JPH10171401A - Gradation display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce spurious contour without impairing quality of a still picture and to improve display quality of a time serial picture with an indefinite degree of movement by varying a frame form in accordance with a degree of movement of a display object between two adjacent frames. SOLUTION: A movement detection circuit 85 reads video data DR, DG, DB of two adjacent frames from a frame memory 82 at each transmission cycle, detects a degree of movement of a display object, and outputs a signal S85 presenting whether or not the degree of movement exceeds a set value, namely, whether or not a spurious contour is in danger of being generated and supplies the signal to a controller 81, an address generator 83, and a picture processing circuit 84. When the degree of movement is relatively small, the detection signal is inactive, the following frame is operated as 'a normal frame', and when the signal is active, the following frame is processed as 'special frame' splitting a specific sub-frame to a field for preventing spurious contour.

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 in conjunction with the practical use of color screens, PDPs have been widely used for applications such as television images and computer monitors. In addition, it is attracting attention as a large-screen flat device for high-definition television.

[0003] The brightness of the display by the PDP depends on the number of discharges per unit time. Therefore, by appropriately setting the number of discharges in one frame for each display element (pixel or sub-pixel) of the matrix display, reproduction of halftone is performed. Color display is a type of gradation display,
This is realized by changing the luminance ratio 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. Normally, the frequency of the sustain pulse defining the discharge cycle is fixed, and the luminance is determined by the length of the sustain period.

FIG. 13 is a block diagram of a conventional frame. P
As a DP gradation display method, one frame is composed of a plurality of subframes weighted by the number of discharges, and addressing is performed for each subframe to set the total number of discharges of one frame (intra-frame modulation method). Is widely known. For example, as shown in FIG. 13A, the frame F is divided into four subframes sf1 to sf4, and the ratio of the lengths of the sustain periods TS is 1: 2: 4: 8. That is, so-called “binary weighting” is performed on each of the subframes sf1 to sf4 using a geometric progression having a common ratio of “2”. The display period of each of the sub-frames sf1 to sf4 includes a reset period TR, an address period TA, and a sustain period TS. In the example of FIG. 13A, display of 16 gradations with gradation levels of “0” to “15” is possible. Note that the frame F is actually composed of 6 to 8 sub-frames, and displays 64 gradations, 128 gradations, or 256 gradations.

[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 an observer separates and recognizes subframes 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 conspicuous as the change in the lighting sequence is larger. For example, in the case of 256 gradations, between the gradation levels 191 and 192, between the gradation levels 127 and 128, and between the gradation levels 127 and 192.
The false contour is relatively remarkable between the image and the gradation level 64.

Hitherto, a so-called superposition method has been proposed as a gradation display method effective for reducing false contours (Japanese Patent Laid-Open No. Hei 7-175439). This is shown in FIG.
As shown in FIG. 3 (B), one or a plurality of subframes sf4 having a relatively large luminance weight among a plurality of subframes sf1 to sf4 obtained by dividing the frame F are divided into two divided subframes sf4a and sf4b. By arranging the divided sub-frames sf4a and sfb so as to be separated from each other in the frame, light emission in the frame is averaged to prevent extreme light emission or non-continuous light emission.
In the example of FIG. 13B, the sub-frame sf4 having the maximum luminance in FIG. 13A is divided.

[0008]

Heretofore, there has been a problem that the number of gradations of a moving image and a still image decreases with the prevention of false contours by the superposition method. That is,
By dividing the subframe, the number of times of addressing in the display of one frame increases, and the frame period 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. In a PDP having 480 or more lines, the time required for one addressing operation is as long as or longer than the longest sustain period. Therefore, it is difficult to compensate for the increased addressing by shortening the sustain. Therefore, with the division of the subframe having a large luminance weight, other subframes must be omitted, and a decrease in the number of gradations cannot be avoided.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce false contours without deteriorating the image quality of a still image, and to improve the display quality of a time-series image whose degree of movement is unspecified, such as a television image. .

[0010]

A display object between two adjacent frames in a time series, that is, an arbitrary frame and a next frame, without uniformly applying a specific frame form to all frames. The frame form is changed according to the magnitude of the movement of. If the movement is relatively small, at least one frame is regarded as a still image and divided so that the number of gradations is maximized. On the contrary,
If the motion is large, at least one of the frames is configured to reduce false contours.

The motion of the display object can be calculated by a known moving image analysis method, for example, a method of obtaining a deviation which minimizes a difference between images.
It can be calculated using a method of finding a deviation that maximizes the cross-correlation function.

The following two forms are effective as frame forms for reducing false contours. In the first mode, a frame is divided into a plurality of subframes, and a subframe having the maximum luminance or a plurality of subframes including the same is composed of a plurality of fields to determine whether or not light emission of a display element is necessary in an interlaced format. To set. According to this, even when the subframes to be subjected to field division are continuous, addressing is inserted between the light emission periods of each subframe. As in the method, the light emission periods are dispersed so that there is no continuation of extreme light emission or non-light emission, thereby preventing a false contour. Moreover, unlike the superposition method, the number of gradations does not decrease.

