JP2004294731A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device which can improve quality of animations by realizing gradation expression in which occurrence of false contours of the animations is suppressed while optimizing subfield structure. <P>SOLUTION: In displaying images by applying a digitalized image signal to a display means 8 in which a plurality of pixels are arranged in matrix shape, the image display device divides one field of the image signal into a plurality of subfields whose periods are shorter than one field period and displays the images based on the image signal by performing the on-display or the off-display of the subfields according to the gradation levels of the image signal. The image display device is equipped with a subfield control means 4 which has a lookup table 12 in which a first group in which a plurality of subfields are arranged so that display periods of the subfields become longer or shorter one by one and a second group in which subfields whose display periods are identical are arranged one by one are set so as to be consecutive. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image display device, in particular, a liquid crystal image display device such as a projection display, a viewfinder, and a head mounted display, a plasma image display device, a digital mirror image display device, an electroluminescence image display device, and a field emission image. The present invention relates to an image display device such as a display device.
[0002]
[Prior art]
Generally, image display devices such as a liquid crystal image display device, a plasma image display device, a digital mirror image display device, an electroluminescence image display device, and a field emission image display device digitize this image signal as a method of displaying the image signal. There is a tendency that a digital system in which this digital signal is applied to each pixel is adopted. In this case, one television field (field) is composed of a plurality of subfields having different weights, and images are displayed by sequentially displaying the subfields in time series.
[0003]
Each of these image display devices has a different structure and a different driving method. However, any of the methods has the above-described subfield structure, and thus a pseudo contour is generated when displaying a moving image. For example, one field has a plurality of 8-bit subfields, and the time width of each subfield is 1 (= 2 ⁰ ): 2 (= 2 ¹ ): 4 (= 2 ² ): 8 (= 2 ³ ). : 16 (= 2 ⁴ ): 32 (= 2 ⁵ ): 64 (= 2 ⁶ ): 128 (= 2 ⁷ ). With the combination of these subfields, the gradation can be expressed in 256 gradation levels from 0 to 255. Here, it is considered that the pseudo contour in the moving image is caused by a temporal shift of light emission timing at the time of displaying each subfield. When the moving speed of the image is high, the time lag is converted into a space lag, so that a moving image false contour occurs and the moving image quality is degraded.
[0004]
FIG. 5 is a diagram for schematically explaining the generation of a moving image false contour. In FIG. 5, the subfield is composed of 1 to 8 (SF1 to SF8), and the boundary between adjacent pixels has a gradation level of “127” and “128”. The rightward direction in the drawing indicates the flow of time, and the display is sequentially performed in this order toward subfields SF1 to SF8. In the figure, a white portion indicates ON display (white), and a satin portion indicates OFF display (black). The higher the gradation level, the closer to white, and the lower the gradation level, the closer to black. S3 indicates the position of the line of sight in the height direction. Here, when the line of sight is fixed at the position S2, as shown by the light Y1, the subfields SF1 to SF7 pass white (showing ON pixels) and the subfield SF8 go black (showing OFF pixels). Since the transmitted light enters the eyes, the gradation level “127” can be properly recognized.
[0005]
However, when the line of sight moves from the position S2 to the upper position S1, as shown by the light Y2, in the subfields SF1 to SF8, all light passing through black (actually, almost no light) enters the eyes. The level becomes "0" (black). Accordingly, the line of sight generates a black level line in a pseudo manner, and this line is seen as an outline.
On the other hand, when the line of sight moves from the position S2 to the position S3 below, as shown by the light Y3, in the subfields SF1 to SF8, light that has passed all white (actually, almost no light) enters the eyes. , The gradation level becomes “255” (white). Therefore, a white level line is generated in a pseudo manner by this line of sight movement, and this line is seen as an outline.
[0006]
The following measures have been proposed to solve the above-described generation of the moving image pseudo contour. For example, as shown in Non-Patent Document 1, a subfield having a long display time in a subfield is divided into subfields having a shorter display time, dispersed into video fields, and the divided subfields are rearranged. As a result, when the subfield that is turned on at the adjacent gray level moves, the shift of the light emitted from the display element in the time direction becomes small, and the pseudo contour becomes difficult to recognize.
