JP2011081335A - Method for driving plasma display panel and plasma display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve image display quality by reducing afterimage phenomenon of a display image in a plasma display panel. <P>SOLUTION: There is provided a method for driving a plasma display panel by providing, in one field, a plurality of sub-fields each having a write-in period and a sustaining period and by driving them and performing gradation display, wherein the plasma display panel includes a plurality of discharge cells which forms one pixel and each of which has a pair of display electrodes composed of a scanning electrode and a sustaining electrode and has a data electrode. The method includes: dividing a display region of the plasma display panel into a plurality of regions; calculating the degree of afterimage for each region based on a gradation value of brightness set to each pixel in accordance with an image signal; calculating the degree of afterimage for each pixel based on the degree of afterimage for each region; and changing a gradation value of brightness of each pixel based on the degree of afterimage for each pixel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a driving method of a plasma display panel and a plasma display device used for a wall-mounted television or a large monitor.

  A typical AC surface discharge type panel as a plasma display panel (hereinafter abbreviated as “panel”) has a large number of discharge cells formed between a front plate and a back plate arranged to face each other. In the front plate, a plurality of pairs of display electrodes composed of a pair of scan electrodes and sustain electrodes are formed on the front glass substrate in parallel with each other. A dielectric layer and a protective layer are formed so as to cover the display electrode pairs. In the back plate, a plurality of parallel data electrodes are formed on a back glass substrate, a dielectric layer is formed so as to cover the data electrodes, and a plurality of barrier ribs are formed thereon in parallel with the data electrodes. . And the fluorescent substance layer is formed in the surface of a dielectric material layer, and the side surface of a partition. Then, the front plate and the back plate are arranged to face each other and sealed so that the display electrode pair and the data electrode are three-dimensionally crossed. In the sealed internal discharge space, for example, a discharge gas containing xenon at a partial pressure ratio of 5% is sealed, and a discharge cell is formed in a portion where the display electrode pair and the data electrode face each other. In the panel having such a configuration, ultraviolet rays are generated by gas discharge in each discharge cell, and the phosphors of red (R), green (G) and blue (B) colors are excited and emitted by the ultraviolet rays, thereby performing color display. It is carried out.

  A subfield method is generally used as a method for driving the panel. In the subfield method, one field is divided into a plurality of subfields, and gradation display is performed by causing each discharge cell to emit light or not emit light in each subfield. Each subfield has an initialization period, an address period, and a sustain period.

  In the initialization period, an initialization waveform is applied to each scan electrode, and an initialization discharge is generated in each discharge cell. Thus, in each discharge cell, wall charges necessary for the subsequent address operation are formed, and priming particles (excited particles for generating the address discharge) for generating the address discharge stably are generated.

  In the address period, a scan pulse is applied to the scan electrode, and an address pulse is applied to the data electrode based on an image signal to be displayed to generate an address discharge in a discharge cell to be displayed to form a wall charge (hereinafter referred to as a wall charge). This operation is also referred to as “writing”).

  In the sustain period, the number of sustain pulses determined for each subfield is alternately applied to the display electrode pairs including the scan electrodes and the sustain electrodes. Thereby, a sustain discharge is generated in the discharge cell in which the address discharge has occurred, and the phosphor layer of the discharge cell is caused to emit light. As a result, each discharge cell emits light at a luminance corresponding to the luminance weight determined for each subfield. In this way, each discharge cell of the panel is caused to emit light with a luminance corresponding to the gradation value of the image signal, thereby performing image display.

  In addition, as one of the subfield methods, gradation discharge is performed by performing initializing discharge using a slowly changing voltage waveform and selectively performing initializing discharge on discharge cells that have undergone sustain discharge. A driving method is disclosed in which light emission not related to the above is reduced as much as possible and the contrast ratio is improved.

  Specifically, among the plurality of subfields, in the initialization period of one subfield, an all-cell initializing operation for generating an initializing discharge in all discharge cells is performed, and in an initializing period of the other subfield. Performs a selective initializing operation in which initializing discharge is generated only in the discharge cells that have undergone sustain discharge in the immediately preceding sustain period. By driving in this way, the luminance of the black display region (hereinafter abbreviated as “black luminance”) that changes due to light emission not related to image display is only weak light emission in the all-cell initialization operation, and has high contrast. Image display is possible (see, for example, Patent Document 1).

  On the other hand, with the recent increase in the definition of the panel and the increase in the screen size, various efforts have been made to improve the light emission efficiency of the panel and improve the luminance. For example, studies are underway to increase the luminous efficiency by increasing the xenon partial pressure of the discharge gas filled in the discharge cell. However, when the xenon partial pressure of the discharge gas is increased, the variation in the timing at which discharge occurs increases, and the emission intensity varies from discharge cell to discharge cell, resulting in non-uniform display brightness. In order to improve this non-uniform brightness, a driving method is disclosed in which, for example, a sustain pulse with a steep rise is inserted at a rate of once every several times so that the timing of the sustain discharge is aligned and the display brightness is made uniform. (For example, refer to Patent Document 2).

JP 2000-242224 A JP-A-2005-338120

  However, if the xenon partial pressure of the discharge gas is increased in order to increase the luminous efficiency, a so-called afterimage phenomenon that the still image is recognized as an afterimage tends to occur when the still image is displayed for a long time. Quality may be impaired.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a panel driving method and a plasma display device capable of reducing the afterimage phenomenon of a display image on the panel and improving the image display quality. To do.

  In the panel driving method of the present invention, a display panel having a plurality of discharge cells each having a display electrode pair and a data electrode each including a scan electrode and a sustain electrode, each pixel being constituted by a plurality of discharge cells, is maintained in an address period. A panel driving method in which a plurality of subfields having a period are provided in one field and driven to display gray scales, and the display area of the panel is divided into a plurality of areas and set to each pixel in accordance with an image signal. The afterimage strength level for each region is calculated based on the brightness gradation value for each pixel, the afterimage strength level for each pixel is calculated based on the afterimage strength level for each region, and the brightness tone value of each pixel is calculated based on the afterimage strength level for each pixel. It is characterized by changing.

  Accordingly, the afterimage strength that is a guide for the occurrence of the afterimage phenomenon is calculated for each pixel on the basis of the luminance gradation value, and the luminance gradation value of each pixel is changed based on the calculated afterimage strength. It is possible to reduce the afterimage phenomenon of the display image and improve the image display quality.

  Also, in this panel driving method, the difference in luminance gradation value between the current field and the field immediately before the current field is calculated for each pixel as the inter-field luminance difference, and the inter-field luminance difference is a predetermined luminance comparison value. The number of pixels that are smaller than each other is counted for each region to be the first count value in each region, and the number of edges at which the difference in luminance gradation value between adjacent pixels is equal to or greater than a predetermined edge comparison value A configuration may be used in which the afterimage strength level is calculated for each area based on the first count value and the second count value by counting each area to be the second count value in each area. As a result, the afterimage strength level can be calculated based on an image in which an afterimage phenomenon is likely to occur, for example, an image in which the number of edges is large and a still region is continuously displayed.

  Further, in this panel driving method, in the region where the first count value is equal to or greater than the first threshold value and the second count value is equal to or greater than the third threshold value, the afterimage strength level for each region is set. The first set value is added, the first count value is less than the first threshold value and greater than or equal to the second threshold value that is smaller than the first threshold value, and the second count value is In an area that is equal to or greater than the third threshold value, the second set value is added to the afterimage strength level for each area, the first count value is less than the second threshold value, and the second count value is the second count value. In an area where the threshold value is 3 or more, the third set value is added to the afterimage strength level for each area. In an area where the second count value is less than the third threshold value, the afterimage strength level for each area is set. It is good also as a structure which adds the 4th setting value and updates the afterimage strength for every area | region. As a result, in a region where the first count value is equal to or greater than the first threshold value and the second count value is equal to or greater than the third threshold value, the first set value is accumulated in the afterimage strength level for each region. And the first count value is less than or equal to the second threshold value that is less than the first threshold value and the second count value is the third threshold value. In the above region, the second set value is cumulatively added to the afterimage strength level for each region, the first count value is less than the second threshold value, and the second count value is the third threshold value. In the above region, the third set value is cumulatively added to the afterimage strength level for each region, and in the region where the second count value is less than the third threshold value, the fourth set value is set for the afterimage strength level for each region. Values can be cumulatively added. Therefore, the afterimage strength level for each area can be updated for each field in accordance with the feature of the image for each area.

  In this panel driving method, the first set value is a positive value, the second set value is “0”, and the third set value and the fourth set value are negative numbers. There may be. As a result, the region where the first count value is equal to or greater than the first threshold value and the second count value is equal to or greater than the third threshold value is defined as a region where the afterimage phenomenon is more likely to occur. The first set value is set to a positive number to increase the afterimage strength level, the first count value is less than the second threshold value, and the second count value is greater than or equal to the third threshold value The area and the area where the second count value is less than the third threshold are areas where the afterimage phenomenon is less likely to occur, and the third set value and the fourth set value are negative numbers. The afterimage strength level is decreased by setting the first count value to be less than the first threshold value and greater than or equal to the second threshold value, and the second count value is greater than or equal to the third threshold value. The afterimage strength can be maintained by setting the second set value to “0” as an area where the afterimage phenomenon is easily generated. .

  In the panel driving method, a predetermined constant may be subtracted from the updated afterimage strength level. This makes it possible to control the timing for starting correction of the luminance to the gradation value based on the afterimage strength.

  In this panel driving method, the updated afterimage strength level may be limited to a predetermined upper limit value or less. This makes it possible to prevent overcorrection of the luminance gradation value due to the afterimage strength.

  Further, in this panel driving method, in each region, the afterimage strength level of each region is set as the afterimage strength level of the central pixel located in the center of the region, and for the pixels other than the central pixel, pixels for which the afterimage strength level is to be calculated. Further, the afterimage strength level for each pixel may be calculated based on the distance from the surrounding central pixels and the afterimage strength level of the center pixel. This makes it possible to appropriately calculate the afterimage strength level for each pixel based on the afterimage strength level for each region.

  In this panel driving method, the afterimage strength for each pixel is subtracted from a predetermined reference value, and the result of dividing the subtraction result by the reference value is multiplied by the luminance gradation value of each pixel. The luminance gradation value of each pixel may be changed. Thereby, it is possible to appropriately correct the luminance gradation value based on the afterimage strength level.

  In addition, in this panel driving method, the luminance gradation value may be changed based on the afterimage strength level only in a pixel where the luminance gradation value of each pixel is equal to or higher than a predetermined high luminance threshold value. Good. Thereby, for example, in a pixel having a high luminance gradation value and a large luminance difference from an adjacent pixel, the luminance gradation value can be corrected according to the magnitude of the afterimage strength level.

