WO2009090751A1 - Plasma display unit and method for processing the same - Google Patents

Plasma display unit and method for processing the same Download PDF

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Publication number
WO2009090751A1
WO2009090751A1 PCT/JP2008/050608 JP2008050608W WO2009090751A1 WO 2009090751 A1 WO2009090751 A1 WO 2009090751A1 JP 2008050608 W JP2008050608 W JP 2008050608W WO 2009090751 A1 WO2009090751 A1 WO 2009090751A1
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WIPO (PCT)
Prior art keywords
subfield
gradation
circuit
plasma display
image signal
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PCT/JP2008/050608
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French (fr)
Japanese (ja)
Inventor
Masanori Takeuchi
Koji Nagata
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Hitachi, Ltd.
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Application filed by Hitachi, Ltd. filed Critical Hitachi, Ltd.
Priority to PCT/JP2008/050608 priority Critical patent/WO2009090751A1/en
Publication of WO2009090751A1 publication Critical patent/WO2009090751A1/en

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    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/22Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
    • G09G3/28Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels
    • G09G3/288Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using luminous gas-discharge panels, e.g. plasma panels using AC panels
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0261Improving the quality of display appearance in the context of movement of objects on the screen or movement of the observer relative to the screen
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0266Reduction of sub-frame artefacts
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00Aspects of the architecture of display systems
    • G09G2360/16Calculation or use of calculated indices related to luminance levels in display data
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2018Display of intermediate tones by time modulation using two or more time intervals
    • G09G3/2022Display of intermediate tones by time modulation using two or more time intervals using sub-frames
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007Display of intermediate tones
    • G09G3/2059Display of intermediate tones using error diffusion

Definitions

  • the present invention relates to a plasma display device and a processing method thereof.
  • a specific subfield lighting pattern is combined with a subfield lighting pattern of an adjacent pixel, so that a large gradation value is displayed for a human eye during animation.
  • a so-called moving image pseudo contour that appears as if there is a pseudo contour may be generated.
  • a technique for displaying an image without using a subfield lighting pattern that easily generates a moving image pseudo contour has been proposed (for example, see Patent Document 1).
  • the number of subfield lighting patterns is smaller than the number of input gradations, and gradation values that cannot be displayed by the subfield lighting pattern are subfield lighting patterns before and after the gradation value. Is expressed in combination with space or time. As a result, gradation expression is performed only with the subfield lighting pattern in which the moving image pseudo contour is less likely to occur. However, since the halftone that cannot be expressed by the subfield lighting pattern is expressed by error diffusion processing, granular noise may be seen in the display image depending on the gradation value.
  • a plasma display apparatus that includes a plurality of subfields each having a weighted number of sustain pulses, and that represents gradation of an image by selecting lighting or non-lighting of the subfield.
  • a measurement circuit that measures the appearance frequency of a specific gradation group in the first image signal for each field, and weights the plurality of subfields according to the appearance frequency measured by the measurement circuit.
  • the first image signal is nonlinearly converted into a second image signal so as not to use a predetermined lighting pattern
  • the second image signal A non-linear conversion circuit that expresses an image signal by a real part and an error part, and an error part of the error part of the second image signal subjected to error diffusion processing spatially or temporally.
  • a plasma display apparatus and a lighting pattern conversion circuit that replaces the predetermined lighting pattern in the other lighting patterns are provided.
  • the appearance frequency of a specific gradation group in the first image signal is measured, and the gradation group having a high appearance frequency has many gradations expressed without performing error diffusion processing and using a predetermined lighting pattern.
  • the weights of the plurality of subfields it is possible to reduce the number of pixels displayed by error diffusion and suppress the generation of granular noise while suppressing the generation of the moving image pseudo contour.
  • FIG. 1 is a diagram illustrating a configuration example of the plasma display device according to the first embodiment.
  • 2A is a diagram showing a cross-sectional configuration example of the display cell shown in FIG.
  • FIG. 2B is a diagram for explaining the panel capacity of the AC-driven plasma display panel.
  • FIG. 2C is a diagram for explaining light emission of the AC drive type plasma display.
  • FIG. 3 is a diagram illustrating a configuration example of one field of an image.
  • FIG. 4 is a diagram illustrating a configuration example of the histogram measurement circuit.
  • FIG. 5 is a diagram showing an example of the subfield arrangement selection table.
  • FIG. 6 is a diagram showing a first subfield arrangement and output gradation values in the first embodiment.
  • FIG. 7 is a diagram showing a second subfield arrangement and output gradation values in the first embodiment.
  • FIG. 8 is a diagram showing a third subfield arrangement and output gradation values in the first embodiment.
  • FIG. 9 is a diagram showing a fourth subfield arrangement and output gradation values in the first embodiment.
  • FIG. 10 is a diagram illustrating a configuration example of the plasma display device according to the second embodiment.
  • FIG. 1 is a diagram illustrating a configuration example of the plasma display device according to the first embodiment.
  • the plasma display device according to the first embodiment includes an inverse gamma conversion processing circuit 10, a delay circuit 20, a nonlinear gain circuit 30, an error diffusion circuit 40, a subfield conversion circuit 50, a display load factor detection circuit 60 for each subfield, a sustain pulse.
  • the address electrode drive circuit 121 supplies a predetermined voltage to the address electrodes A1, A2,.
  • each of the address electrodes A1, A2,... Or their generic name is referred to as an address electrode Aj, where j means a subscript.
  • the sustain electrode drive circuit 122 supplies a predetermined voltage to the X electrodes (sustain electrodes) X1, X2,.
  • X electrodes stain electrodes
  • Xi each of the X electrodes X1, X2,... Or their generic name is referred to as an X electrode Xi, and i means a subscript.
  • the scan electrode driving circuit 123 supplies a predetermined voltage to the Y electrodes (scan electrodes) Y1, Y2,.
  • Y electrodes scan electrodes
  • Y electrode Yi each of the Y electrodes Y1, Y2,... Or their generic name is referred to as a Y electrode Yi, and i means a subscript.
  • the Y electrode Yi and the X electrode Xi form a row extending in parallel in the horizontal direction, and the address electrode Aj forms a column extending in the vertical direction.
  • the Y electrodes Yi and the X electrodes Xi are alternately arranged in the vertical direction.
  • the Y electrode Yi and the address electrode Aj form a two-dimensional matrix with i rows and j columns.
  • the display cell Cij is formed by the intersection of the Y electrode Yi and the address electrode Aj and the X electrode Xi adjacent thereto corresponding thereto.
  • This display cell Cij corresponds to, for example, red, green, and blue sub-pixels, and one pixel is constituted by these three-color sub-pixels.
  • the plasma display panel 124 can display a two-dimensional image by lighting a plurality of pixels arranged two-dimensionally.
  • FIG. 2A is a diagram showing a cross-sectional configuration example of the display cell Cij in FIG.
  • the X electrode Xi and the Y electrode Yi are formed on the front glass substrate 211.
  • a dielectric layer 212 for insulating the discharge space 217 is deposited thereon, and an MgO (magnesium oxide) protective film 213 is further deposited thereon.
  • the address electrode Aj is formed on a rear glass substrate 214 disposed opposite to the front glass substrate 211, and a dielectric layer 215 is deposited thereon, and further a phosphor is deposited thereon. ing. Ne + Xe Penning gas or the like is sealed in the discharge space 217 between the MgO protective film 213 and the dielectric layer 215.
  • FIG. 2B is a diagram for explaining the panel capacitance Cp of the AC drive type plasma display panel.
  • the capacity Ca is the capacity of the discharge space 217 between the X electrode Xi and the Y electrode Yi.
  • the capacitance Cb is the capacitance of the dielectric layer 212 between the X electrode Xi and the Y electrode Yi.
  • the capacitance Cc is the capacitance of the front glass substrate 211 between the X electrode Xi and the Y electrode Yi. The sum of these capacitors Ca, Cb, and Cc determines the panel capacitance Cp between the electrodes Xi and Yi.
  • FIG. 2C is a diagram for explaining light emission of the AC drive type plasma display.
  • red, blue, and green phosphors 218 are arranged and applied in stripes for each color, and the phosphor 218 is excited by the discharge between the X electrode Xi and the Y electrode Yi to emit light. 221 is generated.
  • FIG. 3 is a diagram illustrating a configuration example of one field FD of an image.
  • the image is formed at 60 fields / second, for example.
  • One field FD is formed by a first subfield SF1, a second subfield SF2,..., An nth subfield SFn. This n is, for example, 10.
  • Each of the subfields SF1, SF2, etc. or their generic name is hereinafter referred to as a subfield SF.
  • Each subfield SF includes a reset period Tr, an address period Ta, and a sustain (sustain discharge) period Ts.
  • the reset period Tr the display cell is initialized.
  • the address period Ta light emission or non-light emission of each display cell can be selected by address discharge between the address electrode Aj and the Y electrode Yi.
  • the sustain period Ts a sustain discharge is performed between the X electrode Xi and the Y electrode Yi of the selected display cell to emit light.
  • the number of times of light emission (the length of the sustain period Ts) corresponding to the number of sustain pulses between the X electrode Xi and the Y electrode Yi is different. Thereby, the gradation value can be determined.
  • the plasma display panel 124 is composed of a plurality of subfields each having a weighted sustain pulse number, and the image is expressed in gradation by selecting a pattern of subfields to be lit among the plurality of subfields. Can do.
  • the inverse gamma conversion processing circuit 10 receives the digital image signal S1, performs inverse gamma conversion, and outputs an image signal S2 having linear characteristics.
  • the delay circuit 20 delays and outputs the image signal S2 for a predetermined time corresponding to the processing time in the histogram measurement circuit 130 and the subfield arrangement selection circuit 140.
  • the nonlinear gain circuit 30 nonlinearly converts the delayed image signal S2 into an image signal S3 so as not to use a specific subfield lighting pattern, and the image signal S3 is converted into an integer part (real part) and a decimal part (error part).
  • the nonlinear gain circuit 30 converts the image signal S2 into an image signal S3 based on a nonlinear parameter (mixing ratio distribution related to error diffusion processing) corresponding to the subfield arrangement selected by the subfield arrangement selection circuit 140.
  • the error diffusion circuit 40 receives the image signal S3. When the decimal part of the image signal S3 is not 0, the error diffusion circuit 40 spreads the decimal part spatially or temporally to generate an image signal S4 for performing pseudo gradation expression. Output.
  • a subfield lighting pattern signal S5 is generated.
  • the address electrode drive circuit 121 generates a voltage of the address electrode Aj for selecting a subfield to be lit for each pixel according to the subfield lighting pattern signal S5.
  • the display load factor detection circuit 60 for each subfield calculates a display load factor T2 for each subfield based on the subfield lighting pattern signal S5.
  • the display load factor is detected based on the number of pixels that emit light and the gradation value of the pixels that emit light. For example, when all the pixels of the image are displayed with the maximum gradation value, the display load factor is 100%. Further, when all the pixels of the image are displayed with 1/2 of the maximum gradation value, the display load factor is 50%. The display load factor is also 50% when only half (50%) of the image is displayed with the maximum gradation value.
