KR20020061910A - Method and apparatus for driving plasma display panel - Google Patents

Abstract

PURPOSE: A method and an apparatus for driving a plasma display panel(PDP) are provided, which removes an MPD(Moving Picture Distortion) and also extends an expression range of a gray level value. CONSTITUTION: According to the method, a moving picture region is detected from an input picture, and a moving speed is detected from the moving picture region. Then, codes of data of the moving picture region is converted by selecting one of the first MPD(Moving Picture Distortion) precode and the second MPD precode(S97). The number of expressible gray levels of the first MPD precode varies according to the moving speed of the moving picture region. And the second MPD precode has the same number of gray levels as the number of sub fields without regard to the moving speed of the moving picture region.

Description

Method and apparatus for driving plasma display panel {Method and Apparatus For Driving Plasma Display Panel}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for driving a plasma display panel, and more particularly, to a method and apparatus for driving a plasma display panel to remove moving image pseudo contour noise and to expand a range of expression of gray scale values.

Plasma Display Panel (hereinafter referred to as "PDP") displays an image including text or graphics by emitting phosphors by 147 nm ultraviolet rays generated during discharge of He + Xe or Ne + Xe inert mixed gas. . Such a PDP is not only thin and easy to enlarge, but also greatly improved in quality due to recent technology development. In particular, the three-electrode AC surface discharge type PDP has advantages of low voltage driving and long life because wall charges are accumulated on the surface during discharge and protect the electrodes from sputtering caused by the discharge.

Referring to FIG. 1, a discharge cell of a three-electrode AC surface discharge type PDP is formed on a scan / sustain electrode 30Y and a common sustain electrode 30Z formed on an upper substrate 10, and a lower substrate 18. An address electrode 20X is provided. Each of the scan / sustain electrode 30Y and the common sustain electrode 30Z has a line width smaller than the line widths of the transparent electrodes 12Y and 12Z and the transparent electrodes 12Y and 12Z, and is formed on one edge of the transparent electrode. (13Y, 13Z). The transparent electrodes 12Y and 12Z are usually formed on the upper substrate 10 by indium tin oxide (ITO). The metal bus electrodes 13Y and 13Z are usually formed of metals such as chromium (Cr) and formed on the transparent electrodes 12Y and 12Z to reduce voltage drop caused by the transparent electrodes 12Y and 12Z having high resistance. An upper dielectric layer 14 and a passivation layer 16 are stacked on the upper substrate 10 having the scan / sustain electrode 30Y and the common sustain electrode 30Z side by side. The upper dielectric layer 14 has a wall generated during plasma discharge. Charges accumulate. The protective layer 16 prevents damage to the upper dielectric layer 14 due to sputtering generated during plasma discharge and increases emission efficiency of secondary electrons. As the protective film 16, magnesium oxide (MgO) is usually used. The lower dielectric layer 22 and the partition wall 24 are formed on the lower substrate 18 on which the address electrode 20X is formed, and the phosphor layer 26 is coated on the lower dielectric layer 22 and the partition wall 24. The address electrode 20X is formed in the direction crossing the scan / sustain electrode 30Y and the common sustain electrode 30Z. The partition wall 24 is formed in parallel with the address electrode 20X to prevent ultraviolet rays and visible light generated by the discharge from leaking to the adjacent discharge cells. The phosphor layer 26 is excited by ultraviolet rays generated during plasma discharge to generate visible light of any one of red, green, and blue. An inert mixed gas such as He + Xe or Ne + Xe for discharging is injected into the discharge space of the discharge cells provided between the upper and lower substrates 10 and 18 and the partition wall 24.

The PDP is driven by dividing one frame into several subfields having different number of emission times in order to realize gray level of an image. Each subfield is further divided into a reset period for uniformly generating discharge, an address period for selecting a discharge cell, and a sustain period for implementing gray levels according to the number of discharges. For example, when the image is to be displayed with 256 gray levels, the 8-bit default code method as shown in FIG. 3 is divided into eight subfields in a frame period (16.67 ms) corresponding to 1/60 second. In addition, each of the eight subfields is divided into an address period and a sustain period. Here, the reset period and the address period of each subfield are the same for each subfield, while the sustain period is the same in each subfield. (n = 0,1,2,3,4,5,6,7). As described above, since the sustain period is changed in each subfield, gray levels of an image can be realized.