In the first embodiment, in order to enhance the effect of dispersion of the light emitting periods, it is preferable to display the fields at appropriate time intervals. That is, it is desirable to use a frame configuration in which the display periods of the respective fields are not continuous during the frame period.

For example, when a sub-frame is divided into two fields, a two-to-one interlaced scanning format in which a screen is scanned at a ratio of one line to two lines is adopted. In the two-to-one interlaced scanning, the number of scanning lines is halved compared to the case of non-interlaced scanning, so that the time required for one addressing is halved. Therefore, as a whole, the total addressing time does not change before and after dividing the subframe. Note that, for example, AC
When the reset period is provided immediately before the address period in the type PDP, the frame period is extended by the reset period. However, the reset period is sufficiently shorter than the address period. Extension can be avoided.

When interlaced scanning is performed, focusing on one line, the number of times of light emission is reduced to (1 / division number) as compared with the case of non-interlaced scanning when simply considered. Therefore, when addressing by interlaced scanning, the same number of lines as the number of subframe divisions (the number of fields) obtained by combining the line to be scanned and the line to be skipped are set as a set, and the display contents of the lines belonging to one set are the same. I do. As a result, it is possible to avoid a decrease in luminance due to interlaced scanning. In a PDP, the light emission intensity of a cell depends on the number of light emitting cells in a screen, and the relationship is usually nonlinear. However, by simultaneously illuminating the cells in the same number of lines as the number of divisions, in the entire subframe including a plurality of fields, the increase / decrease of the luminous intensity of the cells between the fields is offset, and the same as in the case of non-interlaced scanning Brightness can be obtained.

When interlaced scanning is performed and the display contents of a plurality of lines are made common as described above, the display in which the gradation level is inverted at the gradation boundary portion where the presence or absence of light emission of the divided subframes differs between fields. Disturbance occurs. In order to reduce the disturbance, when display elements having different gradation levels that cause disturbance are adjacent to each other, the gradation levels of these display elements are unified to the representative level. As the representative level, a maximum value, a minimum value, an average value or the like among the original gradation levels can be adopted. By unifying the gradation levels, at least a large disturbance in which the gradation levels are inverted is eliminated.

In the second mode, a virtual image (insertion frame) for interpolating motion is generated, and its display period is incorporated in one frame period. By incorporating the insertion frame, the degree of motion is apparently reduced and false contours are reduced. However, the time that can be allocated to the display of a frame (actual frame) that is actual information is shortened by the insertion frame.

If the number of sub-frames of the actual frame and the insertion frame whose display period is shortened is made smaller than that of the still image frame, the number of gradations is reduced, but a decrease in the resolution in the column direction can be avoided. On the other hand, if the number of sub-frames is the same as that of a still image frame, a decrease in the number of gradations can be avoided. However, since it is necessary to scan two lines at a time to halve the time of one addressing, the resolution in the column direction is reduced. In order to prevent disturbance such as moiré due to a decrease in resolution, filtering to remove high-frequency components of spatial frequency in the column direction may be performed on an image to be displayed in advance. It should be noted that, in a moving image, the spatial resolution in human vision is lower than that in a still image, so that the effect of the reduction in the resolution is small. Regardless of the number of subframes, if the maximum number of times of light emission (the number of sustain pulses in the case of PDP) in the frame period in which the inserted frame and the actual frame are displayed is selected to be the same as or close to the number of still image frames, No luminance imbalance occurs between the still image and the moving image.

In the method according to the first aspect of the present invention, when a screen is displayed by a matrix display device including display elements capable of binary light emission control, n (n ≧ 3) subframes in which one frame is weighted for luminance. And a line display is performed for each sub-frame so that the luminance of one frame becomes a value corresponding to the gradation level, and the necessity of light emission of the display element is set. The degree of movement of the display object between the frame and the next second frame is checked, and when the degree of movement exceeds the set value,
One or both of the first and second frames are set as a special frame, and m (1 ≦ 1) selected from the n sub-frames corresponding to the special frame in descending order of luminance weight.
k (k ≧ 2) for m <n) specific subframes
And the necessity of light emission of the display element is set in a k-to-1 interlaced scanning format. At that time, the same setting is performed for each of k lines in each field. The necessity of light emission of the display element is set for each line in the race scanning format.

According to a second aspect of the present invention, the k fields corresponding to the specific subframes are displayed at a time interval from each other. The method according to the third aspect of the present invention is configured such that when the necessity of light emission of the specific sub-frame in the k display elements in the same column is different between k lines forming a group in interlaced scanning, the k lines are set to the k lines. The representative level is calculated based on the gradation levels of the display elements, and for the k display elements, the n sub-frames are set so that the luminance of one frame becomes a value corresponding to the calculated representative level. Is set as to whether or not light emission is required.

According to a fourth 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 subframes weighted with luminance. A gray scale display method in which line scanning is performed every time to determine whether light emission of a display element is necessary according to a gray scale level, wherein a display object is displayed between a first frame and a next second frame. The degree of movement is checked, and if the degree of movement exceeds a set value, an interpolated image for the first and second frames is generated, and one of the first and second frames is set as a special frame. A first and a second shortened frame. For the first shortened frame, the necessity of light emission of a display element is set according to a gradation level of the special frame. The second reduced frame is used for setting the necessity of emission of the display element in accordance with the gradation level of the interpolated image.