  • the sustain pulse number setting circuit 70 inputs the timing signal T1 and the display load factor T2, and calculates the total sustain pulse number of one field by constant power control according to the display load factor of one field. Further, the sustain pulse number setting circuit 70 divides the total number of sustain pulses so as to be the ratio of the weights of the subfields according to the subfield arrangement selected by the subfield arrangement selection circuit 140.
  • the total number of sustain pulses in one field is controlled according to the display load factor in one field. Regardless of the display load factor, if the total number of sustain pulses in one field is made constant, the larger the display load factor, the larger the electric power and the greater the amount of heat. Therefore, when the display load factor of one field is large, calculation is performed so as to reduce the total number of sustain pulses in one field, and constant power control is performed.
  • the drive signal generation circuit 80 generates a sustain pulse signal for display according to the output of the sustain pulse number setting circuit 70.
  • the sustain electrode drive circuit 122 and the scan electrode drive circuit 123 generate voltages for the X electrode Xi and the Y electrode Yi in accordance with the sustain pulse signal.
  • the display cell selected by the address electrode Aj emits light by sustain discharge between the X electrode Xi and the Y electrode Yi.
  • the histogram measurement circuit 130 measures a histogram of a specific gradation group in the image signal for each field based on the image signal S2 output from the inverse gamma conversion processing circuit 10.
  • the subfield array selection circuit 140 selects one subfield array from a plurality of subfield arrays based on the measurement result of the histogram measurement circuit 130.
  • the subfield arrangement selection circuit 140 outputs the selected subfield arrangement to the sustain pulse setting circuit 70 and outputs a non-linear parameter corresponding thereto to the non-linear gain circuit 30.
  • the weights (luminance ratios) of the subfields constituting one field are set in each subfield array, and the weight ratios of the subfields are different between the subfield arrays.
  • the histogram measurement circuit 130 has a gradation group discrimination circuit 131, counters 132 to 134, and comparators 135 to 137.
  • the tone group discrimination circuit 131 receives the image signal S2 from the inverse gamma conversion processing circuit 10 and discriminates which tone group the input signal is from.
  • the gradation group includes the highest gradation value (gradation value before carry) among gradation values in which the largest subfield for lighting the display cell Cij is the n-th subfield, and the maximum lighting value.
  • the subfield is configured to include at least the lowest gradation value (gradation value after carry) of the gradation values of the (n + 1) th subfield.
  • the largest subfield to be lit may include a gradation value that is the next smallest to the lowest gradation value among the gradation values of the (n + 1) th subfield.
  • a plurality of tone values may be included in ascending order.
  • the gradation group includes the highest gradation value among gradation values in which the largest subfield for lighting the display cell Cij is the nth subfield, and the largest subfield for lighting (n + 1). ) It is assumed that the lowest gradation value among the gradation values which are the first subfield and the gradation value next to the lowest gradation value are included.
  • Counters 132 to 134 are provided corresponding to each gradation group.
  • the first gradation group counter 132 corresponding to the first gradation group
  • the second gradation group counter 133 corresponding to the second gradation group
  • the Nth gradation corresponding to the Nth gradation group A group counter 134 is illustrated.
  • Each of the counters 132 to 134 is reset (initialized) by the vertical synchronization signal, and counts up according to the determination result in the gradation group determination circuit 131, thereby obtaining the corresponding gradation group in the image signal.
  • the number of appearances of the gradation value to which it belongs is measured for each field.
  • Comparators 135 to 137 compare the values set in advance by the MPU 150 with the counter values measured by the counters 132 to 134 of each gradation value group, and according to the number of appearances of the gradation values belonging to the gradation group.
  • Appearance frequency coefficients AC1 to ACN are determined and output.
  • the number of pixels that display gradation values belonging to a gradation group exceeds 50% among all the pixels in one field, “2” is output as the appearance frequency coefficient of the gradation group.
  • “1” is output as the appearance frequency coefficient of the gradation group
  • “0” is output as the appearance frequency coefficient of the gradation group if it is lower than 15%.
  • the setting value for determining the appearance frequency coefficient may be made different depending on the gradation group by comparing with the counter values of the counters 132 to 134.
  • the difference is conspicuous in the low luminance part of the display image, and the difference is inconspicuous in the high luminance part, so set the setting value so that the appearance frequency coefficient is high in the low luminance gradation group.
  • the set value may be set so that the appearance frequency coefficient is low.
  • the subfield arrangement selection circuit 140 has a subfield arrangement selection table composed of a plurality of subfield arrangements as shown in FIG.
  • the subfield arrangement selection circuit 140 selects a subfield arrangement corresponding to the image to be displayed based on the appearance frequency coefficients AC1 to ACN of each gradation group output from the histogram measurement circuit 130, and nonlinearly according to the selection result.
  • the parameter of the gain circuit 30 is changed.
  • the subfield arrangement selection circuit 140 turns on the subfield without performing diffusion processing on many of the gradation values belonging to the gradation group having a high appearance frequency according to the appearance frequency coefficients AC1 to ACN of each gradation group.
  • a subfield arrangement is selected so as to reduce the average luminance difference between gradations expressed by the subfield lighting pattern so that it can be expressed by a pattern. That is, the subfield arrangement is selected so that the number of gradation values that cannot be expressed only by the subfield lighting pattern is reduced in the gradation group having a high appearance frequency.
  • the number of gradation values that can be expressed only by the subfield lighting pattern without performing the diffusion process is increased according to the appearance frequency of the gradation in the image signal without changing the subfield lighting pattern.
  • the weight (luminance ratio) of each subfield is changed. This reduces the ratio of the number of pixels displayed by error diffusion to the total number of pixels while suppressing the occurrence of moving image pseudo contours, thereby suppressing the generation of granular noise and realizing a smooth gradation expression. be able to.
  • FIG. 6 is a diagram showing a first subfield array (array 1 shown in FIG. 5) and output gradation values.
  • FIG. 7 is a diagram showing a second subfield array (array 2 shown in FIG. 5) and output gradation values.
  • FIG. 8 is a diagram showing a third subfield array (array 3 shown in FIG. 5) and output gradation values.
  • FIG. 9 is a diagram showing a fourth subfield array (array 4 shown in FIG. 5) and output gradation values.
  • each column in the leftmost first column indicates a pattern number
  • each column in the rightmost twelfth column indicates an output gradation value.
  • Each column of the first row indicates the weight (luminance ratio) of each subfield in the subfield arrangement
  • the first row, (n + 1) th column corresponds to the weight of the subfield SFn.
  • the other columns (columns 2nd to 11th in the 2nd to 57th rows) indicate subfield lighting patterns, that is, whether or not the display cells are lit in each subfield. When “” is written, it is turned on, and when nothing is written, it is turned off.
  • the weight of the subfield SFn differs depending on the subfield arrangement, and the subfield lighting pattern corresponding to each pattern number is the same regardless of the subfield arrangement.
  • the subfield lighting pattern is set such that the temporal deviation of the light emission center of gravity is small between the subfield lighting patterns corresponding to the preceding and following gradation values. Thereby, generation
  • the minimum weight set in the subfield SFn and the sum of the set weights are the same regardless of the subfield arrangement. That is, the gradation that can be expressed by the subfield lighting pattern is constant regardless of the subfield arrangement. In the examples shown in FIGS. 6 to 9, the minimum value of the weight set in the subfield SFn is “1”, and the total sum of the set weights is 255.
  • the largest subfield to be lit is the highest gradation value in the subfield SF (k + 3) and the largest subfield to be lit. Includes the lowest gradation value and the next smallest gradation value in the subfield SF (k + 4).
  • the first gradation group LV1 includes gradation values “15”, “19”, and “23”
  • the second gradation group LV2 includes gradation values “27”, “35”, and “39”.
  • the third gradation group LV3 includes gradation values “47”, “57”, and “65”
  • the fourth gradation group LV4 includes gradation values “77”, “89”, and “99”.
  • the fifth gradation group LV5 includes gradation values “119”, “133”, and “145”
  • the sixth gradation group LV6 includes gradation values “175”, “199”, and “213”. Including.
  • the number of gradation values that can be expressed only by the subfield lighting pattern in the first to third gradation groups LV1 to LV3 is increased as shown in FIG. Also in the fifth gradation group LV5, the number of gradation values that can be expressed only by the subfield lighting pattern increases, and the occurrence of granular noise can be reduced.
  • the subfield The array selection circuit 140 may select the first subfield array (array 1).
  • the subfield arrangement selection circuit 140 selects the subfield arrangement in accordance with the measurement result of the histogram measurement circuit 130, thereby suppressing the generation of the moving image pseudo contour and performing the subdiffusion without performing error diffusion. It is possible to increase the number of pixels displayed only by the field lighting pattern and suppress the occurrence of granular noise.
  • gradation values that can be expressed only by the subfield lighting pattern in the third gradation group LV3 are shown in FIG. As shown, the gradation values are 47, 57, and 65 only.
  • a total of 16 gradation values of gradation values 48, 49, 50, 51, 52, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 64 Is displayed by error diffusion processing.
  • the first subfield array (array 1) is used to display the gradation value. Granular noise will be noticeable in the image.
  • the gradation values that can be expressed only by the subfield lighting pattern in the third gradation group LV3 are gradation values as shown in FIG. 47, 51, 57, 59, 61, 63, 65.
  • the gradation values displayed by the error diffusion process in the third gradation group LV3 are 12 gradations of 48, 49, 50, 52, 53, 54, 55, 56, 58, 60, 62, and 64 in total. Decrease to value. Therefore, when the number of pixels displaying the gradation value to which the third gradation group LV3 belongs in the input image signal is more than 50% of all the pixels, the fourth subfield array (array 4) is used. The occurrence of granular noise can be reduced as compared with the case where the first subfield array (array 1) is used.
  • FIG. 10 is a diagram illustrating a configuration example of the plasma display device according to the second embodiment.
  • the plasma display device according to the second embodiment is different from the plasma display device according to the first embodiment in that it has a motion detection circuit 150, and the others are the same. Therefore, different points will be described below.
  • the motion detection circuit 150 detects the amount of motion for each pixel based on the image signal S2 output from the inverse gamma conversion processing circuit. Then, the motion detection circuit 150 notifies the subfield arrangement selection circuit 140 when the number of pixels whose motion amount is larger (faster) than a predetermined value is detected by a predetermined number or more.
  • the subfield arrangement selection circuit 140 When the subfield arrangement selection circuit 140 receives the notification, the subfield arrangement selection circuit 140 does not change the subfield arrangement and the corresponding nonlinear parameter according to the measurement result (output frequency coefficient) of the histogram measurement circuit 130.
  • the subfield arrangement selection circuit 140 determines the subfield arrangement and the nonlinear parameters corresponding thereto according to the measurement result (output frequency coefficient) of the histogram measurement circuit 130. As appropriate.
  • the first and second embodiments described above are merely examples, and the present invention is not limited thereto.
