JPH1152912A - Gradation display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of spurious profile and to increase the number of gray levels. SOLUTION: One frame F is divided into plural subframes SF1 to SF6 weighted in luminance in order to conduct a screen display by the matrix display device composed of display elements capable of performing binary light emitting control, and a gradation display is conducted by setting the presence and the absence of the light emitting of each display element in a subframe unit in accordance with an output gray level. In this case, the luminance is weighted so that a difference (2×(1/3), 2×(1/4)) which is the difference between a largest weight and a next largest weight becomes smaller than the smallest weight (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gradation display method suitable for a PDP (Plasma Display Panel).

[0002] PDPs are more suitable for displaying moving images than liquid crystal devices, and have come to be widely used for applications such as television images and computer monitors with the practical use of color screens. In addition, it is attracting attention as a large-screen flat device for high-definition television.

[0003] The luminance of a display by a PDP depends on the number of discharges per unit time. Therefore, reproduction of halftone is realized by appropriately setting the number of discharges in one frame for each display element (cell) of the matrix display. Color display is a type of gradation display, and the display color is determined by a combination of the luminance ratios of the three primary colors.

[0004]

2. Description of the Related Art In an AC type PDP of a matrix display type, line-sequential addressing for forming a charged state according to display contents is performed after resetting for uniform charging state, and thereafter, wall charges are used. Sustaining is performed to periodically generate a discharge. If the discharge cycle is shortened, an apparently continuous light emission state can be obtained. The luminance of the display depends on the “integrated light emission intensity” which is the total light emission amount during the sustain period. Normally, the frequency of the sustain pulse that defines the discharge cycle is fixed, and the length of the sustain period (ie, the number of discharges) is set according to the luminance.

FIG. 8 is a diagram showing a conventional frame configuration, and FIG. 9 is a diagram showing a conventional gradation conversion characteristic. As a PDP gradation display method, there is a method in which one frame is divided into a plurality of subframes by weighting the luminance (that is, the number of discharges), and addressing is performed for each subframe to set the total number of discharges in one frame. It is widely known (Japanese Patent Laid-Open No. 4-195
188). For example, as shown in FIG. 8A, the frame Fa is divided into five sub-frames SFa, SFb, SFc, SFd,
SFe, and the ratio of the lengths of the sustain periods TS is 1: 2: 4: 8: 16. That is, so-called “binary weighting” is performed on each of the sub-frames SFa to SFe using a geometric progression having a common ratio of “2”. The length of the address period TA (including the reset period) of each of the sub-frames SFa to SFe is constant regardless of the luminance weight. In the example of FIG. 8A, the gradation levels are “0” to “3”.
It is possible to display 32 gradations of "1".

[0006] In the method of reproducing the halftone by the combination of the luminance in the sub-frame unit, a false contour (moving false contour) is generated when a moving image with a sharp movement is displayed. False contour is a phenomenon in which a viewer separates and perceives sub-frames in a portion where a gradation changes smoothly in a moving image display, and perceives light and shade different from the display content. This is caused by apparent motion that is recognized as motion by continuously chasing moving images that are projected. In particular, in a flesh-color image, a color false contour having a different color and luminance occurs in a portion where the gradation changes smoothly, and the display quality is significantly reduced. Such a false contour becomes more remarkable as the change in the lighting sequence is larger, that is, as the center of the lighting time in a frame is greatly different between adjacent frames. For example, in the case of 32 gradations, false contours are relatively prominent between gradation levels 15 and 16 and between gradation levels 7 and 8.

Hitherto, a so-called "superposition method" has been proposed as a gradation display method effective for reducing false contours (JP-A-7-175439). This is because, as shown in FIG. 8B, one or a plurality of subframes selected in descending order of the luminance weight among the subframes SFa to SFe constituting the frame Fa are divided into a plurality of divided subframes SFe1, SFe2, SFd1, and SFd2, and the display order is selected so that the display periods of the divided sub-frames corresponding to the same sub-frame are separated from each other. This is to prevent the continuation. FIG. 8 (B)
In the example of FIG. 8A, the sub-frame SFe having the highest luminance and the sub-frame SFd having the second highest luminance in FIG. 8A are divided, and the ratio of the length of the sustain period TS corresponding to one frame Fb is 8: 4. 1: 2: 4: 8.