According to a fifth aspect of the present invention, each of the first and second shortened frames is divided into a smaller number of subframes than frames other than the special frame.

In the method of the present invention, each of the first and second shortened frames is divided into the same number of subframes as frames other than the special frame, and the first and second shortened frames are divided into the first and second shortened frames. For each of the corresponding sub-frames, when setting whether or not light emission of a display element is necessary, k
(K ≧ 2) The same setting is performed for each line.

According to a seventh aspect of the present invention, in the method of the present invention, the special frame and the interpolated image are subjected to filtering for removing high frequency components in a column direction, and the filtering is performed in accordance with a gradation level of image information obtained by the filtering. For each of the sub-frames corresponding to the first and second shortened frames, the necessity of light emission of the display element is set.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] FIG. 1 is a configuration diagram of a plasma display device 100 according to a first embodiment.

The plasma display device 100 comprises 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 (display elements) constituting a screen. It is used as a type television receiver and 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 display line direction, and one of the sustain electrodes Y is used as a scan electrode for selecting a cell for each line at the time of addressing. The address electrodes A are data electrodes for selecting cells in column units, and extend in the column direction.

The drive unit 80 includes a controller 81,
It has a frame memory 82, an address generator 83, an image processing circuit 84, a motion detection circuit 85, an X driver circuit 86, a Y driver circuit 87, and an address driver circuit 88. Multi-valued video data DR, DG, and DB indicating the RGB luminance level (gray level) of each pixel are input to the drive unit 80 from an external device together with various synchronization signals. The video data DR, DG, and DB are temporarily stored in the frame memory 82, converted into sub-frame data R0-3, G0-3, and B0-3 by the image processing circuit 84, and stored again in the frame memory 82. . The subframe data R0-3, G0-3, B0-3 is a set of binary data indicating whether or not light emission of cells is required in each subframe obtained by dividing one frame. In the present embodiment, the subframe data R0-3, G0-3, B0
The number of bits of 3 is 4. That is, 1 division number of frames is 4, R, can be G, color display setting by 16 ^three colors of the luminance of 16 gradations of each B from "0" to "15".

The motion detection circuit 85 is a component unique to the present invention, and is provided to apply different frame division modes between a still image and a moving image only when there is a possibility that a false contour may occur. That is, the motion detection circuit 85 outputs the video data D of two adjacent frames every frame transfer cycle.
R, DG, and DB are read from the frame memory 82, and the degree of movement of the display object is detected. In the present embodiment, one frame is a frame to be displayed at that time (this is called “current frame”), and the other frame is a frame next to the current frame (this is called “next frame”).
It is. Then, the motion detection circuit 85 outputs a detection signal S85 indicating whether or not the degree of motion exceeds a set value, that is, whether or not there is a possibility that a false contour may occur. Detection signal S
85 is provided to the controller 81, the address generator 83, and the image processing circuit 84.

When the degree of movement is relatively small, the detection signal S85 is inactive. In this case, the subsequent frame is hereinafter treated as a “normal frame” in which the subframe is not divided into fields. On the other hand, when the detection signal S85 is active, the next frame is treated as a “special frame” that divides a specific subframe into fields in order to prevent false contours. That is, the subframe configuration of each time-series frame is switched according to the degree of motion. Before the next frame becomes the current frame, the image processing circuit 84 generates sub-frame data R0-3, G0-
3, B0-3 are generated and stored in the frame memory 82.

When addressing the current frame, subframe data R0-3, G3
0 to 3 and B0 to 3 are read out one line at a time and transferred to the address driver circuit 88. The designation of the read address is performed by the address generator 83. As described later, in the case of non-interlaced scanning, data of all lines are sequentially transferred from the first line, and in the case of interlaced scanning,
Data of a predetermined number of lines is sequentially transferred. The address driver circuit 88 selectively applies an address pulse to the address electrode A according to the transferred sub-frame data R0-3, G0-3, B0-3. In parallel with this, the Y driver circuit 85 applies a scan pulse to each sustain electrode (scan electrode) Y according to an instruction from the controller 81. In the sustain following addressing, the X driver circuit 86 applies a sustain pulse to all the sustain electrodes X in common, and the Y driver circuit 87 applies a sustain pulse to all the sustain electrodes Y in common. However, the application is performed alternately on the sustain electrodes X and the sustain electrodes Y.

