JP2009163091A - Image display device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the luminance linearity of a display panel. <P>SOLUTION: When displaying gradation X in which a moving image pseudo contour is easily generated, gradation A in which the moving image pseudo contour is hardly generated, located below the gradation X, and gradation B in which the moving image pseudo contour is hardly generated, located above the gradation X, are mixed and displayed. A first dither circuit 22 outputs the gradation A, and a second dither circuit 24 outputs the gradation B. Each effective gradation is output to the gradations A, B using first and second luminance value conversion tables. Since the effective gradation is a gradation equivalent to brightness measured on the panel, luminance linearity can be improved if error diffusion is performed using the effective gradation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image display apparatus and method, and more particularly, to an apparatus and method for improving luminance linearity for ensuring linearity of luminance of an image displayed on a panel such as a plasma display panel (PDP).

  An image display device that performs binary control of lighting or non-lighting, such as a PDP or a digital mirror device, often performs halftone display using a subfield method. In the subfield method, one field is time-divided using a plurality of subfields weighted by the number of times of lighting or the amount of lighting, and binary control of each pixel is performed for each subfield. That is, each subfield has a predetermined luminance weight, and a gradation is displayed by the sum of the luminance weights of the subfields to be lit.

  FIG. 1 shows an example of a subfield configuration in a conventional PDP. In this example, one field is divided into eight subfields (SF1, SF2,..., SF8), and each subfield has a luminance of (1, 2, 4, 8, 16, 32, 64, 128). Is weighted. In each subfield, an initialization period T1 in which initialization discharge is performed, a writing period (also referred to as an address period) T2 in which data writing is performed for each pixel, or a pixel in which lighting data is written, are collectively performed. It consists of a maintenance period T3 for lighting. By turning on these subfields in various combinations, 256 gradation levels from “0” to “255” can be displayed. For example, as shown in FIG. 2, gradation 15 can be displayed by turning on SF1, SF2, SF3, and SF4 having luminance weights 1, 2, 4, and 8, and gradation 16 has luminance weight 16. It can be displayed by turning on SF5. In the table of FIG. 2, 1 indicates a subfield to be used, and 0 indicates a subfield that is not used. In this way, all gradations 0 to 225 can be displayed by the combination of subfields.

However, when one field is divided into a plurality of subfields and gradations are displayed according to on / off of each subfield, it is known that a moving image pseudo contour is generated due to human visual characteristics. .
Various methods for suppressing such a moving image pseudo contour have been proposed. One of them is a method of using only the gradation satisfying a certain condition and not using the gradation not satisfied (paragraphs 0043 and 0049 of Patent Document 1).

According to Patent Document 1, the satisfactory gradation is
Condition 1: the first subfield SF1 is lit,
Condition 2: The number of consecutive non-light emitting subfields does not exceed two,
The gradation that satisfies the conditions 1 and 2 is not satisfied. For example, in FIG. 2, gradations 15 and 19 satisfy conditions 1 and 2, but gradations 16, 17 and 18 do not satisfy conditions 1 and 2. Therefore, gradation 15 is displayed using SF1, SF2, SF3, and SF4, and gradation 19 is displayed using SF1, SF2, and SF5. On the other hand, the gradation 16 can be displayed using only SF5. However, since a moving image pseudo contour is generated, use of only SF5 is prohibited. Then, what to do when it is desired to express gradation 16 is a gradation larger than gradation 16 (in this case, gradation 19) and a smaller gradation (in this case gradation 15), and the above condition is satisfied. The two gradations to be satisfied are selected, and the gradations 16 are expressed by mixing the selected two gradations 19 and 15 at a constant ratio in space and time. For example, if gradation 19 and gradation 15 are mixed at a ratio of 1: 3, gradation 16 can be expressed. Such mixing can be performed by a dither circuit.
However, when the two selected gradations are mixed as described above, there is a further problem that the linearity of luminance is lost.
JP 2006-195439 A JP 2005-141203 A

  Therefore, the present invention provides an image display apparatus and method that can suppress moving image pseudo contours and that does not cause disturbance in luminance linearity.