In the PDP, contour noise may be generated in a moving image due to the characteristic of realizing the gray level of the image by the combination of subfields. If pseudo contour noise occurs, pseudo contour appears on the screen, and thus the display quality is deteriorated. For example, as shown in FIGS. 2 and 3, when the left half of the screen is displayed with 127 gradation values and the right half of the screen is displayed with 128 gradation values, and the screen is moved to the right, two pixels on the boundary portion are displayed. Since the emitted light is viewed simultaneously with the naked eye, peak white, or white band, appears at the boundary between the gray scale values 127 and 128. On the contrary, when the left half of the screen is displayed with a gradation value of 128 and the right half of the screen is displayed with a gradation value of 127, the screen is moved to the right. A black belt will appear.

As a method for removing the pseudo pseudo contour noise, a subfield is divided into one or two subfields, a subfield is rearranged, a subfield is added, and the subfields are ordered. The rearrangement method and error diffusion method have been proposed. However, adding subfields causes insufficient sustain periods, making it difficult to increase the resolution and complicate the circuit configuration. Recently, in order to remove moving picture pseudo contour noise, a code in which subfields having a low luminance relative ratio are sequentially turned on in a subfield having a low luminance relative ratio has been proposed in response to an increase in gray level as shown in FIG. 4. This code is called a moving picture distortion free code (hereinafter referred to as "MPD precode"). As can be seen from FIG. 5, the MPD precode is set so that the gray level value of each subfield is linearly increased so that light emission is linearly increased in the gray scale value and the time axis so that video pseudo contour noise does not occur. However, the MPD precode has a disadvantage in that the expressible gray value is limited to the number of subfields. For example, the MPD precode shown in FIG. 4 corresponds to the luminance relative ratios 1, 2, 4, 8, 16, 24, 32, 40, 56, and 72 of each subfield, and its gray scale value is 0, 1, 3, respectively. , 7, 15, 31, 55, 87, 183, 255. For this reason, when an image is displayed using the MPD precode, the image cannot be represented in detail.

Referring to FIG. 6, a conventional driving apparatus of a PDP compares a frame memory 44 for storing one frame of image data with a moving region by comparing the image data stored in the frame memory 44 with image data from an input line. A motion detector 43 for detecting a signal, an adaptive code converter 41 for coding input data into one of an MPD precode and an 8-bit default code according to whether or not the motion is detected, and an error spreader for coded data An error diffusion section 46 is provided. The motion detector 43 compares the previous frame data stored in the frame memory 44 with the current frame data from the input line, and determines the corresponding area as the motion area when the luminance difference between the frames is larger than a predetermined threshold value. The adaptive code conversion section 41 codes the data of the motion area detected by the motion detection section 43 into MPD precodes and supplies them to the PDP 42. In contrast, the adaptive code conversion unit 41 codes data with an 8-bit default code in the region where there is no motion, and supplies the data to the PDP 42. A subtractor 47 is provided between the input terminal and the output terminal of the adaptive code conversion unit 41, and an adder 45 is provided between the input terminal and the input line 40 of the adaptive code conversion unit 41. The subtractor 47 serves to supply the difference value between the input data and the output data of the adaptive code conversion unit 41 to the error diffusion unit 46. This data difference value is error-spread by the error diffusion section 46 and fed back to the adder 45. In detail, the error diffusion unit 46 has a difference between the grayscale value of the input data and the MPD precode in order to reduce the static false contour noise phenomenon in which the grayscale value is limited to the number of subfields. In other words, the error diffusion processing using the quantization error compensates for the static fall-container noise. As a result, the data converted to MPD precode in the motion region is not visible to the still image in the case where the movement speed is high. The adder 45 adds an error diffusion value to the data from the input line 40 and supplies it to the adaptive code converter 41.

