KR20090103038A - Plasma display, and driving method thereof - Google Patents

Abstract

PURPOSE: A plasma display and a driving method thereof are provided to locate a prime number pixel uniformly within one frame by reducing a possibility of overlapping in prime number pixel. CONSTITUTION: A plasma display and a driving method thereof are comprised of the steps: outputting a plurality of image data by compensating for a reverse gamma of a plurality of image data corresponding to a plurality of cells; dividing the gray scale of the plurality image data with a integer component and a prime number component ; renewing a threshold value of each cell(224-2); and determining an error to be extended to around cell and output of the prime number of each cell based on a threshold value and image data.

Description

Plasma display device and driving method thereof {PLASMA DISPLAY, AND DRIVING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device and a driving method thereof, and more particularly to an error diffusion method capable of preventing overlapping of a few pixels.

The plasma display device is a display device using a plasma display panel that displays text or an image by using plasma generated by gas discharge.

The plasma display apparatus drives by dividing one frame into a plurality of subfields having respective luminance weights. Light emitting cells and non-light emitting cells are selected during the address period of each subfield, and sustain discharge is performed on the light emitting cells in order to actually display an image during the sustain period. The gray level is expressed by a combination of the weights of the subfields in which the cells emit light.

Such a plasma display device requires inverse gamma correction for an input image signal due to a nonlinear input / output characteristic of a cathode ray tube (CRT). However, the inverse gamma corrected video signal cannot exhibit sufficient gray scale at low gray scale. Therefore, the plasma display device spreads the inverse gamma corrected image signal by error in order to increase the number of gray levels that can be expressed at low gray levels.

Assuming that the target gradation value of the input image signal is β.xx, an integer gradation β is displayed in some of the k × k pixels due to error diffusion, and an integer gradation (β + 1) is displayed in the remaining pixels. In this case, when the fractional value 0.xx of the target grayscale value is less than 0.5, the number of pixels having an integer gray level (β + 1) is less than the number of pixels having the integer gray level β, and the fractional value 0.xx of the target grayscale value is less than 0.5. If large, the number of pixels having an integer magnitude β is smaller than the coefficient of pixels having an integer gray level (β + 1). For a given fractional value, a pixel having the smallest number among the integer numbers β and integer numbers (β + 1) is defined as a decimal pixel.

However, when the input image signal is a single gray level image signal, the inverse gamma corrected image signal has a constant gray level value regardless of the position of the pixel. Therefore, a few pixels due to the error diffusion are located at the same position every frame. In addition, when the same gray value is input for each of the R, G, and B image signals, a few pixels for each of the R, G, and B cells are positioned at the same position within a given frame. Such superposition of the minority pixels increases the luminance difference between the minority pixel and the surrounding pixels, and the high luminance difference between the minority pixel and the surrounding pixels is recognized as noise by human vision.

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma display device and a driving method thereof capable of reducing a luminance difference between a few pixels and surrounding pixels.

According to an embodiment of the present invention, a driving method of a plasma display device including a plurality of cells is provided. The driving method includes the steps of outputting a plurality of video data by inverse gamma correction of a plurality of video signals corresponding to a plurality of cells, separating the grays of the plurality of video data into integer grays and decimal grays, and each cell. Updating a threshold of the cell, determining an output value of the minority grayscale of each cell and an error to be spread to neighboring cells based on the updated threshold value of each cell and the image data corresponding to each cell, and the integer And displaying the gray level of each cell by adding the gray level and the output value of the fractional gray level. At this time, the threshold of each cell is updated based on the error spreading to each cell.

