JP2005148297A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in which it is hard to avoid a pseudo-contour since a conventional display device which has two coding processes differing in subframe output gradation and display 256 gradations by averaging their results can select only one subframe. <P>SOLUTION: A display device which perform multi-gradation display by dividing a one-frame period of an input image signal into a plurality of subframes and selecting necessary subframes according to input gradations of the input image signal alternates and uses two tables having mutually different characteristics of output gradations to input gradations (one table for coding (a) of 256 gradations and the other table for coding (b) of 230 gradations) by frames of the input image signal. Consequently, a place where a pseudo-contour of a carry on a screen is easily generated can be made to move to another place in a next frame. Consequently, the generation of a pseudo-contour can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a display device, and in particular, a plasma display panel (hereinafter referred to as PDP) that performs multi-gradation display by configuring one frame period of an image signal by a plurality of subframes and selecting the subframes as appropriate. The present invention relates to a display device.

  In a PDP as an example of a display device, an operation state is used as a binary display of lighting or non-lighting. In order to obtain a halftone, one frame period (16.7 ms) of an image signal is used for a plurality of lighting times. The image is divided into subframes, and this subframe is appropriately selected and displayed according to the gradation of the image signal, and multi-gradation display is performed using the visual integration effect. A display device that performs display by such an intra-frame time-division drive display method is conventionally known (for example, see Patent Document 1).

  FIG. 16 is a block diagram showing an example of a conventional display device. In the figure, an image signal to be displayed is input to an image processing circuit 1, where image processing such as error diffusion processing, dither generation, and inverse gamma correction is performed. The image signal image-processed by the image processing circuit 1 is input to the sub-frame association circuit 2 where the corresponding R (red), G (green) and B (blue) pixels should emit light. Converted to subframe. At the time of the conversion of the subframe, the subframe association circuit 2 uses the coding table 4 stored in the external storage device as a correspondence table, and lights up the luminance of each subframe corresponding to the coding table 4 The number of times is determined using the weighting table 3 stored in the external storage device.

  The output signal associated with the subframe association circuit 2 is transferred to the subframe processing circuit 5. The sub-frame processing circuit 5 temporarily stores the input signal, and then reads it for each display time of each sub-frame, sends a control signal to the drive pulse generation circuit 6 and sends pixel data to the address electrode drive circuit 7. In order to display each pixel selected by the address electrode drive circuit 7, the drive pulse generation circuit 6 supplies a drive pulse to the X electrode drive circuit 8 and the Y electrode drive circuit 9 to start a sustain discharge and is selected. The displayed pixels are displayed on the plasma display panel (PDP) 10. This is continuously performed for each subframe.

  FIG. 17 shows an example of a subframe configuration used for multi-gradation display in a conventional display device using the subframe method. In the figure, the vertical axis Y1 to Yn represents the display line, and the horizontal axis represents the time axis. In the figure, in order to obtain 256 gradations (8 bits), one frame is divided into 8 sub-frames (SF1 to SF8) having different luminance weights, and the LSB (least significant bit) of 8-bit image data. To MSB (most significant bit) are assigned in order to form a subframe. In this example, the multi-gradation display divides one frame into M subframes, selects a subframe based on the gradation of the image data, and uses the visual integration effect to increase the power of 2M. The method of expressing the gradation of the image on the PDP 10 is adopted.

  Each subframe includes a reset period, an address period, and a sustain discharge period. Line sequential writing is performed in the address period. In addition, the length of the sustain discharge period with the pattern in FIG. 17 is different for each subframe because the number of sustain pulses (sustain pulses) corresponding to luminance weighting is applied. The number of sustain pulses applied in this case is 1, 2, 4, 8, 16, 32, 64, 128 from the LSB side, and is further increased by N times (N is a natural number) in order to increase the emission luminance. The number of pulses is applied.

  Although the number of subframes varies depending on the display device, PDP often uses 10 to 12 subframes depending on device characteristics of a reset period, an address period, and a sustain discharge period within the frame time.

  In display devices that perform multi-gradation display using such a subframe method, it is well known that pseudo contours appear during moving image display. Next, the pseudo contour that appears during the moving image display will be described.

  FIG. 18 shows a state where gradations 127 and 128 are displayed on adjacent pixels on the PDP. The vertical direction indicates the gradations 127 and 128 of the pixels, and the horizontal direction indicates the passage of time displayed on the PDP. A sub-frame with a pattern is selected and lit as an image. Here, it is assumed that the number of subframes is 8 as indicated by SF1 to SF8, and each subframe is weighted to 1, 2, 4, 8, 16, 32, 64, 128.