However, if the motion area is processed as MPD precode, the MPD of the PDP is removed, but the image quality is degraded due to the relatively small number of gray-scales. This is especially true in areas where motion blur is low due to the small speed of movement.

Accordingly, it is an object of the present invention to provide a method and apparatus for driving a PDP that eliminates the MPD and expands the display range of gray scale values.

1 is a perspective view showing a conventional three-electrode AC surface discharge type plasma display panel.

FIG. 2 is a view for explaining video pseudo contour noise appearing in the plasma display panel shown in FIG. 1. FIG.

FIG. 3 is a diagram illustrating an 8-bit default code in which video pseudo contour noise as shown in FIG. 2 is generated.

FIG. 4 is a diagram illustrating gray level values and luminance relative ratios of subfields of an MPD precode for removing video pseudo-contour noise as shown in FIG. 2; FIG.

5 is a view for explaining the principle that the video pseudo contour noise disappears in the MPD precode.

6 is a block diagram schematically illustrating a conventional PDP driving apparatus to which an adaptive code conversion unit is applied.

7 is a diagram illustrating a discrete on / off code applied by a method and apparatus for driving a PDP according to the present invention.

8 is a block diagram showing a PDP driving apparatus according to an embodiment of the present invention.

9 is a flowchart showing step by step the control procedure code-coded by the motion detector and the adaptive code converter shown in FIG.

<Description of Symbols for Main Parts of Drawings>

10: upper substrate 12Y, 12Z: transparent electrode

13Y, 13Z: metal bus electrode 14, 22: dielectric layer

16: protective film 18: lower substrate

20X: address electrode 24: partition wall

26: phosphor 30Y: scan / sustain electrode

30Z: common sustain electrode 34: error diffusion part

40,50 input line 41,51: adaptive code conversion unit

42,52: PDP 43,53: motion detector

44,54: frame memory 45,55: adder

46,56: error diffusion unit 47,57: subtractor

58: ROM

In order to achieve the above object, a method of driving a PDP according to the present invention includes detecting a moving picture area in an input image, detecting a moving speed in the moving picture area, and varying the number of gradations that can be expressed according to the moving speed of the moving picture area. Transcoding the data of the video region by selecting any one of the first MPD precode and a second MPD precode having the same gray level as the number of subfields regardless of the moving speed of the video region.

The driving apparatus of the PDP according to the present invention includes a video detecting means for detecting a moving picture area from an input image, a first MPD precode for detecting a moving speed in the moving picture area and a number of gradations that can be expressed according to the moving speed of the moving picture area; And a code converting means for transcoding the data of the moving picture area by selecting any one of the second MPD precodes having the same gray level as the number of subfields regardless of the moving speed of the moving picture area.

Other objects and features of the present invention in addition to the above object will become apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 7 to 9.

Referring to FIG. 7, assuming that a moving object moves at the same speed as a whole, the subfields seen at the last pixel on the viewing path while the eye tracks the video for one frame time are displayed at the end of the viewing path about the time axis. The subfields seen in the locating pixel do not generate MPD even if they are turned ON / OFF discontinuously on the time axis. The code in which MPD does not occur even when subfields are discontinuous on / off with respect to the time axis is abbreviated as "discontinuous on / off MPD precode". This discontinuous on / off MPD precode also sets the luminance relative weights of the various subfields later in a frame time, even when the subfields are turned on / off discontinuously on the time axis. More gray levels than the number of subfields may be represented.

It is assumed that a discrete on / off MPD precode constitutes a frame of 12 subfields, and the luminance relative ratio weight of each subfield is [37 35 33 30 20 16 1 2 4 8 25 44].

In the discontinuous on / off MPD precode, subfields in which MPD does not occur even when discontinuous on / off with respect to the time axis are subfields existing in a section satisfying Equation 1 below.

here, , = time the nth subfield is located)

The number of gray levels that can be expressed in this discrete on / off MPD precode is shown in Table 1 below according to the moving speed.

