KR100658345B1 - Driving apparauts and driving method of plasma display panel - Google Patents

Abstract

A driving device and method of a plasma display panel are provided to improve the grayscale expression performance by removing a still error diffusion pattern by adding random noise to an error value and preventing the distortion of an image signal. A driving device of a plasma display panel includes a VSC(Video Signal Control Circuit) receiving a video signal; a first inverted gamma correction unit, a halftone processing unit(106), a subfield mapping unit, and a data aligning unit connected between the VSC and the plasma display panel; a waveform generating unit for supplying a timing control signal to the plasma display panel; and a second inverted gamma correction unit and an APL(Average Picture Level) detecting unit connected between the VSC and the waveform generating unit. The halftone processing unit comprises an error extracting unit(130) extracting an error value from the image signal; an error diffusion block(140) generating carry by an error diffusion coefficient corresponding to the sum of the error value and randomly generated noise; and a signal generating unit(150) generating a signal by adding the carry and the image signal from which the error value has been extracted.

Description

Driving device and method of plasma display panel {DRIVING APPARAUTS AND DRIVING METHOD OF PLASMA DISPLAY PANEL}

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

2 is a diagram showing a frame structure of a conventional plasma display panel.

3 shows a dither mask for dithering.

4 shows a dither pattern.

5 is a view schematically showing error diffusion.

6 is a block diagram showing an error diffusion method of adding noise to a conventional input signal.

7 is a view showing a driving device of a plasma display panel according to an embodiment of the present invention.

8 is a view illustrating in detail the halftone processing unit of FIG.

9 is a view showing in detail the error diffusion block of FIG.

FIG. 10 is a detailed view of the lookup table of FIG. 7. FIG.

<Explanation of symbols for the main parts of the drawings>

10: upper substrate 14: upper dielectric layer

16: protective film 18: lower substrate

20X: address electrode 22: lower dielectric layer

24: partition 26: phosphor layer

30Y: scan / sustain electrode 30Z: common sustain electrode

102A and 102B: first and second inverse gamma correction units

104: gain control unit 106: halftone processing unit

108: subfield mapping unit 110: data alignment unit

112: APL detector 118: waveform generator

120: plasma display panel 122: VSC

130: error extraction unit 140: error diffusion block

150; Signal generator

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving apparatus and method of a plasma display panel, and more particularly, to a halftone processing unit and a driving apparatus and method of a plasma display panel using the same, capable of improving gray scale expression.

In general, a plasma display panel (Plasma Display Panel) is an image containing characters or graphics by emitting a phosphor by ultraviolet light of 147nm generated when the discharge of an inert gas such as He + Xe, Ne + Xe or He + Ne + Xe Will be displayed. The plasma display panel is not only thin and large in size, but also greatly improved in image quality due to recent technology development. In particular, the three-electrode AC surface discharge type plasma display panel 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.

1 is a perspective view illustrating a discharge cell structure of a general plasma display panel.

Referring to FIG. 1, a discharge cell of a three-electrode AC surface discharge type plasma display panel includes a scan / sustain electrode 30Y and a common sustain electrode 30Z formed on an upper substrate 10, and a lower substrate 18. And formed address electrode 20X. 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 formed of a metal such as chromium (Cr) on the transparent electrodes 12Y and 12Z, thereby reducing the voltage drop caused by the transparent electrodes 12Y and 12Z having high resistance. The upper dielectric layer 14 and the 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. In the upper dielectric layer 14, wall charges generated during plasma discharge are accumulated. 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 surfaces of 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, Ne + Xe or He + 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 three-electrode AC surface discharge plasma display panel is driven by dividing one frame into several subfields SF having different emission counts in order to realize gray levels of an image. The subfield SF is divided into an sustain period for implementing gradation according to an address period for selecting a discharge cell and the number of discharges. Here, an erase period for erasing the sustain discharge is added after the sustain period in each subfield SF. For example, when the image is to be displayed with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight subfields SF1 to SF8 as shown in FIG. In addition, each of the eight subfields SF1 to SF8 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 and the number of discharges are 2 ⁿ (n = 0,1,2,3,4,5,6,7) in each subfield. Is increased in proportion.

Therefore, using a large number of subfields allows more gray scales to be represented. However, since the time allocated for one frame is limited, the number of usable subfields is about 12 or less. The number of gradations that can be obtained by using all 12 subfields is 2 ¹² , which is quite large. But not all of them can be used. This is due to the pseudo contour in moving picture which is pointed out as a problem according to the subfield driving method of PDP.