  Further, in this panel driving method, the average luminance level of the image signal is detected, and when the average luminance level is large, the afterimage strength is smaller than when the average luminance level is small. The afterimage strength of the image may be changed. As a result, the afterimage strength that is a measure of occurrence of the afterimage phenomenon can be changed based on the detected average luminance level, and the luminance gradation value of each pixel can be changed based on the afterimage strength after the change. Therefore, in an image with a high average luminance level that is considered to be relatively less likely to cause an afterimage phenomenon, the magnitude of the afterimage strength can be reduced compared to an image with a low average luminance level, for example, the average luminance level is high. It is possible to reduce the occurrence of an afterimage phenomenon while preventing a decrease in luminance of the display image in the image.

  Further, in this panel driving method, the number of sustain pulses generated by multiplying the luminance weight set for each subfield by the luminance magnification is generated in the sustain period, and when the luminance magnification is small, compared to when the luminance magnification is large. The afterimage strength for each pixel may be changed based on the luminance magnification so that the afterimage strength is reduced. As a result, it is possible to change the afterimage strength that is a measure of occurrence of the afterimage phenomenon based on the luminance magnification, and to change the luminance gradation value of each pixel based on the afterimage strength after the change. Therefore, when it is considered that the afterimage phenomenon is relatively unlikely to occur with a small luminance magnification, the magnitude of the afterimage strength can be reduced as compared with the case where the luminance magnification is large. Therefore, for example, it is possible to reduce the occurrence of an afterimage phenomenon while preventing a decrease in luminance of an image displayed when the luminance magnification is small.

  In this panel driving method, the number of sustain pulses obtained by multiplying the luminance weight set for each subfield by the luminance magnification is generated in the sustain period, and the first set value is set according to the luminance magnification. You may change the size of. As a result, it is possible to change the afterimage strength that is a measure of occurrence of the afterimage phenomenon based on the luminance magnification, and to change the luminance gradation value of each pixel based on the afterimage strength after the change.

  In this panel driving method, the first set value is a positive value when the luminance magnification is greater than or equal to the fourth threshold value, and the first set value when the luminance magnification is less than the fourth threshold value. May be set to “0”. As a result, when it is considered that the afterimage phenomenon is relatively unlikely to occur with a small luminance magnification, the afterimage strength level can be made smaller than when the luminance magnification is large. Therefore, for example, it is possible to reduce the occurrence of an afterimage phenomenon while preventing a decrease in luminance of an image displayed when the luminance magnification is small.

  Also, in this panel driving method, a plurality of boundaries are provided in the direction in which the display electrode pair extends and a plurality of boundaries are provided in the direction in which the data electrode extends so that the number of pixels is equal to each other. May be.

  In addition, the plasma display device of the present invention includes a plurality of discharge cells each having a display electrode pair including a scan electrode and a sustain electrode, and a plurality of discharge cells constitute one pixel, and a sub-period having an address period and a sustain period A panel in which a plurality of fields are provided in one field and gradation display is performed, and gradation values of luminance and saturation are set for each pixel according to an image signal, and the gradation values of luminance and saturation are set according to the magnitude of the gradation value. An image signal processing circuit for generating image data indicating light emission / non-light emission for each subfield in the discharge cell. The image signal processing circuit divides the display area of the panel into a plurality of areas, and Calculate the afterimage strength for each region based on the gradation value of brightness set for the pixel, calculate the afterimage strength for each pixel based on the afterimage strength for each region, and calculate the afterimage strength for each pixel based on the afterimage strength for each pixel. And changes the gray scale value of the brightness.

  Accordingly, the afterimage strength that is a guide for the occurrence of the afterimage phenomenon is calculated for each pixel on the basis of the luminance gradation value, and the luminance gradation value of each pixel is changed based on the calculated afterimage strength. It is possible to reduce the afterimage phenomenon of the display image and improve the image display quality.

  According to the present invention, it is possible to provide a panel driving method and a plasma display device capable of reducing the afterimage phenomenon of a display image on the panel and improving the image display quality.

It is a disassembled perspective view which shows the structure of the panel in Embodiment 1 of this invention. It is an electrode array figure of the panel. It is a drive voltage waveform figure applied to each electrode of the panel. It is a circuit block diagram of the plasma display apparatus in Embodiment 1 of the present invention. It is a figure which shows roughly an example of the several area | region provided in the display area of the panel in Embodiment 1 of this invention. FIG. 3 is a circuit block diagram illustrating a configuration example of an image signal processing circuit according to the first embodiment of the present invention. It is a circuit block diagram which shows one structural example of the afterimage strength level calculation circuit in Embodiment 1 of this invention. It is a figure which shows roughly the calculation performed in the afterimage strength interpolation circuit in Embodiment 1 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 1 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 2 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 3 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 4 of this invention. It is a circuit block diagram which shows one structural example of the afterimage strength level calculation circuit in Embodiment 5 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 6 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 7 of this invention.

  Hereinafter, a plasma display device according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is an exploded perspective view showing the structure of panel 10 in accordance with the first exemplary embodiment of the present invention. A plurality of display electrode pairs 24 each including a scanning electrode 22 and a sustain electrode 23 are formed on a glass front plate 21. A dielectric layer 25 is formed so as to cover the scan electrode 22 and the sustain electrode 23, and a protective layer 26 is formed on the dielectric layer 25. The protective layer 26 is made of a material mainly composed of magnesium oxide (MgO).

  A plurality of data electrodes 32 are formed on the back plate 31, a dielectric layer 33 is formed so as to cover the data electrodes 32, and a grid-like partition wall 34 is formed thereon. A phosphor layer 35 that emits light of each color of red (R), green (G), and blue (B) is provided on the side surface of the partition wall 34 and on the dielectric layer 33.

  The front plate 21 and the back plate 31 are arranged to face each other so that the display electrode pair 24 and the data electrode 32 intersect with each other with a minute discharge space interposed therebetween. And the outer peripheral part is sealed with sealing materials, such as glass frit. A mixed gas of neon and xenon is sealed as a discharge gas in the internal discharge space. In the present embodiment, a discharge gas having a xenon partial pressure of about 10% is used in order to improve luminous efficiency. The discharge space is partitioned into a plurality of sections by partition walls 34, and discharge cells are formed at the intersections between the display electrode pairs 24 and the data electrodes 32. These discharge cells discharge and emit light to display an image.

  In the panel 10, three continuous discharge cells arranged in the extending direction of the display electrode pair 24, that is, a discharge cell that emits red (R), a discharge cell that emits green (G), and a blue ( One pixel is constituted by three discharge cells adjacent to the discharge cell emitting light in B).

  Note that the structure of the panel 10 is not limited to the above-described structure, and for example, a structure having a stripe-shaped partition may be used. Further, the mixing ratio of the discharge gas is not limited to the above-described numerical values, and may be other mixing ratios.

  FIG. 2 is an electrode array diagram of panel 10 in accordance with the first exemplary embodiment of the present invention. The panel 10 includes n scan electrodes SC1 to SCn (scan electrodes 22 in FIG. 1) and n sustain electrodes SU1 to SUn (sustain electrodes 23 in FIG. 1) that are long in the row direction. M data electrodes D1 to Dm (data electrodes 32 in FIG. 1) that are long in the column direction are arranged. A discharge cell is formed at a portion where one pair of scan electrode SCi (i = 1 to n) and sustain electrode SUi intersects one data electrode Dk (k = 1 to m), and the discharge cell is in the discharge space. M × n are formed. A region where m × n discharge cells are formed becomes a display region of the panel 10. For example, in a panel having 1920 × 1080 pixels, m = 1920 × 3 and n = 1080.

  Next, a driving voltage waveform for driving the panel 10 and an outline of the operation will be described. In the plasma display device in this embodiment, one field is divided into a plurality of subfields on the time axis, luminance weights are set for each subfield, and light emission / non-light emission of each discharge cell is performed for each subfield. It is assumed that gradation display is performed by a subfield method for controlling the above.

  In this subfield method, for example, one field is composed of eight subfields (first SF, second SF,..., Eighth SF), and each weight is increased so that the luminance weight increases in the later subfield. Each subfield may have a luminance weight of (1, 2, 4, 8, 16, 32, 64, 128). In addition, in the initializing period of one subfield among a plurality of subfields, an all-cell initializing operation for generating an initializing discharge in all discharge cells is performed (hereinafter, the subfield for performing the all-cell initializing operation is referred to as a subfield for performing all-cell initializing operations). In the initializing period of other subfields, a selective initializing operation for selectively generating initializing discharge is performed for the discharge cells that have undergone sustain discharge (hereinafter referred to as “all-cell initializing subfield”). The subfield that performs the selective initialization operation is referred to as “selective initialization subfield”), and it is possible to reduce light emission not related to gradation display as much as possible and improve the contrast ratio.

  In the present embodiment, the all-cell initialization operation is performed in the initialization period of the first SF, and the selective initialization operation is performed in the initialization period of the second SF to the eighth SF. Thereby, the light emission not related to the image display is only the light emission due to the discharge of the all-cell initializing operation in the first SF. Therefore, the black luminance, which is the luminance of the black display region where no sustain discharge is generated, is only weak light emission in the all-cell initializing operation, and an image display with high contrast is possible. In the sustain period of each subfield, the number of sustain pulses obtained by multiplying the luminance weight of each subfield by a predetermined luminance magnification is applied to each display electrode pair 24. For example, in the above-described subfield configuration, if the luminance magnification is double, the number of sustain pulses generated in the sustain period of each subfield is (2, 4, 8, 16, 32, 64, 128, 256), respectively. If the luminance magnification is 3 times, then (3, 6, 12, 24, 48, 96, 192, 384).

  However, in the present embodiment, the number of subfields and the luminance weight of each subfield are not limited to the above values, and the subfield configuration may be switched based on an image signal or the like.

  FIG. 3 is a drive voltage waveform diagram applied to each electrode of panel 10 in accordance with the first exemplary embodiment of the present invention. FIG. 3 shows scan electrode SC1 that scans first in the address period, scan electrode SCn that scans last in the address period (for example, scan electrode SC1080), sustain electrode SU1 to sustain electrode SUn, and data electrode D1 to data. The drive waveform of the electrode Dm is shown.

  FIG. 3 also shows driving voltage waveforms of two subfields, that is, a first subfield (first SF) that is an all-cell initializing subfield and a second subfield (second SF) that is a selective initializing subfield. It shows. The drive voltage waveform in the other subfields is substantially the same as the drive voltage waveform of the second SF except that the number of sustain pulses generated in the sustain period is different. Scan electrode SCi, sustain electrode SUi, and data electrode Dk in the following represent electrodes selected based on image data (data indicating light emission / non-light emission for each subfield) from among the electrodes.

  First, the first SF, which is an all-cell initialization subfield, will be described.

