WO2012098904A1

WO2012098904A1 - Image display device and drive method for image display device

Info

Publication number: WO2012098904A1
Application number: PCT/JP2012/000337
Authority: WO
Inventors: 広史本田
Original assignee: パナソニック株式会社
Priority date: 2011-01-20
Filing date: 2012-01-20
Publication date: 2012-07-26

Abstract

To reduce the time required for a write period in an image display device, an image display device has: a 2-line average unit (42) for calculating an average value for an image signal in relation to a pixel of interest; a 2-line difference unit (43) for calculating a difference value for the image signal in relation to the pixel of interest, and comparing the difference value with the gradient weight of a first type subfield; a subtraction unit (44) for subtracting a prescribed coefficient determined by the comparison result in the 2-line difference unit from the average value; an average code conversion unit (45) for converting the output from the subtraction unit into a subfield code having a prescribed subfield set as a non-emitting subfield, and outputting the same; a difference code generation unit (91) for generating a subfield code for controlling the prescribed subfield on the basis of the comparison result in the 2-line difference unit; and a display code synthesis unit (92) for synthesizing the subfield code outputted by the average code conversion unit and the subfield code generated by the difference code generation unit, and generating a display code.

Description

Image display device and driving method of image display device

The present invention relates to an image display device that displays an image in an image display region by combining binary control of light emission and non-light emission in a light emitting element that constitutes a pixel, and a driving method of the image display device.

A plasma display panel (hereinafter abbreviated as “panel”) is a typical image display device that displays an image in an image display area by combining binary control of light emission and non-light emission in a light emitting element constituting a pixel. is there.

In the panel, a large number of discharge cells, which are light-emitting elements constituting pixels, are formed between a front substrate and a rear substrate that are arranged to face each other. In the front substrate, 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.

The back substrate has a plurality of parallel data electrodes formed on the glass substrate on the back side, 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. ing. 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 substrate and the rear substrate are arranged opposite to 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 each color of red (R), green (G) and blue (B) are excited and emitted by the ultraviolet rays. Display an image.

A subfield method is generally used as a method for displaying an image in an image display region by combining binary control of light emission and non-light emission in a light emitting element.

In the subfield method, one field is divided into a plurality of subfields having different emission luminances. In each discharge cell, light emission / non-light emission of each subfield is controlled by a combination according to a desired gradation value. Thus, each discharge cell emits light with the emission luminance of one field set to a desired gradation value, and an image composed of various combinations of gradation values is displayed in the image display area of the panel.

In the subfield method, each subfield has an address period and a sustain period.

In the address period, the scan pulse is sequentially applied to the scan electrodes, and the address pulse is selectively applied to the data electrodes based on the image signal to be displayed. As a result, an address discharge is generated between the scan electrode and the data electrode of the discharge cell to emit light, and a wall charge is formed in the discharge cell (hereinafter, these operations are also collectively referred to as “address”). ).

In the sustain period, the number of sustain pulses based on the gradation weights determined for each subfield is alternately applied to the display electrode pairs composed of the scan electrodes and the sustain electrodes. As a result, a sustain discharge is generated in the discharge cell that has generated the address discharge, and the phosphor layer of the discharge cell emits light (hereinafter referred to as “lighting” that the discharge cell emits light by the sustain discharge, and “non-emitting”). Also written as “lit”.) Thereby, in each subfield, each discharge cell is made to emit light with the luminance according to the gradation weight. 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, and an image is displayed in the image display area of the panel.

In the subfield method described above, when the number of scan electrodes increases due to an increase in the screen size and resolution, the time required for the writing period becomes longer, and the time that can be allocated to the sustain period decreases. Arise.

In order to solve this problem, a driving method that performs “two-line simultaneous writing operation” has been proposed. The simultaneous writing operation every two lines is a driving method in which a scanning pulse is simultaneously applied to two adjacent scanning electrodes to perform the writing operation simultaneously for two lines (see, for example, Patent Document 1). If the simultaneous write operation is performed every two lines, the time spent for the write operation can be shortened and the write period can be shortened. For example, the number of subfields is increased or the time of the sustain period is increased. It becomes possible.

However, the driving method that performs the simultaneous writing operation every two lines may cause a decrease in resolution in the direction orthogonal to the scanning electrodes. Hereinafter, the direction orthogonal to the scan electrode is referred to as “vertical direction”, and the resolution in the direction orthogonal to the scan electrode is referred to as “vertical resolution”. This is because a write operation is simultaneously performed on two adjacent scan electrodes within one field period, so that each discharge formed on the two adjacent scan electrodes in one image displayed on the panel. This is because the cells emit light in the same pattern. Therefore, the resolution of the image is reduced to half of the number of scan electrodes in the direction orthogonal to the scan electrodes (vertical direction).

When the vertical resolution is reduced, the smoothness of the diagonal lines is impaired particularly when the diagonal lines are displayed on the panel, so that the user may feel that the image display quality has deteriorated.

Also, it is considered to apply a plasma display device as a three-dimensional (3-dimension: hereinafter referred to as “3D”) image display device.

In this plasma display device, a right-eye image and a left-eye image constituting a stereoscopic image (3D image) are alternately displayed on a panel, and a user uses special glasses called shutter glasses to display the images. Observe.

The shutter glasses include a right-eye shutter and a left-eye shutter, and the right-eye shutter is opened (a state in which visible light is transmitted) during a period in which the right-eye image is displayed on the panel, and the left-eye shutter. Is closed (a state in which visible light is blocked), and while the left-eye image is displayed, the left-eye shutter is opened and the right-eye shutter is closed. As a result, the user can observe the right-eye image only with the right eye and the left-eye image with only the left eye, so that the display image can be stereoscopically viewed.

As described above, in the plasma display device used as the 3D image display device, in order to display one 3D image, two images of one right eye image and one left eye image are displayed. There must be. Therefore, a user who observes a 3D image through shutter glasses observes the number of images displayed on the panel per second as half the number of fields per second.

For example, when the field frequency of the image displayed on the panel (the number of fields generated per second) is 60 Hz, if the image is a normal image (2D image) that is not a 3D image, 60 images per second. A 2D image is displayed. If the image is a 3D image, 30 3D images are displayed per second.

Therefore, in order to display 60 3D images per second, the field frequency must be set to 120 Hz, which is twice 60 Hz. In that case, the time that can be used to display one right-eye image or one left-eye image is limited to one-half of the time that can be used to display one 2D image.

In such a case, as a method for reducing the time required for driving the panel, the above-described driving method using the simultaneous writing operation every two lines is effective. However, in the driving method using the simultaneous writing operation for every two lines, as described above, the vertical resolution tends to be lowered.

When the vertical resolution is lowered, when the image including the diagonal line pattern is displayed on the panel, the smoothness of the diagonal line is easily lost as compared with an image having a high vertical resolution.

In a plasma display device used as a 3D image display device, smoothness of diagonal lines is prevented from being impaired when a panel is driven to display a 3D image by a driving method using a simultaneous writing operation every two lines. Therefore, it is desired to prevent deterioration of image display quality.

JP 2008-116894 A

In the present invention, a plurality of subfields having gradation weights constitute one field, and each of the plurality of subfields is expressed using a subfield code indicating a combination of light emission and non-light emission in each of the plurality of subfields. This is an image display device that controls the light emission and non-light emission, displays a gradation value based on an image signal on each of a plurality of pixels constituting the image display area, and displays an image in the image display area. In this image display device, at least one first-type subfield that performs a line-by-line addressing operation that applies a scan pulse to each of the scan electrodes in the address period and two adjacent scan electrodes in the address period simultaneously. A display code, which is a subfield code for displaying a gradation value based on an image signal on a pixel, is composed of a plurality of second-type subfields that perform simultaneous writing operation every two lines to which a scan pulse is applied. A drive circuit for outputting is provided. The drive circuit includes a two-line average unit, a two-line difference unit, a subtraction unit, an average code conversion unit, a difference code creation unit, and a display code synthesis unit. The two-line average unit calculates an average value of image signals corresponding to each pixel of a pair of pixels that are adjacent to each other in the direction orthogonal to the scanning electrode and perform the address operation simultaneously in the address period of the second type subfield. The two-line difference unit calculates a difference value between the image signals corresponding to each pixel of the pair of pixels described above, and compares the difference value with the gradation weight of the first type subfield. The subtraction unit subtracts a predetermined variable determined by the comparison result in the two-line difference unit from the above average value. The average code conversion unit converts the output of the subtraction unit into a subfield code having a predetermined subfield determined by the comparison result of the two-line difference unit as a non-lighting subfield, and outputs the subfield code. The difference code creation unit generates a subfield code for controlling a predetermined subfield based on the comparison result of the two-line difference unit. The display code synthesis unit generates a display code by synthesizing the subfield code output from the average code conversion unit and the subfield code generated by the difference code creation unit.

Thereby, the conversion from the image signal to the display code can be performed by the calculation using the calculation circuit. Therefore, even in an image display device that needs to cope with high functionality and multi-function, it is not necessary to provide a huge number of conversion tables for converting image signals into display codes. That is, it is not necessary to configure the image signal processing circuit so as to select an optimal one from a vast number of conversion tables according to various conditions. Furthermore, the time required for the writing period can be shortened while preventing the image display quality from being deteriorated in the image display device.

Further, the image display device of the present invention includes a base code generation unit, a rule generation unit, an upper and lower code generation unit, and an average code selection unit in the average code conversion unit. The base code generation unit selects a gradation value that is larger than the gradation value of the image signal in the target pixel pair and closest to the gradation value of the image signal in the target pixel pair from among a plurality of basic subfield codes. The sub-field code having the upper gradation base code is selected. The rule generation unit generates a rule for generating a new subfield code by changing the light-emitting subfield in the upper gradation base code to a non-light-emitting subfield based on the image signal in the target pixel pair. The upper / lower code generation unit applies the above-described rule to the upper gradation base code and newly generates an image signal in the target pixel pair that is larger than the gradation value of the image signal in the target pixel pair. The subfield code having the gradation value closest to the gradation value is selected as the upper gradation code, and is the closest to the gradation value of the image signal in the target pixel pair below the gradation value of the image signal in the target pixel pair A subfield code having a gradation value is selected as the lower gradation code. The average code selection unit calculates a gradation value to be displayed on the target pixel pair by adding a predetermined value to the gradation value of the image signal in the target pixel pair. A subfield code having a gradation value closer to the gradation value to be displayed on the target pixel pair is selected and output.

In the image display device of the present invention, the plurality of basic subfield codes described above are all subfields having the largest gradation weight among the subfields that emit light, and all having a gradation weight smaller than that subfield. The sub-field is a base code that emits light, or a deleted base code that uses a predetermined sub-field determined by the comparison result of the two-line difference portion from the base code as a non-lighting sub-field.

Further, in the image display device of the present invention, the predetermined value described above is a dither value calculated by dither processing and an error generated by error diffusion processing.

The present invention also comprises a plurality of subfields using a subfield code indicating a combination of light emission and non-light emission in each of the plurality of subfields, with a plurality of subfields having gradation weights defined. By controlling the light emission and non-light emission of each of these, the gradation value based on the image signal is displayed on each of the plurality of pixels constituting the image display area to display the image in the image display area, and scanning in the writing period At least one first-type subfield that performs a line-by-line addressing operation that applies a scan pulse to each electrode and a line-by-line simultaneous address that simultaneously applies a scan pulse to two adjacent scan electrodes in the address period A plurality of second type subfields that perform the operation constitute one field, and gradation values based on image signals are displayed on the pixels. A driving method of an image display device for generating a display code is a sub-field code. The driving method includes calculating an average value of image signals corresponding to each pixel of a pair of pixels that are adjacent to each other in a direction orthogonal to the scanning electrode and simultaneously perform the writing operation in the writing period of the second type subfield. Calculating a difference value between the image signals corresponding to each pixel of the pair of pixels, comparing the difference value with the gradation weight of the first type subfield, and the difference value and the first type The subtraction result in the step of subtracting the predetermined variable determined from the comparison result in the step of comparing the gradation weight of the subfield from the average value and the step of subtracting the predetermined variable from the average value Comparison results in the step of converting the field into a non-lighting subfield code into a subfield code and the step of comparing the difference value with the gradation weight of the first type subfield Based on the subfield code generated in the step of generating a subfield code for controlling a predetermined subfield and the step of converting the predetermined subfield into a subfield code having a non-lighting subfield, and the predetermined subfield are controlled. Generating a display code by combining the subfield code generated in the step of generating the subfield code.

In addition, the driving method of the image display device according to the present invention includes a plurality of basic subfield codes that are larger than the gradation value of the image signal in the pixel pair of interest and the gradation value of the image signal in the pixel pair of interest. Selecting the subfield code having the gradation value closest to the upper gradation base code, and changing the light emission subfield in the upper gradation base code to the non-light emission subfield based on the image signal in the pixel pair of interest. Generating a rule for generating a new subfield code, and applying the above-mentioned rule to the upper gradation base code, the image signal in the pixel pair of interest from the newly generated subfield code The sub-field code that has a gradation value that is larger than the gradation value of the pixel signal and that is closest to the gradation value of the image signal in the pixel of interest Selecting a subfield code having a gradation value that is equal to or less than the gradation value of the image signal in the pixel pair of interest and that is closest to the gradation value of the image signal in the pixel pair of interest as the lower gradation code. Then, a predetermined value is added to the gradation value of the image signal in the target pixel pair to calculate a gradation value to be displayed on the target pixel pair, and the target pixel pair of the upper gradation code and the lower gradation code is calculated. Selecting a subfield code having a gradation value closer to the gradation value to be displayed.

FIG. 1 is an exploded perspective view showing a structure of a panel used in an image display apparatus according to an embodiment of the present invention. FIG. 2 is an electrode array diagram of a panel used in the image display apparatus according to the embodiment of the present invention. FIG. 3 is a diagram schematically showing drive voltage waveforms applied to the respective electrodes of the panel used in the image display device according to the embodiment of the present invention. FIG. 4 is a diagram schematically showing the subfield configuration of the image display device and the opening / closing operation of the shutter glasses in the embodiment of the present invention. FIG. 5 is a diagram showing an example of a code set when one field is composed of five subfields. FIG. 6 is a diagram schematically showing an example of a circuit block and an image display system constituting the image display apparatus according to the embodiment of the present invention. FIG. 7 is a diagram schematically showing an example of a circuit block constituting the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8A is a diagram schematically showing an example of a writing operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8B is a diagram schematically showing another example of the writing operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8C is a diagram schematically showing another example of the write operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8D is a diagram schematically showing another example of the writing operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8E is a diagram schematically showing another example of the writing operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8F is a diagram schematically showing another example of the writing operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 8G is a diagram schematically showing another example of the writing operation in the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 9 is a diagram schematically showing an example of a circuit block constituting the average code conversion unit of the image display device according to the embodiment of the present invention. FIG. 10A is a diagram illustrating an example of a base code set used in the image display device according to the embodiment of the present invention. FIG. 10B is a diagram showing an example of a deleted base code set used in the image display device according to the embodiment of the present invention. FIG. 11A is a diagram illustrating an example of an intermediate code set generated by the intermediate code generation unit of the image display device according to the embodiment of the present invention. FIG. 11B is a diagram showing another example of the intermediate code set generated by the intermediate code generation unit of the image display device according to the embodiment of the present invention. FIG. 11C is a diagram illustrating another example of the intermediate code set generated by the intermediate code generation unit of the image display device according to the embodiment of the present invention. FIG. 12A is a diagram illustrating an example of a dither pattern used in the image display device according to the embodiment of the present invention. FIG. 12B is a diagram showing another example of the dither pattern used in the image display device according to the embodiment of the present invention. FIG. 13 is a diagram showing the error diffusion coefficient of the error diffusion unit of the image display device according to the embodiment of the present invention. FIG. 14 is a flowchart showing the operation of the image signal processing circuit of the image display device according to the embodiment of the present invention. FIG. 15 is a diagram schematically showing another example of a drive voltage waveform applied to each electrode of the panel used in the image display device according to the embodiment of the present invention. FIG. 16A is a diagram illustrating an example of a base code set used in the image display device according to the embodiment of the present invention. FIG. 16B is a diagram showing another example of the deleted base code set used in the image display device according to the embodiment of the present invention. FIG. 16C is a diagram showing another example of the deleted base code set used in the image display device according to the embodiment of the present invention.

Hereinafter, an image display device according to an embodiment of the present invention will be described with reference to the drawings, taking a 3D plasma display device using a plasma display panel as an example.

(Embodiment)
FIG. 1 is an exploded perspective view showing the structure of panel 10 used in the image display apparatus according to the embodiment of the present invention.

A plurality of display electrode pairs 14 each including a scanning electrode 12 and a sustaining electrode 13 are formed on a glass front substrate 11. A dielectric layer 15 is formed so as to cover the scan electrode 12 and the sustain electrode 13, and a protective layer 16 is formed on the dielectric layer 15.

