixels B and F in the second frame, for pixels C and G in the third frame, for pixels D and H in the fourth frame, and the pixel control rules for the first through fourth frames are repeated in the fifth through eighth frames. This cycle is then repeated. Thus, in displaying the 2/8 gradation level, two pixels are turned ON in all frames and each of pixels A through H is turned ON equally twice during the eight frame time periods.
In displaying the 3/8 gradation level, the ON state is selected for pixels A and E in the first frame, for pixels B, C, F and G in the second frame, for pixels C and G in the third frame, for pixels A, D, E and H in the fourth frame, for pixels D and H in the fifth frame, for pixels B, C, F and G in the sixth frame, for pixels B and F in the seventh frame, and for pixels A, D, E and H in the eighth frame. This cycle is then repeated. Thus, in displaying the 3/8 gradation level, a frame in which two pixels are turned ON and another frame in which four pixels are turned ~,~
ON are alternately displayed, and each of pixels A through H is turned ON equally three times during the eight frame time periods.
In displaying the 4/8 gradation level, the ON state is selected for pixels A, C, E and G in the first frame and for pixels B, D, F and H in the second frame. The gradation rules for the first and second frames are repeated in the third through eighth frames. This cycle is then repeated.
Thus, in displaying the 4/8 gradation level, four pixels are turned ON in all eight frames and each of pixels A through H is turned ON equally four times during the eight frames.
In displaying the 6/8 gradation level, the ON state is selected for pixels B, C, D, F, G and H in the first frame, for pixels A, C, D, E, G and H in the second frame, for pixels A, B, D, E, F and H in the third frame, for pixels A, B, C, E, F and G in the fourth frame, and the gradation rules for the first through fourth frames are repeated in the fifth through eighth frames. This cycle is then repeated. Thus, in displaying the 6/8 gradation level, six pixels are turned ON in all frames and each of pixels A
through H is turned ON equally six times during the eight frame time periods.
In displaying the 7/8 gradation level, the ON state is selected for pixels B, C, D, F, G and H in the first frame, for all pixels A through H in the second frame, for pixels A, C, D, E, G and H in the third frame, for all pixels A through H in the fourth frame, for pixels A, B, D, E, F and H in the fifth frame, for all pixels A through H in the sixth frame, for pixels A, B, C, E, F and G in the seventh frame, and for all pixels A through H in the eighth frame. This cycle is then repeated. Thus, in displaying the 7/8 gradation level, a frame in which six pixels are turned ON and another frame in which eight pixels are turned ON are alternately displayed and each of pixels A through H
is turned ON equally seven times during the eight frame time periods.
. . .
~i~
~12 201 7757 In displaying the 8/8 gradation level, the ON state is always selected for all eight pixels A through H during the eight frame time periods, and this cycle is then repeated.
5According to these gradation rules, the controller 2 drives eight pixels A through H forming one group in the display panel 8 of the liquid crystal display device 3. In these cases, the brightness levels as a whole of one group of eight pixels in the display panel 8 are as shown in 10Figures 9(a), 9(b), 9(c), 9(d), 9(e), 9(f), 9(g) and 9(h).
That is to say, in displaying the 0/8 gradation level, since all eight pixels A through H are turned OFF
throughout all frame time periods, the brightness level is always "0", as shown in Figure 9(a). Accordingly, the average brightness level is also "0" during one integration time period consisting of eight frame time periods. In this case, since the brightness level does not vary, there is no flicker.
In displaying the 1/8 gradation level, as shown in Figure 9(b), since two pixels are turned ON in the first frame, the brightness level is "2/8" and since all eight pixels are turned OFF in the second frame the brightness level becomes "0", and this cycle is repeated. As a result, the 1/8 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "2/8" and "0" brightness levels is half the frame frequency and (quadruple) greater than the frequency having eight frame periods as one integration period, flicker is reduced significantly.
In displaying the 2/8 gradation level, as shown in Figure 9(c), since two pixels are always turned ON
throughout all frame time periods, the brightness level is always "2/8". Accordingly, the average brightness level is also "2/8" during one integration time period consisting of eight frame time periods. In this case, since the brightness level does not vary, there is no flicker.