  In the first half of the initializing period of the first SF, 0 (V) is applied to data electrode D1 to data electrode Dm, sustain electrode SU1 to sustain electrode SUn, and voltage Vi1 is applied to scan electrode SC1 to scan electrode SCn. To do. At this time, voltage Vi1 is set to a voltage lower than the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn. Further, a ramp voltage (hereinafter referred to as “up-ramp voltage”) L1 that gently rises from the voltage Vi1 toward the voltage Vi2 (for example, with a slope of about 1.3 V / μsec) is applied. At this time, voltage Vi2 is set to a voltage exceeding the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn.

  While the rising ramp voltage L1 rises, between scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and between scan electrode SC1 through scan electrode SCn and data electrode D1 through data electrode Dm. Each weak initializing discharge occurs continuously. Negative wall voltage is accumulated above scan electrode SC1 through scan electrode SCn, and positive wall voltage is accumulated above data electrode D1 through data electrode Dm and sustain electrode SU1 through sustain electrode SUn. The wall voltage above the electrode represents a voltage generated by wall charges accumulated on the dielectric layer covering the electrode, the protective layer, the phosphor layer, and the like.

  In the latter half of the initialization period, positive voltage Ve1 is applied to sustain electrode SU1 through sustain electrode SUn, 0 (V) is applied to data electrode D1 through data electrode Dm, and scan electrode SC1 through scan electrode SCn. Sustain electrode SU1 to sustain electrode SUn gradually decrease from voltage Vi3 that is less than the discharge start voltage toward negative voltage Vi4 that exceeds the discharge start voltage (for example, with a gradient of about −2.5 V / μsec). A ramp voltage (hereinafter referred to as “down-ramp voltage”) L2 is applied.

  During this time, weak initialization discharges occur between scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and between scan electrode SC1 through scan electrode SCn and data electrode D1 through data electrode Dm, respectively. . Then, the negative wall voltage above scan electrode SC1 through scan electrode SCn and the positive wall voltage above sustain electrode SU1 through sustain electrode SUn are weakened, and the positive wall voltage above data electrode D1 through data electrode Dm is used for the write operation. It is adjusted to a suitable value. Thus, the all-cell initializing operation for performing the initializing discharge on all the discharge cells is completed.

  In the subsequent address period, scan pulse voltage Va is sequentially applied to scan electrode SC1 through scan electrode SCn, and data electrode Dk (k = k = corresponding to the discharge cell to emit light to data electrode D1 through data electrode Dm). 1 to m) is applied with a positive address pulse voltage Vd to selectively generate an address discharge in each discharge cell.

  Specifically, voltage Ve2 is first applied to sustain electrode SU1 through sustain electrode SUn, and voltage Vc (voltage Vc = voltage Va + voltage Vsc) is applied to scan electrode SC1 through scan electrode SCn.

  The negative scan pulse voltage Va is applied to the scan electrode SC1 in the first row, and the data electrode Dk (k = 1 to m) of the discharge cell that should emit light in the first row among the data electrodes D1 to Dm. A positive write pulse voltage Vd is applied to. At this time, the voltage difference at the intersection between the data electrode Dk and the scan electrode SC1 is the difference between the externally applied voltage (voltage Vd−voltage Va) between the wall voltage on the data electrode Dk and the wall voltage on the scan electrode SC1. The difference is added and exceeds the discharge start voltage. As a result, a discharge is generated between data electrode Dk and scan electrode SC1. Further, since voltage Ve2 is applied to sustain electrode SU1 through sustain electrode SUn, the voltage difference between sustain electrode SU1 and scan electrode SC1 is maintained at a difference between externally applied voltages (voltage Ve2−voltage Va). The difference between the wall voltage on the electrode SU1 and the wall voltage on the scan electrode SC1 is added. At this time, by setting the voltage Ve2 to a voltage value that is slightly lower than the discharge start voltage, the sustain electrode SU1 and the scan electrode SC1 are not easily discharged but are likely to be discharged. Can do. Thereby, the discharge generated between data electrode Dk and scan electrode SC1 can be triggered to generate a discharge between sustain electrode SU1 and scan electrode SC1 in the region intersecting with data electrode Dk. Thus, an address discharge occurs in the discharge cell to emit light, a positive wall voltage is accumulated on scan electrode SC1, a negative wall voltage is accumulated on sustain electrode SU1, and a negative wall voltage is also accumulated on data electrode Dk. Accumulated.

  In this manner, an address operation is performed in which an address discharge is caused in the discharge cells to be lit in the first row and wall voltage is accumulated on each electrode. On the other hand, the voltage at the intersection of data electrode D1 to data electrode Dm to which scan pulse SC1 is not applied with address pulse voltage Vd does not exceed the discharge start voltage, so that address discharge does not occur. The above address operation is sequentially performed until the discharge cell in the nth row, and the address period ends.

  In the subsequent sustain period, sustain pulses of the number obtained by multiplying the luminance weight by a predetermined luminance magnification are alternately applied to the display electrode pair 24 to generate a sustain discharge in the discharge cells that have generated the address discharge, thereby causing light emission.

  In this sustain period, first, positive sustain pulse voltage Vs is applied to scan electrode SC1 through scan electrode SCn, and a ground potential serving as a base potential, that is, 0 (V) is applied to sustain electrode SU1 through sustain electrode SUn. Then, in the discharge cell in which the address discharge has occurred, the voltage difference between scan electrode SCi and sustain electrode SUi is the difference between the wall voltage on scan electrode SCi and the wall voltage on sustain electrode SUi. Exceeds the discharge start voltage.

  Then, a sustain discharge occurs between scan electrode SCi and sustain electrode SUi, and phosphor layer 35 emits light by the ultraviolet rays generated at this time. Then, a negative wall voltage is accumulated on scan electrode SCi, and a positive wall voltage is accumulated on sustain electrode SUi. Further, a positive wall voltage is accumulated on the data electrode Dk. In the discharge cells in which no address discharge has occurred during the address period, no sustain discharge occurs, and the wall voltage at the end of the initialization period is maintained.

  Subsequently, 0 (V) as the base potential is applied to scan electrode SC1 through scan electrode SCn, and sustain pulse voltage Vs is applied to sustain electrode SU1 through sustain electrode SUn. Then, in the discharge cell in which the sustain discharge has occurred, the voltage difference between sustain electrode SUi and scan electrode SCi exceeds the discharge start voltage, so that a sustain discharge occurs again between sustain electrode SUi and scan electrode SCi, and the sustain cell is maintained. Negative wall voltage is accumulated on electrode SUi, and positive wall voltage is accumulated on scan electrode SCi. Similarly, the address discharge was caused in the address period by alternately applying the number of sustain pulses obtained by multiplying the brightness weight to the brightness magnification to scan electrode SC1 to scan electrode SCn and sustain electrode SU1 to sustain electrode SUn. Sustain discharge is continuously generated in the discharge cell.

  Then, after the sustain pulse is generated in the sustain period, 0 (V) is applied to scan electrode SC1 to scan electrode SCn while 0 (V) is applied to sustain electrode SU1 to sustain electrode SUn and data electrode D1 to data electrode Dm. Is applied with a ramp voltage (hereinafter referred to as “erasing ramp voltage”) L3 that gradually increases (for example, about 10 V / μsec) toward the voltage Vers exceeding the discharge start voltage. Thereby, a weak discharge is generated between sustain electrode SUi and scan electrode SCi of the discharge cell in which the sustain discharge has occurred. This weak discharge is continuously generated while the voltage applied to scan electrode SC1 through scan electrode SCn increases. When the increasing voltage reaches the predetermined voltage Vers, the voltage applied to scan electrode SC1 through scan electrode SCn is decreased to 0 (V) as the base potential.

  At this time, the charged particles generated by this weak discharge are accumulated on sustain electrode SUi and scan electrode SCi so as to alleviate the voltage difference between sustain electrode SUi and scan electrode SCi. Therefore, in the discharge cell in which the sustain discharge has occurred, the wall voltage between scan electrode SC1 on scan electrode SCn and sustain electrode SU1 on sustain electrode SUn is the difference between the voltage applied to scan electrode SCi and the discharge start voltage, That is, it is weakened to the level of (voltage Vers−discharge start voltage). As a result, in the discharge cell in which the sustain discharge has occurred, part or all of the wall voltage on scan electrode SCi and sustain electrode SUi is erased while leaving the positive wall charge on data electrode Dk. That is, the discharge generated by the erasing ramp voltage L3 serves as an “erasing discharge” for erasing unnecessary wall charges accumulated in the discharge cell in which the sustain discharge has occurred (hereinafter, the discharge generated by the erasing ramp voltage L3 is “ This is called “erase discharge”).

  Thereafter, scan electrode SC1 to scan electrode SCn are returned to 0 (V), and the sustain operation in the sustain period is completed.

  In the initialization period of the second SF, a drive voltage waveform in which the first half of the initialization period of the first SF is omitted is applied to each electrode. That is, voltage Ve1 is applied to sustain electrode SU1 through sustain electrode SUn, and 0 (V) is applied to data electrode D1 through data electrode Dm. Scan electrode SC1 to scan electrode SCn have a voltage that is less than the discharge start voltage (for example, The down-ramp voltage L4 that gradually decreases (for example, with a gradient of about −2.5 V / μsec) from 0 (V) toward the negative voltage Vi4 that exceeds the discharge start voltage is applied.

  As a result, a weak initializing discharge is generated in the discharge cell that has caused the sustain discharge in the sustain period of the immediately preceding subfield (first SF in FIG. 3), and the wall voltage on the scan electrode SCi and the sustain electrode SUi is weakened. The wall voltage above the data electrode Dk (k = 1 to m) is also adjusted to a value suitable for the write operation. On the other hand, initializing discharge does not occur in the discharge cells that did not cause sustain discharge in the sustain period of the immediately preceding subfield. As described above, the initializing operation in the second SF is a selective initializing operation in which the initializing discharge is performed on the discharge cells in which the sustain operation has been performed in the sustain period of the immediately preceding subfield.

  In the address period of the second SF, the same drive waveform as that in the address period of the first SF is applied to scan electrode SC1 through scan electrode SCn, sustain electrode SU1 through sustain electrode SUn, and data electrode D1 through data electrode Dm. In the sustain period of the second SF, similarly to the sustain period of the first SF, a predetermined number of sustain pulses are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn.

  In the subfields after the third SF, scan electrodes SC1 to SCn, sustain electrodes SU1 to SUn, and data electrodes D1 to Dm are different from each other except that the number of sustain pulses generated in the sustain period is different. A drive waveform similar to 2SF is applied.

  The above is the outline of the driving voltage waveform applied to each electrode of the panel 10.

  Next, the configuration of the plasma display device in the present embodiment will be described. FIG. 4 is a circuit block diagram of plasma display device 1 according to the first exemplary embodiment of the present invention. The plasma display apparatus 1 includes a panel 10, an image signal processing circuit 41, a data electrode drive circuit 42, a scan electrode drive circuit 43, a sustain electrode drive circuit 44, a timing generation circuit 45, and a power supply circuit that supplies necessary power to each circuit block. (Not shown).