  In the pixel of gradation 127, as shown in FIG. 18, the subframes SF1, SF2, SF3, SF4, SF5, SF6, and SF7 are turned on, and the sum of the weights of these subframes SF1 to SF7 is 127, The brightness is 127. On the other hand, in the pixel of gradation 128, only the subframe SF8 is lit, and this weight is 128, which is the brightness of gradation 128.

  If a still image is displayed on the PDP, the line of sight is fixed. Therefore, the line of sight does not move to the adjacent pixel during the period in which the weighting of the subframe is integrated, so that the image is correctly recognized and no pseudo contour is generated. However, in the case of a moving image, the line of sight moves following the movement of the picture, so the line of sight moves to the next pixel within the integration time of the eye, and an image that should not be seen by It will be integrated and recognized.

  For example, it is assumed that a pixel of gradation 127 and a pixel of gradation 128 are in contact with each other and cross over the PDP. At this time, it is assumed that the line of sight moves to the adjacent pixel within the integration time of the eye. In FIG. 18, when the image moves upward in the screen, the eye follows the line a, and there is no subframe to be integrated at that time, so that the eye can see black. On the other hand, when the image moves in the opposite direction and the eye follows the line b, since the subframes SF1 to SF8 are integrated, it is recognized that the brightness has the weight of gradation 256. Originally, the gradation 127 and the gradation 128 must be output as images regardless of the movement of the image here, but they are visible as white stripes or black stripes.

  This is a phenomenon called moving image pseudo contour or moving image pseudo contour. This phenomenon is peculiar to a display device that employs the intra-subframe time-division drive display method, and is particularly desired to be improved because it deteriorates the moving image characteristics.

  Thus, as a countermeasure, a display device that has two codings with different output gradations of subframes and displays 256 gradations on average has been known (for example, see Patent Document 2). That is, in this conventional display device, the first and second values in which the average value of the sum of the input pixel data is the same as the value of the pixel data are obtained, and the first value is used as the number of gradations in each subframe. And a light emission pattern A for illuminating the pixel by assigning the second value and a light emission pattern B for causing the pixel to emit light by assigning the second value as the number of gradations of each subframe. In this configuration, the light emission of the pixels by B is alternately repeated for each frame.

JP 7-271325 A JP 2003-66892 A

  However, in the conventional display device described in Patent Document 2 above, there is data in which the number of subframes in which the light emission pattern A and the light emission pattern B are lit is the same and the number of subframes in which the light is lit is the same. However, there is a problem that it is difficult to avoid pseudo contours.

  The present invention has been made in view of the above points, and an object thereof is to provide a display device that improves a moving image pseudo contour and a still image pseudo contour.

  In order to achieve the above object, the display device of the first invention divides one frame period of the input image signal into a plurality of sub-frames having different luminance weights, and according to the input gradation of the input image signal. In a display device that performs multi-grayscale display by selecting one or more subframes of necessary luminance weighting from a plurality of subframes, two or more sets having different output grayscale characteristics with respect to input grayscale The table generating means for generating the table and two or more tables generated by the table generating means are sequentially and cyclically switched using one or both of one frame or pixel of the input image signal as a unit. And an image processing means for outputting an image signal having an output gradation corresponding to the input gradation of the input image signal.

  According to the present invention, two or more sets of tables having different output gradation characteristics with respect to input gradations are sequentially and cyclically switched using one or both of one frame or pixel of the input image signal as a unit. As a result, the place where the carry-out pseudo contour is likely to occur on the screen can be moved to another location in the next frame, and the position of the pseudo contour can be dispersed to the surrounding pixels in terms of time.

  In order to achieve the above object, the display device of the second invention divides one frame period of the input image signal into a plurality of sub-frames with different luminance weights to obtain the input gradation of the input image signal. Accordingly, in a display device that performs multi-grayscale display by selecting one or more subframes of necessary luminance weighting from a plurality of subframes, the number of subframes selected according to an increase in input grayscale The table generating means for generating two or more sets of tables whose characteristics increase nonlinearly, and the two or more sets of tables generated by the table generating means are either one frame or pixel of the input image signal or An image processing unit that sequentially switches in units of both and outputs an image signal having an output gradation corresponding to the input gradation of the input image signal. Than it is.