Number of gradations that can be displayed for discrete on / off MPD precodes Number of gradations that can be expressed in MPD precode 1 pixel / field 133G 12G 2 pixel / field 24G 12G 3 pixel / field 17G 12G 4 pixel / field 14G 12G 5 pixel / field 14G 12G 6 pixel / field 12G 12G 6 pixel / field or higher speed 12G 12G

As can be seen from Table 1, the MPD precode is fixed in the number of subfields regardless of the movement speed, whereas the discrete on / off MPD precode has the MPD precode at 5 Pixel / field or less. In comparison with this, many gray values can be expressed. Therefore, when the discontinuous on / off MPD precode is applied, the image may be expressed with more grayscale values than the grayscale value expressible by the MPD precode without the MPD when the movement speed is 5 pix / field or less.

On the other hand, when a frame is composed of 12 subfields, the sustain period may be insufficient. This lack of sustain period can be solved by dividing the PDP 42 into the upper half and the lower half to simultaneously address the upper half and the lower half, thereby reducing the address period by approximately half. In this case, since the driver IC for splitting the upper half and the lower half is added, the circuit configuration cost and power consumption may be a problem, but the number of subfields constituting one frame is reduced to 10, and the gradation value expression is reduced. You can also compensate.

Referring to FIG. 8, the driving apparatus of the PDP according to the present invention compares the frame memory 54 for storing one frame of image data with the image data stored in the frame memory 54 and image data from an input line. Read-only memory (hereinafter, " ROM ") in which a motion detection unit 53 for detecting a motion area and a movement speed are indexed and 8-bit default codes, MPD precodes, and discrete on / off MPD precodes are stored in the form of a mapping table. 58, an adaptive code conversion unit 51 for transcoding the input data into different code schemes according to movement and speed of movement, and an error diffusion unit 56 for error diffusion of the coded data. It is provided. The motion detector 53 compares the previous frame data stored in the frame memory 54 with the current frame data from the input line and determines the corresponding area as the motion area when the luminance difference between the frames is larger than a predetermined threshold value. The adaptive code converting unit 51 codes the data of the motion region detected by the motion detecting unit 53 into either MPD precode or discrete on / off MPD precode according to the movement speed. To this end, the adaptive code conversion unit 51 is set a discrimination reference speed for selecting any one of the MPD precode and the discrete on / off MPD precode. At motion speeds below the discrimination reference speed, the data of the motion region is code-converted by the discrete on / off MPD precode, and at motion speeds above the discrimination reference speed, the data of the motion region is transcoded by the MPD precode. In addition, the adaptive code conversion unit 51 transcodes the input data of the region where there is no movement into an 8 bit default code. A subtractor 57 is provided between the input terminal and the output terminal of the adaptive code conversion unit 51, and an adder 45 is provided between the input terminal and the input line 50 of the adaptive code conversion unit 51. The subtractor 57 serves to supply the difference value between the input data and the output data of the adaptive code conversion unit 51 to the error diffusion unit 56. This data difference value is error-spread by the error diffusion unit 56 and fed back to the adder 55. The adder 55 adds an error diffusion value to the data from the input line 50 and supplies it to the adaptive code converter 41.

As a result, the driving apparatus of the PDP according to the present invention compares data between previous and current frames to determine whether to move, and to display an image at all grayscale values (full gray scale) in the case of a still image or an area without movement. bit Convert the input data to the default code. On the other hand, the input data is transcoded using the MPD precode or the discontinuous on / off MPD precode of the ROM 58 in the moving or moving region. If the moving speed is less than or equal to the discrimination reference speed, the discontinuous on / off MPD precode is applied, and if it is more than that, the MPD precode is applied. In other words, the driving apparatus of the PDP according to the present invention expresses the image with all gray values in the still area of the image when the field image is input. In the moved region, the image is expressed with more gray values than the number of gray levels of the MPD precode without generating an MPD.

9 is a flowchart showing step by step the control procedure of the code conversion performed by the motion detector 54 and the adaptive code converter 51.