According to another embodiment of the present invention, a method of driving a plasma display device including a first cell of a first color, a second cell of a second color, and a third cell of a third color is provided. The driving method may include outputting first, second and third image data by inverse gamma correction of the first, second and third image signals corresponding to the first, second and third cells, respectively. Separating the grays of the first, second, and third image data into integer grays and decimal grays, updating the thresholds of the first, second, and third cells, and Determining an output value of the minority grayscales of the first, second, and third cells and an error to diffuse into the neighboring cells based on the threshold value and the image data corresponding to the first, second, and third cells; Summing the integer gradations of the first, second, and third cells and the output values of the fractional gradations of the first, second, and third cells, respectively, to display the gradations of the first, second, and third cells. . In this case, the threshold value of the first cell is updated based on the error spreading to the first, second and third cells, and the threshold value of the second cell is spread to the first, second and third cells. The threshold value of the third cell is updated based on an error spread to the first, second and third cells.

According to another embodiment of the present invention, a plasma display device is provided. The plasma display device includes a plurality of cells, a controller, and a driver. The controller outputs a plurality of image data by inverse gamma correction of the plurality of image signals corresponding to the plurality of cells, and separates the gray levels of the plurality of video data into integer gray scales and decimal gray scales, respectively. Based on the threshold and the image data of each cell, an output value of the minority gray level of each cell and an error to be diffused to surrounding cells are determined, and the integer gray level of each cell and the output value of the minority gray level of each cell are respectively summed up to each cell. Displays the gradation of. The driving unit drives the plurality of cells in accordance with the gradation of each of the displayed cells. In this case, the controller updates the threshold value of each cell based on the error spread to each cell.

According to an embodiment of the present invention, it is possible to reduce the overlap probability of the decimal pixels and to uniformly position the decimal pixels in a single frame.

1 is a diagram schematically illustrating a plasma display device according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram of the control unit shown in FIG. 1;

3 is a flowchart illustrating an operation of the controller illustrated in FIG. 1;

4 is a block diagram of an error diffusion unit illustrated in FIG. 2;

5 is a diagram illustrating an error diffusion method of the error diffusion unit illustrated in FIG. 2.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, except to exclude other components unless specifically stated otherwise.

In addition, the wall charge referred to in the present invention refers to a charge formed close to each electrode on the wall of the cell (eg, the dielectric layer). The wall charge is not actually in contact with the electrode itself, but is described here as "formed", "accumulated" or "stacked" on the electrode. In addition, the wall voltage refers to the potential difference formed in the wall of the cell by the wall charge. The weak discharge refers to a discharge weaker than the address discharge in the address period and the sustain discharge in the sustain period.

A plasma display device and a driving method thereof according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

1 is a diagram schematically illustrating a plasma display device according to an exemplary embodiment of the present invention.

As shown in FIG. 1, a plasma display device according to an exemplary embodiment of the present invention includes a plasma display panel 100, a controller 200, an address electrode driver 300, a sustain electrode driver 400, and a scan electrode driver 500. It includes.

The plasma display panel 100 includes a plurality of address electrodes (hereinafter referred to as "A electrodes") A1-Am extending in the column direction, and a plurality of sustain electrodes extending in pairs with each other in the row direction (hereinafter, " X electrodes "(X1-Xn) and scan electrodes (hereinafter referred to as" Y electrodes ") (Y1-Yn). In general, each of the X electrodes X1 to Xn is formed corresponding to each of the Y electrodes Y1 to Yn, and the X electrodes X1 to Xn and the Y electrodes Y1 to Yn are used for displaying an image in the sustain period. Perform the display operation. The Y electrodes Y1-Yn and the X electrodes X1-Xn are arranged to be orthogonal to the A electrodes A1-Am. Further, the discharge space at the intersection of the A electrodes A1-Am and the X and Y electrodes X1-Xn and Y1-Yn forms a discharge cell (hereinafter referred to as a cell) 110. The structure of the plasma display panel 100 is an example, and a panel having another structure to which the driving waveform described below may be applied may also be applied to the present invention.

The controller 200 receives an image signal from the outside and outputs driving control signals of the A electrodes A1-Am, the X electrodes X1-Xn, and the Y electrodes Y1-Yn. In addition, the controller 200 divides one frame into a plurality of subfields having respective weights to drive the plasma display panel 100. Each subfield includes an address period and a sustain period.