In displaying the 3/8 gradation level, as shown in Figure 9(d), since two pixels are turned ON in the first frame the brightness level is "2/8" and since four pixels are turned ON in the second frame the brightness level becomes "4/8", and this cycle is repeated. As a result, the 3/8 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "2/8" and "4/8" brightness levels is half the frame frequency and (quadruple) greater than the frequency having eight frame periods as one integration period, flicker is reduced significantly.
In displaying the 4/8 gradation level, as shown in Figure 9(e), since four pixels are always turned ON
throughout all frame time periods, the brightness level is always "4/8". Accordingly, the average brightness level is also "4/8" during one integration time period consisting of eight frame time periods. In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 6/8 gradation level also, as shown in Figure 9(f), since six pixels are always turned ON
throughout all frame time periods, the brightness level is always "6/8". In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 7/8 gradation level, as shown in Figure 9(g), since six pixels are turned ON in the first frame, the brightness level is "6/8" and since all eight pixels are turned ON in the second frame, the brightness level becomes "8/8", and this cycle is repeated. As a result, the 7/8 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since a frequency of alternating the "6/8"
and "8/8" brightness levels is half the frame frequency and greater than the frequency of one integration time period, flicker is reduced significantly.
In displaying the 8/8 gradation level, as shown in Figure 9(h), since all eight pixels are always turned ON
throughout all frame time periods, the brightness level is always "8/8". Accordingly, the average brightness level is also "8/8" during one integration time period consisting of 8 frame time periods. In this case, since the brightness level does not vary, there is no flicker.
As mentioned above, since the ON/OFF state of pixels A and B in the upper row of pixels A through H of one group is the same as the ON/OFF state of pixels E and F in the lower row and the ON/OFF state of pixels C and D in the lower row is the same as the ON/OFF state of pixels G and H
in the upper row, the number of pixels turned ON of pixels A, B, G and H in the upper row and the number of pixels turned ON of pixels C, D, E and F in the lower row are always equal to each other. Accordingly, when the same brightness level is displayed all over the screen, the number of pixels turned ON out of the pixels arranged in one scanning line in a frame is always the same as that in any other frame. As a result, the brightness of the pixels turned ON does not vary in each frame and any delicate shades of brightness do not occur among pixels.
Referring now to Figures 10, 11 and 12 for displaying a checker pattern as shown in Figure 12 on the basis of the gradation rules shown in Figure 8, Figures ll(a) through ll(h) are schematic diagrams showing the variation of brightness level in a gradational display obtained by the gradation rules of Figure 10.
In Figure 12, a pixel to be turned ON is indicated as a blank box and a pixel to be turned OFF is indicated as a hatched box. The pixel in the upper left hand corner of the screen and the pixels alternately disposed thereafter are turned ON. Accordingly, the gradation rules shown in Figure 10 are equivalent to those according to which pixels B, C, E and H controlled according to the gradation rules shown in Figure 8 are turned OFF throughout all frame time periods.
As mentioned above, since the gradation rules shown in Figure 8 are set so that the ON/OFF state of pixels A and ~f~
B of the group of pixels shown in Figure 7 may be equal to the ON/OFF state of pixels E and F and the ON/OFF state of pixels C and D may be equal to the ON/OFF state of pixels G
and H. Pixels F and G to be set in the same ON/OFF state as pixels B and C are not changed to be turned OFF among the pixels E, F, G and H in order to display a checker pattern, even in case wherein pixels B and C to be originally turned ON are changed to be turned OFF in order to display a checker pattern among pixels A, B, C and D. In other words, it is pixels E and H that are changed to be turned OFF among pixels E, F, G and H in order to display a checker pattern in spite of being originally turned ON.
On the other hand, even when pixels E and H of the group of pixels E, F, G and H are changed to be turned OFF
lS in order to display a checker pattern in spite of being originally turned ON, pixels A and D of the group of pixels A, B, C and D to be set in the same ON/OFF state as pixels E and H are not changed to be turned OFF in order to display a checker pattern. Accordingly, the number of pixels turned ON in each frame according to the gradation rules for displaying a checker pattern is reduced to one half as compared with that according to the gradation rules shown in Figure 8. However, the corresponding relation between the number of pixels turned ON and the gradation levels is kept equal in both cases.
