JP2011257515A - Driving method for plasma display panel and plasma display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an afterimage phenomenon of a displayed picture in a plasma display panel and improve picture display quality.SOLUTION: An average picture level is calculated, and an absolute value of a variation of the average picture level between fields and a sudden picture change comparison value are compared, making the comparison result a sudden picture change detection result. A display area of a plasma display panel is divided into plural regions, and an upper limit value of an afterimage occurrence probability is calculated for each region according to a luminance gradation value of each pixel, and an afterimage occurrence probability of each region is calculated according to the luminance gradation value, the sudden picture change detection result and the upper limit value of the afterimage occurrence probability. An afterimage occurrence probability of each pixel is calculated according to the afterimage occurrence probability of each region, and the highest gradation value among three gradation values of red, green and blue is selected for each pixel, and the highest gradation value is corrected according to the afterimage occurrence probability to calculate a corrected highest gradation value. A size ratio of the corrected highest gradation value to the highest gradation value is calculated, and two gradation values other than the highest gradation value are corrected according to the ratio.

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, for example, a driving method is disclosed in which a sustain pulse having a steep rising edge 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.

  The panel driving method of the present invention includes a plurality of discharge cells each having a display electrode pair and a data electrode each composed of a scan electrode and a sustain electrode, and one pixel is formed by three discharge cells that emit light in red, green, and blue colors. The constructed panel is driven by providing a plurality of subfields each having an address period and a sustain period in one field, and each of the three discharge cells has a red, green, and blue gradation value based on an image signal. A method of driving a panel that emits light at a brightness according to the gradation display and calculates the average luminance level of the image signal for each field and calculates the absolute value of the amount of change in the average luminance level between the fields. Comparing the calculated absolute value with the preset image sudden change comparison value and making the comparison result the image sudden change detection result, dividing the display area of the panel into a plurality of areas, and for each pixel based on the image signal The afterimage strength level upper limit value is calculated for each area based on the gradation value of the degree, and the afterimage strength level for each area is calculated based on the luminance gradation value, the image sudden change detection result, and the afterimage strength level upper limit value. The afterimage strength level is calculated for each pixel based on the frequency, and the maximum gradation value among the three gradation values of red, green, and blue is selected for each pixel, and the maximum gradation value is set for each pixel based on the afterimage strength level. The corrected maximum gradation value is calculated by adding correction, and the ratio of the size of the corrected maximum gradation value to the maximum gradation value is obtained, and two gradation values excluding the maximum gradation value are obtained based on the ratio. It is characterized in that a correction is added to.

  As a result, the afterimage strength level, which is a measure for the occurrence of the afterimage phenomenon, is calculated for each pixel based on the luminance gradation value, and the gradation value of each pixel is corrected based on the calculated afterimage strength level. It is possible to reduce the afterimage phenomenon of the 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 The afterimage strength level and the afterimage strength level upper limit value for each region may be calculated based on the first count value and the second count value by counting each region to obtain the second count value in each region. As a result, an image having a pattern that is likely to cause an afterimage phenomenon, for example, a pattern in which a large number of edges are displayed and a stationary region is continuously displayed is detected based on the image signal, and the afterimage frequency is based on the detection result. Can be calculated.

  In this panel driving method, when the afterimage strength level upper limit value is updated, 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. In the region, the first set value is added to the afterimage strength level upper limit value, and the second count value is smaller than the first threshold value and the first count value is smaller than the first threshold value. In the region where the second count value is equal to or greater than the third threshold value, the second set value is added to the afterimage strength upper limit value, and the first count value is less than the second threshold value. In a region where the second count value is equal to or greater than the third threshold value, a region where the third set value is added to the afterimage strength upper limit value and the second count value is less than the third threshold value Then, when adding the fourth set value to the afterimage strength level upper limit value and updating the afterimage strength level for each region, the first count value is equal to or greater than the first threshold value, In the region where the count value is equal to or greater than the third threshold value, when the afterimage strength level for each region is less than the fourth threshold value, the eleventh set value is added to the afterimage strength level for each region, and the afterimage strength level for each region Is equal to or greater than the fourth threshold value and less than the afterimage strength level upper limit value, a twelfth set value having a value larger than the eleventh set value is added to the afterimage strength level for each region, and the first count value is the first count value. In an area that is less than the 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 second set value is added to the afterimage strength level for each area, and the average brightness When the absolute value of the amount of change between the level fields is less than the image sudden change comparison value, 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. In the area, the third set value is added to the afterimage strength level for each area, and the second count value is less than the third threshold value. In the area, the fourth set value is added to the afterimage strength level for each area, and when the absolute value of the change amount between the fields of the average luminance level is equal to or greater than the image sudden change comparison value, the first count value is the second value. In the area where the second count value is less than the third threshold value or less than the threshold value, the first value set to a negative value is set until the afterimage strength level for each area reaches a preset lower limit value. The set value of 5 may be continuously added to the afterimage strength level for each region. Thereby, the afterimage strength level for each region can be updated for each field according to the feature of the image.

  In this panel driving method, the first set value is set to a positive numerical value, the first set value and the eleventh set value are set to be equal to each other, and the second set value is set to “ 0 ”, the third set value and the fourth set value are set to negative numbers, and the absolute value of the fifth set value is set to be larger than the absolute values of the third set value and the fourth set value. It may be set to a large numerical value, and the above lower limit value may be set to a numerical value smaller than the fourth threshold value. As a result, the 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 is an afterimage as an area where the probability of occurrence of the afterimage phenomenon has increased. The frequency is increased, 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 the third threshold value. The area that is less than the threshold value reduces the afterimage strength as an area in which the afterimage phenomenon is less likely to occur, and the first count value is less than the first threshold value and greater than or equal to the second threshold value, The region where the second count value is equal to or greater than the third threshold value maintains the afterimage strength level as a region in which the afterimage phenomenon is easily generated. Can be increased or decreased.

  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 to the gradation value based on the afterimage strength level.

  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. The magnitude of the eleventh set value may be changed. This makes it possible to change how much to increase when the afterimage strength level is increased according to the luminance magnification.

  In this panel driving method, when the luminance magnification is greater than or equal to the fifth threshold value, the first set value and the eleventh set value are positive numbers, and the luminance magnification is less than the fifth threshold value. Sometimes the first set value and the eleventh set 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.

  In this panel driving method, the afterimage strength upper limit value may be limited to a predetermined upper limit value or less. As a result, it is possible to prevent overcorrection of the 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. Then, 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.

  Further, in this panel driving method, the afterimage strength level for each pixel is subtracted from a predetermined reference value, and the maximum gradation value of each pixel is corrected based on the result obtained by dividing the subtraction result by the reference value. Good. Thereby, it is possible to appropriately perform correction to the gradation value based on the afterimage strength level.

  In this panel driving method, the afterimage strength level for each pixel may be changed based on the average brightness level so that the afterimage strength level is smaller when the average brightness level is large than when the average brightness level is small. Thereby, the afterimage strength level can be changed based on the detected average luminance level, and the gradation value of each pixel can be corrected based on the changed afterimage strength level. 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. Accordingly, 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 correct the 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.

  Also, in this panel driving method, when the maximum gradation value is larger than the preset high gradation value threshold, the high gradation value threshold is subtracted from the maximum gradation value, and the result of the subtraction The correction based on the afterimage strength level may be added to the result, and the result of adding the high gradation value threshold to the correction result may be used as the corrected maximum gradation value. As a result, a pixel that is considered to be easily recognized when the afterimage phenomenon occurs with high emission luminance causes the red, green, and blue discharge cells to emit light with a gradation value that is corrected based on the afterimage strength level. Pixels that are considered to be difficult to recognize even if the afterimage phenomenon is low can emit red, green, and blue discharge cells with gradation values that are not corrected based on the afterimage strength, so the luminance of the display image Can be minimized.

  Further, in this panel driving method, each gradation value of each pixel is smoothed based on the afterimage strength level for each pixel so that the gradation value is smoothed when the afterimage strength level is large than when the afterimage strength level is small. May be.

  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 composed of a scan electrode and a sustain electrode, and one discharge pixel is composed of three discharge cells that emit light in red, green, and blue colors. A plurality of subfields having an address period and a sustain period are provided in one field, and each of the three discharge cells emits light with brightness corresponding to the magnitude of each of the red, green, and blue gradation values based on the image signal. The gradation display panel and the gradation values of red, green, and blue are set for each of the three discharge cells of each pixel in accordance with the image signal. And an image signal processing circuit for creating image data indicating light emission / non-light emission for each subfield, and the image signal processing circuit calculates an average luminance level of the image signal for each field and a field of the average luminance level. An image sudden change detection circuit that calculates an absolute value of a change amount of the image, compares the calculated absolute value with a preset image sudden change comparison value, and outputs the comparison result as an image sudden change detection result; Are divided into a plurality of regions, and afterimage strength level upper limit values are calculated for each region based on the luminance gradation value of each pixel based on the image signal. Based on the afterimage strength for each area, calculate the afterimage strength for each pixel based on the afterimage strength for each area, and select the maximum gradation value among the three gradation values of red, green, and blue for each pixel. For each pixel, the maximum gradation value is corrected based on the afterimage strength level to calculate the corrected maximum gradation value, and the ratio of the corrected maximum gradation value to the maximum gradation value is obtained, and the ratio Based on the two floors excluding the maximum gradation value It characterized by having a RGB correction circuit adding the correction value.

  As a result, the afterimage strength level, which is a measure for the occurrence of the afterimage phenomenon, is calculated for each pixel based on the luminance gradation value, and the gradation value of each pixel is corrected based on the calculated afterimage strength level. It is possible to reduce the afterimage phenomenon of the image and improve the image display quality.

  In addition, the image signal processing circuit in this plasma display device calculates the difference in luminance gradation value between the current field and the field immediately before the current field for each pixel as the luminance difference between fields, and the luminance difference between fields is predetermined. The number of pixels smaller than the brightness comparison value is counted for each region to be the first count value in each region, and the edge at which the difference in luminance gradation value between adjacent pixels is equal to or greater than a predetermined edge comparison value Is counted as a second count value in each area, and when the afterimage strength level upper limit value is updated, the first count value is equal to or greater than the first threshold value, In the region where the count value is equal to or greater than the third threshold value, the first set value is added to the upper limit value of the afterimage strength level, and the first count value is less than the first threshold value and greater than the first threshold value. Is more than the second small threshold value In an area where the second count value is equal to or greater than the third threshold value, the second set value is added to the afterimage strength upper limit value, the first count value is less than the second threshold value, In the region where the count value of is equal to or greater than the third threshold value, the third set value is added to the upper limit value of the afterimage strength level, and in the region where the second count value is less than the third threshold value, the afterimage strength level When the fourth set value is added to the upper limit value and the afterimage strength level is updated for each region, the first count value is equal to or greater than the first threshold value, and the second count value is the third threshold value. In an area that is greater than or equal to the threshold value, when the afterimage strength level for each area is less than the fourth threshold value, the eleventh set value is added to the afterimage strength level for each area, and the afterimage strength level for each area is the fourth threshold value. When the value is smaller than the upper limit value of the afterimage strength level, the twelfth set value having a numerical value larger than the eleventh set value is added to the afterimage strength level for each region, and the first count value is In an area that is less than the threshold value of 1 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 second set value is added to the afterimage strength level for each area; When it is determined that the absolute value calculated by the image sudden change detection circuit is less than the image sudden change comparison value, the first count value is less than the second threshold value, and the second count value is the third threshold value. In a region that is greater than or equal to the value, the third set value is 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. When the absolute value calculated by the image sudden change detection circuit is greater than or equal to the image sudden change comparison value, the first count value is less than the second threshold value or the second count value is In an area that is less than the third threshold value, the afterimage strength for each area reaches a preset lower limit value. Up to this point, the fifth setting value set to a negative numerical value may be continuously added to the afterimage strength level for each region. Thereby, the afterimage strength level for each region can be updated for each field according to the feature of the image.