This protective layer 16 has been used as a panel material in order to lower the discharge start voltage in the discharge cell, and has a large secondary electron emission coefficient and durability when neon (Ne) and xenon (Xe) gas is sealed. It is made of a material mainly composed of magnesium oxide (MgO).

The protective layer 16 may be composed of a single layer or may be composed of a plurality of layers. Moreover, the structure which particle | grains exist on a layer may be sufficient.

A plurality of data electrodes 22 are formed on the rear substrate 21, a dielectric layer 23 is formed so as to cover the data electrodes 22, and a grid-like partition wall 24 is further formed thereon. On the side surfaces of the barrier ribs 24 and on the dielectric layer 23, a phosphor layer 25R that emits red (R), a phosphor layer 25G that emits green (G), and a phosphor layer 25B that emits blue (B). Is provided. Hereinafter, the phosphor layer 25R, the phosphor layer 25G, and the phosphor layer 25B are collectively referred to as a phosphor layer 25.

The front substrate 11 and the rear substrate 21 are arranged to face each other so that the display electrode pair 14 and the data electrode 22 intersect each other with a minute space therebetween, and a discharge space is provided in the gap between the front substrate 11 and the rear substrate 21. . And the outer peripheral part is sealed with sealing materials, such as glass frit. For example, a mixed gas of neon and xenon is sealed in the discharge space as a discharge gas.

The discharge space is partitioned into a plurality of sections by the barrier ribs 24, and discharge cells, which are light-emitting elements constituting the pixels, are formed at the intersections between the display electrode pairs 14 and the data electrodes 22.

Then, a discharge is generated in these discharge cells, and the phosphor layer 25 of the discharge cells emits light (lights the discharge cells), thereby displaying a color image on the panel 10.

In the panel 10, one pixel is composed of three consecutive discharge cells arranged in the direction in which the display electrode pair 14 extends. The three discharge cells are a discharge cell having a phosphor layer 25R and emitting red (R) (red discharge cell), and a discharge cell having a phosphor layer 25G and emitting green (G) (green). And a discharge cell having a phosphor layer 25B and emitting blue (B) light (blue discharge cell).

Note that the structure of the panel 10 is not limited to the above-described structure, and may be, for example, provided with a stripe-shaped partition wall.

FIG. 2 is an electrode array diagram of panel 10 used in the plasma display device according to one embodiment of the present invention.

The panel 10 includes n scan electrodes SC1 to SCn (scan electrode 12 in FIG. 1) extended in the horizontal direction (row direction and line direction) and n sustain electrodes SU1 to SUn (FIG. 1). The sustain electrodes 13) are arranged, and m data electrodes D1 to Dm (data electrodes 22 in FIG. 1) extending in the vertical direction (column direction) are arranged.

One discharge cell as a light emitting element is formed in a region where a pair of scan electrode SCi (i = 1 to n) and sustain electrode SUi intersects with one data electrode Dj (j = 1 to m). . In other words, m discharge cells are formed on one pair of display electrodes 14 and m / 3 pixels are formed. Then, m × n discharge cells are formed in the discharge space, and an area where m × n discharge cells are formed becomes an image display area of the panel 10. For example, in a panel having 1920 × 1080 pixels, m = 1920 × 3 and n = 1080.

For example, a discharge cell having a data electrode Dp (p = 3 × q−2: q is a positive integer less than or equal to m / 3) is coated with a red phosphor as a phosphor layer 25R, and has a data electrode Dp + 1. The cell is coated with a green phosphor as a phosphor layer 25G, and the discharge cell having the data electrode Dp + 2 is coated with a blue phosphor as a phosphor layer 25B.

Next, a driving voltage waveform for driving the panel 10 and an outline of its operation will be described.

The plasma display device in the present embodiment drives the panel 10 by the subfield method. In the subfield method, one field of an image signal is divided into a plurality of subfields on the time axis, and a gradation weight is set for each subfield. Therefore, each field has a plurality of subfields having different gradation weights.

And based on the image signal, light emission / non-light emission of each discharge cell is controlled for each subfield. That is, a plurality of gradations based on the image signal are displayed on the panel 10 by combining the light-emitting subfield and the non-light-emitting subfield based on the image signal.

In the present embodiment, the image signal input to the image display device is a 3D image signal. The 3D image signal is a stereoscopic image signal in which a right-eye image signal and a left-eye image signal are alternately repeated for each field.

Then, the right-eye field for displaying the right-eye image signal on the panel 10 and the left-eye field for displaying the left-eye image signal on the panel 10 are alternately repeated, and the panel 10 includes the stereoscopic image including the right-eye image and the left-eye image. Display an image for At the same time, the stereoscopic image (3D image) displayed on the panel 10 is observed by the user through shutter glasses that open and close the right-eye shutter and the left-eye shutter in synchronization with the right-eye field and the left-eye field, respectively. To do. Thereby, the user can stereoscopically view the 3D image displayed on the panel 10.

The right-eye field and the left-eye field differ only in the image signal to be displayed, and the field configuration is the same, such as the number of subfields constituting one field, the gradation weight of each subfield, and the arrangement of subfields. is there. First, the configuration of one field and the drive voltage waveform applied to each electrode will be described.

Hereinafter, when it is not necessary to distinguish between “for right eye” and “for left eye”, the field for right eye and the field for left eye are simply abbreviated as “field”. Further, the image signal for the right eye and the image signal for the left eye are simply abbreviated as “image signal”.

In this embodiment, the field frequency (the number of fields generated per second) is set to twice the normal frequency (for example, 120 Hz) so that the user can smoothly observe a 3D moving image. ing.

Each field has a plurality of subfields, and each subfield has an initialization period, an address period, and a sustain period.

In the initializing period, an initializing operation is performed in which initializing discharge is generated in the discharge cells and wall charges necessary for the address discharge in the subsequent address period are formed on each electrode.

Initialization operation includes “forced initialization operation” that forcibly generates an initializing discharge in all discharge cells regardless of the operation of the immediately preceding subfield and an addressing discharge that occurs in the addressing period of the immediately preceding subfield. There is a “selective initialization operation” in which initializing discharge is selectively generated only in the discharge cells. In the forced initializing operation, the rising ramp waveform voltage and the falling ramp waveform voltage are applied to the scan electrode 12 to generate an initializing discharge in the discharge cell.

Then, among the plurality of subfields constituting one field, the forced initializing operation is performed in all discharge cells in the initializing period of one subfield, and all the discharge cells are selected in the initializing period of the other subfield. Perform initialization.

Hereinafter, the initialization period in which the forced initialization operation is performed is referred to as “forced initialization period”, and the subfield having the forced initialization period is referred to as “forced initialization subfield”. An initialization period for performing the selective initialization operation is referred to as a “selective initialization period”, and a subfield having the selective initialization period is referred to as a “selective initialization subfield”.

In the present embodiment, subfield SF1 is a forced initialization subfield, and the other subfields (subfields subsequent to subfield SF2) are selected initialization subfields. However, the present invention is not limited to the above-described subfields as subfields for forced initialization subfields and subfields for selective initialization subfields. Moreover, the structure which switches a subfield structure based on an image signal etc. may be sufficient.

In the address period, a scan pulse is applied to the scan electrode 12 and an address pulse is selectively applied to the data electrode 22 to selectively generate an address discharge in the discharge cells to emit light. Then, an address operation is performed to form wall charges in the discharge cells for generating a sustain discharge in the subsequent sustain period.

In the image display device according to the present embodiment, either the simultaneous writing operation for every two lines or the writing operation for every one line is performed in the writing period.

The simultaneous writing operation for every two lines is an addressing operation in which a scanning pulse is simultaneously applied to two adjacent scanning electrodes 12 and a writing pulse is selectively applied to the data electrodes 22. In the simultaneous address operation for every two lines, the address discharge is simultaneously generated in the discharge cells in which the sustain discharge is to be generated.

The address operation for each line is an address operation in which a scan pulse is sequentially applied to each of scan electrode SC1 to scan electrode SCn and an address pulse is selectively applied to data electrode 22. In the address operation for each line, an address discharge is generated for each line in a discharge cell in which a sustain discharge is to be generated.

Therefore, in the writing period in which the simultaneous writing operation is performed every two lines, the length of the writing period can be shortened as compared with the writing period in which the writing operation is performed every line.

Hereinafter, in the present embodiment, a subfield that performs a write operation for each line in the write period is referred to as a “first type subfield”. Further, a subfield that performs the simultaneous writing operation every two lines during the writing period is referred to as a “second type subfield”.

In the image display apparatus according to the present embodiment, the first type subfield and the second type subfield are mixed in one field. That is, in the present embodiment, one field includes at least one first type subfield and a plurality of second type subfields.

In addition, the above-mentioned 1 line is a row | line which consists of all the discharge cells formed on one pair of display electrode pairs 14. FIG.

In the sustain period, sustain pulses of the number obtained by multiplying the gradation weight set in each subfield by a predetermined proportional constant are alternately applied to the scan electrode 12 and the sustain electrode 13 to generate an address discharge in the immediately preceding address period. A sustain discharge is generated in the discharged discharge cell, and a sustain operation for emitting light from the discharge cell is performed. This proportionality constant is a luminance multiple.

The gradation weight represents the ratio of the magnitude of the luminance displayed in each subfield, and the number of sustain pulses corresponding to the gradation weight is generated in the sustain period in each subfield. Therefore, for example, the subfield with the gradation weight “8” emits light with a luminance about eight times that of the subfield with the gradation weight “1”, and about four times as high as the subfield with the gradation weight “2”. Emits light. Therefore, for example, if the subfield with the gradation weight “8” and the subfield with the gradation weight “2” are emitted, the discharge cell can emit light with a luminance corresponding to the gradation value “10”.

Thus, each discharge cell emits light with various gradation values by selectively emitting light in each subfield by controlling light emission / non-light emission of each discharge cell for each subfield in a combination according to the image signal. That is, a gradation value corresponding to an image signal can be displayed on each discharge cell, and an image based on the image signal can be displayed on the panel 10.

In the panel 10, as described above, one pixel includes three consecutive discharge cells arranged in the direction in which the display electrode pair 14 extends, that is, a red discharge cell, a green discharge cell, and a blue discharge. In the present embodiment, a red discharge cell is also referred to as a “red pixel”, a green discharge cell as a “green pixel”, and a blue discharge cell as a “blue pixel”.

In the present embodiment, the right-eye field and the left-eye field are each composed of five subfields (subfield SF1, subfield SF2, subfield SF3, subfield SF4, subfield SF5), and subfield SF1. To (1), (10), (6), (3), (2)) is set to each subfield of subfield SF5. Further, the subfield SF1, the subfield SF3, the subfield SF4, and the subfield SF5 are the second type subfield, and the subfield SF2 is the first type subfield.

However, in the present invention, the subfields that are the first type subfield and the subfields that are the second type subfield are not limited to the subfields described above. Further, the number of subfields constituting one field and the gradation weight set in each subfield are not limited to the above-described subfield configuration. They are preferably set optimally according to the specifications of the image display device.

FIG. 3 is a diagram schematically showing drive voltage waveforms applied to the respective electrodes of panel 10 used in the plasma display device according to one embodiment of the present invention.

FIG. 3 shows data electrode D1 to data electrode Dm, 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 The drive voltage waveform applied to each of the sustain electrodes SUn is shown. 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.

FIG. 3 also shows a subfield SF1 that is a forced initialization subfield and the second type subfield, a subfield SF2 that is a selective initialization subfield and the first type subfield, and a selective initialization subfield. And the subfield SF3 which is the second type subfield. The subfield SF1, the subfield SF2, and the subfield SF3 have different waveform shapes of the drive voltage applied to the scan electrode 12 in the initialization period. In addition, the subfield SF1, the subfield SF3, and the subfield SF2 have different write operations in the write period.

It should be noted that each subfield after subfield SF4 is a selective initialization subfield and is a second type subfield, and therefore generates substantially the same drive voltage waveform as subfield SF3 except for the number of sustain pulses.

First, the subfield SF1, which is a forced initialization subfield, will be described.

In the first half of the initialization period Ti1 of the subfield SF1 in which the forced initialization operation is performed, the voltage 0 (V) is applied to the data electrode D1 to the data electrode Dm and the sustain electrode SU1 to the sustain electrode SUn. A voltage Vi1 is applied to scan electrode SC1 through scan electrode SCn after voltage 0 (V) is applied, and a ramp waveform voltage that gradually rises from voltage Vi1 to voltage Vi2 (hereinafter referred to as an “upward ramp waveform voltage”). ) Is applied. At this time, voltage Vi1 is set to a voltage lower than the discharge start voltage for sustain electrode SU1 to sustain electrode SUn, and voltage Vi2 is set to a voltage exceeding the discharge start voltage for sustain electrode SU1 to sustain electrode SUn. To do.

While the rising ramp waveform voltage rises, scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn, and scan electrode SC1 through scan electrode SCn and data electrode D1 through data electrode Dm of each discharge cell. In between, weak initializing discharges are continuously generated. Negative wall voltage is accumulated on scan electrode SC1 through scan electrode SCn, and positive wall voltage is accumulated on data electrode D1 through data electrode Dm and sustain electrode SU1 through sustain electrode SUn. The wall voltage on 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 Ti1 of the subfield SF1, the positive voltage Ve is applied to the sustain electrodes SU1 to SUn, and the voltage 0 (V) is applied to the data electrodes D1 to Dm. A scan waveform SC1 to scan electrode SCn are applied with a ramp waveform voltage that gently falls from voltage Vi3 to negative voltage Vi4 (hereinafter referred to as “down ramp waveform voltage”). Voltage Vi3 is set to a voltage lower than the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn, and voltage Vi4 is set to a voltage exceeding the discharge start voltage with respect to sustain electrode SU1 through sustain electrode SUn.

While this downward ramp waveform voltage is applied to scan electrode SC1 through scan electrode SCn, between discharge electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn of each discharge cell, and scan electrode SC1 through scan electrode SCn. Between the data electrode D1 and the data electrode Dm, a weak initializing discharge is generated. As a result, the negative wall voltage on scan electrode SC1 through scan electrode SCn and the positive wall voltage on sustain electrode SU1 through sustain electrode SUn are weakened, and the positive wall voltage on data electrode D1 through data electrode Dm is written. The voltage is adjusted to a voltage suitable for the writing operation in the period Tw1.

The above voltage waveform is a forced initializing waveform that generates an initializing discharge in the discharge cell regardless of the operation of the immediately preceding subfield. The operation for applying the forced initialization waveform to the scan electrode 12 is the forced initialization operation.

Thus, the forced initialization operation in the initialization period Ti1 of the forced initialization subfield (subfield SF1) ends. In the initializing period Ti1 of the forced initializing subfield, initializing discharge is forcibly generated in all the discharge cells in the image display area of the panel 10.

Next, the writing period will be described.

In the image display apparatus according to the present embodiment, either the “simultaneous writing operation for every two lines” or the “writing operation for every line” is performed during the writing period.

In the simultaneous writing operation every two lines, scan electrode SC1 and scan electrode SC2, scan electrode SC3 and scan electrode SC4, scan electrode SC5 and scan electrode SC6,..., Scan electrode SCn-1 and scan electrode SCn are adjacent in this order. A scanning pulse is simultaneously applied to the two scanning electrodes 12 to be performed. That is, the two-line simultaneous write operation is a write operation in which scan pulses are sequentially applied to two adjacent scan electrodes 12 in the order in which the scan electrodes 12 are arranged on the panel 10.

In the write operation for each line, the scan pulse is applied to each scan electrode 12 in the order of scan electrode SC1, scan electrode SC2, scan electrode SC3, scan electrode SC4,..., Scan electrode SCn-1, and scan electrode SCn. Are sequentially applied. That is, the line-by-line address operation is an address operation in which scan pulses are sequentially applied to each of the scan electrodes 12 in the order in which the scan electrodes 12 are arranged on the panel 10.

In the address period Tw1 of the subfield SF1 in which the simultaneous address operation is performed every two lines, the voltage Ve is applied to the sustain electrode SU1 to the sustain electrode SUn, and the voltage 0 (V) is applied to the data electrode D1 to the data electrode Dm. Voltage Vc is applied to scan electrode SC1 through scan electrode SCn.

Next, a negative scan pulse with a negative voltage Va is applied to the first (first line) scan electrode SC1 and the second (second line) scan electrode SC2 from the top in terms of arrangement. Then, a positive address pulse having a positive voltage Vd is applied to the data electrodes Dk of the discharge cells that should emit light in the first and second lines of the data electrodes D1 to Dm.

In the discharge cell at the intersection of the data electrode Dk to which the address pulse voltage Vd is applied and the scan electrode SC1 and the scan electrode SC2 to which the scan pulse voltage Va is applied, the voltage difference between the data electrode Dk and the scan electrode SC1; The voltage difference between data electrode Dk and scan electrode SC2 exceeds the discharge start voltage, and discharge occurs between data electrode Dk and scan electrode SC1, and between data electrode Dk and scan electrode SC2.

