WO2012098884A1

WO2012098884A1 - Image display device and drive method for image display device

Info

Publication number: WO2012098884A1
Application number: PCT/JP2012/000295
Authority: WO
Inventors: 広史本田; 健二西村
Original assignee: パナソニック株式会社
Priority date: 2011-01-20
Filing date: 2012-01-19
Publication date: 2012-07-26

Abstract

Conversion from an image signal to a subfield code in an image display device is computed without using a conversion table. To this end, the image display device has a base code generation unit (50), a rule generation unit (61), a higher/lower code generation unit (70), and a display code selection unit (80). The base code generation unit (50) selects a higher gradient base code from a plurality of foundation subfield codes. The rule generation unit (61) generates a rule for generating new subfield codes from the higher gradient base code. The higher/lower code generation unit (70) selects a higher gradient code and a lower gradient code from among the subfield codes to be newly generated. The display code selection unit (80) adds a prescribed value to the gradient value of an image signal in a pixel of interest, calculates a gradient value that must be displayed in the pixel of interest, and selects, as the display code, either the higher gradient code or the lower gradient code, whichever has the gradient value closer to the gradient value that must be displayed in the pixel of interest.

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.

The plasma display device has an image signal processing circuit. The image signal processing circuit converts an image signal (hereinafter simply referred to as “image signal”) input to the plasma display device into a subfield code indicating lighting / non-lighting for each subfield in each discharge cell.

The image signal processing circuit has a conversion table composed of a plurality of subfield codes. In the conversion table, one subfield code is associated with one gradation value. That is, when one gradation value is input, the conversion table outputs one subfield code associated with the gradation value.

The conversion table is stored in a semiconductor storage element such as a ROM and provided in the image signal processing circuit. Then, using the conversion table, the image signal processing circuit converts each gradation value of the image signal into a subfield code (data indicating light emission / non-light emission for each subfield) corresponding to each gradation value. Output to the circuit.

Therefore, in the plasma display device, the number of gradation values that can be displayed on the panel is determined by the number of subfield codes constituting the conversion table. If the number of subfield codes constituting the conversion table is large, the number of gradation values that can be displayed on the panel increases, and if the number of subfield codes constituting the conversion table is small, the number of gradation values that can be displayed on the panel. Decrease.

The number of gradation values that can be displayed on the panel is related to the power consumption of the plasma display device, and the number of gradation values that can be displayed on the panel is relatively reduced when the power consumption is reduced. Therefore, the subfield codes constituting the conversion table are generally determined in consideration of the power consumption of the plasma display device, the smoothness of the image that can be displayed on the panel, and the like.

When the number of gradation values that can be displayed on the panel decreases, the gradation values that cannot be displayed on the panel increase. For example, if the conversion table includes the subfield code of gradation value “7” and gradation value “9” and does not include the subfield code of gradation value “8”, the gradation value “8” is displayed on the panel. "Cannot be displayed. However, gradation values that cannot be displayed on the panel can be displayed on the panel in a pseudo manner by using a generally known method such as a dither method or an error diffusion method.

In the plasma display device, when a moving image is displayed on the panel, a false contour that is not included in the original image signal may be observed by the user. This false contour is generally called a moving image pseudo contour. It is known that this moving image pseudo contour changes according to the number of subfield codes constituting the conversion table, and when the number of subfield codes constituting the conversion table increases, the moving image pseudo contour is likely to occur. .

In the plasma display device, it is desirable to display the image with a smooth gradation change by increasing the gradation values that can be displayed on the panel as much as possible, while reducing the moving image pseudo contour as much as possible. In order to achieve both smooth gradation display and suppression of moving image pseudo contour, the plasma display device includes a plurality of conversion tables having different numbers and types of subfield codes constituting the conversion table, and the plurality of conversion tables. Has been disclosed (for example, see Patent Document 1).

In the technique described in Patent Document 1, a plasma display device includes a plurality of conversion tables. Then, a minimum value and an average value of the image signal are obtained, and a threshold value is calculated from the minimum value and the average value. Then, one conversion table is selected from a plurality of conversion tables based on this threshold value. Then, the image signal is converted into a subfield code based on the selected conversion table.

However, in order to make the plasma display device compatible with a larger screen, higher definition, further improvement of image display quality, diversification of broadcasting methods, multi-functionality such as 3D image display function for stereoscopic viewing, etc. In this case, the number of conversion tables to be provided in the plasma display device is very large as compared with the conventional plasma display device. For this reason, it is difficult to configure an image signal processing circuit having such a large number of conversion tables and selecting an optimum one from a large number of conversion tables according to various conditions. It is coming.