  • the number of subfield arrays is arbitrary.
  • the weight of each subfield shown in the subfield arrangement is also an example, and may be set as appropriate according to the display image and the gradation range to be expressed.
  • a gradation that is expressed without performing error diffusion processing and using a predetermined lighting pattern in a gradation group having a high appearance frequency according to the appearance frequency of a specific gradation group in the measured first image signal The weights of the plurality of subfields are determined so as to increase the number of subfields. Thereby, it is possible to suppress the generation of granular noise while suppressing the generation of the moving image pseudo contour, and to realize a smooth gradation expression.

Abstract

A plasma display unit, wherein a single field consists of a plurality of weighted subfields, includes a measurement circuit (130) to measure an occurrence rate of a specific gray-scale group in a first image signal (S2) for each field, a processing circuit (140) to determine weighting of a plurality of subfields according to measured occurrence rate, a nonlinear converter circuit (30) which nonlinearly converts the first image signal (S2) into a second image signal (S3) on the basis of the processed result to represent the second image signal (S3) using a real part and an error part such that use of the specified lighting pattern may be avoided, and lighting pattern converter circuits (40, 50) which perform spatial or temporal error spreading processing operation of the error part in the second image signal (S3) to replace the specified lighting pattern with another lighting pattern. No error spreading processing operation is carried out for a gray-scale group with high occurrence rate, and weighting of each subfield is determined such that a gray-scale represented without use of the specified lighting pattern increases in number, thereby reducing occurrence of pseudo profile of a motion picture and granular noise.

Description

プラズマディスプレイ装置及びその処理方法Plasma display device and processing method thereof
 本発明は、プラズマディスプレイ装置及びその処理方法に関する。 The present invention relates to a plasma display device and a processing method thereof.
 サブフィールド法を用いて階調表示を行うプラズマディスプレイ装置においては、特定のサブフィールド点灯パターンが、隣接する画素のサブフィールド点灯パターンとあいまって、人間の目には動画の際に大きな階調値の擬似輪郭が存在するかのように見えてしまう、いわゆる動画擬似輪郭が発生することがある。この動画擬似輪郭の発生を抑制するために、動画擬似輪郭が発生し易いサブフィールド点灯パターンを使用しないようにして画像表示を行う技術が提案されている(例えば、特許文献1参照)。 In a plasma display device that performs gradation display using the subfield method, a specific subfield lighting pattern is combined with a subfield lighting pattern of an adjacent pixel, so that a large gradation value is displayed for a human eye during animation. In other words, a so-called moving image pseudo contour that appears as if there is a pseudo contour may be generated. In order to suppress the occurrence of the moving image pseudo contour, a technique for displaying an image without using a subfield lighting pattern that easily generates a moving image pseudo contour has been proposed (for example, see Patent Document 1).
 特許文献1に記載されたプラズマディスプレイ装置は、サブフィールド点灯パターンの数を入力階調数より少なくし、サブフィールド点灯パターンで表示できない階調値は、その階調値の前後のサブフィールド点灯パターンを空間的又は時間的に組み合わせて表現している。これにより、動画擬似輪郭が発生しにくいサブフィールド点灯パターンのみで階調表現を行う。しかし、そのサブフィールド点灯パターンで表現できない中間調は誤差拡散処理により表現するため、階調値によっては表示画像において粒状ノイズが見えることがある。 In the plasma display device described in Patent Document 1, the number of subfield lighting patterns is smaller than the number of input gradations, and gradation values that cannot be displayed by the subfield lighting pattern are subfield lighting patterns before and after the gradation value. Is expressed in combination with space or time. As a result, gradation expression is performed only with the subfield lighting pattern in which the moving image pseudo contour is less likely to occur. However, since the halftone that cannot be expressed by the subfield lighting pattern is expressed by error diffusion processing, granular noise may be seen in the display image depending on the gradation value.
 また、フルHD信号のプログレシブ表示のように解像度が増えると、画素の点灯/非点灯を選択するアドレス期間の長さが増大する。そのため、従来のインターレース表示と同様のサブフィールド数を維持したまま階調表示を行うと、各サブフィールドあたりのサステインパルス数が減少して輝度が低下してしまう。この輝度低下を抑制して輝度を従来並みに維持しようとすると、サブフィールド数を少なくしなければならず、サブフィールド点灯パターンの数が減少する。その結果、拡散処理により表現する階調の数が多くなり、粒状ノイズが見えてしまう階調の数が増加し、階調表現力が低下する。 Also, as the resolution increases as in the progressive display of full HD signals, the length of the address period for selecting lighting / non-lighting of pixels increases. For this reason, if gradation display is performed while maintaining the same number of subfields as in conventional interlaced display, the number of sustain pulses per subfield decreases and luminance decreases. In order to suppress the decrease in luminance and maintain the luminance as usual, the number of subfields must be reduced, and the number of subfield lighting patterns decreases. As a result, the number of gradations expressed by the diffusion processing increases, the number of gradations where the granular noise can be seen increases, and the gradation expression ability decreases.
特開2006-276201号公報JP 2006-276201 A
 本発明は、動画擬似輪郭及び粒状ノイズの発生を抑制することができるプラズマディスプレイ装置及びその処理方法を提供することを目的とする。 It is an object of the present invention to provide a plasma display device and a processing method thereof that can suppress the generation of a moving image pseudo contour and granular noise.
 本発明の一観点によれば、1フィールドが重み付けされたサステインパルス数を有する複数のサブフィールドからなり、前記サブフィールドの点灯又は非点灯を選択することにより画像を階調表現するプラズマディスプレイ装置であって、第1の画像信号における特定の階調群の出現頻度を前記フィールド毎に計測する計測回路と、前記計測回路により計測された出現頻度に応じて、前記複数のサブフィールドの重み付けを前記フィールド毎に決定する処理回路と、前記処理回路の処理結果に基づいて、所定の点灯パターンを使用しないように、前記第1の画像信号を第2の画像信号に非線形変換し、前記第2の画像信号を実部及び誤差部で表現する非線形変換回路と、前記第2の画像信号の誤差部を空間的又は時間的に誤差拡散処理し前記所定の点灯パターンを他の点灯パターンに置き換える点灯パターン変換回路とを備えるプラズマディスプレイ装置が提供される。 According to one aspect of the present invention, there is provided a plasma display apparatus that includes a plurality of subfields each having a weighted number of sustain pulses, and that represents gradation of an image by selecting lighting or non-lighting of the subfield. A measurement circuit that measures the appearance frequency of a specific gradation group in the first image signal for each field, and weights the plurality of subfields according to the appearance frequency measured by the measurement circuit. Based on a processing circuit determined for each field and a processing result of the processing circuit, the first image signal is nonlinearly converted into a second image signal so as not to use a predetermined lighting pattern, and the second image signal A non-linear conversion circuit that expresses an image signal by a real part and an error part, and an error part of the error part of the second image signal subjected to error diffusion processing spatially or temporally. A plasma display apparatus and a lighting pattern conversion circuit that replaces the predetermined lighting pattern in the other lighting patterns are provided.
 第1の画像信号における特定の階調群の出現頻度を計測し、出現頻度の高い階調群については誤差拡散処理を行わずかつ所定の点灯パターンを使用せずに表現される階調が多くなるように、複数のサブフィールドの重み付けを決定することで、動画擬似輪郭の発生を抑制しながらも、誤差拡散により表示される画素数の低減を図り粒状ノイズの発生を抑制することができる。 The appearance frequency of a specific gradation group in the first image signal is measured, and the gradation group having a high appearance frequency has many gradations expressed without performing error diffusion processing and using a predetermined lighting pattern. As described above, by determining the weights of the plurality of subfields, it is possible to reduce the number of pixels displayed by error diffusion and suppress the generation of granular noise while suppressing the generation of the moving image pseudo contour.
図1は、第1の実施形態によるプラズマディスプレイ装置の構成例を示す図である。FIG. 1 is a diagram illustrating a configuration example of the plasma display device according to the first embodiment. 図2Aは、図1に示した表示セルの断面構成例を示す図である。2A is a diagram showing a cross-sectional configuration example of the display cell shown in FIG. 図2Bは、交流駆動型プラズマディスプレイパネルのパネル容量を説明するための図である。FIG. 2B is a diagram for explaining the panel capacity of the AC-driven plasma display panel. 図2Cは、交流駆動型プラズマディスプレイの発光を説明するための図である。FIG. 2C is a diagram for explaining light emission of the AC drive type plasma display. 図3は、画像の1フィールドの構成例を示す図である。FIG. 3 is a diagram illustrating a configuration example of one field of an image. 図4は、ヒストグラム計測回路の構成例を示す図である。FIG. 4 is a diagram illustrating a configuration example of the histogram measurement circuit. 図5は、サブフィールド配列選択テーブルの一例を示す図である。FIG. 5 is a diagram showing an example of the subfield arrangement selection table. 図6は、第1の実施形態における第1のサブフィールド配列と出力階調値を示す図である。FIG. 6 is a diagram showing a first subfield arrangement and output gradation values in the first embodiment. 図7は、第1の実施形態における第2のサブフィールド配列と出力階調値を示す図である。FIG. 7 is a diagram showing a second subfield arrangement and output gradation values in the first embodiment. 図8は、第1の実施形態における第3のサブフィールド配列と出力階調値を示す図である。FIG. 8 is a diagram showing a third subfield arrangement and output gradation values in the first embodiment. 図9は、第1の実施形態における第4のサブフィールド配列と出力階調値を示す図である。FIG. 9 is a diagram showing a fourth subfield arrangement and output gradation values in the first embodiment. 図10は、第2の実施形態によるプラズマディスプレイ装置の構成例を示す図である。FIG. 10 is a diagram illustrating a configuration example of the plasma display device according to the second embodiment.
 以下、本発明の実施形態を図面に基づいて説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(第1の実施形態)
 本発明の第1の実施形態について説明する。
 図1は、第1の実施形態によるプラズマディスプレイ装置の構成例を示す図である。第1の実施形態によるプラズマディスプレイ装置は、逆ガンマ変換処理回路10、遅延回路20、非線形ゲイン回路30、誤差拡散回路40、サブフィールド変換回路50、サブフィールド毎表示負荷率検出回路60、サステインパルス数設定回路70、駆動信号生成回路80、アドレス電極駆動回路121、維持電極駆動回路122、走査電極駆動回路123、プラズマディスプレイパネル124、ヒストグラム計測回路130、及びサブフィールド配列選択回路140を有する。
(First embodiment)
A first embodiment of the present invention will be described.
FIG. 1 is a diagram illustrating a configuration example of the plasma display device according to the first embodiment. The plasma display device according to the first embodiment includes an inverse gamma conversion processing circuit 10, a delay circuit 20, a nonlinear gain circuit 30, an error diffusion circuit 40, a subfield conversion circuit 50, a display load factor detection circuit 60 for each subfield, a sustain pulse. A number setting circuit 70, a drive signal generation circuit 80, an address electrode drive circuit 121, a sustain electrode drive circuit 122, a scan electrode drive circuit 123, a plasma display panel 124, a histogram measurement circuit 130, and a subfield arrangement selection circuit 140.