  According to a first aspect of the present invention, there is provided an image display apparatus that receives an input gradation, outputs a gradation with adjusted luminance linearity, and drives a display panel. A dither processing unit that outputs a second gradation, and a luminance that converts the first gradation and the second gradation into a first effective gradation and a second effective gradation that represent brightness substantially equal to the brightness on the panel, respectively. A value conversion table, a mixer that generates a mixed gradation by mixing the first effective gradation and the second effective gradation, and a line memory that records a difference between the input gradation and the mixed gradation as an error adjustment value; And an error diffusion unit that accumulates error adjustment values at a predetermined rate on newly received input gradations and generates error-adjusted input gradations, and the error-adjusted input gradations are subjected to the above dither processing. The display panel is driven using the first gradation and the second gradation from the dither processing section. An image display device.

  In a preferred embodiment, the image display apparatus further includes means for determining a gradation at which a moving image pseudo contour is generated and a gradation at which the moving image pseudo contour is not generated.

  In a preferred embodiment, the image display apparatus further includes means for rounding off the decimal point in the input gradation adjusted for error and expressing the input gradation only by an integer part.

  In a preferred embodiment, the luminance value conversion table includes a first luminance value conversion table for converting the first gradation into a first effective gradation representing a brightness substantially equal to the brightness on the panel, and a second gradation. Is a second luminance value conversion table for converting the second luminance value into a second effective gradation representing a brightness substantially equal to the brightness on the panel.

  In a preferred embodiment, the first luminance value conversion table and the second luminance value conversion table are image display devices in which information of the same content is stored.

  In a preferred embodiment, the display device further includes a changeover switch for alternately switching the first gradation and the second gradation.

  According to a second aspect of the present invention, there is provided an image display method for driving a display panel that receives an input gradation, outputs a gradation with adjusted luminance linearity, and a) receives the input gradation, A step of outputting a tone and a second gradation; b) converting the first gradation and the second gradation into a first effective gradation and a second effective gradation representing brightness substantially equal to the brightness on the panel, respectively. C) a step of generating a mixed gradation by mixing the first effective gradation and the second effective gradation; and d) recording a difference between the input gradation and the mixed gradation as an error adjustment value. And e) accumulating error adjustment values at a predetermined ratio to newly received input gradations to generate error-adjusted input gradations. Used as the input gradation in step a), and the display panel is driven using the first gradation and the second gradation. That is an image display method.

  The image display device and the image display method according to the present invention can suppress the disturbance of luminance linearity with respect to the input gradation. That is, the change amount of the input gradation and the change amount of the luminance value on the panel can be matched, and a faithful luminance display can be performed.

Before describing the embodiment of the present invention, the basic principle of the present invention will be described.
<Basic principle of the present invention>
In the case of the PDP, the brightness on the panel can be adjusted, for example, from the darkest 0 level to the brightest 255 level. This adjustment is performed by determining the number of plasma discharges. For example, in a certain pixel, if the number of plasma discharges is 0, the pixel is expressed darkest, and if the number of plasma discharges is 255, it is expressed brightest. In addition, a plurality of subfields (SF), for example, SF1, SF2, SF3, SF4, SF5, SF6, SF7, and SF8 are set in one field period, and predetermined gradation weighting is performed on each subfield. Each subfield is subjected to plasma discharge a number of times corresponding to its weighting. For example, if the weights of the subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, and SF8 are 1, 2, 4, 8, 16, 32, 64, and 128, respectively, Plasma discharge, two times of plasma discharge in subfield SF2, four times of plasma discharge in subfield SF3,..., 128 times of plasma discharge in subfield SF8. By combining the subfields SF1 to SF8, the number of plasma discharges can be controlled to any one level (that is, gradation) from 0 to 255 times. For example, 25 gradations require 25 plasma discharges. For this purpose, SF1 (1 time), SF4 (8 times), and SF5 (16 times) may be combined. In addition, weighting is obtained not only in the case of increasing by the factorial of 2, such as 1, 2, 4, 8,. You may make it increase according to the number.