  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 arrangement | sequence figure of the panel in Embodiment 1 of this invention. It is a wave form diagram which shows an example of the drive voltage waveform applied to each electrode of the panel in Embodiment 1 of this invention. It is a circuit block diagram which shows the example of 1 structure of the plasma display apparatus in Embodiment 1 of this 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 the example of 1 structure of the RGB correction circuit in Embodiment 1 of this invention. It is a circuit block diagram which shows one structural example of the image sudden change detection circuit in Embodiment 1 of this 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 circuit block diagram which shows the example of 1 structure of the afterimage strength upper limit calculation circuit in Embodiment 1 of this invention. It is a circuit block diagram which shows one structural example of the afterimage strength level calculating 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 the schematic which shows one operation example of the afterimage strength level calculation 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 the example of 1 structure of the afterimage strength upper limit calculation circuit in Embodiment 4 of this invention. It is a circuit block diagram which shows the example of 1 structure of the afterimage strength level calculation circuit in Embodiment 4 of this invention. It is a circuit block diagram which shows one structural example of the correction circuit in Embodiment 5 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 according to Embodiment 1 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 discharge space inside. 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, one pixel is composed of three consecutive discharge cells arranged in the direction in which the display electrode pair 24 extends. These three discharge cells are discharge cells that emit red light (R) (hereinafter referred to as “R discharge cells”), discharge cells that emit light green (G) (hereinafter referred to as “G discharge cells”), A discharge cell that emits blue light (B) (hereinafter referred to as a “B discharge cell”).

  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) arranged in the row direction. In addition, 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 a pair of scan electrode SCi (i = 1 to n) and sustain electrode SUi intersects with one data electrode Dk (k = 1 to m). Therefore, m × n discharge cells are formed in the discharge space. 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. It is assumed that the plasma display device in the present embodiment displays gradation on panel 10 by the subfield method. In this subfield method, one field is divided into a plurality of subfields on the time axis, and a luminance weight is set for each subfield. 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. In the address period of each subfield, an address discharge is generated in the discharge cell to emit light, thereby controlling light emission / non-light emission of each discharge cell for each subfield. That is, the R discharge cell emits light with brightness according to the magnitude of the R gradation value based on the image signal, and the G discharge cell emits light with brightness according to the magnitude of the G gradation value based on the image signal. The B discharge cells are caused to emit light at a brightness corresponding to the magnitude of the B gradation value based on the image signal, and the gradation is displayed on each discharge cell. By driving the panel 10 in this manner, a color image is displayed on the panel 10.

  In the present embodiment, it is assumed that one of two different initialization operations, that is, an “all-cell initialization operation” and a “selective initialization operation” is performed in the initialization period. The all-cell initializing operation is an initializing operation for generating an initializing discharge in all the discharge cells regardless of the operation of the immediately preceding subfield. The selective initializing operation is an initializing operation that generates an initializing discharge only in a discharge cell that has generated a sustaining discharge in the sustaining period of the immediately preceding subfield.

  In this embodiment, it is assumed that the all-cell initializing operation is performed in the initializing period of the first subfield (first SF) of one field, and the selective initializing operation is performed in the initializing period of the other subfield. 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, and the high-contrast image display with reduced black luminance in the display image is possible.

  In the present embodiment, one field is composed of eight subfields from the first subfield (first SF) to the eighth subfield (eighth SF), and each subfield has (1, 2, 4). , 8, 16, 32, 64, 128) will be described as follows. Also, the first SF is an all-cell initialization subfield that performs the all-cell initialization operation, and the second SF to the eighth SF are the selection initialization subfield that performs the selection initialization operation. 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 waveform diagram showing an example of a drive voltage waveform applied to each electrode of panel 10 in the first exemplary embodiment of the present invention. FIG. 3 shows scan electrode SC1 that performs the address operation first in the address period, scan electrode SCn that performs the address operation last in the address period (for example, scan electrode SC1080), sustain electrode SU1 to sustain electrode SUn, and data electrode D1. ~ Shows drive voltage waveforms of the data electrode Dm.

  FIG. 3 shows driving voltage waveforms in two subfields. That is, the first SF that is an all-cell initializing subfield and the first half of the second SF that is a selective initializing subfield are shown. Although not shown after the second half of the second SF, subfields other than the first SF are selective initialization subfields, and the drive voltage waveform in each subfield excludes the number of sustain pulses generated in the sustain period, In each period, substantially the same drive voltage waveform is generated.

  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 the data electrode D1 to the data electrode Dm and the sustain electrode SU1 to the sustain electrode SUn. Then, voltage Vi1 is applied to scan electrode SC1 through scan electrode SCn, and a ramp voltage (hereinafter referred to as “increase”) gently rising from voltage Vi1 to voltage Vi2 (for example, with a gradient of about 1.3 V / μsec). A lamp voltage L1 "). 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, and 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, the voltage applied to scan electrode SC1 through scan electrode SCn is lowered from voltage Vi2 to voltage Vi3 lower than voltage Vi2, and positive voltage Ve is applied to sustain electrode SU1 through sustain electrode SUn. 0 (V) is applied to D1 to the data electrode Dm. Then, a ramp voltage (hereinafter referred to as “down-ramp voltage L2”) that gradually falls from scan voltage SC1 to scan electrode SCn toward negative voltage Vi4 from voltage Vi3 (eg, with a slope of about −2.5 V / μsec). Applied). At this time, voltage Vi3 is set to a voltage lower than the discharge start voltage with respect to sustain electrode SU1 to sustain electrode SUn, and voltage Vi4 is set to a voltage exceeding the discharge start voltage with respect to sustain electrode SU1 to sustain electrode SUn.

  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, voltage Ve is applied to sustain electrode SU1 through sustain electrode SUn, and voltage Vcc (for example, voltage Vcc = voltage Va + voltage Vsc) is applied to scan electrode SC1 through scan electrode SCn. Then, a negative scan pulse voltage Va is applied to the first (first row) scan electrode SC1 from the top in terms of arrangement, and a discharge cell to emit light in the first row among the data electrodes D1 to Dm. The positive address pulse voltage Vd is applied to the data electrode Dk (k = 1 to m). As a result, a discharge is generated between data electrode Dk and scan electrode SC1, and a discharge is generated between sustain electrode SU1 and scan electrode SC1 in a region intersecting 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. 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. In the address period, an address discharge is selectively generated in each discharge cell in this way. The above address operation is sequentially performed from the discharge cell in the first row to the discharge cell in the nth row, and the address period ends.

  In the subsequent sustain period, positive sustain pulse voltage Vs is applied to scan electrode SC1 through scan electrode SCn, and 0 (V) as the base potential is applied to sustain electrode SU1 through sustain electrode SUn. In the discharge cell in which the address discharge has occurred, the voltage difference between scan electrode SCi and sustain electrode SUi exceeds the discharge start voltage, and a sustain discharge occurs between scan electrode SCi and sustain electrode SUi. The phosphor layer 35 emits light by the ultraviolet rays generated at this time. Further, due to this discharge, 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. Note that no sustain discharge occurs in the discharge cells in which no address discharge has occurred during the address period.

  Subsequently, 0 (V) 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. In the discharge cell in which the sustain discharge has occurred, the voltage difference between the sustain electrode SUi and the scan electrode SCi exceeds the discharge start voltage. Therefore, a sustain discharge occurs again between the sustain electrode SUi and the scan electrode SCi, and the voltage is applied to the sustain electrode SUi. A negative wall voltage is accumulated, and a positive wall voltage is accumulated on scan electrode SCi. Thereafter, similarly, sustain pulses of the number obtained by multiplying the luminance weight by a predetermined luminance magnification are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and an address discharge is caused in the address period. Sustain discharge is generated continuously in the discharge cell.

  After generation of the sustain pulse in the sustain period, 0 (V) is applied to scan electrode SC1 through scan electrode SCn while 0 (V) is applied to sustain electrode SU1 through sustain electrode SUn and data electrode D1 through data electrode Dm. A ramp voltage (hereinafter referred to as “erase ramp voltage L3”) that gradually rises to the voltage Vers (for example, with a gradient of about 10 V / μsec) is applied. By setting voltage Vers to a voltage exceeding the discharge start voltage, 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. The charged particles generated by the weak discharge are accumulated as wall charges on the sustain electrode SUi and the scan electrode SCi so as to alleviate the voltage difference between the sustain electrode SUi and the scan electrode SCi. Go. Thus, in the discharge cell in which the sustain discharge has occurred, the wall voltage on the scan electrode SCi and the wall voltage on the sustain electrode SUi are the voltages applied to the scan electrode SCi while leaving the positive wall charges on the data electrode Dk. And the discharge start voltage, for example, (voltage Vers−discharge start voltage). Hereinafter, this discharge is referred to as “erase discharge”. That is, the discharge generated by the erasing ramp voltage L3 functions as an “erasing discharge” for erasing unnecessary wall charges accumulated in the discharge cell in which the sustain discharge has occurred.

  When the increasing voltage reaches predetermined voltage Vers, the voltage applied to scan electrode SC1 through scan electrode SCn is returned to 0 (V), and the sustain operation in the sustain period is completed.

  In the initializing period of the second SF, the selective initializing waveform is applied to scan electrode SC1 through scan electrode SCn. This selective initialization waveform is a drive voltage waveform in which the first half of the initialization period in the first SF is omitted. Specifically, voltage Ve 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 receive down-ramp voltage L4 that decreases from the voltage lower than the discharge start voltage (for example, 0 (V)) toward negative voltage Vi4 at the same gradient as down-ramp voltage L2. Apply.

  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 sustain electrode SUi is weakened. . Further, 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.

  This completes the selective initialization operation in the initialization period of the selective initialization subfield.

  In the address period of the second SF, the same drive voltage 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. Further, 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 voltage waveform similar to 2SF is applied.

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

  In this embodiment, the voltage values applied to the electrodes are, for example, voltage Vi1 = 147 (V), voltage Vi2 = 357 (V), voltage Vi3 = 210 (V), voltage Vi4 = −160 (V). , Voltage Ve = 125 (V), voltage Vers = 210 (V), voltage Vs = 210 (V), voltage Va = −185 (V), and voltage Vd = 60 (V). The voltage Vcc can be generated by superimposing the positive voltage Vsc = 147 (V) on the negative voltage Va = −185 (V) (Vcc = Va + Vsc). In this case, the voltage Vcc = −38 (V )

  Note that these voltage values are merely examples. Each voltage value is desirably set to an optimal value as appropriate in accordance with the characteristics of the panel 10 and the specifications of the plasma display device 1.

  Next, the configuration of the plasma display device in the present embodiment will be described. FIG. 4 is a circuit block diagram showing a configuration example of the plasma display device 1 according to the first 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 image signal sig input to the image signal processing circuit 41 into image data indicating light emission / non-light emission for each subfield in each discharge cell according to the number of pixels of the panel 10.

  In the present embodiment, the image signal sig includes an R signal, a G signal, and a B signal, and the image signal processing circuit 41 discharges each of R, G, and B based on the R signal, the G signal, and the B signal. An R gradation value, a G gradation value, and a B gradation value (hereinafter referred to as an R gradation value, a G gradation value, and a B gradation value) are assigned to the cells, respectively. Note that the gradation value is a gradation value expressed in one field. 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.

  The image signal processing circuit 41 calculates a numerical value called “afterimage strength” for each pixel. The afterimage strength level is a numerical value calculated based on the gradation value of the luminance (Y) of each pixel based on the image signal sig, and is a numerical value that is a guideline for occurrence of the afterimage phenomenon. Then, the image signal processing circuit 41 corrects the R, G, and B tone values based on the R signal, the G signal, and the B signal based on the calculated afterimage strength for each pixel, and the corrected R, G, B Are converted into image data (hereinafter referred to as corrected R gradation value, corrected G gradation value, corrected B gradation value). Details of this correction operation will be described later.

  The image signal processing circuit 41 calculates the gradation value of the luminance (Y) of each pixel based on the R signal, the G signal, and the B signal, and calculates the afterimage strength based on the calculated gradation value of the luminance (Y). It shall be calculated. However, when the 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, etc.), the afterimage strength is based on the luminance signal. R gradation value, G gradation value, and B gradation value are calculated based on the luminance signal and the saturation signal, and the calculated R gradation value, G gradation value, and B gradation value are calculated. On the other hand, the configuration may be such that correction based on the afterimage strength is added.