In addition, since voltage Ve is applied to sustain electrode SU1 through sustain electrode SUn, sustain electrode SU1 in a region intersecting data electrode Dk is induced by a discharge generated between data electrode Dk and scan electrode SC1. Discharge also occurs between scan electrode SC1 and scan electrode SC1. Similarly, a discharge is also generated between sustain electrode SU2 and scan electrode SC2 in a region intersecting data electrode Dk, induced by a discharge generated between data electrode Dk and scan electrode SC2. Thus, address discharge is generated in the discharge cells (discharge cells to emit light) to which the scan pulse voltage Va and the address pulse voltage Vd are simultaneously applied.

In the discharge cell in which the address discharge has occurred, positive wall voltage is accumulated on scan electrode SC1 and scan electrode SC2, negative wall voltage is accumulated on sustain electrode SU1 and sustain electrode SU2, and data electrode Dk is accumulated. Even negative wall voltage is accumulated.

In this manner, the address operation in the first-line discharge cells and the second-line discharge cells is completed. In the discharge cell having the data electrode Dh to which the address pulse is not applied (the data electrode Dh is the data electrode D1 to the data electrode Dm excluding the data electrode Dk), the intersection of the data electrode Dh and the scan electrode SC1. Since the voltage at the portion and the voltage at the intersection between the data electrode Dh and the scan electrode SC2 do not exceed the discharge start voltage, the address discharge does not occur and the wall voltage after the end of the initialization period Ti1 is maintained.

Next, a scan pulse of voltage Va is applied to the third (third line) scan electrode SC3 and the fourth (fourth line) scan electrode SC4 from the top, and the third and fourth lines are arranged. An address pulse of voltage Vd is applied to the data electrode Dk corresponding to the discharge cell that should emit light to the eye. As a result, address discharge occurs in the discharge cells of the third line and the discharge cells of the fourth line to which the scan pulse and the address pulse are simultaneously applied. Thus, the address operation is performed in the discharge cells of the third line and the fourth line.

The same addressing operation is sequentially performed in the order of scan electrode SC5 and scan electrode SC6, scan electrode SC7 and scan electrode SC8,..., Scan electrode SCn-1 and scan electrode SCn up to the discharge cell in the nth row. An address discharge is selectively generated in the discharge cell to emit light, and a wall charge for sustain discharge is formed in the discharge cell. Thus, the writing period Tw1 of the subfield SF1 ends.

As described above, in the address period Tw1 of the subfield SF1, the simultaneous write operation for every two lines in which the scan pulse is simultaneously applied to the scan electrode SCp (p = odd number) of the odd-numbered line and the scan electrode SCp + 1 of the next even-numbered line. Thus, the same address operation is simultaneously performed in the p-th line discharge cell and the p + 1-th line discharge cell sharing the data electrode Dk. Thereby, the time required for the writing period for performing the simultaneous writing operation for every two lines is reduced to about half of the time required for the writing period for performing the writing operation for every one line.

Note that the simultaneous write operation for every two lines is not limited to the write operation in which the scan pulse is simultaneously applied to the scan electrode SCp of the odd line and the scan electrode SCp + 1 of the next even line. For example, an address operation may be performed in which a scan pulse is simultaneously applied to the even-numbered scan electrode SCp + 1 and the next odd-numbered scan electrode SCp + 2.

In the present invention, the order in which the scan pulse is applied to the scan electrode 12 is not limited to the order described above. What is necessary is just to set arbitrarily the order which applies a scanning pulse to the scanning electrode 12 according to the specification etc. in an image display apparatus.

Note that voltage Ve applied to sustain electrode SU1 through sustain electrode SUn in the second half of initialization period Ti1 and voltage Ve applied to sustain electrode SU1 through sustain electrode SUn in address period Tw1 may have different voltage values. .

Next, the maintenance period will be described.

In the sustain period Ts1 of the subfield SF1, first, the voltage 0 (V) is applied to the sustain electrodes SU1 to SUn. Then, sustain pulse of positive voltage Vs is applied to scan electrode SC1 through scan electrode SCn.

In the discharge cell in which the address discharge is generated in the address period Tw1 by the application of the sustain pulse, the voltage difference between the scan electrode SCi and the sustain electrode SUi exceeds the discharge start voltage, and is maintained between the scan electrode SCi and the sustain electrode SUi. Discharge occurs. The phosphor layer 25 of the discharge cell in which the sustain discharge has occurred emits light by the ultraviolet rays generated by the sustain discharge. In addition, due to the sustain discharge, a negative wall voltage is accumulated on scan electrode SCi, and a positive wall voltage is accumulated on sustain electrode SUi. Furthermore, a positive wall voltage is also accumulated on the data electrode Dk. However, the sustain discharge does not occur in the discharge cells in which the address discharge has not occurred in the address period Tw1.

Subsequently, voltage 0 (V) is applied to scan electrode SC1 through scan electrode SCn, and a sustain pulse of voltage Vs is applied to sustain electrode SU1 through sustain electrode SUn. In the discharge cell that has generated a sustain discharge immediately before, a sustain discharge occurs again, a negative wall voltage is accumulated on sustain electrode SUi, and a positive wall voltage is accumulated on scan electrode SCi.

Thereafter, similarly, the sustain pulses of the number obtained by multiplying the gradation weight by a predetermined luminance multiple are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn. Thus, the discharge cells that have generated the address discharge in the address period generate the sustain discharges the number of times corresponding to the gradation weight, and emit light with the luminance corresponding to the gradation weight.

After generation of the sustain pulse in sustain period Ts1 (the end of the sustain period), scan electrode SC1 to scan are performed while voltage 0 (V) is applied to sustain electrode SU1 to sustain electrode SUn and data electrode D1 to data electrode Dm. An upward ramp waveform voltage that gradually rises from voltage 0 (V) to voltage Vr is applied to electrode SCn.

By setting the voltage Vr to a voltage exceeding the discharge start voltage, the sustain of the discharge cell that has generated the sustain discharge is maintained while the rising ramp waveform voltage applied to scan electrode SC1 through scan electrode SCn exceeds the discharge start voltage. A weak discharge (erase discharge) is continuously generated between the electrode SUi and the scan electrode SCi.

The charged particles generated by this weak discharge are accumulated as wall charges on the sustain electrode SUi and the scan electrode SCi so as to reduce the voltage difference between the sustain electrode SUi and the scan electrode SCi. Thereby, the wall voltage on scan electrode SCi and the wall voltage on sustain electrode SUi are weakened while the positive wall voltage on data electrode Dk remains. Thus, unnecessary wall charges in the discharge cell are erased.

When the voltage applied to scan electrode SC1 through scan electrode SCn reaches voltage Vr, the voltage applied to scan electrode SC1 through scan electrode SCn is lowered to voltage 0 (V). Thus, the sustain operation in subfield SF1 during sustain period Ts1 ends.

Thus, subfield SF1 is completed.

Next, the selective initialization subfield will be described by taking the subfield SF2 as an example.

In the initialization period Ti2 of the subfield SF2, the voltage 0 (V) is applied to the data electrodes D1 to Dm, and the positive voltage Ve is applied to the sustain electrodes SU1 to SUn.

Scan electrode SC1 to scan electrode SCn decrease from a voltage lower than the discharge start voltage (for example, voltage 0 (V)) toward negative voltage Vi4 at the same gradient as the downward ramp waveform voltage generated in initialization period Ti1. Apply a downward ramp waveform voltage. The voltage Vi4 is set to a voltage exceeding the discharge start voltage.

In the discharge cell in which the sustain discharge is generated in the sustain period Ts1 of the immediately preceding subfield (subfield SF1 in FIG. 3) while the downward ramp waveform voltage is applied to scan electrode SC1 through scan electrode SCn, scan electrode SCi and A weak initializing discharge is generated between sustain electrode SUi and between scan electrode SCi and data electrode Dk.

And, by this initializing discharge, the negative wall voltage on scan electrode SCi and the positive wall voltage on sustain electrode SUi are weakened. In addition, an excessive portion of the positive wall voltage on the data electrode Dk is discharged. Thus, the wall voltage in the discharge cell is adjusted to a wall voltage suitable for the address operation in the address period Tw2.

On the other hand, in the discharge cells that did not generate the sustain discharge in the sustain period Ts1 of the immediately preceding subfield (subfield SF1), the initializing discharge does not occur and the previous wall voltage is maintained.

The voltage waveform described above is a selective initialization waveform in which an initializing discharge is selectively generated in a discharge cell that has performed an address operation in the address period (here, address period Tw1) of the immediately preceding subfield. The operation of applying the selective initialization waveform to the scan electrode 12 is the selective initialization operation.

Thus, the selective initialization operation in the initialization period Ti2 of the subfield SF2, which is the selective initialization subfield, is completed.

In the address period Tw2 of the subfield SF2 in which the address operation is performed for each line, the voltage Ve is applied to the sustain electrode SU1 to the sustain electrode SUn, and the voltage 0 (to the data electrode D1 to the data electrode Dm, as in the address period Tw1. V) is applied, and voltage Vc is applied to scan electrode SC1 through scan electrode SCn.

Next, a negative scan pulse having a negative voltage Va is applied to the first (first line) scan electrode SC1 in terms of arrangement. Then, a positive address pulse of a positive voltage Vd is applied to the data electrode Dk of the discharge cell that should emit light in the first line among the data electrodes D1 to Dm.

In the discharge cell at the intersection of the data electrode Dk to which the address pulse voltage Vd is applied and the scan electrode SC1 to which the scan pulse voltage Va is applied, the voltage difference between the data electrode Dk and the scan electrode SC1 determines the discharge start voltage. The address discharge occurs between the data electrode Dk and the scan electrode SC1 and between the sustain electrode SU1 and the scan electrode SC1 in the region intersecting with the data electrode Dk.

In the discharge cell in which the address discharge has occurred, a positive wall voltage is accumulated on the scan electrode SC1, a negative wall voltage is accumulated on the sustain electrode SU1, and a negative wall voltage is also accumulated on the data electrode Dk.

In this way, the address operation in the discharge cell on the first line is completed. In the discharge cell having the data electrode Dh to which the address pulse is not applied (the data electrode Dh is the data electrode D1 to the data electrode Dm excluding the data electrode Dk), the intersection of the data electrode Dh and the scan electrode SC1. Since the voltage of the part does not exceed the discharge start voltage, the address discharge does not occur, and the wall voltage after the end of the initialization period Ti2 is maintained.

Next, a scan pulse of the voltage Va is applied to the second (second line) scan electrode SC2 from the top, and the voltage Vd is applied to the data electrode Dk corresponding to the discharge cell that should emit light on the second line. Apply the write pulse. As a result, an address discharge is generated in the discharge cells of the second line to which the scan pulse and the address pulse are simultaneously applied. Thus, the write operation in the second line is performed.

The same addressing operation is sequentially performed in the order of scan electrode SC3, scan electrode SC4,..., Scan electrode SCn-1, and scan electrode SCn up to the discharge cell in the nth row, and is selected as a discharge cell to emit light. Address discharge is generated, and wall charges for sustain discharge are formed in the discharge cells. Thus, the writing period Tw2 of the subfield SF2 ends.

Thus, in the address period Tw2 of the subfield SF2, the address operation is performed for each line in which the scan pulse is sequentially applied to each of the scan electrodes SC1 to SCn.

In sustain period Ts2 of subfield SF2, as in sustain period Ts1 of subfield SF1, the number of sustain pulses corresponding to the gradation weights are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn. Apply.

In the initialization period Ti3 of the subfield SF3, a driving voltage waveform for performing a selective initialization operation is applied to each electrode in the same manner as in the initialization period Ti1 of the subfield SF2. In the writing period Tw3 of the subfield SF3, a driving voltage waveform for performing the simultaneous writing operation for every two lines is applied to each electrode as in the writing period Tw1 of the subfield SF1. In sustain period Ts3 of subfield SF3, as in sustain period Ts2 of subfield SF2, the number of sustain pulses corresponding to the gradation weights are alternately applied to scan electrode SC1 through scan electrode SCn and sustain electrode SU1 through sustain electrode SUn. Apply.

In each subfield after subfield SF4, the same drive voltage waveform as in subfield SF3 is applied to each electrode except for the number of sustain pulses generated in the sustain period. That is, in each subfield after subfield SF4, the selective initialization operation is performed in the initialization period, and the simultaneous writing operation is performed every two lines in the writing period.

The above is the outline of the drive voltage waveform applied to each electrode of panel 10 in the present embodiment.

In this embodiment, voltage values applied to the electrodes are, for example, voltage Vi1 = 150 (V), voltage Vi2 = 340 (V), voltage Vi3 = 190 (V), and voltage Vi4 = −160 (V). , Voltage Va = −180 (V), voltage Vc = −30 (V), voltage Vs = 190 (V), voltage Vr = 190 (V), voltage Ve = 120 (V), voltage Vd = 60 (V) It is. Further, the gradient of the rising ramp waveform voltage generated in the initialization period Ti1 is about 1.3 V / μsec, and the gradient of the rising ramp waveform voltage generated in each sustain period is about 10 V / μsec. The gradient of the generated downward ramp waveform voltage is about −1.5 V / μsec.

In the present embodiment, the specific numerical values such as the voltage value and the gradient described above are merely examples, and the present invention is not limited to the numerical values described above for each voltage value and the gradient. Each voltage value, gradient, and the like are preferably set optimally based on the discharge characteristics of the panel and the specifications of the plasma display device.

In the present embodiment, subfield SF1 is a forced initialization subfield for performing a forced initialization operation, and other subfields (subfields subsequent to subfield SF2) are a selective initialization subfield for performing a selective initialization operation. However, the present invention is not limited to this configuration. For example, the subfield SF1 may be a selective initialization subfield and other subfields may be forced initialization subfields, or a plurality of subfields may be forced initialization subfields.

Next, the configuration of subfields in the image display apparatus according to the present embodiment will be described.

FIG. 4 is a diagram schematically showing the subfield configuration of the image display device and the opening / closing operation of the shutter glasses in the embodiment of the present invention.

FIG. 4 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, sustain electrode SU1 to sustain electrode SUn, and data electrode D1 to data electrode Dm. The drive voltage waveform to be applied and the opening / closing operation of the right-eye shutter and the left-eye shutter are shown. FIG. 4 shows three fields (field F1 to field F3).

In the present embodiment, in order to display a 3D image on the panel 10, a right eye field and a left eye field are alternately generated.

For example, among the three fields shown in FIG. 4, the field F1 and the field F3 are right-eye fields, and the field F2 is a left-eye field. Therefore, the right eye image signal is displayed on the panel 10 in the field F1 and the field F3, and the left eye image signal is displayed on the panel 10 in the field F2.

Further, for a user who observes a 3D image displayed on the panel 10 through the shutter glasses, an image (right-eye image and left-eye image) displayed in two fields is recognized as one 3D image. Therefore, the number of images displayed on the panel 10 per second is observed by the user as half the number of fields displayed per second.

For example, if the field frequency of the 3D image displayed on the panel (the number of fields generated per second) is 60 Hz, the user will observe 30 3D images per second. Therefore, in order to display 60 3D images per second, the field frequency must be set to 120 Hz, which is twice 60 Hz.

Therefore, in this embodiment, the field frequency (the number of fields generated per second) is set to twice the normal frequency (for example, 120 Hz) so that the user can smoothly observe the 3D moving image. ing. Therefore, the time that can be used to display one right-eye image or one left-eye image is the time that can be used to display one 2D image (a normal image that is not a 3D image) with a field frequency of 60 Hz. Is limited to one-half of.

The opening / closing operation of the shutter for the right eye and the shutter for the left eye of the shutter glasses is controlled based on on / off of a shutter opening / closing timing signal.

Specifically, the right-eye shutter opens in synchronization with the start of the writing period of the first subfield (subfield SF1) of the right-eye field (for example, field F1), and starts the left-eye field (for example, field F2). The subfield (subfield SF1) is closed in synchronization with the start of the writing period.

The left-eye shutter opens in synchronization with the start of the writing period of the first subfield (subfield SF1) of the left-eye field (eg, field F2), and the first subfield (subfield) of the right-eye field (eg, field F3) Closed in synchronization with the start of the writing period of SF1).

Next, a method for displaying the gradation value corresponding to the image signal on the panel 10 will be described.

As described above, in the subfield method, one field is composed of a plurality of subfields in which gradation weights are determined in advance. Then, by combining a subfield that is lit (lighting subfield) and a subfield that is not lit (non-lighting subfield), each discharge cell emits light with a light emission luminance corresponding to the magnitude of the gradation value based on the image signal. .

Hereinafter, a combination of a lighting subfield and a non-lighting subfield is referred to as a “subfield code” or simply “code”, and a set of a plurality of subfield codes is referred to as a “code set”.

In this embodiment, a subfield code is selected from a plurality of subfield codes constituting a code set according to a gradation value. Then, light emission / non-light emission of each subfield is controlled based on the subfield code, and the discharge cell is caused to emit light with a luminance corresponding to the magnitude of the gradation value, and an image is displayed on the panel 10.

Next, a code set used in this embodiment will be described.

