JP4606735B2 - Display device and display method - Google Patents

Description

  The present invention relates to a display device that performs gradation display by a subfield method and a display method.

  A plasma display device using a plasma display panel as a self-luminous image display device has an advantage that it can be made thin and have a large screen. In this plasma display device, an image is displayed by using light emission at the time of discharge of a discharge cell constituting a pixel. In addition, since the plasma display panel emits light in a binary manner, a subfield method is used in which halftones are displayed by overlapping a plurality of weighted binary images over time.

  In the subfield method, one field is time-divided into a plurality of subfields, and each subfield is weighted. The weight amount of each subfield corresponds to the light emission amount of each subfield. For example, the number of times of light emission is used as a weighting amount, and the total amount of weighting amounts of each subfield corresponds to the luminance of the video signal, that is, the gradation level.

  In the above-mentioned subfield method, since the order of light emission of the plurality of subfields is fixed, the line of sight of the person viewing the light emitting subfield moves on the plurality of pixels, so that a different subfield is seen for each pixel. It will be. As a result, the viewer recognizes a gradation level that is significantly different from the gradation level to be expressed. In particular, when peripheral pixels have continuity, a striped false contour line as if the gradation level is lost is visually recognized. It is known that display quality is significantly impaired by this false contour line. The pseudo contour line that appears only in the case of a moving image is referred to as pseudo contour noise (“pseudo contour noise seen in pulse fluctuation width modulation moving image display”: Television Society Technical Report, Vo 1.19, No. 2, IDY 95-21, pp. 61-66).

  FIG. 11 is a schematic diagram for explaining pseudo contour noise visually recognized when a human line of sight moves on different pixels.

  In FIG. 11, white circles indicate light-emitting subfields, black circles indicate non-light-emitting subfields, and a plurality of subfields are denoted by SF1 to SF10 in ascending order of weight. In addition, columns A, B, C, and D shown in FIG. 11 indicate column numbers of pixels in the horizontal direction, and row 1 indicates row numbers of pixels in the vertical direction.

  In FIG. 11, when the human line of sight does not move from the position of column A row 1 or the position of column B row 1, the human eyes are subfields SF <b> 1 to SF <b> 10 or the column B The subfields SF1 to SF10 of the pixels arranged in the row 1 are recognized. In this case, the light emission patterns of the pixels are “11011110111” and “0111011111”, respectively, and the gradation values recognized by the human eye are “955” and “1006”, respectively. Thus, the gradation value of the pixel arranged in the column A row 1 is originally recognized to be lower than the gradation value of the pixel arranged in the column B row 1.

  As shown by a solid line arrow in FIG. 11, when the human line of sight I1 moves from the pixel arranged in column A row 1 to the pixel arranged in column C row 1, the human eye is arranged in column A row 1. The pixel subfields SF1 to SF3, the pixel subfields SF4 to SF8 arranged in the column B row 1 and the pixel subfields SF9 and SF10 arranged in the column C row 1 are sequentially recognized. In this case, the light emission pattern is “1101011111”, and the gradation value recognized by the human eye is “1003”.

  Similarly, as shown by the dotted arrow in FIG. 11, when the human line of sight I2 moves from the pixel arranged in column B row 1 to the pixel arranged in column D row 1, the human eye moves to column B. The pixel subfields SF1 to SF3 arranged in the row 1, the pixel subfields SF4 to SF8 arranged in the column C row 1, and the pixel subfields SF9 and SF10 arranged in the column D row 1 are sequentially recognized. In this case, the light emission pattern is “0111110111”, and the gradation value recognized by the human eye is “956”.

  Thus, the gradation value that should be originally displayed as “955” is recognized as “1003” by the movement of the line of sight I1, and the gradation value that should be originally displayed as “1006” by the movement of the line of sight I2. It is recognized as low as “956”. In this way, the relationship between the gradation values of adjacent pixels in row 1 is reversed by the movement of the line of sight. Such a change in the gradation value of the pixel is recognized as pseudo contour noise.

  As a method for reducing pseudo contour noise, there is a method in which a tone level where light emission subfields are continuously present is selected as a tone level at which pseudo contour noise is unlikely to occur, and only the selected tone level is used for display. is there. In this case, for gradation levels other than the selected gradation level, two gradation levels that are unlikely to generate pseudo-contour noise that sandwich the gradation level above and below are selected, and the two gradation levels are selected for each field. This is expressed by alternately displaying (see, for example, Patent Document 1).

As another method of reducing pseudo contour noise, there is a method of reducing the occurrence of pseudo contour noise by reducing the number of subfields. In this case, in order to express a gradation level that cannot be expressed by reducing the number of subfields, a set of four pixels that are adjacent to each other vertically and horizontally is taken as one set, and each of the pixel data corresponding to each pixel of this set includes: By assigning and adding four dither coefficients each having different coefficient values, the gradation level that cannot be expressed is expressed as an area gradation. Furthermore, the noise due to the dither pattern is reduced by changing the dither coefficient to be added for each field (see, for example, Patent Document 2).
JP 2000-276100 A Japanese Patent Laid-Open No. 10-98663

  However, in the pseudo contour noise reduction method described above, image quality degradation occurs due to the reduction in the number of gradation levels that can be expressed.

  An object of the present invention is to provide a display device and a display method capable of reducing pseudo contour noise without degrading image quality.

  Another object of the present invention is to provide a display device and a display method capable of effectively reducing pseudo contour noise based on the degree of occurrence of pseudo contour noise.

  A display device according to the present invention is a display device that performs gradation display by a subfield method based on a video signal having a gradation level, and includes a plurality of first to fourth pixels that are adjacent vertically and horizontally. The display panel configured by the area and the first to fourth tables each including a plurality of first to fourth light emission patterns corresponding to the first to fourth pixels are stored, and the gradation level of the video signal The first to fourth light emission patterns corresponding to the first to fourth pixels in the respective regions are selected from the first to fourth tables based on the first to fourth light emission patterns, and based on the selected first to fourth light emission patterns. And a gradation display unit that performs gradation display by causing each of the first to fourth pixels in each region of the display panel to emit light or not emit light for each subfield, and in a predetermined subfield among the plurality of subfields. Luminescence and The non-light emitting combination patterns are different from each other between the first to fourth light emitting patterns, and in each region, the first and second pixels are arranged at one diagonal position, and the third and fourth pixels are the other. The gradation values arranged at the diagonal positions and expressed by the first and second light emission patterns at each gradation level are lower than the average values of the gradations expressed by the first to fourth light emission patterns. The gradation values expressed by the third and fourth light emission patterns are higher than the average value.

  In the display device according to the present invention, the display panel includes a plurality of regions each including first to fourth pixels adjacent in the vertical and horizontal directions. In each region, the first and second pixels are arranged at one diagonal position, and the third and fourth pixels are arranged at the other diagonal position.

  In addition, first to fourth tables each including a plurality of first to fourth light emission patterns corresponding to the first to fourth pixels are stored. First to fourth light emission patterns respectively corresponding to the first to fourth pixels in each region are selected from the first to fourth tables based on the gradation level of the video signal, and a plurality of selected plurality of selected light emission patterns are selected. Based on the first to fourth light emission patterns, the first to fourth pixels in each region of the display panel emit light or not light for each subfield. Thereby, gradation display is performed.

  In this case, a combination pattern of light emission and non-light emission in a predetermined subfield among a plurality of subfields is expressed based on the first to fourth light emission patterns by being different between the first to fourth light emission patterns. The gradation values of the first to fourth pixels are different. The gradation of each region is expressed by an average value of gradation values of the first to fourth pixels.

  In particular, pseudo contour noise can be suppressed by using a sub-field that is less likely to generate pseudo contour noise as a predetermined sub field.

  Regardless of the direction in which the line of sight moves, changes in the gradation values of the first to fourth pixels cancel each other. As a result, a change in the value of the recognized pixel is not recognized as pseudo contour noise.

  As a result, pseudo contour noise can be reduced without degrading the image quality.

  The plurality of subfields have different weight amounts, and the predetermined subfield is a subfield in which pixels emit light in the order of decreasing weight amount from the subfield having the largest weight amount to the subfield having the smallest weight amount. A predetermined number of subfields may be included starting from the subfield having the maximum weight.

  In this case, since the subfield that most affects the expressed gradation value is used as the predetermined subfield, the effect of reducing the pseudo contour noise is increased. Further, since the predetermined subfield is set only to the subfield having a large weight amount in which pseudo contour noise is likely to occur, the design man-hour is reduced.

  In two or more light emission patterns among the first to fourth light emission patterns, the combination patterns in a predetermined subfield may be the same between adjacent gradation levels.

