JP4094089B2 - Image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image display device.
[0002]
[Prior art]
For example, unlike a cathode ray tube, an image display device such as a plasma display device cannot arbitrarily change the light emission intensity of each pixel. Therefore, gradation is expressed by changing the light emission time according to the gradation using the integration effect of the human eye.
[0003]
However, in the case of a plasma display device, light emission is simultaneously performed on a surface basis. That is, it is possible to select whether or not to emit light for each pixel in one light emission, but it is difficult to finely change the light emission time for each pixel.
[0004]
Therefore, for example, “Journal of the Video Information Media Society” Vol. 51, no. 4 (1997), pp. As described in “PDP moving image quality and signal processing” in 464 to 469, in such a display device, the following method is used to display different gradations for each pixel. It has been.
[0005]
That is, as shown in FIG. 10, an image of one frame is divided into a plurality of subfields (in the case of FIG. 10, eight subfield numbers 0 to 7). Each subfield is assigned a light emission time of a predetermined length (T, 2T,..., 64T, 128T). Further, light emission / non-light emission of each subfield can be selected for each pixel of the image.
[0006]
Then, according to the gray level of each pixel, only necessary subfields are selectively emitted to realize display of different gray levels for each pixel.
[0007]
[Problems to be solved by the invention]
However, when gradation display by subfield division as described above is performed, there is no problem when a still image is displayed, but when a moving image is displayed, interference called pseudo contour occurs.
[0008]
This will be described below with reference to FIG.
11A represents a still image, and FIGS. 11B and 11C represent moving images. In FIG. 11, for simplicity of explanation, there are four subfields, and the upper side of the figure is the LSB side and the lower side is the MSB side. In addition, in each of FIGS. 11A, 11B, and 11C, display examples of gradations of two adjacent pixels are shown. The adjacent areas in the figure have slightly different gradations.
[0009]
In the case of FIG. 11A, that is, in the case of a still image, the gradation of adjacent areas is slightly different, so light emission / non-light emission on the MSB side changes and the pattern of the subfield that emits light changes greatly. is doing. However, the frame image perceived as the sum of each subfield is a correct image according to the gradation.
[0010]
On the other hand, in the case of (b) and (c) in FIG. 11, that is, in the case of a moving image, the image is moving at an appropriate speed, so that the human eye has the property of following it. As a result, each subfield image having a slight difference in display time is perceived with a slight shift from the original position, and the frame image perceived as the sum of the subfields is converted into (b) and (c) in FIG. Extra image information as shown in FIG.
[0011]
That is, in the case of FIG. 11B, the light emission amount at the boundary portion between adjacent pixels is larger than that in the case of an accurate image. In the case of FIG. 11C, the light emission amount at the boundary portion between adjacent pixels is smaller than in the case of an accurate image. This is pseudo contour disturbance.
[0012]
As described above, when gradation display is performed by subfield division, there is a problem in that pseudo contour interference occurs during the display of a moving image, leading to a significant deterioration in image quality.
[0013]
An object of the present invention is to divide an image of one frame into a plurality of subframes, and selectively emit only necessary subfields according to the gradation of each pixel to express different gradations for each pixel. In the display device, an image display device capable of suppressing the occurrence of pseudo contour interference is realized.
[0014]
[Means for Solving the Problems]
(1) In order to achieve the above object, the present invention is configured as follows. That is, an image of one frame is divided into a plurality of subfields having different display times, and display and non-display in each subfield can be selected in units of pixels, and light emission is a product of luminance and light emission time in each subfield. A plasma display apparatus that represents a gray level by summing a quantity in a plurality of subfields, and for expressing a specific gray level, any subfield of the plurality of subfields is represented. A selection means for selecting one of the two or more combinations when the specific gradation is expressed, and the selection means includes the above-mentioned selection means, As a representation of the gradation of a pixel to be displayed, a common light emission or non-light emission of the pixel and a plurality of pixels existing around the pixel is displayed. Field to be larger to select one of the two or more combinations.
[0015]
(2) Preferably, in the above (1), the selection means is a method for expressing the gradation of the pixel to be displayed among a plurality of pixels present in the periphery from among the two or more combinations. Then, a pixel having the largest number of pixels among pixels expressing the same gradation and a combination having a large number of subfields sharing light emission or non-light emission are selected.