When gradations 0 to 255 are set by a combination of subfields, there are gradations that are likely to generate moving image pseudo contours and gradations that are difficult to generate. For example, in the gradation table shown in FIG. 3, moving image pseudo contours are likely to occur from gradation 24 to gradation 29. Among the used subfields, there is an unused subfield between the subfield with the lowest weight (SF1) and the subfield with the highest weight (hereinafter referred to as the highest used subfield). When many exist, it is known that a moving image pseudo contour is likely to occur.
Among the subfields used as an example, there are two or more unused subfields (however, the smallest subfield SF1) between the subfield (SF1) having the smallest weight and the highest used subfield. In the following description, it is assumed that a moving image pseudo contour is likely to occur. In the case of gradation 24, the subfield with the smallest weight among the subfields used is SF2, and the highest used subfield is SF6. Two unused subfields SF4 and SF5 exist between SF2 and SF6. Therefore, the gradation 24 is assumed to be a gradation at which a moving image pseudo contour is likely to occur. In the case of gradation 25, there are also two unused subfields. Further, in the case of the gradation 26, there are three unused subfields SF2, SF3, and SF5 before reaching the highest used subfield SF6. Further, in the case of gradation 27, two unused subfields SF3 and SF5 exist until reaching the highest used subfield SF6. Further, in the case of gradation 28, there are two unused subfields SF3 and SF5 before reaching the highest used subfield SF6. Further, in the case of gradation 29, there are two unused subfields SF2 and SF5 before reaching the highest used subfield SF6.

For the description here, a gradation in which a moving image pseudo contour is likely to occur is referred to as a moving image pseudo contour induced gradation (or MPDI (Motion Picture Disturbance Induction) gradation). Therefore, the gradations 24 to 29 are all MPDI gradations.
On the other hand, a gradation in which a moving image pseudo contour is less likely to occur is referred to as a moving image pseudo contour non-induced gradation (or MPDN (Motion Picture Disturbance Non-induction) gradation). Therefore, the gradations 20, 21, 22, 23 and the gradations 30, 31 are MPDN gradations.

  When expressing an MPDI gradation in which a moving image pseudo-contour is likely to occur, the gradation table shown in FIG. 3 does not use a combination of subfields corresponding to the gradation, and the gradation is lower than that gradation. The combination of the subfields of the MPDN gradation (hereinafter referred to as the lower MPDN gradation) for which the first moving image pseudo contour is difficult to generate and the first moving image pseudo contour is generated at a gradation higher than that gradation. A combination of subfields of difficult MPDN gradation (hereinafter referred to as upper MPDN gradation) is used in a predetermined ratio. For example, when the gradation 25 is expressed, the MPDI gradation 25 is expressed by mixing the gradation 23 that is the lower MPDN gradation and the gradation 30 that is the upper MPDN gradation at a predetermined ratio.

  For the mixing, an error diffusion method or a dither diffusion method is used. These methods perform spatial mixing in which an upper MPDN gradation and a lower MPDN gradation are assigned to a target pixel to be expressed and its peripheral pixels according to a predetermined rule, and the brightness levels of the target pixel and the peripheral pixels are area-averaged. To express the gradation of the target pixel. In addition, for example, by switching temporally the upper MPDN gradation and the lower MPDN gradation for each target field according to a predetermined rule for each field, it is possible to express the gradation of the target pixel by averaging over time. It is also possible to express the gradation of the target pixel using both the area average and the time average.

By the way, it was recognized that disturbance of luminance linearity occurs when the MPDN gradation is frequently used. This disturbance of the luminance linearity becomes prominent when the number of addresses described below increases.
In the gradation table shown in FIG. 3, the number of addresses in each gradation is shown. For example, the number of addresses of the MPDN gradation 23 is 5. This is because there are five subfields (SF1, SF2, SF3, SF4, SF5) used. The number of addresses of the MPDI gradation 24 is 3. This is because there are three subfields (SF2, SF3, SF6) used. A voltage is applied every time addressing is performed, and a slight luminance is generated. Therefore, the luminance increases as the number of addresses increases. In particular, in a region where the luminance level is low, the luminance change due to the address appears more prominently, which causes luminance linearity disturbance.

  The graph of FIG. 4 shows the relationship between the input gradation (horizontal axis) and the luminance level (vertical axis). For example, when viewing the section R4 with the input gradation of 23 to 29, the line L1 representing the case where the luminance linearity improvement processing of the present invention has not been performed is displaced in the direction in which the luminance is increased. In this way, there are a plurality of sections that are displaced in the direction in which the brightness is increased. There are six sections (R1, R2, R3, R4, R5, R6) even when the input gradation shown in FIG.