  In this case, since the combination patterns in the predetermined subfield are the same between adjacent gradation levels, it becomes possible to reduce the noise due to the pseudo contour noise and the dither pattern.

The display device further includes a detection unit that detects the degree of pseudo contour noise in the image displayed on the display panel, and the gradation display unit includes a plurality of fifth to eighth pixels corresponding to the first to fourth pixels. The fifth to eighth tables each including the light emission pattern are further stored, and one of the first to fourth table sets and the fifth to eighth table sets is based on the detection result by the detection unit. To the first to fourth pixels in each region from the fifth to eighth tables selected based on the gradation level of the video signal when the fifth to eighth table sets are selected. Corresponding fifth to eighth light emission patterns are selected, and the first to fourth pixels in each region of the display panel are caused to emit light or not for each subfield based on the selected fifth to eighth light emission patterns. Tones are displayed by emitting light, The combination patterns of light emission and non-light emission in a certain subfield are partly the same among the fifth to eighth light emission patterns, and are expressed respectively by the fifth and sixth light emission patterns at each gradation level. The tone value is higher than the average value of the gradation expressed by the fifth to eighth light emission patterns, and the gradation values expressed by the seventh and eighth light emission patterns are the fifth to eighth light emission, respectively. It may be lower than the average value of the gradation expressed by the pattern .

  In this case, the degree of pseudo contour noise in the image displayed on the display panel is detected.

  In addition, fifth to eighth tables each including a plurality of fifth to eighth light emission patterns corresponding to the first to fourth pixels are further stored. Based on the detection result, one of the first to fourth table sets and the fifth to eighth table sets is selected. When the fifth to eighth table sets are selected, the fifth to eighth tables selected based on the gradation level of the video signal correspond to the first to fourth pixels in the respective regions. The fifth to eighth light emission patterns are selected. Based on the selected fifth to eighth light emission patterns, the first to fourth pixels in each region of the display panel emit light or not light for each subfield. Thereby, gradation display is performed.

The gradation of each region is expressed by an average value of gradation values of the first to fourth pixels. As in the case of using the first to fourth light emission patterns, the gradation values respectively expressed by the fifth and sixth light emission patterns are expressed by the fifth to eighth light emission patterns at each gradation level. that gradations higher than the average value, a grayscale value represented respectively by the illumination pattern of the seventh and eighth lower than the average value of the gradation represented by the illumination pattern of the fifth to eighth. Thereby, the pseudo contour noise is canceled.

  In particular, a combination pattern of light emission and non-light emission in a predetermined subfield is the same among some of the fifth to eighth light emission patterns. Thereby, although the effect of reducing the pseudo contour noise is smaller than that in the case where the first to fourth light emission patterns are used, it is possible to reduce noise due to the dither pattern.

  By selectively using the first to fourth light emission patterns or the eighth light emission pattern according to the level of the pseudo contour noise, the noise due to the dither pattern can be minimized and the pseudo contour noise can be reduced. .

  The gradation display unit stores, as first to fourth dither values, differences between the gradation levels and the gradation values respectively represented by the first to fourth light emission patterns, and the gradation of the video signal. A dither value generator for outputting first to fourth dither values corresponding to the level, and coefficient addition for adding the first to fourth dither values generated by the dither value generator to the gradation level of the video signal. And the first to fourth tables, and the first to fourth light emission patterns are selected from the first to fourth tables based on the addition result of the coefficient adder, and the selected first to fourth tables are selected. A drive unit that causes the first to fourth pixels in each region of the display panel to emit light or not emit light for each subfield based on the fourth light emission pattern.

  In this case, the difference between each gradation level and the gradation value represented by each of the first to fourth light emission patterns is stored as the first to fourth dither values and corresponds to the gradation level of the video signal. The first to fourth dither values to be output are output. The first to fourth dither values are added to the gradation level of the video signal. The first to fourth tables are stored, and the first to fourth light emission patterns are selected from the first to fourth tables based on the addition result. Based on the selected first to fourth light emission patterns, the first to fourth pixels in each region of the display panel emit light or not light for each subfield.

  Thus, gradation display is performed using the first to fourth dither values, and pseudo contour noise is reduced.

  In the display device, when the gradation level of the video signal and the average value of the gradation expressed by the first to fourth light emission patterns are different, the gradation level of the video signal and the first to fourth light emission patterns are displayed. Further, a diffusion device may be further provided that diffuses an error from the average value of the gradations expressed respectively by the image signal spatially and / or temporally.

  In this case, when the gradation level of the video signal and the average value of the gradation expressed by the first to fourth light emission patterns are different, the gradation level of the video signal and the first to fourth light emission patterns are used. An error with respect to the average value of each expressed gradation is diffused spatially and / or temporally into the video signal. Thereby, it is possible to express a gradation value corresponding to the gradation level of the video signal.

A display method according to the present invention is a display method in which gradation display is performed on a display panel by a subfield method based on a video signal having a gradation level, and the display panel is first to fourth adjacent to each other vertically and horizontally. In each region, the first and second pixels are arranged at one diagonal position, and the third and fourth pixels are arranged at the other diagonal position, A step of storing first to fourth tables each including a plurality of first to fourth light emission patterns corresponding to the first to fourth pixels, and first to fourth based on a gradation level of the video signal. The first to fourth light emission patterns respectively corresponding to the first to fourth pixels of each region from the table of FIG. 5 and a display panel for each subfield based on the selected first to fourth light emission patterns 1st to 1st region And a step of performing gradation display by causing the four pixels to emit light or not, and a combination pattern of light emission and non-light emission in a predetermined subfield among the plurality of subfields is between the first to fourth light emission patterns. Different from each other, at each gradation level, the gradation value represented by the first and second light emission patterns is higher than the average value of the gradation represented by the first to fourth light emission patterns. The gradation value expressed by each of the fourth light emission patterns is lower than the average value.

  In the display method according to the present invention, the display panel is composed of a plurality of regions each including the first to fourth pixels adjacent vertically and horizontally. In each region, the first and second pixels are arranged at one diagonal position, and the third and fourth pixels are arranged at the other diagonal position.

  In addition, first to fourth tables each including a plurality of first to fourth light emission patterns corresponding to the first to fourth pixels are stored. First to fourth light emission patterns respectively corresponding to the first to fourth pixels in each region are selected from the first to fourth tables based on the gradation level of the video signal, and a plurality of selected plurality of selected light emission patterns are selected. Based on the first to fourth light emission patterns, the first to fourth pixels in each region of the display panel emit light or not light for each subfield. Thereby, gradation display is performed.

  In this case, a combination pattern of light emission and non-light emission in a predetermined subfield among a plurality of subfields is expressed based on the first to fourth light emission patterns by being different between the first to fourth light emission patterns. The gradation values of the first to fourth pixels are different. The gradation of each region is expressed by an average value of gradation values of the first to fourth pixels.

  In particular, pseudo contour noise can be suppressed by using a sub-field that is less likely to generate pseudo contour noise as a predetermined sub field.

  Regardless of the direction in which the line of sight moves, changes in the gradation values of the first to fourth pixels cancel each other. As a result, a change in the value of the recognized pixel is not recognized as pseudo contour noise.

  As a result, pseudo contour noise can be reduced without degrading the image quality.

  The plurality of subfields have different weight amounts, and the predetermined subfield is a subfield in which pixels emit light in the order of decreasing weight amount from the subfield having the largest weight amount to the subfield having the smallest weight amount. A predetermined number of subfields may be included starting from the subfield having the maximum weight.

  In this case, since the subfield that most affects the expressed gradation value is used as the predetermined subfield, the effect of reducing the pseudo contour noise is increased. Further, since the predetermined subfield is set only to the subfield having a large weight amount in which pseudo contour noise is likely to occur, the design man-hour is reduced.

  In two or more light emission patterns among the first to fourth light emission patterns, the combination patterns in a predetermined subfield may be the same between adjacent gradation levels.

  In this case, since the combination patterns in the predetermined subfield are the same between adjacent gradation levels, it becomes possible to reduce the noise due to the pseudo contour noise and the dither pattern.