The address electrode driver 300 applies a driving voltage to the A electrodes A1-Am according to the driving control signal from the controller 200.

The sustain electrode driver 400 applies a driving voltage to the X electrodes X1-Xn according to the drive control signal from the controller 200.

The scan electrode driver 500 applies a driving voltage to the Y electrodes Y1-Yn according to the driving control signal from the controller 200.

2 is a block diagram of the controller shown in FIG. 1, and FIG. 3 is a flowchart illustrating the operation of the controller shown in FIG. 1.

As shown in FIG. 2, the control unit 200 includes an inverse gamma correction unit 210, an error diffusion unit 220, an automatic power control (hereinafter referred to as an “APC unit”) 230, and a maintenance control unit. 240 and the subfield data generator 250.

Referring to FIG. 3, the inverse gamma correction unit 210 reverse-gamma corrects an input n-bit R, G, and B image signal and outputs m-bit (m≥n) image data (S310-S320). For example, n may be 8 and m may be 10 or 12. In this case, the image signal input to the inverse gamma correction unit 210 is a digital signal. When an analog image signal is input to the plasma display panel 100, the analog image signal is converted into a digital image signal by an analog-to-digital converter (not shown). Needs to be converted to. The inverse gamma correction unit 210 maps the R, G, and B image signals to an inverse gamma curve to store inverse gamma corrections of the R, G, and B image signals, and stores a data corresponding to the inverse gamma curve. (Not shown) or a logic circuit (not shown) for generating data corresponding to an inverse gamma curve by a logical operation.

The error diffusion unit 220 spreads an error (m-n) bit into surrounding pixels in the m-bit image data (S330). Error diffusion is a method of displaying an image of the gray level of the lower bit by spreading the gray level of the lower bit to surrounding cells. The error diffusion unit 220 updates the threshold value of each cell based on the error spread to each cell, and determines the output value of the lower bit of each cell and the error to be spread to the neighboring cells by using the updated threshold value of each cell. do. The error diffusion unit 220 displays the gray level of each cell by summing the gray level of the upper bit of each cell and the output value of the lower bit of each cell. In the following, the lower bit is defined as a "decimal part" and the upper bit is defined as an "integer part".

The APC unit 230 calculates the screen load ratio using the error-diffused image data (S340), allocates the number of sustain pulses corresponding to the screen load ratio, and transmits the number to the maintenance controller 240. In this case, the APC unit 230 may calculate the screen load ratio as an average signal level of an image signal input for one frame.

The maintenance controller 240 allocates a sustain pulse to each subfield according to the weight of each subfield using the number of sustain pulses transmitted from the APC unit 230 (S350). In addition, a control signal corresponding to the allocated number of sustain pulses is generated and output to the sustain electrode driver and the scan electrode drivers 400 and 500.

The address data generator 350 generates subfield data corresponding to the gray level of the error-diffused image data (S360), and transfers the generated subfield data to the address electrode driver 300.

However, if the lower bit of the image data is error-diffused, the low gray scale expressive power may be improved, but the overlapping phenomenon of the minority pixels in which the minority pixels are positioned at the same position may occur every frame. Hereinafter, an exemplary embodiment of reducing overlap of decimal pixels will be described in detail with reference to FIGS. 4 and 5.

4 is a block diagram of the error diffusion unit illustrated in FIG. 2, and FIG. 5 is a diagram illustrating an error diffusion method of the error diffusion unit illustrated in FIG. 2.

As shown in FIG. 4, the error diffusion unit 220 includes a separation unit 222, a fractional unit output control unit 224, a delay unit 226, and an output unit 228.

Referring to FIG. 5, the separation unit 222 separates the gray level of the inverse gamma corrected image signal into the integer unit and the fractional unit (S510), outputs the integer unit to the delay unit 226, and outputs the fractional unit to the fractional unit output control unit 224. Output

Again, referring to FIG. 4, the fractional output controller 224 includes a threshold adjustment amount calculator 224-1, a threshold calculator 224-2, a distance calculator 224-3, and a fractional output determiner 224. -4).