When the subframe is divided in this way, 1
The number of times of addressing in the display of the frame increases, and the frame cycle becomes longer. However, in a normal use represented by a television display, since the frame period is specified, the number of times of addressing cannot be increased. Since the actual time required for one addressing is as long as or longer than the longest sustain period,
It is difficult to compensate for the increase in addressing by shortening the sustain. Therefore, with the division of a subframe having a large luminance weight, other subframes must be omitted. In the example of FIG. 8B, the subframe SFc having the weight “4” is omitted.

[0009] With the omission of the sub-frame, the number of reproducible gray scales inevitably decreases. Therefore, conventionally, each divided sub-frame SFe1, SFe2, SFd1, SFd
2 as frame components, sub-frames SFa, SF
The number of gradations has been increased by treating the same as b. That is, the presence or absence of light emission of the divided sub-frames corresponding to the same sub-frame is not always the same, but the necessity or non-emission of light is also set independently of these.
In the example of FIG. 8B, as shown in FIG. 9, the output gradation width (the luminance difference of one gradation) is in the input gradation range (for example, 0 to 255).
28 can be displayed uniformly over the entire region. The luminance of the subframe SFa having the smallest weight corresponds to the output gradation width.

[0010]

Conventionally, when subframes are divided to suppress false contours as described above, the luminance weights of the divided subframes are distributed in order to distribute the light emission period in the frame as evenly as possible. Were selected to be the same value. For this reason, the weight becomes redundant, and there is a problem that the number of gradations is smaller than when binary weighting is performed.

An object of the present invention is to prevent false contours and increase the number of gradations.

[0012]

According to the present invention, each of the time-series frames to be displayed in order is divided into at least one sub-frame group including at least one set of sub-frames whose luminance weights are relatively large and close to each other. It is composed of a plurality of subframes having different luminance weights, and the difference between the weights of the subframes having similar weights is set to a value smaller than the minimum value of the weights of all the subframes. By providing a plurality of sub-frames having similar weights, light emission within the frame is averaged as in the related art, and false contours are prevented. If the difference between the weights is small, a false contour prevention effect substantially equal to that of the conventional example in which subframes having the same weight are provided can be obtained. In addition,
It is desirable to display subframes having similar weights at a time interval. However, since an address period exists between the sustain periods of these subframes and the light emission period is substantially divided, these subframes are displayed. False contours are also prevented in a frame configuration in which On the other hand, if there is even a slight difference in weight between subframes, the combinations of subframes will be more diversified than when subframes with the same weight are provided. However, when the difference between the weights is equal to the minimum value of the weight, redundancy occurs in the combination of the subframes. If the difference between similar weights is equal to or less than the minimum value of the weight, false contours are prevented as described above, and furthermore, gradation display at 2 ^P (P is the total number of subframes) is possible.

With the weighting of the present invention, the gradation width becomes uneven. Therefore, when the number of tones of the frame data is larger than the number of reproducible tones, a known error diffusion method is suitable as a method of increasing the apparent number of tones. In the error diffusion method, unlike the area gradation method in which a certain number of display elements are set as a set and the gradation level is set, the smaller the difference between the input gradation level and the output gradation level is, the less the display elements are affected. The decrease in resolution is slight. If the error diffusion method is applied to the setting of the output gradation level with respect to the input gradation level, the apparent number of gradations can be made approximately equal to the number of input gradations, and the reduction in resolution can be minimized. it can.

According to a first aspect of the present invention, when a screen is displayed by a matrix display device comprising display elements capable of binary light emission control, one frame is divided into a plurality of sub-frames weighted with luminance, and the output floor is divided. A gray scale display method for setting the presence or absence of light emission of each display element in subframe units according to the gray level, wherein the difference between the largest weight and the next largest weight is smaller than the smallest weight. This is to weight the luminance of each subframe.

According to a second aspect of the present invention, in the case where the number of tones of frame data is different from the number of reproducible tones, an error diffusion method is applied to the display of the frame data for each of the display elements. The output gradation level is set based on the following.