In the following description, the gradation value when displaying black (the gradation value when no sustain discharge occurs) is assumed to be “0”. A gradation value corresponding to the gradation weight “N” is expressed as a gradation value “N”.

Therefore, for example, the gradation value displayed by the discharge cells that emit light only in the subfield SF1 having the gradation weight “1” is the gradation value “1”. The gradation value displayed by the discharge cells that emit light only in the subfield SF1 having the gradation weight “1” and the subfield SF2 having the gradation weight “2” is 1 + 2 = 3, so the gradation value is “3”.

FIG. 5 is a diagram showing an example of a code set when one field is composed of five subfields.

In the following drawings, “gradation weight” is simply referred to as “weight”, and “gradation value” is simply referred to as “gradation”.

In the code set shown in FIG. 5, the numerical value written immediately below the notation indicating each subfield represents the gradation weight of each subfield.

In FIG. 5, one field includes five subfields from subfield SF1 to subfield SF5, and each subfield is “1”, “10”, “6”, “3”, “2”. ”Indicates a code set having a tone weight of“. ”

In the code set shown in FIG. 5, “1” indicates a light-emitting subfield, and a blank field indicates a non-light-emitting subfield, and the leftmost column indicates a gradation value to be displayed in each subfield code.

For example, based on the code set shown in FIG. 5, the subfield code corresponding to the gradation value “1” is “10000”.

Therefore, only the subfield SF1 emits light in the discharge cell displaying the gradation value “1”.

In this subfield code, it is assumed that 0 or 1 data is arranged in the order of subfield SF1, subfield SF2, subfield SF3, subfield SF4, and subfield SF5 from the left. In the following description, it is assumed that binary numerical values shown as subfield codes are arranged in the order of subfield SF1, subfield SF2, subfield SF3,.

Further, based on the code set shown in FIG. 5, the subfield code corresponding to the gradation value “10” is “10110”. Accordingly, in the discharge cell displaying the gradation value “10”, the subfield SF1, the subfield SF3, and the subfield SF4 emit light.

Next, the configuration of the 3D plasma display device in the present embodiment will be described.

FIG. 6 is a diagram schematically showing an example of a circuit block and an image display system constituting the image display device 30 according to the embodiment of the present invention.

The image display system shown in the present embodiment includes an image display device 30 and shutter glasses 38 as constituent elements.

The image display device 30 includes a panel 10, a drive circuit that drives the panel 10, and a power supply circuit (not shown) that supplies power necessary for each circuit block. The drive circuit includes an image signal processing circuit 31, a data electrode drive circuit 32, a scan electrode drive circuit 33, a sustain electrode drive circuit 34, and a timing generation circuit 35.

The drive circuit included in the image display device 30 includes one field including a first-type subfield that performs a writing operation for each line and a second-type subfield that performs a simultaneous writing operation for every two lines. Each drive voltage is generated and applied to each electrode.

The image signals input to the image signal processing circuit 31 are a red image signal, a green image signal, and a blue image signal. Based on the red image signal, the green image signal, and the blue image signal, the image signal processing circuit 31 sets each gradation value of red, green, and blue (a gradation value expressed by one field) to each discharge cell. To do. In the image signal processing circuit 31, the input image signal includes a luminance signal (Y signal) and a saturation signal (C signal, or RY signal and BY signal, or u signal and v signal, etc.). In some cases, a red image signal, a green image signal, and a blue image signal are calculated based on the luminance signal and the saturation signal, and then, each gradation value of red, green, and blue is set in each discharge cell. The red, green, and blue gradation values set for each discharge cell are subfield codes indicating lighting / non-lighting for each subfield (light emission / non-light emission corresponds to digital signals “1” and “0”). The subfield code is output as a display code. That is, the image signal processing circuit 31 converts the red image signal, the green image signal, and the blue image signal into a red display code, a green display code, and a blue display code and outputs the converted signals.

The image signal input to the image display device 30 is a 3D image signal having a right-eye image signal and a left-eye image signal. When the 3D image signal is displayed on the panel 10, the right-eye image signal is displayed. And the image signal for the left eye are alternately input to the image signal processing circuit 31 for each field. Therefore, the image signal processing circuit 31 converts the right-eye image signal into a right-eye display code (red right-eye display code, green right-eye display code, blue right-eye display code), and converts the left-eye image signal to the left-eye. Display code (red left eye display code, green left eye display code, blue left eye display code) and output.

In the present embodiment, the image signal processing circuit 31 does not convert an image signal into a subfield code using a conversion table, but converts the image signal into a subfield code by a logical operation. Details of this will be described later.

The timing generation circuit 35 generates various timing signals for controlling the operation of each circuit block based on the horizontal synchronization signal and the vertical synchronization signal. The generated timing signal is supplied to each circuit block (data electrode drive circuit 32, scan electrode drive circuit 33, sustain electrode drive circuit 34, image signal processing circuit 31, etc.).

Scan electrode drive circuit 33 includes a ramp waveform generation unit, a sustain pulse generation unit, and a scan pulse generation unit (not shown in FIG. 6), and generates a drive voltage waveform based on a timing signal supplied from timing generation circuit 35. Then, the voltage is applied to each of scan electrode SC1 to scan electrode SCn. The ramp waveform generator generates a forced initialization waveform and a selective initialization waveform to be applied to scan electrode SC1 through scan electrode SCn during the initialization period based on the timing signal. The sustain pulse generator generates a sustain pulse to be applied to scan electrode SC1 through scan electrode SCn during the sustain period based on the timing signal. The scan pulse generator includes a plurality of scan electrode drive ICs (scan ICs), and generates scan pulses to be applied to scan electrode SC1 through scan electrode SCn during the address period based on the timing signal.

That is, the scanning electrode drive circuit 33 sequentially applies scanning pulses to two adjacent scanning electrodes 12 in the order in which the scanning electrodes 12 are arranged on the panel 10 in the address period in which the simultaneous writing operation is performed every two lines. . In the address period in which the address operation is performed for each line, the scan pulse is sequentially applied to each of the scan electrodes SC1 to SCn in the order in which the scan electrodes 12 are arranged on the panel 10.

Sustain electrode drive circuit 34 includes a sustain pulse generation unit and a circuit (not shown in FIG. 5) for generating voltage Ve, and generates and maintains a drive voltage waveform based on the timing signal supplied from timing generation circuit 35. The voltage is applied to each of electrode SU1 through sustain electrode SUn. In the sustain period, a sustain pulse is generated based on the timing signal and applied to sustain electrode SU1 through sustain electrode SUn. In the initialization period and the address period, voltage Ve is generated based on the timing signal and applied to sustain electrode SU1 through sustain electrode SUn.

The data electrode drive circuit 32 is based on the right eye display code and the left eye display code of each color output from the image signal processing circuit 31 and the timing signal supplied from the timing generation circuit 35. A write pulse corresponding to is generated. Then, the data electrode drive circuit 32 applies the address pulse to the data electrodes D1 to Dm during the address period.

Next, details of the image signal processing circuit 31 and its operation will be described.

The purpose of the image signal processing circuit 31 in the present embodiment is to reduce the time required for the writing period while preventing the image display quality in the image display device 30 from deteriorating. In the following description, the distinction between the image signal for the right eye and the image signal for the left eye is not mentioned, and they are collectively referred to as an image signal. The value of the image signal is assumed to be equal to the gradation value to be displayed on the target pixel.

Note that the pixel of interest is a pixel that is an object of calculation at that time.

FIG. 7 is a diagram schematically showing an example of a circuit block constituting the image signal processing circuit 31 of the image display device 30 according to an embodiment of the present invention.

The image signal processing circuit 31 includes a one horizontal period delay unit 41, a line average unit 42, a two line difference unit 43, a subtraction unit 44, an average code conversion unit 45, a difference code creation unit 91, and a display code synthesis unit 92. . Hereinafter, the one horizontal period delay unit 41 is abbreviated as “1H delay unit 41”.

The 1H delay unit 41 delays the image signal input to the image signal processing circuit 31 by one horizontal period. Therefore, the image signal output from the 1H delay unit 41 is an image signal one line before the target pixel, and is an image signal of a pixel adjacent to the target pixel. That is, if the image signal of the pixel of interest is the image signal of the pixel on the (p + 1) line, the image signal output from the 1H delay unit 41 is the image signal of the pixel on the p line.

In the present embodiment, pixels continuously arranged on one data electrode 22 (pixels continuously arranged in the column direction) are referred to as “vertically continuous pixels”. Further, pixels continuously arranged on one display electrode pair 14 (pixels continuously arranged in the row direction) are referred to as “horizontal pixels”. Therefore, the pixels adjacent above and below the pixel of interest are pixels adjacent to the pixel of interest on one data electrode 22. Further, the pixels adjacent to the left and right of the target pixel are pixels adjacent to the target pixel on one display electrode pair 14. The vertical direction is a direction in which the data electrode 22 extends, and the horizontal direction is a direction in which the display electrode pair 14 extends.

The two-line averaging unit 42 is two pixels adjacent in the vertical direction (two pixels adjacent in the direction orthogonal to the scanning electrode 12), and the writing operation is performed simultaneously when performing the simultaneous writing operation every two lines. An average value of the image signals corresponding to each of the two pixels is calculated. Hereinafter, these two pixels are also referred to as “a pair of pixels”. That is, the 2-line average unit 42 calculates an average value of the image signal corresponding to the pixel on the p-th line and the image signal corresponding to the pixel on the (p + 1) -th line. Hereinafter, this average value is referred to as an “average image signal”. Therefore, the output of the 2-line averaging unit 42 is an average image signal of pixels on the p-th line and the (p + 1) -th line. Note that p is an odd number.

The two-line difference unit 43 is two pixels adjacent in the vertical direction (two pixels adjacent in the direction orthogonal to the scanning electrode 12), and performs a write operation simultaneously when performing a two-line simultaneous write operation. The difference value of the image signal corresponding to each of the two pixels (a pair of pixels) is calculated. Then, the two-line difference unit 43 compares the difference value with the gradation weight of the first type subfield.

In the present embodiment, the 2-line difference unit 43 subtracts the image signal corresponding to the pixel on the (p + 1) line from the image signal corresponding to the pixel on the p line to calculate a difference value. Then, the two-line difference unit 43 compares the calculated difference value with the gradation weight Wth of the first type subfield (subfield SF2 in the present embodiment). Hereinafter, the gradation weight Wth of the first type subfield (subfield SF2 in the present embodiment) is referred to as “gradation threshold Wth”.

At this time, the two-line difference unit 43 outputs “1” if the difference value is equal to or greater than the gradation threshold value Wth.

The 2-line difference unit 43 outputs “−1” if the difference value is equal to or less than (−1) × (tone threshold Wth).

The 2-line difference unit 43 outputs “0” if the difference value is larger than (−1) × (gradation threshold value Wth) and less than the gradation threshold value Wth.

That is, the two-line difference unit 43 performs the following three operations.
1) When Wth ≦ (difference value), “1” is output.
2) When -Wth <(difference value) <Wth, “0” is output.
3) When (difference value) ≦ −Wth, “−1” is output.

The subtracting unit 44 subtracts a predetermined variable determined based on the output of the two-line difference unit 43 from the output of the two-line averaging unit 42. That is, the subtracting unit 44 subtracts a predetermined variable determined by the difference value of the image signal of the pair of pixels from the average image signal of the pair of pixels.

In this embodiment, if the output of the two-line difference unit 43 is “1” or “−1”, this predetermined variable is set to “1/2 of the gradation threshold value Wth”. If the output of the 2-line difference unit 43 is “0”, the predetermined variable is set to “0”.

Accordingly, if the output of the 2-line difference unit 43 is “1” or “−1”, the subtraction unit 44 subtracts ½ of the gradation threshold value Wth from the average image signal output from the 2-line average unit 42. To do. Then, the subtraction result is output as an image signal of a pixel on the p-th line and a pixel on the (p + 1) -th line (a pair of pixels on the p-th line and the (p + 1) -th line).

If the output of the two-line difference unit 43 is “0”, the subtracting unit 44 uses the average image signal output from the two-line averaging unit 42 as it is as the pixel on the p-th line and the pixel on the (p + 1) -th line. This is output as an image signal (a pair of pixels on the p-th line and the (p + 1) -th line).

The average code conversion unit 45 converts the image signal output from the subtraction unit 44 into a subfield code having a predetermined subfield as a non-lighting subfield. This predetermined subfield is a subfield determined by the output of the 2-line difference unit 43 (comparison result in the 2-line difference unit 43).

The average code conversion unit 45 converts the image signal of the pair of pixels on the p-th line and the (p + 1) -th line output from the subtraction unit 44 into a subfield code. At this time, if the output of the two-line difference unit 43 is “1” or “−1”, the average code conversion unit 45 in the present embodiment performs the first type subfield (subfield SF2 in the present embodiment). ) To the non-lit subfield.

Therefore, if the output of the two-line difference unit 43 is “1” or “−1”, the subfield code output from the average code conversion unit 45 is “X0XXX”.

This subfield code represents a lighting subfield as “1” and a non-lighting subfield as “0”, and “X” represents either “0” or “1”. .

In this subfield code, it is assumed that data is arranged in the order of subfield SF1, subfield SF2, subfield SF3, subfield SF4, and subfield SF5 from the left.

If the output of the 2-line difference unit 43 is “0”, no subfield fixed to the non-illuminated subfield is generated, so the subfield code output from the average code conversion unit 45 is “XXXX”. .

Details of the average code converter 45 will be described later.

The difference code creation unit 91 generates a subfield code for controlling the first type subfield (subfield SF2 in the present embodiment), which is a predetermined subfield, based on the output of the two-line difference unit 43.

That is, if the output of the 2-line difference unit 43 is “1”, the difference code creation unit 91 sets the subfield code “ -1 ---- "is output. Further, for the image signal of the pixel on the (p + 1) -th line, a subfield code “−0 −−−” is output that sets the subfield SF2 to a non-lighting subfield.

Further, if the output of the two-line difference unit 43 is “−1”, the difference code creation unit 91 sets the subfield SF2 as a non-lighting subfield for the image signal of the pixel on the p-th line. The code “−0 −−−” is output. Further, for the image signal of the pixel on the (p + 1) -th line, the subfield code “−1 −−−” which outputs the subfield SF2 as the lighting subfield is output.

Further, if the output of the two-line difference unit 43 is “0”, the difference code creation unit 91 applies the subfield SF2 to the image signal of the pixel on the p-th line and the image signal of the pixel on the (p + 1) -th line. The sub-field code “-----” that does not control is output.

In this subfield code, subfields that are not subject to control are represented by “-”.

Note that the image signal processing circuit 31 in the present embodiment synthesizes the output of the average code conversion unit 45 and the output of the difference code creation unit 91 by a logical sum operation in the display code synthesis unit 92. Therefore, the differential code creation unit 91 outputs the bit corresponding to “−” replaced with “0” in consideration of the logical OR operation performed in the subsequent stage.

Note that the above-mentioned “bit” is data constituting a subfield code, and a numerical value of 1 or 0 represented by each bit represents lighting or non-lighting in each subfield.

The display code synthesis unit 92 creates a display code by synthesizing the subfield code output from the average code conversion unit 45 and the subfield code output from the difference code creation unit 91.

The display code synthesis unit 92 includes a subfield code corresponding to the p-th pixel output from the average code conversion unit 45, and a subfield code corresponding to the p-th pixel output from the difference code creation unit 91. Is ORed for each bit. Then, the result of the logical sum operation is output to the data electrode driving circuit 32 as a display code of the pixel on the p-th line. The display code is a subfield code actually used for image display.

Further, the display code synthesis unit 92 applies the subfield code corresponding to the (p + 1) line pixel output from the average code conversion unit 45 and the (p + 1) line pixel output from the difference code creation unit 91. The corresponding subfield code is ORed for each bit. Then, the result of the logical sum operation is output to the data electrode driving circuit 32 as the display code of the pixel on the (p + 1) line.

In the present embodiment, by configuring the image signal processing circuit 31 in this way, the display is performed on the panel 10 even when the simultaneous writing operation is performed every two lines in the writing period in order to shorten the writing period. It is possible to suppress a decrease in the vertical resolution of the image to be displayed.

In the present embodiment, the image signal processing circuit for performing the simultaneous writing operation every two lines with the odd-numbered scan electrode SCp and the next even-numbered scan electrode SCp + 1 as one pair in the write period. Although the operation of 31 has been described, the present invention is not limited to this configuration. When the simultaneous writing operation is performed every two lines with the scan electrode SCp + 1 of the even-numbered line and the scan electrode SCp + 2 of the next odd-numbered line as one pair in the address period, the image signal processing circuit 31 performs the operation on the scan electrode SCp + 1. It is assumed that the same operation as described above is performed with the pixel and the pixel on the scan electrode SCp + 1 as a pair of pixels.

Next, the operation of the image signal processing circuit 31 will be described.