Referring to FIG. 9, the inter-frame data comparison is performed by the motion detector 54, and the luminance difference between the frames is input to the adaptive code converter 51 (step S91). The adaptive code converter 51 performs a frame. The difference between the luminance and the predetermined threshold is compared. As a result of the comparison, if the luminance difference between frames is smaller than a predetermined threshold, the adaptive code conversion unit 51 applies 8-bit default code to code-convert input data from the adder 55 (steps S92 and S93). In contrast, if the inter-frame luminance difference is equal to or greater than a predetermined threshold, the adaptive code conversion unit 51 determines the motion region and compares the inter-frame movement speed with a predetermined discrimination reference speed, for example, 5 pixel / field. As a result of the comparison, if the movement speed is less than or equal to the determination reference speed, the adaptive code conversion unit 51 transcodes the input data by applying the discontinuous on / off MPD precode (steps S95 and S97). If the movement speed is faster than the discrimination reference speed, the adaptive code conversion unit 51 converts the input data by applying the MPD precode (steps S96 and S97). After converting the input code data, by processing the quantization errors in the error diffusion it is displayed on the screen in view of a good image in the eye.

On the other hand, the driving apparatus of the PDP according to the present invention requires only a speed information calculating circuit for applying the MPD precode and the discrete on / off MPD precode compared to the driving apparatus shown in FIG. In addition, since only speed information below the discrimination reference speed is required, the speed information calculating circuit is simplified rather than a complicated calculation method such as motion vector calculation.

As described above, the method and apparatus for driving a PDP according to the present invention apply an 8-bit default code in which all gray values are expressed in a region without motion, and discontinue the MPD precode based on the speed moved in the region with motion. One of the on / off MPD precodes is applied to transcode the input data. As a result, the image is represented with more gray values than the MPD precode without the MPD in the moving image, and the image can be represented with all the gray values in the still image.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (9)

Detecting a video region in the input image; Detecting a movement speed in the video region; Selecting any one of a first MPD precode whose gradation number that can be expressed according to the movement speed of the video region and a second MPD precode having the same gradation number as the number of subfields regardless of the movement speed of the video region; And transcoding the data of the moving image area. The method of claim 1, And converting the still image region data other than the moving image region in the input image into an 8 bit default code having all the gradations within 0 to 256 gradations. The method of claim 1, Code converting the data of the video region may include comparing the movement speed of the video region with a predetermined reference speed; Converting the data of the video region to the first MPD precode when the movement speed and the reference speed of the video region are determined to be less than or equal to the reference speed; And converting data of the video area into the second MPD precode when the moving speed of the video area is smaller than the reference speed. The method of claim 1, The first MPD precode indicates that weights of luminance relative ratios are allocated to the respective subfields so that even if the subfields are discontinuously turned on and off on the time axis, there is no video distortion and the gray level is greater than the number of the subfields. A method of driving a plasma display panel. Video detecting means for detecting a video area in the input image; A first MPD precode in which the moving speed is detected in the moving picture area and the number of gray levels that can be expressed according to the moving speed of the moving picture area and the first number having the same number of subfields regardless of the moving speed of the moving picture area. And code conversion means for transcoding the data of the video region by selecting any one of two MPD precodes. The method of claim 5, And the code converting means converts the still image region data other than the moving image region from the input image into an 8 bit default code having all the gradations within 0 to 256 gradations. The method of claim 6, The code converting means includes a frame memory in which previous frame data is stored; An input line to which current frame data is supplied, A motion detector for comparing the previous frame data with the current frame data to calculate a luminance difference between frames to detect a motion region; A ROM in which the 8-bit default code and the first and second MPD precodes are stored with speed information as an index; The reference speed to be compared with the movement speed is set, and either one of the first and second MPD precodes is selected from the ROM according to a result of the comparison between the movement speed and the reference speed, and the 8-bit default value is set in the still image area. And a code converter for transcoding the input data by selecting a code. The method of claim 7, wherein The code conversion unit converts the data of the video area into the first MPD precode when the movement speed and the reference speed of the moving picture area are less than or equal to the reference speed, and if the moving speed of the moving picture area is less than the reference speed. And converting the data of the video region into the second MPD precode. The method of claim 5, And an error diffusion unit for error diffusion of the input data by using the code-converted data.