FIG. 2 is a perspective view showing the internal structure of the PDP according to the present invention. On the inner surface of the glass substrate 11 on the front side, a pair of sustain electrodes X and Y are arranged for each line L. The sustain electrodes X and Y each include a transparent conductive film 41 and a metal film 42, and are covered with a dielectric layer 17 for AC driving. Mg is applied to the surface of the dielectric layer 17.
A protective film 18 made of O is deposited. An underlayer 22, an address electrode A,
An insulating layer 24, partition walls 29, and phosphor layers 28R, 28G, 28B of three colors (R, G, B) for color display are provided. Each partition 29 is linear in plan view. These partition walls 29 divide the discharge space 30 in the line direction for each sub-pixel (display element), and the gap size of the discharge space 30 is defined to a constant value. Display 1
The pixel is composed of three sub-pixels arranged in the line direction. Since the arrangement pattern of the partition walls 29 is a stripe pattern, a portion of the discharge space 30 corresponding to each column is continuous in the column direction across all the lines.
The emission colors of the sub-pixels in each column are the same. The structure within each sub-pixel is a cell.

In the PDP 1, as described above, the setting (addressing) of lighting (light emission) / non-lighting of the sub-pixels includes:
An address electrode A and a sustain electrode Y are used. That is, screen scanning (line selection) is performed by applying a scan pulse to N (N is the number of lines) sustain electrodes Y, and the sustain electrodes Y and the address electrodes A selected according to the display content are connected to the sustain electrodes Y. A predetermined charge state is formed for each line L by the opposing discharge (address discharge) between the two. At this time, the subframe data R0 to 3 are provided in the column of R, and the subframe data G0 to 3 are provided in the column of G.
However, the subframe data B0 to B3 are applied to the column B. After the addressing, when a sustain pulse having a predetermined peak value is alternately applied to the sustain electrode X and the sustain electrode Y, a surface discharge (sustain discharge) occurs in a cell in which a predetermined amount of wall charge exists at the end of the addressing.

Next, a method of driving the PDP 1 will be described. FIG. 3 is a frame configuration diagram. FIG. 3A shows the configuration of a normal frame, and FIG. 3B shows the configuration of a special frame.

In order to perform gradation display, basically, FIG.
The frame F is divided into four subframes sf1 as shown in FIG.
To sf4. The display period of each of the sub-frames sf1 to sf4 includes a reset period TR, an address period TA, and a sustain period TS. Each subframe sf1
To sf4 so that the relative ratio of luminance is 1: 2: 4: 8.
The number of times of light emission in the sustain period TS of No. 4 is set.
Display of 16 gradations is possible by combining the presence or absence of light emission in subframe units. The above-mentioned sub-frame data R0-3,
Each bit of G0 to 3 and B0 to 3 indicates the presence or absence of light emission of one subframe. That is, the least significant bit corresponds to subframe sf1, and the second bit is subframe sf1.
2, the third bit corresponds to subframe sf3, and the most significant bit corresponds to subframe sf4.

For the special frame, the sub-frame sf4 having the maximum luminance is composed of two divided sub-frames (fields) sf41 and sf42 in order to prevent false contours. The subframe sf4 is a “specific subframe” in the present invention. As shown in FIG. 3B, sf1 → sf41
The display period of each subframe is arranged in the order of → sf3 → sf42 → sf2. Thereby, the divided subframe sf
41 and sf42 are temporally separated. The length of the sustain period TS of each of the divided subframes sf41 and sf42 is substantially half the length of the sustain period TS of the subframe sf4. That is, each divided subframe sf4
The weights of the luminances of 1 and sf42 are both “2”. It should be noted here that the subframe data R0 to R3, G
0 to 3 and B0 to 3 are data in units of subframes, and are commonly applied to the divided subframes sf41 and sf42.

When the subframe sf4 is divided into two, the number of times of addressing for one frame increases by one. In order to avoid extending the total addressing time, the subframe sf4 is divided into subframes sf41 and sf42.
The addressing is performed in a two-to-one interlaced scanning format in which is a field. In the divided sub-frame sf41, the sub-frame data R0-3, G0-3, B
Lighting presence / absence is set according to 0 to 3, and in the divided subframe sf42, the subframe data R0 to R0 of the even-numbered line is set.
3, lighting on / off is set according to G0-3, B0-3. In addition, in order to compensate for a decrease in luminance due to a decrease in the number of times of light emission of each cell, sub-frame data R0 to R0 for one line
3, G0-3, B0-3 are applied to two lines, and the presence or absence of lighting is set for each two lines. By performing the interlaced scanning, the time required for addressing the entire frame is the same as before the subframe sf4 is divided. In the sub-frames sf1 to sf1 other than the sub-frame sf4 (these frames are usually referred to as sub-frames), addressing is performed in a non-interlaced scanning format. Note that the frame period is extended by one reset in accordance with the division of the subframe sf4. However, this extension is a short time that can be compensated for by a slight shortening of the sustain period TA.

FIG. 4 is a waveform diagram of an applied voltage in a normal subframe, and FIG. 5 is a waveform diagram of an applied voltage in a specific subframe. In FIG. 4, the reset period TR is a period in which wall charges in the effective display region are erased (entirely erased) in order to prevent the influence of the previous lighting state. In response to the rise of the write pulse PW, a strong surface discharge is generated in all lines, and a large amount of wall charges are generated in the dielectric layer 17. However, in response to the fall of the write pulse PW, so-called self-discharge occurs due to wall charges, and the wall charges of the dielectric layer 17 disappear. The pulse Paw is applied to suppress accumulation of wall charges on the wall surface on the back side of the discharge space 30.