JP 2000-098959 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. This image display device includes an image signal processing circuit that outputs a display code that is a subfield code for displaying a gradation value based on an image signal on a pixel. The image signal processing circuit includes a base code generation unit, a rule generation unit, an upper and lower code generation unit, and a display code selection unit. The base code generation unit has a gradation value that is larger than the gradation value of the image signal at the target pixel and has the closest gradation value to the gradation value of the image signal at the target pixel, from among a plurality of basic subfield codes. The field code is selected as the upper gradation base code. 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 at the target pixel. The upper / lower code generation unit applies the above-described rule to the upper gradation base code, and the gradation of the image signal at the target pixel is larger than the gradation value of the image signal at the target pixel. The subfield code having the gradation value closest to the value is selected as the upper gradation code, and the gradation value closest to the gradation value of the image signal at the target pixel is equal to or lower than the gradation value of the image signal at the target pixel. The subfield code having the lower gradation code is selected as the lower gradation code. The display code selection unit calculates a gradation value to be displayed on the target pixel by adding a predetermined value to the gradation value of the image signal in the target pixel, and sets the target pixel of the upper gradation code and the lower gradation code. One having a gradation value closer to the gradation value to be displayed is selected as a display code.

Thus, the conversion from the image signal to the subfield code can be performed by 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 subfield 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.

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. This is a sub-field code in which the sub-field emits light.

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

In the image display device of the present invention, the rule generated by the rule generation unit when the image signal at the target pixel is a moving image is the rule generated by the rule generation unit when the image signal at the target pixel is a still image. Include.

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. Method for driving an image display apparatus for controlling each light emission and non-light emission of each of the image display, displaying a gradation value based on an image signal on each of a plurality of pixels constituting the image display area, and displaying an image on the image display area It is. This driving method is a subfield having a gradation value that is larger than the gradation value of the image signal in the pixel of interest and closest to the gradation value of the image signal in the pixel of interest, among a plurality of basic subfield codes. In order to generate a new subfield code by selecting a code as an upper tone base code and changing a light emitting subfield in the upper tone base code to a non-light emitting subfield based on an image signal at a target pixel. And a subfield code newly generated by applying the above-described rule to the upper gradation base code, and the image signal of the target pixel is larger than the gradation value of the image signal of the target pixel. Select the sub-field code having the gradation value closest to the gradation value as the upper gradation code, and select it as the target pixel. Selecting a subfield code having a gradation value that is equal to or smaller than the gradation value of the image signal at the target pixel as the lower gradation code, and the gradation value of the image signal at the target pixel. A step of calculating a gradation value to be displayed on the target pixel by adding a predetermined value, and a gradation value closer to the gradation value to be displayed on the target pixel of the upper gradation code and the lower gradation code Selecting a display value that is a subfield code for displaying a gradation value based on an image signal on a target pixel.

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 showing an example of a code set when one field is composed of eight subfields. FIG. 5 is a diagram schematically showing an example of a circuit block constituting the image display device according to the embodiment of the present invention. FIG. 6 is a diagram schematically showing an example of a circuit block constituting the image signal processing circuit of the image display apparatus according to the embodiment of the present invention. FIG. 7A is a diagram showing an example of a base code set used in the image display device according to the embodiment of the present invention. FIG. 7B is a diagram showing another example of the base code set used in the image display device according to the embodiment of the present invention. FIG. 7C is a diagram illustrating another example of the base code set used in the image display device according to the embodiment of the present invention. FIG. 8A is a diagram illustrating an example of an intermediate code set generated by the rules generated by the rule generation unit of the image display device according to the embodiment of the present invention. FIG. 8B is a diagram showing another example of the intermediate code set generated by the rules generated by the rule generation unit of the image display device according to the embodiment of the present invention. FIG. 8C is a diagram illustrating another example of the intermediate code set generated by the rules generated by the rule generation unit of the image display device according to the embodiment of the present invention. FIG. 9A is a diagram showing an example of a dither pattern used in the image display device according to the embodiment of the present invention. FIG. 9B 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. 10 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. 11 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.

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

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.

Each subfield has an initialization period, an address period, and a sustain period. 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 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 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”.

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 shows a subfield SF1 that is a forced initialization subfield, and a subfield SF2 and a subfield SF3 that are selective initialization subfields. 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.

Although the subfields after subfield SF4 are not shown, each subfield except subfield SF1 is a selective initialization subfield, and substantially the same drive voltage waveform in each period except the number of sustain pulses. Is generated.

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.

In address period Tw1 of subfield SF1, voltage Ve is applied to sustain electrode SU1 through sustain electrode SUn, voltage 0 (V) is applied to data electrode D1 through data electrode Dm, and scan electrode SC1 through scan electrode SCn are applied. Applies a voltage Vc.