[0007]
Further, as disclosed in Patent Literature 1, in a liquid crystal display device, a subfield having a long display time is divided into subfields having a shorter display time for the same reason. The state of the display mode at this time will be described with reference to FIG. FIG. 6 is a schematic diagram for explaining an example of a display mode when a line of sight of a conventional image display device is moved. Here, one field is divided into 19 subfields SF1 to SF19. In the figure, the satin portion indicates off, and the white portion indicates on. The number in the white portion indicates the brightness level. This is the same in FIG. Here, a portion where the gradation level is 126 to 130 is shown. When the gradation level is 128, the subfields SF8 to SF11 are off, and the adjacent subfield SF12 is on.
[0008]
In this case, even if the line of sight moves from the position S2 to the position S1 or to the position S3, all of the lights Y1 to Y3 have a gradation level of 127 and no moving image pseudo contour occurs.
Non-Patent Document 2 proposes a “CLEAR driving method” as another method for improving a pseudo contour. This method is a method of sequentially stacking light emission periods in a PDP according to luminance, and has a great effect of improving a pseudo contour. Further, as another method for improving the pseudo contour, there is a method of sequentially stacking the light emission periods according to the luminance as disclosed in Patent Document 2, and this method is effective for suppressing the generation of the pseudo contour. is there.
[0009]
[Non-patent document 1]
"DLP Projection System" Display and Imaging 2001, Vo1.9, pp79-86
[Patent Document 1]
US Pat. No. 6,151,011 [Non-Patent Document 2]
NIKKEI ELECTRONICS 1999.10.4 (NO.753)
[Patent Document 2]
JP 2001-343950 A
[Problems to be solved by the invention]
However, each of the above-described prior arts has the following problems. That is, in the techniques of Non-patent Document 1 and Patent Document 1, at the grayscale level 128 as shown in FIG. 7, instead of turning on the subfield SF12 shown in FIG. 6, the subfield SF12 shown in FIG. For example, when the subfield SF17 is turned on, when the line of sight is fixed at the position S2, the gradation level is 127. When the line of sight moves from the position S2 to the position S1, the gradation level is 127, and the line of sight moves from the position S2 to the position S3. Then, the gradation level becomes 143. Therefore, when the line of sight moves from the position S2 to the position S3 (from light Y1 to Y3), the gradation level changes by 16 (= 143-127), and a moving image pseudo contour is generated at the boundary. There was a problem.
[0011]
In the case of the technique disclosed in Non-patent Document 2, the number of gradations that can be expressed by 24 subfields in 2 fields is only 24 levels. There is a problem that signal processing is required.
Further, in the case of the technique disclosed in Patent Document 2, the correspondence between each subfield to be accessed and the bit plane to be displayed cannot be given by a conventional simple look-up table. An additional control circuit for calculating from a bit plane to a subfield is required, and there has been a problem that the device structure is complicated.
The present invention has been made in view of such a problem, and an object of the present invention is to optimize a subfield structure, thereby enabling gradation expression in which generation of a moving image false contour is suppressed, and improving image quality of a moving image. It is to provide a display device.
[0012]
[Means for Solving the Problems]
According to the first aspect of the present invention, when a digitized image signal is applied to display means in which a plurality of pixels are arranged in a matrix and displayed, one field of the image signal is shorter than a plurality of one-field periods. An image display device that divides a sub-field into a plurality of periods, and selectively displays the sub-field on or off in accordance with a gradation level of the image signal to display an image based on the image signal; A first group in which a plurality of subfields are sequentially arranged so that the display period of the subfield is sequentially increased or shortened, and a second group in which subfields having the same display period of the subfield are sequentially arranged. Image display apparatus comprising a sub-field control means having a look-up table set to be continuous A.
[0013]
In this case, for example, as defined in claim 2, the look-up table sets the order in which the subfields are turned on from the subfield having the shortest display period to the longest subfield as the gradation level increases. When the subfield having the longest display period among the subfields in the off state is turned on, the turned on subfield is always kept on at the gray level or higher. Is set to
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an image display device according to the present invention will be described in detail with reference to the accompanying drawings.
<First embodiment>
FIG. 1 is a block diagram showing an example of an image display device according to the present invention, FIG. 2 is a graph showing a relationship between an input voltage and an output light intensity, and FIG. 3 is an example of a lookup table used when forming a subfield. FIG. Here, a display device using liquid crystal is described as an example of the image display device. However, the present invention is applied to a plasma image display device, a digital mirror image display device, an electroluminescence image display device, a field emission image display device, and the like. Is also applicable.