Thus, in Figure 10, in displaying the 0/8 gradation level, the ON/OFF state of the pixels is the same as that in Figure 8. However, in displaying the 1/8 gradation level, pixel A is turned ON in the first frame, all pixels are turned OFF in the second frame, pixel F is turned ON in the third frame, all pixels are turned OFF in the fourth frame, pixel G is turned ON in the fifth frame, all pixels are turned OFF in the sixth frame, pixel D is turned ON in the seventh frame, and all pixels are turned OFF in the eighth 3S frame. Thus, in displaying the 1/8 gradation level, a frame in which one pixel is turned ON and another frame in which all eight pixels A through H are turned OFF are alternately displayed.
In displaying the 2/8 gradation level, the ON state is selected for pixel A in the first frame, for pixel F in the second frame, for pixel G in the third frame, for pixel D in the fourth frame, and the same gradation rules as applied in the first through fourth frames are applied to the fifth through eighth frames. Thus, in displaying the 2/8 gradation level, one pixel is turned ON in all frames.
In displaying the 3/8 gradation level, the ON state is selected for pixel A in the first frame, for pixels F and G in the second frame, for pixel G in the third frame, for pixels A and D in the fourth frame, for pixel D in the fifth frame, for pixels F and G in the sixth frame, for pixel F in the seventh frame, and for pixels A and D in the eight frame. Thus, in displaying the 3/8 gradation level, a frame in which one pixel is turned ON and another frame in which two pixels are turned ON are alternately displayed.
In displaying the 4/8 gradation level, the ON state is selected for pixels A and G in the first frame, for pixels D and F in the second frame, and this cycle is then repeated. Thus, in displaying the 4/8 gradation level, two pixels are turned ON in all frames.
In displaying the 6/8 gradation level, the ON state is selected for pixels D, F and G in the first frame, for pixels A, D and G in the second frame, for pixels A, D and F in the third frame, and for pixels A, F and G in the fourth frame. The same gradation rules as applied in first through fourth frames are applied in the fifth through eighth frames. Thus, in displaying the 6/8 gradation level, three pixels are turned on in all frames.
In displaying the 7/8 gradation level, the ON state is selected for pixels D, F and G in the first frame, for pixels A, D, F and G in the second frame, for pixels A, D
and G in the third frame, for pixels A, D, F and G in the fourth frame, for pixels A, D and F in the fifth frame, for pixels A, D, F and G in the sixth frame, for pixels A, F and '~ 17 20 1 7757 G in the seventh frame, and for pixels A, D, F and G in the eighth frame. Thus, in displaying the 7/8 gradation level, a frame in which three pixels are turned ON and another frame in which four pixels are turned ON are alternately displayed.
In displaying the 8/8 gradation level, the ON state is selected for pixels A, D, F and G in all frames. Thus, in displaying the 8/8 gradation level, four pixels are turned ON in all frames.
In these cases, the brightness levels as a whole of one group of eight pixels A through H in the display panel 8 are as shown in Figures ll(a), ll(b), ll(c), ll(d), ll(e), ll(f), ll(g) and ll(h).
That is to say, in displaying the 0/8 gradation level, since all pixels A through H are turned OFF
throughout all frame time periods, the brightness level is always "0" as shown in Figure ll(a).
In displaying the 1/8 gradation level, as shown in Figure ll(b), since one pixel is turned ON in the first frame, the brightness level is "1/8" and since all eight pixels are turned OFF in the second frame the brightness level becomes "0". This cycle is then repeated. As a result the 1/16 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "1/8"
and "0" brightness levels is half the frame frequency and (quadruple) greater than the frequency having eight frame periods as one integration period, flicker is reduced significantly.
