JP2005024684A - Multi-gradation display unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a multi-gradation display unit capable of obtaining better picture quality by reducing a moving false outline with a simple constitution. <P>SOLUTION: The multi-gradation display unit is equipped with an SF (subfield) encoding circuit which encodes an image signal in units of subfields SF while one field is composed of a plurality of SFs; and at least one non-power SF whose luminance ratio has a value other than a value obtained by raising 2 to some power is included and arranged in one field in the increasing or decreasing order of weight; and the SF with the largest weight which illuminates in a large gradation is larger in weight than or equal to the SF with the largest weight which illuminates in a small gradation. In a gradation right before a carry, the largest-weight SF among SFs which illuminate and the SF with following weight illuminate and at least some SFs do not illuminate. The previous gradation is larger than the gradation represented by the total of weights of the SF having the largest weight and two following SFs among the SFs which illuminate and in the gradation right after the carry, a carry SF and two following SFs illuminate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention uses a display device that can control only lighting or astigmatic states, such as a PDP panel, an EL panel, and some LCD panels, and constitutes one field as a plurality of subfields weighted with a predetermined luminance. The present invention relates to a multi-grayscale display device that performs multi-grayscale display by turning on or off each display cell in subfield units.
[0002]
[Prior art]
In a display device using a display element such as a PDP panel, EL panel, and some LCD panels that cannot arbitrarily change the display intensity for each cell, a plurality of subfields in which one field is weighted with a predetermined luminance The multi-gradation display is performed by turning on or off each display cell in sub-field units.
[0003]
When performing multi-gradation display with a subfield configuration, conventionally, it is most common to set the luminance (weight) ratio between subfields to change by a power of 2, such as 1: 2: 4: 8. It was the target. By setting the luminance ratio in such a relationship, gradation display can be performed most efficiently.
[0004]
In the multi-gradation display with the sub-field configuration, there is a problem that false contours are generated in the case of a moving image due to the discrete lighting timing within the field period. In order to solve such a problem, various solutions have been conventionally proposed. For example, in the configuration having the luminance ratio of the above relationship, a method of arranging a sub-field having a large weight in the center of one field has been proposed. However, in this configuration, a moving false contour is generated in a relatively low-brightness image, and the image quality is not sufficient.
[0005]
In view of this, Japanese Patent Application Laid-Open No. 10-116053 and Japanese Patent Application Laid-Open No. 10-153982 propose a subfield configuration including one or more subfields having a weight that is not a power of two.
[0006]
FIG. 1 is a diagram illustrating a conventional subfield coding pattern including one or more subfields having a weight that is not a power of two. This figure has eight subfields SF1 to SF8, and the length ratio of the sustain period, that is, the luminance (weight) ratio is 1: 2: 4: 8: 12: 16: 20: 24. In this example, a circle indicates lighting, and a portion without a mark indicates non-lighting. With this pattern, 87 gradations can be expressed. As shown in the figure, the subfields are arranged in ascending order of weight, and the difference in weight from the adjacent subfield is 4 from SF4. However, in this subfield coding pattern, the false contour cannot be completely prevented at the gradations 2, 4, 8, 16, 28, 44 and 64 of the carry of the subfield.
[0007]
FIG. 2 is a diagram for explaining the generation of dynamic false contours. Here, the field is composed of six subfields SF1 to SF6, the luminance (weight) ratio is 1: 2: 4: 8: 12: 16, the horizontal axis is a pixel, and the leftmost in the field f. Each pixel n has a gradation 24, the right pixel n + 1 has a gradation 25, the pixel n + 2 has a gradation 26, and so on. The vertical axis represents time, and the image of the field f moves to the right by one pixel for each field. The pixel n + 1 in the field f + 1 has a gradation 24, and the pixel n + 2 in the field f + 2 has a gradation 24. In the subfield lighting pattern of this image, SF6 changes from non-lighting to lighting in the pixel n + 4 in the field f, that is, the carry of the subfield occurs. Since a person chases and looks at a moving object, it actually looks as indicated by an arrow, and the visual gradation is gradation 26 after gradation 26, followed by gradation 28 and thereafter. The gradation does not appear to change linearly. This is the principle of generation of dynamic false contours.