As shown in FIG. 5, the threshold adjustment amount calculation unit 224-1 adjusts the threshold adjustment amount in the current frame by the error spreading to each cell in the previous frame and the threshold adjustment amount in the previous frame, as shown in Equation 1. Update (S520).

As illustrated in FIG. 2, the threshold calculator 224-2 determines the threshold value of each pixel in the current frame by using the threshold adjustment amount and the basic threshold value in the current frame (S530).

In Equation 1, FTH represents a threshold adjustment amount, and x and y represent positions of pixels. n denotes a frame, and e denotes an error diffused into each cell. In addition, M ₁ represents a threshold adjustment amount weight of the previous frame and the frame before the previous frame, and M ₂ represents the threshold adjustment amount weight of the previous frame and the current frame.

In Equation 2, TH 'represents a threshold value, 128 is a basic threshold value, and means an intermediate value when the gray level of the fractional part is 0 to 255.

As such, when the threshold of each cell is determined, the probability of overlapping positions of the decimal pixels can be reduced. That is, the error of each cell determined in the previous frame is spatially propagated to the surrounding cells, and the spatially propagated error is propagated to the current frame in time. Therefore, since the threshold value of the current frame is different, the probability that the decimal pixel overlaps at the same cell position as the cell position where the decimal pixel occurred in the previous frame is reduced in the current frame.

In addition, after the threshold value of each cell is determined through Equation 2, the threshold calculator 224-2 updates the threshold value as shown in Equation 3 (S540).

In Equation 3, TH is an updated threshold value, and S represents a weight.

In this way, by updating the threshold value, a few pixels may be uniformly distributed in the current frame. That is, when a few pixels occur around one cell, an error occurs. When the generated error propagates, the threshold of this cell changes. Therefore, since the probability of generating a small number of pixels in this cell becomes low, it is possible to uniformly distribute the small number of pixels within a single frame.

The distance calculator 224-3 updates the fractional part value of the image data of each cell from the error spreading to each cell, and compares the updated threshold value of each cell with the value of the updated fractional part of each cell to determine the fractional part output. Output to the unit 224-4 (S550). In this case, the updated fractional part value of each cell represents the sum of the fractional part value of each cell output from the separator 222 and the error spreading to each cell.

The fractional part output determining unit 224-4 determines the output value of the fractional part of each cell according to the comparison of the updated threshold value of each cell with the updated fractional part value of the image data of each cell (S560). Output That is, if the updated threshold value of each cell is larger than the updated fractional value of the image data of each cell, the fractional part output determiner 224-4 determines the output value of the fractional part of each cell as 0, and updates the updated threshold value of each cell. If the value is equal to or less than the updated fractional part value of the video data of each cell, the output value of the fractional part of each cell is determined as one.

In addition, the fractional part output determiner 224-4 determines an error to be diffused into neighboring cells by using the output value of the fractional part of each cell and the fractional part value of the image data of each cell. In this case, an error to be diffused to neighboring cells may be determined from a difference between the values of the fractional part of the image data of each cell in the output value of the fractional part of each cell.

The delay unit 226 delays the integer unit until the output value of the fractional unit is determined, and outputs it to the output unit 228.

The output unit 228 displays the gray level of each cell by summing the integer value of each pixel and the output value of the fractional part of each pixel, and outputs the gray level of each cell to the subfield data generation unit 250 (S570).

Meanwhile, Equations 1 to 3 have been described assuming one cell as one pixel, but a bundle of R, G, and B cells may form one pixel. As such, even when the bundle of R, G, and B cells forms one pixel, the gray levels of the R, G, and B cells may be displayed through the steps illustrated in FIG. 5.