FIG. 8A is a diagram schematically showing an example of a write operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

FIG. 8B is a diagram schematically showing another example of the writing operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

FIG. 8C is a diagram schematically showing another example of the writing operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

FIG. 8D is a diagram schematically showing another example of the writing operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

FIG. 8E is a diagram schematically showing another example of the writing operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

FIG. 8F is a diagram schematically showing another example of the writing operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

FIG. 8G is a diagram schematically showing another example of the writing operation in the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

Note that FIG. 8A is a diagram schematically illustrating an example of an image signal input to the image signal processing circuit 31. FIG. 8B is a diagram schematically illustrating an example of an image displayed on the panel 10 when it is assumed that the simultaneous writing operation is performed every two lines in the writing period of all the subfields. FIG. 8C is a diagram schematically illustrating an example of an average image signal output from the two-line average unit 42. FIG. 8D is a diagram schematically illustrating an example of an image signal output from the subtracting unit 44. FIG. 8E is a diagram schematically illustrating an example of the output of the 2-line difference unit 43. FIG. 8F is a diagram schematically showing lighting / non-lighting of the first type subfield based on the subfield code output from the difference code creating unit 91. FIG. 8G is a diagram schematically showing an example of a display image based on the subfield code output from the display code synthesis unit 92.

8A to 8G, one column represents one pixel. 8A to 8G (excluding FIG. 8E), white columns represent pixels that are lit, and black columns represent pixels that are not lit. 8E shows the output (“1” or “−1”) of the 2-line difference unit 43, and the output “0” of the 2-line difference unit 43 is indicated by a blank.

Hereinafter, as an example, the operation of the image signal processing circuit 31 when the oblique line image signal illustrated in FIG. 8A is input to the image signal processing circuit 31 will be described.

For example, it is assumed that simultaneous writing operation is performed every two lines in the writing period of all subfields. In that case, the vertical resolution of the display image is greatly reduced, and for example, as shown in FIG. 8B, the diagonal line is displayed on the panel 10 as a rough step-like line.

In addition, if a diagonal line having a line width smaller than the diagonal line shown in FIG. 8A is input to the image signal processing circuit 31, when the simultaneous writing operation is performed every two lines in the writing period of all the subfields, the diagonal line Will be displayed on the panel 10 as a dotted line. Alternatively, in the case of a thin horizontal line (one thin line extending laterally), if the simultaneous writing operation is performed every two lines during the writing period of all the subfields, the line may not be displayed on the panel 10.

In this phenomenon, when two lines are simultaneously written, only information on one line (odd line in FIG. 8B) is displayed on the panel 10, and information on the other line (even line in FIG. 8B) is displayed on the panel 10. Occurs because it is not displayed.

The 2-line average unit 42 is a circuit block provided to prevent such information loss. The two-line averaging unit 42 calculates an average value of the image signal of the pixel on the p-th line and the image signal of the pixel on the (p + 1) -th line, and outputs them as image signals for the p-th line and the (p + 1) -th line. To do. Thereby, as shown to FIG. 8C, it can prevent that the information which should be displayed on the panel 10 is missing.

However, this operation alone cannot improve the decrease in vertical resolution in the displayed image.

In the present embodiment, in order to compensate for the decrease in vertical resolution in the display image, the first type subfield (in this embodiment, subfield SF2) for performing the writing operation for each line is provided in one field. .

The image signal processing circuit 31 includes a two-line difference unit 43 and a difference code creation unit 91. The two-line difference unit 43 is a circuit block for detecting a pixel that should compensate for the decrease in vertical resolution, and the difference code creation unit 91 is a first-type subfield (this embodiment) for compensating for the decrease in vertical resolution. The circuit block for generating a subfield code for controlling the subfield SF2).

Furthermore, the image signal processing circuit 31 includes a subtraction unit 44 and a display code synthesis unit 92. The subtraction unit 44 and the display code synthesis unit 92 are circuit blocks for generating a display code based on the subfield code created by the difference code creation unit 91.

As shown in FIG. 8E, the two-line difference unit 43 changes the gradation value to be equal to or higher than the gradation threshold Wth between the image signal of the pixel on the p-th line and the image signal of the pixel on the (p + 1) -th line. Sometimes, “1” or “−1” is output.

The difference code creation unit 91 turns on the first type subfield (subfield SF2 in the present embodiment) with the pixels marked with “1” in FIG. 8E and does not light up with the pixels marked with “−1”. Create a subfield code. As a result, each pixel is turned on or off in the first type subfield (subfield SF2 in this embodiment) as shown in FIG. 8F. In FIG. 8F, each pixel not shown in the column represents lighting or non-lighting based on the image signal.

As shown in FIG. 8D, the subtracting unit 44 uses a pixel in which the output of the two-line difference unit 43 is “1” or “−1” (for example, a pixel marked “1” or “−1” in FIG. 8E) 2), 1/2 of the gradation threshold value Wth is subtracted from the average image signal output from the two-line average unit 42. This means that the sub-field code for controlling the first type sub-field (sub-field SF2 in the present embodiment) generated by the difference code creating unit 91 is combined with the output of the average code converting unit 45. In anticipation.

The average code conversion unit 45 converts the image signal output from the subtraction unit 44 into a subfield code. At this time, for a pixel (for example, a pixel surrounded by a broken line in FIG. 8D) for which the output of the two-line difference unit 43 is “1” or “−1”, the first type subfield (in this embodiment, the sub-field The field SF2) is not lit, and the second type subfield (in this embodiment, the subfield excluding the subfield SF2) generates a subfield code based on the image signal output from the subtracting unit 44. The average code conversion unit 45 converts all the subfields into subfield codes based on the image signal output from the subtraction unit 44 for the other pixels (pixels whose output from the two-line difference unit 43 is “0”). To do.

Then, the display code synthesis unit 92 synthesizes the subfield code output from the average code conversion unit 45 and the subfield code output from the difference code creation unit 91 by a logical sum operation, and actually displays the image on the image display. A display code to be used is output to the data electrode drive circuit 32.

As a result, as shown in FIG. 8G, the image signal processing circuit 31 in the present exemplary embodiment displays an image in which the vertical resolution is prevented from lowering compared to the original image signal (for example, the image shown in FIG. 8A). 10 can be displayed. That is, the image signal processing circuit 31 in the present embodiment has a vertical resolution compared to an image (for example, the image shown in FIG. 8B) when performing the simultaneous writing operation every two lines in the writing period of all subfields. It is possible to improve and display an image of a smooth diagonal line on the panel 10.

Next, the average code conversion unit 45 will be described.

FIG. 9 is a diagram schematically showing an example of a circuit block constituting the average code conversion unit 45 of the image display device 30 according to the embodiment of the present invention.

The average code conversion unit 45 includes an attribute detection unit 49, a base code generation unit 50, a rule generation unit 61, an upper and lower code generation unit 70, and an average code selection unit 80.

The attribute detection unit 49 specifies the relationship between the image signal and the position of the pixel displaying the image signal. In addition, the time differentiation of the image signal corresponding to each pixel (detecting a change in the image signal between the current field and the next field with respect to the same pixel) determines whether each pixel is in the moving image area or the still image area. Detect if there is any. Further, a change in brightness is detected by spatial differentiation of the image signal (detecting a change in the image signal between adjacent pixels), and it is detected whether or not each pixel corresponds to the contour portion of the image. Then, those detection results are output as attributes of the image signal corresponding to each pixel.

In the present embodiment, a subfield code that is basic in subsequent signal processing is referred to as a “basic code”, and a code set including the base code is referred to as a “basic code set”. The base code is a subfield code generated by lighting one by one or two in order from the subfield having the smallest gradation weight. Therefore, the base code is a subfield code in which a subfield having the largest gradation weight among the subfields to emit light and all subfields having a gradation weight smaller than that subfield emit light.

In this embodiment, “deleted base code” is set based on the base code set. The deleted base code is a subfield code in which a predetermined subfield determined by the output of the two-line difference unit 43 among the lighting subfields of the base code is a non-lighting subfield. Hereinafter, among the lighting subfields of the base code set, a subfield code set in which a predetermined subfield determined by the output of the two-line difference unit 43 is a non-lighting subfield is referred to as a “deleted base code set”.

Then, the base code generation unit 50 selects “base code set” or “deleted base code set” based on the tone value of the image signal output from the subtraction unit 44 (hereinafter referred to as “input tone”). Select "Upper gradation basis code". The upper tone base code is a base code or a deleted base code having a tone value larger than the input tone and having a tone value closest to the input tone.

As described above, the base code generation unit 50 selects a base code having a gradation value larger than the input gradation and closest to the input gradation in the base code set as the upper gradation base code, Output. Alternatively, the base code generation unit 50 selects a deleted base code having a gradation value larger than the input gradation and closest to the input gradation as the upper gradation base code in the deleted base code set, Output it.

Hereinafter, an example of the base code set and the deleted base code set will be described with reference to the drawings.

FIG. 10A is a diagram illustrating an example of a base code set used in the image display device 30 according to an embodiment of the present invention.

FIG. 10B is a diagram showing an example of a deleted base code set used in the image display device 30 according to the embodiment of the present invention.

In the code sets shown in FIGS. 10A and 10B, the light-emitting subfield is “1”, the non-light-emitting subfield is blank, and each subfield code (base code or deleted) is displayed in the second column from the left. Represents a gradation value to be displayed in (base code). Further, the numerical value written immediately below the notation indicating each subfield in each code set represents the gradation weight of each subfield.

FIG. 10A shows a base code set used when the output of the 2-line difference unit 43 is “0”. In the base code set shown in FIG. 10A, one field is composed of five subfields, and each subfield is “1”, “10”, “6”, “3”, “3” in order from the subfield SF1. 2 "gradation weight.

In the base code set shown in FIG. 10A, the first subfield (subfield SF1) of one field is the subfield having the smallest gradation weight, and the second subfield (subfield SF2) is the subfield having the largest gradation weight. After that, the subfields are arranged so that the gradation weights are sequentially reduced. And it is set as a lighting subfield one by one in an order from the subfield with the smallest gradation weight. Therefore, the number of base codes included in this base code set is (the number of subfields constituting one field + 1). For example, in the example of the base code set shown in FIG. 10A, the number of base codes is 6.

FIG. 10B shows a deleted base code set used when the output of the 2-line difference unit 43 is “1” or “−1”. The deleted base code set shown in FIG. 10B is a subfield code set generated from the base code set shown in FIG. 10A with a predetermined subfield determined by the output of the two-line difference unit 43 as a non-lighting subfield. is there.

In the present embodiment, this predetermined subfield is a first type subfield (in this embodiment, subfield SF2). Therefore, the deleted base code set shown in FIG. 10B is a subfield code set in which the subfield SF2 is a non-lighting subfield from the base code set shown in FIG. 10A.

In the present embodiment, the subfield SF2 is a subfield having the largest gradation weight. Therefore, the deleted base code set shown in FIG. 10B is equal to the code set obtained by removing the base code “11111” having the gradation value “22” from the base code set shown in FIG. 10A.

The image display device 30 in the present embodiment generates a new code set based on the code set as described above, and converts the input gradation into a subfield code using the code set.

The base code generation unit 50 includes a base code set selection unit 52 and a base code selection unit 54.

The base code set selection unit 52 stores the base code set and gradation values of a plurality of base codes constituting the base code set. In addition, the base code set selection unit 52 stores the gradation values of the deleted base code set and the plurality of deleted base codes constituting the deleted base code set. Each base code and each gradation value of the base code are stored in the base code set selection unit 52 in association with each other. This base code set is, for example, the base code set shown in FIG. 10A. Each deleted base code and each gradation value of the deleted base code are stored in the base code set selection unit 52 in association with each other. This deleted base code set is, for example, the deleted base code set shown in FIG. 10B.

If the output of the two-line difference unit 43 is “0”, the base code set selection unit 52 selects a base code set (for example, the base code set shown in FIG. If the output is “1” or “−1”, the deleted base code set (for example, the deleted base code set shown in FIG. 10B) is selected.

The base code selection unit 54 includes a subfield code (a base code constituting the base code set or a deleted base code constituting the deleted base code set) constituting the code set selected by the base code set selection unit 52. Code) and the input gradation are compared. Then, a subfield code (base code or deleted base code) having a gradation value larger than the input gradation and closest to the input gradation is selected. Then, the selected subfield code is output as the upper gradation base code.

As described above, the base code generation unit 50 selects a base code (or a deleted base code) having a gradation value larger than the input gradation and closest to the input gradation, and uses the selected base code as the upper gradation base. Output as code.

In the present embodiment, a new subfield code not included in the base code set is obtained by changing the lighting subfield in the upper gradation base code to the non-lighting subfield based on the image signal output from the subtracting unit 44. Is generated. The rule generation unit 61 generates a rule for generating this new subfield code.

That is, the rule generation unit 61 increases the number of subfield codes used for image display, the image signal output from the subtraction unit 44, and the attribute detected by the attribute detection unit 49 (the attribute associated with the image signal). ) To generate a rule for changing the lighting subfield in the upper gradation base code selected by the base code generation unit 50 to the non-lighting subfield.

In other words, in the present embodiment, the rule generated by the rule generation unit 61 defines a rule for changing the lighting subfield in the upper gradation base code to the non-lighting subfield.

The rule generated by the rule generation unit 61 restricts subfields to be changed from lighting to non-lighting in the upper gradation base code. This is because the gradation value of the new subfield code created by changing the lighting subfield to the non-lighting subfield in the upper gradation basis code is smaller than the upper gradation basis code (or the deleted basis). This is so that it does not fall below the gradation value of (code).

For example, if the upper gradation base code allows unlimited subfields to change from lighting to non-lighting, all lighting subfields become non-lighting subfields, and subfield codes with a gradation value of “0” are generated. This is because there is a possibility that it may occur.

The rule generation unit 61 generates a rule so that the subfield code generated based on the rule has the next gradation value.
1) A gradation value equal to or lower than the gradation value of the upper gradation base code.
2) A gradation value equal to or higher than the gradation value of the lower gradation base code.
The “lower gradation base code” is a base code (or a deleted base code) having a gradation value that is equal to or lower than the input gradation and closest to the input gradation.

Specifically, the rule generated by the rule generation unit 61 is composed of one or more of the following three rules.
1) A rule for setting the first subfield to be changed from the lighting subfield to the non-lighting subfield.
2) A rule for setting the second subfield to be changed from the lighting subfield to the non-lighting subfield.
3) A rule for setting a sub-field that prohibits non-lighting.

The upper / lower code generation unit 70 applies the rule generated by the rule generation unit 61 to the upper gradation base code output from the base code generation unit 50 to generate an upper gradation code and a lower gradation code.

The upper gradation code is a sub-field code that can be newly generated based on the rule generated by the rule generation unit 61 and has a gradation value larger than the input gradation and closest to the input gradation. It is a field code.

The lower gradation code has a gradation value that is equal to or lower than the input gradation and closest to the input gradation among subfield codes that can be newly generated based on the rule generated by the rule generation unit 61. It is a subfield code.

The upper / lower code generation unit 70 includes an intermediate code generation unit 72 and an upper / lower code selection unit 74.

Based on the rules generated by the rule generation unit 61, the intermediate code generation unit 72 changes the lighting subfield in the upper gradation base code to the non-lighting subfield and generates a new subfield code. Hereinafter, the newly generated subfield code is referred to as “intermediate code”. A set obtained by adding the original upper tone base code to these intermediate codes is referred to as an “intermediate code set”.

Hereinafter, an example of the intermediate code will be described with reference to the drawings.

FIG. 11A is a diagram illustrating an example of an intermediate code set generated by the intermediate code generation unit 72 of the image display device 30 according to the embodiment of the present invention.

FIG. 11B is a diagram illustrating another example of the intermediate code set generated by the intermediate code generation unit 72 of the image display device 30 according to the embodiment of the present invention.

FIG. 11C is a diagram illustrating another example of the intermediate code set generated by the intermediate code generation unit 72 of the image display device 30 according to the embodiment of the present invention.

In the intermediate code sets shown in FIGS. 11A, 11B, and 11C, the light emitting subfield is indicated by “1”, the non-light emitting subfield is indicated by a blank, and each subfield code (intermediate) is indicated in the second column from the left. Code) represents the gradation value to be displayed. Also, the numerical value written immediately below the notation indicating each subfield in each intermediate code set represents the gradation weight of each subfield.

In the intermediate code set shown in FIGS. 11A, 11B, and 11C, one field includes five subfields, and each subfield is “1”, “10”, and “6” in order from the subfield SF1. , “3” and “2”.

In FIG. 11A, as an example of the intermediate code set, “1) Rules for setting the first subfield to be changed from the lighting subfield to the non-lighting subfield” are shown in FIGS. 10A and 10B. The intermediate code set generated by applying to the base code (or deleted base code) “10111” having the gradation value “12” is shown.

This “1) rule for setting the first subfield to be changed from a lighting subfield to a non-lighting subfield” is a rule that “one of the lighting subfields is changed to a non-lighting subfield”. (Hereinafter referred to as “rule 1”).

In the base code “10111” (No. 5) of the gradation value “12” shown in FIG. 10A (or FIG. 10B), the subfield SF1 and four subfields from the subfield SF3 to the subfield SF5 are lit. It becomes a subfield.