テーブル１ The present invention provides an image display apparatus and method capable of improving luminance linearity even when such an MPDN gradation having a large number of addresses is frequently used. A line L2 in FIG. 4 represents a case where the luminance linearity improvement processing of the present invention is performed.
In the present invention, first, using a luminance meter, the luminance value on the panel is measured for each input gradation. The actually measured luminance value (candela / unit area) is converted into a gradation (effective gradation) corresponding to the luminance value. Table 1 shows an example of input gradation, measured luminance value, and effective gradation.

Table 1

テーブル２ In the case of the input gradation 23, light is emitted using the subfields SF1, SF2, SF3, SF4, and SF5 from FIG. 3, and the measured luminance value on the panel at that time is 322958 candela / unit area. However, in calculation, the luminance value on the panel with respect to the input gradation 23 is 297121 candela / unit area. When the measured luminance value 322958 candela / unit area on the panel is converted to gradation, it corresponds to 25.0 gradations. That is, for the input gradation 23, the brightness on the panel is observed at an ideal brightness when the gradation 25 is input. This converted gradation is called effective gradation. Preferably, the input gradation and the effective gradation should show the same value, but actually, the effective gradation is slightly brighter. Moreover, it is not brightening at the same rate, but the fluctuation degree is non-uniform.
In the present invention, a table 2 in which the input gradation and the effective gradation are compared is created based on the table 1, and is used in the image display apparatus according to the present invention as a luminance value conversion table.

Table 2

  Here, the effective gradation is a value obtained by converting a luminance value actually measured on the panel into a gradation. Therefore, the effective gradation is a gradation representing brightness substantially equal to the brightness on the panel. Note that the effective gradation can also be obtained by calculation in consideration of the number of plasma discharges and the number of addresses instead of the luminance value actually measured on the panel.

<Embodiment>
FIG. 5 is a block diagram of an image display apparatus according to the present invention. 2 is an input unit, 4 is an error diffusion unit, 22 is a first dither circuit, 24 is a second dither circuit, 26 is a changeover switch, 28 is a first luminance value conversion table, 30 is a second luminance value conversion table, and 32 is A mixer, 34 is a subtractor, 36 is a line memory, and 40 is an output unit. The error diffusion unit 4 includes pixel delay circuits 6, 8, 10, coefficient multipliers 12, 14, 16, an adder 18, and an adder 20.
Note that a line L3 in FIG. 4 represents a value indicating the luminance measurement value with respect to the input gradation in gradation, a line L4 represents the contents of the table 2 with respect to the input gradation, and a line L5 represents the number corresponding to the input gradation. The output from the 1 dither circuit 22 indicates the output, and the line L6 indicates the output from the first dither circuit 24 for the input gray level.
An input gradation IGa that is a gradation level for each pixel is input to the input unit 2. The input gradation IGa is added to the adder 20 of the error diffusion unit 4 and output as an error adjustment input gradation IGb. As will be described later, the error adjustment input gradation IGb is a value close to the input gradation IGa, but has an integer part and a decimal part because it has been adjusted.

  The first dither circuit 22 receives the error adjustment input gradation IGb and rounds it to an error adjustment input gradation IGb having only an integer part. In this case, the decimal part is subjected to any processing such as rounding down, rounding up, or rounding off. Further, in the first dither circuit 22, the error adjustment input gradation IGb is a moving image pseudo contour induced gradation (MPDI gradation) belonging to an area (R1 to R6, etc.) where the moving image pseudo contour is likely to occur in FIG. It is determined whether it is a moving image pseudo contour non-induced gradation (MPDN gradation) belonging to an area where the moving image pseudo contour is difficult to occur. This determination is made using, for example, a pre-recorded gradation table (not shown). If the error adjustment input gradation IGb is an MPDN gradation in which a moving image pseudo contour is not easily generated, the error adjustment input gradation IGb is output as it is. On the other hand, if the error adjustment input gradation IGb is an MPDI gradation in which a moving image pseudo contour is likely to be generated, the first dither circuit 22 outputs the lower MPDN gradation using the gradation table.