  The image signal processing circuit 41 converts the input image signal sig into image data indicating light emission / non-light emission for each subfield in the discharge cell.

  For example, when the input image signal sig includes a luminance signal (Y signal) and a saturation signal (C signal, RY signal and BY signal, or u signal and v signal), the luminance signal and Based on the saturation signal, a luminance gradation value and a saturation gradation value are set for each pixel. Then, R, G, and B gradation values (gradation values expressed in one field) are assigned to each discharge cell from the luminance and saturation gradation values set for each pixel.

  When the input image signal sig includes an R signal, a G signal, and a B signal, each gradation value of R, G, and B is assigned to each discharge cell based on the R signal, the G signal, and the B signal.

  Then, the R, G, and B gradation values assigned to each discharge cell are converted into image data indicating light emission / non-light emission for each subfield.

  In the present embodiment, the image signal processing circuit 41 is referred to as an “afterimage frequency” that is a measure of occurrence of an afterimage phenomenon based on the luminance gradation value set for each pixel in accordance with the image signal sig. A numerical value is calculated for each pixel. Based on the calculated afterimage strength level for each pixel, the luminance gradation value of each pixel is changed. Details of this will be described later.

  The image signal processing circuit 41 calculates the R, G, and B tone values to be assigned to the discharge cells based on the brightness tone values after the change.

  When the image signal sig includes an R signal, a G signal, and a B signal, the luminance gradation value of each pixel is temporarily calculated based on the R signal, the G signal, and the B signal, and the luminance gradation value is obtained. The afterimage strength level is calculated based on the above. Then, the brightness gradation value of each pixel is changed based on the calculated afterimage strength level for each pixel, and each of the R, G, and B levels assigned to each discharge cell is changed based on the brightness gradation value after the change. The key value is calculated.

  The timing generation circuit 45 generates various timing signals for controlling the operation of each circuit block based on the horizontal synchronization signal H and the vertical synchronization signal V, and each circuit block (image signal processing circuit 41, data electrode drive circuit 42, Scan electrode drive circuit 43 and sustain electrode drive circuit 44).

  The data electrode drive circuit 42 converts the data for each subfield constituting the image data into signals corresponding to the data electrodes D1 to Dm, and each data electrode based on the timing signal supplied from the timing generation circuit 45. D1 to the data electrode Dm are driven.

  Scan electrode driving circuit 43 generates an initialization waveform generating circuit for generating an initialization waveform to be applied to scan electrode SC1 to scan electrode SCn in the initialization period, and generates a sustain pulse to be applied to scan electrode SC1 to scan electrode SCn in the sustain period. And a scan pulse generating circuit that includes a plurality of scan electrode driving ICs (hereinafter abbreviated as “scan ICs”) and generates scan pulses to be applied to scan electrode SC1 through scan electrode SCn in the address period. Then, each of the scan electrodes SC1 to SCn is driven based on the timing signal supplied from the timing generation circuit 45.

  Sustain electrode drive circuit 44 includes a sustain pulse generation circuit and a circuit (not shown) that generates voltage Ve1 and voltage Ve2. Sustain electrode drive circuit 44 uses sustain signal SU1 through sustain electrode SUn based on a timing signal supplied from timing generation circuit 45. To drive.

  In the panel 10 in which the xenon partial pressure of the discharge gas filled in the discharge cell is increased in order to increase the light emission efficiency in the panel, the still image is recognized as an afterimage when the still image is displayed for a long time. That is, a so-called afterimage phenomenon is likely to occur. This seems to be due to the following reasons.

  When still images are continuously displayed on the panel 10, the discharge cells (discharge cells in which the lighting state continues) with a relatively large number of lighting times per unit time (for example, one field) and the number of lighting times per unit time are obtained. Relatively few discharge cells (discharge cells in which the non-lighting state continues) are likely to occur. Between these discharge cells, a deviation occurs in the component concentration of the discharge gas (for example, a deviation in the concentration of impure gas containing water vapor, etc.), resulting in a difference in the discharge start voltage. In addition, a difference occurs in the temperature in the discharge cell between the discharge cell in which the lighting state continues and the discharge cell in which the non-lighting state continues, and this temperature difference also causes a difference in the discharge start voltage. Then, a difference in the discharge start voltage causes a difference in the timing at which discharge occurs, thereby causing a difference in light emission intensity, resulting in luminance between discharge cells in which the lighting state continues and discharge cells in which the non-lighting state continues. There is a difference. This is considered to be the reason why the afterimage phenomenon occurs.

  Therefore, in the present embodiment, it is determined whether or not the image has a large number of still regions and a large number of regions where the luminance change between adjacent pixels is large, and the luminance gradation value is changed based on the result. Specifically, the image signal processing circuit 41 calculates “afterimage strength” that is a measure of occurrence of the afterimage phenomenon for each pixel, and changes the gradation value of the luminance of each pixel based on the calculated afterimage strength. And Next, the details will be described.

  First, detection of the afterimage strength level will be described. In the present embodiment, the display area of the panel 10 is divided into a plurality of areas, the afterimage strength level for each area is calculated, and the afterimage strength level for each pixel is calculated based on the calculated afterimage strength level for each area. An example of this area is shown in FIG.

  FIG. 5 schematically shows an example of a plurality of areas provided in the display area of panel 10 in accordance with the first exemplary embodiment of the present invention. In FIG. 5, each area is referred to as “block (x, y)” (x and y are natural numbers), and the area is also referred to as “block” in the following description. In FIG. 5, the lines shown in the display area of the panel 10 are supplementarily shown so that the areas can be easily distinguished, and the lines are not actually displayed on the panel 10.

  In the present embodiment, as shown in FIG. 5, the display area of the panel 10 is provided with a plurality of boundaries in the direction in which the display electrode pair 24 extends and a plurality of boundaries in the direction in which the data electrode 32 extends. Each area is set by dividing the number so that they are equal to each other.

  FIG. 5 shows an example in which the panel 10 is divided into N in the direction in which the display electrode pair 24 extends and divided into M in the direction in which the data electrode 32 extends (N and M are natural numbers) to set each region. . In this case, M × N areas from the block (1, 1) to the block (M, N) are set on the panel 10.

  For example, in a configuration in which the number of pixels of the panel 10 is 1920 × 1080 and the number of pixels in one region is set to 60 × 60, N is 32 and M is 18.

  In the present embodiment, the afterimage strength level is calculated for each of the M × N areas from the block (1, 1) to the block (M, N). Then, the afterimage strength level for each pixel is calculated based on the calculated afterimage strength level for each region.

  FIG. 6 is a circuit block diagram showing a configuration example of the image signal processing circuit 41 according to the first embodiment of the present invention. FIG. 6 shows only circuit blocks related to the calculation of afterimage strength and the change of the luminance gradation value based on the afterimage strength, and the other circuit blocks are omitted.

  The image signal processing circuit 41 includes a one-field delay circuit 70, a subtraction circuit 71, a comparison circuit 72, a one-pixel delay circuit 73, a subtraction circuit 74, a comparison circuit 75, a block timing generation circuit 76, and a counting circuit 77 (1, 1) to Counting circuit 77 (M, N), counting circuit 78 (1, 1) to counting circuit 78 (M, N), afterimage strength calculating circuit 79 (1, 1) to afterimage strength calculating circuit 79 (M, N), afterimage A frequency interpolation circuit 80, a delay circuit 81, and a correction circuit 82 are included.

  The one-field delay circuit 70 delays the luminance gradation value set for each pixel by a time corresponding to one field.

  The subtraction circuit 71 subtracts the luminance gradation value set for each pixel from the luminance gradation value of each pixel one field before output from the one-field delay circuit 70, and the absolute result of the subtraction is obtained. The value is output as “brightness difference between fields”. That is, the subtraction circuit 71 calculates the difference in luminance gradation value between the current field and the field immediately before the current field for each pixel as the inter-field luminance difference.

  The comparison circuit 72 compares the inter-field luminance difference output from the subtraction circuit 71 with a preset luminance comparison value, and outputs “1” when the inter-field luminance difference is smaller than the luminance comparison value. When the luminance difference between fields is equal to or greater than the luminance comparison value, “0” is output.

  The counting circuit 77 counts the number of “1” s output from the comparison circuit 72 in each region, and outputs the count result as a “first count value” in each region. For example, the counting circuit 77 (1, 1) counts the number of “1” output from the comparison circuit 72 in the block (1, 1), and the counting result is the first total in the block (1, 1). Output as a numerical value. The counting circuit 77 (M, N) counts the number of “1” output from the comparison circuit 72 in the block (M, N), and uses the counting result as the first count value in the block (M, N). Output.

  That is, the counting circuit 77 counts the number of pixels in which the inter-field luminance difference is smaller than the luminance comparison value for each area, and outputs the counting result as the first count value in each area.

  The one-pixel delay circuit 73 delays the luminance gradation value set for each pixel by a time corresponding to one pixel.

  The subtraction circuit 74 subtracts the luminance gradation value set for each pixel from the luminance gradation value of the previous pixel output from the one-pixel delay circuit 73, and calculates the absolute value of the subtraction result as “ It is output as “luminance difference between adjacent pixels”.

  The comparison circuit 75 compares the luminance difference between adjacent pixels output from the subtraction circuit 74 with a preset edge comparison value, and outputs “1” when the luminance difference between adjacent pixels is larger than the edge comparison value. When the luminance difference between adjacent pixels is equal to or smaller than the edge comparison value, “0” is output.

  The counting circuit 78 counts the number of “1” s output from the comparison circuit 75 in each region, and outputs the count result as a “second count value” in each region. For example, the counting circuit 78 (1, 1) counts the number of “1” output from the comparison circuit 75 in the block (1, 1), and the counting result is the second total in the block (1, 1). Output as a numerical value. The counting circuit 78 (M, N) counts the number of “1” output from the comparison circuit 75 in the block (M, N), and uses the counting result as the second count value in the block (M, N). Output.

  That is, the counting circuit 78 counts, for each region, the number of “edges” at which the luminance gradation value difference between adjacent pixels is equal to or greater than the edge comparison value, and the count result is a second total in each region. Output as a numerical value.

  The block timing generation circuit 76 generates a block timing signal for identifying each region based on the horizontal synchronization signal H and the vertical synchronization signal V supplied from the timing generation circuit 45, and sends the block timing signal to each counting circuit 77 and counting circuit 78. Supply. For example, the counting circuit 77 (1, 1) and the counting circuit 78 (1, 1) are supplied with a block (1, 1) timing signal that becomes “Hi” only during the period of the block (1, 1), and the counting circuit 77 (M, N) and the counting circuit 78 (N, N) are supplied with a block (M, N) timing signal that becomes “Hi” only during the period of the block (M, N).