 アドレス電極駆動回路121は、アドレス電極A1、A2、・・・に所定の電圧を供給する。以下、アドレス電極A1、A2、・・・の各々を又はそれらの総称を、アドレス電極Ajといい、jは添え字を意味する。 The address electrode drive circuit 121 supplies a predetermined voltage to the address electrodes A1, A2,. Hereinafter, each of the address electrodes A1, A2,... Or their generic name is referred to as an address electrode Aj, where j means a subscript.
 維持電極駆動回路122は、X電極(維持電極)X1、X2、・・・に所定の電圧を供給する。以下、X電極X1、X2、・・・の各々を又はそれらの総称を、X電極Xiといい、iは添え字を意味する。 The sustain electrode drive circuit 122 supplies a predetermined voltage to the X electrodes (sustain electrodes) X1, X2,. Hereinafter, each of the X electrodes X1, X2,... Or their generic name is referred to as an X electrode Xi, and i means a subscript.
 走査電極駆動回路123は、Y電極(走査電極)Y1、Y2、・・・に所定の電圧を供給する。以下、Y電極Y1、Y2、・・・の各々を又はそれらの総称を、Y電極Yiといい、iは添え字を意味する。 The scan electrode driving circuit 123 supplies a predetermined voltage to the Y electrodes (scan electrodes) Y1, Y2,. Hereinafter, each of the Y electrodes Y1, Y2,... Or their generic name is referred to as a Y electrode Yi, and i means a subscript.
 プラズマディスプレイパネル124では、Y電極Yi及びX電極Xiが水平方向に並列に延びる行を形成し、アドレス電極Ajが垂直方向に延びる列を形成する。Y電極Yi及びX電極Xiは、垂直方向に交互に配置される。 In the plasma display panel 124, the Y electrode Yi and the X electrode Xi form a row extending in parallel in the horizontal direction, and the address electrode Aj forms a column extending in the vertical direction. The Y electrodes Yi and the X electrodes Xi are alternately arranged in the vertical direction.
 Y電極Yi及びアドレス電極Ajは、i行j列の2次元行列を形成する。表示セルCijは、Y電極Yi及びアドレス電極Ajの交点並びにそれに対応して隣接するX電極Xiにより形成される。この表示セルCijが、例えば赤色、緑色、青色のサブピクセルに対応し、これら3色のサブピクセルで1画素が構成される。プラズマディスプレイパネル124は2次元配列された複数の画素の点灯により2次元画像を表示することができる。 The Y electrode Yi and the address electrode Aj form a two-dimensional matrix with i rows and j columns. The display cell Cij is formed by the intersection of the Y electrode Yi and the address electrode Aj and the X electrode Xi adjacent thereto corresponding thereto. This display cell Cij corresponds to, for example, red, green, and blue sub-pixels, and one pixel is constituted by these three-color sub-pixels. The plasma display panel 124 can display a two-dimensional image by lighting a plurality of pixels arranged two-dimensionally.
 図2Aは、図1の表示セルCijの断面構成例を示す図である。X電極Xi及びY電極Yiは、前面ガラス基板211上に形成されている。その上には、放電空間217に対し絶縁するための誘電体層212が被着されるとともに、更にその上にMgO(酸化マグネシウム)保護膜213が被着されている。 FIG. 2A is a diagram showing a cross-sectional configuration example of the display cell Cij in FIG. The X electrode Xi and the Y electrode Yi are formed on the front glass substrate 211. A dielectric layer 212 for insulating the discharge space 217 is deposited thereon, and an MgO (magnesium oxide) protective film 213 is further deposited thereon.
 一方、アドレス電極Ajは、前面ガラス基板211と対向して配置された背面ガラス基板214上に形成され、その上には誘電体層215が被着され、更にその上に蛍光体が被着されている。MgO保護膜213と誘電体層215との間の放電空間217には、Ne+Xeペニングガス等が封入されている。 On the other hand, the address electrode Aj is formed on a rear glass substrate 214 disposed opposite to the front glass substrate 211, and a dielectric layer 215 is deposited thereon, and further a phosphor is deposited thereon. ing. Ne + Xe Penning gas or the like is sealed in the discharge space 217 between the MgO protective film 213 and the dielectric layer 215.
 図2Bは、交流駆動型プラズマディスプレイパネルのパネル容量Cpを説明するための図である。容量Caは、X電極XiとY電極Yiとの間の放電空間217の容量である。容量Cbは、X電極XiとY電極Yiとの間の誘電体層212の容量である。容量Ccは、X電極XiとY電極Yiとの間の前面ガラス基板211の容量である。これらの容量Ca、Cb、Ccの合計によって、電極Xi及びYi間のパネル容量Cpが決まる。 FIG. 2B is a diagram for explaining the panel capacitance Cp of the AC drive type plasma display panel. The capacity Ca is the capacity of the discharge space 217 between the X electrode Xi and the Y electrode Yi. The capacitance Cb is the capacitance of the dielectric layer 212 between the X electrode Xi and the Y electrode Yi. The capacitance Cc is the capacitance of the front glass substrate 211 between the X electrode Xi and the Y electrode Yi. The sum of these capacitors Ca, Cb, and Cc determines the panel capacitance Cp between the electrodes Xi and Yi.
 図2Cは、交流駆動型プラズマディスプレイの発光を説明するための図である。リブ216の内面には、赤、青、緑色の蛍光体218がストライプ状に各色毎に配列、塗布されており、X電極Xi及びY電極Yiの間の放電によって蛍光体218を励起して光221が生成されるようになっている。 FIG. 2C is a diagram for explaining light emission of the AC drive type plasma display. On the inner surface of the rib 216, red, blue, and green phosphors 218 are arranged and applied in stripes for each color, and the phosphor 218 is excited by the discharge between the X electrode Xi and the Y electrode Yi to emit light. 221 is generated.
 図3は、画像の1フィールドFDの構成例を示す図である。画像は、例えば60フィールド/秒で形成される。1フィールドFDは、第1のサブフィールドSF1、第2のサブフィールドSF2、・・・、第nのサブフィールドSFnにより形成される。このnは、例えば10である。サブフィールドSF1、SF2等の各々を又はそれらの総称を、以下、サブフィールドSFという。 FIG. 3 is a diagram illustrating a configuration example of one field FD of an image. The image is formed at 60 fields / second, for example. One field FD is formed by a first subfield SF1, a second subfield SF2,..., An nth subfield SFn. This n is, for example, 10. Each of the subfields SF1, SF2, etc. or their generic name is hereinafter referred to as a subfield SF.
 各サブフィールドSFは、リセット期間Tr、アドレス期間Ta及びサステイン(維持放電)期間Tsにより構成される。リセット期間Trでは、表示セルの初期化を行う。アドレス期間Taでは、アドレス電極Aj及びY電極Yi間のアドレス放電により各表示セルの発光又は非発光を選択することができる。サステイン期間Tsでは、選択された表示セルのX電極Xi及びY電極Yi間でサステイン放電を行い、発光を行う。各サブフィールドSFでは、X電極Xi及びY電極Yi間のサステインパルス数に対応する発光回数(サステイン期間Tsの長さ)が異なる。これにより、階調値を決めることができる。 Each subfield SF includes a reset period Tr, an address period Ta, and a sustain (sustain discharge) period Ts. In the reset period Tr, the display cell is initialized. In the address period Ta, light emission or non-light emission of each display cell can be selected by address discharge between the address electrode Aj and the Y electrode Yi. In the sustain period Ts, a sustain discharge is performed between the X electrode Xi and the Y electrode Yi of the selected display cell to emit light. In each subfield SF, the number of times of light emission (the length of the sustain period Ts) corresponding to the number of sustain pulses between the X electrode Xi and the Y electrode Yi is different. Thereby, the gradation value can be determined.
 図1の構成を説明する。プラズマディスプレイパネル124は、1フィールドが重み付けされたサステインパルス数を有する複数のサブフィールドからなり、その複数のサブフィールドのうちの点灯するサブフィールドのパターンを選択することにより画像を階調表現することができる。 The configuration of FIG. 1 will be described. The plasma display panel 124 is composed of a plurality of subfields each having a weighted sustain pulse number, and the image is expressed in gradation by selecting a pattern of subfields to be lit among the plurality of subfields. Can do.
 逆ガンマ変換処理回路10は、デジタル形式の画像信号S1を入力し、逆ガンマ変換し、線形特性を有する画像信号S2を出力する。遅延回路20は、ヒストグラム計測回路130及びサブフィールド配列選択回路140での処理時間に応じた所定の時間、画像信号S2を遅延させ出力する。 The inverse gamma conversion processing circuit 10 receives the digital image signal S1, performs inverse gamma conversion, and outputs an image signal S2 having linear characteristics. The delay circuit 20 delays and outputs the image signal S2 for a predetermined time corresponding to the processing time in the histogram measurement circuit 130 and the subfield arrangement selection circuit 140.
 非線形ゲイン回路30は、特定のサブフィールド点灯パターンを使用しないように、遅延された画像信号S2を画像信号S3に非線形変換し、画像信号S3を整数部(実部)及び小数部(誤差部)で表現する。非線形ゲイン回路30は、サブフィールド配列選択回路140で選択されたサブフィールド配列に応じた非線形パラメータ(誤差拡散処理に係る混合比配分)に基づいて画像信号S2を画像信号S3に変換する。誤差拡散回路40は、画像信号S3を入力し、画像信号S3の小数部が0でないときにはその小数部を空間的又は時間的に拡散し、擬似的に階調表現を行うための画像信号S4を出力する。 The nonlinear gain circuit 30 nonlinearly converts the delayed image signal S2 into an image signal S3 so as not to use a specific subfield lighting pattern, and the image signal S3 is converted into an integer part (real part) and a decimal part (error part). Express with The nonlinear gain circuit 30 converts the image signal S2 into an image signal S3 based on a nonlinear parameter (mixing ratio distribution related to error diffusion processing) corresponding to the subfield arrangement selected by the subfield arrangement selection circuit 140. The error diffusion circuit 40 receives the image signal S3. When the decimal part of the image signal S3 is not 0, the error diffusion circuit 40 spreads the decimal part spatially or temporally to generate an image signal S4 for performing pseudo gradation expression. Output.
 サブフィールド変換回路50は、誤差拡散された画像信号S4を基にサブフィールドの点灯パターンを選択する際に、前記特定のサブフィールド点灯パターンを使用せずに他のサブフィールド点灯パターンを選択し、サブフィールド点灯パターン信号S5を生成する。アドレス電極駆動回路121は、サブフィールド点灯パターン信号S5に応じて、各画素について点灯させるサブフィールドを選択するためのアドレス電極Ajの電圧を生成する。 When the subfield conversion circuit 50 selects a subfield lighting pattern based on the error-diffused image signal S4, the subfield conversion circuit 50 selects another subfield lighting pattern without using the specific subfield lighting pattern, A subfield lighting pattern signal S5 is generated. The address electrode drive circuit 121 generates a voltage of the address electrode Aj for selecting a subfield to be lit for each pixel according to the subfield lighting pattern signal S5.