In displaying the 2/8 gradation level, as shown in Figure ll(c), since one pixel is always turned ON throughout all frame time periods, the brightness level is always "1/8". Accordingly, the average brightness level is also "1/8" during one integration time period consisting of 8 frame time periods. In this case, since the brightness level does not vary, there is no flicker.
In displaying the 3/8 gradation level, as shown in Figure ll(d), since one pixel is turned ON in the first frame the brightness level is "1/8" and since two pixels are turned ON in the second frame the brightness level becomes "2/8", and this cycle is repeated. As a result, the 3/16 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "1/8" and "2/8" brightness levels is half the frame frequency and greater than the frequency of an integration period having eight frame time periods, flicker is reduced significantly.
In displaying the 4/8 gradation level, as shown in Figure ll(e), since two pixels are always turned ON
throughout all frame time periods, the brightness level is always "2/8". Accordingly, the average brightness level is also "2/8" during one integration time period consisting of eight frame time periods. In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 6/8 gradation level, as shown in Figure ll(f), since three pixels are always turned ON
throughout all frame time periods, the brightness level is always "3/8". In this case also, since the brightness level does not vary, there is no flicker.
In displaying the 7/8 gradation level, as shown in Figure ll(g), since three pixels are turned ON in the first frame the brightness level is "3/8" and since four pixels are turned ON in the second frame, the brightness level becomes "4/8". This cycle is then repeated. As a result, the 7/16 brightness level is displayed on average during one integration time period consisting of eight frame time periods. Since the frequency of alternating the "3/8" and "4/8" brightness levels is half the frame frequency and greater than the frequency of one integration period, flicker is reduced significantly.
In displaying the 8/8 gradation level, as shown in Figure ll(h), since four pixels are always turned ON
throughout all frame time periods, the brightness level is ~ 19 2~ 1 7757 always "4/8". Accordingly, the average brightness level is also "4/8" during one integration time period consisting of 8 frame time periods. In this case also, since the brightness level does not vary, there is no flicker.
In displaying the checker pattern shown in Figure 12 according to the gradation rules of the previously proposed example shown in Table 1, flicker is noticeable on the screen. This is described below using the 6/8 gradation level of display as an example.
Figure 3 is a schematic diagram showing the gradation rule for the 6/8 gradation level in Table 1. The gradation rule for displaying a checker pattern as shown in Figure 12 is indicated by a schematic diagram shown in Figure 13.
The schematic diagram shown in Figure 13 is equivalent to the case of turning OFF pixels B and C in all frames in the schematic diagram shown in Figure 3.
Accordingly, the brightness as a whole of the unit image area of one group of four pixels A through D is as shown in Figure 14. In Figure 14, pixel D is turned ON in the first frame and the brightness level is "1/4", pixels A and D are turned ON in the second frame and the brightness level is "2/4", pixels A and D are turned ON in the third frame and the brightness level is "2/4", pixel A is turned ON in the fourth frame and the brightness level is "1/4", and the gradation rules applied in the first through fourth frames are repeated in the fifth through eighth frames. Thus, in displaying a checker pattern according to the gradation rule for the 6/8 gradation level, the brightness level is "2/4"
in two consecutive frames and "1/4" in the following two consecutive frames. This cycle is repeated. Accordingly, the frequency of alternating the "1/4" and "2/4" brightness levels is one quarter the frame frequency, and is less than the frequency for the same 6/8 brightness level in the above-mentioned embodiment. Thus, when the frame frequency is about 80 Hz, the frequency of alternating becomes about 20 Hz, and, as a result, flicker is very noticeable and causes a deterioration of the quality of the display.
In contrast, in an embodiment of the present invention, the frequency of alternating the variation of brightness level is at least about half the frame frequency, so flicker is not as noticeable as mentioned above.