  The afterimage strength level calculation circuit 79 calculates the afterimage strength level for each region based on the first count value and the second count value. For example, the afterimage strength level calculation circuit 79 (1, 1) calculates the afterimage strength level of the block (1, 1) based on the first count value and the second count value in the block (1, 1), and calculates the afterimage strength level. The circuit 79 (M, N) calculates the afterimage strength level of the block (M, N) based on the first count value and the second count value in the block (M, N). Details of this will be described later.

  In this embodiment, the afterimage strength level for each region is set as the afterimage strength level of a pixel located in the center of the region in each region (hereinafter referred to as “center pixel”). For the pixels other than the “center pixel”, the afterimage strength level for each pixel is calculated based on the afterimage strength level for each region.

  The afterimage strength level interpolation circuit 80 calculates the afterimage strength level for each pixel for pixels other than the “center pixel”. Specifically, the afterimage strength level is calculated for each pixel based on the distance between the pixel whose afterimage strength level is to be calculated and a plurality of surrounding central pixels and the afterimage strength level of the center pixel. Details of this will be described later.

  The delay circuit 81 delays the luminance gradation value set for each pixel by an appropriate time (for example, the time required to calculate the afterimage strength level for each pixel).

  Then, the correction circuit 82 changes the luminance gradation value of each pixel appropriately delayed by the delay circuit 81 based on the afterimage strength for each pixel calculated by the afterimage strength interpolation circuit 80.

  Note that specific numerical values of the luminance comparison value and the edge comparison value described above include, for example, numerical values corresponding to 50% of the number of pixels in one region. For example, when one area is 60 × 60 pixels, the number of pixels in one area is 3600, and the numerical value corresponding to 50% is 1800. However, the present invention is not limited to these numerical values, and it is desirable that each numerical value is appropriately set according to the characteristics of the panel 10, the specifications of the plasma display device 1, and the like.

  FIG. 7 is a circuit block diagram showing a configuration example of the afterimage strength level calculating circuit 79 according to Embodiment 1 of the present invention. In FIG. 7, an afterimage strength level calculating circuit 79 (1,1) for calculating the afterimage strength level of the block (1,1) is shown as an example, but other blocks (1,2) to ( The afterimage strength level calculation circuit 79 (1,2) to the afterimage strength level calculation circuit 79 (M, N) for calculating the afterimage strength level in (M, N) have the same configuration as in FIG.

  The afterimage strength level calculation circuit 79 includes a comparison circuit 63, a comparison circuit 64, a comparison circuit 65, a selector 66, a selector 67, a selector 68, a cumulative addition circuit 89, a subtraction circuit 90, and a limiting circuit 91.

  The comparison circuit 63 outputs the first count value output from the count circuit 77 (in the example shown in FIG. 7, the first count value of the block (1, 1) output from the count circuit 77 (1, 1)). Is compared with a first threshold value set in advance, and when the first count value is equal to or greater than the first threshold value, “1” is output, and the first count value is the first threshold value. When it is less than the value, “0” is output.

  The comparison circuit 64 includes a first count value (the first count value of the block (1, 1) in the example shown in FIG. 7) and a second threshold value that is smaller than the first threshold value. And “1” is output when the first count value is equal to or greater than the second threshold value, and “0” is output when the first count value is less than the second threshold value.

  The comparison circuit 65 outputs the second count value output from the count circuit 78 (in the example shown in FIG. 7, the second count value of the block (1, 1) output from the count circuit 78 (1, 1)). Is compared with a preset third threshold value, and when the second count value is equal to or greater than the third threshold value, “1” is output and the second count value is the third threshold value. When it is less than the value, “0” is output.

  The selector 66 is, for example, “+1” when the output of the comparison circuit 63 is “1”, for example “+1”, and is, for example, “0” as the second setting value when the output of the comparison circuit 63 is “0”. Is output to the selector 67 at the subsequent stage.

  The selector 67 sets the output of the selector 66 when the output of the comparison circuit 64 is “1”, the third set value when the output of the comparison circuit 64 is “0”, for example, “−4”, and the selector 68 at the subsequent stage. Output to.

  The selector 68 sets the output of the selector 67 as the fourth set value when the output of the comparison circuit 65 is “1” and the fourth set value when the output of the comparison circuit 65 is “0”, for example, “−4”. Output to 89.

  The cumulative addition circuit 89 cumulatively adds the numerical values output from the selector 68 and outputs the result.

  For example, if the cumulative addition result of the cumulative addition circuit 89 in the block (1, 1) is “10” in a certain field, the numerical value output from the selector 68 is accumulated for that “10” in the subsequent field. to add.

  That is, the selector 66, the selector 67, the selector 68, and the cumulative adder circuit 89 are in an area where the first count value is not less than the first threshold value and the second count value is not less than the third threshold value. The first set value is cumulatively added to the afterimage strength level for each region. In addition, the first count value is less than the first threshold value and greater than or equal to the second threshold value that is smaller than the first threshold value, and the second count value is greater than or equal to the third threshold value. In the area, the second set value is cumulatively added to the afterimage strength level for each area. Further, in a region where the first count value is less than the second threshold value and the second count value is greater than or equal to the third threshold value, the third set value is cumulatively added to the afterimage strength level for each region. To do. Then, in a region where the second count value is less than the third threshold value, the fourth set value is cumulatively added to the afterimage strength level for each region. Thus, the afterimage strength for each region is updated for each field.

  In the present embodiment, the region where the first count value is equal to or greater than the first threshold value and the second count value is equal to or greater than the third threshold value is likely to cause an afterimage phenomenon. As the increased area, the first set value is set to a positive number (for example, “+1”), and the afterimage strength level is increased. Further, the first count value is less than the second threshold value, the second count value is greater than or equal to the third threshold value, and the second count value is less than the third threshold value. In the region where the afterimage phenomenon is less likely to occur, the third set value and the fourth set value are set to negative numbers (eg, “−4”) to reduce the afterimage strength. ing. Further, an afterimage phenomenon is likely to occur in a region where the first count value is less than the first threshold value and greater than or equal to the second threshold value, and the second count value is greater than or equal to the third threshold value. As a region in which the image quality is maintained, the second set value is set to “0” so that the afterimage strength is maintained.

  The subtraction circuit 90 subtracts a predetermined constant (for example, “50”) from the cumulative addition result output from the cumulative addition circuit 89, that is, the afterimage strength updated by cumulative addition of the numerical value output from the selector 68. To do. This is because even if an image that is prone to an afterimage phenomenon is displayed, an afterimage does not occur immediately, and an image that is likely to cause an afterimage phenomenon is displayed continuously to some extent, and an afterimage is likely to occur. That's what we considered.

  The limiting circuit 91 updates the cumulative addition result output from the subtracting circuit 90, that is, the numerical value output from the selector 68 by cumulative addition, and further updates the afterimage strength obtained by subtracting a predetermined constant to a predetermined upper limit value ( For example, “100”) or less. This is to prevent overcorrection of the luminance gradation value in the correction circuit 82.

  The specific numerical values described above are merely examples, and the present invention is not limited to these numerical values. It is desirable to set each numerical value appropriately according to the characteristics of the panel 10 and the specifications of the plasma display device 1.

  In this way, the afterimage strength level of each region is output from the afterimage strength level calculation circuit 79. In the example shown in FIG. 7, the afterimage strength level of the block (1,1) is output from the afterimage strength level calculation circuit 79 (1,1).

  FIG. 8 is a diagram schematically showing an operation performed in the afterimage strength interpolation circuit 80 according to the first embodiment of the present invention. In FIG. 8, a part of the panel 10 is shown in an enlarged manner, a broken line indicates the boundary of each region, and a white circle indicates a central pixel located at the center in each region. Moreover, in FIG. 8, the line which connects center pixels is shown with a dashed-dotted line. In FIG. 8, the pixel A12 and the pixel A34 are indicated by black circles as pixels for which the afterimage strength level is to be calculated. Note that the broken lines and the like shown in FIG. 8 are supplementarily shown so as to easily distinguish each region and the like, and these lines are not actually displayed on the panel 10.

  In the present embodiment, the afterimage strength for each region is the afterimage strength of the central pixel located at the center of each region. For example, the afterimage strength level of the block (1, 1) calculated by the afterimage strength level calculation circuit 79 (1, 1) is the afterimage strength level of the central pixel of the block (1, 1). The afterimage strength for each pixel excluding “center pixel” is calculated based on the afterimage strength for each region, that is, the afterimage strength of the center pixel.

  Specifically, the afterimage strength for each region is calculated in the following procedure.

  First, the distance between a pixel for which the afterimage strength level is to be calculated and a plurality of central pixels around it is calculated. For example, assuming that the pixel for which the afterimage strength level is to be calculated is the pixel A34, the distance between the four central pixels around the pixel A34 and the pixel A34 is calculated.

  In FIG. 8, the central pixel around the pixel A34 is the pixel A1, pixel A2, pixel A3, and pixel A4, the distance between the pixel A34 and the pixel A1 is L1, the distance between the pixel A34 and the pixel A2 is L2, and the pixel A34 The distance between the pixel A3 and the pixel A3 is denoted by L3, and the distance between the pixel A34 and the pixel A4 is denoted by L4.

  Then, the afterimage strength level of each central pixel is added at a ratio corresponding to the distance between the pixel whose afterimage strength level is to be calculated and a plurality of surrounding central pixels.

  For example, when the afterimage strength of the pixel A34 is a34, the afterimage strength of the pixel A1 is a1, the afterimage strength of the pixel A2 is a2, the afterimage strength of the pixel A3 is a3, and the afterimage strength of the pixel A4 is a4, the afterimage strength of the pixel A34 a34 is represented by the following equation.

a34 = (a1 × (L2 + L3 + L4) + a2 × (L1 + L3 + L4) + a3 × (L1 + L2 + L4) + a4 × (L1 + L2 + L3) / (3 × (L1 + L2 + L3 + L4))
For pixels located on the line connecting the central pixels, the afterimage strength is calculated based on the two central pixels sandwiching the pixels. For example, if the pixel A12 is a pixel on which a pixel A12 is on a line connecting the pixel A1 and the pixel A2, the afterimage strength of the pixel A12 is calculated based on the afterimage strength of the pixel A1 and the pixel A2. .

  For example, if the distance between the pixel A12 and the pixel A1 is L5, the distance between the pixel A12 and the pixel A2 is L6, and the afterimage strength level of the pixel A12 is a12, the afterimage strength level a12 of the pixel A12 is expressed by the following equation.

a12 = (a1 × L6 + a2 × L5) / (L5 + L6)
These calculations are performed in the afterimage strength interpolation circuit 80, and the afterimage strength for each pixel is calculated.

  FIG. 9 is a circuit block diagram showing a configuration example of the correction circuit 82 according to the first embodiment of the present invention.

  The correction circuit 82 includes a multiplication coefficient calculation circuit 92 and a multiplication circuit 93, and changes the luminance gradation value according to the magnitude of the afterimage strength level.