[0008]
In order to reduce the occurrence of dynamic false contours, Japanese Patent Application Laid-Open No. 7-271325 discloses a slightly reduced display efficiency, but subfields having the same luminance ratio are provided in one field, and the same luminance is expressed by a combination of different subfields. When sub-field coding patterns are prepared and the sub-field configuration of each pixel is determined, the sub-field coding pattern is different for each vertical and horizontal display line or for each pixel, and for each field, A superposition method for reducing the occurrence of contours is disclosed. 3 and 4 are diagrams showing subfield coding patterns for the superposition method. As shown in the figure, there are two types of patterns, A and B, and encoding is performed by switching to A and B lighting patterns for each pixel and each line.
[0009]
In patterns A and B in FIGS. 3 and 4, gradations 16 to 39 and gradations 48 to 63 are different lighting patterns at the same gradation. Therefore, there is a problem that checkered pattern (hatch-like) pattern noise occurs in 40 gradations having different lighting patterns among all 63 gradations. Therefore, Japanese Patent Laid-Open No. 2000-372948 uses the superimposition method only when it is detected that the image is a moving image and the gradation at which a moving false contour is likely to appear. A moving image specific gradation overlay method using a subfield coding pattern is proposed.
[0010]
Since the details of the superposition method are described in the above-mentioned document, further explanation is omitted here.
[0011]
[Patent Document 1]
JP-A-10-116053 [Patent Document 2]
JP 10-153982 A [Patent Document 3]
JP-A-7-271325 [Patent Document 4]
Japanese Patent Laid-Open No. 2000-372948
[Problems to be solved by the invention]
According to the moving image specific gradation superimposing method disclosed in Japanese Patent Laid-Open No. 2000-372948, checkered pattern noise can be reduced. To that end, however, it is necessary to provide a gradient detection circuit, a motion detection circuit, and the like. There is a problem that the configuration becomes complicated.
[0013]
An object of the present invention is to realize a multi-gradation display device that can obtain a better image quality by reducing dynamic false contours with a simple configuration.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the multi-gradation display device of the present invention devise a lighting pattern in subfield coding. Specifically, in the subfield configuration, at least one non-powered subfield having a luminance ratio that is not a power of 2 is provided, and the subfields are arranged in ascending or descending order of weight within one field, and are lit at each gradation. The arrangement position of the sub-field with the maximum weight does not reverse the arrangement order when the gradation changes, and the attention sub-field a having a larger weight than the sub-field with the least weight changes from non-lighting to lighting. In other words, when there is a carry, in the smaller gradation x before and after the carry, the low adjacent subfield a-1 adjacent to the smaller weight side of the subfield a of interest is lit, and the subweight with a smaller weight than that There is always a non-lighting subfield in the field, and the smaller gradation x is on the lower adjacent subfield a-1 and its smaller weight side. 2 larger than the gradation expressed by the sum of the weights of the low-adjacent sub-fields a-2 in contact, in the gradation x + 1 of the larger, second low adjacent subfield a-2 is characterized in that it is a light.
[0015]
Further, in the larger gradation x + 1, the low adjacent subfield a-1 is not lit.
[0016]
The subfield lighting pattern of the present invention is also effective in the superposition method. In the superposition method, a plurality of subfield coding patterns having different lighting / non-lighting patterns of some gradations are prepared. A selection circuit for switching which display data to be used is encoded.
[0017]
Similar to the conventional superposition method, the selection circuit performs staggering for each display pixel or group of a plurality of display pixels, for each horizontal or vertical display line, and for each horizontal and vertical pixel adjacent to the display screen. Alternatively, the pattern to be used may be switched, and the switching may be changed for each field.
[0018]
Although the generation principle of the dynamic false contour has already been described, as a result of further consideration of the generation of the dynamic false contour, the following has been found.
[0019]
(1) When the subfields to be lit are continuous, the dynamic false contour is not generated.
[0020]
A display method has been proposed in which subfields that are lit in one field are always continuous. With this display method, the number of gradations that can be displayed is significantly reduced, but no moving false contour is generated. This is because the SFs that are lit are continuous from SFs having a small weight to SFs having a large weight, and there is no non-lighting SF in between.
[0021]
Furthermore, when a moving image is displayed with a gradation in which SF having a small weight has a non-lighting pattern, a moving false contour is unlikely to occur.
[0022]
From these facts, the non-lighting of the subfield having a large weight in the lighting pattern is a major cause of the occurrence of the dynamic false contour.
[0023]
(2) When an image with a carry moves, a false contour is generated.