 サブフィールド毎表示負荷率検出回路60は、サブフィールド点灯パターン信号S5を基に、サブフィールド毎の表示負荷率T2を演算する。表示負荷率は、発光する画素数及びその発光する画素の階調値を基に検出される。例えば、画像の全画素が最大階調値で表示されている場合には表示負荷率が100%である。また、画像の全画素が最大階調値の1/2で表示されている場合には表示負荷率が50%である。また、画像の半分(50%)の画素のみが最大階調値で表示されているような場合にも、表示負荷率が50%である。 The display load factor detection circuit 60 for each subfield calculates a display load factor T2 for each subfield based on the subfield lighting pattern signal S5. The display load factor is detected based on the number of pixels that emit light and the gradation value of the pixels that emit light. For example, when all the pixels of the image are displayed with the maximum gradation value, the display load factor is 100%. Further, when all the pixels of the image are displayed with 1/2 of the maximum gradation value, the display load factor is 50%. The display load factor is also 50% when only half (50%) of the image is displayed with the maximum gradation value.
 サステインパルス数設定回路70は、タイミング信号T1及び表示負荷率T2を入力し、1フィールドの表示負荷率に応じて電力一定制御による1フィールドの総サステインパルス数を演算する。また、サステインパルス数設定回路70は、サブフィールド配列選択回路140で選択されたサブフィールド配列に応じて、その総サステインパルス数を各サブフィールドの重みの比になるように分割する。 The sustain pulse number setting circuit 70 inputs the timing signal T1 and the display load factor T2, and calculates the total sustain pulse number of one field by constant power control according to the display load factor of one field. Further, the sustain pulse number setting circuit 70 divides the total number of sustain pulses so as to be the ratio of the weights of the subfields according to the subfield arrangement selected by the subfield arrangement selection circuit 140.
 ここで、電力一定制御は、1フィールドの表示負荷率に応じて1フィールドの総サステインパルス数が制御される。表示負荷率にかかわらず、1フィールドの総サステインパルス数を一定にすると、表示負荷率が大きいほど電力が大きくなってしまい、熱量が増加してしまう。そのため、1フィールドの表示負荷率が大きいときには、1フィールドの総サステインパルス数を少なくするように演算し、電力一定制御を行う。 Here, in the constant power control, the total number of sustain pulses in one field is controlled according to the display load factor in one field. Regardless of the display load factor, if the total number of sustain pulses in one field is made constant, the larger the display load factor, the larger the electric power and the greater the amount of heat. Therefore, when the display load factor of one field is large, calculation is performed so as to reduce the total number of sustain pulses in one field, and constant power control is performed.
 駆動信号生成回路80は、サステインパルス数設定回路70の出力に従って、表示のためのサステインパルス信号を生成する。維持電極駆動回路122及び走査電極駆動回路123は、そのサステインパルス信号に応じて、X電極Xi及びY電極Yiの電圧を生成する。アドレス電極Ajにより選択された表示セルは、X電極Xi及びY電極Yi間でサステイン放電して発光する。 The drive signal generation circuit 80 generates a sustain pulse signal for display according to the output of the sustain pulse number setting circuit 70. The sustain electrode drive circuit 122 and the scan electrode drive circuit 123 generate voltages for the X electrode Xi and the Y electrode Yi in accordance with the sustain pulse signal. The display cell selected by the address electrode Aj emits light by sustain discharge between the X electrode Xi and the Y electrode Yi.
 ヒストグラム計測回路130は、逆ガンマ変換処理回路10から出力された画像信号S2を基に、画像信号における特定の階調群のヒストグラムを各フィールド毎に計測する。 The histogram measurement circuit 130 measures a histogram of a specific gradation group in the image signal for each field based on the image signal S2 output from the inverse gamma conversion processing circuit 10.
 サブフィールド配列選択回路140は、ヒストグラム計測回路130での計測結果に基づいて、複数のサブフィールド配列の内から1つのサブフィールド配列を選択する。サブフィールド配列選択回路140は、選択したサブフィールド配列をサステインパルス設定回路70に出力するとともに、それに応じた非線形パラメータを非線形ゲイン回路30に出力する。ここで、それぞれのサブフィールド配列には、1フィールドを構成する各サブフィールドの重み(輝度比)が設定されており、サブフィールド配列間では各サブフィールドの重みの比が互いに異なる。 The subfield array selection circuit 140 selects one subfield array from a plurality of subfield arrays based on the measurement result of the histogram measurement circuit 130. The subfield arrangement selection circuit 140 outputs the selected subfield arrangement to the sustain pulse setting circuit 70 and outputs a non-linear parameter corresponding thereto to the non-linear gain circuit 30. Here, the weights (luminance ratios) of the subfields constituting one field are set in each subfield array, and the weight ratios of the subfields are different between the subfield arrays.
 図4に示すように、ヒストグラム計測回路130は、階調群判別回路131、カウンタ132~134、及び比較器135~137を有する。 As shown in FIG. 4, the histogram measurement circuit 130 has a gradation group discrimination circuit 131, counters 132 to 134, and comparators 135 to 137.
 階調群判別回路131は、逆ガンマ変換処理回路10からの画像信号S2が入力され、入力信号がどの階調群の信号であるかを判別する。ここで、階調群は、表示セルCijを点灯させる最大のサブフィールドがn番目のサブフィールドである階調値の内の最高階調値(桁上げ前の階調値)と、点灯させる最大のサブフィールドが(n+1)番目のサブフィールドである階調値の内の最低階調値(桁上げ後の階調値)とを少なくとも含むように構成される。 The tone group discrimination circuit 131 receives the image signal S2 from the inverse gamma conversion processing circuit 10 and discriminates which tone group the input signal is from. Here, the gradation group includes the highest gradation value (gradation value before carry) among gradation values in which the largest subfield for lighting the display cell Cij is the n-th subfield, and the maximum lighting value. The subfield is configured to include at least the lowest gradation value (gradation value after carry) of the gradation values of the (n + 1) th subfield.
 なお、階調群には、点灯させる最大のサブフィールドが(n+1)番目のサブフィールドである階調値の内の最低階調値の次に小さい階調値を含むようにしても良いし、最低階調値に加えて小さい順に複数の階調値を含むようにしても良い。 In the gradation group, the largest subfield to be lit may include a gradation value that is the next smallest to the lowest gradation value among the gradation values of the (n + 1) th subfield. In addition to the tone value, a plurality of tone values may be included in ascending order.
 以下の説明では、階調群には、表示セルCijを点灯させる最大のサブフィールドがn番目のサブフィールドである階調値の内の最高階調値と、点灯させる最大のサブフィールドが(n+1)番目のサブフィールドである階調値の内の最低階調値と、この最低階調値の次に小さい階調値とを含むものとする。 In the following description, the gradation group includes the highest gradation value among gradation values in which the largest subfield for lighting the display cell Cij is the nth subfield, and the largest subfield for lighting (n + 1). ) It is assumed that the lowest gradation value among the gradation values which are the first subfield and the gradation value next to the lowest gradation value are included.
 カウンタ132~134は、各階調群に対応して設けられている。図4においては、第1階調群に対応する第1階調群カウンタ132、第2階調群に対応する第2階調群カウンタ133、及び第N階調群に対応する第N階調群カウンタ134を図示している。各カウンタ132~134は、垂直同期信号によってカウンタ値がリセット(初期化)され、階調群判別回路131での判別結果に従ってカウント値をカウントアップすることにより、画像信号において対応する階調群に属する階調値の出現回数をフィールド毎に計測する。 Counters 132 to 134 are provided corresponding to each gradation group. In FIG. 4, the first gradation group counter 132 corresponding to the first gradation group, the second gradation group counter 133 corresponding to the second gradation group, and the Nth gradation corresponding to the Nth gradation group. A group counter 134 is illustrated. Each of the counters 132 to 134 is reset (initialized) by the vertical synchronization signal, and counts up according to the determination result in the gradation group determination circuit 131, thereby obtaining the corresponding gradation group in the image signal. The number of appearances of the gradation value to which it belongs is measured for each field.
 比較器135~137は、予めMPU150により設定された値と各階調値群のカウンタ132~134による計測結果であるカウンタ値とを比較し、階調群に属する階調値の出現回数に応じて出現頻度係数AC1~ACNを決定し出力する。本実施形態では、一例として1フィールド内の全画素のうち階調群に属する階調値を表示する画素が50%を越える場合には当該階調群の出現頻度係数として“2”を出力し、15~50%までの場合には当該階調群の出現頻度係数として“1”を出力し、15%より低い場合には当該階調群の出現頻度係数として“0”を出力するものとする。 Comparators 135 to 137 compare the values set in advance by the MPU 150 with the counter values measured by the counters 132 to 134 of each gradation value group, and according to the number of appearances of the gradation values belonging to the gradation group. Appearance frequency coefficients AC1 to ACN are determined and output. In this embodiment, as an example, when the number of pixels that display gradation values belonging to a gradation group exceeds 50% among all the pixels in one field, “2” is output as the appearance frequency coefficient of the gradation group. In the case of 15 to 50%, “1” is output as the appearance frequency coefficient of the gradation group, and “0” is output as the appearance frequency coefficient of the gradation group if it is lower than 15%. To do.
 なお、カウンタ132~134のカウンタ値との比較を行い、出現頻度係数を決定するための設定値を階調群に応じて異ならせるようにしても良い。一般に、表示画像において輝度が低い部分については違いが目立ちやすく、輝度が高い部分については違いが目立ちにくいので、低輝度の階調群では出現頻度係数が高くなるように設定値を設定し、高輝度の階調群では出現頻度係数が低くなるように設定値を設定するようにしても良い。 It should be noted that the setting value for determining the appearance frequency coefficient may be made different depending on the gradation group by comparing with the counter values of the counters 132 to 134. In general, the difference is conspicuous in the low luminance part of the display image, and the difference is inconspicuous in the high luminance part, so set the setting value so that the appearance frequency coefficient is high in the low luminance gradation group. In the luminance gradation group, the set value may be set so that the appearance frequency coefficient is low.
 サブフィールド配列選択回路140は、図5に一例を示すような複数のサブフィールド配列からなるサブフィールド配列選択テーブルを有している。サブフィールド配列選択回路140は、ヒストグラム計測回路130から出力された各階調群の出現頻度係数AC1~ACNに基づいて、表示する画像にあったサブフィールド配列を選択し、その選択結果に応じて非線形ゲイン回路30のパラメータを変更する。 The subfield arrangement selection circuit 140 has a subfield arrangement selection table composed of a plurality of subfield arrangements as shown in FIG. The subfield arrangement selection circuit 140 selects a subfield arrangement corresponding to the image to be displayed based on the appearance frequency coefficients AC1 to ACN of each gradation group output from the histogram measurement circuit 130, and nonlinearly according to the selection result. The parameter of the gain circuit 30 is changed.