  The multiplication coefficient calculation circuit 92 calculates a multiplication coefficient for multiplying the luminance gradation value from the afterimage strength level for each pixel. Specifically, the afterimage strength for each pixel is subtracted from a predetermined reference value (for example, “255”), and the result obtained by dividing the subtraction result by the reference value (for example, “255”) is the luminance gradation value. The multiplication factor for multiplying by.

  The multiplication circuit 93 multiplies the luminance gradation value by the multiplication coefficient calculated by the multiplication coefficient calculation circuit 92.

  The operation of the correction circuit 82 will be described taking the pixel A34 shown in FIG. 8 as an example. For example, the afterimage strength of the pixel A34 is a34, the luminance gradation value of the pixel A34 is Y34, and the predetermined reference value is “255”. In this case, the luminance gradation value Y34 ′ after correction of the pixel A34 is expressed by the following equation.

Y34 ′ = ((255−a34) / 255) × Y34
As a result, the luminance gradation value can be corrected according to the magnitude of the afterimage strength level in a pixel that is considered to be prone to the afterimage phenomenon. Therefore, in a pixel having a high afterimage strength, it is possible to reduce the luminance difference from the adjacent pixels and reduce the occurrence of afterimage phenomenon.

  The predetermined reference value described above is a numerical value set based on the maximum gradation value “255” of the luminance, but the predetermined reference value is not limited to this numerical value in the present invention. The predetermined reference value is desirably set appropriately according to the characteristics of the panel 10, the specifications of the plasma display device 1, and the like.

  As described above, according to the present embodiment, the “afterimage strength”, which is a measure of occurrence of the afterimage phenomenon, is calculated for each pixel based on the gradation value of the luminance, and the luminance of each pixel is calculated based on the calculated afterimage strength. The gradation value is changed. As a result, the tone value of the luminance is corrected in accordance with the magnitude of the afterimage strength level in an image in which afterimage phenomenon is likely to occur, that is, an image in which the number of edges is large and a still region is continuously displayed. It is possible to reduce the luminance difference between adjacent pixels and reduce the occurrence of afterimage phenomenon.

(Embodiment 2)
In the first embodiment, the configuration in which the luminance gradation value is changed in accordance with the afterimage strength level for each pixel has been described. For example, a pixel having a high luminance gradation value (a pixel having a predetermined high luminance threshold value or more). ), The luminance gradation value may be changed in accordance with the afterimage strength level.

  FIG. 10 is a circuit block diagram showing a configuration example of the correction circuit 83 according to the second embodiment of the present invention. Since the procedure until calculating the afterimage strength level for each pixel in this embodiment is the same as that in the first embodiment, only the correction circuit 83 having a configuration different from that in the first embodiment will be described in this embodiment. .

  The correction circuit 83 includes a multiplication coefficient calculation circuit 94, a comparison circuit 95, and a multiplication circuit 93. The correction circuit 83 changes the luminance gradation value according to the magnitude of the afterimage strength level only for a pixel having a high luminance gradation value. .

  The comparison circuit 95 calculates the luminance gradation value of each pixel and a preset high luminance threshold value (for example, a value that is approximately 60% of the maximum gradation value. When the maximum gradation value is “255”) , For example, “150”), and the result is output to the multiplication count calculation circuit 94.

  The multiplication coefficient calculation circuit 94 calculates a multiplication coefficient for multiplying the luminance gradation value based on the afterimage strength level for each pixel and the comparison result in the comparison circuit 95. Specifically, when the luminance gradation value is equal to or lower than the high luminance threshold value, “1” is output so that the luminance gradation value is not corrected. Further, when the luminance gradation value is larger than the high luminance threshold value, the afterimage strength level for each pixel is equivalent to the luminance gradation value exceeding the high luminance threshold value as in the first embodiment. Based on this, a multiplication coefficient for multiplying the gradation value of the luminance is calculated.

  The multiplication circuit 93 multiplies the luminance gradation value by the multiplication factor calculated by the multiplication factor calculation circuit 94, similarly to the multiplication circuit 93 shown in the first embodiment.

  The operation of the correction circuit 83 will be described by taking the pixel A34 shown in FIG. 8 as an example. For example, the afterimage strength level of the pixel A34 is a34, the luminance gradation value of the pixel A34 is Y34, and the predetermined reference value is “255”. When the high luminance threshold is “150”, the luminance gradation value Y34 ″ after correction of the pixel A34 is expressed by the following equation. However, it is assumed that the gradation value Y34 is larger than the high luminance threshold value (when the gradation value Y34 is equal to or less than the high luminance threshold value, the corrected luminance gradation value Y34 '' Equal to value Y34).

Y34 ″ = ((255−a34) / 255) × (Y34−150) +150
Thereby, for example, in a pixel having a high luminance gradation value and a large luminance difference from adjacent pixels, the luminance gradation value can be corrected according to the magnitude of the afterimage strength level.

  The above-described high luminance threshold is a numerical value set based on the maximum gradation value “255” of luminance, but the present invention is not limited to this numerical value as a predetermined reference value. It is desirable to set the high brightness threshold appropriately in accordance with the characteristics of the panel 10 and the specifications of the plasma display device 1.

  As described above, according to the present embodiment, the afterimage strength that is a measure of occurrence of the afterimage phenomenon is calculated for each pixel based on the luminance gradation value, and the calculated afterimage strength and the magnitude of the luminance gradation value are calculated. Based on the above, the luminance gradation value of each pixel is changed. As a result, in an image in which afterimage phenomenon is likely to occur, that is, an image in which the number of edges is large and a still area is continuously displayed, the afterimage strength level and the luminance gradation value Thus, the luminance gradation value is corrected to reduce the luminance difference between adjacent pixels, and the occurrence of afterimage phenomenon can be reduced.

(Embodiment 3)
An image having a high average luminance level (hereinafter referred to as “APL”) of the display image has a high luminance as a whole, and accordingly, a change in luminance between adjacent pixels is small, and the number of edges is also large. It is thought that it will decrease. That is, it is considered that the afterimage phenomenon is less likely to occur compared to an image with a low APL. Therefore, the APL of the image signal may be detected, and the afterimage strength may be changed according to the APL so that when the APL is large, the afterimage strength is smaller than when the APL is small.

  FIG. 11 is a circuit block diagram showing a configuration example of the correction circuit 84 according to the third embodiment of the present invention. Note that the procedure until the afterimage strength level for each pixel is calculated in the present embodiment is the same as that in the first embodiment, and therefore, only the correction circuit 84 having a configuration different from that in the first embodiment will be described in the present embodiment. .

  The correction circuit 84 includes an APL detection circuit 97, an afterimage strength level correction circuit 96, a multiplication coefficient calculation circuit 92, and a multiplication circuit 93. When the APL is large, the magnitude of the APL is smaller so that the afterimage strength is smaller than when the APL is small. The afterimage strength level is changed according to the change, and the luminance gradation value is changed according to the changed afterimage strength level.

  The APL detection circuit 97 detects APL by using a generally known technique such as adding luminance gradation values of all pixels.

  The afterimage strength level correction circuit 96 changes the afterimage strength level for each pixel so that when the APL is large, the afterimage strength level is smaller than when the APL is small, according to the APL detected by the APL detection circuit 97.

  When the APL value detected by the APL detection circuit 97 is apl, the afterimage strength level correction circuit 96 is, for example, 100% − (apl−40%) (however, when apl−40% becomes 0 or less, apl The afterimage strength level is changed by multiplying the afterimage strength level by a numerical value obtained by (-40% = 0).

  The multiplication count calculation circuit 92 performs the same operation as the multiplication count calculation circuit 92 shown in the first embodiment, and multiplies the luminance gradation value based on the afterimage strength level changed in the afterimage strength level correction circuit 96. Calculate the multiplication factor.

  Then, the multiplication circuit 93 multiplies the luminance gradation value by the multiplication coefficient calculated by the multiplication coefficient calculation circuit 92, as in the multiplication circuit 93 shown in the first embodiment.

  Thereby, the afterimage strength level can be changed according to the APL, and the luminance gradation value can be corrected according to the magnitude of the afterimage strength level after the change.

  The numerical value “40%” subtracted from the APL described above is merely an example. It is desirable to set this numerical value appropriately according to the characteristics of the panel 10 and the specifications of the plasma display device 1.

  As described above, according to the present embodiment, the afterimage strength is changed based on the detected APL, and the luminance gradation value of each pixel is changed based on the afterimage strength after the change. Change the configuration. As a result, in an image with a high APL where it is considered that an afterimage phenomenon is relatively difficult to occur, the magnitude of the afterimage strength can be reduced as compared with an image with a low APL. It is possible to reduce the occurrence of an afterimage phenomenon while preventing a decrease in luminance.

(Embodiment 4)
The number of sustain pulses generated varies depending on the luminance magnification. As the luminance magnification decreases, the number of sustain pulses decreases, the luminance of the display image decreases, and the contrast ratio also decreases. That is, it is considered that the afterimage phenomenon is less likely to occur when the luminance magnification is small than when the luminance magnification is large. In view of this, the afterimage strength may be changed according to the luminance magnification so that the afterimage strength is smaller when the luminance magnification is small than when the luminance magnification is large.

  FIG. 12 is a circuit block diagram showing a configuration example of the correction circuit 87 according to Embodiment 4 of the present invention. Since the procedure until calculating the afterimage strength level for each pixel in this embodiment is the same as that in the first embodiment, only the correction circuit 87 having a configuration different from that in the first embodiment will be described in this embodiment. .

  The correction circuit 87 includes an afterimage strength correction circuit 101, a multiplication coefficient calculation circuit 92, and a multiplication circuit 93.

  The afterimage strength level correction circuit 101 changes the afterimage strength level for each pixel in accordance with the magnitude of the brightness magnification so that the afterimage strength level becomes smaller when the brightness magnification is small than when the brightness magnification is large.

  The afterimage strength correction circuit 101 is, for example, 0.5 when the luminance magnification is 1, 0.7 when the luminance magnification is 2, 0.9 when the luminance magnification is 3, and 4 times the luminance magnification. In this case, the afterimage strength level is changed by multiplying the afterimage strength level by a value that increases as the luminance magnification increases, such as 1.0.

  The multiplication count calculation circuit 92 performs the same operation as the multiplication count calculation circuit 92 shown in the first embodiment, and multiplies the luminance gradation value based on the afterimage strength level changed in the afterimage strength level correction circuit 101. Calculate the multiplication factor.

  Then, the multiplication circuit 93 multiplies the luminance gradation value by the multiplication coefficient calculated by the multiplication coefficient calculation circuit 92, as in the multiplication circuit 93 shown in the first embodiment.

  Thereby, the afterimage strength level can be changed according to the luminance magnification, and the luminance gradation value can be corrected according to the magnitude of the afterimage strength level after the change.