Next, a negative scan pulse having a negative voltage Va is applied to the first (first row) 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 row 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 to which the scan pulse voltage Va is applied, the voltage difference between the data electrode Dk and the scan electrode SC1 exceeds the discharge start voltage. A discharge occurs between the data electrode Dk and the scan electrode SC1.

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. 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, 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 cells in the first row 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 portion does 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 the voltage Va is applied to the second (second row) scan electrode SC2 from the top, and the voltage Vd is applied to the data electrode Dk corresponding to the discharge cell to emit light in the second row. Apply the write pulse. As a result, address discharge occurs in the discharge cells in the second row to which the scan pulse and address pulse are simultaneously applied. Thus, the address operation in the discharge cells in the second row is performed.

The same address operation is sequentially performed in the order of scan electrode SC3, scan electrode SC4,..., Scan electrode SCn until reaching the discharge cell in the n-th row, and the address period Tw1 of the subfield SF1 ends. In this manner, in the address period Tw1, address discharge is selectively generated in the discharge cells to emit light, and wall charges for sustain discharge are formed in the discharge cells.

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. .

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, the same drive voltage waveform as that in the address period Tw1 of the subfield SF1 is applied to each electrode. In the subsequent sustain period Ts2, similarly to the sustain period Ts1 of the subfield SF1, the number of sustain pulses corresponding to the gradation weights are alternately applied to the scan electrodes SC1 to SCn and the sustain electrodes SU1 to SUn.

In each subfield after subfield SF3, the same drive voltage waveform as in subfield SF2 is applied to each electrode except for the number of sustain pulses generated in the sustain 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, the voltage values applied to the electrodes are, for example, the voltage Vi1 = 140 (V), the voltage Vi2 = 340 (V), the voltage Vi3 = 200 (V), and the voltage Vi4 = −190 (V). , Voltage Vc = −60 (V), voltage Va = −200 (V), voltage Vs = 200 (V), voltage Vr = 200 (V), voltage Ve = 130 (V), voltage Vd = 70 (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.

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. 4 is a diagram showing an example of a code set when one field is composed of eight subfields.

In the code set shown in FIG. 4, the numerical value shown immediately below the notation indicating each subfield represents the gradation weight of each subfield.

FIG. 4 includes eight subfields SF1 to SF8 in one field, and each subfield is “1”, “2”, “3”, “5”, “8”, respectively. ”,“ 13 ”,“ 21 ”, and“ 34 ”indicate code sets having gradation weights.

In the code set shown in FIG. 4, the light emitting subfield is indicated by “1”, the non-light emitting subfield is indicated by a blank, and the leftmost column indicates the gradation value to be displayed in each subfield code.

For example, based on the code set shown in FIG. 4, the subfield code corresponding to the gradation value “2” is “01000000”.

Therefore, only the subfield SF2 emits light in the discharge cell displaying the gradation value “2”.

In this subfield code,

data

0 or 1 is arranged in the order of subfield SF1, subfield SF2, subfield SF3, subfield SF4, subfield SF5, subfield SF6, subfield SF7, and subfield SF8 from the left. Suppose that 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. 4, the subfield code corresponding to the gradation value “14” is “11101000”. Accordingly, in the discharge cell displaying the gradation value “14”, the subfield SF1, the subfield SF2, the subfield SF3, and the subfield SF5 emit light.

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

FIG. 5 is a diagram schematically showing an example of a circuit block constituting the image display device 30 according to the embodiment of the present invention.

The image display device 30 includes a panel 10 and a drive circuit that drives the panel 10. 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, a timing generation circuit 35, and a power supply circuit (not shown) that supplies necessary power to each circuit block. It has.

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.

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. 5), 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.

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 generates an address pulse corresponding to each of the data electrodes D1 to Dm based on the display code of each color output from the image signal processing circuit 31 and the timing signal supplied from the timing generation circuit 35. . 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.

FIG. 6 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 the embodiment of the present invention.

The image signal processing circuit 31 includes an attribute detection unit 41, a base code generation unit 50, a rule generation unit 61, an upper and lower code generation unit 70, and a display code selection unit 80.

The attribute detection unit 41 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.

Then, the base code generation unit 50 selects “upper tone base” from the base code set based on the tone value (hereinafter referred to as “input tone”) of the image signal input to the image signal processing circuit 31. Select “Code”. The upper tone base code is a base code having a tone value larger than the input tone and having a tone value closest to the input tone. Accordingly, in the upper gradation base code, the subfield having the largest gradation weight among the lighting subfields and all subfields having the gradation weight smaller than that subfield are the lighting subfields.