 具体的には、サブフィールド配列選択回路140は、各階調群の出現頻度係数AC1~ACNに応じて出現頻度が高い階調群に属する階調値の多くが拡散処理を行わずにサブフィールド点灯パターンによって表現可能になるように、言い換えれば出現頻度が高い階調群では、サブフィールド点灯パターンにより表現される各階調間の輝度差の平均を小さくするようなサブフィールド配列を選択する。すなわち、出現頻度が高い階調群においてサブフィールド点灯パターンのみでは表現できない階調値の数が少なくなるようにサブフィールド配列を選択する。 Specifically, the subfield arrangement selection circuit 140 turns on the subfield without performing diffusion processing on many of the gradation values belonging to the gradation group having a high appearance frequency according to the appearance frequency coefficients AC1 to ACN of each gradation group. In other words, in a gradation group having a high appearance frequency, a subfield arrangement is selected so as to reduce the average luminance difference between gradations expressed by the subfield lighting pattern so that it can be expressed by a pattern. That is, the subfield arrangement is selected so that the number of gradation values that cannot be expressed only by the subfield lighting pattern is reduced in the gradation group having a high appearance frequency.
 このように、サブフィールド点灯パターンは変更することなく、画像信号における階調の出現頻度に応じて、拡散処理を行わずにサブフィールド点灯パターンのみで表現できる階調値の数が増加するように各サブフィールドの重み(輝度比)を変更する。これにより、動画擬似輪郭の発生を抑制しながらも、映像において誤差拡散により表示される画素数の全画素に対する割合を低減して、粒状ノイズの発生を抑制でき、滑らかな階調表現を実現することができる。 As described above, the number of gradation values that can be expressed only by the subfield lighting pattern without performing the diffusion process is increased according to the appearance frequency of the gradation in the image signal without changing the subfield lighting pattern. The weight (luminance ratio) of each subfield is changed. This reduces the ratio of the number of pixels displayed by error diffusion to the total number of pixels while suppressing the occurrence of moving image pseudo contours, thereby suppressing the generation of granular noise and realizing a smooth gradation expression. be able to.
 以下、ヒストグラム計測回路130及びサブフィールド配列選択回路140によって実行されるサブフィールド配列の選択動作例について、図6~図9を参照して具体的に説明する。 Hereinafter, an example of subfield arrangement selection operation executed by the histogram measurement circuit 130 and the subfield arrangement selection circuit 140 will be described in detail with reference to FIGS.
 図6は、第1のサブフィールド配列(図5に示した配列1)と出力階調値を示す図である。図7は、第2のサブフィールド配列(図5に示した配列2)と出力階調値を示す図である。図8は、第3のサブフィールド配列(図5に示した配列3)と出力階調値を示す図である。図9は、第4のサブフィールド配列(図5に示した配列4)と出力階調値を示す図である。 FIG. 6 is a diagram showing a first subfield array (array 1 shown in FIG. 5) and output gradation values. FIG. 7 is a diagram showing a second subfield array (array 2 shown in FIG. 5) and output gradation values. FIG. 8 is a diagram showing a third subfield array (array 3 shown in FIG. 5) and output gradation values. FIG. 9 is a diagram showing a fourth subfield array (array 4 shown in FIG. 5) and output gradation values.
 図6~図9において、最も左側の第1列の各欄はパターン番号を示しており、最も右側の第12列の各欄は出力階調値を示している。また、第1行の各欄には、サブフィールド配列における各サブフィールドの重み(輝度比)を示しており、第1行第(n+1)列がサブフィールドSFnの重みに対応している。その他の欄(第2行~第57行における第2列~第11列の欄)は、サブフィールド点灯パターン、すなわち各サブフィールドにて表示セルを点灯させるか否かを示しており、“1”が記載されている場合には点灯とし、何も記載されていない場合には非点灯とする。 6 to 9, each column in the leftmost first column indicates a pattern number, and each column in the rightmost twelfth column indicates an output gradation value. Each column of the first row indicates the weight (luminance ratio) of each subfield in the subfield arrangement, and the first row, (n + 1) th column corresponds to the weight of the subfield SFn. The other columns (columns 2nd to 11th in the 2nd to 57th rows) indicate subfield lighting patterns, that is, whether or not the display cells are lit in each subfield. When “” is written, it is turned on, and when nothing is written, it is turned off.
 なお、図6~図9に示すように、サブフィールドSFnの重みはサブフィールド配列に応じて異なり、各パターン番号に対応するサブフィールド点灯パターンはサブフィールド配列にはかかわらず同じである。サブフィールド点灯パターンは、前後の階調値に対応するサブフィールド点灯パターンとの間で時間的な発光重心のずれが小さくなるように設定されている。これにより、動画擬似輪郭の発生を抑制することができる。 As shown in FIGS. 6 to 9, the weight of the subfield SFn differs depending on the subfield arrangement, and the subfield lighting pattern corresponding to each pattern number is the same regardless of the subfield arrangement. The subfield lighting pattern is set such that the temporal deviation of the light emission center of gravity is small between the subfield lighting patterns corresponding to the preceding and following gradation values. Thereby, generation | occurrence | production of a moving image pseudo contour can be suppressed.
 また、サブフィールドSFnに設定される重みの最小値、及び設定される重みの総和は、サブフィールド配列にかかわらず同じとする。すなわち、サブフィールド配列にかかわらずサブフィールド点灯パターンによって表現可能な階調は一定である。図6~図9に示す例では、サブフィールドSFnに設定される重みの最小値は“1”とし、設定される重みの総和は255としている。 Also, the minimum weight set in the subfield SFn and the sum of the set weights are the same regardless of the subfield arrangement. That is, the gradation that can be expressed by the subfield lighting pattern is constant regardless of the subfield arrangement. In the examples shown in FIGS. 6 to 9, the minimum value of the weight set in the subfield SFn is “1”, and the total sum of the set weights is 255.
 本実施形態では、第1のサブフィールド配列(配列1)を標準のサブフィールド配列とする。すなわち、図6に示したように、各サブフィールドの重みを(SF1、SF2、SF3、SF4、SF5、SF6、SF7、SF8、SF9、SF10)=(1、2、4、8、12、20、30、42、56、80)とする。第k階調群LVk(k=1、2、3、4、5、6)は、点灯させる最大のサブフィールドがサブフィールドSF(k+3)での最高階調値と、点灯させる最大のサブフィールドがサブフィールドSF(k+4)での最低階調値及び次に小さい階調値とを含む。 In this embodiment, the first subfield array (array 1) is a standard subfield array. That is, as shown in FIG. 6, the weight of each subfield is (SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8, SF9, SF10) = (1, 2, 4, 8, 12, 20 , 30, 42, 56, 80). In the k-th gradation group LVk (k = 1, 2, 3, 4, 5, 6), the largest subfield to be lit is the highest gradation value in the subfield SF (k + 3) and the largest subfield to be lit. Includes the lowest gradation value and the next smallest gradation value in the subfield SF (k + 4).
 すなわち、第1階調群LV1は、階調値“15”、“19”、“23”を含み、第2階調群LV2は、階調値“27”、“35”、“39”を含む。第3階調群LV3は、階調値“47”、“57”、“65”を含み、第4階調群LV4は、階調値“77”、“89”、“99”を含む。また、第5階調群LV5は、階調値“119”、“133”、“145”を含み、第6階調群LV6は、階調値“175”、“199”、“213”を含む。 That is, the first gradation group LV1 includes gradation values “15”, “19”, and “23”, and the second gradation group LV2 includes gradation values “27”, “35”, and “39”. Including. The third gradation group LV3 includes gradation values “47”, “57”, and “65”, and the fourth gradation group LV4 includes gradation values “77”, “89”, and “99”. The fifth gradation group LV5 includes gradation values “119”, “133”, and “145”, and the sixth gradation group LV6 includes gradation values “175”, “199”, and “213”. Including.
 ここで、ヒストグラム計測回路130での計測の結果、第4階調群LV4の出現頻度係数AC4が“2”である場合、すなわち全画素のうち第4階調群LV4に属する階調値を表示する画素が50%を越える場合には、サブフィールド配列選択回路140は、第2のサブフィールド配列(配列2)を選択する。すなわち、各サブフィールドの重みを(SF1、SF2、SF3、SF4、SF5、SF6、SF7、SF8、SF9、SF10)=(1、2、4、6、8、12、16、44、50、112)とする。このように各サブフィールドの重みを変更することにより、図7に示すように第4階調群LV4に属する階調値のうち、誤差拡散処理を行わずにサブフィールド点灯パターンのみで表現可能な階調値の数が増加し、第1のサブフィールド配列を用いた場合と比較して粒状ノイズの発生を低減することができる。 Here, as a result of the measurement by the histogram measurement circuit 130, when the appearance frequency coefficient AC4 of the fourth gradation group LV4 is “2”, that is, gradation values belonging to the fourth gradation group LV4 among all the pixels are displayed. When the number of pixels to be exceeded exceeds 50%, the subfield array selection circuit 140 selects the second subfield array (array 2). That is, the weight of each subfield is set to (SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8, SF9, SF10) = (1, 2, 4, 6, 8, 12, 16, 44, 50, 112 ). By changing the weight of each subfield in this way, it is possible to express only the subfield lighting pattern without performing error diffusion processing among the gradation values belonging to the fourth gradation group LV4 as shown in FIG. The number of gradation values increases, and the occurrence of granular noise can be reduced as compared with the case where the first subfield arrangement is used.
 また、ヒストグラム計測回路130での計測の結果、第1階調群LV1、第2階調群LV2、第3階調群LV3の何れかの出現頻度係数が“2”であり、かつ第5階調群LV5の出現頻度係数が“1”である場合には、サブフィールド配列選択回路140は、第3のサブフィールド配列(配列3)を選択する。すなわち、各サブフィールドの重みを(SF1、SF2、SF3、SF4、SF5、SF6、SF7、SF8、SF9、SF10)=(1、2、4、6、8、10、16、20、58、130)とする。このように各サブフィールドの重みを変更することにより、図8に示すように第1~第3階調群LV1~LV3においてサブフィールド点灯パターンのみで表現可能な階調値の数が増加するとともに、第5階調群LV5においてもサブフィールド点灯パターンのみで表現可能な階調値の数が増加し、粒状ノイズの発生を低減することができる。 As a result of the measurement by the histogram measurement circuit 130, the appearance frequency coefficient of any one of the first gradation group LV1, the second gradation group LV2, and the third gradation group LV3 is “2”, and the fifth floor. When the appearance frequency coefficient of the key group LV5 is “1”, the subfield arrangement selection circuit 140 selects the third subfield arrangement (array 3). That is, the weight of each subfield is set to (SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8, SF9, SF10) = (1, 2, 4, 6, 8, 10, 16, 20, 58, 130). ). By changing the weight of each subfield in this way, the number of gradation values that can be expressed only by the subfield lighting pattern in the first to third gradation groups LV1 to LV3 is increased as shown in FIG. Also in the fifth gradation group LV5, the number of gradation values that can be expressed only by the subfield lighting pattern increases, and the occurrence of granular noise can be reduced.