  Note that the numerical values that change in accordance with the above-described luminance magnification are merely examples. It is desirable to set this numerical value appropriately according to the characteristics of the panel 10 and the specifications of the plasma display device 1.

  As described above, according to the present embodiment, the afterimage strength is changed based on the luminance magnification, and the luminance gradation value of each pixel is changed based on the afterimage strength after the change. The configuration is as follows. As a result, when it is considered that the afterimage phenomenon is relatively unlikely to occur with a small luminance magnification, the afterimage strength level can be made smaller than when the luminance magnification is large. Therefore, for example, it is possible to reduce the occurrence of an afterimage phenomenon while preventing a decrease in luminance of an image displayed when the luminance magnification is small.

(Embodiment 5)
In the fourth embodiment, even if the images have the same pattern, the afterimage strength level is changed according to the size of the brightness magnification so that the afterimage strength level is smaller when the brightness magnification is small than when the brightness magnification is large. Explained. As a specific example of the configuration, an afterimage strength correction circuit 101 that multiplies the afterimage strength of each pixel calculated by the afterimage strength interpolation circuit 80 by a numerical value that changes in accordance with the magnitude of the luminance magnification. The structure which provides is shown. However, the present invention is not limited to this configuration, and the same effect can be obtained using other configurations.

  FIG. 13 is a circuit block diagram showing a configuration example of the afterimage strength level calculating circuit 110 according to the fifth embodiment of the present invention. In FIG. 13, an afterimage strength level calculating circuit 110 (1,1) for calculating the afterimage strength level of the block (1,1) is shown as an example, but other blocks (1,1) to ( The afterimage strength level calculating circuit 110 (1,2) to the afterimage strength level calculating circuit 110 (M, N) for calculating the afterimage strength level at M, N) have the same configuration as in FIG.

  In this embodiment, the afterimage strength level calculating circuit 110 shown in FIG. 13 is different from the afterimage strength level calculating circuit 79 shown in FIG. 7 in that the first set value can be changed according to the luminance magnification. This is the point. For this purpose, the afterimage strength level calculation circuit 110 has a configuration in which a selector 88 and a comparison circuit 69 are further provided in addition to the configuration of the afterimage strength level calculation circuit 79 shown in FIG. However, other circuit configurations and operations of the respective circuit blocks are the same as those shown in the afterimage strength level calculating circuit 79. Therefore, in the present embodiment, circuit blocks that perform the same operations as the afterimage strength level calculating circuit 79 are not illustrated. The same reference numerals as those shown in FIG.

  The comparison circuit 69 compares the luminance magnification with a preset fourth threshold value, outputs “1” when the luminance magnification is equal to or greater than the fourth threshold value, and the luminance magnification is the fourth threshold value. When it is less than the threshold value, “0” is output.

  The selector 88 outputs a positive numerical value, for example, “+1” when the output of the comparison circuit 69 is “1”, and outputs “0”, for example, when the output of the comparison circuit 63 is “0”.

  The numerical value output from the selector 88 is input to the subsequent selector 66 as the first set value. For example, if the fourth threshold value is “3”, “+1” is input to the selector 66 as the first setting value when the luminance magnification is 3 times or more, and the first setting value is input when the luminance magnification is less than 3 times. “0” is input to the selector 66 as a set value.

  Thus, in the afterimage strength level calculation circuit 110 shown in the present embodiment, the size of the first set value can be changed according to the size of the luminance magnification. Therefore, even if the images have the same pattern, it is possible to change the calculated afterimage strength level when the luminance magnification is large and the emission luminance is relatively high, and when the luminance magnification is small and the emission luminance is relatively low. .

  Thus, the afterimage strength level calculating circuit 110 operates in the same manner as the afterimage strength level calculating circuit 79 shown in FIG. 7 when the luminance magnification is equal to or higher than the fourth threshold value, and when the luminance magnification is lower than the fourth threshold value. It is possible to operate so that the afterimage strength does not increase regardless of the design of the display image.

  It should be noted that the above-described numerical value selected by the selector 88 is merely an example. It is desirable to set each numerical value appropriately according to the characteristics of the panel 10 and the specifications of the plasma display device 1. Further, the selector 88 is not limited to a selection circuit having two inputs and one output. For example, the comparison circuit 69 may compare two or more threshold values with the luminance magnification, and the selector 88 may be a selection circuit that can select three inputs, one output, or more.

  As described above, the present embodiment is configured to change the first set value based on the comparison result between the luminance magnification and the fourth threshold value. As a result, when the luminance magnification is equal to or higher than the fourth threshold value, that is, when it is considered that the emission luminance is relatively high and the afterimage phenomenon is relatively likely to occur, the afterimage strength is calculated by the same operation as the afterimage strength calculating circuit 79. When the calculated luminance magnification is smaller than the fourth threshold value, that is, when it is considered that the after-image phenomenon is relatively unlikely to occur, the afterimage strength does not increase regardless of the design of the display image. Can be. Therefore, for example, it is possible to reduce the occurrence of an afterimage phenomenon while preventing a decrease in luminance of an image displayed when the luminance magnification is small.

(Embodiment 6)
For example, by smoothing the luminance signal, a change in luminance between adjacent pixels can be reduced, and the occurrence of an afterimage phenomenon can be further reduced. Therefore, in the present embodiment, a configuration will be described in which smoothing according to the afterimage strength is applied to the corrected luminance signal.

  FIG. 14 is a circuit block diagram showing a configuration example of the correction circuit 85 according to the sixth embodiment of the present invention. Since the procedure until calculating the afterimage strength level for each pixel in this embodiment is the same as that in the first embodiment, only the correction circuit 85 having a configuration different from that in the first embodiment will be described in this embodiment. .

  The correction circuit 85 includes a multiplication coefficient calculation circuit 92, a multiplication circuit 93, and a smoothing circuit 98, and smoothes the corrected luminance signal according to the afterimage strength level.

  The multiplication coefficient calculation circuit 92 performs the same operation as the multiplication coefficient calculation circuit 92 shown in the first embodiment, and calculates a multiplication coefficient for multiplying the luminance gradation value based on the afterimage strength level for each pixel.

  Then, the multiplication circuit 93 multiplies the luminance gradation value by the multiplication coefficient calculated by the multiplication coefficient calculation circuit 92, as in the multiplication circuit 93 shown in the first embodiment.

  The smoothing circuit 98 smoothes the luminance gradation value output from the multiplication circuit 93 according to the afterimage strength level. Examples of the smoothing means include a generally known median filter. When the afterimage strength is small, the smoothing is reduced, and as the afterimage strength increases, the smoothing is increased. For example, when the afterimage strength is small, the median filter area is 1 pixel × 1 pixel, and as the afterimage strength increases, the median filter area is 2 pixels × 2 pixels, 3 pixels × 3 pixels, 4 pixels × 4 pixels, It expands to 5 pixels x 5 pixels.

  As a result, smoothing with a weight corresponding to the afterimage strength level is applied to the luminance signal, the change in luminance between adjacent pixels can be reduced by the smoothing, and the occurrence of the afterimage phenomenon can be further reduced.

  The smoothing means in the smoothing circuit 98 is not limited to the median filter, and other generally known two-dimensional filters for images, such as a moving average filter, a Gaussian filter, an average value filter, etc. Any filter may be used as long as the weight of smoothing can be changed according to the magnitude of the afterimage strength. However, it is desirable to set the smoothing means in the smoothing circuit 98 to an optimum one according to the characteristics of the panel 10, the specifications of the plasma display device 1, the quality of the display image after smoothing, and the like.

  As described above, the present embodiment is configured to change the luminance gradation value of each pixel based on the calculated afterimage strength level and to perform smoothing according to the afterimage strength level on the corrected luminance signal. And As a result, the luminance gradation value can be corrected according to the magnitude of the afterimage strength level, and the corrected luminance signal can be smoothed according to the magnitude of the afterimage strength level. Therefore, it is possible to further reduce the change in luminance between adjacent pixels and further reduce the occurrence of the afterimage phenomenon.

(Embodiment 7)
In the first to sixth embodiments, the configuration in which the luminance gradation value of each pixel is changed based on the calculated afterimage strength level has been described. However, the occurrence of the afterimage phenomenon can be reduced by changing the gradation value of the saturation based on the calculated afterimage strength level. Therefore, in the present embodiment, a configuration in which the saturation gradation value is changed based on the calculated afterimage strength level will be described.

  FIG. 15 is a circuit block diagram showing a configuration example of the correction circuit 86 according to the seventh embodiment of the present invention. Since the procedure until calculating the afterimage strength level for each pixel in the present embodiment is the same as that in the first embodiment, only the correction circuit 86 having a configuration different from that in the first embodiment will be described in this embodiment. .

  The correction circuit 86 includes a multiplication coefficient calculation circuit 99 and a multiplication circuit 100 in addition to the multiplication coefficient calculation circuit 92, the multiplication circuit 93, and the smoothing circuit 98 described in the fourth embodiment, and in addition to the luminance gradation value, Saturation gradation values (gradation values based on the C signal, RY signal and BY signal, or u signal and v signal, etc.) are also corrected according to the magnitude of the afterimage strength.

  Since the multiplication count calculation circuit 92, the multiplication circuit 93, and the smoothing circuit 98 perform the same operations as in the sixth embodiment, description thereof is omitted.

  The multiplication coefficient calculation circuit 99 calculates a multiplication coefficient for multiplying the gradation value of saturation from the afterimage strength level for each pixel. The multiplication coefficient calculation circuit 99 may operate in the same manner as the multiplication coefficient calculation circuit 92, but the numerical value calculated by the same operation as the multiplication coefficient calculation circuit 92 is further multiplied by a predetermined saturation constant. It may be a configuration.

  The multiplication circuit 100 multiplies the gradation value of saturation by the multiplication coefficient calculated by the multiplication coefficient calculation circuit 99.

  The operation of the correction circuit 86 will be described using the pixel A34 shown in FIG. 8 as an example. For example, the afterimage strength level of the pixel A34 is a34, the chroma gradation value of the pixel A34 is C34, and the predetermined reference value is “255”. “When the saturation constant is Ca, the saturation gradation value C34 ′ of the pixel A34 after correction is expressed by the following equation.

C34 ′ = ((255−a34) / 255) × Ca × C34
Thereby, the gradation value of saturation can be corrected according to the magnitude of the afterimage strength for each pixel. An image having a high saturation, that is, an image having a deep color, is likely to have a larger difference in gradation value of each RGB discharge cell constituting one pixel than an image having a low saturation and a light color. Therefore, by lowering the saturation according to the magnitude of the afterimage strength level, it is possible to reduce the difference between the gradation values of the RGB discharge cells and further reduce the occurrence of the afterimage phenomenon.

  The saturation constant Ca described above is desirably set to an optimum value according to the characteristics of the panel 10, the specifications of the plasma display device 1, the quality of the display image after correction, and the like.