Therefore, by changing any one of these four lighting subfields to a non-lighting subfield based on Rule 1, as shown in FIG. 11A, four subfield codes, “00111”, “10110” , “10101”, “10011” can be generated.

However, the subfield code “10011” obtained by changing the subfield SF3 to the non-lighting subfield is the base code (or the deleted base code) of the gradation value “6” shown in FIG. 10A (or FIG. 10B) (No. It is equal to 4). Accordingly, three subfield codes excluding the subfield code “10011” are newly generated intermediate codes.

That is, if the rule 1 described above is applied to the base code of the gradation value “12” shown in FIG. 10A (or the deleted base code of the gradation value “12” shown in FIG. 10B) “10111”, Three new subfield codes can be generated as intermediate codes.

In FIG. 11B, as an example of the intermediate code set, in addition to the above-described rule 1, “2) a rule for setting the second subfield to be changed from the lighting subfield to the non-lighting subfield” is shown in FIG. The intermediate code set generated by applying to the base code of the gradation value “12” shown in FIG. 10 (or the deleted base code of the gradation value “12” shown in FIG. 10B) “10111”.

This “2) Rule for setting the second subfield to be changed from the lighting subfield to the non-lighting subfield” is “the subfield code having the smallest gradation value among the newly generated intermediate codes”. The sub-field SF5 is a non-lighting sub-field ”(hereinafter referred to as“ rule 2 ”).

By applying rule 1 to the base code of gradation value “12” shown in FIG. 10A (or the deleted base code of gradation value “12” shown in FIG. 10B) “10111” (No. 5). As shown in FIG. 11A, three new subfield codes are generated. Of these three subfield codes, the “subfield code with the smallest gradation value among the newly generated intermediate codes” is the subfield code “10101” with the gradation value “9”.

Therefore, by changing the subfield SF5 of the subfield code of the gradation value “9” to the non-lighting subfield based on the rule 2, as shown in FIG. 11B, a new subfield of the gradation value “7” is obtained. The code “10100” can be generated.

That is, the above-described rule 1 and rule 2 are applied to the base code of the gradation value “12” shown in FIG. 10A (or the deleted base code of the gradation value “12” shown in FIG. 10B) “10111”. Then, four new subfield codes can be generated as intermediate codes.

In FIG. 9C, as an example of the intermediate code set, in addition to the above-described rule 1, “3) a rule for setting a subfield that prohibits non-lighting” is shown in the gradation value “ The intermediate code set generated by applying to the base code of “12” (or the deleted base code of the gradation value “12” shown in FIG. 10B) “10111” is shown.

This “3) rule for setting a subfield that prohibits non-lighting” is a rule that “subfield SF1 is prohibited from being a non-lighting subfield” (hereinafter referred to as “rule 3”). ).

By applying rule 1 to the base code of gradation value “12” shown in FIG. 10A (or the deleted base code of gradation value “12” shown in FIG. 10B) “10111” (No. 5). As shown in FIG. 11A, three new subfield codes are generated. Of these three subfield codes, the “subfield code whose subfield SF1 is a non-lighting subfield” is a subfield code “00111” having a gradation value of “11”.

Therefore, based on rule 3, the subfield code having the gradation value “11” is excluded from the intermediate code set.

That is, rule 1 and rule 3 described above are applied to the base code of the gradation value “12” shown in FIG. 10A (or the deleted base code of the gradation value “12” shown in FIG. 10B) “10111”. Then, two new subfield codes can be generated as intermediate codes.

As described above, the intermediate code generation unit 72 applies the rule generated by the rule generation unit 61 to the upper gradation base code output from the base code generation unit 50 to generate an intermediate code, and the intermediate code set Is generated.

In the following, an example in which rule 1 and rule 3 are used when generating intermediate code will be described. However, if the number of intermediate codes to be generated is increased, rule 2 may be added when generating intermediate code. For example, when the image display device 30 displays an image with relatively low power consumption, or when an image with relatively little occurrence of moving image pseudo contour is displayed, the number of intermediate codes generated can be increased. It is. Then, by increasing the number of intermediate codes generated, an image can be displayed with a smoother gradation change.

The upper / lower code selection unit 74 compares each gradation value of the subfield code constituting the intermediate code set generated by the intermediate code generation unit 72 with the input gradation. Then, the upper / lower code selection unit 74 selects a subfield code having a gradation value larger than the input gradation and closest to the input gradation, and outputs it as an upper gradation code. In addition, the upper / lower code selection unit 74 selects a subfield code having a gradation value equal to or lower than the input gradation and closest to the input gradation, and outputs it as a lower gradation code.

The average code selection unit 80 adds a predetermined value to the input gradation and calculates a gradation value to be displayed on the pixel pair of interest. Then, the average code selection unit 80 selects one of the upper gradation code and the lower gradation code that has a gradation value closer to the gradation value to be displayed on the target pixel pair, and outputs it.

Note that the pixel-of-interest pair is a pair of pixels that are the targets of gradation value calculation at that time.

In the present embodiment, the above-described predetermined value added to the input gradation is an error diffused by the error diffusion process and a dither value calculated by the dither process. Therefore, the average code selection unit 80 adds the error and the dither value to the input gradation, calculates the gradation value to be displayed on the pixel pair of interest, and selects the attention value of the upper gradation code and the lower gradation code. The one having a gradation value closer to the gradation value to be displayed on the pixel pair is selected.

Furthermore, the average code selection unit 80 calculates the difference between the gradation value to be displayed on the target pixel pair and the selected gradation value, and diffuses the difference as an error to surrounding pixels.

The average code selection unit 80 includes a dither selection unit 82, an error diffusion unit 84, and an average code determination unit 86.

The dither selection unit 82 stores a plurality of dither patterns. Then, one dither pattern based on the image signal output from the subtraction unit 44 (hereinafter simply referred to as “image signal”) and the attribute detected by the attribute detection unit 49 from among the plurality of stored dither patterns. Select.

Also, the dither selection unit 82 selects a dither element corresponding to the position of the pixel from the selected dither pattern based on the position of the pixel displaying the image signal. Further, the dither selection unit 82 calculates the dither value by multiplying the selected dither element by the difference between the gradation value of the upper gradation code and the gradation value of the lower gradation code.

In the present embodiment, the same dither element is given to each of a pair of pixels that simultaneously perform the write operation in the second type subfield.

An example of these operations will be described with reference to the drawings.

FIG. 12A is a diagram showing an example of a dither pattern used in the image display device 30 according to the embodiment of the present invention.

FIG. 12B is a diagram showing another example of the dither pattern used in the image display device 30 according to the embodiment of the present invention.

In FIGS. 12A and 12B, one column represents one pixel.

FIG. 12A shows the simplest binary dither. In FIG. 12A, “+0.25” and “−0.25” are arranged in a checkered pattern as dither elements. FIG. 12B is a diagram showing an example of a quaternary dither. In FIG. 12B, dither elements “+0.375”, “+0.125”, “−0.375” and “−0.125” are arranged.

The error diffusion unit 84 outputs an error to be added to the target pixel pair to the average code determination unit 86 and diffuses the error output from the average code determination unit 86 to the peripheral pixels of the target pixel pair.

Note that the error diffusion unit 84 diffuses the same error to each of a pair of pixels that simultaneously perform the write operation in the second type subfield.

Then, the dither selection unit 82 stores, for example, the two types of dither patterns shown in FIGS. 12A and 12B, and selects one of the dither patterns based on the attributes detected by the image signal and the attribute detection unit 49. . When the dither pattern shown in FIG. 12A is selected, the dither element is either “+0.25” or “−0.25”. When the dither pattern shown in FIG. 12B is selected, the dither element is “+0”. .375 ”,“ +0.125 ”,“ −0.375 ”, and“ −0.125 ”.

Then, the dither selection unit 82 selects any one of these dither elements based on the position of the pixel displaying the image signal. Further, the dither value is calculated by multiplying the selected dither element by the difference between the tone value of the upper tone code and the tone value of the lower tone code. Then, the calculated dither value is added to the input gradation in the average code selection unit 80.

FIG. 13 is a diagram showing error diffusion coefficients of the error diffusion unit 84 of the image display device 30 according to the embodiment of the present invention.

In FIG. 13, one column represents one pixel. The middle column in FIG. 13 represents a pair of pixels (target pixel pair) that are to be subjected to error diffusion processing.

The error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the pair of pixels arranged at the upper left of the target pixel pair by the diffusion coefficient k1 to the target pixel pair. Further, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the pair of pixels arranged on the target pixel pair by the diffusion coefficient k2 to the target pixel pair. Further, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the pair of pixels arranged at the upper right of the target pixel pair by the diffusion coefficient k3 to the target pixel pair. Further, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying an error generated in a pair of pixels arranged on the left of the target pixel pair by a diffusion coefficient k4.

Then, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the target pixel pair by the diffusion coefficient k4 to a pair of pixels arranged to the right of the target pixel pair. In addition, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the target pixel pair by the diffusion coefficient k3 to a pair of pixels arranged at the lower left of the target pixel pair. Further, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the target pixel pair by the diffusion coefficient k2 to a pair of pixels arranged below the target pixel pair. In addition, the error diffusion unit 84 diffuses (adds) a value obtained by multiplying the error generated in the target pixel pair by the diffusion coefficient k1 to a pair of pixels arranged at the lower right of the target pixel pair.

In this embodiment, the diffusion coefficients are k1 = 1/16, k2 = 4/16, k3 = 3/16, and k4 = 8/16. Alternatively, k1 = 3/16, k2 = 4/16, k3 = 1/16, and k4 = 8/16. In the present embodiment, which diffusion coefficient is selected is determined using a random number generated by a random number generator (not shown).

Based on the input tone, the dither value output from the dither selection unit 82, and the error output from the error diffusion unit 84, the average code determination unit 86 converts the subfield code output to the subsequent stage into the upper tone code or the lower tone code. Determine one of the gradation codes.

Specifically, the average code determination unit 86 adds a dither value and an error to the input gradation, and calculates a gradation value to be displayed on the target pixel pair. Then, of the upper gradation code and the lower gradation code, the one having the gradation value closer to the gradation value to be displayed on the target pixel pair is selected as the subfield code to be output to the subsequent stage.

Then, the average code determination unit 86 calculates a difference between the gradation value to be displayed on the target pixel pair and the gradation value of the selected subfield code, and uses the difference as a newly generated error. Output to.

Next, the operation of the image signal processing circuit 31 will be described. In the following description, it is assumed that the image signal processing circuit 31 operates based on the following conditions.
1) The deleted base code set shown in FIG. 10B is used as the code set.
2) The rules used in the description of FIG. 11A are used. That is, rule 1 “change any one of the lighting subfields to a non-lighting subfield” is used.
3) Based on the attribute accompanying the image signal, “Rule for setting sub-field forbidden to turn off” (rule 3) is added to rule 1.

FIG. 14 is a flowchart showing the operation of the image signal processing circuit 31 of the image display device 30 according to the embodiment of the present invention.

The image signal processing circuit 31 executes the following series of steps.

(Step S42)
The 2-line averaging unit 42 calculates an average value of the image signal corresponding to the target pixel on the p-th line and the image signal corresponding to the target pixel on the (p + 1) -th line. Then, the calculation result is output as an average image signal of the target pixel pair on the p-th line and the (p + 1) -th line.

For example, if the tone value of the image signal corresponding to the target pixel of the p-th line is “5” and the tone value of the image signal corresponding to the target pixel of the (p + 1) -th line is “18”, 2 The line average unit 42 outputs “11.5” as the gradation value of the average image signal of the target pixel pair in the p-th line and the (p + 1) -th line.

(Step S43)
The two-line difference unit 43 calculates a difference value by subtracting the image signal corresponding to the target pixel on the (p + 1) line from the image signal corresponding to the target pixel on the p-th line. Then, the difference value is compared with the gradation threshold value Wth, and the comparison result is output.

That is, the two-line difference unit 43 outputs “1” if the difference value is equal to or greater than the gradation threshold Wth, and “−1” if the difference value is equal to or less than (−1) × (gradation threshold Wth). Is output, and if the difference value is larger than (−1) × (tone threshold Wth) and less than the tone threshold Wth, “0” is output.

For example, if the image signal corresponding to the target pixel on the p-th line is “5” and the image signal corresponding to the target pixel on the (p + 1) -th line is “18”, the difference value between them is “−13”. It becomes. In the present embodiment, the gradation threshold value Wth is a numerical value equal to the gradation weight of the first type subfield (subfield SF2 in the present embodiment). Therefore, for example, if the gradation weight of the subfield SF2 is “10”, the gradation threshold value Wth is “10”. At this time, the difference value “−13” is equal to or less than (−1) × (tone threshold Wth). Therefore, the two-line difference unit 43 outputs “−1”.

(Step S44)
If the output of the two-line difference unit 43 is “1” or “−1”, the subtraction unit 44 subtracts ½ × tone threshold Wth from the average image signal of the target pixel pair, and the result is p-line It outputs as an image signal of the target pixel pair of the eye and the (p + 1) -th line. If the output of the two-line difference unit 43 is “0”, the subtracting unit 44 outputs the average image signal of the target pixel pair as it is.

For example, if the output of the 2-line difference unit 43 is “−1”, the gradation threshold Wth is “10”, and the gradation value of the average image signal of the pixel pair of interest is “11.5”, 11 .5-10 / 2 = 6.5. Therefore, the subtracting unit 44 outputs “6.5” as the gradation value of the target pixel pair on the p-th line and the (p + 1) -th line.

(Step S49)
The attribute detection unit 49 of the average code conversion unit 45 receives the image signal (input gradation) of the target pixel pair on the p-th line and the (p + 1) -th line output from the subtraction unit 44. The attribute detection unit 49 detects an attribute associated with the image signal.

Hereinafter, the image signal corresponding to the pixel pair of interest has a gradation value (input gradation) of “6.5”, and the attribute attached to the image signal corresponding to the pixel pair of interest in the attribute detection unit 49 is a moving image. The description will be made assuming that the detection result of the contour portion is obtained.

(Step S52)
Based on the output of the two-line difference unit 43, the base code set selection unit 52 of the average code conversion unit 45 is either a base code set stored in the base code set selection unit 52 or a deleted base code set. Select. If the output of the 2-line difference unit 43 is “0”, the base code set selection unit 52 selects a base code set (for example, the base code set shown in FIG. 10A), and the output of the 2-line difference unit 43 is If it is “1” or “−1”, the deleted base code set (for example, the deleted base code set shown in FIG. 10B) is selected.

(Step S54)
The base code selection unit 54 of the average code conversion unit 45 selects the upper tone base code for the input tone.

That is, in step S54, the gradation that is larger than the gradation value (input gradation) of the image signal in the pixel pair of interest and is closest to the input gradation from the code set selected by the base code set selection unit 52. A subfield code having a value is selected as the upper gradation base code.

Specifically, the base code selection unit 54 sets each gradation value of the base code constituting the base code set stored in the base code set selection unit 52 (or the deleted base code constituting the deleted base code set). Are compared with the input gradation. Then, a base code (or a deleted base code) having a gradation value larger than the input gradation and closest to the input gradation is selected, and is output as an upper gradation base code.

For example, if the output of the 2-line difference unit 43 is “−1” and the input gradation is “6.5”, the base code set selection unit 52 selects the deleted base code set shown in FIG. 10B. . Then, the base code selection unit 54 has a gradation value that is larger than the gradation value “6.5” and closest to the gradation value “6.5” in the deleted base code set shown in FIG. 10B. Select the deleted base code. At this time, the deleted base code “10111” having the gradation value “12” is the deleted base code having the gradation value larger than the gradation value “6.5” and having the gradation value closest to the gradation value “6.5”. Is. Therefore, the base code selection unit 54 selects the deleted base code “10111” and outputs it as the upper gradation base code.

(Step S61)
The rule generation unit 61 of the average code conversion unit 45 generates a rule for generating an intermediate code set.

That is, in step S61, a rule for generating a new subfield code by changing the light emitting subfield in the upper gradation base code to a non-light emitting subfield is generated based on the image signal in the pixel pair of interest.

Specifically, the rule generation unit 61 performs a basic rule (rule 1) “change any one of the lighting subfields to the non-lighting subfield” if the attribute attached to the image signal is a still image. ) Is generated.

If the attribute attached to the image signal is a moving image, the rule generation unit 61 restricts the subfield codes that can be used for displaying the image in order to suppress the moving image pseudo contour.

In the image display device 30 using the panel 10, when a moving image is displayed on the panel 10, a false contour that is not included in the original image signal may be observed by the user. This false contour is a moving image pseudo contour. The subfield codes include those that have a high effect of suppressing moving image pseudo contours and those that do not. For example, the subfield codes shown in FIGS. 10A and 10B are subfield codes that have a high effect of suppressing the moving image pseudo contour.