The display method includes detecting a degree of pseudo contour noise in an image displayed on the display panel, and fifth to eighth light emission patterns each including a plurality of fifth to eighth light emission patterns corresponding to the first to fourth pixels. A step of further storing eight tables, and a step of selecting one of the first to fourth table sets and the fifth to eighth table sets based on the detection result of the degree of pseudo contour noise; , Corresponding to the first to fourth pixels in each region from the fifth to eighth tables selected based on the gradation level of the video signal when the fifth to eighth table sets are selected. A step of selecting fifth to eighth light emission patterns, and light emission or non-light emission of each of the first to fourth pixels in each area of the display panel for each subfield based on the selected fifth to eighth light emission patterns By letting the floor A step of performing display, wherein a combination pattern of light emission and non-light emission in a predetermined subfield is partly the same among the fifth to eighth light emission patterns, and the fifth and sixth at each gradation level. The gradation values expressed by the respective light emission patterns are lower than the average values of the gradations expressed by the fifth to eighth light emission patterns, and the gradation values expressed by the seventh and eighth light emission patterns respectively. The value may be higher than the average value of the gradation expressed by the fifth to eighth light emission patterns .

  In this case, the degree of pseudo contour noise in the image displayed on the display panel is detected.

  In addition, fifth to eighth tables each including a plurality of fifth to eighth light emission patterns corresponding to the first to fourth pixels are further stored. Based on the detection result, one of the first to fourth table sets and the fifth to eighth table sets is selected. When the fifth to eighth table sets are selected, the fifth to eighth tables selected based on the gradation level of the video signal correspond to the first to fourth pixels in the respective regions. The fifth to eighth light emission patterns are selected. Based on the selected fifth to eighth light emission patterns, the first to fourth pixels in each region of the display panel emit light or not light for each subfield. Thereby, gradation display is performed.

The gradation of each region is expressed by an average value of gradation values of the first to fourth pixels. As in the case of using the first to fourth light emission patterns, the gradation values respectively expressed by the fifth and sixth light emission patterns are expressed by the fifth to eighth light emission patterns at each gradation level. The gradation value expressed by the seventh and eighth light emission patterns is lower than the average value of the gradation expressed by the fifth to eighth light emission patterns . Thereby, the pseudo contour noise is canceled.

  In particular, a combination pattern of light emission and non-light emission in a predetermined subfield is the same among some of the fifth to eighth light emission patterns. Thereby, although the effect of reducing the pseudo contour noise is smaller than that in the case where the first to fourth light emission patterns are used, it is possible to reduce noise due to the dither pattern.

  By selectively using the first to fourth light emission patterns or the eighth light emission pattern according to the level of the pseudo contour noise, the noise due to the dither pattern can be minimized and the pseudo contour noise can be reduced. .

  The step of performing gradation display includes the step of storing the difference between each gradation level and the gradation value respectively represented by the first to fourth light emission patterns as the first to fourth dither values, Outputting first to fourth dither values corresponding to the gradation level, adding first to fourth dither values generated to the gradation level of the video signal, and first to fourth. A step of storing the first table, a step of selecting the first to fourth light emission patterns from the first to fourth tables based on the addition result, and a sub-step based on the selected first to fourth light emission patterns. A step of causing each of the first to fourth pixels in each region of the display panel to emit light or not emit light for each field.

  In this case, the difference between each gradation level and the gradation value represented by each of the first to fourth light emission patterns is stored as the first to fourth dither values and corresponds to the gradation level of the video signal. The first to fourth dither values to be output are output. The first to fourth dither values are added to the gradation level of the video signal. The first to fourth tables are stored, and the first to fourth light emission patterns are selected from the first to fourth tables based on the addition result. Based on the selected first to fourth light emission patterns, the first to fourth pixels in each region of the display panel emit light or not light for each subfield.

  Thus, gradation display is performed using the first to fourth dither values, and pseudo contour noise is reduced.

  In the display method, when the gradation level of the video signal and the average value of the gradation expressed by the first to fourth light emission patterns are different, the gradation level of the video signal and the first to fourth light emission patterns are used. The method may further comprise the step of diffusing an error from the average value of the gradations expressed by each of the video signals spatially and / or temporally into the video signal.

  In this case, when the gradation level of the video signal and the average value of the gradation expressed by the first to fourth light emission patterns are different, the gradation level of the video signal and the first to fourth light emission patterns are used. An error with respect to the average value of each expressed gradation is diffused spatially and / or temporally into the video signal. Thereby, it is possible to express a gradation value corresponding to the gradation level of the video signal.

  According to the present invention, pseudo contour noise can be suppressed by using a subfield in which pseudo contour noise hardly occurs as a predetermined subfield. Regardless of the direction in which the line of sight moves, changes in the gradation values of the first to fourth pixels cancel each other. As a result, a change in the value of the recognized pixel is not recognized as pseudo contour noise. As a result, pseudo contour noise can be reduced without degrading the image quality.

  In the following embodiments, a case where the present invention is applied to a plasma display device having a PDP (plasma display panel) as an example of a display device will be described. The PDP is composed of a plurality of regions each including four pixels that are adjacent vertically and horizontally.

  In the following, monochrome display using one color will be described for the sake of simplicity of explanation, but color display using three colors of R (red), G (green), and B (blue) is also used. The present invention can be similarly applied.

  Further, in the plasma display device of the present embodiment, the gradation level of the input video signal is expressed by the average value of gradation values displayed by the four pixels adjacent vertically and horizontally in each area of the PDP. To do.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the plasma display device according to the first embodiment of the present invention.

  1 includes an A / D converter (analog / digital converter) 100, a scanning number conversion unit 200, an error diffusion device 300, a coefficient adder 310, a dither value generator 320, a subfield conversion unit 400, a discharge. A control timing generation circuit 500, a PDP (plasma display panel) 600, a data driver 700, a scan driver 800, and a sustain driver 900 are included.

  The video signal VS is input to the A / D converter 100. The discharge control timing generation circuit 500, the A / D converter 100, the scanning number conversion unit 200, the error diffusion device 300, the coefficient adder 310, the dither value generator 320, and the subfield conversion unit 400 include a horizontal synchronization signal H and a vertical signal. A synchronization signal V is given.

  The A / D converter 100 converts the video signal VS into digital image data VD, and supplies the image data VD to the scanning number conversion unit 200.

  The scanning number conversion unit 200 converts the image data VD into image data having the number of lines corresponding to the number of pixels of the PDP 600, and gives the image data of each line to the error diffusion device 300. The image data of each line is composed of a plurality of image data respectively corresponding to a plurality of pixels of each line.

  The error diffusion device 300 diffuses an error (described later) output from a dither value generator 320 (described later) spatially and temporally. Details will be described later. The image data VV obtained by the error diffusion device 300 is supplied to the coefficient adder 310 and the dither value generator 320. The value of the image data VV indicates the gradation level of the corresponding pixel.

  The dither value generator 320 stores a dither table indicating the relationship between the plurality of gradation levels represented by the image data VV and the plurality of dither values, and also the dither corresponding to the gradation level of the image data VV from the dither table. The value is read and given to the coefficient adder 310. Here, the dither value corresponds to the difference between each gradation level and the gradation value displayed by each pixel.

  The coefficient adder 310 adds the dither value given by the dither value generator 320 to the image data VV given by the error diffusion device 300, and gives the addition result to the subfield conversion unit 400 as image data VV1.

  The image data VV1 indicates gradation values displayed by the four pixels in each region.

  The subfield conversion unit 400 stores a light emission pattern table indicating the relationship between gradation values respectively displayed by the four pixels in each region and the light emission patterns of a plurality of subfields, and based on the light emission pattern table. The image data VV1 is converted into serial data SD corresponding to a plurality of subfields, and the serial data SD is supplied to the data driver 700.

  Discharge control timing generation circuit 500 generates discharge control timing signals SC and SU with reference to horizontal synchronizing signal H and vertical synchronizing signal V. Discharge control timing generation circuit 500 provides discharge control timing signal SC to scan driver 800 and discharge control timing signal SU to sustain driver 900.

  The PDP 600 includes a plurality of data electrodes 50, a plurality of scan electrodes 60 and a plurality of sustain electrodes 70. The plurality of data electrodes 50 are arranged in the vertical direction of the screen, and the plurality of scan electrodes 60 and the plurality of sustain electrodes 70 are arranged in the horizontal direction of the screen. The plurality of sustain electrodes 70 are connected in common.

  A discharge cell is formed at each intersection of the data electrode 50, the scan electrode 60, and the sustain electrode 70, and each discharge cell constitutes a pixel on the screen.

  The data driver 700 converts the serial data SD supplied from the subfield conversion unit 400 into parallel data, and selectively applies a write pulse to the plurality of data electrodes 50 based on the parallel data.

  The scan driver 800 drives each scan electrode 60 based on the discharge control timing signal SC supplied from the discharge control timing generation circuit 500. The sustain driver 900 drives the sustain electrode 70 based on the discharge control timing signal SU given from the discharge control timing generation circuit 500.

  In the plasma display device shown in FIG. 1, an ADS (Address Display-Period Separation) method is used as a gradation display driving method.