However, when a bundle of R, G, and B cells forms one pixel, the thresholds of the R, G, and B cells of one pixel may be different from their own cells at the determined thresholds of the R, G, and B cells. It can be updated using the error spreading to the cell. Thresholds of the R, G, and B cells may be determined based on Equations 1 and 2, and each of the thresholds of the R, G, and B cells may not only adjust the threshold of the cell but also the threshold of the other cells. I use it.

In this way, when a fractional pixel is generated in one cell (e.g., R cell), the threshold value of another cell (e.g., G and B cells) is changed so that the other cell (e.g., G and The occurrence probability of the minority pixels in cell B can be reduced.

After the threshold values of the R, G, and B cells are updated, the distance calculator 224-3 updates the values of the fractional parts of the image data of the R, G, and B cells from the error spreading to the R, G, and B cells. The updated threshold values of the R, G, and B cells are compared with the values of the updated fractional parts of the R, G, and B cells, and are output to the decimal part output determination unit 224-4.

Then, the fractional part output determining unit 224-4 outputs the output values of the fractional parts of the R, G, and B cells according to the updated threshold values of the R, G, and B cells and the updated fractional parts of the R, G, and B cells. Decide That is, if the updated fractional value of the R, G, and B cells is greater than the updated threshold values of the R, G, and B cells, respectively, the output value of the fractional part of the R, G, and B cells is output as 1; Output

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (13)