In other words, the appearance of the moving image pseudo contour depends on the subfield code that can be used to display the image, and the image is displayed using the subfield code that is highly effective in suppressing the moving image pseudo contour. The moving image pseudo contour can be suppressed. In that case, the subfield code that can be used for displaying an image is limited as compared with the case where the suppression of the moving image pseudo contour is unnecessary. This is the reason why the rule generation unit 61 restricts the subfield codes that can be used for image display in order to suppress the moving image pseudo contour.

Then, if the attribute attached to the image signal is a moving image, the rule generating unit 61 sets “a subfield that prohibits non-lighting” in the basic rule 1 in order to suppress the moving image pseudo contour. Add “When the rule”. This additional rule is, for example, the rule 3 described with reference to FIG. 11C, which is “prohibiting the subfield SF1 from being a non-lighting subfield”. As a result, the rule generation unit 61 limits the subfield codes that can be used for displaying an image.

Therefore, when the attribute attached to the image signal is a moving image (that is, when the image signal in the target pixel pair is a moving image), the rule generated by the rule generation unit 61 is that the attribute attached to the image signal is a still image. The rule generation unit 61 includes a rule generated when the image signal in the pixel pair of interest is a still image.

(Step S72)
The intermediate code generation unit 72 of the average code conversion unit 45 generates an intermediate code set.

Specifically, the intermediate code generation unit 72 generates an intermediate code from the upper gradation base code based on the rules generated by the rule generation unit 61, and generates an intermediate code set.

For example, if the upper gradation base code selected in step S50 is the deleted base code “10111” having the gradation value “12” and the rules generated by the rule generation unit 61 are rule 1 and rule 3, The code generation unit 72 applies the

rules

1 and 3 generated by the rule generation unit 61 to the base code “10111” to generate a new intermediate code.

Specifically, out of subfield SF1 and subfield SF3 to subfield SF5, which are lighting subfields of the deleted base code “10111”, the subfield (from subfield SF3 to subfield SF1 is excluded based on rule 3). The subfield SF5) is to be replaced with a non-lighting subfield. Then, based on rule 1, the subfields SF3 to SF5 are set to non-lighting subfields. In this way, the intermediate code generating unit 72 generates three intermediate codes “10011”, “10101”, and “10110”. The intermediate code set thus obtained is, for example, the intermediate code set shown in FIG. 11C.

(Step S74)
The upper / lower code selection unit 74 of the average code conversion unit 45 selects an upper gradation code and a lower gradation code.

That is, in step S74, the gradation of the image signal in the target pixel pair is larger than the gradation value of the image signal in the target pixel pair from the intermediate code set generated by applying the above-described rule to the upper gradation base code. The subfield code having the gradation value closest to the value is selected as the upper gradation code, and the gradation closest to the gradation value of the image signal in the target pixel pair is equal to or smaller than the gradation value of the image signal in the target pixel pair A subfield code having a value is selected as a lower gradation code.

Specifically, the upper / lower code selection unit 74 compares each gradation value of the subfield code constituting the intermediate code set with the input gradation. Then, a subfield code having a gradation value larger than the input gradation and closest to the input gradation is selected and output as an upper gradation code. Also, a subfield code having a gradation value that is equal to or lower than the input gradation and closest to the input gradation is selected, and is output as a lower gradation code.

For example, if the input gradation is the gradation value “6.5” and the intermediate code set generated in step S72 is the intermediate code set shown in FIG. 11C, the subfield code corresponding to the upper gradation code is This is a subfield code of gradation value “9”. Further, the subfield code corresponding to the lower gradation code is a subfield code having a gradation value “6”. Therefore, the upper / lower code selection unit 74 selects the subfield code “10101” having the gradation value “9” as the upper gradation code and the subfield code “10011” having the gradation value “6” as the lower gradation code. ”Is selected.

(Step S82)
The dither selection unit 82 of the average code conversion unit 45 selects a dither element based on the attribute of the image signal.

For example, if the dither pattern shown in FIG. 12A and the dither pattern shown in FIG. 12B are stored in the dither selection unit 82, the dither selection unit 82 uses the attribute detected by the image signal and attribute detection unit 49. Based on the above, one of the dither patterns is selected.

If the attribute attached to the image signal is a contour portion, the dither pattern shown in FIG. 12A is selected. If the attribute attached to the image signal is not a contour portion, the dither pattern shown in FIG. 12B is selected. If the selection unit 82 is set, when the attribute attached to the image signal is a contour portion, the dither selection unit 82 selects the dither pattern shown in FIG. 12A. Then, the dither selection unit 82 selects one of the dither elements set in the dither pattern based on the position of the target pixel pair. For example, the dither selection unit 82 selects “0.25” as the dither element based on the dither pattern shown in FIG. 2A.

(Step S83)
The dither selector 82 calculates a dither value.

The dither selection unit 82 calculates the dither value by multiplying the selected dither element by the difference between the tone value of the upper tone code and the tone value of the lower tone code.

For example, the upper gradation code selected in step S74 is the gradation value “9”, the gradation value of the lower gradation code selected in step S74 is “6”, and the dither selected in step S82. If the element is “0.25”, the dither selector 82 multiplies the difference “3” between the gradation value of the upper gradation code and the gradation value of the lower gradation code by the dither element “0.25”. Then, the dither value “0.75” is calculated.

(Step S86)
The average code determination unit 86 of the average code conversion unit 45 calculates a gradation value to be displayed on the target pixel pair.

That is, in step S86, a predetermined value is added to the gradation value of the image signal in the target pixel pair to calculate the gradation value to be displayed on the target pixel pair.

Specifically, the average code determination unit 86 adds the dither value calculated in step S83 to the input gradation, and further adds the error output from the error diffusion unit 84 based on the calculation result in step S88. Thus, the gradation value to be displayed on the target pixel pair is calculated. Therefore, the predetermined value is a numerical value obtained by adding the dither value output from the dither selection unit 82 and the error output from the error diffusion unit 84.

For example, the input gradation is the gradation value “6.5”, the dither value calculated in step S83 is “0.75”, and the error output from the error diffusion unit 84 based on the calculation result in step S88. Is “−0.1”, 6.5 + 0.75−0.1 = 7.15. Therefore, the gradation value to be displayed on the target pixel is “7.15”.

(Step S87)
The average code determination unit 86 determines a subfield code to be used when displaying a gradation value on the target pixel pair.

That is, in step S87, the one having the gradation value closer to the gradation value to be displayed on the target pixel pair among the upper gradation code and the lower gradation code is selected as the subfield code to be output to the subsequent stage.

Specifically, the average code determination unit 86 compares the gradation value to be displayed on the target pixel pair with the gradation value of the upper gradation code and the gradation value of the lower gradation code. If the tone value to be displayed on the target pixel pair is closer to the tone value of the upper tone code than the tone value of the lower tone code, it is used to display the tone value on the target pixel pair. The upper gradation code is selected as the subfield code to be output, and is output. When the gradation value to be displayed on the target pixel pair is closer to the lower gradation code gradation value than the upper gradation code gradation value, the gradation value is displayed on the attention pixel pair. A lower gradation code is selected as a subfield code to be used, and is output.

For example, the gradation value of the upper gradation code is “9”, the gradation value of the lower gradation code is “6”, and the gradation value to be displayed on the target pixel pair is “7.15”. For example, the difference between the gradation value of the upper gradation code and the gradation value to be displayed on the target pixel pair is “1.85”, and the gradation value to be displayed on the lower pixel code and the target pixel pair The difference from the value is “1.15”. Therefore, in this case, the average code determination unit 86 selects the lower gradation code “10011” having the gradation value “6” and outputs it to the subsequent stage.

(Step S88)
The average code determination unit 86 calculates a newly generated error and outputs it to the error diffusion unit 84.

The average code determination unit 86 subtracts the gradation value of the subfield code selected for output to the subsequent stage from the gradation value to be displayed on the pixel pair of interest, and the subtraction result is error diffusion as a newly generated error. To the unit 84.

For example, if the gradation value to be displayed on the target pixel pair is “7.15” and the gradation value of the subfield code selected for output to the subsequent stage is “6”, 7.15−6 = 1.15. Therefore, the average code determination unit 86 outputs “1.15” to the error diffusion unit 84 as a newly generated error.

(Step S91)
Based on the output of the two-line difference unit 43, the difference code creation unit 91 generates a subfield code for controlling the first type subfield (subfield SF2 in the present embodiment) that performs the write operation for each line during the write period. Generate.

If the output of the two-line difference unit 43 is “1”, the difference code creation unit 91 sets the first type subfield to the lighting subfield for the image signal of the pixel of interest on the p-th line. And a subfield code for making the first type subfield a non-lighting subfield is output for the image signal of the target pixel on the (p + 1) -th line.

Further, if the output of the two-line difference unit 43 is “−1”, the difference code creation unit 91 sets the first type subfield to the non-lighting subfield for the image signal of the target pixel on the p-th line. And outputs a subfield code for setting the first type subfield to the lighting subfield for the image signal of the target pixel on the (p + 1) -th line.

Further, if the output of the two-line difference unit 43 is “0”, the difference code creation unit 91 applies the first to the image signal of the target pixel of the p-th line and the image signal of the target pixel of the (p + 1) -th line. A subfield code that does not control one type of subfield is output.

For example, if the first type subfield is the subfield SF2 and the output of the two-line difference unit 43 is “−1”, the difference code creation unit 91 does not process the image signal of the pixel of interest on the p-th line. , The subfield code “−0 −−−”, which makes the subfield SF2 a non-lighting subfield, is output. Further, for the image signal of the pixel of interest on the (p + 1) -th line, a subfield code “−1 −−−” that outputs the subfield SF2 as a lighting subfield is output.

In this subfield code, a subfield that is not subject to control is represented by “−”. However, in this embodiment, “−” is set to “0” in consideration of a logical operation in a later stage. Yes. Therefore, the difference code creation unit 91 outputs the above-described subfield code “−0 −−−” as the subfield code “00000”, and outputs the above subfield code “−1 −−−” as the subfield code “01000”. "Is output.

(Step S92)
The display code synthesis unit 92 synthesizes the subfield code output from the average code conversion unit 45 and the subfield code output from the difference code creation unit 91 to create a display code.

Specifically, the display code synthesis unit 92 includes the sub-field code corresponding to the p-th pixel of interest output from the average code converter 45 and the p-th pixel of interest output from the difference code creation unit 91. The sub-field code corresponding to is ORed for each bit. Then, the result of the logical sum operation is output to the data electrode drive circuit 32 as a display code of the pixel of interest on the p-th line.

The display code synthesis unit 92 also outputs the subfield code corresponding to the pixel of interest on the (p + 1) th line output from the average code conversion unit 45 and the target of the (p + 1) th line output from the difference code creation unit 91. The subfield code corresponding to the pixel is ORed for each bit. Then, the result of the logical sum operation is output to the data electrode driving circuit 32 as the display code of the pixel on the (p + 1) line.

Note that the display code is a subfield code actually used for image display.

For example, if “10011” is output from the average code conversion unit 45 and “00000” is output from the difference code creation unit 91 as the subfield code of the pixel of interest on the p-th line, the display code synthesis unit 92 “10011” is output as the display code of the pixel of interest on the line.

Alternatively, if “10011” is output from the average code conversion unit 45 and “01000” is output from the difference code creation unit 91 as the subfield code of the pixel of interest on the (p + 1) -th line, the display code synthesis unit 92 , “11011” is output as the display code of the pixel of interest on the (p + 1) -th line.

When step S92 ends, the process returns to step S42. In this way, a series of steps from step S42 to step S92 is repeatedly executed.

As described above, in the present embodiment, one field is constituted by the first type subfield that performs the write operation for each line during the write period and the second type subfield that performs the simultaneous write operation for every two lines during the write period. To do.

Then, when the difference value of the image signal corresponding to a pair of pixels (target pixel pair) performing the write operation at the same time in the second type subfield is smaller than the gradation weight of the first type subfield, it corresponds to the target pixel pair. The average value of the image signal to be converted is converted into a display code.

Further, when the above-described difference value is equal to or greater than the gradation weight of the first type subfield, a display code for lighting one pixel of the target pixel pair and turning off the other pixel in the first type subfield is created. .

Thereby, the time required for the writing period can be shortened while preventing the image display quality in the image display device 30 from deteriorating.

Further, in the present embodiment, by configuring the image signal processing circuit 31 as described above, conversion from an image signal to a display code (subfield code) is performed using a conversion table including a number of subfield codes. Rather than doing so, it can be done by an arithmetic circuit.

In other words, in this embodiment, an image that needs to cope with an increase in the screen size of the panel, higher definition, improvement in image display quality, diversification of broadcasting methods, multi-functionality such as a 3D image display function, and the like. In the display device, it is not necessary to configure an image signal processing circuit so as to select an optimum one from a vast number of conversion tables according to various conditions. According to the present embodiment, conversion from an image signal to a display code (subfield code) can be performed by calculation using an arithmetic circuit. Therefore, even in such an image display device, it is not necessary to provide a huge number of conversion tables, but a necessary minimum table (for example, the base code set shown in FIG. 10A and the deleted base code shown in FIG. 10B). Set) and an arithmetic circuit for converting the image signal into the display code.

As described above, according to the present embodiment, in the image display device 30, the conversion from the image signal to the subfield code can be performed by the logical operation, which is necessary for the writing period while preventing the image display quality from being deteriorated. Time can be shortened.

In the present embodiment, only the subfield having the largest gradation weight (subfield SF2 in the present embodiment) is the first type subfield, and the other subfields are the second type subfield. Although described, the present invention is not limited to this configuration.

FIG. 15 is a diagram schematically showing another example of a drive voltage waveform applied to each electrode of panel 10 used in image display device 30 in one embodiment of the present invention.

FIG. 15 shows data electrode D1 to data electrode Dm, 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 The drive voltage waveform applied to each of the sustain electrodes SUn is shown.

In the drive voltage waveform shown in FIG. 15, one field is composed of five subfields (subfield SF1, subfield SF2, subfield SF3, subfield SF4, subfield SF5), and subfield SF1 to subfield SF5 It is assumed that gradation weights of (1, 10, 6, 3, 2) are set in each subfield.

In the drive voltage waveform shown in FIG. 15, subfield SF1 is a forced initialization subfield and is a second type subfield. The subfield SF2 and the subfield SF3 are selective initialization subfields and are type 1 subfields. Each subfield after subfield SF4 is a selective initialization subfield and is a second type subfield.

For example, as shown in FIG. 15, a subfield having the largest gradation weight (for example, subfield SF2) and a subfield having the second largest gradation weight (for example, subfield SF3) are set to one line in the writing period. The first type subfield that performs each write operation may be used, and the other subfield may be the second type subfield that performs the simultaneous write operation every two lines during the write period.

In such a driving voltage waveform, the gradation weight Wth of the first type subfield (subfield SF2 in FIG. 15) having the largest gradation weight is set to the first gradation threshold Wth1, and the gradation weight is the second. The gradation weight Wth of the large first type subfield (subfield SF3 in FIG. 15) is set as the second gradation threshold Wth2.

Then, the two-line difference unit 43 compares the calculated difference value (difference value of the image signal corresponding to each pixel of the target pixel pair) with the first gradation threshold Wth1 and the second gradation threshold Wth2.

The 2-line difference unit 43 outputs “2” if the difference value is equal to or greater than the first gradation threshold Wth1.

Also, the two-line difference unit 43 outputs “1” if the difference value is less than the first gradation threshold value Wth1 and greater than or equal to the second gradation threshold value Wth2.

The 2-line difference unit 43 outputs “0” if the difference value is less than the second gradation threshold Wth2 and greater than (−1) × (second gradation threshold Wth2).

The two-line difference unit 43 outputs “−1” if the difference value is equal to or smaller than (−1) × (second gradation threshold Wth2) and is larger than (−1) × (first gradation threshold Wth1). To do.

The 2-line difference unit 43 outputs “−2” if the difference value is equal to or less than (−1) × (first gradation threshold Wth1).

That is, the 2-line difference unit 43 performs the following five operations.
1) When Wth1 ≦ (difference value), “2” is output.
2) When Wth2 ≦ (difference value) <Wth1, “1” is output.
3) When -Wth2 <(difference value) <Wth2, “0” is output.
4) When -Wth1 <(difference value) ≦ Wth2, “−1” is output.
5) When (difference value) ≦ −Wth1, “−2” is output.

The subtracting unit 44 subtracts a predetermined variable determined based on the output of the two-line difference unit 43 from the average image signal output from the two-line averaging unit 42. That is, the subtracting unit 44 subtracts a predetermined variable determined by the difference value of the image signal of the pair of pixels from the average image signal of the pair of pixels.

If the output of the two-line difference unit 43 is “2” or “−2”, the subtraction unit 44 sets this predetermined variable to “½ of the first gradation threshold value Wth1”. If the output of the two-line difference unit 43 is “1” or “−1”, the subtracting unit 44 sets the predetermined variable to “½ of the second gradation threshold value Wth2”. The subtractor 44 sets the predetermined variable to “0” if the output of the two-line difference unit 43 is “0”.