As described above, the base code generation unit 50 selects a base code having a tone value larger than the input tone and closest to the input tone as the upper tone base code, and outputs it.

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

FIG. 7A 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. 7B 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. 7C 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.

In the base code set shown in FIGS. 7A, 7B, and 7C, the light-emitting subfield is “1”, the non-light-emitting subfield is blank, and each subfield code (base) is displayed 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 base code set represents the gradation weight of each subfield.

FIG. 7A shows an example of a base code set often used in the NTSC standard. The base code set shown in FIG. 7A is composed of 8 subfields, and each subfield is “1”, “2”, “3”, “5”, “ It has gradation weights of “8”, “13”, “21”, and “34”.

In the base code set shown in FIG. 7A, the first subfield (subfield SF1) of one field is set to the subfield having the smallest gradation weight, and thereafter, the subfields are arranged so that the gradation weight is sequentially increased. . 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. 7A, the number of base codes is nine.

FIG. 7B shows an example of a base code set often used in the PAL standard. In the base code set shown in FIG. 7B, one field is composed of 12 subfields, and each subfield is “1”, “2”, “4”, “9”, “9” in order from the subfield SF1. It has gradation weights of “18”, “36”, “65”, “5”, “7”, “15”, “33”, “60”.

The base code set shown in FIG. 7B has two subfield groups. The first subfield group is composed of subfields SF1 to SF7, and the second subfield group is composed of subfields SF8 to SF12.

Each subfield group has the first subfield of each subfield group (subfield SF1 and subfield SF8 in the example shown in FIG. 7B) as the subfield having the smallest gradation weight in each subfield group. Thereafter, the subfields are arranged so that the gradation weights are sequentially increased. In each subfield group, one or two lighting subfields are set in order from the subfield having the smallest gradation weight. Therefore, the number of base codes included in this base code set is equal to or less than (the number of subfields constituting one field + 1). For example, in the example of the base code set shown in FIG. 7B, the number of base codes is 10.

FIG. 7C shows an example of a base code set used in a 3D display device (stereoscopic display device). In the base code set shown in FIG. 7C, one field is composed of five subfields, and each subfield is “1”, “16”, “8”, “4”, “ 2 "gradation weight.

In the base code set shown in FIG. 7C, 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. 7C, the number of base codes is 6.

The image display device 30 in the present embodiment generates a new code set based on the base 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 storage unit 52 and a base code selection unit 54.

The base code storage unit 52 stores a base code set and gradation values of a plurality of base codes constituting the base code set. Each base code and each gradation value of the base code are stored in the base code storage unit 52 in association with each other.

The base code selection unit 54 compares each tone value of the base code constituting the base code set with the input tone. Then, a base code having a gradation value larger than the input gradation and closest to the input gradation is selected. Then, the selected base code is output as an upper gradation base code.

In the present embodiment, based on the image signal input to the image signal processing circuit 31, by changing the lighting subfield in the upper gradation base code to the non-lighting subfield, a new subcode not included in the base code set is obtained. Generate field codes. The rule generation unit 61 generates a rule for generating this new subfield code.

That is, the rule generation unit 61 generates a base code based on the image signal and the attribute (attribute associated with the image signal) detected by the attribute detection unit 41 in order to increase the number of subfield codes used for image display. A rule for changing the lighting subfield in the upper gradation base code selected in the unit 50 to the non-lighting subfield is generated.

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 base code is smaller than the upper gradation base code. This is in order not to fall below.

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

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”. In the present embodiment, the intermediate code is a subfield code used when displaying an image on panel 10. Therefore, each discharge cell of panel 10 emits light with a luminance of a gradation value based on the intermediate code.

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

FIG. 8A is a diagram illustrating an example of an intermediate code set generated by the rules generated by the rule generation unit 61 of the image display device 30 according to the embodiment of the present invention.

FIG. 8B is a diagram illustrating another example of the intermediate code set generated by the rules generated by the rule generation unit 61 of the image display device 30 according to the embodiment of the present invention.

FIG. 8C is a diagram illustrating another example of the intermediate code set generated by the rules generated by the rule generation unit 61 of the image display device 30 according to the embodiment of the present invention.

In the intermediate code sets shown in FIGS. 8A, 8B, and 8C, the light-emitting subfield is “1”, the non-light-emitting subfield is blank, and the second column from the left indicates each subfield code (intermediate code set). 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. 8A, 8B, and 8C, one field includes eight subfields, and each subfield is “1”, “2”, and “3” in order from the subfield SF1. , “5”, “8”, “13”, “21”, “34”.