[0015]
As shown in FIG. 1, the image display device 2 includes a subfield control unit 4 for digitizing an image signal S to form a predetermined plurality of subfields for one field, and a plurality of pixels in a matrix. And a display unit 6 formed by the subfield control unit 4 and displaying an image by applying a digital signal. Specifically, the sub-field control unit 4 includes an A / D conversion unit 8 for digitizing an analog image signal and a digital signal (image signal) output from the A / D conversion unit 8. A subfield conversion circuit 10 for forming a plurality of fields, here 19 subfields, a lookup memory 12 for storing a lookup table as shown in FIG. It has first and second two frame memories 14 and 16 for storing signals formed by the subfield conversion circuit 10. Further, there are provided 20 shift registers SR1 to SR20 for storing sub-field data output from the first and second frame memories 14 and 16.
[0016]
The display means 6 has a display section 20 in which, for example, 640 × 480 pixels (not shown) are arranged in a matrix. One side of the display section 20 is provided with a row scanning electrode drive circuit 22. In addition, a column signal electrode drive circuit 24 is provided on the other side. The column signal electrode drive circuit 24 includes shift registers DSR1 to DSR20, and receives and holds data from the control-side shift registers SR1 to SR20.
[0017]
Next, the operation of the liquid crystal image display device 2 configured as described above will be described.
First, the A / D converter 8 converts the input analog image signal S into a digital signal. Here, an 8-bit input signal is used. The input image signal S is normally based on the inverse gamma characteristic of a CRT. In general, the relationship between the intensity of emitted light when a liquid crystal is driven as shown in FIG. The key cannot be correctly expressed. In FIG. 2, Vth indicates a threshold value, and Vsat indicates a saturation voltage. Therefore, as shown in FIG. 3, the display period of the subfield is adjusted so that the gradation can be correctly expressed and the pseudo contour does not occur by using the look-up table corresponding to the grayscale level and the subfield which is a feature of the present invention. , And on / off display of each subfield at each gradation level. The look-up table for performing the gamma correction and the suppression of the pseudo contour corresponds to a specific example of the present invention. Here, 256 levels of gradation levels from 0 to 255 are shown, and descriptions of intermediate portions are partially omitted. In the gradation levels described here, “1” indicates ON (lighting), and blank indicates OFF. At the time of display, the images are displayed in chronological order from subfield SF1 to subfield SF19.
[0018]
In the case shown in FIG. 3, each subfield is a first group in which a plurality of subfields are sequentially arranged such that the display period of the subfield becomes longer or shorter, for example, subfields SF1 to SF10. (In FIG. 3, the sub-fields are arranged so as to be sequentially longer), and a plurality of sub-fields having the longest sub-field display period, for example, a second group in which sub-fields SF11 to SF19 are sequentially arranged are two groups. And both are set to be continuous in this order.
Specifically, in the first group, the display period of each subfield is set to be sequentially longer, such as 30 μsec, 60 μsec, 90 μsec... 240 μsec, in the order of SF1, SF2,. In the second group, the display period of each of the subfields SF11 to SF19 is the same at 260 μsec. Also, here, the difference between the display periods of the adjacent subfields is set to be the same or shorter as the display period of the subfield becomes longer. For example, when the display period of a subfield is short, the difference between the display periods of adjacent subfields is 30 μsec. However, as the display period of the subfield becomes longer, the difference between the display periods of the subfields is gradually reduced to 20 μsec and 0 μsec. ing.
[0019]
Specifically, the difference between the display periods of the adjacent subfields is the same in 30 μsec for SF1 to SF4, 20 μsec for SF4 to SF11, and 0 μsec for SF11 to SF19. As described above, the difference between the display periods of the adjacent subfields is gradually reduced every several subfields, such as 30 μsec → 20 μsec → 0 μsec, as the display period of the subfield becomes longer.