  In the present invention, when the number of subframe selections is a first value at a certain display gradation k, the number of subframe selections is the same as the first value or one larger than that at the next largest display gradation k + 1. The display gradation number is set to a value of 2, and the display gradation number k + 2 is larger than that, and the display gradation number is the same as or one larger than the subframe selection number when the display gradation k + 1. As the number of subframes increases non-linearly with the increase in the number of sub-frames, not only the number of pulses in the sustain discharge period but also the PDP that determines the display gradation by discharging in the address period for selecting light emission or non-light emission of the pixel. In such a display device, the gradation step can be eliminated.

  According to the first aspect of the present invention, the place where the pseudo contour of the carry on the screen is likely to occur can be moved to another place in the next frame, and the temporally surrounding pixels can be moved. Since the position of the pseudo contour can be dispersed, the place where the pseudo contour is likely to occur does not move together with the movement of the line of sight of the viewer of the display image, and the generation of the pseudo contour in the moving image display is reduced and a good image is obtained. Can be displayed.

  According to the second aspect of the present invention, in addition to the number of pulses in the sustain discharge period, the PDP that determines the display gradation by discharging in the address period in which light emission or non-light emission of the pixel is selected. In such a display device, the gradation step can be eliminated.

  Next, the best mode for carrying out the display device according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing first and second embodiments of a display device according to the present invention. In the figure, the same components as those in FIG. 16 are denoted by the same reference numerals, and the description thereof is omitted. In the embodiment shown in FIG. 1, a subframe weighting table 11 and a coding table 12 corresponding to the subframe weighting table 11 are added to the conventional display device shown in FIG. Thus, in this embodiment, there are two combinations corresponding to the coding and weighting of the subframe. The subframe association circuit 13 is slightly different in operation from the subframe association circuit 2 of FIG. Other circuit configurations are the same as those of the conventional display device. Hereinafter, a configuration having two coding tables as in the present embodiment will be referred to as double coding.

  Incidentally, the gradation of an image displayed by a display device using PDP is usually 256 gradations. In this case, the minimum number of subframes necessary for gradation display is eight. However, in order to easily avoid the problem of pseudo contour, 10 to 12 subframes are actually used.

<First Embodiment>
In the first embodiment of the present invention, the number of sub-frames is changed for each frame in order to solve the above problem. FIG. 2 shows a configuration of a subframe according to the first embodiment of this invention. As shown in FIG. 2, the number of subframes in this embodiment is 11, as shown by SF1 to SF11, and each of the subframes SF1 to SF11 is formed in a reset period, an address period, and a sustain discharge period. The sustain discharge period is shown with a pattern. The reset periods are the same in SF1 to SF11, and the address periods are also the same in SF1 to SF11, but the sustain discharge periods are different in SF1 to SF11.

  The brightness of the image is determined by the number of sustain pulses in the sustain discharge period, that is, the weight of the subframe. As shown in FIG. 2, the weights of the subframes are 1, 2, 3, 5, 8, 13, 18, 26, 39, 57, and 83 from the first subframe to the eleventh subframe. Further, the Fibonacci sequence is used for weighting the first subframe SF1 to the sixth subframe SF6 that are part of the subframe. In the Fibonacci sequence, αn + 1 = αn + αn−1. This Fibonacci number sequence is a regular number sequence. By using this Fibonacci number sequence for subframes (SF1 to SF5) having a small weight of the subframe, inversion of the selected number of subframes can be prevented well. . For this reason, luminance inversion due to address light emission can be prevented.

  FIG. 3 shows an example of a method for changing the gradation of the input signal in the present invention. In the figure, the horizontal axis represents the gradation of the input signal, and the vertical axis represents the gradation of the output signal. When the input signal has 256 gradations, in coding a, the gradation of the output signal is output with the same 256 as the input signal. In coding b, the gradation of the output signal is output at 230 which is lower than that of the input signal. These codings a and b are characteristics in which the gradation characteristics of the input signal versus the gradation characteristics of the output signal both change linearly.

  On the other hand, in coding c, when the gradation of the input signal is small or when the number of subframe selections is small, the gradation of the output signal is selected to be low, and the input signal of the middle or higher is made to have a characteristic of inclination parallel to coding a. Has been. It should be noted that selection may be made so that the number of output gradations is reduced by the number of gradations corresponding to the luminance of the address light emission by subframe selection in the coding table.

  4, FIG. 5 and FIG. 6 show the coding table 4 of FIG. 7, 8 and 9 show the coding table 12 of FIG. The leftmost columns in the coding tables 4 and 12 in FIGS. 4 to 9 indicate the gradation of the input signal, the second to twelfth columns indicate whether or not the subframes SF1 to SF11 can emit light, and are marked with a circle. The subframe that is on emits light. The thirteenth column in the coding tables 4 and 12 of FIGS. 4 to 9 indicates the gradation of the converted output signal, and the rightmost column indicates the number of subframes selected when displaying a certain gradation. Is shown.