In FIG. 8A, as an example of the intermediate code set, the above-described “1) rule for setting the first subfield to be changed from the lighting subfield to the non-lighting subfield” is shown in FIG. An intermediate code set generated by applying to the base code “11111100” of the value “32” 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 “11111100” (No. 7) of the gradation value “32” shown in FIG. 7A, six subfields from the subfield SF1 to the subfield SF6 are lighting subfields.

Therefore, by changing any one of these six lighting subfields to a non-lighting subfield based on Rule 1, as shown in FIG. 8A, six subfield codes “11111000”, “11110100” , “11101100”, “11011100”, “10111100”, and “01111100” can be generated.

However, the subfield code “11111000” obtained by changing the subfield SF6 to the non-lighting subfield is equal to the base code (No. 6) of the gradation value “19” illustrated in FIG. 7A. Accordingly, five subfield codes excluding the subfield code “11111000” are newly generated intermediate codes.

That is, if the above-described rule 1 is applied to the base code “11111100” having the gradation value “32” shown in FIG. 7A, five new subfield codes can be generated as intermediate codes.

In FIG. 8B, 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. An intermediate code set generated by applying to the base code “11111100” having the gradation value “32” shown in FIG.

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 SF2 is a non-lighting sub-field ”(hereinafter referred to as“ rule 2 ”).

By applying rule 1 to the base code “11111100” (No. 7) of the gradation value “32” shown in FIG. 7A, five new subfield codes are generated as shown in FIG. 8A. The Among these five subfield codes, the “subfield code with the smallest gradation value among the newly generated intermediate codes” is the subfield code “11110100” with the gradation value “24”.

Accordingly, by changing the subfield SF2 of the subfield code of the gradation value “24” to the non-lighting subfield based on the rule 2, as shown in FIG. 8B, a new subfield of the gradation value “22” is obtained. The code “10110100” can be generated.

That is, if the above-described rule 1 and rule 2 are applied to the base code “11111100” having the gradation value “32” shown in FIG. 7A, six new subfield codes can be generated as intermediate codes. .

In FIG. 8C, 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 “ An intermediate code set generated by applying to the base code “11111100” of “32” is shown.

This “3) rule for setting a subfield that prohibits non-lighting” is a rule that “subfield SF1 and subfield SF2 are prohibited from being non-lighting subfield” (hereinafter “rule”). 3 ”).

By applying rule 1 to the base code “11111100” (No. 7) of the gradation value “32” shown in FIG. 7A, five new subfield codes are generated as shown in FIG. 8A. The Among these five sub-field codes, “sub-field code in which sub-field SF1 or sub-field SF2 is a non-lighting sub-field” has a sub-field code “10111100” with a gradation value “30” and a gradation value “ 31 ”is a sub-field code“ 01111100 ”.

Therefore, based on the rule 3, the subfield codes having the gradation value “30” and the gradation value “31” are excluded from the intermediate code set.

That is, if the above-described rule 1 and rule 3 are applied to the base code “11111100” having the gradation value “32” shown in FIG. 7A, three 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 display code selection unit 80 calculates a gradation value to be displayed on the target pixel by adding a predetermined value to the input gradation. Then, the display 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, and outputs it as a display code.

Note that the pixel of interest is a pixel that is a target of calculation of a gradation value 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 display code selection unit 80 adds the error and the dither value to the input gradation to calculate the gradation value to be displayed on the target pixel, and selects the target pixel from the upper gradation code and the lower gradation code. The one having a gradation value closer to the gradation value to be displayed is selected as a display code. Further, the display code selection unit 80 calculates the difference between the gradation value to be displayed on the target pixel and the gradation value of the display code, and diffuses the difference as an error to surrounding pixels.

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

The dither selection unit 82 stores a plurality of dither patterns. Then, one dither pattern is selected from a plurality of stored dither patterns based on the image signal and the attribute detected by the attribute detection unit 41.

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.

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

FIG. 9A 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. 9B 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. 9A and 9B, one column represents one pixel.

FIG. 9A shows the simplest binary dither. In FIG. 9A, “+0.25” and “−0.25” are arranged in a checkered pattern as dither elements. FIG. 9B is a diagram showing an example of a four-value dither. In FIG. 9B, 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 to the display code determination unit 86 and diffuses the error output from the display code determination unit 86 to the peripheral pixels of the target pixel.

Then, the dither selection unit 82 stores, for example, two types of dither patterns shown in FIGS. 9A and 9B, and selects one of the dither patterns based on the image signal and the attribute detected by the attribute detection unit 41. . When the dither pattern shown in FIG. 9A is selected, the dither element is either “+0.25” or “−0.25”. When the dither pattern shown in FIG. 9B 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. The calculated dither value is added to the input gradation in the display code selection unit 80.