  Similarly, the second dither circuit 24 receives the error adjustment input gradation IGb and rounds it to an error adjustment input gradation IGb having only an integer part. In this case, the decimal part is subjected to any processing such as rounding down, rounding up, or rounding off. Further, also in the second dither circuit 24, the error adjustment input gradation IGb is a moving image pseudo contour induced gradation (MPDI gradation) belonging to an area (R1 to R6, etc.) where the moving image pseudo contour is likely to occur in FIG. It is determined whether it is a moving image pseudo contour non-induced gradation (MPDN gradation) belonging to an area where the moving image pseudo contour is difficult to occur. This determination is made using, for example, a pre-recorded gradation table (not shown). If the error adjustment input gradation IGb is an MPDN gradation in which a moving image pseudo contour is not easily generated, the error adjustment input gradation IGb is output as it is. On the other hand, if the error adjustment input gradation IGb is an MPDI gradation in which a moving image pseudo contour is likely to be generated, the second dither circuit 24 outputs the upper MPDN gradation using the gradation table.

  That is, when the error adjustment input gradation IGb is a moving image pseudo contour induced gradation (MPDI gradation), the first dither circuit 22 outputs the lower MPDN gradation, while the second dither circuit 24 MPDN gradation is output. When the error adjustment input gradation IGb is a moving image pseudo contour non-induced gradation (MPDN gradation), both the first dither circuit 22 and the second dither circuit 24 are errors processed to integer values. The adjusted input gradation IGb is output.

    The changeover switch 26 is, for example, a changeover switch that can be switched in units of frames or fields (or in units of multiple frames or in units of multiple fields). Therefore, when the error adjustment input gradation IGb is the moving image pseudo contour induced gradation (MPDI gradation), the upper MPDN gradation and the lower MPDN gradation are temporally mixed at a determined ratio and are changed over. Is sent to the output unit 40. When the error adjustment input gradation IGb is a moving image pseudo contour non-induced gradation (MPDN gradation), the error adjustment input gradation IGb processed to an integer value is continuously output. In this case, the changeover switch 26 may perform a monotonous changeover operation and alternately output the same error adjustment input gradation IGb from the first dither circuit 22 and the second dither circuit 24. Alternatively, it may be fixed to the first dither circuit 22 side (or the second dither circuit 24 side).

The outputs of the first dither circuit 22 and the second dither circuit 24 are further sent to the first luminance value conversion table 28 and the second luminance value conversion table 30, respectively. The first luminance value conversion table 28 and the second luminance value conversion table 30 are collectively referred to as a luminance value conversion table. The first luminance value conversion table 28 and the second luminance value conversion table 30 have the same contents, that is, the data of Table 2 shown above, and the effective gradation (integer value) for the input gradation (integer value only). And decimal value) are output.
The input gradation input to each of the first luminance value conversion table 28 and the second luminance value conversion table 30 is when the error adjustment input gradation IGb is a moving image pseudo contour induction gradation (MPDI gradation). , Lower MPDN gradation, upper MPDN gradation, and the same MPDN gradation when the error adjustment input gradation IGb is a moving image pseudo contour non-induced gradation (MPDN gradation).

The former case, that is, the case where the lower MPDN gradation and the upper MPDN gradation are input to the first luminance value conversion table 28 and the second luminance value conversion table 30, respectively, will be described.
The first luminance value conversion table 28 receives the lower MPDN gradation from the first dither circuit 22 as an input gradation and outputs an effective gradation (referred to as a first effective gradation). The second luminance value conversion table 30 receives the upper MPDN gradation from the second dither circuit 24 as an input gradation and outputs an effective gradation (referred to as a second effective gradation).

Next, the latter case, that is, a case where the same MPDN gradation is input to each of the first luminance value conversion table 28 and the second luminance value conversion table 30 will be described.
The first luminance value conversion table 28 and the second luminance value conversion table 30 receive the same MPDN gradation as the input gradation from the first dither circuit 22 and the second dither circuit 24, and the first effective gradation and the second Outputs effective gradation (both have the same value).
The first effective gradation and the second effective gradation thus obtained are mixed in the mixer 32, and a mixed luminance value (also referred to as a mixed gradation) is output. The mixing ratio may be 1: 1, or may be a ratio at which the changeover switch 26 selects the outputs of the first dither circuit 22 and the second dither circuit 24. The subtractor 34 calculates the difference between the mixed gradation and the error adjustment input gradation IGb, and the difference value is sequentially recorded in the line memory 36 as an adjustment value. Accordingly, adjustment values (ΔPa, ΔPb, ΔPc,...) Described later are recorded in the line memory 36 for one line.