[0017]
( 3 ) An image of one frame is divided into a plurality of subfields having different display times, and display and non-display in each subfield can be selected in units of pixels, and is a product of luminance and light emission time in each subfield. A plasma display device that expresses gradations by summing light emission amounts in a plurality of subfields, wherein pixels belonging to a specific range of gradations are assigned to other gradations belonging to the specific range for each pixel. Gradation conversion means for independently converting the pixel, and the gradation conversion means has the pixel to be displayed in common for light emission or non-light emission between the pixel and a plurality of pixels present around the pixel. The pixel is converted into the pixels in the specific range of gradation so that the number of subfields increases.
[0018]
( 4 ) Preferably, in the above (3), the conversion means has the longest light emission time common to light emission or non-light emission between the pixel to be displayed and an adjacent pixel whose gradation is in the specific range. The gradation of the pixel to be displayed is converted so that the number of subfields increases.
[0020]
By adopting the configuration as shown in the above (1) to ( 4 ), it is possible to suppress a difference in gradation expression between adjacent pixels and to realize a plasma display device capable of suppressing the occurrence of pseudo contour interference. be able to.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a main part configuration diagram of an image display apparatus according to a first embodiment of the present invention, and FIG. 2 is an overall schematic configuration diagram of the image display apparatus according to the first embodiment. In addition, this 1st Embodiment is an example at the time of applying this invention to a plasma display apparatus.
[0022]
In FIG. 2, the image signal input to the plasma display device 1 is divided into subfields in the subfield processing unit 2 for each frame. The signal subfielded by the subfield processing unit 2 is input to the drive circuit 3, and the drive circuit 3 causes the display panel 4 to emit light for each subfield.
[0023]
FIG. 1 is an internal block diagram of the subfield processing unit 2. The input image signal is supplied to the memory 23 and also to the subfield candidate calculation unit 22. Then, the subfield candidate calculation unit 22 performs subfield division in consideration of the weighting for each subfield.
[0024]
In general, by appropriately selecting the ratio of the light emission time to be assigned to each subfield in advance, for the specific gradation of the input image signal, there are two or more ways of assigning the subfield to express it. can do.
[0025]
For example, as shown in FIG. 3, a case where an image of one frame is expressed by eight subfields (SF0 to SF7) is considered. Here, assuming that the ratio of the light emission times of the subfields is a power of 2 as shown in FIG. 3 (a), such as 1, 2, 4, 8,. Only one set of subfields is used to represent it.
[0026]
However, if the ratio of the light emission times of the subfields is selected as (1, 2, 4, 7, 14, 28, 56, 112) as shown in FIG. To do this, there are two methods: a method of selecting subfields SF0, SF1, and SF2, and a method of selecting only subfield SF3.
[0027]
Similarly, there are two combinations of subfields representing values such as 14, 28, 56, and 112, respectively. That is, for example, in the case of 14, there are two types of subfields (SF0, SF1, SF2, SF3) and subfield SF14. In the case of 28, there are two types of subfields (SF0, SF1, SF2, SF3, SF4) and subfield SF5.
[0028]
In the first embodiment of the present invention, the weighting shown in FIG. 3B is used.
[0029]
In FIG. 1, the subfield candidate calculation unit 22 outputs, when there is only one type of subfield allocation method for expressing a specific gradation of an input image signal, . If there are two types as described above, combinations of both are output as candidates 1 and 2.
The memory unit 23 stores the pixel value input to the subfield processing unit 2.
[0030]
The subfield allocation determination unit (selection means) 24 outputs the subfield allocation method output from the subfield candidate calculation unit 22 as it is when the subfield allocation method is one type. When there are a plurality (two types) of subfield allocation methods output from the subfield candidate calculation unit 22, one is selected and output. The selection is performed as follows with reference to the values of the peripheral pixels stored in the memory unit 23.
[0031]
That is, as shown in FIG. 4, there are two types of expression methods ((SF0, SF1, SF2), (SF3)) for the value of 7 (a) and (b) in FIG. Assuming that the value of the adjacent region is 6 based on the information read from the memory unit 23, even if pseudo contour interference occurs in the moving image, it is difficult to notice that the subfield allocation method is relatively close to (a). (SF1 and SF2 are common to 6 and 7). If the value of the adjacent area is 8, the interference is less noticeable in (b) where SF3 is common.