  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) for generating voltage Ve, and drives sustain electrode SU1 through sustain electrode SUn based on a timing signal supplied from timing generation circuit 45.

  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 high number of lighting times per unit time (for example, one field) and the lighting times per unit time are relatively high. A small number of 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. And between these discharge cells, a difference arises in the discharge start voltage, and a difference arises in the timing which discharge generate | occur | produces. As a result, a difference occurs in light emission intensity between a discharge cell in which the lighting state continues and a discharge cell in which the non-lighting state continues, resulting in a luminance 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, that is, whether or not the image is likely to cause an afterimage phenomenon. It is assumed that correction is made to the gradation value, the G gradation value, and the B gradation value. Specifically, in the image signal processing circuit 41, an “afterimage strength” that is a measure of occurrence of the afterimage phenomenon is calculated for each pixel, and based on the calculated afterimage strength, the R gradation value and the G gradation value of each pixel are calculated. , B gradation value is corrected. Next, the details will be described.

  First, detection of the afterimage strength level in the present embodiment 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. The present invention is not limited to a configuration in which the number of pixels in each region is the same. The number of pixels in each area may be different from each other depending on the position of the area on the panel 10 or the like.

  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.

  Next, details of the image signal processing circuit 41 will be described. 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 relating to calculation of afterimage strength and correction to R gradation value, G gradation value, and B gradation value based on the afterimage strength, and other circuit blocks are omitted.

  The image signal processing circuit 41 includes a luminance gradation value calculation circuit 51, a delay circuit 55, and an RGB correction circuit 56.

  The luminance gradation value calculation circuit 51 calculates a gradation value of luminance (Y) from the R gradation value (R), the G gradation value (G), and the B gradation value (G) based on a predetermined calculation formula. To do. As an example of the predetermined calculation formula, for example, the following calculation formula can be cited.

Y = 0.299 × R + 0.587 × G + 0.114 × B
This calculation formula is merely an example of a calculation formula used when calculating the luminance (Y) gradation value from the R, G, and B gradation values. The calculation formula to be used is not limited to this calculation formula. For the calculation of the gradation value of the luminance (Y), it is desirable to use an optimal calculation formula according to the specifications of the plasma display device 1.

  The delay circuit 55 appropriately delays the R gradation value, the G gradation value, and the B gradation value so that the timing is matched with other signals in the subsequent RGB correction circuit 56. Hereinafter, the R gradation value, the G gradation value, and the B gradation value delayed in the delay circuit 55 are respectively referred to as “delayed R gradation value”, “delayed G gradation value”, and “delayed B gradation value”. Value ”(in FIG. 6,“ post-delay R ”,“ post-delay G ”,“ post-delay B ”).

  The RGB correction circuit 56 calculates the afterimage strength level for each pixel based on the luminance (Y) tone value, and the delayed R tone value, delayed G tone value, and delayed B tone based on the calculated afterimage strength level. The value is corrected, and the corrected R gradation value, the corrected G gradation value, and the corrected B gradation value are output (in FIG. 6, “after correction R”, “after correction G”, “after correction”). B ”).

  Next, details of the RGB correction circuit 56 will be described. FIG. 7 is a circuit block diagram showing a configuration example of the RGB correction circuit 56 according to Embodiment 1 of the present invention.

  The RGB correction circuit 56 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 strength An interpolation circuit 80, a correction circuit 82, and an image sudden change detection circuit 110 are included.

  The one-field delay circuit 70 delays the luminance (Y) gradation value of each pixel by a time corresponding to one field.

  The subtraction circuit 71 subtracts the luminance (Y) gradation value of each pixel from the luminance (Y) gradation value of each pixel one field before output from the one-field delay circuit 70, and performs the subtraction. The absolute value of the result is output as “brightness difference between fields”. That is, the subtraction circuit 71 calculates the difference in the luminance (Y) 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 less than the luminance comparison value. “0” is output when the luminance difference between the two is equal to or greater than the luminance comparison value.

  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 (Y) gradation value of each pixel by a time corresponding to one pixel.

  The subtraction circuit 74 subtracts the gradation value of the luminance (Y) of each pixel from the gradation value of the luminance (Y) one pixel before output from the one-pixel delay circuit 73, and the absolute value of the subtraction result The value is output as “brightness 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 the number of pixels in which the difference in the gradation value of the luminance (Y) between adjacent pixels is equal to or greater than the edge comparison value for each region as the number of “edges”, Is output as the second count value in the region.

  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 image sudden change detection circuit 110 detects whether or not a sharp change occurs in the brightness of the display image for each field, and outputs the image sudden change detection result, which is the detection result, to the afterimage strength level calculation circuit 79 in the subsequent stage. Details of the image sudden change detection circuit 110 will be described later.

  The afterimage strength level calculation circuit 79 calculates the afterimage strength level for each region based on the first count value, the second count value, and the image sudden change detection result. 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 the image sudden change detection result. The afterimage strength level calculation circuit 79 (M, N) calculates the afterimage strength level of the block (M, N) based on the first count value, the second count value and the image sudden change detection result in the block (M, N). Is calculated. The first count value and the second count value are numerical values that change for each region, and the image sudden change detection result is a numerical value that changes in units of fields. Details of the afterimage strength level calculating circuit 79 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, except for the “center pixel”. More 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.

  Then, the correction circuit 82 calculates the delayed R gradation value, the delayed G gradation value, and the delayed B gradation value of each pixel appropriately delayed in the delay circuit 55 in the afterimage strength interpolation circuit 80. Correction is performed based on the afterimage strength for each pixel, and the corrected R gradation value, the corrected G gradation value, and the corrected B gradation value are output (in FIG. 7, R after correction, G after correction, and after correction). B)). Details of the correction circuit 82 will be described later.

  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. 8 is a circuit block diagram showing a configuration example of the image sudden change detection circuit 110 according to Embodiment 1 of the present invention.

  The sudden image change detection circuit 110 includes an APL calculation circuit 111, a one-field delay circuit 112, a subtraction circuit 113, and a comparison circuit 114.

  The APL calculation circuit 111 uses a generally known method such as calculating the sum of the gradation values of the luminance (Y) of all the pixels, thereby using an average luminance level (Average Picture Level, hereinafter referred to as “APL”). (Abbreviated) is calculated for each field.

  The one-field delay circuit 112 delays the APL calculated by the APL calculation circuit 111 by a time corresponding to one field.

  The subtraction circuit 113 subtracts the APL output from the APL calculation circuit 111 and the APL one field before output from the one-field delay circuit 112, and outputs the absolute value of the subtraction result. Therefore, the output of the subtracting circuit 113 is a numerical value representing the change amount (absolute value) of APL between two consecutive fields.

  The comparison circuit 114 compares the output of the subtraction circuit 113 with a preset image sudden change comparison value, and detects whether or not the APL change amount is equal to or greater than the image sudden change comparison value. Then, “1” is output when the output of the subtraction circuit 113 is equal to or greater than the image sudden change comparison value, and “0” is output when the output of the subtraction circuit 113 is less than the image sudden change comparison value. This output value becomes the image sudden change detection result.

  As described above, the image sudden change detection circuit 110 calculates the amount of change (absolute value) of APL between two consecutive fields, and detects whether the amount of change of APL is equal to or greater than the image sudden change comparison value. Whether or not a steep change occurs in the brightness of the image is detected, and the detection result is output to the subsequent stage as the image sudden change detection result.

  FIG. 9 is a circuit block diagram showing a configuration example of the afterimage strength level calculating circuit 79 in Embodiment 1 of the present invention. As shown in FIG. 9, the afterimage strength level calculating circuit 79 in this embodiment includes an afterimage strength level upper limit calculating circuit 179 and an afterimage strength level calculating circuit 279. In FIG. 9, an afterimage strength level calculation 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 calculating circuit 79 (1,2) to the afterimage strength level calculating circuit 79 (M, N) for calculating the afterimage strength level at M, N) have the same configuration as in FIG.

  FIG. 10 is a circuit block diagram showing a configuration example of the afterimage strength level upper limit calculation circuit 179 according to the first embodiment of the present invention. In FIG. 10, an afterimage strength level upper limit value calculation circuit 179 (1, 1) for calculating the afterimage strength level upper limit value of the block (1, 1) is shown as an example. ) To an afterimage strength upper limit calculating circuit 179 (1,2) to an afterimage strength upper limit calculating circuit 179 (M, N) for calculating an afterimage strength upper limit value of the block (M, N) have the same configuration as FIG. .

  The afterimage strength level upper limit calculation circuit 179 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 restriction circuit 91.

  The comparison circuit 63 outputs the first count value output from the count circuit 77 (in the example shown in FIG. 10, 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. 10) 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 (the second count value of the block (1, 1) output from the count circuit 78 (1, 1) in the example shown in FIG. 10). 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 sets the first set value (for example, “+1”) when the output of the comparison circuit 63 is “1”, and sets the second set value (for example, “0” when the output of the comparison circuit 63 is “0”). ”) Is output to the selector 67 at the subsequent stage.

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

  The selector 68 accumulates the output of the selector 67 when the output of the comparison circuit 65 is “1”, and the fourth set value (for example, “−4”) when the output of the comparison circuit 65 is “0”. The result is output to the adder circuit 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. The result is added and the result is output as a new cumulative addition result.

  That is, the circuit constituted by the selector 66, the selector 67, the selector 68, and the cumulative addition circuit 89 operates as follows. 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 cumulatively added to the afterimage strength level upper limit value. The first count value is less than or equal to the second threshold value that is less than the first threshold value and 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 upper limit value. 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, the third set value is cumulatively added to the afterimage strength level upper limit value. In an area where the second count value is less than the third threshold value, the fourth set value is cumulatively added to the afterimage strength upper limit value. Thus, the afterimage strength upper limit value for each area 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 upper limit value 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. Is set to a negative number (for example, “−4”), and the afterimage strength level upper limit value is set to a negative number (for example, “−4”). It is decreasing. 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 the area where the image quality is maintained, the second set value is set to “0” so that the upper limit value of the afterimage strength level is maintained.

  The subtraction circuit 90 subtracts a predetermined constant (for example, “50”) from the output of the cumulative addition circuit 89. 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. This is to be able to cope with the phenomenon. Note that the subtraction circuit 90 outputs “0” when the subtraction result becomes a negative numerical value.

  The limiting circuit 91 compares the output of the subtracting circuit 90 with a predetermined upper limit value (for example, “100”), and when the output of the subtracting circuit 90 is less than or equal to the upper limit value, the output of the subtracting circuit 90 is used as it is. When the output of the subtracting circuit 90 exceeds the upper limit value, the upper limit value is output. That is, this upper limit value is the largest value of the afterimage strength level upper limit value. Thus, the output of the limiting circuit 91 limited to be equal to or lower than the predetermined upper limit value is the afterimage strength upper limit value output from the afterimage strength upper limit calculation circuit 179 (in the example shown in FIG. 10, in the block (1, 1)). Afterimage strength level upper limit).

  FIG. 11 is a circuit block diagram showing a configuration example of the afterimage strength level calculation circuit 279 according to Embodiment 1 of the present invention. In FIG. 11, an afterimage strength level calculation circuit 279 (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 calculating circuit 279 (1,2) to the afterimage strength level calculating circuit 279 (M, N) for calculating the afterimage strength level of M, N) have the same configuration as that in FIG.

  The afterimage strength level calculation circuit 279 includes a comparison circuit 263, a comparison circuit 264, a comparison circuit 265, a selector 262, a selector 266, a selector 267, a selector 268, a selector 269, a cumulative addition circuit 289, a subtraction circuit 290, a limit circuit 291 and a comparison circuit 260. And a comparison circuit 261, an AND gate 278, an inverter 273, an inverter 274, an OR gate 275, an AND gate 276, an OR gate 277, a comparison circuit 270, a selector 271, and a delay circuit 272.

  The comparison circuit 263 performs the same operation as that of the comparison circuit 63 in the afterimage strength level upper limit calculation circuit 179, and the output of the comparison circuit 263 is input to the selector 266.

  The comparison circuit 264 performs the same operation as the comparison circuit 64 in the afterimage strength level upper limit calculation circuit 179, and the output of the comparison circuit 264 is input to the selector 267.