[0016]

FIG. 1 is a configuration diagram of a plasma display device 100 according to the present invention. Plasma display device 100
Is composed of an AC type PDP 1 which is a matrix type color display device and a drive unit 80 for selectively lighting a large number of cells constituting a screen (screen), and is a wall-mounted television receiver. It is used as a monitor of a computer system.

The PDP 1 has a pair of sustain electrodes X and Y
Are surface discharge type PDPs arranged in parallel, and each cell has a sustain electrode X, Y and an address electrode A corresponding to each other.
It has an electrode matrix with an electrode structure. The sustain electrodes X and Y extend in the line direction (horizontal direction) of the screen, and one of the sustain electrodes Y is used as a scan electrode for selecting cells on a line-by-line basis during addressing. The address electrode A is a data electrode for selecting a cell in a column unit, and extends in the column direction (vertical direction).

The drive unit 80 includes a controller 81,
It has a frame memory 82, a data processing circuit 83, a sub-frame memory 84, a power supply circuit 85, an X driver 87, a Y driver 88, and an address driver 89. The driving unit 80 has an R for specifying the color of a pixel from an external device.
Frame data Df of m bits per color indicating a luminance level (gradation level) of each color of GB is input together with various synchronization signals.

The frame data Df is stored in the frame memory 8
2 and then sent to the data processing circuit 83. The data processing circuit 83 is a data conversion unit that sets a combination of sub-frames to be turned on, and outputs sub-frame data Dsf having a bit number corresponding to the frame data Df. The subframe data Dsf is stored in the subframe memory 84. The value of each bit of the subframe data Dsf is information indicating whether or not light emission of a cell is necessary in a subframe for gradation display.

The X driver circuit 87 applies a drive voltage to the sustain electrode X, and the Y driver circuit 88 applies a drive voltage to the sustain electrode Y. Address driver circuit 89
Is the address electrode A according to the subframe data Dsf.
Is applied with a drive voltage.

FIG. 2 is an exploded perspective view showing the internal structure of the PDP 1. In the PDP 1, the sustain electrodes X and Y
Are a transparent conductive film 41 and a metal film (bus conductor) 4 respectively.
2 and are arranged on the inner surface of the glass substrate 11 on the front side. A protective film (MgO) is formed on the surface of the dielectric layer (low-melting glass) 17 covering these sustain electrodes X and Y.
18 are provided. The address electrodes A are arranged on the inner surface of the glass substrate 21 on the back side. Between each address electrode A, one partition wall 29 having a linear shape in plan view is provided,
These partition walls 29 divide the discharge space 30 into sub-pixels (unit light-emitting regions) EU in the line direction. Then, phosphor layers 28 of three colors of R, G and B for color display are provided so as to cover the wall surface on the back side including the upper part of the address electrode A and the side surface of the partition wall 29. The phosphor layer 28 is locally excited by ultraviolet rays generated by the discharge and emits visible light of a predetermined color. One line of the matrix display corresponds to the sustain electrode pair 12, and one column corresponds to one address electrode A. One pixel EG includes three sub-pixels EU of R, G, and B arranged in the line direction.
Consists of A structure corresponding to one sub-pixel EU is a cell.

FIG. 3 is a voltage waveform diagram showing an example of the driving sequence. Display period T assigned to subframe
sf is divided into a reset period TR, an address period TA, and a sustain period TS. The lengths of the reset period TR and the address period TA are fixed, but the length of the sustain period TS increases as the luminance weight increases.

In the reset period TR, erasure (initialization) of wall charges on the entire screen is performed in order to prevent the influence of the previous lighting state.
Is the period during which A positive reset pulse Pw whose peak value exceeds the surface discharge starting voltage is applied to the sustain electrodes X of all the lines (the number of lines is n), and at the same time, to all the address electrodes A in order to prevent charging and ion bombardment on the back side. A positive pulse is applied. In response to the rise of the reset pulse Pw, a strong surface discharge is generated in all lines, and a large amount of wall charges are generated in the cell. The effective voltage decreases due to the cancellation of the wall voltage and the applied voltage. When the reset pulse Pw falls, the wall voltage becomes the effective voltage as it is, self-discharge occurs, almost all wall charges disappear in all cells, and the entire screen becomes a uniform non-charged state.