[0032]
In consideration of the above, the subfield allocation determination unit 24 selects an allocation method that is less likely to cause pseudo contour interference from the values of surrounding pixels. For example, a display method having a large number of subfields in common with the value of the largest number of pixels among the plurality of surrounding pixels of the pixel to be displayed is selected (the values of the plurality of surrounding pixels are, for example, 6, 6, 6, 6 , 6, 8, 8, and 8 select a display method having many display subfields in common with 6 display subfields).
[0033]
A method other than the above-described method is conceivable as to which pixel value among the peripheral pixels of the pixel to be displayed is adopted. For example, among the peripheral pixels, the pixels adjacent to the left and right of the pixel to be displayed are weighted and compared with other peripheral pixels, and any of them can be adopted. Which of these peripheral pixels is employed can be expressed as a predetermined function (a function that employs the largest number of the peripheral pixels described above, a function that is employed by weighting, etc.), In accordance with this predetermined function, the value of the surrounding pixels is adopted, and a display method whose expression is closer to the adopted value is selected.
[0034]
As described above, according to the first embodiment of the present invention, in order to express a predetermined gradation, there are at least two types of combinations of which subfields are displayed among a plurality of subfields. When a predetermined gradation is expressed, the values of the pixels located around the pixel expressing the gradation are stored in the memory unit 23, and the gradation expression of the stored pixel is combined with the closest combination. An expression is selected by the subfield allocation determination unit 24.
[0035]
Accordingly, it is possible to realize an image display device that can suppress the difference in gradation expression between adjacent pixels and can suppress the occurrence of pseudo contour interference. That is, in the first embodiment, it is possible to realize a plasma display device in which pseudo contour interference in a moving image is reduced.
[0036]
Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in the subfield processing unit 2. Since other parts are the same as those in the first embodiment, the description thereof is omitted. The second embodiment is also an example in the case where the present invention is applied to a plasma display device.
[0037]
FIG. 5 is an internal block diagram of the subfield processing unit 2 in the image display apparatus according to the second embodiment of the present invention.
In FIG. 5, the subfield candidate calculation unit 22 performs exactly the same processing as the subfield candidate calculation unit 22 in FIG. That is, when there is only one type of subfield assignment method for expressing a specific gradation of an input image signal, it is output. When there are two types as described above, a combination of both is output.
[0038]
The random number generation unit 25 generates a random number from “1” to “the maximum number of subfield combinations output from the subfield candidate calculation unit 22”. That is, in the case of the second embodiment, the random number generator 25 generates a value of 1 or 2 as a random number.
[0039]
The subfield allocation determination unit 24 outputs the subfield allocation method output from the subfield candidate calculation unit 22 as it is when the subfield allocation method is one type. In addition, when there are a plurality (two types) of subfield allocation methods output from the subfield candidate calculation unit 22, one is selected and output. The selection is determined by the random number output from the random number generator 25.
[0040]
That is, when the random number generated from the random number generator 25 is 1, candidate 1 is selected from the subfield assignments output from the subfield candidate calculator 22. If the random number generated by the random number generator 25 is 2, candidate 2 is selected from the subfield assignments output from the subfield candidate calculator 22.
[0041]
In this way, by randomly selecting the subfield assignment method using random numbers, that is, randomly, even if pseudo contour interference occurs, it is dispersed and becomes inconspicuous.
[0042]
As described above, according to the second embodiment of the present invention, as in the first embodiment, it is possible to suppress the difference in gradation expression between adjacent pixels and to suppress the occurrence of pseudo contour interference. A plasma display device which is a possible image display device can be realized.
[0043]
Next, a third embodiment of the present invention will be described. The third embodiment is different from the first embodiment in the subfield processing unit 2. Since other parts are the same as those in the first embodiment, the description thereof is omitted. The third embodiment is also an example in the case where the present invention is applied to a plasma display device.
[0044]
FIG. 6 is an internal block diagram of the subfield processing unit 2 in the image display apparatus according to the third embodiment of the present invention.
In FIG. 6, the memory unit 23 stores the pixel value input to the subfield processing unit 2.
[0045]
The gradation converter 26 performs the following conversion on the input image signal. That is, if the gradation value of the input image signal does not belong to a predetermined specific range, the value is output as it is, and if it belongs to the specific range, it is changed to another gradation value within that range. Convert.