  The comparison circuit 265 performs the same operation as the comparison circuit 65 in the afterimage strength level upper limit calculation circuit 179, and the output of the comparison circuit 265 is input to the selector 268.

  The selector 262 sets the eleventh setting value (eg, “+1”) when the output of the AND gate 278 is “0”, and sets the twelfth setting value (eg, “+10” when the output of the AND gate 278 is “1”). ”) Is output to the selector 266 at the subsequent stage. This eleventh set value is set to a value equal to the first set value in the afterimage strength level upper limit calculation circuit 179.

  The selector 266 performs the same operation as the selector 66 in the afterimage strength level upper limit calculation circuit 179 based on the comparison result in the comparison circuit 263. However, it differs from the selector 66 in that the output of the selector 262 is input to the selector 266 instead of the first set value.

  The selector 267 performs the same operation as the selector 67 in the afterimage strength level upper limit calculation circuit 179 based on the comparison result in the comparison circuit 264.

  The selector 268 performs the same operation as the selector 68 in the afterimage strength level upper limit calculation circuit 179 based on the comparison result in the comparison circuit 265. However, it differs from the selector 68 in that the output of the selector 268 is input to the selector 269.

  The selector 269 outputs the output of the selector 268 when the output of the OR gate 277 is “0”, the fifth set value (for example, “−10”) when the output of the OR gate 277 is “1”, and the cumulative addition circuit at the subsequent stage. To 289. In the present embodiment, the third set value, the fourth set value, and the fifth set value are set to negative numbers, and the absolute value of the fifth set value is set to the third set value. And a value larger than the absolute value of the fourth set value (the fifth set value is set to a value larger in the negative direction than the third set value and the fourth set value). .

  The cumulative addition circuit 289 performs the same operation as the cumulative addition circuit 89 in the afterimage strength level upper limit calculation circuit 179. However, the cumulative addition circuit 89 is different in that the output of the selector 269 is cumulatively added.

  The subtraction circuit 290 performs the same operation as the subtraction circuit 90 in the afterimage strength level upper limit calculation circuit 179, and outputs “0” when the subtraction result becomes a negative numerical value.

  The limiting circuit 291 compares the output of the subtraction circuit 290 with the afterimage strength level upper limit value output from the afterimage strength level upper limit calculation circuit 179, and outputs the output of the subtraction circuit 290 when the output of the subtraction circuit 290 is equal to or less than the afterimage strength level upper limit value. When the output of the subtracting circuit 290 exceeds the afterimage strength level upper limit value, the afterimage strength level upper limit value is output. In this way, the output of the subtraction circuit 290 limited to the upper limit value of the afterimage strength level in the limit circuit 291 is the afterimage strength level output from the afterimage strength level calculation circuit 279 (in the example shown in FIG. 11, the afterimage strength level of the block (1, 1)). It becomes. Note that, by limiting the afterimage strength level to the upper limit value of the afterimage strength level, the maximum value of the afterimage strength level becomes the predetermined upper limit value shown in FIG. As described above, the maximum value of the afterimage strength level is limited by the predetermined upper limit value in order to prevent the correction circuit 82 from overcorrecting each gradation value.

  The inverter 273 logically inverts the output of the comparison circuit 264 and outputs the result. That is, the inverter 273 outputs “0” when the output of the comparison circuit 264 is “1”, and outputs “1” when the output is “0”.

  The inverter 274 logically inverts the output of the comparison circuit 265 and outputs the result. That is, the inverter 274 outputs “0” when the output of the comparison circuit 265 is “1”, and outputs “1” when the output is “0”.

  The OR gate 275 performs an OR operation (OR operation) between the output of the inverter 273 and the output of the inverter 274. That is, the OR gate 275 outputs “0” only when both the output of the inverter 273 and the output of the inverter 274 are “0”, and outputs “1” otherwise. In other words, when the first count value is equal to or greater than the second threshold value and the second count value is equal to or greater than the third threshold value, that is, the eleventh set value or the second count value is output to the selector 268. When the set value of 12 or the second set value is selected (when the afterimage strength increases or does not change), the output of the OR gate 275 becomes “0”, otherwise, that is, the selector 268. The output of the OR gate 275 becomes “1” when the third set value or the fourth set value is selected for the output of (when the afterimage strength decreases).

  The AND gate 276 performs an AND operation (AND operation) between the output of the OR gate 275 and the image sudden change detection result. That is, the AND gate 276 outputs “1” only when both the output of the OR gate 275 and the image sudden change detection result are “1”, and outputs “0” otherwise. In other words, when the third set value or the fourth set value is selected for the output of the selector 268 (the afterimage strength is reduced) and the brightness of the display image changes sharply, the AND gate The output of 276 is “1”. In other cases, that is, the eleventh set value, the twelfth set value, or the second set value is selected as the output of the selector 268 (the afterimage strength level is decreased). Or the output of the AND gate 276 is “0” when there is no steep change in the brightness of the display image.

  The OR gate 277 performs a logical OR operation (OR operation) between the output of the AND gate 276 and the output of the delay circuit 272. That is, the OR gate 277 outputs “0” only when both the output of the AND gate 276 and the output of the delay circuit 272 are “0”, and outputs “1” otherwise.

  The comparison circuit 270 compares the afterimage strength level output from the limiting circuit 291 with a predetermined lower limit value (for example, “0”) set in advance, and sets “1” when the afterimage strength level is greater than the lower limit value. When the afterimage strength is less than or equal to this lower limit value, “0” is output.

  The selector 271 outputs the output of the OR gate 277 when the output of the comparison circuit 270 is “1”, “0” when the output of the comparison circuit 270 is “0”, and the delay circuit 272 of the subsequent stage.

  The delay circuit 272 delays the output of the selector 271 by a time corresponding to one field. The output of the delay circuit 272 is input to the OR gate 277 and is logically ORed with the output of the AND gate 276.

  Therefore, the circuit composed of the OR gate 277, the comparison circuit 270, the selector 271 and the delay circuit 272 continues once the output of the AND gate 276 becomes “1” for a period in which the afterimage strength is greater than the predetermined lower limit value. The OR gate 277 outputs “1”, and when the output of the AND gate 276 is “0” and the afterimage strength is equal to or lower than a predetermined lower limit value, the OR gate 277 outputs “0”. . Then, in the cumulative addition circuit 289, when the output of the OR gate 277 is “1”, the fifth set value (for example, “−10”) is cumulatively added, whereby the afterimage strength is sharply reduced, and the OR gate 277 When the output is “0”, the output of the selector 268 is cumulatively added to the afterimage strength level.

  In other words, in the afterimage strength level calculation circuit 279, when the third set value or the fourth set value is selected as the output of the selector 268 and the afterimage strength level decreases, the brightness of the display image changes sharply. When this occurs, the afterimage strength starts to decrease sharply with a magnitude based on the fifth set value, and the sharp decrease continues until the afterimage strength reaches a predetermined lower limit value.

  The comparison circuit 260 compares the afterimage strength level upper limit value output from the afterimage strength level upper limit calculation circuit 179 with the afterimage strength level output from the limit circuit 291, and sets “1” when the afterimage strength level is less than the afterimage strength level upper limit value. When the afterimage strength level is equal to the upper limit value of the afterimage strength level, “0” is output.

  The comparison circuit 261 compares the afterimage strength level output from the limiting circuit 291 with a preset fourth threshold value, and outputs “1” when the afterimage strength level is equal to or greater than the fourth threshold value. When the afterimage strength is less than the fourth threshold value, “0” is output.

  The AND gate 278 performs an AND operation (AND operation) between the output of the comparison circuit 260 and the output of the comparison circuit 261. Therefore, the AND gate 278 indicates that when both the output of the comparison circuit 260 and the output of the comparison circuit 261 are “1”, that is, when the afterimage strength is equal to or greater than the fourth threshold value and less than the upper limit of the afterimage strength. 1 ”is output, otherwise“ 0 ”is output when the afterimage strength is less than the fourth threshold value or the afterimage strength is equal to the upper limit of the afterimage strength.

  The output of the AND gate 278 is input to the selector 262, and the signal output from the selector 262 has the same value as the first set value in the afterimage strength level upper limit calculation circuit 179 when the output of the AND gate 278 is “0”. When the output of the AND gate 278 is “1”, it becomes a twelfth set value (eg, “+10”) that is larger than the eleventh set value.

  Therefore, in the afterimage strength level calculation circuit 279, when the signal output from the selector 262 is cumulatively added to the afterimage strength level in the cumulative addition circuit 289, the afterimage strength level is reached until the afterimage strength level reaches the fourth threshold value. Is added with the 11th set value, and the afterimage strength increases relatively slowly. After the afterimage strength reaches the fourth threshold value or higher, the afterimage strength level reaches the upper limit value. After the set value of 12 is added, the afterimage strength level increases relatively steeply, and after the afterimage strength level reaches the upper limit value of the afterimage strength level, the 11th set value is added to the afterimage strength level again. .

  Summarizing these operations, the operation in the afterimage strength level calculation circuit 279 is as follows. 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 eleventh set value or the twelfth set value is accumulated in the afterimage strength level. to add. 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 region, the second set value is cumulatively added to the afterimage strength level. 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. 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.

  However, when the eleventh set value or the twelfth set value is cumulatively added to the afterimage strength level, if the afterimage strength level is equal to or greater than the fourth threshold value and less than the afterimage strength level upper limit value, it is greater than the eleventh set value. The twelfth set value is cumulatively added to the afterimage strength level to sharply increase the afterimage strength level. When the afterimage strength level is less than the fourth threshold value or equal to the afterimage strength level upper limit value, the eleventh set value is set to the afterimage strength level. To increase the afterimage strength level gently (note that the eleventh set value is set equal to the first set value in the afterimage strength upper limit calculation circuit 179).

  In addition, when the third set value or the fourth set value is selected as the numerical value to be cumulatively added to the afterimage strength level, the sudden change in the brightness of the display image has occurred. Until the afterimage strength reaches a predetermined lower limit value by continuously accumulating the third set value and the fifth set value, which is larger in the negative direction than the fourth set value, to the afterimage strength. Reduce sharply.

  In this embodiment, the afterimage strength level calculation circuit 79 calculates the afterimage strength level in this way, and updates and outputs it for each field.

  As described above, the afterimage strength level does not exceed the upper limit value of the afterimage strength level due to the operation of the limiting circuit 291.

  In addition, as a specific numerical value of the first threshold value, for example, a numerical value corresponding to 50% of the largest value that can be taken as the first count value in one block can be given. Moreover, as a specific numerical value of the second threshold value, for example, a numerical value corresponding to 30% of the largest value that can be taken as the first count value in one block can be given. Moreover, as a specific numerical value of the third threshold value, for example, a numerical value corresponding to 50% of the largest value that can be taken as the second count value in one block can be given. Moreover, as a specific numerical value of the fourth threshold value, for example, a numerical value corresponding to 20% of the largest value (predetermined upper limit value shown in FIG. 10) that can be taken as the afterimage strength level can be given. However, the threshold values in the present invention are not limited to the numerical values listed here. Also shown as a first set value, an eleventh set value, a twelfth set value, a second set value, a third set value, a fourth set value, a fifth set value, and a predetermined lower limit value Each specific numerical value is merely an example, and each setting value in the present invention is not limited to the numerical value shown in the present embodiment. It is desirable that each threshold value and each set value are appropriately set according to the characteristics of the panel 10, the specifications of the plasma display device 1, or the like, or by conducting a visual experiment of an afterimage phenomenon in the display image. However, in the present embodiment, the twelfth set value is set to a value larger than the eleventh set value. This is to increase the afterimage strength sharply when the afterimage strength is less than the upper limit value of the afterimage strength and equal to or greater than the fourth threshold value. The predetermined lower limit value is set to a numerical value smaller than the fourth threshold value. Further, the fifth set value is set to a numerical value smaller than the third set value and the fourth set value (a large value in the negative direction). This is because, when the third set value or the fourth set value is selected as the output of the selector 268 in order to reduce the afterimage strength level, when a sharp change occurs in the brightness of the display image, the afterimage strength level This is because of a sharp decrease.