[0020]
Also, here, as the gradation level increases, the display period is moved from the shortest subfield to the longest subfield in the first group for each subfield, and the first group is moved to the first group in the second group. Is turned on, and as the gradation level further increases, the subfield SF11 is moved from the shortest subfield to the longest subfield in the first group every subfield, and In each of the two groups, the subfield position is moved from the position closest to the first group to the position farthest from the first group for each subfield, and the subfield of the second group farthest from the first group among the subfields in the OFF state. When SF19 is turned on, In the above gray level sub-fields please caution so as to retain always on state. When the gradation level further increases, the same sub-field movement is sequentially repeated.
[0021]
The subfield conversion circuit 10 is a circuit that receives a digitized image signal and converts a pixel signal corresponding to each pixel into 19 subfields having a predetermined subfield display period. . Specifically, referring to a look-up table as shown in FIG. 3 in which information to be converted according to the gradation level of the input digital image signal is determined, a predetermined number, here 19, The image signal is divided into subfields. In the subfield conversion circuit 10, as shown in FIG. 1, a physical address is specified by a write control address signal, and data of a look-up table is written in the first and second frame memories 14 and 16.
[0022]
Each of the first and second frame memories 14 and 16 includes 19 subfield memories (not shown) corresponding to 19 subfields, and the subfield memory stores 640 × 480 pixels (640 × 480) for each pixel. ) Of subfield data are stored. The data held in the subfield memory is read out, for example, 20 bits at a time, and held in the shift registers SR1 to SR20. The held 20-bit data is transferred to the shift registers DSR1 to DSR20 of the display unit 20 and held. A memory for holding data is arranged in each pixel, and the data held in the shift registers DSR1 to DSR20 is transferred to the memory of each pixel and held. When 20 bits are held in each pixel and 640 bits of data are held in one column, data in the second column is held. Data transfer is sequentially repeated in three columns,... 480 columns, and data transfer for one subfield is completed. After the data is held in the memories of all pixels, the data of the memories of all pixels are all The liquid crystal is transferred to the pixels, and the liquid crystal of each pixel is driven simultaneously.
[0023]
After that, the operation is similarly performed in two subfields,..., 19 subfields, and one field ends. At the same time that data is being read from the first frame memory 14, data is being written from the subfield conversion circuit 10 to the second frame memory 16 at the same time. After reading of data for one field from the first frame memory 14 is completed, data for one field is read from the second frame memory 16. Thereafter, the first and second frame memories 14 and 16 alternately perform writing and reading operations for each field.
[0024]
Next, the reason why the generation of a moving image false contour is suppressed by forming the look-up table as shown in FIG. 3 will be described.
Returning to FIGS. 6 and 7, as shown in FIGS. 6 and 7, in the subfield pattern in which the pseudo contour is unlikely to occur, it is necessary that the position of the subfield to be turned on (lighted) is close in the adjacent gradation level. For example, when the gradation level changes from 127 to 128, the subfields SF8 to SF11 are turned off, and when the subfield SF19 is turned on (see FIG. 10), the brightness is 127 even if the line-of-sight movement speed is low. From 143 to 143, which are likely to be recognized and cause false contours. However, when the subfield SF12 is turned on instead of the subfield 19 (see FIG. 9), the brightness changes from 127 to 143 unless the line-of-sight moving speed is increased as shown by the light Y4 (position S4). And false contours are less likely to occur.
[0025]
Also, at the grayscale level 127, the brightness 15 is generated by turning on the subfields SF8 to SF11. In this case, the emission center of gravity of the subfields SF8 to SF11 is located between the subfields SF9 and SF10, and the grayscale level is Even if the subfield SF12 is turned on at 128, the movement of the center of light emission cannot be minimized. The emission center of gravity indicates an average position (SF) of brightness of a set of a certain subfield. Now, if the brightness 15 is arranged alone in the subfield SF11, when the gradation level changes from 127 to 128, the emission center of gravity changes from the subfield SF11 to the subfield SF12, and the shift of the emission center of gravity is one of the minimum. Can be a subfield. Therefore, the movement of the subfield can be made smaller as the difference between the display periods of the subfields is smaller at the adjacent grayscale levels, but the display period of each subfield is determined by the expressed grayscale level.
[0026]
Therefore, the following two conditions are required to achieve both the reduction of the pseudo contour and the gradation expression.
(1) The smaller the difference between the display periods of the subfields, the better.
(2) At the adjacent gradation level, the smaller the movement of the position of the light emission center of gravity of the subfield, the better.