[0046]
FIG. 7 is a graph showing the relationship between the input value and the output value in the gradation conversion unit 26. For example, if the input gradation value is a value belonging to the range from 126 to 129, one of the values in the range from 126 to 129 is selected and output. A method of selecting values will be described below.
[0047]
If the ratio of the light emission times of each subfield is set to a power of 2, the gradation values from 126 to 129 are expressed by subfields as shown in FIG. In FIG. 8, 126 and 127 are different from 128 and 129 in whether or not the MSB is used, and the subfield expression pattern changes greatly. That is, it is a portion where a pseudo contour is likely to occur when the values interfere with each other in the moving image.
[0048]
Therefore, if the information read from the memory unit 23 is used and the value of the adjacent region is 126 or 127, the converted value is also 126 or 127, so that the pseudo contour interference can be made inconspicuous. .
Note that either 126 or 127 is selected so that it is closer to the original input value.
[0049]
Similarly, if the value of the adjacent region is 128 or 129, the pseudo contour disturbance can be made inconspicuous by setting the value after conversion to 128 or 129.
Note that whether 128 or 129 is selected is selected to be closer to the original input value.
[0050]
The output of the gradation conversion unit 26 is subjected to subfield division according to the weighting for each subfield in the subfield calculation unit 27.
[0051]
As described above, according to the third embodiment of the present invention, when the gradation value of the input image signal does not belong to a predetermined specific range, the value is output as it is, and the specific range is output. If the value of the adjacent area greatly changes the expression pattern of the subfield, the pixel to be displayed is converted to the value of the adjacent area using the information read from the memory unit. Configured as follows.
[0052]
Therefore, similarly to the first embodiment, it is possible to suppress a difference in gradation expression between adjacent pixels, and to realize a plasma display device that is an image display device capable of suppressing the occurrence of pseudo contour interference. it can.
[0053]
Next, a fourth embodiment of the present invention will be described. The difference from the third example of the fourth embodiment is the part of the subfield processing unit 2. The other parts are the same as those of the third embodiment, and the description thereof is omitted. The fourth embodiment is also an example when the present invention is applied to a plasma display device.
[0054]
FIG. 9 is an internal block diagram of the subfield processing unit 2 in the image display apparatus according to the fourth embodiment of the present invention.
In FIG. 9, the gradation converting unit 26 performs the following conversion on the input image signal. That is, if the gradation value of the input image signal does not belong to a predetermined specific range, that value is output as it is, and if it belongs to the specific range, other gradation values within that range are output. Convert to
[0055]
As shown in the graph of FIG. 7, if the input value is a value belonging to the range from 126 to 129, for example, one of the values in the range from 126 to 129 is selected and output. . As a method for selecting a value, a random number generated by the random number generator 25 is used to select a value at random.
[0056]
Since the subfield calculation unit 27 is the same as that of the third embodiment, the description thereof is omitted.
[0057]
As described above, according to the fourth embodiment of the present invention, as in the third embodiment, it is possible to suppress the difference in gradation expression between adjacent pixels and to suppress the occurrence of pseudo contour interference. A plasma display device which is a possible image display device can be realized.
[0058]
As another example of the above-described embodiment, an example in which the first embodiment or the second embodiment is combined with the third embodiment or the fourth embodiment can be considered. In this case, when the gradation value of the input image signal does not belong to a predetermined range, the value is subjected to signal processing of the first embodiment or the second embodiment. When the gradation value of the input image signal belongs to a predetermined range, signal processing according to the third embodiment or the fourth embodiment is performed.
[0059]
In each of the above-described embodiments, the ratio of the light emission time for each subfield used as an example and the number of subfields are not limited thereto.
[0060]
Further, the range of values for gradation conversion in the third and fourth embodiments is not limited to the values exemplified in the text.
[0061]
Further, the above-described example is an example where the present invention is applied to a plasma display device. However, the present invention is not limited to the plasma display device, and an image of one frame is divided into a plurality of subfields. As long as it is an image display device that expresses gradation by adding the light emission amount, which is the product of the luminance and the light emission time, in a plurality of subfields, it can also be applied to other devices.