  FIG. 2 is a diagram for explaining an ADS method applied to the plasma display apparatus shown in FIG. FIG. 2 shows an example of a negative pulse that discharges at the fall of the drive pulse, but the basic operation is the same as below even in the case of a positive pulse that discharges at the rise. In FIG. 2, one field includes five subfields SF1 to SF5 in order to simplify the illustration.

  In the ADS system, one field is temporally divided into a plurality of subfields. In the example of FIG. 2, one field is divided into five subfields SF1 to SF5. Each subfield SF1 to SF5 is divided into an initialization period R1 to R5, a write period AD1 to AD5, a sustain period SUS1 to SUS5, and an erase period RS1 to RS5. In the initialization periods R1 to R5, initialization processing of each subfield is performed. In the writing periods AD1 to AD5, address discharge for selecting the discharge cells to be lit is performed, and in the sustain periods SUS1 to SUS5. A sustain discharge for display is performed.

  In the initialization period R1 to R5, a single initialization pulse is applied to the sustain electrode 70, and a single initialization pulse is also applied to the scan electrode 60, respectively. Thereby, preliminary discharge is performed.

  In the write periods AD1 to AD5, the scan electrode 60 is sequentially scanned, and a predetermined write process is performed only on the discharge cells that have received the write pulse from the data electrode 50. As a result, address discharge is performed.

  In sustain periods SUS1 to SUS5, sustain pulses corresponding to values weighted in subfields SF1 to SF5 are output to sustain electrode 70 and scan electrode 60. For example, in the subfield SF1, the sustain pulse is applied once to the sustain electrode 70, the sustain pulse is applied once to the scan electrode 60, and the discharge cell 14 selected in the write period AD1 performs sustain discharge twice. In the subfield SF2, the sustain pulse is applied twice to the sustain electrode 70, the sustain pulse is applied twice to the scan electrode 60, and the discharge cell 14 selected in the write period AD2 performs sustain discharge four times.

  As described above, in each of the subfields SF1 to SF5, the sustain pulse is applied to the sustain electrode 70 and the scan electrode 60 once, twice, four times, eight times, and 16 times, and brightness according to the number of pulses ( The discharge cell emits light. That is, the sustain periods SUS1 to SUS5 are periods in which the discharge cells selected in the write periods AD1 to AD5 are discharged at a number corresponding to the weighting amount of brightness.

  FIG. 3 is a schematic diagram showing an example of a light emission pattern of a plurality of subfields of 4 pixels in each region based on the dither table of the dither value generator 320. In the following example, one field is divided into 10 subfields.

  In FIG. 3, white circles indicate light-emitting subfields, black circles indicate non-light-emitting subfields, and a plurality of subfields are denoted by SF1 to SF10 in ascending order of weight. 3, columns A, B, C,... Indicate horizontal pixel column numbers, and rows 1, 2, 3,... Indicate vertical pixel row numbers. The area of the PDP 600 is R1, R2, R3, R4,.

  The subfields SF1 to SF10 are used for expressing the gradation value of one pixel. For example, the weight amounts of the subfields SF1 to SF10 are “1”, “2”, “4”, “8”, “16”, “32”, “64”, “128”, “256” and “ 512 ".

  Here, gradation display by four pixels arranged in column A row 1, column B row 1, column A row 2 and column B row 2 in the region R1 will be described. The gradation level to be displayed by the four pixels in the region R1 is “959”.

  The pixel in column B row 2 (lower right) is the first pixel P1, the pixel in column A row 1 (upper left) is the second pixel P2, and the pixel in column A row 2 (lower left) is the third pixel P2. The pixel is P3, and the pixel in column B row 1 (upper right) is the fourth pixel P4.

  The light emission pattern of the first pixel P1 is “1110111011 (1 indicates light emission, 0 indicates no light emission)” in order from the subfield SF1 to the subfield SF10, and the gradation value of “887” in one field. Express.

  The light emission pattern of the second pixel P2 is “11011110111” in order from the subfield SF1 to the subfield SF10, and represents a gradation value of “955” in one field.

  The light emission pattern of the third pixel P3 is “1011101111” in order from the subfield SF1 to the subfield SF10, and represents a gradation value of “989” in one field.

  The light emission pattern of the fourth pixel P4 is “0111011111” in order from the subfield SF1 to the subfield SF10, and represents a gradation value of “1006” in one field.

  The average value of the gradation values displayed by the first to fourth pixels P1 to P4 is “959.25” calculated from (955 + 1006 + 989 + 887) / 4.

  In the present embodiment, for example, “1101”, “0111”, “1011”, and “1110” so that the light emission patterns of the subfields SF5 to SF8 of the first to fourth pixels P1 to P4 are different from each other. Is set to

  In the present embodiment, the light emission patterns of the subfields SF5 to SF8 of the first to fourth pixels P1 to P4 are set to be different from each other. However, the present invention is not limited to this, and the first to fourth pixels are not limited thereto. The light emission patterns of arbitrary n to m-th subfields of the pixels P1 to P4 may be set different from each other. Here, m and n are positive integers smaller than the total number of subfields, and m> n.

  Here, “959”, which is a gradation level to be displayed by each of the first to fourth pixels P1 to P4, and the first to fourth of the above-described actual representations by the light emission patterns of the subfields SF1 to SF10. The difference from “959.25” that is the average value of the gradation values of the pixels P1 to P4 is “−0.25”.

  The dither value generator 320 outputs the difference of “−0.25” to the error diffusion device 300 as an error of each of the first to fourth pixels P1 to P4. The error diffusion device 300 diffuses this error spatially and temporally. The configuration of the error diffusion device 300 and the error diffusion method will be described later.

  Thus, in the present embodiment, the light emission patterns of the n to m-th subfields in the first to fourth pixels P1 to P4 are different (Condition 1).

  In the present embodiment, among the first to fourth pixels P1 to P4 adjacent to each other in each region of the PDP 600, the first pixel P1 and the second pixel disposed at one diagonal position. The gradation value displayed by the pixel P2 is lower than the average value of the gradation values displayed by the first to fourth pixels P1 to P4, and the gradation values displayed at the other diagonal position are arranged. The gradation value displayed by each of the third pixel P3 and the fourth pixel P4 is higher than the average value of the gradation values displayed by the first to fourth pixels P1 to P4 (condition 2). ).

  In the present embodiment, the light emission patterns of the subfields SF5 to SF8 in the first pixel P1, the second pixel P2, the third pixel P3, and the fourth pixel P4 are set to be different. (Indicated by a thick line in FIGS. 4a to 4d), the present invention is not limited to this, and the light emission patterns of arbitrary n to m-th subfields in the first to fourth pixels P1 to P4 are different. May be set.

  The light emission and non-light emission combination patterns in any of the n to m-th subfields among the plurality of subfields are different from each other among the light emission patterns of the first to fourth pixels P1 to P4, thereby allowing the first to fourth. The gradation values expressed based on the light emission patterns of the pixels P1 to P4 are different.

  Moreover, pseudo contour noise can be suppressed by using a subfield in which pseudo contour noise hardly occurs as an arbitrary n to m-th subfield.

  4A to 4E are explanatory diagrams showing a dither table included in the dither value generator 320 and a light emission pattern table included in the subfield conversion unit 400. FIG.

  The relationship between the gradation level and the first to fourth dither values in FIGS. 4 a to 4 d and the relationship between the gradation level and the error in FIG. 4 e are included in the dither table included in the dither value generator 320. The dither value generator 320 determines which of the first to fourth pixels P1 to P4 the image data VV corresponds to based on the horizontal synchronization signal H and the vertical synchronization signal V, and the dither value corresponding to this pixel. Select.

  Further, the relationship between the first to fourth gradation values and the first to fourth light emission patterns in FIGS. 4A to 4D is included in the light emission pattern table included in the subfield conversion unit 400. 4a indicates the gradation level of the first pixel P1, the gradation level illustrated in FIG. 4b indicates the gradation level of the second pixel P2, and the gradation level illustrated in FIG. The gradation level of the third pixel P3 is shown, and the gradation level shown in FIG. 4d shows the gradation level of the fourth pixel P4.

  Here, for example, the gradation display by the first pixel P1 when the gradation level of the image data VV corresponding to the first pixel P1 is “959” will be described.

  As shown in FIG. 4a, when the image data VV of the gradation level “959” is input to the dither value generator 320, the dither value generator 320 uses the first dither value “−72” based on the dither table. Is output to the coefficient adder 310.

  The coefficient adder 310 adds the first dither value “−72” and the gradation level “959” of the image data VV, and the image data VV1 having the first gradation value “887” as the addition result. Is output to the subfield conversion unit 400.