[0027]
One example according to this policy is the look-up table shown in FIG. As described above, in the lookup table of FIG. 3, the display period of the subfield gradually increases as the number of subfields increases. When the display period of the subfield is short, the difference between the display times of the adjacent subfields is 30 μsec (SF1 to SF4), but as the display period of the subfield becomes longer, the display period of the adjacent subfield becomes longer. The difference is as short as 20 μsec and 0 μsec (in the case of the second group). This is because the relationship between the input voltage (effective voltage value) applied to the liquid crystal and the output light intensity does not change linearly but changes in an S-shape as shown in FIG. Even if it is equal to the display period of one subfield, the brightness of one subfield is brighter than the brightness of a plurality of subfields. Therefore, in order to perform accurate gradation expression, it is necessary to reduce the difference between the display periods of adjacent subfields as the number of subfields increases.
[0028]
Next, the change of the subfield when the gradation level increases from 0 will be described. When the gradation level is 0, for example, all the subfields are turned off. This determines the black level of the liquid crystal image display device, and the ON state of each subfield is set according to the required black level.
When the gradation level changes to 1, 2,..., The amount of movement of the subfield to be turned on becomes every subfield, and the display period of the subfield is 260 μsec after the subfield SF11 is turned on. Subfields to be further turned on move for each subfield like subfields SF12, SF13,... SF19. When the subfield SF12 is turned on, the subfield SF1 is also turned on at the same time, and two or more subfields SF2 and SF13, subfield SF3 and subfield SF14,... Two subfields are turned on at the same time.
[0029]
When the gradation level is 29 or less, the amount of movement of the subfield in which the gradation level is turned on is every subfield, and the occurrence of the pseudo contour is suppressed. When the gradation level is between 29 and 30, the subfield SF7 to be turned on does not move, and the subfield SF1 is turned on. However, the subfield SF1 has a short display period and is not recognized as a pseudo contour. This point is the same between the gradation levels 31 and 32. In an adjacent gradation level, a subfield to be turned on does not move but a subfield with a short display period is turned on, and also exists between other gradation levels. In this case, a subfield that is turned on at the same time has a short display period. The subfield may be a subfield, and is not limited to the subfield SF1.
[0030]
As described above, the display period of the subfield is set so as to become gradually longer halfway (first group), and thereafter, the display period is set to be constant (second group). It depends on the reason. That is, in the liquid crystal image display device, when the display period of the subfield becomes longer, it becomes considerably difficult to control the gradation level. Therefore, the display period is stopped from being further extended in the middle of the arranged subfields. ing. In this case, the brightness is reduced by an amount corresponding to the suppression of the increase in the display period of the subfield having the longer display period. To compensate for this, the subfield having the longer display period is turned on, and at the same time, the display period is reduced. Are set so that the short subfields are also turned on in order. As a result, even when the gradation level is increased, fine control of the gradation level can be performed.
[0031]
Also, in an image display device using liquid crystal, if the difference in display period between adjacent subfields is fixed without changing, the amount of movement of the subfield turned on between adjacent gradation levels is always one subfield. (For example, refer to the gradation levels 1 to 19), the relationship between the gradation level and the output light intensity becomes a quadratic curve as shown by a characteristic B1 in FIG. Undesirably, it shows characteristics that have jumped upward. Therefore, as the display period of the subfield becomes longer, the difference in the display period between adjacent subfields is gradually reduced, for example, for each of the plurality of subfields as described above. Good characteristics can be obtained.
[0032]
As described above, by adopting the look-up table structure as shown in FIG. 3, even if the gradation level changes, the movement amount of the light emission center of gravity at that time is reduced, so that the generation of the pseudo contour is largely suppressed. It becomes possible.
In addition, since the display period is set so as to be sequentially longer according to the display order of the subfields, the occurrence of so-called motion blur can be suppressed. Note that motion blur refers to a phenomenon in which, even in a still image, even if the resolution is good, the resolution of the image itself deteriorates due to the movement of the image and the image is blurred. Explaining this motion blur, the CRT (cathode ray tube) generally has less motion blur among image display devices, and the liquid crystal image display device has much motion blur. This is because the light emission pattern of the CRT is impulse light emission, whereas the light emission pattern of the liquid crystal image display device is retention light emission. In such a situation, if the display period gradually increases as the subfield number increases and forms one peak to end, that is, a so-called one-peak pattern, the above-described motion blur is generated. Generation can be greatly suppressed.