Therefore, if the output of the two-line difference unit 43 is “2” or “−2”, the subtracting unit 44 uses the average image signal output from the two-line averaging unit 42 to ½ the first gradation threshold value Wth1. Is output as an image signal of a pixel on the p-th line and a pixel on the (p + 1) -th line (a pair of pixels on the p-th line and the (p + 1) -th line).

Further, if the output of the two-line difference unit 43 is “1” or “−1”, the subtracting unit 44 calculates ½ of the second gradation threshold Wth2 from the average image signal output from the two-line averaging unit 42. Is output as an image signal of a pixel on the p-th line and a pixel on the (p + 1) -th line (a pair of pixels on the p-th line and the (p + 1) -th line).

The average code conversion unit 45 converts the image signal of the target pixel pair on the p-th line and the (p + 1) -th line output from the subtraction unit 44 into a subfield code. At this time, if the output of the two-line difference unit 43 is “2” or “−2”, the average code conversion unit 45 in the present embodiment has the first type subfield having the largest gradation weight (in this embodiment). In the embodiment, the subfield SF2) is a non-lighting subfield.

Therefore, if the output of the 2-line difference unit 43 is “2” or “−2”, the subfield code output from the average code conversion unit 45 is “X0XXX”.

Further, if the output of the two-line difference unit 43 is “1” or “−1”, the average code conversion unit 45 in the present embodiment has the second largest tone weight. One type of subfield (in this embodiment, subfield SF3) is set as a non-lighting subfield.

Therefore, if the output of the two-line difference unit 43 is “1” or “−1”, the subfield code output from the average code conversion unit 45 is “XX0XX”.

In order to control the subfield code output from the average code conversion unit 45 as described above, the base code set selection unit 52 of the average code conversion unit 45 may be configured as follows.

FIG. 16A is a diagram showing another example of the base code set used in the image display device 30 according to the embodiment of the present invention.

FIG. 16B is a diagram showing another example of the deleted base code set used in the image display device 30 according to the embodiment of the present invention.

FIG. 16C is a diagram showing another example of the deleted base code set used in the image display device 30 according to the embodiment of the present invention.

In the code sets shown in FIGS. 16A, 16B, and 16C, the light-emitting subfield is “1”, the non-light-emitting subfield is blank, and each subfield code (base code) is displayed in the second column from the left. (Or a deleted base code) represents a gradation value to be displayed. Further, the numerical value written immediately below the notation indicating each subfield in each code set represents the gradation weight of each subfield.

FIG. 16A shows a base code set used when the output of the 2-line difference unit 43 is “0”. In the base code set shown in FIG. 16A, one field is composed of five subfields, and each subfield is “1”, “10”, “6”, “3”, “3” in order from the subfield SF1. 2 "gradation weight.

The base code set shown in FIG. 16A is the same base code set as the base code set shown in FIG. 10A, and is set to the lighting subfield one by one in order from the subfield having the smallest gradation weight. Therefore, the number of base codes included in this base code set is six.

FIG. 16B shows a deleted base code set used when the output of the 2-line difference unit 43 is “2” or “−2”. The deleted base code set shown in FIG. 16B is a subfield code set generated from the base code set shown in FIG. 16A with a predetermined subfield determined by the output of the two-line difference unit 43 as a non-lighting subfield. is there.

In the present embodiment, this predetermined subfield is a first type subfield (in this embodiment, subfield SF2) having the largest gradation weight. Accordingly, the deleted base code set shown in FIG. 16B is a sub-field code set in which the sub-field SF2 is a non-lighting sub-field from the base code set shown in FIG. 16A.

In the present embodiment, the subfield SF2 is a subfield having the largest gradation weight. Therefore, the deleted base code set shown in FIG. 16B is equal to the code set obtained by removing the base code “11111” having the gradation value “22” from the base code set shown in FIG. 16A.

FIG. 16C shows a deleted base code set used when the output of the two-line difference unit 43 is “1” or “−1”. The deleted base code set shown in FIG. 16C is a sub-field code set generated from the base code set shown in FIG. 16A using a predetermined sub-field determined by the output of the two-line difference unit 43 as a non-lighting sub-field. is there.

In the present embodiment, this predetermined subfield is the first type subfield having the second largest gradation weight (subfield SF3 in the present embodiment). Therefore, the deleted base code set shown in FIG. 16C is a subfield code set in which the subfield SF3 is set as a non-lighting subfield from the base code set shown in FIG. 16A.

The base code set selection unit 52 stores the base code set and gradation values of a plurality of base codes constituting the base code set. In addition, the base code set selection unit 52 stores the gradation values of the deleted base code set and the plurality of deleted base codes constituting the deleted base code set. Each base code and each gradation value of the base code are stored in the base code set selection unit 52 in association with each other. This base code set is, for example, the base code set shown in FIG. 16A. Each deleted base code and each gradation value of the deleted base code are stored in the base code set selection unit 52 in association with each other. This deleted base code set is, for example, the deleted base code set shown in FIGS. 16B and 16C.

Then, if the output of the 2-line difference unit 43 is “0”, the base code set selection unit 52 selects a base code set (for example, the base code set shown in FIG. 16A). If the output of the 2-line difference unit 43 is “2” or “−2”, the base code set selection unit 52 deletes the base code that has been deleted by setting the first type subfield having the highest gradation weight as a non-lighting subfield. A set (eg, a deleted base code set shown in FIG. 16B) is selected. Then, if the output of the two-line difference unit 43 is “1” or “−1”, the base code set selection unit 52 sets the second-type first subfield with the second largest gradation weight as a non-lighting subfield. A deleted base code set (for example, the deleted base code set shown in FIG. 16C) is selected.

Then, the base code selection unit 54 compares each gradation value of the subfield code constituting the code set selected by the base code set selection unit 52 with the input gradation, and forms a subfield that becomes an upper gradation base code. Select a code.

That is, to realize the drive voltage waveform shown in FIG. 15, the image signal processing circuit 31 may be configured as described above.

In the present embodiment, the base code generation unit 50 includes a base code set selection unit 52, and the base code set selection unit 52 stores the base code set and the deleted base code set in advance. Explained. However, the present invention is not limited to this configuration. For example, a configuration may be adopted in which a rule for generating a base code or a deleted base code is determined in advance, and the base code or the deleted base code is generated based on the rule.

In the present embodiment, the upper / lower code generation unit 70 selects the upper gradation code and the lower gradation code by the upper / lower code selection unit 74 after the intermediate code set is generated by the intermediate code generation unit 72. Explained. However, the present invention is not limited to this configuration. For example, an intermediate code is generated in order of increasing gradation value, and at the same time, the intermediate code and the input gradation are sequentially compared to select the upper gradation code and the lower gradation code.

In the present embodiment, dither processing and error diffusion processing are performed after setting a subfield for prohibiting the write operation. Therefore, even in the image display device 30 that generates display codes from an intermediate code set having a limited number of subfield codes and uses them for image display, it is possible to prevent image display quality from being deteriorated.

In the present embodiment, the configuration in which the average code selection unit 80 includes the dither selection unit 82 and the error diffusion unit 84 has been described. However, the present invention is not necessarily limited to this configuration. For example, when the dither process is not performed, the dither selection unit 82 may be omitted. Alternatively, the error diffusion unit 84 may be omitted when the error diffusion process is not performed.

In this embodiment, a common error and a common dither element are used for the p-line target pixel and the (p + 1) -line target pixel, and the output of the average code selection unit 80 is the p-line target pixel. In the above description, the common subfield code is used for the target pixel in the (p + 1) -th line. However, the present invention is not limited to this configuration. For example, the following configuration may be used. First, the difference between the upper gradation code and the lower gradation code selected by the upper / lower code selection unit 74 is calculated. Next, for pixels in which the difference occurs only in the first type subfield, different errors and dither elements are used for the pixel of interest on the p-th line and the pixel of attention on the (p + 1) -th line. Then, the output of the average code selection unit 80 is set to a different subfield code for the target pixel on the p-th line and the target pixel on the (p + 1) -th line. For example, such a configuration may be used.

In the present invention, the number of subfields constituting one field, the subfields that are forced initialization subfields, the gradation weights of each subfield, and the like are not limited to the above-described numerical values. Moreover, the structure which switches a subfield structure based on an image signal etc. may be sufficient.

Note that the drive voltage waveforms shown in FIGS. 3, 4, and 15 are merely examples in the embodiment of the present invention, and the present invention is not limited to these drive voltage waveforms.

Also, the circuit configurations shown in FIGS. 6, 7, and 9 are merely examples in the embodiment of the present invention, and the present invention is not limited to these circuit configurations.

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 embodiment of the present invention, an example in which one field is composed of five subfields has been described. However, in the present invention, the number of subfields constituting one field is not limited to the above number. For example, by increasing the number of subfields, the number of gradations that can be displayed on the panel 10 can be further increased. Alternatively, the time required for driving panel 10 can be shortened by reducing the number of subfields.

In the embodiment of the present invention, an example in which one pixel is constituted by discharge cells of three colors of red, green, and blue has been described. However, a panel in which one pixel is constituted by discharge cells of four colors or more. However, it is possible to apply the configuration shown in the embodiment of the present invention, and the same effect can be obtained.

The specific numerical values shown in the embodiment of the present invention are set based on the characteristics of the panel 10 having a screen size of 50 inches and the number of display electrode pairs 14 of 1024. It is just an example. The present invention is not limited to these numerical values, and each numerical value is desirably set optimally in accordance with panel specifications, panel characteristics, plasma display device specifications, and the like. Each of these numerical values is allowed to vary within a range where the above-described effect can be obtained. Further, the number of subfields constituting one field, the gradation weight of each subfield, and the like are not limited to the values shown in the embodiment of the present invention, and the subfield configuration is based on an image signal or the like. May be configured to switch.

In the present invention, since conversion from an image signal to a subfield code can be performed by calculation, it is not necessary to use a conversion table composed of a large number of subfield codes, and the writing period is prevented while preventing a decrease in image display quality. The time required for the image display device can be shortened, so that it is useful as an image display device that displays an image in an image display region by combining binary control of light emission and non-light emission in a light emitting element that constitutes a pixel, and an image display device driving method It is.

DESCRIPTION OF SYMBOLS 10 Panel 11 Front substrate 12 Scan electrode 13 Sustain electrode 14

Display electrode pair

15,23 Dielectric layer 16 Protective layer 21 Back substrate 22 Data electrode 24

Partition

25, 25R, 25G, 25B Phosphor layer 30 Image display device 31 Image signal processing Circuit 32 Data electrode drive circuit 33 Scan electrode drive circuit 34 Sustain electrode drive circuit 35 Timing generation circuit 38 Shutter glasses 41 1H delay unit 42 2-line average unit 43 2-line difference unit 44 subtraction unit 45 average code conversion unit 49 attribute detection unit 50 Base code generation unit 52 Base code set selection unit 54 Base code selection unit 61 Rule generation unit 70 Upper and lower code generation unit 72 Intermediate code generation unit 74 Upper and lower code selection unit 80 Average code selection unit 82 Dither selection unit 84 Error diffusion unit 86 Average code Decision Part 91 differential code creating unit 92 display code combining unit Wth tone threshold Wth1 first gradation threshold Wth2 second gradation threshold

Claims

Each of the plurality of subfields is formed using a subfield code indicating a combination of light emission and non-light emission in each of the plurality of subfields. An image display device that controls non-light emission and displays a gradation value based on an image signal on each of a plurality of pixels constituting the image display region and displays an image in the image display region,
Applying a scan pulse simultaneously to at least one first-type subfield that performs a write operation for each line that applies a scan pulse to each one of the scan electrodes in the address period, and two adjacent scan electrodes in the address period 2 A drive circuit that forms a field with a plurality of second-type subfields that perform simultaneous writing operation for each line and outputs a display code that is a subfield code for displaying a gradation value based on the image signal on the pixel With
The drive circuit is
A two-line average unit that calculates an average value of image signals corresponding to each pixel of a pair of pixels that are adjacent to each other in a direction orthogonal to the scan electrodes and simultaneously perform an address operation in the address period of the second type subfield ,
A two-line difference unit that calculates a difference value between image signals corresponding to each pixel of the pair of pixels, and compares the difference value with a gradation weight of the first type subfield;
A subtraction unit that subtracts a predetermined variable determined by the comparison result in the two-line difference unit from the average value;
An average code conversion unit for converting the output of the subtraction unit into a subfield code having a predetermined subfield determined by the comparison result of the two-line difference unit as a non-lighting subfield, and outputting the subfield code;
A difference code creating unit that generates a subfield code for controlling the predetermined subfield based on a comparison result of the two-line difference unit;
An image display device comprising: a display code synthesis unit that generates the display code by synthesizing a subfield code output from the average code conversion unit and a subfield code generated by the difference code creation unit.
The average code converter is
Among the plurality of basic subfield codes, a subfield code having a gradation value that is larger than the gradation value of the image signal in the target pixel pair and closest to the gradation value of the image signal in the target pixel pair. A base code generation unit to select as an upper gradation base code;
A rule generation unit that generates a rule for generating a new subfield code by changing a light-emitting subfield in the upper gradation base code to a non-light-emitting subfield based on an image signal in the target pixel pair;
Among the subfield codes newly generated by applying the rule to the upper tone base code, the tone value of the image signal in the target pixel pair is larger than the tone value of the image signal in the target pixel pair. The subfield code having the closest gradation value is selected as the upper gradation code, and the gradation closest to the gradation value of the image signal in the target pixel pair is equal to or smaller than the gradation value of the image signal in the target pixel pair An upper and lower code generation unit for selecting a subfield code having a value as a lower gradation code;
A predetermined value is added to the gradation value of the image signal in the target pixel pair to calculate a gradation value to be displayed on the target pixel pair, and the attention value is selected from the upper gradation code and the lower gradation code. The image display apparatus according to claim 1, further comprising: an average code selection unit that selects and outputs a subfield code having a gradation value closer to the gradation value to be displayed on the pixel pair.
In the average code converter,
The plurality of basic subfield codes emit light from subfields having the largest gradation weight among the subfields to emit light and all subfields having gradation weights smaller than the subfield having the largest gradation weight. The base code to be used or a deleted base code in which the predetermined subfield determined by the comparison result of the two-line difference portion from the base code is a non-lighting subfield. Image display device.
In the average code selector,
The image display apparatus according to claim 2, wherein the predetermined value is a dither value calculated by dither processing and an error generated by error diffusion processing.
Each of the plurality of subfields is formed using a subfield code indicating a combination of light emission and non-light emission in each of the plurality of subfields. And the non-light emission are controlled to display the gradation value based on the image signal in each of the plurality of pixels constituting the image display area to display the image in the image display area. At least one first-type subfield that performs a line-by-line address operation that applies a scan pulse line by line, and a line-by-line simultaneous address operation that simultaneously applies a scan pulse to two adjacent scan electrodes in the address period A plurality of second-type subfields constitute one field, and gradation values based on the image signal are displayed on the pixels. A driving method of an image display apparatus for generating a display code is a sub-field code because,
Calculating an average value of image signals corresponding to each pixel of a pair of pixels that are adjacent to each other in a direction orthogonal to the scan electrodes and simultaneously perform an address operation during an address period of the second type subfield;
Calculating a difference value between image signals corresponding to each pixel of the pair of pixels, and comparing the difference value with a gradation weight of the first type subfield;
Subtracting a predetermined variable determined by the comparison result in the step of comparing the difference value and the gradation weight of the first type subfield from the average value;
Converting a subtraction result in the step of subtracting the predetermined variable from the average value into a subfield code in which the predetermined subfield is a non-lighting subfield;
Generating a subfield code for controlling the predetermined subfield based on a comparison result in the step of comparing the difference value and the gradation weight of the first type subfield;
The subfield code generated in the step of converting the predetermined subfield into a subfield code having a non-lighting subfield and the subfield code generated in the step of generating a subfield code for controlling the predetermined subfield And a step of generating the display code by synthesizing the display code.
Among the plurality of basic subfield codes, a subfield code having a gradation value that is larger than the gradation value of the image signal in the target pixel pair and closest to the gradation value of the image signal in the target pixel pair. Selecting as the upper tone base code;
Generating a rule for generating a new subfield code by changing a light-emitting subfield in the upper gradation base code to a non-light-emitting subfield based on an image signal in the target pixel pair;
Among the subfield codes newly generated by applying the rule to the upper tone base code, the tone value of the image signal in the target pixel pair is larger than the tone value of the image signal in the target pixel pair. The subfield code having the closest gradation value is selected as the upper gradation code, and the gradation closest to the gradation value of the image signal in the target pixel pair is equal to or smaller than the gradation value of the image signal in the target pixel pair Selecting a subfield code having a value as a lower gradation code;
A predetermined value is added to the gradation value of the image signal in the target pixel pair to calculate a gradation value to be displayed on the target pixel pair, and the attention value is selected from the upper gradation code and the lower gradation code. 6. The method of driving an image display device according to claim 5, further comprising: selecting a subfield code having a gradation value closer to the gradation value to be displayed on the pixel pair.