In the present invention, since the first luminance value conversion table 28 and the second luminance value conversion table 30 are used, information on the luminance value fed back to the error diffusion unit 4 to be described below is predicted by calculation. It is not information related to the luminance value, but information related to the luminance value measured on the screen. Therefore, the luminance value on the screen can be controlled more accurately.
The first luminance value conversion table 28 and the second luminance value conversion table 30 may have effective gradations for all gradations (gradation 1 to gradation 255). A table for only the contour non-induced gradation (MPDN gradation) may be used. In the latter case, the table size can be reduced.

Next, the error diffusion unit 4 will be described.
In the error diffusion unit 4, the data of the processed peripheral pixels is added with a predetermined weight to the target pixel to be processed, and the target pixel is processed. Here, the processing of the target pixel using the peripheral pixels performed in the error diffusion unit 4 will be described.

  FIG. 6 shows an arrangement of pixels. With respect to the target pixel Po, the immediately preceding pixel is Pd, the pixel immediately above one line is Pb, and the pixels adjacent to both sides of Pb are Pa and Pc. In the line memory 36, error adjustment values ΔPa, ΔPb, ΔPc,... For pixel data on one line including the peripheral pixels Pa, Pb, Pc are recorded. The line memory 36 has the effect of one line delay. The error adjustment values ΔPa, ΔPb, and ΔPc output from the line memory 36 are delayed in pixel units by the pixel delay circuits 6, 8, and 10, and further given weights by the coefficient multipliers 12, 14, and 16. Further, the error adjustment value ΔPd based on the immediately preceding pixel Pd is obtained from the subtractor 34. These error adjustment values ΔPa, ΔPb, ΔPc, ΔPd are weighted, added by the adder 18, and then added to the input gradation IGa of the target pixel Po by the adder 20. That is, the input gradation IGa is changed to the input gradation IGb after error adjustment (referred to as error adjustment input gradation IGb) by adding the adjustment value adjusted by error diffusion. The adjustment value takes a positive or negative value and has an integer part and a decimal part. The input gradation IGa is a gradation represented by any positive integer from 0 to 255, but the error adjustment input gradation IGb is close to the input gradation IGa, but has been adjusted. It has an integer part and a decimal part.

  Such error adjustment input gradation IGb is input to the first dither circuit 22 and the second dither circuit 24, and the above-described processing is performed.

Next, the operation of the image display apparatus of FIG. 5 will be described using the flowchart of FIG.
In step S1, it is assumed that the input gradation IGa from the input unit 2 is 25 gradations. In the error diffusion unit 4, errors are accumulated and the input gradation IGa is adjusted to become the error adjustment input gradation IGb. In other words, the error diffusion unit 4 accumulates the error adjustment value from the line memory 36 at a predetermined ratio with the newly received input gradation, and generates an error-adjusted input gradation. The error adjustment input gradation IGb is sent to the first dither circuit 22 and the second dither circuit 24, and is converted into an integer. Assume that the error adjustment input gradation IGb is 26.35. If the integer processing here is rounded off, the decimal part after the decimal point is rounded off to generate 26 gradations. Further, in the first dither circuit 22 and the second dither circuit 24, the gradation 26 that has been processed to be an integer is a moving image pseudo contour induced gradation (MPDI gradation) or a moving image pseudo contour non induced gradation (MPDN gradation). ) Is determined. As shown in FIG. 3, since the 26th gradation is the moving image pseudo contour induced gradation (MPDI gradation), the lower MPDN gradation (23 gradation) is output from the first dither circuit 22 (step S2), while the second The upper MPDN gradation (30 gradations) is output from the dither circuit 24 (step S3). Note that the error diffusion unit 4 may perform the integer process of the error adjustment input gradation IGb.