 また、ヒストグラム計測回路130での計測の結果、第1階調群LV1、第2階調群LV2、第3階調群LV3の何れかの出現頻度係数が“2”であり、かつ第4階調群LV4の出現頻度係数が“1”である場合には、サブフィールド配列選択回路140は、第4のサブフィールド配列(配列4)を選択する。すなわち、各サブフィールドの重みを(SF1、SF2、SF3、SF4、SF5、SF6、SF7、SF8、SF9、SF10)=(1、2、4、6、8、10、16、20、24、164)とする。このように各サブフィールドの重みを変更することにより、図9に示すように第1~第4階調群LV1~LV4においてサブフィールド点灯パターンのみで表現可能な階調値の数が増加し、粒状ノイズの発生を低減することができる。 As a result of the measurement by the histogram measurement circuit 130, the appearance frequency coefficient of any one of the first gradation group LV1, the second gradation group LV2, and the third gradation group LV3 is “2”, and the fourth floor. When the appearance frequency coefficient of the key group LV4 is “1”, the subfield array selection circuit 140 selects the fourth subfield array (array 4). That is, the weight of each subfield is (SF1, SF2, SF3, SF4, SF5, SF6, SF7, SF8, SF9, SF10) = (1, 2, 4, 6, 8, 10, 16, 20, 24, 164). ). By changing the weight of each subfield in this way, the number of gradation values that can be expressed only by the subfield lighting pattern in the first to fourth gradation groups LV1 to LV4 as shown in FIG. Generation of granular noise can be reduced.
 ヒストグラム計測回路130での計測の結果、上述した以外の階調群の出力頻度係数が“2”となる場合や、どの階調群も出現頻度係数が“2”とならない場合には、サブフィールド配列選択回路140は、第1のサブフィールド配列(配列1)を選択するようにすれば良い。 As a result of the measurement by the histogram measurement circuit 130, when the output frequency coefficient of gradation groups other than those described above is “2”, or when the appearance frequency coefficient of any gradation group is not “2”, the subfield The array selection circuit 140 may select the first subfield array (array 1).
 上述のようにヒストグラム計測回路130での計測の結果に応じてサブフィールド配列選択回路140がサブフィールド配列を選択することにより、動画擬似輪郭の発生を抑制しながらも、誤差拡散を行うことなくサブフィールド点灯パターンのみで表示される画素数の増加を図り、粒状ノイズの発生を抑制することができる。 As described above, the subfield arrangement selection circuit 140 selects the subfield arrangement in accordance with the measurement result of the histogram measurement circuit 130, thereby suppressing the generation of the moving image pseudo contour and performing the subdiffusion without performing error diffusion. It is possible to increase the number of pixels displayed only by the field lighting pattern and suppress the occurrence of granular noise.
 例えば、第1のサブフィールド配列(配列1)を用いると、第3階調群LV3(階調値47~65)のうちサブフィールド点灯パターンのみで表現可能な階調値は、図6に示したように階調値47、57、65だけである。第3階調群LV3のうち階調値48、49、50、51、52、53、54、55、56、58、59、60、61、62、63、64の計16個の階調値は誤差拡散処理によって表示される。したがって、入力された画像信号において第3階調群LV3の属する階調値を表示する画素が全画素の50%より多い場合に第1のサブフィールド配列(配列1)を用いると、表示された画像において粒状ノイズが目立つことになる。 For example, when the first subfield array (array 1) is used, gradation values that can be expressed only by the subfield lighting pattern in the third gradation group LV3 (gradation values 47 to 65) are shown in FIG. As shown, the gradation values are 47, 57, and 65 only. In the third gradation group LV3, a total of 16 gradation values of gradation values 48, 49, 50, 51, 52, 53, 54, 55, 56, 58, 59, 60, 61, 62, 63, 64 Is displayed by error diffusion processing. Therefore, when the number of pixels displaying the gradation value to which the third gradation group LV3 belongs in the input image signal is more than 50% of all pixels, the first subfield array (array 1) is used to display the gradation value. Granular noise will be noticeable in the image.
 それに対して、第4のサブフィールド配列(配列4)を用いると、第3階調群LV3のうちサブフィールド点灯パターンのみで表現可能な階調値は、図9に示したように階調値47、51、57、59、61、63、65となる。第3階調群LV3のうち誤差拡散処理によって表示される階調値は、48、49、50、52、53、54、55、56、58、60、62、64の計12個の階調値に減少する。したがって、入力された画像信号において第3階調群LV3の属する階調値を表示する画素が全画素の50%より多い場合には、第4のサブフィールド配列(配列4)を用いることで、第1のサブフィールド配列(配列1)を用いた場合と比較して粒状ノイズの発生を低減することができる。 On the other hand, when the fourth subfield arrangement (array 4) is used, the gradation values that can be expressed only by the subfield lighting pattern in the third gradation group LV3 are gradation values as shown in FIG. 47, 51, 57, 59, 61, 63, 65. The gradation values displayed by the error diffusion process in the third gradation group LV3 are 12 gradations of 48, 49, 50, 52, 53, 54, 55, 56, 58, 60, 62, and 64 in total. Decrease to value. Therefore, when the number of pixels displaying the gradation value to which the third gradation group LV3 belongs in the input image signal is more than 50% of all the pixels, the fourth subfield array (array 4) is used. The occurrence of granular noise can be reduced as compared with the case where the first subfield array (array 1) is used.
(第2の実施形態)
 次に、本発明の第2の実施形態について説明する。
(Second Embodiment)
Next, a second embodiment of the present invention will be described.
 図10は、第2の実施形態によるプラズマディスプレイ装置の構成例を示す図である。第2の実施形態によるプラズマディスプレイ装置は、第1の実施形態によるプラズマディスプレイ装置に対して動き検出回路150を有する点が異なり、他は同様であるので、以下では異なる点について説明する。 FIG. 10 is a diagram illustrating a configuration example of the plasma display device according to the second embodiment. The plasma display device according to the second embodiment is different from the plasma display device according to the first embodiment in that it has a motion detection circuit 150, and the others are the same. Therefore, different points will be described below.
 動き検出回路150は、逆ガンマ変換処理回路から出力された画像信号S2を基に、画素毎の動き量を検出する。そして、動き検出回路150は、動き量が所定の値より大きい(速い)画素が所定の画素数以上検出された場合には、サブフィールド配列選択回路140に通知する。 The motion detection circuit 150 detects the amount of motion for each pixel based on the image signal S2 output from the inverse gamma conversion processing circuit. Then, the motion detection circuit 150 notifies the subfield arrangement selection circuit 140 when the number of pixels whose motion amount is larger (faster) than a predetermined value is detected by a predetermined number or more.
 サブフィールド配列選択回路140は、その通知を受けた場合には、ヒストグラム計測回路130の計測結果(出力頻度係数)に応じたサブフィールド配列及びそれに対応する非線形パラメータの変更を行わない。 When the subfield arrangement selection circuit 140 receives the notification, the subfield arrangement selection circuit 140 does not change the subfield arrangement and the corresponding nonlinear parameter according to the measurement result (output frequency coefficient) of the histogram measurement circuit 130.
 すなわち、動き検出回路150によって動き量が所定の値より大きい画素が所定の画素数以上検出された場合には、ヒストグラム計測回路130の計測結果(出力頻度係数)にかかわらず、サブフィールド配列及び非線形パラメータの切り替えは行われない。それ以外の場合には、第1の実施形態と同様にして、サブフィールド配列選択回路140は、ヒストグラム計測回路130の計測結果(出力頻度係数)に応じて、サブフィールド配列及びそれに対応する非線形パラメータを適宜変更する。 That is, when the motion detection circuit 150 detects more than a predetermined number of pixels with a motion amount greater than a predetermined value, the subfield arrangement and the nonlinearity are irrespective of the measurement result (output frequency coefficient) of the histogram measurement circuit 130. There is no parameter switching. In other cases, as in the first embodiment, the subfield arrangement selection circuit 140 determines the subfield arrangement and the nonlinear parameters corresponding thereto according to the measurement result (output frequency coefficient) of the histogram measurement circuit 130. As appropriate.
 これにより、第1の実施形態と同様に動画擬似輪郭及び粒状ノイズの発生を抑制できるとともに、広い面積で速い動きのある映像以外では、サブフィールド配列及びそれに対応する非線形パラメータの変更を行わないので、切り替えによる微小な輝度変化や発光重心の変動による微小なフリッカ等を抑制することができる。 As a result, similar to the first embodiment, it is possible to suppress the generation of the moving image pseudo contour and the granular noise, and the subfield arrangement and the corresponding non-linear parameter are not changed except for a video having a large area and a fast motion. Therefore, it is possible to suppress a minute luminance change due to switching, a minute flicker due to a change in the light emission center of gravity, and the like.
 なお、上述した第1及び第2の実施形態は一例であり、本発明はこれに限定されるものではない。例えば、サブフィールド配列として4つの配列を設けているが、サブフィールド配列の数は任意である。また、サブフィールド配列に示した各サブフィールドの重みも一例であり、表示画像や表現する階調範囲に応じて適宜設定すれば良い。 Note that the first and second embodiments described above are merely examples, and the present invention is not limited thereto. For example, although four arrays are provided as subfield arrays, the number of subfield arrays is arbitrary. Further, the weight of each subfield shown in the subfield arrangement is also an example, and may be set as appropriate according to the display image and the gradation range to be expressed.
 また、前記実施形態は、何れも本発明を実施するにあたっての具体化のほんの一例を示したものに過ぎず、これらによって本発明の技術的範囲が限定的に解釈されてはならないものである。すなわち、本発明はその技術思想、またはその主要な特徴から逸脱することなく、様々な形で実施することができる。 In addition, each of the above-described embodiments is merely an example of implementation in carrying out the present invention, and the technical scope of the present invention should not be interpreted in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.
 計測した第1の画像信号における特定の階調群の出現頻度に応じて、出現頻度の高い階調群にて誤差拡散処理を行わずかつ所定の点灯パターンを使用せずに表現される階調が多くなるように、複数のサブフィールドの重み付けを決定する。これにより、動画擬似輪郭の発生を抑制しながらも、粒状ノイズの発生を抑制することができ、滑らかな階調表現を実現することができる。 A gradation that is expressed without performing error diffusion processing and using a predetermined lighting pattern in a gradation group having a high appearance frequency according to the appearance frequency of a specific gradation group in the measured first image signal The weights of the plurality of subfields are determined so as to increase the number of subfields. Thereby, it is possible to suppress the generation of granular noise while suppressing the generation of the moving image pseudo contour, and to realize a smooth gradation expression.