Claims (6)
1. A method for driving a display device having a plurality of scanning lines to make a gradationally toned display with several brightness levels by setting a plurality of frame time periods, during which each of pixels on a screen is controlled for displaying an image, as one integration time period and by turning on pixels for a number of specified frame time periods corresponding to display data of the image within the integration time period, comprising the steps of:
grouping the pixels of the display device into groups, each of which is composed of a plurality of pixels contiguous to each other;
selecting the number of pixels to be turned on for each of the frame time periods within one integration time period corresponding to specified gradation data of each group of pixels, so that the number of pixels to be turned on for one frame time period may be equal between subgroups of pixels in the scanning lines within the same group of pixels; and setting the frame time period during which the number of pixels to be turned on is kept constant to a period shorter than a predetermined period.
grouping the pixels of the display device into groups, each of which is composed of a plurality of pixels contiguous to each other;
selecting the number of pixels to be turned on for each of the frame time periods within one integration time period corresponding to specified gradation data of each group of pixels, so that the number of pixels to be turned on for one frame time period may be equal between subgroups of pixels in the scanning lines within the same group of pixels; and setting the frame time period during which the number of pixels to be turned on is kept constant to a period shorter than a predetermined period.
2. A method for driving a display device according to claim 1, wherein the gradationally toned display is made by using multiple gradation data for each frame time period on the basis of a plurality of gradation data which are apart by a nearly equal level from the specified gradation data in directions opposite to each other.
3. A method for driving a display device according to claim 1, wherein the gradationally toned display is made by turning on a number of pixels corresponding to the specified gradation data for each frame time period.
4. A method for driving a display device according to claim 3, wherein each pixel to be turned on is selected from pixels in different locations within each of the groups of pixels for each frame time period.
5. A method for driving a display device according to claim 2, wherein the difference between the plurality of gradation data is selected so as to be the minimum unit of the specified gradation data.
6. A method for driving a display device according to claim 2, wherein a period of variation among the plurality of gradation data is selected so as to be the same period as the frame time period.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1138807A JP2637822B2 (en) | 1989-05-30 | 1989-05-30 | Driving method of display device |
| JP1-138807 | 1989-05-30 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2017757A1 CA2017757A1 (en) | 1990-11-30 |
| CA2017757C true CA2017757C (en) | 1995-02-14 |
Family
ID=15230699
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002017757A Expired - Lifetime CA2017757C (en) | 1989-05-30 | 1990-05-30 | Method for driving display device |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US5412395A (en) |
| EP (1) | EP0400992B1 (en) |
| JP (1) | JP2637822B2 (en) |
| CA (1) | CA2017757C (en) |
| DE (1) | DE69025983T2 (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3349527B2 (en) | 1991-10-01 | 2002-11-25 | 株式会社日立製作所 | Liquid crystal halftone display |
| EP0536975B1 (en) * | 1991-10-07 | 1997-06-04 | Fujitsu Limited | Method of driving surface-stabilised ferroelectric liquid crystal display element for increasing the number of gray scales |
| US5751265A (en) * | 1991-12-24 | 1998-05-12 | Cirrus Logic, Inc. | Apparatus and method for producing shaded images on display screens |
| GB2278223A (en) * | 1993-05-21 | 1994-11-23 | Sharp Kk | Spatial light modulator and directional display |