FIG. 10 is a diagram showing error diffusion coefficients of the error diffusion unit 84 of the image display device 30 in the embodiment of the present invention.

In FIG. 10, one column represents one pixel. The middle column in FIG. 10 represents a pixel (target pixel) that is a target of error diffusion processing.

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

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

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 gradation, the dither value output from the dither selection section 82, and the error output from the error diffusion section 84, the display code determination section 86 converts the display code actually used for image display into the upper gradation code. Alternatively, it is determined as one of the lower gradation codes.

Specifically, the display code determination unit 86 calculates a gradation value to be displayed on the target pixel by adding the dither value and the error to the input gradation. 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 is selected as the display code.

Then, the display code determination unit 86 calculates the difference between the gradation value to be displayed on the target pixel and the gradation value of the display code, and outputs the difference to the error diffusion unit 84 as a newly generated error.

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 base code set shown in FIG. 7A is used as the base code set.
2) The rules used in the description of FIG. 8A 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. 11 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 S41)
An image signal corresponding to one pixel (target pixel) is input to the image signal processing circuit 31. The attribute detection unit 41 detects an attribute associated with the image signal.

Hereinafter, the image signal corresponding to the target pixel has a gradation value (input gradation) of “25”, and the attribute detection unit 41 detects that the attribute associated with the image signal is a moving image and a contour portion. The description will be given on the assumption that it was obtained.

(Step S50)
The base code generation unit 50 selects an upper tone base code corresponding to the image signal.

That is, in step S50, the sub-field code having a gradation value that is larger than the gradation value of the image signal at the target pixel and closest to the gradation value of the image signal at the target pixel is selected from the plurality of basic sub-field codes. The field code is selected as the upper gradation base code.

Specifically, the base code generation unit 50 compares each gradation of the base code constituting the base code set stored in the base code storage unit 52 with the input gradation. Then, a base code having a gradation value larger than the input gradation and closest to the input gradation is selected and output as an upper gradation base code.

For example, if the input gradation is a gradation value “25”, the gradation value larger than the gradation value “25” and closest to the gradation value “25” in the base code set shown in FIG. The base code possessed is a base code having a gradation value of “32”. Therefore, the base code generation unit 50 selects the base code “11111100” having the gradation value “32” and outputs it as the upper gradation base code.

(Step S61)
The rule generation unit 61 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 at the target pixel.

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 base codes shown in FIGS. 7A to 7C 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, rule 3 described with reference to FIG. 8C, which is “prohibiting subfield SF1 and subfield SF2 from being turned off”. 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 at the target pixel 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 that is generated when the image signal at the target pixel is a still image.

(Step S72)
The intermediate code generation unit 72 generates an intermediate code set.

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.

For example, if the upper tone base code selected in step S50 is the base code “11111100” having the tone value “32” and the rules generated by the rule generation unit 61 are rule 1 and rule 3, intermediate code generation is performed. The unit 72 applies the

rules

1 and 3 generated by the rule generation unit 61 to the base code “11111100” to generate a new intermediate code.

Specifically, among the subfields SF1 to SF6, which are the lighting subfields of the base code “11111100”, the subfields (subfield SF3 to subfield are excluded based on rule 3 except for subfield SF1 and subfield SF2). SF6) is to be replaced with a non-lighting subfield. Then, based on rule 1, the subfields SF3 to SF6 are set to non-lighting subfields. In this way, the intermediate code generation unit 72 generates four intermediate codes “11111000”, “11110100”, “11101100”, and “11011100”. The intermediate code set thus obtained is, for example, the intermediate code set shown in FIG. 8C.

(Step S74)
The upper / lower code selection unit 74 selects an upper gradation code and a lower gradation code.

That is, in step S74, the tone value of the image signal at the target pixel is larger than the tone value of the image signal at the target pixel from the intermediate code set generated by applying the above-described rule to the upper tone base code. The subfield code having the closest gradation value is selected as the upper gradation code, and the subfield code having the gradation value closest to the gradation value of the image signal at the target pixel is equal to or smaller than the gradation value of the image signal at the target pixel. Select the field code as the 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 “25” and the intermediate code set generated in step S72 is the intermediate code set shown in FIG. 8C, the subfield code corresponding to the upper gradation code is gradation. It is a subfield code of the value “27”. The subfield code corresponding to the lower gradation code is a subfield code having a gradation value of “24”. Therefore, the upper / lower code selection unit 74 selects the subfield code “11101100” having the gradation value “27” as the upper gradation code, and the subfield code “11110100” having the gradation value “24” as the lower gradation code. ”Is selected.