  Therefore, for example, in the coding table 4, when the gradation of the input signal is 18, the second, third, and sixth subframes SF2, SF3, and SF6 are selected as shown in FIG. The weights in the weighting table 3 corresponding to these are 2, 3 and 13, respectively, as shown immediately below the subframe in FIG. 4, so the gradation of the output signal is a total of 18 gradations. The number of subframes selected at this time is three.

  On the other hand, for example, in the coding table 12, when the gradation of the input signal is 18, the first, third, and sixth subframes SF1, SF3, and SF6 are selected as shown in FIG. The weights in the weighting table 11 corresponding to these are 1, 3 and 13 as shown immediately below the subframe in FIG. 6, respectively, so that the gradation of the output signal is a total of 17 gradations. The number of subframes selected at this time is three.

  By the way, in the display device using PDP, the display gradation is determined by the number of sustain pulses in the sustain discharge period of FIG. 2, but discharge is also performed in the address period in which light emission or non-light emission of each pixel is selected. The discharge in this address period is often brighter than one pulse of the sustain discharge, and if the number of subframes is not increased as the number of gradations is increased, a gradation step occurs in the output signal.

  Therefore, in the coding table 4 in FIGS. 4 to 6 and the coding table 12 in FIGS. 7 to 9, the subframe selection number is selected to increase as necessary as the number of gradations increases, and once the subframe is selected. When the selection number increases, the selection is made so that the selection number of the subframe is the same or increases by one in the next gradation. As a result, the gradation step peculiar to the display device using the PDP can be eliminated.

  Further, the coding table 4 and the coding table 12 are selected so that the carry gradation of the uppermost subframe of the display gradation does not match (is different by one output gradation or more). For example, in the coding table 4 of FIG. 4, the highest subframe is moved up from SF6 to SF7 when the gradation of the input signal is changed from 28 to 29. On the other hand, in the coding table 12 of FIG. 7, the gradation at which the uppermost subframe shifts from SF6 to SF7 changes to the input gradations 31 to 32. As a result, the gradation position of the uppermost subframe, in which pseudo contour interference is most likely to occur in a display device that performs subframe display, moves in the output video and becomes inconspicuous.

  In the present embodiment, the subframe association circuit 13 in FIG. 1 includes a weighting table 3 and a coding table 4 corresponding thereto for a certain frame period for the image signal processed by the image processing circuit 1. Using the combination of the first table, the sub-frames of 256 gradations are associated, and for the next one frame period, the combination of the second table including the weighting table 11 and the corresponding coding table 12 is used. , 230-tone subframe association is repeated alternately for each frame.

  Here, the subframe associating circuit 13 divides one frame period of the input image signal into 11 subframes SF1 to SF11 with predetermined luminance weighting, and according to the gradation of each pixel of the input image signal. When the combination of the first table is used, the optimum display gradation is selected from the tables shown in FIGS. 4 to 6, and when the combination of the second table is used, FIGS. The optimum display gradation is selected from the table shown in FIG.

  As a result, as shown schematically in FIG. 10, the subframe association circuit 13 associates the subframes with 256 gradation subframes when the combination of the first table indicated by coding a is used. The image signal and the image signal associated with the 230 gray-scale subframe when the combination of the second table indicated by coding b is used are alternately switched and output for each frame. Note that the above codings a and b are also codings a and b shown in FIG.

  The weighting of the weighting table 3 shown in FIGS. 4 to 6 and the weighting of the weighting table 11 shown in FIGS. 7 to 9 are set to be the same, and only the coding tables 3 and 12 are changed. Thus, 256 gradations of coding a and 230 gradations of coding b are realized.

  Next, the effect of the first embodiment of the present invention will be described with reference to FIG. FIG. 11 shows an example in which input image signals of gradation 94 and gradation 95 are displayed. Here, a carry of the uppermost subframe occurs. The horizontal direction in FIG. 11 is the time direction, and there are a total of 11 subframes SF1 to SF11 within one frame period (16.7 ms). Here, the boundary between the gradation 94 and gradation 95 pixels of the input image signal moves upward in the figure at 2 pixels / frame.