[0024]
In the coding pattern of FIG. 1, the gradation p smaller than the gradation o in which the subfield digit increases is not illuminated in the subfield having a relatively small weight. However, for the reason of (1) above, the dynamic false contour is not present. Hard to occur. In the case of a moving image in which the gradation p + 1 is smaller than the gradation o where the subfield digit is increased and is adjacent to the pixel of the gradation p, a moving false contour is less likely to occur.
[0025]
In addition, in the gradation q (for example, q = 65) larger than the gradation o where the digit of the subfield increases, the subfield (SF7) having a relatively large weight and the subfield (SF2) having a relatively small weight are not lit. In the case of a moving image in which the gradation q + 1 is larger than the gradation o in which the subfield digit is increased and is adjacent to the pixel of the gradation q, a moving false contour is hardly generated.
[0026]
However, in the case of a moving image in which the gradation p and the gradation q are adjacent, a moving false contour is generated. That is, the gradations q and q + 1 are patterns in which dynamic contours are likely to occur.
[0027]
Therefore, patterns that are likely to generate dynamic false contours are when the subfield with relatively large weight is not lit, and there are gradations of patterns that are unlikely to generate dynamic false contours and gradations of patterns that are likely to generate dynamic false contours. In the case of adjacent moving images, a moving false contour is generated.
[0028]
In other words, in the case of a moving image having a gradation of a pattern in which adjacent pixels are less likely to generate a moving false contour and a gradation of a pattern in which a moving false contour is more likely to occur, a moving false contour is generated. However, in the case of the gradation of a pattern in which adjacent false pixels are less likely to generate dynamic false contours and a pattern in which dynamic false contours are both likely to occur, dynamic false contours are less likely to occur.
[0029]
From the above, if all the encoded patterns are patterns in which dynamic false contours are not easily generated, or all patterns are easily generated in dynamic false contours, even if there is a carry, dynamic false contours are not easily generated. However, a lighting table cannot be created with a pattern in which subfields having a relatively large weight are lit, such as a gray scale smaller than the gray scale o where the digit increases.
[0030]
The subfield coding pattern of the present invention satisfies the condition that the above-described dynamic false contour is less likely to occur. Further, since the present invention can be realized only by changing the subfield coding pattern, the cost does not increase.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 5 is a diagram showing the overall configuration of the multi-gradation display device of the first embodiment of the present invention. In FIG. 1, reference numeral 1 is an input terminal to which an analog image signal is inputted, 2 is an input terminal to which a synchronizing signal such as a horizontal synchronizing signal (Hsync), a vertical synchronizing signal (Vsync) and a dot clock are inputted, and 3 is an input An A / D conversion circuit that converts an analog image signal input to the terminal 1 into a digital signal having a predetermined number of bits, 4 can express the maximum number of gradations of the output signal of the A / D conversion circuit by a subfield encoding circuit. A gain control circuit 5 for obtaining the maximum number of gradations, 5 is a subfield coding circuit for converting an image signal having a predetermined number of gradations output from the gain control circuit into information for each subfield for each pixel, and 6 is a subfield code. A field memory for storing subfield information in units of pixels output from the conversion circuit 5 for two fields, 7 a drive circuit for driving the display unit 9, and 8 an input terminal 2 A control circuit for controlling the operations of the A / D converter 3, the gain control circuit 4, the subfield encoding circuit 5, the field memory 6 and the drive circuit 7 from the inputted synchronization signal, 9 is a plasma display panel And so on. When the field memory 6 stores subfield information in units of pixels for one field, the information is output in units of subfields in the next field.
[0032]
FIG. 6 is a diagram illustrating a subfield coding pattern used by the subfield coding circuit of the display device according to the first embodiment. Circles indicate lighting and no marks indicate non-lighting. As shown in the figure, one field is composed of eight subfields SF1 to SF8, and the luminance (weight) ratio of SF1 to SF8 is 1: 2: 4: 8: 12: 16: 20: 24. , 87 gradations can be expressed. The subfield structure of the first embodiment is the same as that of the conventional example of FIG. 1, but includes SF5 (weight 12), SF7 (weight 20), and SF8 (weight 24) that are not powers of 2. It is important that the present invention is applied to a subfield configuration having SFs having weights that are not a power of 2 as described above.