The address period TA is a period during which line-sequential addressing is performed. The sustain electrodes X are biased to the positive potential Vax with respect to the ground potential, and all the sustain electrodes Y are biased to the negative potential Vsc. In this state,
Select each line in order from the top line one by one,
A scan pulse Py of negative polarity is applied to the sustain electrode Y. At the same time as selecting the line, the subframe data R0
A positive address pulse Pa having a peak value Va is applied to the address electrodes A corresponding to the cells to be turned on indicated by 〜3, G0-3, and B0-3. In the selected line, in the cell to which the address pulse Pa is applied, an address discharge occurs between the sustain electrode Y and the address electrode A. Since the 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 during which the lighting state set by addressing is maintained in order to secure luminance according to the gradation level. In order to prevent the counter discharge, all the address electrodes A are biased to a positive potential (for example, Vs / 2), and first, a positive sustain pulse Ps having a peak value Vs is applied to all the sustain electrodes Y. Thereafter, the sustain electrode X and the sustain electrode Y
, A positive sustain pulse Ps having a peak value Vs is alternately applied. 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 drive sequence in the address period TA differs between the normal subframe and the specific subframe.
In the case of the specific sub-frame, adjacent odd lines and even lines are grouped as shown in FIG. 5, that is, the (2i-1) -th (i = 1, 2, 3,...) And the 2i-th line, a line scan is performed for each two lines. In parallel with this, in the divided subframe sf41, the subframe data R0 of the odd line is
3, G0-3, B0-3, an address pulse Pa is applied to the address electrode A. In the divided subframe sf42, the subframe data R0-3, G0
3, an address pulse Pa is applied to the address electrode A according to B0 to B3.

FIG. 6 is a diagram for explaining the data correction function of the image processing circuit 84. In the figure, black circles (●) indicate lighting when addressing is performed line by line in an interlaced scanning format, and white circles (○) indicate subordinate lighting by addressing two lines at a time.

When the addressing for setting the necessity of lighting two lines at a time in the interlaced scanning format is performed as described above, the change in gradation may be disturbed. For example, FIG.
As shown in (A), the cells in the same column from the (2i-1) -th odd line to the (2i + 4) -th even line are set as 10, 9, 8, and
Consider the case where 7, 6, and 5 are given. (2i-
In the 1) th line, since the gradation level is 10,
For example, if the cell of interest is an R cell, the subframe data R0 to R3 require lighting of the subframe sf2 (weight 2) and the subframe sf4 (weight 8). But,
Since the (2i-1) -th line is an odd-numbered line, the sub-frame data R0 to 3 become invalid in the divided sub-frame sf42 corresponding to the even-numbered line. From these facts, the subframe data R of the (2i-1) th line
On the basis of 0 to 3, the (2i-1) -th line and the 2i-th line paired with the (2i-1) -th line in the divided sub-frame sf41 are turned on, and the (2i-th) line is displayed in the sub-frame sf2.
-1) The first line is turned on. On the other hand, since the gradation level of the 2i-th line is 9, the sub-frame data R
0 to 3 request lighting of the subframe sf1 (weight 1) and the subframe sf4 (weight 8). Since the 2i-th line is an even-numbered line, the sub-frame data R0 to R0 in the divided sub-frame sf41 corresponding to the odd-numbered line
3 becomes invalid. From these facts, based on the sub-frame data R0 to 3 of the 2i-th line, the 2i-th line is turned on in the sub-frame sf1, and the (2i-1) -th and 2i-th lines are turned on in the divided sub-frame sf42. I do. As a result of such addressing, a correct luminance level corresponding to the gradation level can be obtained for the entire frame.

On the other hand, the (2i + 1) -th and (2i + 1) -th
In the (+2) th line, not only the gradation level is different from the luminance level but also the tendency of the change is reversed, so that a remarkable disturbance occurs in a smooth gradation change. This means that, at the gradation level 8, the sub-frame data R0 to 3 requires lighting of the sub-frame sf4 which is the specific sub-frame, whereas at the gradation level 7, the sub-frame data R0 to 3 This is because lighting is not required. That is, it is because the necessity of light emission of the specific sub-frame is different.

Therefore, the image processing circuit 84 sets the 2
When the necessity of light emission of a specific sub-frame in a cell in the same column differs between the two lines, a representative level is calculated based on the gray level of the two cells, and the representative level is calculated for the two cells. The sub-frame data R0-3, G0-3, and B0-3 requesting corresponding lighting are generated and output to the address driver circuit 88.

The calculation of the representative level is described in detail in FIG.
(B) As in (C), this is a process of selecting the larger or smaller gradation level of the two cells. Note that the average value of the gradation levels may be used as the representative level.

FIG. 7 shows the data correction unit 8 of the image processing circuit 84.
It is a block diagram of 40. The data correction unit 840 includes a buffer 848 for delaying data of one line, a logic circuit 841 for determining whether data correction is necessary, a filter 846 for calculating a representative level, and a data selector 847.