  FIG. 12 is a diagram schematically showing a calculation performed in the afterimage strength interpolation circuit 80 in the first embodiment of the present invention. In FIG. 12, a part of the panel 10 is shown in an enlarged manner, a broken line indicates a boundary between the regions, and a white circle indicates a pixel (center pixel) positioned at the center in each region. In FIG. 12, a line connecting the central pixels is indicated by a one-dot chain line. In FIG. 12, 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. 12 are supplementarily shown so as to easily distinguish each region and the like, and this line is not actually displayed on the panel 10.

  In the present embodiment, the afterimage strength calculated for each region is the afterimage strength of the central pixel located in 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 level of each pixel excluding “center pixel” is calculated based on the afterimage strength level of the center pixel.

  Specifically, the afterimage strength level of each pixel 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. 12, the center pixel around the pixel A34 is shown as a 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 The distance between A34 and pixel A3 is indicated as L3, and the distance between pixel A34 and pixel A4 is indicated as 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, if the afterimage strength level of the pixel A34 is a34, the afterimage strength level of the pixel A1 is a1, the afterimage strength level of the pixel A2 is a2, the afterimage strength level of the pixel A3 is a3, and the afterimage strength level of the pixel A4 is a4, the afterimage strength level a34 is It is expressed by a formula.

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 for which the afterimage strength level is to be calculated is the pixel A12 and the pixel A12 is on the line connecting the pixel A1 and the pixel A2, the afterimage strength level of the pixel A12 is equal to the afterimage strength level of the pixel A1 and the pixel A2. Based on the calculation.

  For example, when 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 is expressed by the following equation.

a12 = (a1 × L6 + a2 × L5) / (L5 + L6)
These calculations are performed for each pixel in the afterimage strength interpolation circuit 80 to calculate the afterimage strength of each pixel.

  FIG. 13 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, a maximum value selection circuit 52, a subtraction circuit 53, a multiplication circuit 54, an addition circuit 57, a multiplication ratio calculation circuit 58, a multiplication circuit 93, and a switch circuit 59. Have Then, the delayed R gradation value, the delayed G gradation value, and the delayed B gradation value of each pixel are corrected based on the afterimage strength level, and the corrected R gradation value, the corrected G gradation value, and the corrected value are corrected. The B gradation value is output (in FIG. 13, written as R after correction, G after correction, and B after correction).

  The multiplication coefficient calculation circuit 92 calculates a multiplication coefficient used in the subsequent multiplication circuit 54 from the afterimage strength level for each pixel. Specifically, the multiplication coefficient calculation circuit 92 subtracts the afterimage strength for each pixel from a predetermined reference value (eg, “255”), and divides the subtraction result by the reference value (eg, “255”). Perform the operation. The result calculated in this manner is output as a multiplication coefficient, and is used for correcting the gradation value in the subsequent multiplication circuit 54.

  The maximum value selection circuit 52 compares the sizes of the three gradation values of the delayed R gradation value, the delayed G gradation value, and the delayed B gradation value for each pixel, and the largest gradation among them. A value (hereinafter referred to as “maximum gradation value”) is selected. That is, the maximum gradation value among the three gradation values of R, G, and B constituting one pixel is selected for each pixel. Then, the maximum gradation value is output to the subsequent subtraction circuit 53 and the multiplication ratio calculation circuit 58, and the other two gradation values are output to the subsequent multiplication circuit 93. For example, if the R gradation value is “200”, the G gradation value is “100”, and the B gradation value is “80”, the subtraction circuit 53 and the multiplication ratio calculation circuit with the R gradation value as the maximum gradation value 58, the G gradation value and the B gradation value are outputted to the multiplication circuit 93.

  The subtraction circuit 53 subtracts a preset high gradation value threshold value from the maximum gradation value output from the maximum value selection circuit 52. As an example of the high gradation value threshold value, for example, a numerical value that is about 60% with respect to the largest value that the gradation value can take (for example, when the largest value that the gradation value can take is “255”). The high gradation value threshold value is “150”. For example, if the maximum gradation value is “200” and the high gradation value threshold is “150”, the numerical value output from the subtraction circuit 53 is “50”.

  In the present invention, the high gradation value threshold value is not limited to this value. It is desirable that the high gradation value threshold value is appropriately set according to the characteristics of the panel 10, the specifications of the plasma display device 1, and the like.

  The subtracting circuit 53 outputs “0” when the maximum gradation value is equal to or lower than the high gradation threshold.

  The multiplication circuit 54 multiplies the numerical value output from the subtraction circuit 53 by the multiplication coefficient calculated by the multiplication coefficient calculation circuit 92. For example, if the maximum gradation value is “200”, the high gradation value threshold is “150”, and the numerical value output from the multiplication coefficient calculation circuit 92 is “0.6”, the multiplication circuit 54 is Then, “30” obtained by multiplying “50” output from the subtracting circuit 53 by “0.6” is output.

  The adder circuit 57 adds the output from the multiplier circuit 54 and the high gradation value threshold value. For example, if the high gradation value threshold is “150” and the numerical value output from the multiplication circuit 54 is “30”, the adder circuit 57 adds “180” obtained by adding “30” to “150”. Output. As described above, the numerical value output from the adder circuit 57 is a gradation value obtained by adding a correction based on the afterimage strength level to the portion of the maximum gradation value that exceeds the high gradation value threshold (hereinafter referred to as “correction”). It is referred to as a “maximum tone value after”.

  That is, the operations executed in the subtraction circuit 53, the multiplication coefficient calculation circuit 92, the multiplication circuit 54, and the addition circuit 57 are as follows.

Maximum gradation value after correction = ((predetermined reference value−afterimage frequency) / predetermined reference value) × (maximum gradation value−high gradation value threshold value) + high gradation value threshold value For example, as shown in FIG. When the afterimage strength level of the pixel A34 is a34, the maximum gradation value of the pixel A34 is M34, the predetermined reference value is “255”, and the high luminance threshold is “150”, the pixel A34 is output from the adder circuit 57. The corrected maximum gradation value M34 ′ is expressed by the following equation.

M34 ′ = ((255−a34) / 255) × (M34−150) +150
However, as will be described later, this calculation formula is effective only for pixels whose maximum gradation value is larger than the high luminance threshold.

  The multiplication ratio calculation circuit 58 divides the corrected maximum gradation value by the maximum gradation value. That is, the output of the multiplication ratio calculation circuit 58 is a numerical value that represents the ratio of the magnitude of the corrected maximum gradation value to the maximum gradation value. For example, if the maximum gradation value is “200” and the corrected maximum gradation value is “180”, the output of the multiplication ratio calculation circuit 58 is “0.9”.

  The multiplication circuit 93 multiplies the output of the multiplication ratio calculation circuit 58 by the two gradation values determined not to be the maximum value by the maximum value selection circuit 52. Then, the multiplication result is output as a corrected gradation value. For example, when the corrected maximum gradation value is corrected to 90% of the maximum gradation value by the above-described calculation based on the afterimage strength level (for example, R gradation value), the remaining of the same pixel Two tone values (for example, G tone value and B tone value) are also corrected to 90%. Accordingly, the magnitude of the corrected R gradation value with respect to the R gradation value before correction (post-delay R gradation value) and the corrected G gradation with respect to the pre-correction G gradation value (delayed G gradation value) The magnitude of the value and the magnitude of the B gradation value after correction with respect to the B gradation value before correction (B gradation value after delay) can be made equal to each other.

  The switch circuit 59 is corrected in accordance with the output of the addition circuit 57, that is, the corrected maximum gradation value to which the correction based on the afterimage strength is applied, and the output of the multiplication circuit 93, that is, the corrected maximum gradation value. The two corrected gradation values, the delayed R gradation value, the delayed G gradation value, the delayed B gradation value, and the output of the subtraction circuit 53, to which no correction is applied, are input. To do.

  Then, when the output of the subtraction circuit 53 is positive, that is, when the maximum gradation value is larger than the high luminance threshold value, the switch circuit 59 outputs a corrected maximum gradation value output from the addition circuit 57 and a multiplication circuit. The corrected gradation value output from the output terminal 93 is an R gradation value from the corrected R gradation value output terminal, and a G gradation value from the corrected G gradation value output terminal. A signal path switching process is appropriately performed internally so that the B gradation value is output from the B gradation value output terminal, and the corrected R gradation value, the corrected G gradation value, and the corrected B gradation value are output. Outputs gradation values. At this time, each gradation value is appropriately delayed and output so that the timing of the other stage signal matches with the other signal.

  When the output of the subtraction circuit 53 is “0”, that is, when the maximum gradation value is equal to or lower than the high luminance threshold value, the switch circuit 59 has a delayed R gradation value, a delayed G gradation value, and a delay. The post-B gradation value is appropriately delayed so as to match the timing of other signals in the subsequent circuit, and is output as a corrected R gradation value, a corrected G gradation value, and a corrected B gradation value. .

  Thus, the signal output from the switch circuit 59, that is, the corrected R gradation value, the corrected G gradation value, and the corrected B gradation value output from the correction circuit 82, has a maximum gradation value of a high gradation. For pixels larger than the value threshold value, a gradation value obtained by correcting the delayed R gradation value, the delayed G gradation value, and the delayed B gradation value based on the afterimage strength is obtained, and the maximum gradation value is For pixels that are equal to or lower than the high gradation value threshold value, they are gradation values that are not corrected for the delayed R gradation value, the delayed G gradation value, and the delayed B gradation value.

  Therefore, a pixel that is considered to be easily recognized when the afterimage phenomenon occurs with high emission luminance causes each discharge cell of R, G, and B to emit light with a gradation value that is corrected based on the afterimage strength, and the emission luminance is low. A pixel that is considered to be difficult to recognize even after the afterimage phenomenon can cause the R, G, and B discharge cells to emit light with gradation values that are not corrected based on the afterimage strength.

  As described above, the correction circuit 82 applies correction based on the afterimage strength level to the maximum gradation value, and corrects the remaining two gradation values according to the ratio of the corrected maximum gradation value to the maximum gradation value. Therefore, the magnitude of the corrected R gradation value with respect to the R gradation value before correction (delayed R gradation value) and the corrected G gradation with respect to the G gradation value before correction (delayed G gradation value) The magnitude of the value and the magnitude of the B gradation value after correction with respect to the B gradation value before correction (B gradation value after delay) can be made equal to each other. Accordingly, it is possible to reduce the luminance difference from the adjacent pixels and reduce the occurrence of the afterimage phenomenon while preventing a change in hue from occurring in the pixel to which correction based on the afterimage strength level is performed.

  Further, since the correction circuit 82 performs correction based on the afterimage strength level only for the pixels whose maximum gradation value is larger than the high gradation threshold value, it is possible to prevent the brightness of the display image from being lowered unnecessarily. it can.

  The predetermined reference value described above is an example of a numerical value that is set when the maximum value that the gradation value can take is “255”. However, in the present invention, the predetermined reference value is not limited to this value. 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.

  Next, the operation of the afterimage strength level calculation circuit 79 in a certain area will be described again with a specific example. FIG. 14 is a schematic diagram showing an operation example of the afterimage strength level calculating circuit 79 according to Embodiment 1 of the present invention. In FIG. 14, the vertical axis represents the afterimage strength level, the horizontal axis represents time, the solid line represents the afterimage strength level output from the afterimage strength level calculation circuit 279, and the broken line represents the afterimage strength level output from the afterimage strength level upper limit calculation circuit 179. Represents. In the afterimage strength level upper limit calculation circuit 179 and the afterimage strength level calculation circuit 279, it is assumed that the predetermined constant is set to “0”. It is assumed that the lower limit value is also set to “0”. At time t0, both the afterimage strength upper limit value and the afterimage strength level are “0”.

  Assuming that 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 at time t0, the first set value ( For example, “+1”) is cumulatively added, and the afterimage strength upper limit starts to increase at a rate of “+1” in one field. In addition, in the afterimage strength calculation circuit 279, the 11th set value or afterimage strength B is added to the afterimage strength, and the afterimage strength starts to increase. However, since the afterimage strength level is limited to the afterimage strength level upper limit value by the limiting circuit 291, it increases at the same rate as the afterimage strength level upper limit value.