Claims (15)

  1.  1フィールドが重み付けされたサステインパルス数を有する複数のサブフィールドからなり、前記サブフィールドの点灯又は非点灯を選択することにより画像を階調表現するプラズマディスプレイ装置であって、
     第1の画像信号における特定の階調群の出現頻度を前記フィールド毎に計測する計測回路と、
     前記計測回路により計測された出現頻度に応じて、前記複数のサブフィールドの重み付けを前記フィールド毎に決定する処理回路と、
     前記処理回路の処理結果に基づいて、所定の点灯パターンを使用しないように、前記第1の画像信号を第2の画像信号に非線形変換し、前記第2の画像信号を実部及び誤差部で表現する非線形変換回路と、
     前記第2の画像信号の誤差部を空間的又は時間的に誤差拡散処理し前記所定の点灯パターンを他の点灯パターンに置き換える点灯パターン変換回路とを備えることを特徴とするプラズマディスプレイ装置。
    A plasma display apparatus that includes a plurality of subfields each having a weighted number of sustain pulses in one field, and expresses an image in gradation by selecting lighting or non-lighting of the subfield,
    A measurement circuit for measuring the frequency of appearance of a specific gradation group in the first image signal for each field;
    A processing circuit that determines the weights of the plurality of subfields for each field according to the appearance frequency measured by the measurement circuit;
    Based on the processing result of the processing circuit, the first image signal is nonlinearly converted into a second image signal so as not to use a predetermined lighting pattern, and the second image signal is converted into a real part and an error part. A non-linear conversion circuit to express,
    A plasma display apparatus comprising: a lighting pattern conversion circuit that performs error diffusion processing on an error part of the second image signal spatially or temporally and replaces the predetermined lighting pattern with another lighting pattern.
  2.  前記処理回路は、前記計測回路により計測された出現頻度に応じて、各サブフィールドの重み付けを予め規定した複数種類の配列の内から1つの配列を選択することを特徴とする請求項1記載のプラズマディスプレイ装置。 The said processing circuit selects one arrangement | sequence from the several types of arrangement | sequence which prescribed | regulated the weight of each subfield beforehand according to the appearance frequency measured by the said measurement circuit, The said arrangement | sequence is characterized by the above-mentioned. Plasma display device.
  3.  前記処理回路は、前記計測回路により計測された前記特定の階調群の出現頻度が所定値以上である場合には、当該階調群にて前記誤差拡散処理を行うことなく前記所定の点灯パターンを使用せずに表現される各階調間の輝度差の平均を小さくするようにサブフィールドの重み付けを決定することを特徴とする請求項1記載のプラズマディスプレイ装置。 When the frequency of appearance of the specific gradation group measured by the measurement circuit is equal to or higher than a predetermined value, the processing circuit performs the predetermined lighting pattern without performing the error diffusion process on the gradation group. 2. The plasma display apparatus according to claim 1, wherein the weighting of the subfield is determined so as to reduce the average of the luminance difference between the gradations expressed without using.
  4.  前記処理回路は、前記計測回路により計測された前記特定の階調群の出現頻度が所定値以上である場合には、当該階調群において前記誤差拡散処理を行うことなく前記所定の点灯パターンを使用せずに表現される階調値の数を増加させるようにサブフィールドの重み付けを決定することを特徴とする請求項1記載のプラズマディスプレイ装置。 When the frequency of appearance of the specific gradation group measured by the measurement circuit is equal to or higher than a predetermined value, the processing circuit displays the predetermined lighting pattern without performing the error diffusion process in the gradation group. 2. The plasma display apparatus as claimed in claim 1, wherein the weighting of the subfield is determined so as to increase the number of gradation values expressed without being used.
  5.  前記特定の階調群は複数の階調群であって、
     前記計測回路は、前記第1の画像信号が何れの階調群の信号であるかを画素毎に判別する判別回路と、
     前記判別回路での判別結果を基に、各階調群に属する階調値の出現回数をカウントするカウンタ回路と、
     前記カウンタ回路のカウント値と設定されている値とを比較し、比較結果を前記処理回路に出力する比較回路とを有することを特徴とする請求項1記載のプラズマディスプレイ装置。
    The specific gradation group is a plurality of gradation groups,
    The measurement circuit includes a determination circuit that determines for each pixel which gradation group the first image signal is,
    A counter circuit that counts the number of appearances of gradation values belonging to each gradation group based on the determination result in the determination circuit;
    2. The plasma display device according to claim 1, further comprising a comparison circuit that compares a count value of the counter circuit with a set value and outputs a comparison result to the processing circuit.
  6.  前記階調群の各々は、点灯する最大のサブフィールドがn番目のサブフィールドである階調と、点灯する最大のサブフィールドが(n+1)番目のサブフィールドである少なくとも1つの階調とを含む複数の階調であることを特徴とする請求項1記載のプラズマディスプレイ装置。 Each of the gradation groups includes a gradation in which the largest subfield to be lit is the nth subfield and at least one gradation in which the largest subfield to be lit is the (n + 1) th subfield. 2. The plasma display device according to claim 1, wherein there are a plurality of gradations.
  7.  前記サブフィールドに割り当てる重みの最小値は、前記フィールド毎に変えないことを特徴とする請求項1記載のプラズマディスプレイ装置。 The plasma display device according to claim 1, wherein the minimum weight assigned to the sub-field is not changed for each field.
  8.  前記サブフィールドに割り当てる重みの総和は、一定であることを特徴とする請求項1記載のプラズマディスプレイ装置。 The plasma display apparatus according to claim 1, wherein the sum of weights assigned to the subfields is constant.
  9.  前記第1の画像信号における動き量を画素毎に検出する動き検出回路を備え、
     前記処理回路は、前記計測回路により計測された出現頻度に加え、前記動き検出回路による検出結果に応じて、前記複数のサブフィールドの重み付けを前記フィールド毎に決定することを特徴とする請求項1記載のプラズマディスプレイ装置。
    A motion detection circuit for detecting a motion amount in the first image signal for each pixel;
    The processing circuit determines the weighting of the plurality of subfields for each field in accordance with a detection result by the motion detection circuit in addition to an appearance frequency measured by the measurement circuit. The plasma display device described.
  10.  前記処理回路は、前記動き検出回路によって動き量が所定の値より大きい画素が所定数以上検出された場合には、前記計測回路により計測された出現頻度にかかわらず、所定のサブフィールドの重み付けに決定することを特徴とする請求項9記載のプラズマディスプレイ装置。 The processing circuit weights a predetermined subfield regardless of the appearance frequency measured by the measurement circuit when a predetermined number or more of pixels having a motion amount larger than a predetermined value are detected by the motion detection circuit. The plasma display device according to claim 9, wherein the plasma display device is determined.
  11.  前記処理回路は、前記計測回路により計測された出現頻度に応じて、各サブフィールドの重み付けを予め規定した複数種類の配列の内から1つの配列を選択することを特徴とする請求項9記載のプラズマディスプレイ装置。 The said processing circuit selects one arrangement | sequence from the multiple types of arrangement | sequence which prescribed | regulated the weighting of each subfield beforehand according to the appearance frequency measured by the said measurement circuit, The array of Claim 9 characterized by the above-mentioned. Plasma display device.
  12.  前記処理回路は、前記計測回路により計測された前記特定の階調群の出現頻度が所定値以上である場合には、当該階調群にて前記誤差拡散処理を行うことなく前記所定の点灯パターンを使用せずに表現される各階調間の輝度差の平均を小さくするようにサブフィールドの重み付けを決定することを特徴とする請求項9記載のプラズマディスプレイ装置。 When the frequency of appearance of the specific gradation group measured by the measurement circuit is equal to or higher than a predetermined value, the processing circuit performs the predetermined lighting pattern without performing the error diffusion process on the gradation group. 10. The plasma display apparatus according to claim 9, wherein the weighting of the subfield is determined so as to reduce the average of the luminance difference between the gradations expressed without using.
  13.  前記処理回路は、前記計測回路により計測された前記特定の階調群の出現頻度が所定値以上である場合には、当該階調群において前記誤差拡散処理を行うことなく前記所定の点灯パターンを使用せずに表現される階調値の数を増加させるようにサブフィールドの重み付けを決定することを特徴とする請求項9記載のプラズマディスプレイ装置。 When the frequency of appearance of the specific gradation group measured by the measurement circuit is equal to or higher than a predetermined value, the processing circuit displays the predetermined lighting pattern without performing the error diffusion process in the gradation group. 10. The plasma display apparatus as claimed in claim 9, wherein the weight of the subfield is determined so as to increase the number of gradation values expressed without using the subfield.
  14.  1フィールドが重み付けされたサステインパルス数を有する複数のサブフィールドからなり、前記サブフィールドの点灯又は非点灯を選択することにより画像を階調表現するプラズマディスプレイ装置の処理方法であって、
     第1の画像信号における特定の階調群の出現頻度を前記フィールド毎に計測する計測ステップと、
     計測された前記出現頻度に応じて、前記複数のサブフィールドの重み付けを前記フィールド毎に決定する処理ステップと、
     前記処理ステップでの処理結果に基づいて、所定の点灯パターンを使用しないように、前記第1の画像信号を第2の画像信号に非線形変換し、前記第2の画像信号を実部及び誤差部で表現する非線形変換ステップと、
     前記第2の画像信号の誤差部を空間的又は時間的に誤差拡散処理し前記所定の点灯パターンを他の点灯パターンに置き換える点灯パターン変換ステップとを有することを特徴とするプラズマディスプレイ装置の処理方法。
    A processing method of a plasma display device, wherein one field is composed of a plurality of subfields having a weighted sustain pulse number, and gradation is expressed by selecting lighting or non-lighting of the subfield,
    A measurement step of measuring the appearance frequency of a specific gradation group in the first image signal for each field;
    A processing step of determining weights of the plurality of subfields for each field according to the measured appearance frequency;
    Based on the processing result in the processing step, the first image signal is nonlinearly converted into a second image signal so that a predetermined lighting pattern is not used, and the second image signal is converted into a real part and an error part. A nonlinear transformation step expressed by
    A processing method of a plasma display device, comprising: a lighting pattern conversion step of spatially or temporally performing error diffusion processing on the error portion of the second image signal and replacing the predetermined lighting pattern with another lighting pattern .
  15.  前記第1の画像信号における動き量を画素毎に検出する動き検出ステップを有し、
     前記処理ステップでは、計測された前記出現頻度に加え、前記動き検出ステップでの検出結果に応じて、前記複数のサブフィールドの重み付けを前記フィールド毎に決定することを特徴とする請求項14記載のプラズマディスプレイ装置の処理方法。
    A motion detection step of detecting a motion amount in the first image signal for each pixel;
    15. The weighting of the plurality of subfields is determined for each field according to the detection result in the motion detection step in addition to the measured appearance frequency in the processing step. A processing method of a plasma display device.
PCT/JP2008/050608 2008-01-18 2008-01-18 Plasma display unit and method for processing the same WO2009090751A1 (en)

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JPH06332398A (en) * 1993-05-19 1994-12-02 Fujitsu General Ltd Method for processing video signal and device therefor
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