The data correction unit 840 has the video data DR0 converted into the same bit format as the sub-frame data.
, DG0-3, and DB0-3 are input in the order of pixel arrangement. The filter 846 includes video data DR0-3, DG0-3, and DB0 delayed by the buffer 848.
And video data DR0-3 and DG not delayed
0-3 and DB0-3 are input in parallel. That is, two lines of video data DR0-3, DG0-3, and DB0-3, which form a group of interlaced scanning, are input simultaneously.

The logic circuit 841 includes a total of three 2-input XOR circuits 8 provided one for each of R, G, and B colors.
42 to 844, and an OR circuit 845 for calculating the logical sum of the outputs of the XOR circuits 842 to 844. The XOR circuits 842 to 844 have respective video data DR0 to DG3 before and after the delay by the buffer 848, and DG0 to DG0.
3, the most significant bits of DB0 to DB3 are input. The most significant bit indicates whether it is necessary to light the sub-frame sf4 having the maximum luminance, which is the specific sub-frame in the present embodiment. J-th (j = 1, 2, 3,...) Of each of the two lines forming the set
If the necessity of lighting of the sub-frame sf4 is different among the cells of, the output of the OR circuit 845 becomes active.
In this case, the data selector 847 sets the representative level calculated by the filter 846 to the sub-frame data R0.
-3, G0-3, B0-3. OR circuit 8
When the output of D.45 is inactive, the data selector 847 converts the video data DR0-3, DG0-3, and DB0-3 delayed by the buffer 846 into sub-frame data R0-3, G0-3, B0 Output as 3.

In the above embodiment, the frame configuration of 16 gradations has been exemplified, but the number of gradations is 32, 64, 128, 25.
It may be six or more. The luminance weight of the sub-frame does not necessarily have to be a binary weight. 1
One subframe may be composed of three or more k divided subframes. In that case, addressing is performed in a k-to-1 interlace format in which each divided subframe is a field. Two or more subframes selected in descending order of luminance from maximum luminance may be divided. [Second Embodiment] FIG. 8 is a configuration diagram of a plasma display device 200 according to a second embodiment. In FIG. 8, FIG.
The components having the same functions as those of the example are denoted by the same reference numerals, and their description is omitted or simplified.

The plasma display device 200 comprises an AC type PDP 1 which is a matrix type color display device, and a drive unit 90 for selectively lighting a number of cells (display elements) constituting a screen.

The drive unit 90 includes a controller 91,
It has a frame memory 82, an address generator 83, an image processing circuit 94, a motion detection circuit 85, an X driver circuit 86, a Y driver circuit 87, and an address driver circuit 88. The image processing circuit 94 of the present embodiment converts the multi-value video data DR, DG, DB into binary sub-frame data R
0-3, G0-3, B0-3, and at that time, an interpolation operation for generating an insertion frame, which is virtual image information for softening the movement between frames, is performed as necessary. Sub-frame data R0-6, G0 in this embodiment
The number of bits of 6, B0 to B6 is 6. That is, one frame is composed of a maximum of six subframes.

The motion detection circuit 85 provides the video data DR, DG,
The DB is read from the frame memory 82, and the degree of movement of the display object is detected. The detection signal S85 output from the motion detection circuit 85 is a signal that becomes active when the degree of motion exceeds a set value. It is provided to the image processing circuit 94. When the detection signal S85 is non-active, the next frame is treated as a “normal frame” composed of six sub-frames. On the other hand, the detection signal S
If 85 is active, the next frame is treated as a "special frame" where interpolation information is inserted to prevent false contours. Before the next frame becomes the current frame, the image processing circuit 94 generates subframe data R0-6, G0-6, and B0-6 corresponding to the next frame, and stores them in the frame memory 82. At the time of addressing the current frame, the sub-frame data R0-6, G0-6, and B0-6 are read from the frame memory 82 one line at a time and transferred to the address driver circuit 88. Basically, data of all lines is transferred sequentially from the first line. However, when the number of sub-frames of the special frame is twice as large as that of the normal frame as described later, data of odd-numbered lines or even-numbered lines is sequentially transferred. The address driver circuit 88 selectively applies an address pulse to the address electrode A according to the transferred sub-frame data R0-6, G0-6, B0-6. In parallel with this, the Y driver circuit 85
According to the instruction from 1, a scan pulse is applied to each sustain electrode (scan electrode) Y line by line or line by line. In the sustain period after the addressing, the X driver circuit 86 applies a sustain pulse to all the sustain electrodes X in common, and the Y driver circuit 87
Applies a sustain pulse to all the sustain electrodes Y in common.

FIG. 9 shows an example of frame division.
0 is a diagram showing another example of frame division. In these figures, the j-th frame F (j) is the current frame, and the (j + 1) -th frame F (j + 1) is the next frame.