  The subfield conversion unit 400 reads the first light emission pattern “1110111011” corresponding to the first gradation value “887” included in the image data VV1 from the light emission pattern table of FIG. 4A and converts it into serial data SD. Based on the serial data SD, the data electrode corresponding to the first pixel P1 of the PDP 600 is driven by the data driver 700.

  Note that gradation display similar to the above is also performed for the second pixel P2, the third pixel P3, and the fourth pixel P4.

  The dither value generator 320 reads the error “−0.25” corresponding to the gradation level “959” of the input image data VV from the dither table of FIG. In other words, the dither value generator 320 is a difference between the gradation level “959” and the average value “959.25” of the first to fourth gradation values of the first to fourth pixels P1 to P4. A certain “−0.25” is output to the error diffusion device 300 as an error.

  Next, the first to fourth pixels P1 to P4 are caused to emit light or not to emit light based on the light emission pattern satisfying the above conditions 1 and 2 of the first to fourth pixels P1 to P4 in each region of the PDP 600. A mechanism for reducing pseudo contour noise will be described. Note that the pseudo contour noise occurs when the gradation levels of adjacent pixels are the same or approximate.

  FIG. 5A is an explanatory diagram showing the brightness and darkness of each pixel recognized when the human line of sight does not move, and FIG. 5B shows the case where the human line of sight moves in the direction of the arrow (from left to right). It is explanatory drawing which shows the brightness and darkness of each pixel recognized.

  In FIG. 5A and FIG. 5B, the pixel indicated as “bright” has a gray level higher than the average value of the gray level values displayed by the first to fourth pixels P1 to P4 in each region. The pixel indicating “dark” indicates a gradation value lower than the average value of the gradation values displayed by the first to fourth pixels P1 to P4 in each region. It is a pixel to do.

  As shown in FIG. 5A, the gradation values of the first pixel P1 and the second pixel P2 in each region R1, R2, R3, R4 of the PDP 600 are the first to fourth pixels P1 to P4. The gradation values of the third pixel P3 and the fourth pixel P4 are set lower than the average value of the gradation values of the first to fourth pixels P1 to P4. Higher than.

  In particular, in the present embodiment, in each region R1, R2, R3, R4,... Of the PDP 600, the pixels of the first pixel P1, the second pixel P2, the third pixel P3, and the fourth pixel P4. Are p1, p2, p3 and p4, respectively, and the average value of the gradation values of the first to fourth pixels P1 to P4 is pa, the first to fourth pixels so that the following relationship holds: The gradation values P1 to P4 are set.

p1 <p2 <pa <p3 <p4 (1)
All the regions of the PDP 600 have the relationship of the above formula (1).

  Further, as shown in FIG. 5B, when the human line of sight moves in the direction of the arrow, the gradation of the first pixel P1 and the second pixel P2 of each region R1, R2, R3, R4 of the PDP 600 Is recognized to be higher than the average value of the gradation values of the first to fourth pixels P1 to P4, and the gradation values of the third pixel P3 and the fourth pixel P4 are the first to first values. It is recognized to be lower than the average value of the gradation values of the four pixels P1 to P4.

  As described above, the relationship between the gradation values of the adjacent pixels is reversed by the movement of the line of sight, but the change in the gradation value of the second pixel P2 and the change of the gradation value of the third pixel P3 are different. The change in the gradation value of the first pixel P1 and the change in the gradation value of the fourth pixel P4 are canceled each other. As a result, a change in the value of the recognized pixel is not recognized as pseudo contour noise.

  Further, when the human line of sight moves in the direction from the second pixel P2 toward the first pixel P1 (from the upper left to the lower right), the first of the regions R1, R2, R3, R4,. It is recognized that the relationship between the gradation value of the pixel P1 and the gradation value of the second pixel P2 is reversed, and the gradation value of the third pixel P3 and the gradation value of the fourth pixel P4 are recognized. It is recognized that the relationship with is reversed.

  Thus, although the relationship between the gradation values of the pixels adjacent in the diagonal direction is reversed by the movement of the line of sight in the diagonal direction, the gradation values of the second pixel P2 and the first pixel P1 are changed. The change and the change in the gradation value of the third pixel P3 and the fourth pixel P4 cancel each other. As a result, a change in the value of the recognized pixel is not recognized as pseudo contour noise.

  The line of sight moves not only in the direction of the arrow, but also in the direction opposite to the direction of the arrow (from right to left), the second and fourth pixels P2, P4 to the third and first pixels. The direction toward P3, P1 (downward direction) and the opposite direction (upward direction), the direction from the first pixel P1 toward the second pixel P2 (lower right to upper left), and the fourth pixel P4 to third pixel Even when the line of sight moves in the direction toward P3 (upper right to lower left) and in the opposite direction (lower left to upper right), the recognized pixel value change is not recognized as pseudo contour noise.

  As a result, pseudo contour noise can be reduced without degrading the image quality.

  In addition, since the human eye recognizes the gradation value in the area formed by the first to fourth pixels P1 to P4, a unique striped pattern that is visible when the pseudo-contour noise is concentrated on the part. Degradation of image quality due to the like is prevented.

  The above example shows the case where the gradation levels of the image data VV corresponding to the first to fourth pixels P1 to P4 in each region are the same, but corresponds to the first to fourth pixels P1 to P4. The gradation levels of the image data VV to be performed are not necessarily the same. Even when the gradation levels of the image data VV corresponding to the first to fourth pixels P1 to P4 in each region are different, they have similar gradation levels (the difference in gradation levels is 1 or 2 or the like). In the case of (1), the light emission pattern table is set so that the relationship of the above equation (1) is established. When the gradation levels of the image data VV corresponding to the first to fourth pixels P1 to P4 in each region are greatly different, the relationship of the above equation (1) does not hold. However, when the gradation levels to be displayed differ greatly between the first to fourth pixels P1 to P4 in each region, there is no problem because pseudo contour noise does not occur.

  In the present embodiment, the first pixel P1 and the second pixel P2 in each region are set to a level lower than the average value of the gradation values displayed by the first to fourth pixels P1 to P4. Pixels for displaying tone values are used, and the third pixel P3 and the fourth pixel P4 in each region are higher than the average value of the gradation values displayed by the first to fourth pixels P1 to P4. Although the pixel for displaying the gradation value is not limited to this, the first pixel P1 and the second pixel P2 in each area are displayed by the first to fourth pixels P1 to P4. A pixel that displays a gradation value higher than the average value of the tone values is displayed, and the third pixel P3 and the fourth pixel P4 in each region are displayed by the first to fourth pixels P1 to P4. A pixel that displays a gradation value lower than the average value of the gradation values may be used.

  Next, the error diffusion device 300 that diffuses the error e1 output from the dither value generator 320 spatially and temporally will be described.

  FIG. 6 is a block diagram showing a configuration of the error diffusion device 300 shown in FIG.

  As shown in FIG. 6, the error diffusion device 300 includes adders 11 and 12, multipliers 13 to 16, an inter-field delay unit 5, and an intra-field delay unit 6. The intra-field delay device 6 includes delay devices 61 to 64.

  The error e1 output from the dither value generator 320 is input to the inter-field delay unit 5. The inter-field delay unit 5 delays the error e1 by a period of 1 field (1V) and outputs it to the adder 12.

  Further, the error e1 is input to the delay devices 61 to 64 in the intra-field delay device 6, respectively.

  The delay unit 61 delays the error e1 by a period of 1 pixel (1T) and outputs the delayed result to the multiplier 13. The delay unit 62 delays the error e1 by a period (1H + 1T) longer than one line by one pixel and outputs the delayed error to the multiplier. Further, the delay unit 63 delays the error e1 by the period of one line (1H) and outputs the delayed result to the multiplier 15. The delay unit 64 delays the error e1 by a period (1H-1T) shorter by one pixel than one line, and outputs the delayed result to the multiplier 16.

  The multiplier 13 multiplies the error e1 output from the delay unit 61 by a predetermined coefficient K1 and outputs the result to the adder 12. The multiplier 14 multiplies the error e1 output from the delay unit 62 by a predetermined coefficient K2, and outputs the result to the adder 12. The multiplier 15 multiplies the error e1 output from the delay unit 63 by a predetermined coefficient K3 and outputs the result to the adder 12. The multiplier 16 multiplies the error e1 output from the delay unit 64 by a predetermined coefficient K4 and outputs the result to the adder 12.

  Here, the coefficients K1, K2, K3, and K4 are set to appropriate values that satisfy the relationship of K1 + K2 + K3 + K4 = 1. For example, 7/16, 1/16, 5/16, and 3/16 are used as the coefficients K1 to K4, respectively.