In the driving method of a plasma display device including a plurality of cells, Inversely gamma correcting a plurality of video signals corresponding to the plurality of cells to output a plurality of video data; Dividing the gradations of the plurality of image data into integer gradations and decimal gradations, Updating the threshold of each cell, Determining an output value of the minority gray level of each cell and an error to be spread to neighboring cells based on the updated threshold value of each cell and the image data corresponding to each cell; and Displaying the gray level of each cell by summing output values of the integer gray level and the decimal gray level; Including; The threshold value of each cell is updated based on an error spreading to each cell. The method of claim 1, The updating step, And updating the threshold by subtracting a threshold value before the update by a weight multiplied by an error spreading to each cell. The method of claim 1, Before updating the threshold of each cell, Updating the threshold adjustment amount of each cell, and Determining a threshold value of each cell by using the threshold adjustment amount of each cell and a basic threshold value More, And the threshold adjustment amount is updated based on an error spreading to each cell in a previous frame and a threshold adjustment amount of each cell in the previous frame. The method of claim 3, The updating of the threshold adjustment amount may include: And updating the threshold adjustment amount by summing the error spreading to each cell in the previous frame by multiplying the first weight by the first weight and the threshold adjustment amount in the previous frame by the second weight. Driving method. The method of claim 1, Determining the output value of the fractional gray scale, Updating the fractional gray scale of the image data of each cell from the error spreading to each cell; If the updated threshold value is greater than the updated fractional grayscale, determining an output value of the fractional grayscale as 0, and And determining the output value of the fractional grayscale as 1 when the updated threshold value is less than or equal to the updated fractional grayscale. The method according to any one of claims 1 to 5, Generating subfield data corresponding to the gray level of each cell; and Selectively emitting each cell according to the subfield data The driving method of the plasma display device further comprising. A driving method of a plasma display device comprising a first cell of a first color, a second cell of a second color, and a third cell of a third color, Outputting first, second and third image data by inverse gamma correcting the first, second and third image signals corresponding to the first, second and third cells, respectively; Dividing the gray level of the first, second and third image data into an integer gray scale and a decimal gray scale, Updating the threshold values of the first, second and third cells, Based on the updated threshold values of the first, second, and third cells and the image data corresponding to the first, second, and third cells, the output values of the gray scales of the first, second, and third cells, and the surroundings. Determining the error to diffuse into the cell, and Displaying the gray levels of the first, second, and third cells by adding the integer grays of the first, second, and third cells and the output values of the decimal grays of the first, second, and third cells, respectively. Including; The threshold of the first cell is updated based on an error spreading to the first, second and third cells, and the threshold of the second cell is based on an error spreading to the first, second and third cells. And the threshold value of the third cell is updated based on an error diffused into the first, second and third cells. The method of claim 7, wherein Before updating the thresholds of the first, second and third cells, Updating the threshold adjustment amounts of the first, second and third cells, and Determining threshold values of the first, second, and third cells, respectively, using threshold adjustment amounts and basic threshold values of the first, second, and third cells; More, The threshold adjustment amount of the first cell is updated based on the error spreading from the previous frame to the first cell and the threshold adjustment amount of the first cell in the previous frame, and the error spreading from the previous frame to the second cell. And the threshold adjustment amount of the second cell is updated based on the threshold adjustment amount of the second cell in the immediately preceding frame, and the error spreads to the third cell in the immediately preceding frame and the third cell in the immediately preceding frame. And the threshold adjustment amount of the third cell is updated based on the threshold adjustment amount of the plasma display device. The method of claim 7, wherein Determining the output value of the fractional gray scale, Updating the fractional gray scale of the first, second and third image data from the error spreading into the first, second and third cells; If the updated threshold values of the first, second, and third cells are greater than the fractional gray levels of the updated first, second, and third cells, the fractional gray levels of the first, second, and third cells are determined to be zero. To do, and If the updated threshold values of the first, second, and third cells are less than or equal to the updated decimal scales of the first, second, and third cells, the decimal scales of the first, second, and third cells are set to one. Decision Step Method of driving a plasma display device comprising a. The method according to any one of claims 7 to 9, Generating first, second and third subfield data corresponding to the gray levels of the output first, second and third cells; and Selectively emitting the first, second and third cells according to the first, second and third subfield data The driving method of the plasma display device further comprising. Multiple Cells, Inversely gamma corrects a plurality of video signals corresponding to the plurality of cells to output a plurality of video data, and separates the grays of the plurality of video data into integer grays and decimal grays, respectively, and updates the threshold values of each cell. And an output value of the minority gradation of each cell and an error to be diffused to neighboring cells based on the image data of each cell, and add the integer gradation of each cell and the output value of the minority gradation of each cell, respectively, and the gradation of each cell. A control unit for displaying and A driving unit for driving the plurality of cells in accordance with the gray level of each of the displayed cells Including; And the controller is further configured to update the threshold value of each cell based on an error spread to each cell. The method of claim 11, The control unit, A first calculator configured to update the threshold adjustment amount of each cell based on an error spread to each cell in a previous frame and a threshold adjustment amount of each cell in the previous frame; A second calculator configured to determine a threshold value of each cell by using a basic threshold value and an updated threshold adjustment amount of each cell, and to update the determined threshold value of each cell, and A fractional part output determination unit configured to determine an output value of the fractional gray level of each cell by using the updated threshold value of each cell and the updated fractional gray level of the image data of each cell; And a fractional gray scale of the image data of each cell is updated from the error spreading into each cell. The method of claim 11, The plurality of cells includes a plurality of first cells emitting light of a first color, a plurality of second cells emitting light of a second color, and a plurality of third cells emitting light of a third color, One first cell, one second cell, and one third cell are defined as one pixel, The controller may be configured based on an error spreading into the first, second and third cells of each pixel in the immediately preceding frame and threshold adjustment amounts of the first, second and third cells of each pixel in the immediately preceding frame. A first calculator for updating threshold adjustment amounts of the first, second and third cells of each pixel; The threshold values of the first, second and third cells of each pixel are determined by using a basic threshold value and the updated threshold adjustment amounts of the first, second and third cells of each pixel, and the determined threshold values of the respective pixels are determined. A second calculator for updating threshold values of the first, second, and third cells, and The first, second, and third cells of the first, second, and third cells of each pixel and the updated fractional gray level of the image data of the first, second, and third cells of each pixel may be used. A decimal part output determining part which determines an output value of the decimal gray levels of the second and third cells, And a fractional gray scale of the image data of the first, second, and third cells of each pixel is updated from an error diffused into the first, second, and third cells of each pixel.