The address period TA is a period in which addressing (lighting / non-lighting setting) is performed. The sustain electrodes X are biased to a positive potential with respect to the ground potential, and all the sustain electrodes Y are biased to a negative potential. In this state, each line is selected one by one in order from the first line, and a negative scan pulse Py is applied to the corresponding sustain electrode Y.
Is applied. Simultaneously with the selection of the line, a positive address pulse Pa is applied to the address electrode A corresponding to the cell to be lit indicated by the sub-frame data Dsf. In the selected line, in the cell to which the address pulse Pa is applied, a counter discharge is generated between the sustain electrode Y and the address electrode A, and the discharge is changed to a surface discharge. These series of discharges are address discharges. Sustain electrode X
Is biased to a potential having the same polarity as the address pulse Pa, the bias cancels the address pulse Pa, and no discharge occurs between the sustain electrode X and the address electrode A.

The sustain period TS is a period for maintaining a set lighting state in order to secure luminance according to a gradation level. In order to prevent unnecessary discharge, all address electrodes A are biased to a positive potential, and a positive sustain pulse Ps is first applied to all sustain electrodes Y. Thereafter, the sustain electrode X and the sustain electrode Y
And a sustain pulse Ps is applied alternately to Each time the sustain pulse Ps is applied, surface discharge occurs in the cell in which the wall charges are accumulated in the address period TA. The application cycle of the sustain pulse Ps is constant, and the number of sustain pulses Ps set according to the weight of the luminance is applied.

Next, a gradation display method in the plasma display device 100 will be described. In the following, the frame data Df
The number of bits m per color is “8”. That is,
The data value range of the frame data Df is set to “0 to 255”. For convenience, the frame configuration is illustrated by regarding the reset period TR as a part of the address period TA.

FIG. 4 is a diagram showing a frame structure, FIG. 5 is a diagram showing the correspondence between output gradation levels and sub-frame data, and FIG. 6 is a diagram showing the correspondence between gradation levels of an input signal and panel luminance. In order to perform gradation display, frame F is divided into six sub-frames SF1, SF2, SF3, SF4, SF5, SF
Divide into six. However, when reproducing an image scanned in an interlaced format like a television, a plurality of fields are allocated to one frame F, and each field is divided into six sub-frames SF1 to SF6. At this time, the luminance weights of the sub-frames SF1 to SF6 are sequentially set to, for example, “1”, “2”, “4- (）)”.
“4+ (1/4)” “8− (1/3)” “8+ (1 /
3) ". Then, these sub-frames SF1 to S
The arrangement order (display order) of F6 is changed from SF5 to SF3 to SF1.
→ SF2 → SF4 → SF6. That is, similarly to the conventional example in FIG. 8B, the subframes having relatively large weights are distributed and arranged to prevent false contours. The difference from the conventional example is that a set of subframes having similar weights (subframe group) is provided instead of a set of subframes having the same weight. In the present embodiment, the subframe S
A set of F5 and subframe SF6 and subframe S
A set of F3 and subframe SF4 is a group of subframes having similar weights. In each of these two subframe groups, the difference between the weights is smaller than the minimum value of the weights of all the subframes (“1” which is the weight of subframe SF1).

According to such a frame configuration, false contours can be prevented, and by setting the necessity of lighting for each of the sub-frames SF1 to SF6 as shown in FIG. Key display can be performed. However, since the luminance weight of the sub-frames SF3 to SF6 is not an integral multiple of the minimum weight (“1”), the gradation width becomes uneven as shown in FIG.

By setting the necessity of lighting for the sub-frames SF1 to SF6, that is, at the time of converting the frame data Df to the sub-frame data Dsf, by applying the error diffusion method, the apparent number of gradations can be increased. .

FIG. 7 is a diagram for explaining an outline of the error diffusion processing. The data processing circuit 83 (see FIG. 1) sequentially focuses on cells having the same emission color, and calculates an ideal output gray level Hg corresponding to the input gray level Hi of the target cell and an output gray level Hp actually displayed. 7B, data processing is performed to distribute the error ΔH to peripheral cells at a fixed ratio as shown in FIG. 7B. In the second and subsequent cells, the output gradation level Hp is determined by the sum of the ideal output gradation level Hg corresponding to the frame data Df and the sum of the distributed errors (the gradation level to be displayed). Is calculated. In the present embodiment, the ideal output gradation level Hg is represented by the following equation.