[0033]
The carry gradation of the maximum lighting subfield is 2, 4, 8, 16, 24, 36, 56. Compared with the conventional pattern of FIG. 1, in this embodiment, the carry of SF6, SF7 and SF8 is gradations 24, 36 and 56, whereas in the conventional pattern of FIG. It is. For example, comparing the carry of SF8, in this embodiment, SF4 and SF7 are not lit in the lighting pattern of gradation 56, and SF4 is not lit in the lighting pattern of gradation 55 that is one lower. Both of them are factors that cause dynamic false contours, but dynamic false contours are difficult to appear. Further, in the gradations 55 and 56, only SF7 changes in the subfield having a relatively large weight. In this way, the dynamic false contour can be suppressed by making the change in the lighting pattern of the subfield as small as possible.
[0034]
In addition, it is possible to suppress the occurrence of a false contour by obtaining the center of gravity of lighting from the lighting pattern of carry gradation and minimizing the movement of the center of gravity.
[0035]
FIG. 7 is a diagram illustrating another example of the subfield coding pattern of the first embodiment. The false contour is relatively likely to occur not only in the carry of the sub-field of the maximum weight that is turned on, but also in the carry of the sub-field of one smaller weight and the carry of the intermediate sub-field. The subfield coding pattern of FIG. 7 has the same subfield configuration as the pattern of FIG. 6, and the carry gradation of the subfield with the maximum weight to be lit is also the same. However, the carry of the subfield with one weight less than the maximum weight subfield that is lit is gradations 6, 12, 20, 32, 48, and 68 in FIG. In the case of 12, 20, 32, 44, and 64, the carry of subfields with smaller weights similarly reduces the change in subfields with relatively large weights, and can further suppress dynamic false contours.
[0036]
FIG. 8 is a diagram showing the overall configuration of the multi-gradation display device of the second embodiment of the present invention. The multi-tone display device of the second embodiment is an embodiment in which the present invention is applied to an apparatus using the above-described superposition method. Only differences from the apparatus of the first embodiment of FIG. 5 will be described.
[0037]
In FIG. 8, input terminals 11 and 12, an A / D conversion circuit 13, a gain control circuit 14, a field memory 16, a drive circuit 17, a control circuit 18 and a display unit 19 are elements of the first embodiment of FIG. Correspond. As shown in the figure, instead of the subfield encoding circuit 5, two first and second subfield encoding units 15A and 15B and one of the two outputs are selected and output to the field memory 16. This is different from the first embodiment in that a switching circuit 20 for switching is provided.
[0038]
The output of the gain control circuit 14 is input to the two first and second subfield encoding means 15A and 15B. The first subfield encoding means 15A performs encoding using a subfield encoding pattern A as shown in FIG. 9, and the second subfield encoding means 15B is a subfield code as shown in FIG. Encoding is performed using the encoding pattern B. The switching circuit 20 selects and outputs one of the two outputs of the two first and second subfield encoding units 15A and 15B in accordance with the control signal from the control circuit 18. As shown in FIG. 11A, this switching is performed so that the encoding by the subfield encoding pattern A and the encoding by the subfield encoding pattern B are performed for each horizontal line on the display screen. Thereby, the position of the lighting subfield in the field is averaged by the upper and lower lines, and the moving false contour is reduced.
[0039]
Note that various modifications are possible as to how the pixels using two different coding patterns are arranged. For example, as shown in FIG. 11B, the arrangement shown in FIG. 11A may be alternately changed for each field. Furthermore, as shown in FIG. 12A, it is also possible to alternately perform encoding with the subfield encoding pattern A and encoding with the subfield encoding pattern B for each vertical line on the display screen. Further, as shown in FIG. 12B, the line position may be changed for each field.
[0040]
Further, as shown in FIG. 13A, encoding by subfield encoding pattern A and encoding by subfield encoding pattern B are alternately performed for each adjacent pixel on the display screen, that is, staggered encoding is performed. It is also possible to make them different. Further, as shown in FIG. 13B, the line position may be changed for each field.
[0041]
Here, subfield coding patterns A and B of the second embodiment shown in FIGS. 9 and 10 will be described. In pattern A, the carry gradation of SF7 is 36, in pattern B, the gradation is 40, in pattern A, the carry gradation of SF8 is 56, in pattern B, the gradation is 60, and in pattern A, the light is on. In the case of non-maximum luminance, SF6 carry gradations are 44 and 68, in pattern B, gradations are 48 and 72, and in pattern A, the non-maximum luminance of SF7 carry gradation is 64, In the pattern B, the gradation is 68. Of all the 88 gradations, the difference between patterns A and B is 20 gradations. As shown in FIG. 9 or FIG. 10, subfield coding of patterns A and B is performed for each pixel, line, and field. Even when switching, hatched noise becomes inconspicuous.