  For example, even when the image sudden change detection circuit 110 detects that a sharp change has occurred in the brightness of the display image at time t1, even if the image sudden change detection result changes from “0” to “1”, the first If the 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 operations in the afterimage strength level upper limit calculation circuit 179 and the afterimage strength level calculation circuit 279 do not change. The afterimage strength continues to increase as before.

  When the first count value is less than the second threshold value or the second count value is less than the third threshold value at time t2, the afterimage strength level upper limit value is the third set value. (For example, “−4”) or a fourth set value (for example, “−4”) is cumulatively added, and the afterimage strength level upper limit value starts decreasing at a rate of “−4” in one field. At this time, when the sudden change in the brightness of the display image is detected in the image sudden change detection circuit 110, and the image sudden change detection result changes from “0” to “1”, the afterimage strength level is the fifth. A set value (for example, “−10”) is cumulatively added, and the afterimage strength starts to decrease more steeply (at a rate of −10 in one field) than the afterimage strength upper limit value.

  Once a steep decrease in the afterimage strength starts, even if the first count value or the second count value changes and the afterimage strength upper limit value starts to increase, the afterimage strength frequency is set to the lower limit value (for example, “0”). The steep decrease in the afterimage strength is continued until time t3 when) is reached.

  Then, at time t4 after the afterimage strength reaches the lower limit value, the first count value becomes greater than or equal to the first threshold value, the second count value becomes greater than or equal to the third threshold value, and the afterimage strength level. When the first set value is cumulatively added to the upper limit value and the afterimage strength upper limit value starts increasing at a rate of “+1” in one field, the eleventh set value is also cumulatively added to the afterimage strength level, and the afterimage strength level increases. Begin to. At this time, in the afterimage strength calculation circuit 279, the eleventh set value is selected by the selector 262 until the time t5 when the afterimage strength reaches the fourth threshold value. It increases at the rate of “+1”.

  When the afterimage strength reaches the fourth threshold value at time t5, the afterimage strength calculation circuit 279 selects the twelfth set value in the selector 262, and the afterimage strength is steep at a rate of “+10” in one field. To increase.

  Then, after time t6 when the afterimage strength reaches the afterimage strength upper limit, the afterimage strength becomes a value equal to the afterimage strength upper limit.

  The afterimage strength level is calculated in this way by the afterimage strength level calculation circuit 279 in the present embodiment for the following reason.

  For example, if an image on which a stationary white character is displayed on a dark background is continuously displayed on the panel 10, when the image changes from the symbol to another symbol, the region where the white character is displayed is displayed. An afterimage of white text may occur. Then, the afterimage of the region becomes stronger as the time during which white characters are continuously displayed (hereinafter referred to as “display duration”) becomes longer.

  The afterimage correction in this embodiment (referred to as “correction” described in the text) is a correction that detects the likelihood of afterimage generation for each pixel as the afterimage strength level, and lowers the light emission luminance in accordance with the magnitude of the afterimage strength level. It is to add to the image signal. This lowers the light emission luminance in the region where the afterimage is likely to occur, prevents the pattern that is likely to cause the afterimage from being burned onto the panel 10, and reduces the afterimage phenomenon. In addition, the afterimage frequency is gradually increased in accordance with the display duration time of the pattern where the afterimage is likely to be generated, so that the emission luminance can be further reduced as the display duration time of the pattern where the afterimage is likely to be generated becomes longer. In this way, the strength of correction is changed according to the ease of occurrence of afterimages.

  On the other hand, when the pattern of the display image changes from a pattern that tends to cause an afterimage to a pattern that hardly causes an afterimage (for example, a white image, etc.), correction was made to the area where the pattern that caused an afterimage was displayed If it is left as it is, the light emission luminance of the area is lowered and an unnatural image is displayed. For example, if the display image changes from an image with a static white character on a dark background to a full white image, and the area where the white character is displayed remains corrected, In the image, the luminance of the area remains lowered, and an unnatural image is displayed.

  In order to prevent such an unnatural image from being displayed, when the display image changes greatly, the afterimage strength of the area changes from a pattern that tends to cause an afterimage to a pattern that hardly causes an afterimage. It is desirable to reduce the correction as quickly as possible.

  Therefore, in the present embodiment, whether or not the display image changes suddenly is detected, and whether or not the pattern in which afterimages are likely to occur is changed to a pattern in which afterimages are unlikely to occur, and the afterimage strength is steeply determined based on the detection result. It is assumed that the correction is weakened.

  In the present embodiment, as shown in FIG. 8, the image sudden change detection circuit 110 compares the amount of change between the APL fields with the image sudden change comparison value to determine whether or not a sharp change occurs in the brightness of the display image. By detecting this, it is determined whether or not the display image changes suddenly. Further, as shown in FIG. 11, in the afterimage strength calculation circuit 279, the first count value is less than the second threshold value, or the second count value is less than the third threshold value. By detecting whether or not, it is determined whether or not the pattern from which an afterimage is likely to occur is changed to a pattern that is less likely to cause an afterimage.

  Then, a sudden change of the display image is detected by the image sudden change detection circuit 110 (in the example shown in FIG. 8, the image sudden change detection result is “1”), and the afterimage strength level calculation circuit 279 sets the first count value to the first count value. 2 or less than the third threshold value (in the example shown in FIG. 11, the comparison result of the comparison circuit 264 is “0”). Or the comparison result of the comparison circuit 265 is “0”), the selector 269 selects the fifth set value (“−10” in the example shown in FIG. 11), and the cumulative addition circuit 289. In FIG. 5, the fifth set value is added to the afterimage strength level, and the afterimage strength level in that region is sharply decreased until the lower limit value is reached.

  Thereby, in the present embodiment, when the display image changes greatly, in the region where the afterimage is likely to occur to the pattern in which the afterimage is unlikely to occur, the afterimage strength of the region is sharply decreased to weaken the correction, It is possible to prevent an unnatural image from being displayed by suppressing a decrease in luminance in the region.

  Note that the reason why the afterimage strength level is continuously decreased sharply until the afterimage strength level reaches the lower limit value is because processing for reducing the magnitude (tone value) of the image signal in proportion to the afterimage strength level is performed. This is because it is necessary to quickly restore the magnitude (gradation value) of the image signal when the value changes greatly.

  It should be noted that, when the pattern in which afterimages are likely to occur changes to a pattern in which afterimages are unlikely to occur but there is no significant change in the brightness of the display image (the first count value is less than the second threshold value, or the first When the count value of 2 is less than the third threshold value, but the image sudden change detection result is “0”), the design has only moved or changed, and the afterimage strength of the area is steeply changed. It can be determined that there is no need to decrease the value. Therefore, at that time, the selector 269 selects the third set value or the fourth set value (“−4” in the example shown in FIG. 11), and the cumulative adder 289 selects the third set value or It is assumed that the fourth set value is added to reduce the afterimage strength level of the area relatively slowly.

  Next, a description will be given of a case where after changing from a pattern that tends to cause an afterimage to a pattern that hardly causes an afterimage, the pattern is changed again to a pattern that tends to cause an afterimage. In such a case, depending on the time during which the pattern that is less likely to cause an afterimage is displayed, the area in which the pattern that is likely to cause an afterimage is displayed in the original image is more burned than the other areas. It is likely that afterimages are likely to occur.

  For this reason, when the pattern changes from a pattern in which afterimages are unlikely to occur to a pattern in which afterimages are likely to occur, it is desirable to increase the afterimage strength in that region as quickly as possible to increase the correction. Therefore, in the present embodiment, when the pattern is changed from a pattern in which an afterimage is unlikely to be generated to a pattern in which an afterimage is likely to be generated, the afterimage strength in that region is sharply increased to enhance the correction.

  That is, the first count value is equal to or greater than the first threshold value, the second count value is equal to or greater than the third threshold value, and the afterimage strength is equal to or greater than the fourth threshold value and less than the upper limit value of the afterimage strength level. (In the example shown in FIG. 11, the comparison result of the comparison circuit 263 and the comparison circuit 264 is “1”, the comparison result of the comparison circuit 265 is “1”, and When the comparison result of the comparison circuit 260 and the comparison circuit 261 is “1”), the selector 262 selects the twelfth set value (“+10” in the example shown in FIG. 11), and the cumulative addition circuit 289 It is assumed that the set value of 12 is added to the afterimage strength level, and the afterimage strength level of the area is increased sharply until reaching the upper limit value of the afterimage strength level.

  As a result, in the present embodiment, after changing from a pattern that tends to cause an afterimage to a pattern that is less likely to cause an afterimage, when the image changes again to a pattern that tends to cause an afterimage, the afterimage strength in that region is sharply increased. The correction of the area can be strengthened quickly.

  Note that if the time during which a pattern that is difficult to cause an afterimage is displayed is increased, the likelihood of image sticking also decreases. For this reason, if the afterimage strength is excessively increased, the correction is unnecessarily increased and the afterimage correction may be overcorrected. However, in the present embodiment, the afterimage strength level is limited by the afterimage strength level upper limit value, and the afterimage strength level upper limit value decreases according to the time during which the pattern in which afterimages are less likely to occur is displayed. Overcorrection can be prevented.

  In the present embodiment, when the afterimage strength level is increased in the afterimage strength level calculation circuit 279, the afterimage strength is relatively moderately increased using the 11th set value until the afterimage strength level reaches the fourth threshold value. After the frequency is increased and the afterimage strength reaches the fourth threshold, the afterimage strength is increased relatively steeply using the twelfth set value for the following reason.

  When the display image changes to a pattern that tends to cause an afterimage after changing from a pattern that tends to cause an afterimage to a pattern that tends to cause an afterimage, the display time of the pattern that tends to cause an afterimage is short, and an afterimage immediately appears. It may change to a pattern that is hard to occur. In such a case, it is desirable to reduce the afterimage strength in as short a time as possible. On the other hand, when the display image is changed to a pattern in which the afterimage is likely to occur again after changing from a pattern in which the afterimage is likely to occur to a pattern in which the afterimage is likely to occur, As described above, it is desirable to increase the afterimage strength as steep as possible.

  Therefore, in the present embodiment, in order to cope with these, the output of the selector 262 is changed based on the time until the afterimage strength reaches the fourth threshold value. That is, until the afterimage strength reaches the fourth threshold value, the display time of a pattern that tends to cause afterimage is short, the output of the selector 262 is set to the 11th set value, and the afterimage strength is relatively low. Increase gently. After the afterimage strength reaches the fourth threshold value, it is assumed that the display time of a pattern in which afterimages are likely to occur is long, and the output of the selector 262 is set to a twelfth set value that is larger than the eleventh set value. Increase frequency relatively steeply.

  As a result, when the afterimage strength level changes to a pattern in which afterimage strength hardly occurs until the fourth threshold value is reached, the increase in afterimage strength level can be relatively reduced in that region, and thereafter the afterimage strength level is quickly reduced. Can be made. Further, after the afterimage strength reaches the fourth threshold value, the afterimage strength in that region can be increased relatively steeply when a pattern that is likely to cause an afterimage is still displayed.

  The above is the reason why the output of the selector 262 is changed in the afterimage strength calculation circuit 279 until and after the afterimage strength reaches the fourth threshold value.

  As described above, in the present embodiment, the “afterimage strength”, which is a guide for occurrence of the afterimage phenomenon, is calculated for each pixel based on the gradation value of the luminance (Y), and the calculated afterimage strength and the maximum order are calculated. Based on the magnitude of the tone value, the R tone value, G tone value, and B tone value of each pixel are corrected. As a result, in an image in which an afterimage phenomenon is likely to occur, that is, in an image having a pattern in which the number of edges having a large luminance difference from adjacent pixels is large and a still area is continuously displayed, the luminance difference from adjacent pixels It is possible to reduce the occurrence of the afterimage phenomenon by reducing. At this time, since the ratio of the R, G, and B gradation values can be made the same before and after the correction, it is possible to prevent a hue change from occurring in the pixel to which the correction is applied. Can do. Further, since the correction is made based on the comparison between the maximum gradation value and the high gradation threshold value, it is possible to prevent the brightness of the display image from being lowered unnecessarily.