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

For example, if the dither pattern shown in FIG. 9A and the dither pattern shown in FIG. 9B 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 41. 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. 9A is selected. If the attribute attached to the image signal is not a contour portion, the dither pattern shown in FIG. 9B 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. 9A. 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. For example, the dither selection unit 82 selects “0.25” as the dither element based on the dither pattern shown in FIG. 9A.

(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 “27”, the gradation value of the lower gradation code selected in step S74 is “24”, 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 display code determination unit 86 calculates a gradation value to be displayed on the target pixel.

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

Specifically, the display 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 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 “25”, 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 “ If “−0.4”, 25 + 0.75−0.4 = 25.35. Therefore, the gradation value to be displayed on the target pixel is “25.35”.

Alternatively, the input gradation is the gradation value “25”, 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 “ +0.4 ”, 25 + 0.75 + 0.4 = 26.15. Therefore, the gradation value to be displayed on the target pixel is “26.15”.

(Step S87)
The display code determining unit 86 determines a display code to be used when displaying the gradation value on the target pixel.

That is, in step S87, the upper gradation code and the lower gradation code having the gradation value closer to the gradation value to be displayed on the target pixel is selected as the display code.

Specifically, the display code determination unit 86 compares the gradation value to be displayed on the target pixel with the gradation value of the upper gradation code and the gradation value of the lower gradation code. If the gradation value to be displayed on the target pixel is closer to the gradation value of the upper gradation code than the gradation value of the lower gradation code, the display used when displaying the gradation value on the attention pixel Select the upper gradation code as the code and output it. Further, when the gradation value to be displayed on the target pixel is closer to the gradation value of the lower gradation code than the gradation value of the upper gradation code, it is used when displaying the gradation value on the attention pixel. The lower gradation code is selected as the display code and is output.

For example, if the gradation value of the upper gradation code is “27”, the gradation value of the lower gradation code is “24”, and the gradation value to be displayed on the target pixel is “25.35”. The difference between the gradation value of the upper gradation code and the gradation value to be displayed on the target pixel is “1.65”, and the difference between the gradation value of the lower gradation code and the gradation value to be displayed on the target pixel is The difference is “1.35”. Therefore, in this case, the display code determination unit 86 outputs the lower gradation code “11110100” having the gradation value “24” as the display code.

If the gradation value of the upper gradation code is “27”, the gradation value of the lower gradation code is “24”, and the gradation value to be displayed on the target pixel is “26.15”. The difference between the gradation value of the upper gradation code and the gradation value to be displayed on the target pixel is “0.85”, and the difference between the gradation value of the lower gradation code and the gradation value to be displayed on the target pixel is The difference is “2.15”. Therefore, in this case, the display code determination unit 86 outputs the upper gradation code “11101100” having the gradation value “27” as the display code.

(Step S88)
The display code determination unit 86 calculates the error and outputs it to the error diffusion unit 84.

The display code determination unit 86 subtracts the gradation value of the display code from the gradation value to be displayed on the target pixel, and outputs the subtraction result to the error diffusion unit 84 as a newly generated error.

For example, if the gradation value to be displayed on the target pixel is “25.35” and the gradation value of the display code is “24”, 25.35-24 = 1.35. Therefore, the display code determination unit 86 outputs “1.35” as an error to the error diffusion unit 84.

Or, if the gradation value to be displayed on the target pixel is “26.15” and the gradation value of the display code is “27”, 26.15−27 = −0.85. Therefore, the display code determination unit 86 outputs this “−0.85” to the error diffusion unit 84 as an error.

When step S88 is completed, the process returns to step S41. In this way, a series of steps from step S41 to step S88 are repeatedly executed.

As described above, the image signal processing circuit 31 in the present embodiment includes the base code generation unit 50, the rule generation unit 61, the upper and lower code generation unit 70, and the display code selection unit 80.

Then, 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 from the base code set, and outputs it as an upper gradation base code.

The rule generation unit 61 illuminates the upper gradation base code based on the image signal and the attribute (attribute associated with the image signal) detected by the attribute detection unit 41 in order to generate an intermediate code used for image display. Generate a rule for changing a subfield to a non-lit subfield.

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 intermediate code. An upper gradation code having a gradation value larger than the input gradation and closest to the input gradation, and a lower gradation code having a gradation value equal to or lower than the input gradation and closest to the input gradation Is selected from the intermediate code and output.

The display code selection unit 80 adds an error and a dither value to the input gradation, and calculates a gradation value to be displayed on the target pixel. Then, 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 target pixel is selected and output as a display code. Further, the display code selection unit 80 calculates a difference between the gradation value to be displayed on the target pixel and the gradation value of the display code, and diffuses the difference as an error to surrounding pixels.