[0062]
【The invention's effect】
Since the present invention is configured as described above, the following effects are obtained. In order to express a predetermined gradation in an image display apparatus that divides an image of one frame into a plurality of subframes and selectively emits only necessary subfields according to the gradation of each pixel to express different gradations. In addition, at least two types of combinations of which subfields among a plurality of subfields are displayed are included. When a predetermined gradation is expressed, a gradation expression of a pixel located around the pixel expressing the gradation and an expression based on a combination of the closer ones are selected.
[0063]
Accordingly, it is possible to realize an image display device that can suppress the difference in gradation expression between adjacent pixels and can suppress the occurrence of pseudo contour interference.
[0064]
Further, an image display device capable of suppressing the occurrence of pseudo contour interference can be realized even when two types of combinations of subfields are selected at random.
[0065]
If the gradation value of the input image signal does not belong to a predetermined specific range, the value is output as it is. If it belongs to the specific range, information read from the memory unit is used. When the value of the adjacent area changes greatly in the subfield expression pattern, the occurrence of pseudo contour interference can be suppressed even if the pixel to be displayed is converted to the value of the adjacent area. An image display device can be realized.
[0066]
If the gradation value of the input image signal does not belong to a specific range determined in advance, the value is output as it is. If it belongs to the specific range, a value belonging to the specific range is randomly selected. Even when configured to select, it is possible to realize an image display device capable of suppressing the occurrence of pseudo contour interference.
[Brief description of the drawings]
FIG. 1 is a main part configuration diagram of an image display apparatus according to a first embodiment of the present invention.
FIG. 2 is an overall schematic configuration diagram of the image display apparatus according to the first embodiment.
FIG. 3 is a diagram illustrating an example of a subfield dividing method.
FIG. 4 is a diagram illustrating selection of a gradation level expression method.
FIG. 5 is a main part configuration diagram of an image display apparatus according to a second embodiment of the present invention.
FIG. 6 is a main part configuration diagram of an image display apparatus according to a third embodiment of the present invention.
FIG. 7 is a graph showing an input / output relationship of a gradation conversion unit.
FIG. 8 is a diagram illustrating selection of a gradation level expression method.
FIG. 9 is a main part configuration diagram of an image display apparatus according to a fourth embodiment of the present invention.
FIG. 10 is a diagram for explaining subfield division;
FIG. 11 is a diagram for explaining pseudo contour interference;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma display apparatus 2 Subfield-izing process part 3 Drive circuit 4 Display panel 22 Subfield candidate calculation part 23 Memory part 24 Subfield allocation determination part 25 Random number generation part 26 Gradation conversion part 27 Subfield calculation part

Claims (4)

An image of one frame is divided into a plurality of subfields having different display times, and display and non-display in each subfield can be selected in units of pixels, and a light emission amount that is a product of luminance and light emission time in each subfield is determined. A plasma display device for expressing gradation by summing up a plurality of subfields ,
In order to express a specific gradation, it has at least two or more combinations of which subfields among the plurality of subfields are displayed;
A selection means for selecting one of the two or more combinations when expressing the specific gradation,
The selection unit is configured to display the gradation of the pixel to be displayed so that the number of subfields common to light emission or non-light emission increases between the pixel and a plurality of pixels existing around the pixel. A plasma display device, wherein one is selected from a combination of at least types. The plasma display device according to claim 1,
The selection means is the most representative pixel among the plurality of pixels presenting the same gradation among the plurality of combinations as a representation of the gradation of the pixel to be displayed. A plasma display device, wherein a combination of a large number of pixels and a large number of subfields that share light emission or non-light emission is selected. An image of one frame is divided into a plurality of subfields having different display times, and display and non-display in each subfield can be selected in units of pixels, and a light emission amount that is a product of luminance and light emission time in each subfield is determined. A plasma display device for expressing gradation by summing up a plurality of subfields ,
Gradation conversion means for independently converting pixels belonging to a specific range of gradations to other gradations belonging to the specific range for each pixel ;
The gradation conversion unit is configured to display pixels in the specific range so that a number of subfields that are common to light emission or non-light emission are increased between the pixel and a plurality of pixels existing around the pixel. A plasma display device, wherein the plasma display device is converted into gradation pixels . The plasma display device according to claim 3,
The conversion means attempts to display the display so that the number of subfields having the longest light emission time common to light emission or non-light emission increases between the pixel to be displayed and an adjacent pixel whose gradation is in the specific range. A plasma display device characterized by converting a gradation of a pixel to be operated.

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