  The adder 12 adds the output of the inter-field delay unit 5 and the outputs of the multipliers 13 to 16 and outputs the addition result to the adder 11 as the final error component e2.

  Then, the adder 11 adds the image data VD and the final error component e2 output from the adder 12, whereby the final error component e2 is diffused spatially and temporally.

  In this embodiment, the error e1 output from the dither value generator 320 is diffused temporally and spatially into the video signal. However, the present invention is not limited to this, and the error e1 is temporally spread. Or only spatially may be diffused into the image data VD.

  FIG. 7A is a diagram illustrating spatial diffusion of the error e1, and FIG. 7B is a diagram illustrating temporal diffusion of the error e1.

  As shown in FIG. 7A, the error e1 of the target pixel Px0 is the pixel Px1 adjacent to the right side of the same line, the pixel Px2 diagonally lower right in the lower line, the pixel Px3 adjacent to the lower side of the target pixel Px0, It is spatially diffused to the pixel Px4 diagonally below.

  A value obtained by multiplying the error e1 by the coefficient K1 is diffused to the pixel Px1, a value obtained by multiplying the error e1 by the coefficient K2 is diffused to the pixel Px2, and a value obtained by multiplying the error e1 by the coefficient K3 Is diffused, and a value obtained by multiplying the error e1 by the coefficient K4 is diffused to the pixel Px4.

  By such error diffusion processing, when the gradation level of the image data VD and the average value of the gradation values expressed by the first to fourth light emission patterns are different, the gradation level of the image data VD is set. It is possible to express the corresponding gradation value.

  As shown in FIG. 7B, the error e1 of the target pixel Px0 is temporally diffused to the pixel Px6 having the same coordinates as the target pixel Px0 in the next field.

  Note that the gradation levels of the image data VD corresponding to the first to fourth pixels P1 to P4 are not necessarily equal, but for example, when determining the error corresponding to the first pixel P1, the first to first pixels Assuming that the gradation levels of the image data VD corresponding to the fourth pixels P1 to P4 are equal, the gradation level and the average value of the gradation values represented by the first to fourth light emission patterns, respectively, The error which is the difference between the two is read from the dither table.

  Next, another example of the dither table included in the dither value generator 320 and the light emission pattern table included in the subfield conversion unit 400 will be described.

  8a to 8e are explanatory diagrams showing other examples of the dither table included in the dither value generator 320 and the light emission pattern table included in the subfield conversion unit 400. FIG.

  The relationship between the gradation level and the first to fourth dither values in FIGS. 8 a to 8 d and the relationship between the gradation level and the error in FIG. 8 e are included in the dither table included in the dither value generator 320. Further, the relationship between the first to fourth gradation values and the first to fourth light emission patterns in FIGS. 8A to 8D is included in the light emission pattern table included in the subfield conversion unit 400. The gradation level shown in FIG. 8a indicates the gradation level of the first pixel P1, the gradation level shown in FIG. 8b indicates the gradation level of the second pixel P2, and the gradation level shown in FIG. The gradation level of the third pixel P3 is shown, and the gradation level shown in FIG. 8d shows the gradation level of the fourth pixel P4.

  8a to 8d, the subfield having the largest weight amount among the subfields in which the pixels emit light in the order of the weight amount decreasing from the subfield SF10 having the largest weight amount to the subfield SF1 having the smallest weight amount. The combination patterns of light emission and non-light emission up to a predetermined number of subfields starting from the field are all different in the first to fourth pixels P1 to P4 (condition 3).

  Hereinafter, the subfield in which the pixel emits light is referred to as a light emitting subfield, and the subfield in which the pixel does not emit light is referred to as a non-light emitting subfield.

  In the present embodiment, the predetermined number of subfields includes four subfields starting from the subfield having the maximum weight among the light emission subfields in the first to fourth light emission patterns.

  In this case, the combination pattern of light emission and non-light emission of the four subfields in the first to fourth light emission patterns is selected from five patterns “1110”, “1101”, “1011”, “0111”, and “1111”. Is done.

  For example, when the gradation level of the image data VV is “13”, the subfields SF4 to SF1 satisfy the condition 3 as indicated by the thick lines in FIGS. 8a to 8d. As shown in FIG. 8A, the combination pattern of light emission and non-light emission of the first pixel P1 that satisfies the condition 3 is “1011”, and the combination pattern of light emission and non-light emission of the second pixel P2 that satisfies the condition 3 is FIG. As shown in FIG. 8C, the combination pattern of light emission and non-light emission of the third pixel P3 that satisfies the condition 3 is “1110” and that of the fourth pixel P4 that satisfies the condition 3 is “1110”. The combination pattern of light emission and non-light emission is “1111” as shown in FIG.

  In this way, the subfield having the largest weight amount among the subfields that emit light from the subfield SF10 having the largest weight amount to the subfield SF1 having the smallest weight amount in the order in which the weight amount decreases in this order. As described above, the combination patterns of light emission and non-light emission in the four subfields are all different in the first to fourth pixels P1 to P4. The pseudo contour noise generated by the combined light-emitting and non-light-emitting patterns of the subfield having a large amount of weight generates significant image quality degradation. Therefore, the effect of reducing the pseudo contour noise is increased by changing the combination pattern of light emission and non-light emission of the subfield that most affects the expressed gradation value.

  In addition, since the light emission pattern is set only for the subfield having a large weight amount in which pseudo contour noise is likely to occur, the design man-hour is reduced.

  In addition to the setting of the light emission pattern that satisfies the above conditions 1 and 2, or the setting of the light emission pattern that satisfies the conditions 2 and 3, the first to fourth light emission in FIGS. 4a to 4d and FIGS. 8a to 8d. In two or more light emission patterns among the patterns, a combination pattern of light emission and non-light emission in a predetermined subfield may be the same between adjacent gradation levels (condition 4).

  Hereinafter, as an example, the setting of the light emission pattern satisfying the condition 2, the condition 3, and the condition 4 will be described with reference to FIGS.

  In the first to fourth light emission patterns of FIGS. 8a to 8d, for example, when the gradation level “23” of the image data VV is expressed, the subfields SF5 to SF2 of the first to fourth light emission patterns are respectively “0111”, “1011”, “1101”, and “1110”.

  When the gradation level “24” adjacent to the gradation level “23” is expressed, the subfields SF5 to SF2 of the first to fourth light emission patterns are “0111”, “1011”, “ 1110 "and" 1111 ".

  In this case, the subfields SF5 to SF2 and the second subfields SF5 to SF2 of the first light emission pattern among the subfields SF5 to SF2 of the first to fourth light emission patterns expressing the gradation level “23” and the gradation level “24”. The subfields SF5 to SF2 of the light emission pattern are the same.

  In this case, the dither value changes by 1 or 2 between adjacent gradation levels. Therefore, the change in the dither value between the pixels becomes smooth in the pixels where the pixels with small difference in gradation level are adjacent to each other. As a result, pseudo contour noise and noise due to a dither pattern can be reduced.

  Thus, in two or more light emission patterns among the first to fourth light emission patterns, the combination pattern of light emission and non-light emission in a predetermined subfield is the same between adjacent gradation levels, so that the image quality is improved. More improved.

  In the present embodiment, PDP 600 corresponds to a display panel, coefficient adder 310, dither value generator 320, and subfield conversion unit 400 correspond to a gradation display unit, and data driver 700, scan driver 800, and sustain driver. 900 corresponds to a drive unit, and the error diffusion device 300 corresponds to a diffusion device.

  In each of the first to fourth light emission patterns, the light emission patterns may be set so that the number of places where the non-light emission subfield is sandwiched between the light emission subfields is reduced. Thereby, pseudo contour noise is hardly generated. For example, in the subfield having the smallest weight amount from the light emitting subfield having the largest weight amount, the number of non-light emitting subfields sandwiched between the light emitting subfields may be limited to 2 or less.

  In the present embodiment, among the four pixels in each region, the gradation value of the first pixel P1 is the smallest, and the gradation value of the second pixel P2 is that of the first pixel P1. The gray level value is the next largest, the gray level value of the third pixel P3 is the second largest after the gray level value of the second pixel P2, and the gray level value of the fourth pixel P4 is the largest. In the next field, the gradation value of the fourth pixel P4 is the smallest, the gradation value of the third pixel P3 is the second largest after the gradation value of the fourth pixel P4, and the first pixel The gradation display may be performed such that the gradation value of P1 is the second largest after the gradation value of the third pixel P3, and the gradation value of the second pixel P2 is the maximum.