  Also, in the present embodiment, when the display image changes greatly, in an area where the pattern where an afterimage is likely to occur is changed to a pattern where an afterimage is unlikely to occur, the afterimage strength in that area is sharply decreased to weaken the correction. And This makes it possible to prevent the display of an unnatural image by suppressing a decrease in luminance in the area when the pattern from which an afterimage is likely to occur is changed to a pattern in which an afterimage is unlikely to occur.

  Further, in the present embodiment, the afterimage strength level calculation circuit 279 changes the output of the selector 262 with reference to the time until the afterimage strength level reaches the fourth threshold value, and the afterimage strength level is the fourth threshold value. Until the threshold value is reached, the output of the selector 262 is set to the eleventh set value, and after the afterimage strength reaches the fourth threshold value, the output of the selector 262 is set to a value greater than the eleventh set value. It is assumed that the set value is 12. As a result, when the afterimage strength changes to a pattern in which afterimage strength hardly occurs until the fourth threshold value is reached, the increase in afterimage strength in that region is relatively small, and then the afterimage strength is rapidly reduced. Can do. In addition, after the afterimage strength reaches the fourth threshold value, the afterimage strength in that region can be increased relatively steeply when a pattern that is likely to cause an afterimage is still displayed.

(Embodiment 2)
An image having a high average luminance level (APL) of the display image has high luminance as a whole, and accordingly, it is considered that there is little change in light emission luminance between adjacent pixels, and the number of edges is also reduced. 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 may be calculated from the image signal, and the afterimage strength may be changed according to the APL so that the afterimage strength is smaller when the APL is large than when the APL is small.

  FIG. 15 is a circuit block diagram showing a configuration example of the correction circuit 84 in the second embodiment of the present invention.

  The correction circuit 84 includes an APL calculation circuit 97, an afterimage strength correction circuit 96, a multiplication coefficient calculation circuit 92, a maximum value selection circuit 52, a subtraction circuit 53, a multiplication circuit 54, an addition circuit 57, and a multiplication ratio calculation. A circuit 58, a multiplier circuit 93, and a switch circuit 59 are included. In the correction circuit 84, the operation after the multiplication coefficient calculation circuit 92 is the same as the operation after the multiplication coefficient calculation circuit 92 in the correction circuit 82 shown in the first embodiment. Circuit blocks that perform the same operations as those in FIG. 82 are denoted by the same reference numerals as those shown in FIG.

  The APL calculation circuit 97 calculates the APL by using a generally known method such as calculating the sum of the gradation values of the luminance (Y) of all the pixels.

  The afterimage strength level correction circuit 96 changes the afterimage strength level according to the APL calculated by the APL calculation circuit 97. At this time, when the APL is large, the afterimage strength is changed so that the afterimage strength is smaller than when the APL is small.

  When the APL value calculated by the APL calculation circuit 97 is ap1, the afterimage strength level correction circuit 96 changes the afterimage strength level by multiplying the afterimage strength level by, for example, a numerical value obtained by the following calculation formula.

100%-(apl-40%)
(However, when apl-40% becomes 0 or less, apl-40% = 0)
Multiplication coefficient calculation circuit 92 and subsequent circuits perform the same operation as in the first embodiment. Thus, the corrected R gradation value, the corrected G gradation value, and the corrected B gradation value are output from the correction circuit 84.

  Thereby, in the correction circuit 84, the afterimage strength level can be changed according to the magnitude of the APL so that when the APL calculated by the APL calculation circuit 97 is large, the afterimage strength becomes smaller than when the APL is small. Each gradation value can be corrected according to the magnitude of the afterimage strength.

  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, in the present embodiment, the APL is calculated from the image signal, the afterimage strength is changed based on the calculated APL, and each tone value is corrected based on the changed afterimage strength. To change. Thereby, in an image with a high APL 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 APL. For example, a display image in an image with a high APL It is possible to reduce the occurrence of the afterimage phenomenon while preventing a decrease in luminance.

(Embodiment 3)
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. 16 is a circuit block diagram showing a configuration example of the correction circuit 87 according to Embodiment 3 of the present invention.

  The correction circuit 87 includes an afterimage strength correction circuit 101, a multiplication coefficient calculation circuit 92, a maximum value selection circuit 52, a subtraction circuit 53, a multiplication circuit 54, an addition circuit 57, a multiplication ratio calculation circuit 58, and a multiplication circuit. 93 and a switch circuit 59. In the correction circuit 87, the operation after the multiplication coefficient calculation circuit 92 is the same as the operation after the multiplication coefficient calculation circuit 92 in the correction circuit 82 shown in the first embodiment. Therefore, in this embodiment, the correction circuit Circuit blocks that perform the same operations as those in FIG. 82 are denoted by the same reference numerals as those shown in FIG. 13 and description thereof will be omitted, and only differences in configuration from the first embodiment will be described.

  The afterimage strength level correction circuit 101 changes the afterimage strength level according to 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.

  Multiplication coefficient calculation circuit 92 and subsequent circuits perform the same operation as in the first embodiment. Thus, the corrected R gradation value, the corrected G gradation value, and the corrected B gradation value are output from the correction circuit 87.

  Thereby, in the correction circuit 87, the afterimage strength level can be changed in accordance with the magnitude of the luminance magnification so that the afterimage strength level is smaller when the luminance magnification is small than when the luminance magnification is large. Each tone value can be corrected in accordance with the size of.

  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, in this embodiment, the afterimage strength level is changed based on the luminance magnification, and each gradation value is changed based on the changed afterimage strength level. 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 4)
In the third embodiment, the example in which the afterimage strength level is changed in accordance with the size of the brightness magnification is described so that the afterimage strength level becomes smaller when the brightness magnification is small than when the brightness magnification is large. Then, a correction circuit 87 is shown as a specific configuration example, and the afterimage strength correction is performed by multiplying the afterimage strength calculated by the afterimage strength interpolation circuit 80 by a numerical value that changes in accordance with the magnitude of the luminance magnification. A configuration in which the circuit 101 is provided is shown. However, the present invention is not limited to this configuration, and the same effect can be obtained using other configurations.

  FIG. 17 is a circuit block diagram showing a configuration example of the afterimage strength level upper limit calculation circuit 181 according to Embodiment 4 of the present invention. FIG. 18 is a circuit block diagram showing a configuration example of the afterimage strength level calculation circuit 281 in Embodiment 4 of the present invention. In FIG. 17, an afterimage strength level upper limit value calculation circuit 181 (1, 1) for calculating the afterimage strength level upper limit value of the block (1, 1) is shown as an example. ) To afterimage strength upper limit calculation circuit 181 (1, 2) to afterimage power upper limit calculation circuit 181 (M, N) for calculating the afterimage strength upper limit value in block (M, N) have the same configuration as FIG. . In FIG. 18, an afterimage strength level calculation circuit 281 (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 281 (1,2) to the afterimage strength level calculating circuit 281 (M, N) for calculating the afterimage strength level in (M, N) have the same configuration as that in FIG.

  In the present embodiment, the afterimage strength level upper limit calculation circuit 181 shown in FIG. 17 is different from the afterimage strength level upper limit calculation circuit 179 shown in FIG. 10 in that the first set value is changed according to the magnitude of the luminance magnification. It is the point which comprised so that it could do. Further, the afterimage strength level calculating circuit 281 shown in FIG. 18 is different from the afterimage strength level calculating circuit 279 shown in FIG. 11 in that the eleventh set value can be changed according to the luminance magnification. .

  For this purpose, the afterimage strength level upper limit calculation circuit 181 is configured to further include a selector 88 and a comparison circuit 69 in addition to the configuration of the afterimage strength level upper limit calculation circuit 179 shown in FIG. Further, the afterimage strength level calculation circuit 281 is configured to further include a selector 283 and a comparison circuit 282 in addition to the configuration of the afterimage strength level calculation circuit 279 shown in FIG.

  In the afterimage strength level upper limit calculation circuit 181, the circuit configuration excluding the selector 88 and the comparison circuit 69 and the operation of each circuit block are the same as those shown in the afterimage strength level upper limit calculation circuit 179. In the afterimage strength level calculation circuit 281, the circuit configuration excluding the selector 283 and the comparison circuit 282 and the operation of each circuit block are the same as those shown in the afterimage strength level calculation circuit 279. Therefore, in this embodiment, in the afterimage strength level upper limit calculation circuit 181, a circuit block that performs the same operation as that of the afterimage strength level upper limit calculation circuit 179 is assigned the same code as that shown in FIG. In the circuit 281, circuit blocks that perform the same operation as the afterimage strength level calculation circuit 279 are assigned the same reference numerals as those shown in FIG. 11 and description thereof is omitted.

  In the afterimage strength level upper limit calculation circuit 181, the comparison circuit 69 compares the luminance magnification with a preset fifth threshold value, and outputs “1” when the luminance magnification is equal to or greater than the fifth threshold value. When the luminance magnification is less than the fifth 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 fifth 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 first when the luminance magnification is less than 3 times. “0” is input to the selector 66 as a set value.

  In the afterimage strength level calculation circuit 281, the comparison circuit 282 compares the luminance magnification with the fifth threshold value, and outputs “1” when the luminance magnification is equal to or higher than the fifth threshold value. When it is less than the threshold value, “0” is output.

  The selector 283 outputs a positive numerical value, for example, “+1” when the output of the comparison circuit 282 is “1”, and outputs “0”, for example, when the output of the comparison circuit 282 is “0”.

  The numerical value output from the selector 283 is input to the subsequent selector 262 as the eleventh set value. For example, if the fifth threshold value is “3”, “+1” is input to the selector 262 as the eleventh set value when the luminance magnification is three times or more, and eleventh when the luminance magnification is less than three times. As a set value, “0” is input to the selector 262.

  As described above, in the afterimage strength level upper limit calculation circuit 181 shown in the present embodiment, the size of the first set value can be changed according to the magnitude of the luminance magnification. In the afterimage strength level calculation circuit 281, The eleventh set value can be changed according to the luminance magnification. Therefore, 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.

  As a result, the afterimage strength level upper limit calculation circuit 181 and the afterimage strength level calculation circuit 281 are shown in, for example, the afterimage strength level upper limit value calculation circuit 179 shown in FIG. 10 and the FIG. 11 when the luminance magnification is the fifth threshold value or more. It is possible to operate in the same manner as the afterimage strength level calculation circuit 279 so that the afterimage strength level does not increase regardless of the design of the display image when the luminance magnification is less than the fifth threshold value.

  It should be noted that the above-described numerical values selected by the selector 88 and the selector 283 are merely examples. 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 and the selector 283 are not limited to a 2-input 1-output selection circuit. For example, the comparison circuit 69 and the comparison circuit 282 may compare two or more threshold values with the luminance magnification, and the selector 88 and the selector 283 may be a selection circuit that can select three inputs, one output, or more. It doesn't matter.

  As described above, in the present embodiment, the luminance magnification and the fifth threshold value are compared, and the first set value and afterimage strength level calculation circuit 281 in the afterimage strength level upper limit calculation circuit 181 based on the comparison result. The eleventh set value at is changed. Accordingly, when the luminance magnification is equal to or higher than the fifth threshold value, that is, when it is considered that the emission luminance is relatively high and the afterimage phenomenon is relatively likely to occur, for example, the afterimage strength upper limit calculation circuit 179 and the afterimage strength calculation When the afterimage strength is calculated by the same operation as the circuit 279 and the luminance magnification is smaller than the fifth threshold value, that is, when the emission luminance is relatively low and the afterimage phenomenon is considered to be relatively difficult to occur, for example, It is possible to prevent the afterimage strength from increasing regardless of the design of the display image. Therefore, it is possible to reduce the occurrence of the afterimage phenomenon while preventing a decrease in luminance of an image displayed when the luminance magnification is small.

(Embodiment 5)
In the plasma display device 1, for example, by smoothing each gradation value, it is possible to reduce the change in light emission luminance between adjacent pixels and further reduce the occurrence of an afterimage phenomenon. Therefore, in the present embodiment, a configuration will be described in which smoothing according to the afterimage strength level is applied to each corrected gradation value.

  FIG. 19 is a circuit block diagram showing a configuration example of the correction circuit 85 according to the fifth embodiment of the present invention.