[0042]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a multi-tone display device that can reduce false contours and hatched noise of moving images with a simple circuit and can improve the quality of moving images as well as still images.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a conventional subfield coding pattern.
FIG. 2 is a diagram for explaining the principle of generation of dynamic false contours.
FIG. 3 is a diagram illustrating a conventional superfield subfield coding pattern.
FIG. 4 is a diagram illustrating a conventional subfield coding pattern for superposition method.
FIG. 5 is a block diagram illustrating a configuration of a multi-gradation display device according to a first embodiment of the present invention.
FIG. 6 is a diagram illustrating a subfield coding pattern according to the first embodiment.
FIG. 7 is a diagram illustrating another example of a subfield coding pattern according to the first embodiment.
FIG. 8 is a block diagram showing a configuration of a multi-tone display device according to a second embodiment of the present invention.
FIG. 9 is a diagram illustrating a subfield coding pattern A according to the second embodiment.
FIG. 10 is a diagram illustrating a subfield coding pattern B of the second embodiment.
FIG. 11 is a diagram illustrating an arrangement example of an overlay pattern according to the second embodiment.
FIG. 12 is a diagram showing an example of the layout pattern arrangement of the second embodiment.
FIG. 13 is a diagram illustrating an arrangement example of an overlay pattern according to the second embodiment.
[Explanation of symbols]
3 ... A / D conversion circuit 4 ... gain control circuit 5 ... subfield coding circuit 6 ... field memory 7 ... drive circuit 8 ... control circuit 9 ... display unit

Claims (8)

A subfield in which one field of an image signal is replaced with n (n is a positive integer greater than or equal to 2) subfields weighted according to a predetermined luminance ratio, and is encoded on or off for each display cell in subfield units. A multi-grayscale display device comprising a coding circuit and performing display based on multi-grayscale encoded display data, wherein the subfield coding circuit comprises:
The n subfields include at least one non-powered subfield having a weight ratio that is not a power of 2.
The n subfields are arranged in ascending or descending order of weight within one field,
A subfield lighting pattern showing lighting and non-lighting up to the maximum gradation that can be expressed by gradations 0 to n subfields, and the largest weight is lit in the larger gradation of any two gradations The subfield has a greater or equal weight than the most weighted subfield that is lit at the lower gray level,
In the two adjacent gradations x and x + 1, when the attention subfield a having a larger weight than the non-powered subfield having the smallest weight changes from non-lighting to lighting, the target subfield is smaller in the smaller gradation x. The low adjacent subfield a-1 adjacent to the lower weight side of a is lit, and there is a non-lighted subfield with a weight smaller than that of the low adjacent subfield, and the smaller gradation x is the lower adjacent subfield a. -1 and the gray level represented by the sum of the weights of the two low adjacent subfields a-2 adjacent to the small weight side of the low adjacent subfield a-1 and larger grayscale x + 1, A multi-gradation display device, wherein the field a-2 is lit. The multi-gradation display device according to claim 1,
In the larger gradation x + 1, the multi-gradation display device in which the low adjacent subfield a-1 is not lit. The multi-gradation display device according to claim 1 or 2,
A plurality of the subfield encoding circuits having different lighting / non-lighting patterns of some gradations,
A multi-gradation display device further comprising a selection circuit for switching which display data output from the plurality of subfield encoding circuits is to be used. The multi-gradation display device according to claim 3,
The multi-grayscale display device in which the selection circuit sequentially switches between display pixels or groups of the plurality of display pixels. The multi-gradation display device according to claim 3,
The selection circuit is a multi-gradation display device that sequentially switches for each horizontal display line. The multi-gradation display device according to claim 3,
The selection circuit is a multi-gradation display device that sequentially switches for each vertical display line. The multi-gradation display device according to claim 3,
The selection circuit is a multi-gradation display device that switches in a zigzag manner for each pixel in the horizontal and vertical directions adjacent to each other on the display screen. The multi-gradation display device according to any one of claims 4 to 7,
The multi-grayscale display device in which the selection circuit changes the selection for each field.

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