  That is, the light emission pattern table is set so that the gradation values p1 to p4 and the average value pa of the first to fourth pixels P1 to P4 repeat the relationship of the following expressions (1) and (2) alternately for each field. May be.

p1 <p2 <pa <p3 <p4 (1)
p1>p2>pa>p3> p4 (2)
In this way, the gradation display is performed so that the magnitude relationship of the gradation values of the first to fourth pixels P1 to P4 circulates for each field, so that the first to fourth pixels P1 to P1 for each field are displayed. Noise generated when the magnitude relationship of the P4 gradation values is the same is reduced.

  Furthermore, in this embodiment, a plasma display device is used as an example of a display device that performs gradation display by the subfield method. However, the present invention is not limited to this, and other display devices such as a digital mirror device are used. May be used.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described. FIG. 9 is a block diagram showing the configuration of the plasma display device according to the second embodiment of the present invention.

  As shown in FIG. 9, the plasma display device in the present embodiment is different from the plasma display device in the first embodiment in that a second coefficient adder 330, a second dither value generator 340, and a selection are selected. And a pseudo contour detector 360.

  Discharge control timing generation circuit 500, A / D converter 100, scan number conversion unit 200, error diffusion device 300, first coefficient adder 310, first dither value generator 320, second coefficient adder 330, second The dither value generator 340, the selector 350, the pseudo contour detector 360, and the subfield conversion unit 400 are supplied with the horizontal synchronizing signal H and the vertical synchronizing signal V.

  The error diffusion device 300 diffuses the errors e2 and e3 output from the first dither value generator 320 or the second dither value generator 340 spatially and temporally.

  The image data VV obtained by the error diffusion device 300 includes a first coefficient adder 310, a first dither value generator 320, a second coefficient adder 330, a second dither value generator 340, and a selector 350. Given to. The value of the image data VV indicates the gradation level of the corresponding pixel.

  The first dither value generator 320 stores a dither table indicating the relationship between a plurality of gradation levels represented by the image data VV and a plurality of dither values, and converts the dither table to the gradation level of the image data VV. The corresponding dither value is read and provided to the first coefficient adder 310. Here, the dither value corresponds to the difference between each gradation level and the gradation value displayed by each pixel.

  The first coefficient adder 310 adds the dither value given by the first dither value generator 320 to the image data VV given by the error diffusion device 300, and selects the result as the image data VV1 as a selector 350. To give. The image data VV1 indicates gradation values displayed by the four pixels in each region.

  The second dither value generator 340 stores a dither table indicating the relationship between the plurality of gradation levels represented by the image data VV and the plurality of dither values, and converts the dither table to the gradation level of the image data VV. The corresponding dither value is read and provided to the second coefficient adder 330.

  The second coefficient adder 330 adds the dither value given by the second dither value generator 340 to the image data VV given by the error diffusion device 300, and selects the addition result as image data VV 2. To give. The image data VV2 indicates gradation values displayed by the four pixels in each region.

  The pseudo contour detector 360 detects the degree of occurrence of pseudo contour noise from the subfield emission pattern, the gradation level change amount, the image moving speed, the image moving direction, etc. as information included in the image data VD. Then, this detection result is given to the selector 350. In the present embodiment, the pseudo contour detector 360 includes a motion amount detection circuit that detects the motion amount of an image.

  Note that the pseudo contour detector 360 is not limited to the motion amount detection circuit, and other circuits that can detect a value related to the degree of occurrence of pseudo contour noise may be used.

  The selector 350, based on the detection result given from the pseudo contour detector 360, the image data VV given from the error diffusion device 300, the image data VV1 given from the first coefficient adder 310, and the second data. One of the image data VV <b> 2 given from the coefficient adder 330 is selected and given to the subfield conversion unit 400.

  The subfield conversion unit 400 stores a light emission pattern table indicating the relationship between gradation values respectively displayed by the four pixels in each region and the light emission patterns of a plurality of subfields, and based on the light emission pattern table. Any one of the image data VV, VV1, and VV2 is converted into serial data SD corresponding to a plurality of subfields, and the serial data SD is supplied to the data driver 700.

  The dither table included in the first dither value generator 320 and the light emission pattern table included in the subfield conversion unit 400 corresponding to the dither table are the same as the dither table and the light emission pattern table illustrated in FIGS. 8a to 8e described above. .

  Hereinafter, a dither table included in the second dither value generator 340 and a light emission pattern table included in the subfield conversion unit 400 corresponding to the dither table will be described.

  10a to 10e are explanatory diagrams illustrating a dither table included in the second dither value generator 340 and a light emission pattern table included in the subfield conversion unit 400.

  The relationship between the gradation level and the first to fourth dither values in FIGS. 10a to 10d and the relationship between the gradation level and the error in FIG. 10e are included in the dither table included in the second dither value generator 340. . In the first dither value generator 320 and the second dither value generator 340, the image data VV corresponds to any of the first to fourth pixels P1 to P4 based on the horizontal synchronizing signal H and the vertical synchronizing signal V. And a dither value corresponding to this pixel is selected.

  The relationship between the first to fourth gradation values and the first to fourth light emission patterns in FIGS. 10 a to 10 d is included in the light emission pattern table included in the subfield conversion unit 400. 10a indicates the gradation level of the first pixel P1, the gradation level illustrated in FIG. 10b indicates the gradation level of the second pixel P2, and the gradation level illustrated in FIG. The gradation level of the third pixel P3 is shown, and the gradation level shown in FIG. 10d shows the gradation level of the fourth pixel P4.

  When the pseudo contour detector 360 detects that the pseudo contour noise is generated at a high level, the selector 350 selects the image data VV1 of the first coefficient adder 320, and the pseudo contour noise is generated at a low level. When detected by the pseudo contour detector 360, the selector 350 selects the image data VV2 of the second coefficient adder 340. When the pseudo contour detector 360 detects that no pseudo contour noise is generated, the selector 350 selects the image data VV of the error diffusion device 300.

  In the present embodiment, some of the combination patterns of light emission and non-light emission of predetermined subfields of the first to fourth light emission patterns in the dither table included in the second dither value generator 340 are the same.

  For example, the subfields SF5 to SF2 of the first to fourth light emission patterns corresponding to the gradation level “23” are “1010”, “1011”, “1011”, and “1101”, respectively. The combined patterns of light emission and non-light emission in the subfields SF5 to SF2 of the light emission pattern are the same.

  Accordingly, the effect of reducing the pseudo contour noise is smaller than that in the case where the first to fourth light emission patterns in the dither table included in the first dither value generator 320 are used, but the noise due to the dither pattern is reduced. It becomes possible.

  Thus, in the present embodiment, the image data VV, the image data VV1 output from the first coefficient adder 320, or the image output from the second coefficient adder 340 according to the degree of pseudo contour noise. By selectively using the data VV2, pseudo contour noise can be reduced while minimizing noise due to the dither pattern.

  In the present embodiment, the first coefficient adder 310, the second coefficient adder 330, the first dither value generator 320, the second dither value generator 340, the selector 350, and the subfield conversion unit 400. Corresponds to the gradation display unit, the pseudo contour detector 360 corresponds to the detection unit, the data driver 700, the scan driver 800, and the sustain driver 900 correspond to the drive unit, and the error diffusion device 300 corresponds to the diffusion device.

  The present invention can be used in an image display device that displays a video signal as an image.

The block diagram which shows the structure of the plasma display apparatus in the 1st Embodiment of this invention. The figure for demonstrating the ADS system applied to the plasma display apparatus shown in FIG. The schematic diagram which shows an example of the light emission pattern of the several subfield of 4 pixels of each area | region based on the dither table of a dither value generator. Explanatory drawing which shows the dither table which a dither value generator has, and the light emission pattern table which a subfield conversion part has. Explanatory drawing which shows the dither table which a dither value generator has, and the light emission pattern table which a subfield conversion part has. Explanatory drawing which shows the dither table which a dither value generator has, and the light emission pattern table which a subfield conversion part has. Explanatory drawing which shows the dither table which a dither value generator has, and the light emission pattern table which a subfield conversion part has. Explanatory drawing which shows the dither table which a dither value generator has, and the light emission pattern table which a subfield conversion part has. (A) is explanatory drawing which shows the contrast of each pixel recognized when a human eyes | visual_axis does not move, (b) is recognized when a human eyes | visual_axis moves to the direction (left to right) of an arrow. Explanatory drawing which shows the lightness and darkness of each pixel. The block diagram which shows the structure of the error diffusion apparatus shown in FIG. (A) is a figure which shows the spatial spreading | diffusion of an error, (b) is a figure which shows the temporal spreading | diffusion of an error. Explanatory drawing which shows the other example of the light emission pattern table which the dither table which a dither value generator has, and the subfield conversion part. Explanatory drawing which shows the other example of the light emission pattern table which the dither table which a dither value generator has, and the subfield conversion part. Explanatory drawing which shows the other example of the light emission pattern table which the dither table which a dither value generator has, and the subfield conversion part. Explanatory drawing which shows the other example of the light emission pattern table which the dither table which a dither value generator has, and the subfield conversion part. Explanatory drawing which shows the other example of the light emission pattern table which the dither table which a dither value generator has, and the subfield conversion part. The block diagram which shows the structure of the plasma display apparatus in the 2nd Embodiment of this invention. Explanatory drawing which shows the light emission pattern table which the dither table which a 2nd dither value generator has, and the subfield conversion part. Explanatory drawing which shows the light emission pattern table which the dither table which a 2nd dither value generator has, and the subfield conversion part. Explanatory drawing which shows the light emission pattern table which the dither table which a 2nd dither value generator has, and the subfield conversion part. Explanatory drawing which shows the light emission pattern table which the dither table which a 2nd dither value generator has, and the subfield conversion part. Explanatory drawing which shows the light emission pattern table which the dither table which a 2nd dither value generator has, and the subfield conversion part. The schematic diagram for demonstrating the pseudo contour noise visually recognized when a human eyes | visual_axis moves on a different pixel.