Hg = (28/256) Hi In the above embodiment, an example has been given in which the frame F is divided into a total of six subframes SF1 to SF6 including two subframe groups having similar weights. The total number P of subframes, the number M ′ of subframe groups with similar weights, and the difference in weight between subframes with similar weights are not limited to the examples. The object of the present invention can be achieved if the frame configuration satisfies the following conditions.

Here, the subframes are arranged in ascending order of the weights, and each subframe is given a rank (i, j). i is
It indicates the order in which a group of subframes having similar weights is regarded as one subframe, and takes a value in the range of 1 ≦ i ≦ N. j
Indicates the order in each subframe group, and 1 ≦ j ≦ k
The condition of (i) is satisfied. k (i) is the number of subframes belonging to the subframe group, and the value of k (i) in a single subframe whose weight is not similar to the others is “1”
It is. In the superposition method, weighting is performed so that subframe groups are provided from the side with the larger weight, so that the weight of a single subframe is small. There may be no single subframe. The sum of the number M of single subframes and the number M ′ of subframe groups is N.

The integrated luminous intensity L (i, j) of each sub-frame (single sub-frame or individual sub-frame belonging to a sub-frame group) is represented by a basic component l (i) and a small variable component α (i, j). And is expressed by equation (1).

L (i, j) = 1 (i) + α (i, j) (1) where 1 ≦ i ≦ N 1 ≦ j ≦ k (i) l (i) = 2 ⁱ⁻¹ × l (1) [1 ≦ i ≦ M] k (i) = 1 [1 ≦ i ≦ M] k (i)> 1 [M + 1 ≦ i ≦ N] α (i, j) = 0 [1 ≦ i ≦ M | Α (i, j) −α (i, j + 1) | ≦ l (1) [M + 1 ≦ i ≦ N, 1 ≦ j <k (i)] Note that the relationship between the example of FIG. The correspondence with the variables is as follows.

M = 2, M ′ = 2, N = 4 SF1: (1, 1) SF2: (2, 1) SF3: (3, 1) SF4: (3, 2) SF5: (4, 1) SF6: (4,2) k (i) = 2 [M + 1 ≦ i ≦ N] l (3) = 4 × l (1) l (4) = 8 × l (1) α (3,1) = − (1/4) × 1 (1) α (3,2) = (1/4) × 1 (1) α (4,1) = − (1/3) × 1 (1) α (4,2 ) = (1/3) × l (1)

[0036]

According to the first or second aspect of the present invention,
The number of gradations can be increased while preventing false contours.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a plasma display device according to the present invention.

FIG. 2 is an exploded perspective view showing an internal structure of the PDP.

FIG. 3 is a voltage waveform diagram showing an example of a driving sequence.

FIG. 4 is a frame configuration diagram.

FIG. 5 is a diagram showing the correspondence between output gradation levels and sub-frame data.

FIG. 6 is a diagram showing a correspondence between a gradation level of an input signal and panel luminance.

FIG. 7 is a diagram illustrating an outline of an error diffusion process.

FIG. 8 is a configuration diagram of a conventional frame.

FIG. 9 is a diagram showing a conventional gradation conversion characteristic.

[Explanation of symbols]

 1 PDP (matrix display device) F frame SF1-6 subframe Df frame data

Claims (2)

[Claims] When a screen is displayed by a matrix display device comprising display elements capable of binary light emission control, one frame is divided into a plurality of sub-frames weighted with luminance, and the sub-frames are divided according to an output gradation level. A gradation display method for setting the presence / absence of light emission of each display element in units, wherein weighting of luminance for each of the sub-frames is performed such that a difference between the largest weight and the next largest weight is smaller than the smallest weight. And a gradation display method. 2. When the number of gradations of frame data is different from the number of reproducible gradations, the output gradation level is set for each of the display elements based on the frame data by applying an error diffusion method. The gradation display method according to claim 1.