In the present embodiment, by configuring the image signal processing circuit 31 in this manner, conversion from an image signal to a display code (subfield code) is not performed using a conversion table including a number of subfield codes. Without using 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 the 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 apparatus, it is not necessary to provide a huge number of conversion tables, and a minimum necessary table (for example, the base code set shown in FIGS. 7A, 7B, and 7C) and an image signal It is only necessary to provide an arithmetic circuit for conversion from the display code to the display code.

In the present embodiment, the configuration in which the base code generation unit 50 has the base code storage unit 52 and the base code set is stored in advance in the base code storage unit 52 has been described. 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 is determined in advance and the base code is generated based on the rule. In that case, the upper gradation base code may be selected by sequentially comparing the gradation value of the generated base code and the input gradation.

In the present embodiment, the upper and lower code generation unit 70 selects the upper gradation code and the lower gradation code by the upper and 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, the configuration in which the display 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 limited to this configuration. For example, when the dither process is not performed, the dither selection unit 82 can be omitted. Further, when the error diffusion process is not performed, the error diffusion unit 84 can be omitted. However, care should be taken because the fidelity of gradation display may be lost if the error diffusion process is omitted.

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 selects a display code from an intermediate code set having a limited number of subfield codes and uses it to display an image, it is possible to prevent a decrease in image display quality.

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.

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

Also, the circuit configurations shown in FIGS. 5 and 6 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, an example composed of eight subfields, and an example composed of twelve 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 present embodiment, the configuration in which the display 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 limited to this configuration. For example, when the dither process is not performed, the dither selection unit 82 can be omitted. Further, when the error diffusion process is not performed, the error diffusion unit 84 can be omitted. However, if the error diffusion process is omitted, the image display quality may be lowered, so care must be taken.

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 light emission and non-light emission in a light emitting element constituting a pixel The present invention is useful as an image display apparatus that displays an image in an image display area by combining binary control and a method for driving the image display apparatus.

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 41 Attribute detection unit 50 Base code generation unit 52 Base code storage unit 54 Base code selection unit 61 Rule generation unit 70 Upper and lower code generation unit 72 Intermediate Code generation unit 74 Upper / lower code selection unit 80 Display code selection unit 82 Dither selection unit 84 Error diffusion unit 86 Display code determination unit

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,
An image signal processing circuit that outputs a display code that is a subfield code for displaying a gradation value based on the image signal on the pixel;
The image signal processing circuit includes:
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 at the target pixel and that is closest to the gradation value of the image signal at the target pixel A base code generator to select as a key 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;
Among sub-field codes newly generated by applying the rule to the upper gradation base code, the gradation value of the image signal at the target pixel is greater than the gradation value of the image signal at the target pixel and is closest A sub-field code having a gradation value is selected as an upper gradation code, and a sub-field code having a gradation value which is equal to or smaller than the gradation value of the image signal at the target pixel and which is equal to or smaller than the gradation value of the image signal at the target pixel. An upper / lower code generator for selecting a field code as a lower gradation code;
A predetermined value is added to the gradation value of the image signal in the pixel of interest to calculate a gradation value to be displayed on the pixel of interest, and is displayed on the pixel of interest among the upper gradation code and the lower gradation code An image display apparatus comprising: a display code selection unit that selects a display code having a gradation value closer to a gradation value to be used as the display code.
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 image display device according to claim 1, wherein the image display device is a subfield code.
The image display apparatus according to claim 1, wherein the predetermined value is an error generated by error diffusion processing and a dither value generated by dither processing.
The rule generated by the rule generation unit when the image signal at the target pixel is a moving image includes the rule generated by the rule generation unit when the image signal at the target pixel is a still image. The image display device according to claim 1.
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 a method of driving an image display device that controls gradation 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. ,
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 at the target pixel and that is closest to the gradation value of the image signal at the target pixel Selecting as a key 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;
Among sub-field codes newly generated by applying the rule to the upper gradation base code, the gradation value of the image signal at the target pixel is greater than the gradation value of the image signal at the target pixel and is closest A sub-field code having a gradation value is selected as an upper gradation code, and a sub-field code having a gradation value which is equal to or smaller than the gradation value of the image signal at the target pixel and which is equal to or smaller than the gradation value of the image signal at the target pixel. Selecting a field code as a lower gradation code;
Calculating a gradation value to be displayed on the target pixel by adding a predetermined value to the gradation value of the image signal in the target pixel;
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 target pixel is displayed on the subpixel for displaying the gradation value based on the image signal on the target pixel. And a step of selecting as a display code which is a field code.