[0033]
In each of the lookup tables shown in FIG. 3, the display periods are arranged such that the display period is gradually increased halfway in the order in which the subfields are displayed, and the display period is fixed thereafter. Instead, this may be reversed, that is, the first group of subfields SF1 to SF9 having the longest display period of the subfield, and the shortest one may be set to the subfield SF19. In this case, the on / off pattern of each gradation level is completely reversed. For example, in FIG. 3, an array of "1" s that progress obliquely from the upper left direction to the lower right direction changes from the upper right direction to the lower left direction. The arrangement of “1” proceeds obliquely, and in this case, the same effect as described above can be obtained.
In each of the above embodiments, the case where the field is divided into 19 subfields has been described as an example. However, it is needless to say that the number of subfields is not limited.
[0034]
Further, the lookup table shown in FIG. 3 is set so that the difference in display period between adjacent subfields in the first group becomes shorter for each of the plurality of subfields as the display period of the subfield becomes longer. Alternatively, the difference between the display periods of adjacent subfields in the first group may be set to be shorter for each subfield as the display period of the subfield becomes longer. For example, when the display period of SF1 is 30 μsec and the difference between the display periods of the adjacent subfields is reduced by 1 μsec for each subfield, the display periods of SF2, SF3,... SF11, SF19 are 59 μsec, 87 μsec,. 275 μsec,... 275 μsec. Also in this case, the same lookup table as in FIG. 3 can be applied.
Further, the lookup table shown in FIG. 3 is set so that the difference in display period between adjacent subfields in the first group becomes shorter for each of the plurality of subfields as the display period of the subfield becomes longer. Alternatively, the difference in display period between adjacent subfields in the first group may always be the same. For example, if the display period of SF1 is 30 μsec and the difference between the display periods of adjacent subfields is 30 μsec, the display periods of SF2, SF3,... SF11,... SF19 are 60 μsec, 90 μsec,. Also in this case, the same lookup table as in FIG. 3 can be applied. Further, the present invention can be applied to image display devices such as a plasma image display device, a digital mirror image display device, an electroluminescence image display device, and a field emission image display device, in which the display period of the subfield is proportional to the brightness of the display device. , The occurrence of a pseudo contour can be largely suppressed.
[0035]
【The invention's effect】
As described above, according to the image display device of the present invention, it is possible to suppress the occurrence of a false contour, to provide a moving image with excellent gradation and little motion blur.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of an image display device according to the present invention.
FIG. 2 is a graph showing a relationship between an input voltage and an output light intensity.
FIG. 3 is a diagram showing an example of a lookup table used when forming a subfield.
FIG. 4 is a graph showing a relationship between a gradation level and an output light intensity.
FIG. 5 is a diagram for schematically explaining the generation of a moving image pseudo contour.
FIG. 6 is a schematic diagram for explaining an example of a display mode when a line of sight of a conventional image display device is moved.
FIG. 7 is another schematic diagram for explaining an example of a display mode when a line of sight of a conventional image display device is moved.
[Explanation of symbols]
2 ... image display device, 4 ... subfield control means, 6 ... display means, 8 ... A / D converter, 10 ... subfield conversion circuit, 12 ... lookup memory, 14 ... first frame memory, 16 ... 2 frame memories, 20 ... display unit.

Claims (2)

When applying the digitized image signal to a display unit in which a plurality of pixels are arranged in a matrix to display the image signal, one field of the image signal is divided into a plurality of subfields shorter than one field period. An image display device that selectively displays on or off the subfield according to a gradation level of the image signal and displays an image based on the image signal;
A first group in which a plurality of subfields are sequentially arranged so that the display period of the subfield becomes longer or shorter sequentially, and a second group in which subfields having the same display period of the subfield are sequentially arranged. An image display device comprising: a subfield control unit having a look-up table in which groups are set to be continuous. The look-up table moves the order in which the sub-fields are turned on from the sub-field having the shortest display period to the longest sub-field as the gradation level becomes higher. 2. The apparatus according to claim 1, wherein when the sub-field having the longest display period is turned on, the turned-on sub-field is always kept on at a gray level or higher. The image display device as described in the above.

Images