  In the correction circuit 86 shown in the present embodiment, the luminance gradation value is corrected, the luminance gradation value is smoothed, and the saturation gradation value is corrected according to the magnitude of the afterimage strength level. For example, when the afterimage strength is small, only the luminance gradation value is smoothed, and when the afterimage strength is medium, only the saturation gradation value is corrected. It is also possible to selectively perform any one of the above in accordance with the magnitude of the afterimage strength level, such that when the afterimage strength level is large, only the correction of the luminance gradation value is performed. Or it is good also as a structure performed by combining any two above-mentioned according to the magnitude | size of an afterimage strength.

  It should be noted that the configurations shown in Embodiments 1 to 7 of the present invention may be used in combination.

  Note that each circuit block shown in the embodiment of the present invention may be configured as an electric circuit that performs each operation shown in the embodiment, or a microcomputer that is programmed to perform the same operation. May be used.

  In the first embodiment of the present invention, the subtraction circuit 74 subtracts the luminance gradation value set for each pixel from the luminance gradation value one pixel before output from the one-pixel delay circuit 73. The configuration in which the luminance difference between adjacent pixels is calculated and used between two pixels (horizontal adjacent pixels) adjacent in the direction in which the display electrode pair 24 extends is described. However, the present invention is not limited to this configuration. For example, two pixels adjacent to each other in the direction in which the data electrode 32 extends (vertical adjacent pixels) are obtained by subtracting the luminance gradation value set for each pixel from the luminance gradation value one horizontal period before. It may be configured to calculate and use a luminance difference between adjacent pixels. Alternatively, the luminance gradation value set for each pixel is subtracted from the luminance gradation value before (one horizontal period + 1 pixel) and the luminance gradation value before (one horizontal period−1 pixel) In other words, the panel 10 may calculate and use a luminance difference between adjacent pixels between two pixels adjacent in the diagonal direction in the panel 10. Alternatively, the maximum value of the luminance difference between adjacent pixels calculated between horizontal adjacent pixels, the luminance difference between adjacent pixels calculated between vertical adjacent pixels, and the luminance difference between adjacent pixels calculated between adjacent pixels in an oblique direction is used. It may be a configuration.

  In the first embodiment of the present invention, the configuration for changing the luminance comparison value and the edge comparison value is not particularly mentioned. For example, one or both of the luminance comparison value and the edge comparison value are displayed on the panel. It is good also as a structure changed with 10 places. As typical examples of symbols that are displayed stationary for a certain period of time, there are characters by subtitles, the current time, etc., but these are generally displayed on the periphery of the panel 10 in many cases. Therefore, the brightness comparison value and the edge comparison value are set to be smaller in the peripheral portion than in the central portion of the panel 10 so that the afterimage strength is likely to increase in the peripheral portion rather than the central portion of the panel 10. Good.

  The drive voltage waveform shown in FIG. 3 is merely an example in the embodiment, and the present invention is not limited to these drive voltage waveforms.

  In the embodiment of the present invention, scan electrode SC1 to scan electrode SCn are divided into a first scan electrode group and a second scan electrode group, and an address period is a scan electrode belonging to the first scan electrode group. Of a panel by so-called two-phase driving, which includes a first address period in which a scan pulse is applied to each of the first and second address periods in which a scan pulse is applied to each of the scan electrodes belonging to the second scan electrode group. The present invention can also be applied to a driving method, and the same effect as described above can be obtained.

  In the embodiment of the present invention, the scan electrode and the scan electrode are adjacent to each other, and the sustain electrode and the sustain electrode are adjacent to each other, that is, the arrangement of the electrodes provided on the front plate is “... , Scan electrode, sustain electrode, sustain electrode, scan electrode, scan electrode,...

  The specific numerical values shown in the embodiment of the present invention are set based on the characteristics of a 50-inch panel having 1080 display electrode pairs, and are merely examples of the embodiment. Absent. The present invention is not limited to these numerical values, and is desirably set optimally according to the characteristics of the panel, the specifications of the plasma display device, and the like. Each of these numerical values is allowed to vary within a range where the above-described effect can be obtained.

  The present invention can reduce the afterimage phenomenon of the display image on the panel and improve the image display quality, and is useful as a panel driving method and a plasma display device.

DESCRIPTION OF SYMBOLS 1 Plasma display apparatus 10 Panel 21 Front plate (made of glass) 22 Scan electrode 23 Sustain electrode 24 Display electrode pair 25, 33 Dielectric layer 26 Protective layer 31 Back plate 32 Data electrode 34 Partition 35 Phosphor layer 41 Image signal processing circuit 42 data electrode drive circuit 43 scan electrode drive circuit 44 sustain electrode drive circuit 45 timing generation circuit 63, 64, 65, 69, 72, 75, 95 comparison circuit 66, 67, 68, 88 selector 70 1 field delay circuit 71, 74 , 90 Subtraction circuit 73 1-pixel delay circuit 76 Block timing generation circuit 77, 78 Count circuit 79, 110 Afterimage strength calculation circuit 80 Afterimage strength interpolation circuit 81 Delay circuit 82, 83, 84, 85, 86, 87 Correction circuit 89 Cumulative addition Circuit 91 Limit circuit 92, 94, 99 Multiplication count calculation Circuit 93, 100 Multiplier circuit 96, 101 Afterimage strength correction circuit 97 APL detection circuit 98 Smoothing circuit

Claims (17)

A plasma display panel comprising a plurality of discharge cells each having a display electrode pair and a data electrode each consisting of a scan electrode and a sustain electrode, each pixel being constituted by a plurality of discharge cells, and a subfield having an address period and a sustain period A driving method of a plasma display panel that provides a plurality of gradations in one field to display gray scales,
Dividing the display area of the plasma display panel into a plurality of areas;
Calculate the afterimage strength for each region based on the luminance gradation value set for each pixel according to the image signal, calculate the afterimage strength for each pixel based on the afterimage strength for each region,
A driving method of a plasma display panel, wherein a luminance gradation value of each pixel is changed based on the afterimage strength level for each pixel. The difference in luminance gradation value between the current field and the field immediately before the current field is calculated for each pixel as an inter-field luminance difference, and the number of pixels for which the inter-field luminance difference is smaller than a predetermined luminance comparison value is calculated. Count for each region to be the first count value in each region,
The number of edges at which the difference in luminance gradation value between adjacent pixels is equal to or greater than a predetermined edge comparison value is counted for each of the areas to be a second count value in each of the areas,
The method of driving a plasma display panel according to claim 1, wherein an afterimage strength level for each of the regions is calculated based on the first count value and the second count value. In an area where the first count value is equal to or greater than the first threshold value and the second count value is equal to or greater than the third threshold value, the first set value is added to the afterimage strength level for each area. And
The first count value is less than the first threshold value and greater than or equal to a second threshold value that is smaller than the first threshold value, and the second count value is the third threshold value. In a region that is greater than or equal to the threshold value, the second set value is added to the afterimage strength for each region,
In an area where the first count value is less than the second threshold value and the second count value is greater than or equal to the third threshold value, a third set value is set as the afterimage strength for each area. And add
In a region where the second count value is less than the third threshold value, the fourth set value is added to the afterimage strength level for each region, and the afterimage strength level for each region is updated. The method for driving a plasma display panel according to claim 2. The first set value is a positive number, the second set value is “0”, and the third set value and the fourth set value are negative numbers. The method for driving a plasma display panel according to claim 3. 4. The method of driving a plasma display panel according to claim 3, wherein a predetermined constant is subtracted from the updated afterimage strength. 4. The method of driving a plasma display panel according to claim 3, wherein the afterimage strength after the update is limited to a predetermined upper limit value or less. In each of the regions, the afterimage strength for each region is the afterimage strength of the central pixel located in the center of the region,
For the pixels other than the center pixel, the afterimage strength level is calculated for each pixel based on the distance between the pixel for which the afterimage strength level is calculated and the plurality of central pixels around it and the afterimage strength level of the center pixel. The method of driving a plasma display panel according to claim 1. By subtracting the afterimage strength level for each pixel from a predetermined reference value and dividing the subtraction result by the reference value, the luminance gradation value of each pixel is multiplied by the result. The method of driving a plasma display panel according to claim 1, wherein the method is changed. 2. The plasma display according to claim 1, wherein the luminance gradation value is changed based on the afterimage strength level only in a pixel in which the luminance gradation value of each pixel is equal to or higher than a predetermined high luminance threshold value. Panel drive method. The average luminance level of the image signal is detected, and when the average luminance level is high, the afterimage strength level for each pixel is changed based on the average luminance level so that the afterimage strength level is smaller than when the average luminance level is low. The method of driving a plasma display panel according to claim 1. A number of sustain pulses generated by multiplying the brightness weight set for each subfield by the brightness magnification is generated in the sustain period, and
The plasma display according to claim 1, wherein when the luminance magnification is small, the afterimage strength for each pixel is changed based on the luminance magnification so that the afterimage strength is smaller than when the luminance magnification is large. Panel drive method. A number of sustain pulses generated by multiplying the brightness weight set for each subfield by the brightness magnification is generated in the sustain period, and
4. The method of driving a plasma display panel according to claim 3, wherein the magnitude of the first set value is changed according to the magnitude of the luminance magnification. When the luminance magnification is greater than or equal to a fourth threshold value, the first set value is a positive numerical value,
13. The method of driving a plasma display panel according to claim 12, wherein when the luminance magnification is less than a fourth threshold value, the first set value is set to “0”. The luminance gradation value of each pixel is smoothed based on the afterimage strength level of each pixel so that the luminance gradation value is smoothed when the afterimage strength level is large compared to when the afterimage strength level is small. The method for driving a plasma display panel according to claim 1. 2. The saturation set for each pixel based on an image signal is changed based on the afterimage strength for each pixel, and when the afterimage strength is large, the saturation is lowered than when the afterimage strength is small. A driving method of the plasma display panel as described. The plurality of boundaries are provided in a direction in which the display electrode pair extends so that the number of pixels is equal to each other, and the region is set by providing a plurality of boundaries in a direction in which the data electrode extends. 2. A driving method of a plasma display panel according to 1. A plurality of discharge cells each having a display electrode pair composed of a scan electrode and a sustain electrode are provided. A plurality of discharge cells constitute one pixel, and a plurality of subfields having an address period and a sustain period are provided in one field. A plasma display panel to display the tone,
Brightness and saturation gradation values are set for each pixel according to the image signal, and light emission / non-light emission for each subfield in the discharge cell is performed according to the magnitude of the luminance and saturation gradation values. An image signal processing circuit for creating image data to be shown,
The image signal processing circuit includes:
Dividing the display area of the plasma display panel into a plurality of areas;
Calculate the afterimage strength for each region based on the luminance gradation value set for each pixel according to the image signal, calculate the afterimage strength for each pixel based on the afterimage strength for each region,
A plasma display apparatus, wherein the gradation value of luminance of each pixel is changed based on the afterimage strength level for each pixel.

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