  In the first frame, a first table combination (hereinafter also referred to as coding a) consisting of the weighting table 3 and the corresponding coding table 4 is used, and an image corresponding to the input gradation 94 and the input gradation 95 is used. However, the output gradation 94 and the output gradation 95 are selected as they are, and there is a carry of the uppermost subframe. In the next frame, a combination of a second table (hereinafter also referred to as coding b) consisting of the weighting table 11 and the corresponding coding table 12 is used by switching, and corresponds to the input gradation 94 and the input gradation 95. The image is selected as output gradation 84 and output gradation 85.

  At this time, it is assumed that the eye follows the moving image with the line of sight I in FIG. The first frame is the output gradation 94, and integration is performed from the subframe SF1 of coding a to the highest subframe SF9. At this time, as shown in FIG. 5, SF3, SF5, SF7, SF8, and SF9 are turned on, and a total 94 of their weights is integrated by the eyes and recognized as gradation 94.

  In the next frame, since the output gradation with respect to the input gradation 94 is 84 gradations, the integration is performed from the subframe SF1 of coding b to the highest subframe SF9. At this time, as shown in FIG. 8, SF 1, SF 4, SF 6, SF 8, and SF 9 are turned on, and their total weight 84 is integrated by the eyes and recognized as gradation 84.

  Similarly, it is assumed that the eye follows the moving image at the line of sight II in FIG. In this case, since the first frame is the output gradation 95, as shown in FIG. 5, the subframes SF1, SF3, SF5, SF8, and SF10 are turned on by coding a, but the line of sight II moves from SF1 to SF4. After that, the subframes SF5 to SF10 of adjacent pixels of 94 gradations are moved. At this time, the sub-frames SF3, SF5, SF7, SF8, and SF9 are turned on at the 94th gradation by coding a. Therefore, the subframes that are lit on the movement locus of the line of sight II are SF1, SF3, SF5, SF7, SF8, and SF9. A total 95 of these weights is integrated by the eyes and recognized as gradation 95.

  In the next frame, as shown in FIG. 11, the line of sight II moves from SF1 to SF4 on the pixel of the output gradation 85, and then moves in the subframes SF5 to SF11 of the adjacent pixels of the output gradation 84. Therefore, at this time, as shown in FIG. 8 by coding b, the subframes that are lit on the movement locus of the line of sight II are SF2, SF4, SF6, SF8, and SF9. And is recognized as gradation 85.

  Similarly, it is assumed that the eye follows the moving image at the line of sight III in FIG. In this case, in the first frame, the line of sight III moves on the subframes SF1 to SF11 of the pixel of the output gradation 95, but as shown in FIG. 5 by the coding a, the subframes SF1, SF3, SF5, SF8, The SF 10 is turned on, and the sum 95 of the weights is integrated by the eyes and recognized as the gradation 95.

  In the next frame, the line of sight III moves on the subframes SF1 to SF10 of the pixel whose output gradation is 85, but the subframes SF2, SF4, SF6, SF8, and SF9 are changed by coding b as shown in FIG. The light is turned on, and the sum 85 of these weights is integrated by the eyes and recognized as a gradation 85.

  Therefore, the time average value between two frames when following the line of sight I is 89 (= (94 + 84) / 2) gradations. Further, the time average value between two frames when following the line of sight II is 90 (= (95 + 85) / 2) gradation, and the time average value between two frames when following the line of sight III is also 90 ( = (95 + 85) / 2) gradation. In addition, the number of subframes selected at this time is 5 in the gradation 94 and gradation 95 and in the coding table 4 and the coding table 12 according to FIGS. Assuming that the light emission luminance in the address period corresponds to the number of sustain pulses 1 in the sustain period, the output gradations are 94 and 95 with 5 added, which match the original gradation to be expressed.

Thus, according to the present embodiment, since coding is switched between frames, a place where a carry-out pseudo contour is likely to occur moves to another place in the next frame, and thus the line of sight is changed. Locations where pseudo contours are likely to occur with movement do not move together. Then, the position of the pseudo contour is dispersed in the temporally surrounding pixels. For this reason, generation | occurrence | production of a moving image pseudo contour can be suppressed.
<Second Embodiment>
Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 12 shows the pixel configuration in the display panel and the progress of each frame in the second embodiment of the present invention. In this embodiment, as shown in FIG. 12, the pixels are divided into two groups A and B, respectively, and arranged in a staggered pattern. For example, the pixel B is arranged on the top, bottom, left and right of the pixel A, and the pixel A is arranged on the top, bottom, left and right of the pixel B.