The lower MPDN gradation (23 gradations) from the first dither circuit 22 and the upper MPDN gradation (30 gradations) from the second dither circuit 24 are sent to the changeover switch 26 (step S7), from the output unit 40. It is output and used as a panel display gradation.
Further, the lower MPDN gradation (23 gradations) from the first dither circuit 22 is sent to the first luminance value conversion table 28 and converted to 25.0 gradations as the first effective gradation (step S4). . The upper MPDN gradation (30 gradations) from the second dither circuit 24 is sent to the second luminance value conversion table 30 and converted to 31.0 gradation as the second effective gradation (step S5). In the mixer 32, the first effective gradation and the second effective gradation are mixed at a predetermined ratio. Here, when mixing is performed at a ratio of 1: 1, the mixed gradation is 28.0 gradation (step S6).
The mixed 28.0 gradation is sent to the subtractor 34,
(Error adjustment input gradation IGb)-(Mixed gradation)
Or (integerized error adjustment input gradation IGb) − (mixed gradation)
The difference value is recorded in the line memory as an adjustment value (step S9) and sent to the error diffusion unit 4 as it is.

  As described above, in the image display device according to the present invention, the gradation output from the first dither circuit 22 and the second dither circuit 24 is converted into the gray level by the first luminance value conversion table 28 and the second luminance value conversion table 30. Since the error diffusion is performed based on the value obtained by converting the luminance value actually measured by the panel into the effective gradation, the luminance adjustment can be performed more accurately. A line L2 in FIG. 4 shows a result of the luminance linearity improvement processing of the present invention, and shows a linear luminance change with respect to the input gradation.

  The present invention can be used for an image display device and an image display method.

Explanatory drawing which shows an example of a structure of the subfield in PDP based on the prior art example A table showing the relationship between input tone and subfield weighting according to the conventional example A table showing the relationship between the input gradation and the weight of the subfield according to the present invention. Graph showing the relationship between input gradation and effective gradation Block diagram of an image display device according to the present invention Explanatory diagram showing the pixel of interest on the panel and surrounding pixels for error diffusion The flowchart which shows the image display method based on this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Input part 4 ... Error diffusion part 22 ... 1st dither circuit 24 ... 2nd dither circuit 26 ... Changeover switch 28 ... 1st luminance value conversion table 30 ... 2nd luminance value conversion table 32 ... Mixer 34 ... Subtractor 36 ... Line memory 40 ... Output unit

Claims (7)

An image display device that receives an input gradation, outputs a gradation with adjusted luminance linearity, and drives a display panel,
A dither processing unit that receives an input gradation and outputs a first gradation and a second gradation;
A luminance value conversion table for converting the first gradation and the second gradation into a first effective gradation and a second effective gradation representing brightness substantially equal to the brightness on the panel;
A mixer that mixes the first effective gradation and the second effective gradation to generate a mixed gradation;
A line memory that records the difference between the input gradation and the mixed gradation as an error adjustment value;
An error diffusion unit that accumulates error adjustment values at a predetermined rate on newly received input gradations and generates error-adjusted input gradations;
An image display device that sends an input gradation adjusted in error to the dither processing unit and drives the display panel using the first gradation and the second gradation from the dither processing unit.   The image display device according to claim 1, further comprising means for determining a gradation at which a moving image pseudo contour is generated and a gradation at which the moving image pseudo contour is not generated.   The image display device according to claim 1, further comprising means for rounding off the decimal part of the input gradation adjusted for error and expressing the input gradation only by an integer part.   The luminance value conversion table includes a first luminance value conversion table for converting the first gradation into a first effective gradation representing brightness substantially equal to the brightness on the panel, and a second gradation for brightness on the panel. 2. The image display device according to claim 1, further comprising: a second luminance value conversion table for converting to a second effective gradation representing a brightness substantially equal to the second brightness gradation.   The image display device according to claim 4, wherein the first luminance value conversion table and the second luminance value conversion table store information having the same contents.   The image display apparatus according to claim 1, further comprising a changeover switch that alternately switches the first gradation and the second gradation. An image display method for receiving an input gradation, outputting a gradation with adjusted luminance linearity, and driving a display panel,
a) receiving an input gradation and outputting a first gradation and a second gradation;
b) converting the first gradation and the second gradation into a first effective gradation and a second effective gradation representing brightness substantially equal to the brightness on the panel;
c) mixing the first effective gradation and the second effective gradation to generate a mixed gradation;
d) recording the difference between the input gradation and the mixed gradation as an error adjustment value;
e) accumulating error adjustment values at a predetermined rate on newly received input gradations to generate error-adjusted input gradations;
An image display method in which an error-adjusted input gradation is used as an input gradation in step a) and a display panel is driven using a first gradation and a second gradation.

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