When the degree of movement between frames is small,
The next frame F (j + 1) is divided into six subframes sf1 to sf6 as shown in FIGS. 9A and 10A in order to perform gradation display. Each subframe sf1
The display period of sf4 includes a reset period, an address period, and a sustain period. Each subframe sf1-s
The relative ratio of luminance at f6 is 1: 2: 4: 8: 16:
32 so that each subframe sf
The number of light emission in the sustain period of 1 to sf6 is set. Display of 64 gradations is possible by combining the presence or absence of light emission in subframe units. The above-described subframe data R0
Each bit of 6, G0 to 6, B0 to 6 indicates the presence or absence of light emission of one subframe. The least significant bit corresponds to subframe sf1, and the second to fifth bits correspond to subframe sf1.
2 to sf5, and the most significant bit is the subframe sf
Corresponds to 6.

On the other hand, when the degree of movement between the frames is large, the next frame F (j + 1) is divided into two shortened frames f1 and f2 as shown in FIGS. 9B and 10B in order to prevent false contours. It is replaced by the set of f2. The previous shortened frame f1 is composed of the current frame F (j) and the next frame F (j
+1), and an interpolated image (virtual information) generated based on the next frame F (j +
This is an image (actual information) having the same contents as in 1). That is, the display period of the next frame F (j + 1) is reduced, and
An interpolation image is inserted between (j) and the next frame F (j + 1). The display period of each of the shortened frames f1 and f2 is about の of the display period (frame period) of the normal frame. Such shortened frames f1 and f2 are also divided into a predetermined number of sub-frames for performing gradation display.

In the example of FIG. 9, each shortened frame f1, f2 is divided into two sub-frames sf5, sf6. The upper two bits of the subframe data R0-6, G0-6, B0-6 correspond to these subframes sf5, sf6. In this example, since the number of times of addressing in one frame period does not increase, line scanning can be performed line by line similarly to the normal frame, and the resolution in the column direction does not decrease. However, since the number of sub-frames is small, the gradation is lower than that of a normal frame.

In the example of FIG. 10, each shortened frame f1, f2
Is divided into six subframes sf1 ′ to sf6 ′ weighted in the same manner as the normal frame. These sub-frames sf1 'to sf6' correspond to bits of sub-frame data R0 to 6, G0 to 6, and B0 to 6, respectively. In this example, the same gradation property as that of the normal frame can be secured for the special frame. However, since the number of times of addressing in one frame period is doubled, line scanning cannot be performed line by line, and the resolution in the column direction decreases.

In both the examples of FIGS. 9 and 10,
Although it is possible to arbitrarily set the weight of the luminance of the subframe, in the two illustrated examples, the addressing of each subframe can be performed using the subframe data generated in the same manner as the normal frame. The load of the generation process is small.

FIG. 11 is a view showing a form of line scanning of a normal frame, and FIG. 12 is a view showing a form of line scanning of a special frame corresponding to FIG. Normal frame and FIG.
With respect to the shortened frame having the above structure, line scanning is performed line by line in the address period TA of each subframe. Specifically, as shown in FIG. 11, first, the sustain electrode X is biased to the positive potential Vax with respect to the ground potential, and all the sustain electrodes Y are biased to the negative potential Vsc. In this state, each line is selected one by one sequentially from the top line, and a negative scan pulse Py is applied to the sustain electrode Y. Simultaneously with the selection of the line, with respect to the address electrode A corresponding to the cell to be lit indicated by the predetermined bits of the sub-frame data R0-6, G0-6, B0-6,
A positive address pulse Pa having a peak value Va is applied.
In the selected line, in the cell to which the address pulse Pa is applied, an address discharge occurs between the sustain electrode Y and the address electrode A. Since the sustain electrode X is biased to a potential having the same polarity as the address pulse Pa, the bias cancels the address pulse Pa,
No discharge occurs between the sustain electrode X and the address electrode A.

For the special frame having the sub-frame configuration shown in FIG. 10, the line scanning is performed two lines at a time during the address period TA of each sub-frame as shown in FIG. Specifically, an odd-numbered line and an even-numbered line are paired, that is, the (2i−1) -th (i = 1, 2, 3,...) Line and the 2i-th line counted from the top line are paired. , A scan pulse Py is applied simultaneously for every two lines. In parallel with this, an address pulse Pa is applied to the address electrode A according to, for example, the odd-numbered line sub-frame data R0-6, G0-6, B0-6. By performing the same content addressing on the lines forming a set, it is possible to prevent a decrease in luminance. However, since the resolution in the column direction (line arrangement direction) is halved, aliasing may occur depending on the resolution of the external video data DR, DG, and DB, and image distortion such as moire may appear. Therefore, the subframe data R0-6
At the stage of generating G0 to B6 and B0 to 6, it is desirable to perform filtering for removing high frequency components in the column direction on the original information.

In order to prevent fluctuations in luminance, the number of sustain pulses in a special frame needs to be equal to that in a normal frame. For example, in the example of FIG. 10, the subframes sf1 ′ forming each of the shortened frames f1 and f2 are provided.
The number of pulses of 〜sf6 ′ to ｓsf6 ′ may be set to の of the number of pulses of the corresponding subframes sf1 to sf6 or a value close to そ れ に of the number of pulses of the corresponding subframe sf1 after weighting the normal frame.