  Then, in the time direction of the frame, the pixels that were in group A select group B in the next frame, and the pixels that were in group B select group A in the next frame. This is repeated alternately for each frame. FIG. 13 shows the passage of time at this time. In the pixel group A, coding 256 of gradation 256 and coding b of gradation 230 are alternately repeated for each frame. On the other hand, the pixel group B alternately repeats coding b and coding a for each frame.

  Next, the effect of the second embodiment will be described. FIG. 14 is an explanatory diagram of the effect on the still image pseudo contour of the present embodiment. In a display device using a PDP, a gradation step unique to a digital display device is visibly displayed. FIG. 14 shows the boundary between the input gradation 94 and the input gradation 95 still image. Here, a carry of the uppermost subframe occurs. The horizontal direction in FIG. 14 indicates the time direction, and each frame is divided into 11 subframes SF1 to SF11. The vertical direction in FIG. 14 represents the arrangement of pixels, and coding a and coding b are alternately arranged in units of pixels. The positions of coding a and b for each pixel are inverted for each frame. Further, in FIG. 14, a subframe with a pattern is selected and lit.

  Assume that an image is viewed at the line of sight IV in FIG. In this case, the input gradation is 94 gradations in a certain frame, and SF1 and SF4 among subframes S1 to S11 as shown in FIGS. 8 and 14 by coding b arranged in pixel group B. SF6, SF8, and SF9 are lit, and the total weight 84 at this time is integrated by the eyes and recognized as the luminance of the gradation 84. In the next frame, the line of sight IV moves on the pixel of the input gradation 94 of the pixel group A, and the coding a arranged in the pixel group A causes the subframes SF1 to SF11 as shown in FIGS. Among them, SF3, SF5, SF7, SF8, and SF9 are turned on, and the total 94 of their weights is integrated by the eyes and recognized as the luminance of the gradation 94.

  Similarly, it is assumed that an image is viewed at the line of sight V in FIG. In this case, in a certain frame, the line of sight V moves on the pixel of the input gradation 95 of the pixel group A, and the coding a arranged in the pixel group A causes the subframe SF1 to appear as shown in FIGS. Of SF11, SF1, SF3, SF5, SF8, and SF10 are turned on, and the total 95 of these weights is integrated by the eyes and recognized as the luminance of gradation 95. In the next frame, the line of sight V moves over the pixels of the input gradation 95 of the pixel group B, and the coding frames b arranged in the pixel group B cause subframes SF1 to SF11 as shown in FIGS. Of these, SF2, SF4, SF6, SF8, and SF9 are turned on, and the total 85 of these weights is integrated by the eyes and recognized as the luminance of gradation 85.

  Accordingly, in FIG. 14, the time average value of two frames when viewing a still image with the line of sight IV is 89 (= (84 + 94) / 2) gradations. On the other hand, the time average value of two frames when viewing a still image with the line of sight V is 90 (= (95 + 85) / 2) gradation. Also, the number of subframes selected at this time is 5 for gradations 94 and 95 and coding a and coding b, respectively, according to FIGS. Assuming that the emission luminance in the address period corresponds to the number of pulses of 1 in the sustain period, the respective gradations are 94 and 95 obtained by adding 5, which match the original gradation to be expressed.

  As described above, in this embodiment, even if the coding is switched in a staggered pattern, the gradation of the image is not disturbed. Moreover, this can have dithering and error diffusion effects. In this embodiment, since the coding is changed to a staggered pattern for each pixel direction and each frame, the carry position of the uppermost subframe is distributed in the time direction and the pixel direction, and the gradation is changed. There are fewer steps. Therefore, the still image pseudo contour peculiar to the digital display device can be greatly reduced.

  Next, the effect on the moving image pseudo contour of the second embodiment of the present invention will be described with reference to FIG. The horizontal direction in FIG. 15 is the time direction, and there are a total of 11 subframes SF1 to SF11 within one frame period (16.7 ms). Here, the boundary between the gradation 94 and gradation 95 pixels of the input image signal moves upward in the figure at 2 pixels / frame, as in FIG. The vertical direction in FIG. 15 represents the arrangement of pixels, and coding a and coding b are alternately arranged in units of pixels. The positions of coding a and b for each pixel are inverted for each frame. Further, in FIG. 15, a subframe with a pattern is selected and lit.