Explanation of symbols

300 Error diffusion device 310 First coefficient adder 320 First dither value generator 330 Second coefficient adder 340 Second dither value generator 350 Selector 360 Pseudo contour detector 400 Subfield conversion unit 600 PDP
700 Data Driver 800 Scan Driver 900 Sustain Driver P1, P2, P3, P4 Pixel R1, R2, R3, R4 Area

Claims (12)

A display device that performs gradation display by a subfield method based on a video signal having a gradation level,
A display panel composed of a plurality of regions each including first to fourth pixels adjacent vertically and horizontally;
The first to fourth tables each including a plurality of first to fourth light emission patterns corresponding to the first to fourth pixels are stored, and the first to fourth tables are stored based on the gradation level of the video signal. The first to fourth light emission patterns corresponding to the first to fourth pixels in each region are selected from the four tables, and the subfields are selected based on the selected first to fourth light emission patterns. A gradation display unit that performs gradation display by causing the first to fourth pixels in each region of the display panel to emit light or not to emit light,
A combination pattern of light emission and non-light emission in a predetermined subfield among the plurality of subfields is different between the first to fourth light emission patterns,
In each region, the first and second pixels are arranged at one diagonal position, and the third and fourth pixels are arranged at the other diagonal position,
At each gradation level, the gradation value expressed by the first and second light emission patterns is lower than the average value of the gradation expressed by the first to fourth light emission patterns, and the third and fourth The display device is characterized in that gradation values expressed by the respective light emission patterns are higher than the average value. The plurality of subfields have different weights;
The predetermined subfield starts with the subfield having the maximum weight among the subfields in which the pixels emit light in the order of decreasing weight from the subfield having the maximum weight to the subfield having the minimum weight. The display device according to claim 1, further comprising: a predetermined number of subfields. 3. The combination pattern in the predetermined subfield is the same between adjacent gradation levels in two or more light emission patterns among the first to fourth light emission patterns. Display device. A detection unit for detecting the degree of pseudo contour noise in the image displayed on the display panel;
The gradation display unit further stores fifth to eighth tables each including a plurality of fifth to eighth light emission patterns corresponding to the first to fourth pixels, and a detection result by the detection unit. When one of the first to fourth table sets and the fifth to eighth table sets is selected on the basis of the first to fourth table sets, and the fifth to eighth table sets are selected, an image is displayed. Based on the gradation level of the signal, the fifth to eighth light emission patterns respectively corresponding to the first to fourth pixels in each region are selected from the selected fifth to eighth tables, and selected. In addition, gradation display is performed by causing the first to fourth pixels in each region of the display panel to emit or not emit light for each subfield based on the fifth to eighth emission patterns.
A combination pattern of light emission and non-light emission in the predetermined subfield is partially the same among the fifth to eighth light emission patterns,
At each gradation level, the gradation values expressed by the fifth and sixth light emission patterns are higher than the average values of the gradations expressed by the fifth to eighth light emission patterns. The gradation value expressed by each of the light emission patterns is lower than the average value of the gradations expressed by the fifth to eighth light emission patterns . Display device. The gradation display section
The difference between each gradation level and the gradation values respectively represented by the first to fourth light emission patterns is stored as first to fourth dither values, and the first corresponding to the gradation level of the video signal. A dither value generator for outputting a fourth dither value;
A coefficient adder for respectively adding the first to fourth dither values generated by the dither value generator to the gradation level of the video signal;
The first to fourth tables are stored, the first to fourth light emission patterns are selected from the first to fourth tables based on the addition result of the coefficient adder, and the selected first to fourth tables are selected. 5. The driving unit according to claim 1, further comprising: a driving unit configured to emit or not emit light in the first to fourth pixels of each region of the display panel for each subfield based on a fourth light emission pattern. The display device described in 1. When the gradation level of the video signal and the average value of the gradation expressed by the first to fourth light emission patterns are different, the gradation level of the video signal and the first to fourth light emission patterns respectively. The display device according to claim 1, further comprising a diffusion device that diffuses an error from the expressed gradation average value spatially and / or temporally into the video signal. A display method for performing gradation display on a display panel by a subfield method based on a video signal having a gradation level,
The display panel is composed of a plurality of regions each including first to fourth pixels adjacent vertically and horizontally, and in each region, the first and second pixels are arranged at one diagonal position, The third and fourth pixels are arranged at the other diagonal position;
Storing first to fourth tables each including a plurality of first to fourth light emission patterns corresponding to the first to fourth pixels;
Selecting first to fourth light emission patterns respectively corresponding to the first to fourth pixels in each region from the first to fourth tables based on a gradation level of a video signal;
Performing gradation display by causing the first to fourth pixels in each region of the display panel to emit light or not to emit light for each subfield based on the selected first to fourth light emission patterns,
A combination pattern of light emission and non-light emission in a predetermined subfield among the plurality of subfields is different between the first to fourth light emission patterns,
At each gradation level, the gradation value expressed by the first and second light emission patterns is higher than the average value of the gradation expressed by the first to fourth light emission patterns. The display method according to claim 1, wherein a gradation value expressed by each of the light emission patterns is lower than the average value. The plurality of subfields have different weights;
The predetermined subfield starts with the subfield having the maximum weight among the subfields in which the pixels emit light in the order of decreasing weight from the subfield having the maximum weight to the subfield having the minimum weight. The display method according to claim 7, further comprising: a predetermined number of subfields. 9. The combination pattern in the predetermined subfield is the same between adjacent gradation levels in two or more light emission patterns among the first to fourth light emission patterns. How to display. Detecting the degree of pseudo contour noise in the image displayed on the display panel;
Further storing fifth to eighth tables each including a plurality of fifth to eighth light emission patterns corresponding to the first to fourth pixels;
Selecting one of the first to fourth table sets and the fifth to eighth table sets based on the detection result of the degree of pseudo contour noise;
When the set of the fifth to eighth tables is selected, the first to fourth pixels in each region are selected from the selected fifth to eighth tables based on the gradation level of the video signal. Selecting the corresponding fifth to eighth light emission patterns;
And a step of performing gradation display by causing the first to fourth pixels in each region of the display panel to emit light or not to emit light for each subfield based on the selected fifth to eighth light emission patterns. ,
A combination pattern of light emission and non-light emission in the predetermined subfield is partially the same among the fifth to eighth light emission patterns,
At each gradation level, the gradation values expressed by the fifth and sixth light emission patterns are lower than the average values of the gradations expressed by the fifth to eighth light emission patterns. The gradation value represented by each of the light emission patterns is higher than the average value of the gradations represented by the fifth to eighth light emission patterns . Display method. The step of performing gradation display stores the difference between each gradation level and the gradation value respectively represented by the first to fourth light emission patterns as first to fourth dither values;
Outputting first to fourth dither values corresponding to the gradation level of the video signal;
Adding each of the first to fourth dither values generated in the gradation level of the video signal;
Storing the first to fourth tables;
Selecting the first to fourth light emission patterns from the first to fourth tables based on the addition result;
And a step of causing the first to fourth pixels in each region of the display panel to emit light or not to emit light for each subfield based on the selected first to fourth light emission patterns. The display method in any one of -10. When the gradation level of the video signal and the average value of the gradation expressed by the first to fourth light emission patterns are different, the gradation level of the video signal and the first to fourth light emission patterns respectively. The display method according to claim 7, further comprising a step of diffusing an error from the expressed gradation average value into the video signal spatially and / or temporally.

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