In the first and second embodiments described above,
It is not always necessary to check the degree of motion for the pair of the current frame and the next frame. For example, a frame that has not been displayed, such as a set of a current frame and a previous frame and a set of adjacent frames before the current frame, may be checked. When examining the current frame and the next frame pair, it is meaningless to make the current frame being displayed a special frame. However, when examining the frame pair displayed “after” the current frame, either Even if a frame is set as a special frame, the image quality is similarly improved. At the stage before the display, the frame division mode can be arbitrarily changed.

[0064]

According to the first to seventh aspects of the present invention,
False contours can be reduced without impairing the image quality of a still image, and the display quality of a time-series image whose degree of movement is unspecified, such as a television image, can be improved.

According to the first aspect of the present invention, it is possible to secure the same gradation for a moving image as for a still image. According to the second aspect of the invention, false contours can be reduced more reliably.

According to the third aspect of the invention, it is possible to make the gradation reproduction disturbance caused by sharing the display contents of a plurality of lines inconspicuous. According to the fifth aspect of the present invention, it is possible to secure the same resolution for a moving image as for a still image.

According to the invention of claim 6, it is possible to secure the same gradation for a moving image as for a still image. According to the seventh aspect of the present invention, it is possible to reduce the image disturbance caused by the decrease in the resolution of the matrix display in the column direction.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a plasma display device according to a first embodiment.

FIG. 2 is a perspective view showing an internal structure of a PDP according to the present invention.

FIG. 3 is a frame configuration diagram.

FIG. 4 is a waveform diagram of an applied voltage in a normal subframe.

FIG. 5 is a waveform diagram of an applied voltage in a specific subframe.

FIG. 6 is a diagram for explaining a data correction function of the image processing circuit.

FIG. 7 is a block diagram of a data correction unit of the image processing circuit.

FIG. 8 is a configuration diagram of a plasma display device according to a second embodiment.

FIG. 9 is a diagram illustrating an example of frame division.

FIG. 10 is a diagram showing another example of frame division.

FIG. 11 is a diagram illustrating a form of line scanning of a normal frame.

12 is a diagram showing a form of line scanning of a special frame corresponding to FIG.

FIG. 13 is a configuration diagram of a conventional frame.

[Explanation of symbols]

 1 PDP (matrix display device) F frame F (j) current frame (first frame) F (j + 1) next frame (second frame) f1 shortened frame (second shortened frame) f2 shortened frame (first Shortened frame) sf1 to 4 subframe sf4 specific subframe sf41 divided subframe (field) sf42 divided subframe (field) sf1 ′ to 6 ′ subframe

Claims (7)

[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 n (n.gtoreq.3) subframes weighted with luminance, and one frame is divided into n (n.gtoreq.3) subframes. This is a gradation display method in which line scanning is performed for each sub-frame so that the luminance becomes a value corresponding to the gradation level, and the necessity of light emission of a display element is set. The degree of movement of the display object between the first and second frames is checked. If the degree of movement exceeds a set value, the first
And one or both of the second frame and the second frame are special frames, and among the n sub-frames corresponding to the special frames, m (1 ≦ m <
For n) specific subframes, k (k ≧ 2) fields are set, and necessity of light emission of display elements is set in a k: 1 interlaced scanning format. At that time, k lines are set in each field. A gradation display method wherein the same setting is performed, and for other sub-frames, the necessity of light emission of a display element is set line by line in a non-interlaced scanning format. 2. The k fields corresponding to each specific sub-frame are displayed at a time interval from each other.
The gradation display method described. 3. The k which forms a set during interlaced scanning
When the necessity of light emission of the specific subframe in the k display elements in the same column differs between the book lines, a representative level is calculated based on the gray level of the k display elements, and 3. The floor according to claim 1, wherein the necessity of light emission in the n subframes is set so that the luminance of one frame has a value corresponding to the calculated representative level for the k display elements. 4. Key display method. 4. A screen display 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 line scanning is performed for each sub-frame. A gradation display method for setting necessity of light emission of a display element according to a gradation level, wherein a degree of movement of a display object between a first frame and a next second frame is checked. Is greater than the set value, the first
And generating an interpolated image for the second frame and configuring one of the first and second frames as a special frame with the first and second shortened frames,
For the first shortened frame, the necessity of light emission of the display element is set according to the gradation level of the special frame. For the second shortened frame, the display element is determined according to the gradation level of the interpolation image. A gradation display method comprising setting whether light emission is necessary or not. 5. The gradation display method according to claim 4, wherein each of said first and second shortened frames is divided into a smaller number of sub-frames than frames other than said special frame. 6. The first and second shortened frames are each divided into the same number of subframes as frames other than the special frame, and each of the subframes corresponding to the first and second shortened frames is divided. 5. The gradation display method according to claim 4, wherein when the necessity of light emission of the display element is set, the same setting is performed for every k (k ≧ 2) lines. 7. A filter for removing high-frequency components in a column direction from said special frame and said interpolated image, and said first and second shortening are performed in accordance with a gradation level of image information obtained by said filtering. 7. The gradation display method according to claim 6, wherein the necessity of light emission of a display element is set for each of the sub-frames corresponding to a frame.