  Now, assume that the eye follows the moving image at line of sight VI in FIG. When the input gradation of the first frame is 94 gradations, the output gradation of coding b is 84 as shown in FIG. 8, where integration is performed from subframes SF1 to SF4. At this time, as shown in FIG. 8, SF <b> 1 and SF <b> 4 are lit, and the sum of their weights is 6. Further, the subframes of adjacent pixels are integrated according to the movement of the line of sight VI, and at this time, the subframes SF5 to SF9 of the output gradation 94 of coding a are integrated. At this time, as shown in FIG. 5, SF5, SF7, SF8, and SF9 are turned on, and the sum of their weights is 91. Therefore, the total weight of the lighting subframes in this frame is 97 (= 6 + 91), and the subframes are integrated by the eyes and recognized as gradation 97.

  In the next one frame, 94 gradation sub-frames SF1 to SF4 of coding a are integrated, and the sub-frames of adjacent pixels are integrated according to the movement of the line of sight VI. At this time, as shown in FIG. 5, the subframe SF3 is lit and its weight is 3. Further, the subframes of adjacent pixels are integrated according to the movement of the line of sight VI, and at this time, the subframes SF5 to SF9 of the output gradation 84 of coding b are integrated. At this time, as shown in FIG. 8, among SF5 to SF9, SF6, SF8, and SF9 are lit, so the sum of the weights at that time is 78. Therefore, the total weight of the lighting subframes in this frame is 81 (= 3 + 78), and the subframes are integrated by the eyes and recognized as gradation 81.

  Similarly, it is assumed that the eyes follow the moving image as indicated by a line of sight VII in FIG. In this case, since the first frame moves the pixel A with the output gradation 95, as shown in FIG. 5, the subframes SF1, SF3, SF5, SF8, and SF10 are turned on by coding a, but the line of sight VII is SF1. To SF4, the subframes SF5 to SF10 of the adjacent pixel B of the input gradation 94 are moved. At this time, the subframes SF6, SF8, and SF9 are turned on at the input gradation 94 by coding b as shown in FIGS. Therefore, the subframes that are lit on the movement locus of the line of sight VII are SF1, SF3, SF6, SF8, and SF9, and the sum 82 of these weights is integrated by the eyes and recognized as the gradation 82.

  In the next frame, as shown in FIG. 15, the line of sight VII moves on the pixel B of the input gradation 95 from SF1 to SF4. The subframes SF2, SF4, SF6, SF8, and SF9 are turned on, but the line of sight VII moves from SF1 to SF4 and then moves to the adjacent pixel A of the input gradation 94. SF5, SF7, SF8, and SF9 are lit, but the line of sight VII moves in the sub-frames SF5 to SF10 of the adjacent pixel A. Therefore, the subframes that are lit on the movement locus of the line of sight VII are SF2, SF4, SF5, SF7, SF8, and SF9, and the total 98 of their weights is integrated by the eyes and recognized as the gradation 98.

  Similarly, it is assumed that the eye follows the moving image at the line of sight VIII in FIG. In this case, in the first frame, the line of sight VIII moves on the subframes SF1 to SF4 of the pixel B of the input gradation 95, but the subframes SF2 and SF4 are turned on by coding b as shown in FIG. After that, the line of sight VIII integrates the sub-frames whose input gradation of the adjacent pixel A is 95 gradations, and at this time, integrates the sub-frames SF5 to SF10 of the output gradation 95 of coding a. At this time, SF2, SF4, SF5, SF8, and SF10 are lit, and a total 98 of their weights is integrated by the eyes and recognized as a gradation 98.

  In the next frame, the line of sight VIII moves on the sub-frames SF1 to SF4 of the pixel A of the input gradation 95, but SF1 and SF3 are lit as shown in FIG. VIII integrates subframes whose input gradation of the adjacent pixel B is 95 gradations, and at this time, integrates subframes SF5 to SF10 of the output gradation 85 of coding b. At this time, SF1, SF3, SF6, SF8, and SF9 are lit, and the total 82 of their weights is integrated by the eyes and recognized as the gradation 82.

  The time average value of the two frames when following the line of sight VI in FIG. 15 is 89 (= (97 + 81) / 2) gradations. Further, the time average value of the two frames when following the line of sight VII is 90 (= (82 + 98) / 2) gradation. On the other hand, the time average value of two frames when following the line of sight VIII is 90 (= (98 + 82) / 2) gradation.

  In addition, the number of subframes selected at this time is 5 in each of the gradations 94 and 95 and coding a and coding b according to FIGS. Assuming that the emission luminance in the address period corresponds to the number of pulses of 1 in the sustain period, the respective gradations are 94 and 95 obtained by adding 5, which match the original gradation to be expressed. Even if the coding table is switched in a staggered pattern, the gradation of the image is not disturbed.