  The correction circuit 85 includes a multiplication coefficient calculation circuit 92, a maximum value selection circuit 52, a subtraction circuit 53, a multiplication circuit 54, an addition circuit 57, a multiplication ratio calculation circuit 58, a multiplication circuit 93, and a switch circuit 59. , A delay circuit 99 and a smoothing circuit 98. In the correction circuit 85, the operation of each circuit block excluding the smoothing circuit 98 and the delay circuit 99 is the same as the operation of each circuit block in the correction circuit 82 shown in the first embodiment. Then, the same reference numerals as those shown in FIG. 13 are given to circuit blocks that perform the same operations as those of the correction circuit 82, and the description thereof will be omitted. Only the parts different in configuration from the first embodiment will be described.

  The delay circuit 99 appropriately delays the afterimage strength so that the R, G, and B gradation values coincide with the afterimage strength in the smoothing circuit 98.

  The smoothing circuit 98 applies the R, G, and B gradation values output from the switch circuit 59 to the same color gradation values of other pixels, that is, for the R gradation value. Between the R gradation value of another pixel, for the G gradation value, between the G gradation value of the other pixel, and for the B gradation value, Smoothing according to the afterimage strength level is performed between the B gradation values of the pixels. 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 each gradation value, and a change in light emission luminance between adjacent pixels can be reduced by this smoothing to further reduce the occurrence of afterimage phenomenon.

  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, in the present embodiment, each gradation value after correction based on the afterimage strength level is smoothed according to the afterimage strength level. Thereby, each corrected gradation value can be smoothed according to the magnitude of the afterimage strength level. Therefore, it is possible to further reduce the change in light emission luminance between adjacent pixels and further reduce the occurrence of afterimage phenomenon.

  In the present invention, the configurations shown in the first to fifth embodiments 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, in the subtraction circuit 74, the gradation value of the luminance (Y) of each pixel and the gradation value of the luminance (Y) one pixel before output from the one-pixel delay circuit 73. In the above description, the luminance difference between adjacent pixels is calculated and used between two adjacent pixels (horizontal adjacent pixels) in the direction in which the display electrode pair 24 extends. However, the present invention is not limited to this configuration. For example, by subtracting the gradation value of the luminance (Y) of each pixel from the gradation value of the luminance (Y) one horizontal period ago, two pixels (vertical) adjacent in the direction in which the data electrode 32 extends. A configuration in which a luminance difference between adjacent pixels is calculated and used between adjacent pixels) may be used. Alternatively, the luminance value (Y) of each pixel is subtracted from the gradation value of the luminance (Y) before (one horizontal period + 1 pixel), and the luminance (Y) before (one horizontal period−1 pixel). The luminance difference between the adjacent pixels may be calculated and used between the two pixels adjacent in the diagonal direction on the panel 10 by performing subtraction with the gradation value of (). 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 in 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. Similarly, the first setting value, the eleventh setting value, the twelfth setting value, the second setting value, the third setting value, the fourth setting value, the fifth setting value, the first setting value, The threshold value, the second threshold value, and the third threshold value may be changed depending on the location of the panel 10.

  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 electrode structure in which 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 “. It is also effective in a panel having an electrode structure of “electrode, 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 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 51 Luminance gradation value calculation circuit 52 Maximum value selection circuit 53, 71, 74, 90, 113, 290 Subtraction circuit 54, 93 Multiplication circuit 55, 99, 272 Delay Circuit 56 RGB correction circuit 57 Addition circuit 58 Multiplication ratio calculation circuit 59 Switch circuit 63, 64, 65, 69, 72, 75, 114, 260, 261, 263, 264, 265, 270, 282 Comparison circuit 66, 67, 68 , 88, 262, 266, 267, 268, 269, 27 , 283 selector 70, 112 1 field delay circuit 73 1 pixel delay circuit 76 block timing generation circuit 77, 78 counting circuit 79 afterimage strength level calculation circuit 80 afterimage strength level interpolation circuit 82, 84, 85, 87 correction circuit 89, 289 cumulative addition circuit 91,291 Limiting circuit 92 Multiplication coefficient calculating circuit 96,101 Afterimage strength level correcting circuit 97,111 APL calculating circuit 98 Smoothing circuit 110 Image sudden change detecting circuit 179,181 Afterimage strength level upper limit calculating circuit 279,281 Afterimage strength level calculating circuit 273 274 Inverter 275,277 or gate 276,278 AND gate

Claims (17)

A plasma display panel comprising a plurality of discharge cells each having a display electrode pair consisting of a scan electrode and a sustain electrode and a data electrode and having one pixel composed of three discharge cells emitting light in red, green and blue colors, And a plurality of subfields having a sustain period are driven in one field, and each of the three discharge cells has a brightness according to the size of each of the red, green, and blue gradation values based on the image signal. A method of driving a plasma display panel that emits light and displays gradation,
The average luminance level of the image signal is calculated for each field, the absolute value of the amount of change in the average luminance level between the fields is calculated, the absolute value is compared with a preset image sudden change comparison value, and the comparison result is calculated. The image sudden change detection result,
Dividing the display area of the plasma display panel into a plurality of areas;
An afterimage strength upper limit value is calculated for each region based on the luminance gradation value of each pixel based on an image signal, and the region is based on the luminance gradation value, the image sudden change detection result, and the afterimage strength upper limit value. Calculating the afterimage strength for each pixel, calculating the afterimage strength for each pixel based on the afterimage strength for each region,
Select the maximum gradation value among the three gradation values of red, green, and blue for each pixel,
For each pixel, the corrected maximum gradation value is calculated by correcting the maximum gradation value based on the afterimage strength level, and the ratio of the size of the corrected maximum gradation value to the maximum gradation value is obtained. A method for driving a plasma display panel, comprising: correcting two gradation values excluding the maximum gradation value based on the ratio. 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,
2. The method of driving a plasma display panel according to claim 1, wherein the afterimage strength level and the afterimage strength level upper limit value for each region are calculated based on the first count value and the second count value. When updating the afterimage strength upper limit value,
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 first set value is added to the afterimage strength level upper limit value. ,
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 an area that is greater than or equal to the threshold value, the second set value is added to the afterimage strength upper limit value,
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, a third set value is set as the afterimage strength level upper limit value. Add,
In a region where the second count value is less than the third threshold value, a fourth set value is added to the afterimage strength level upper limit value,
When updating the afterimage strength for each area,
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 afterimage strength level for each area is a fourth threshold value. An eleventh set value is added to the afterimage strength level for each region when the value is less than the value, and the afterimage strength level for each region when the afterimage strength level for each region is equal to or greater than the fourth threshold and less than the upper limit value for the afterimage strength level. To the twelfth set value whose numerical value is larger than the eleventh set value,
In the 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, for each region The second set value is added to the afterimage strength of
When the absolute value of the amount of change between fields of the average luminance level is less than the image sudden change comparison value,
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, the afterimage strength level for each area is set to the third setting value. In the 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,
When the absolute value of the amount of change between the fields of the average luminance level is equal to or greater than the image sudden change comparison value,
In a region where the first count value is less than the second threshold value or the second count value is less than the third threshold value, a lower limit in which the afterimage strength level for each region is set in advance 3. The method of driving a plasma display panel according to claim 2, wherein the fifth set value set to a negative value is continuously added to the afterimage strength level for each area until the value is reached. Setting the first set value to a positive value, setting the first set value and the eleventh set value to be equal to each other, and setting the second set value to “0”; The third set value and the fourth set value are set to negative numbers, and the absolute value of the fifth set value is larger than the absolute values of the third set value and the fourth set value. 4. The method of driving a plasma display panel according to claim 3, wherein a numerical value is set, and the lower limit value is set to a numerical value smaller than the fourth threshold value. 4. The method of driving a plasma display panel according to claim 3, wherein a predetermined constant is subtracted from the updated afterimage strength. 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 first set value and the eleventh set value are changed according to the magnitude of the luminance magnification. When the luminance magnification is greater than or equal to a fifth threshold value, the first set value and the eleventh set value are positive numbers,
7. The method of driving a plasma display panel according to claim 6, wherein when the luminance magnification is less than a fifth threshold value, the first set value and the eleventh set value are set to “0”. 2. The method of driving a plasma display panel according to claim 1, wherein the upper limit value of the afterimage strength level 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. 2. The maximum gradation value of each pixel is corrected based on a result obtained by subtracting the afterimage strength level for each pixel from a predetermined reference value and dividing the subtraction result by the reference value. Driving method of plasma display panel. The afterimage strength level for each pixel is changed based on the average brightness level so that the afterimage strength level is smaller when the average brightness level is large than when the average brightness level is small. Driving method of the plasma display panel. 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. When the maximum gradation value is larger than a preset high gradation value threshold value, the high gradation value threshold value is subtracted from the maximum gradation value, and the afterimage strength level is subtracted from the subtraction result. 2. The method of driving a plasma display panel according to claim 1, wherein the correction is based on the result, and the result of adding the high gradation value threshold to the correction result is used as the corrected maximum gradation value. 2. The gradation value of each pixel is smoothed based on the afterimage strength level for each pixel so that the gradation value is smoothed when the afterimage strength level is large compared to when the afterimage strength level is small. A method for driving a plasma display panel according to claim 1. 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 plurality of boundaries are provided in a direction in which the data electrode extends to set the region. 2. A driving method of a plasma display panel according to 1. A plurality of discharge cells each having a display electrode pair consisting of a scan electrode and a sustain electrode, each pixel being composed of three discharge cells emitting light in red, green and blue colors, and having an address period and a sustain period A plasma display panel in which a plurality of fields are provided in one field, and each of the three discharge cells emits light at a brightness corresponding to the size of each gradation value of red, green, and blue based on an image signal. When,
In accordance with the image signal, each gradation value of red, green, and blue is set for each of the three discharge cells of each pixel, and according to the magnitude of the gradation value, the light emission for each subfield in the discharge cell is set. An image signal processing circuit for creating image data indicating non-light emission,
The image signal processing circuit includes:
The average luminance level of the image signal is calculated for each field, the absolute value of the amount of change in the average luminance level between the fields is calculated, the absolute value is compared with a preset image sudden change comparison value, and the comparison result is calculated. It has an image sudden change detection circuit that outputs as an image sudden change detection result,
Dividing the display area of the plasma display panel into a plurality of areas;
An afterimage strength upper limit value is calculated for each region based on the luminance gradation value of each pixel based on an image signal, and the region is based on the luminance gradation value, the image sudden change detection result, and the afterimage strength upper limit value. Calculating the afterimage strength for each pixel, calculating the afterimage strength for each pixel based on the afterimage strength for each region,
Select the maximum gradation value among the three gradation values of red, green, and blue for each pixel,
For each pixel, the corrected maximum gradation value is calculated by correcting the maximum gradation value based on the afterimage strength level, and the ratio of the size of the corrected maximum gradation value to the maximum gradation value is obtained. A plasma display apparatus comprising an RGB correction circuit for correcting two gradation values excluding the maximum gradation value based on the ratio. The image signal processing circuit includes:
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,
When updating the afterimage strength upper limit value,
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 first set value is added to the afterimage strength level upper limit value. ,
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 an area that is greater than or equal to the threshold value, the second set value is added to the afterimage strength upper limit value,
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, a third set value is set as the afterimage strength level upper limit value. Add,
In a region where the second count value is less than the third threshold value, a fourth set value is added to the afterimage strength level upper limit value,
When updating the afterimage strength for each area,
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 afterimage strength level for each area is a fourth threshold value. The eleventh set value is added to the afterimage strength level for each region when the value is less than the value, and the afterimage strength level for each region when the afterimage strength level for each region is equal to or greater than the fourth threshold value and less than the upper limit value for the afterimage strength level. To the twelfth set value whose numerical value is larger than the eleventh set value,
In the 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, for each region The second set value is added to the afterimage strength of
When the image sudden change detection circuit determines that the absolute value is less than the image sudden change comparison value,
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, the afterimage strength level for each area is set to the third setting value. In the 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,
When the image sudden change detection circuit determines that the absolute value is greater than or equal to the image sudden change comparison value,
In a region where the first count value is less than the second threshold value or the second count value is less than the third threshold value, a lower limit in which the afterimage strength level for each region is set in advance The plasma display device according to claim 16, wherein the fifth set value set to a negative numerical value is continuously added to the afterimage strength level for each region until the value is reached.

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