| JPH06347758A (en) * | 1993-06-02 | 1994-12-22 | Nec Corp | Driving method for liquid crystal display device |
| US6714212B1 (en) * | 1993-10-05 | 2004-03-30 | Canon Kabushiki Kaisha | Display apparatus |
| TW280901B (en) * | 1994-04-19 | 1996-07-11 | Matsushita Electric Ind Co Ltd | |
| JP3426723B2 (en) * | 1994-08-30 | 2003-07-14 | 富士通ディスプレイテクノロジーズ株式会社 | Liquid crystal display device and driving method thereof |
| EP0703561A3 (en) * | 1994-09-26 | 1996-12-18 | Canon Kk | Driving method for display device and display apparatus |
| US5748164A (en) | 1994-12-22 | 1998-05-05 | Displaytech, Inc. | Active matrix liquid crystal image generator |
| US6025818A (en) * | 1994-12-27 | 2000-02-15 | Pioneer Electronic Corporation | Method for correcting pixel data in a self-luminous display panel driving system |
| JP3618948B2 (en) | 1996-03-11 | 2005-02-09 | キヤノン株式会社 | Image display device and driving method thereof |
| WO1998002773A1 (en) * | 1996-07-15 | 1998-01-22 | Hitachi, Ltd. | Display device |
| JP2002196728A (en) * | 2000-12-27 | 2002-07-12 | Matsushita Electric Ind Co Ltd | Method for driving simple matrix-type liquid crystal panel and liquid crystal display device |
| JP2002229505A (en) * | 2001-01-31 | 2002-08-16 | Nec Corp | Display device |
| US20040222954A1 (en) * | 2003-04-07 | 2004-11-11 | Lueder Ernst H. | Methods and apparatus for a display |
| US20060066549A1 (en) * | 2004-09-24 | 2006-03-30 | Sony Corporation | Flat display apparatus and driving method for flat display apparatus |
| EP1931127B1 (en) * | 2005-09-16 | 2015-05-27 | Sharp Kabushiki Kaisha | Display |
| US8330474B2 (en) * | 2008-10-15 | 2012-12-11 | Synaptics Incorporated | Sensor device and method with at surface object sensing and away from surface object sensing |
| CN101599253B (en) * | 2009-03-30 | 2012-08-22 | 南京中电熊猫液晶显示科技有限公司 | Driving method of liquid crystal display |
| JP4810711B2 (en) | 2010-01-14 | 2011-11-09 | オンキヨー株式会社 | Amplification equipment |
| KR102266064B1 (en) * | 2014-10-15 | 2021-06-18 | 삼성디스플레이 주식회사 | Method of driving display panel, display panel driving apparatus and display apparatus having the display panel driving apparatus |
| CN108111767B (en) * | 2018-01-24 | 2020-07-28 | 努比亚技术有限公司 | Shooting method, terminal and computer readable storage medium |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1399371A (en) * | 1972-03-15 | 1975-07-02 | Int Computers Ltd | Image display apparatus |
| US3997719A (en) * | 1975-03-19 | 1976-12-14 | Bell Telephone Laboratories, Incorporated | Bi-level display systems |
| US4531160A (en) * | 1983-05-03 | 1985-07-23 | Itek Corporation | Display processor system and method |
| DE3686428T2 (en) * | 1985-03-08 | 1993-01-14 | Ascii Corp | DISPLAY CONTROL SYSTEM. |
| US4827255A (en) * | 1985-05-31 | 1989-05-02 | Ascii Corporation | Display control system which produces varying patterns to reduce flickering |
| JPS6397921A (en) * | 1986-10-14 | 1988-04-28 | Seiko Epson Corp | Liquid crystal display device |
| JP2612863B2 (en) * | 1987-08-31 | 1997-05-21 | シャープ株式会社 | Driving method of display device |
| US5266940A (en) * | 1988-03-05 | 1993-11-30 | Sharp Kabushiki Kaisha | Method of gray scale display for dot matrix type display device |
| JP2784005B2 (en) * | 1988-03-05 | 1998-08-06 | シャープ株式会社 | Display device gradation display method |
| JPH0789265B2 (en) * | 1989-03-07 | 1995-09-27 | シャープ株式会社 | Driving method of display device |
-
1989
- 1989-05-30 JP JP1138807A patent/JP2637822B2/en not_active Expired - Lifetime
-
1990
- 1990-05-30 DE DE69025983T patent/DE69025983T2/en not_active Expired - Lifetime
- 1990-05-30 CA CA002017757A patent/CA2017757C/en not_active Expired - Lifetime
- 1990-05-30 EP EP90305884A patent/EP0400992B1/en not_active Expired - Lifetime
-
1992
- 1992-06-01 US US07/892,736 patent/US5412395A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0400992B1 (en) | 1996-03-20 |
| CA2017757A1 (en) | 1990-11-30 |
| EP0400992A2 (en) | 1990-12-05 |
| DE69025983D1 (en) | 1996-04-25 |
| EP0400992A3 (en) | 1992-06-03 |
| US5412395A (en) | 1995-05-02 |
| JP2637822B2 (en) | 1997-08-06 |
| JPH032722A (en) | 1991-01-09 |
| DE69025983T2 (en) | 1996-09-26 |
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