  In the first frame and the next frame, the carry position of the uppermost subframe is moved by one pixel on the image. For this reason, the place where the pseudo contour is likely to be generated can be diffused in the adjacent pixel direction and the time direction for each frame. Thus, according to the present embodiment, the moving image pseudo contour can be greatly reduced.

  Note that the present invention is not limited to the above-described embodiment. For example, the coding tables 4 and 12 and the weighting tables 3 and 11 are not stored in the external storage device, but are stored by an internal calculation formula. May be calculated. In the above embodiment, the codings a and b shown in FIG. 3 are used. However, the codings c and a (or b) shown in FIG. 3 may be used. Furthermore, three or more sets of weighting tables and corresponding coding tables may be provided. For example, in the case of three sets, coding is performed with 230 gradations, 242 gradations, and 256 gradations.

  Also, means for adaptively changing the number of output gradations during power control may be provided. Furthermore, although the display device using PDP has been described in the above embodiment, the present invention can also be applied to a display device that drives liquid crystal or organic electroluminescence (EL). Further, when there are two coding tables, one coding table may be configured to be smaller by 1 to 15% gradation than the number of display gradations of the other coding table. Further, a plurality of sets of weighting tables and corresponding coding tables may be switched and used for each pixel.

It is a block diagram of the 1st and 2nd embodiment of this invention. It is a frame structure of the 1st and 2nd embodiment of this invention. It is a figure which shows each example of the characteristic of the gradation of an input signal, and the gradation of an output signal. It is an example (the 1) of the 1st coding table and weighting table which are used in the 1st and 2nd embodiment of the present invention. It is an example (the 2) of the 1st coding table and weighting table which are used in the 1st and 2nd embodiment of the present invention. It is an example (the 3) of the 1st coding table and weighting table which are used in the 1st and 2nd embodiment of the present invention. It is an example (the 1) of the 2nd coding table used in the 1st and 2nd embodiment of this invention, and a weighting table. It is an example (the 2) of the 2nd coding table used in the 1st and 2nd embodiment of this invention, and a weighting table. It is an example (the 3) of the 2nd coding table and weighting table which are used in the 1st and 2nd embodiment of the present invention. It is a figure which shows the time arrangement | sequence of the flame | frame of the 1st Embodiment of this invention. It is a figure explaining the effect of the 1st Embodiment of this invention. It is a figure which shows the pixel array on the display panel for demonstrating the 2nd Embodiment of this invention. It is a figure which shows the frame structure of each pixel for demonstrating the 2nd Embodiment of this invention. It is a figure for demonstrating the effect with respect to the still image pseudo contour of the 2nd Embodiment of this invention. It is a figure for demonstrating the effect with respect to the moving image pseudo contour of the 2nd Embodiment of this invention. It is a block diagram of an example of the conventional display apparatus. It is a figure which shows an example of the sub-frame structure of the conventional display apparatus. It is a figure which shows the principle of the pseudo contour which generate | occur | produces with the sub-frame drive method by the conventional display apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image processing circuit 2, 13 Sub-frame matching circuit 3, 11 Weighting table 4, 12 Coding table 5 Sub-frame processing circuit 6 Drive pulse generation circuit 7 Address electrode drive circuit 8 X electrode drive circuit 9 Y electrode drive circuit 10 Plasma display Panel (PDP)

Claims (2)

One frame period of the input image signal is divided into a plurality of subframes with different luminance weights, and one or more of the necessary luminance weightings are selected from the plurality of subframes according to the input gradation of the input image signal. In a display device that performs multi-gradation display by selecting two or more subframes,
Table generating means for generating two or more sets of tables having different output gradation characteristics with respect to the input gradation;
The two or more sets of tables generated by the table generating means are sequentially and cyclically switched using one or both of one frame or pixel of the input image signal as a unit, and the input image signal An image processing means for outputting an image signal having an output gradation corresponding to an input gradation. One frame period of the input image signal is divided into a plurality of subframes with different luminance weights, and one or more of the necessary luminance weightings are selected from the plurality of subframes according to the input gradation of the input image signal. In a display device that performs multi-gradation display by selecting two or more subframes,
Table generating means for generating two or more sets of tables having characteristics in which the number of subframes selected in accordance with an increase in the input gradation increases nonlinearly;
The two or more sets of tables generated by the table generating means are sequentially switched cyclically in units of either one or both of one frame and pixels of the input image signal, and the input image signal is input. An image processing means for outputting an image signal having an output gradation corresponding to the gradation.

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