After subtracting all the specific subfield combinations that produce a lot of pseudo contours, the actual number of real tones that can be created is significantly reduced, which may be less than 100. To express more gray scales with such a small gray scale, another method must be additionally used. The method used here is half-toning, which is a half-tone generation method that fills the gap between the real gray scale and the real gray scale. . This halftone method mainly uses error diffusion or dithering.

In the dithering method, as shown in FIG. 3, it is determined that a carry is generated through a dither mask and each pixel is greater than or equal to a certain threshold, and the carry-on is turned on for the pixel on which the carry is generated. By turning off the pixels that have not occurred, the insufficient gray scale expression power is improved. However, such a dithering scheme shows a dither pattern as shown in FIG. 4 for a still image or a region having a uniform value. In addition, this dithering method has a disadvantage that an error with a threshold value is not considered when a carry occurs.

As a result, there is a growing number of companies that prefer to spread errors.

Error diffusion uses a slightly modified form based on the Floyd Steinberg method. This error diffusion is a technique that is mainly used in a printing device such as a printer to spread the gray level error value of the input pixel to adjacent cells. In particular, error diffusion in AV video can provide a very good expression and can prevent constant pattern noise caused by using dithering.

However, when a large number of still images are displayed, such as the PC mode, error diffusion represents a stationary error diffusion pattern. When the luminance difference of the real gradation is large, the error diffusion pattern appears to be quite strong and appears as pattern noise. This is especially true on dark screens with many low gradations. In order to improve the pattern noise, an improved error diffusion method using different error diffusion coefficients according to the input gray level error has been developed. That is, the improved error diffusion method is a method of spatially correcting an error that is discarded by causing an error generated when the corresponding pixel is quantized to affect neighboring pixels. In detail, as shown in FIG. 5, the i-th pixel is a coefficient specific to an error occurring in neighboring pixels a, b, c, and d. For example, 1/16 for a pixel and 5/16 for b pixel. In other words, multiply c by 3/16 and d by 7/16, add the added value to the i value, and quantize and store the error in line memory and repeat it every pixel. The improved error diffusion method of this method can express the shape of the pattern more naturally, thereby solving problems such as worm artifacts in Floyd Steinberg error diffusion. However, since the improved error diffusion method appears to be a stationary form on the screen, it is seen as pattern noise on a screen with a low Average Picture Level (APL).

In order to eliminate such patterns, a method of adding some noise to the input signal as shown in FIG. 6 is used. 6 is a block diagram showing 10-bit actual gradation + 8-bit error spreading. Specifically, the conventional error diffusion method is a form in which a carry is added through an error diffusion block after random noise generated from a random noise generator is added to an input signal. In this way, the error diffusion pattern takes a moving shape rather than a fixed shape. However, the noise applied to the input signal eventually causes distortion of the video signal itself, resulting in an increase of noise on the screen.

Accordingly, an object of the present invention is to provide a halftone processing unit for improving the image quality on a still image without distortion of an input image signal, and a driving apparatus and a driving method of a plasma display panel using the halftone processing unit.

In order to achieve the above object, a driving apparatus of a plasma display panel according to an embodiment of the present invention includes an image signal control circuit unit to which an image signal is input; A first inverse gamma correction unit, a halftone processing unit, a subfield mapping unit, and a data alignment unit connected between the image signal control circuit unit and the plasma display panel; A waveform generator for supplying a timing control signal to the plasma display panel; A second inverse gamma correction unit and an average image level detection unit connected between the image signal control circuit unit and the waveform generation unit; The halftone processing unit extracts an error value from the image signal, an error extracting unit, an error diffusion block generating a carry with an error diffusion coefficient corresponding to a sum of a randomly generated noise, and the error value, the carry and the error value And a signal generator for generating a signal by adding the extracted video signal.

The error diffusion block includes a random generator for generating random noise; An adder for adding a random noise and an error value; A look-up table which previously stores an error diffusion coefficient corresponding to a result value from the adder; And a carry generator for calculating a carry based on the error diffusion coefficient.

The random generator is characterized in that to generate the random noise in accordance with the change in brightness.

The brightness change is characterized in that it has a value in the range of 0 to 5.

The lookup table is characterized by having a 4x256 coefficient table in the case of an 8-bit error diffusion coefficient.

A method of driving a plasma display panel according to an exemplary embodiment of the present invention includes extracting an error value from an image signal and generating random noise in a predetermined range according to a change in brightness; Designating an error diffusion coefficient corresponding to the sum of the error value and the random noise; Generating a carry using the error diffusion coefficient; And adding the carry and the video signal from which the error value is removed.

Other objects and features of the present invention in addition to the above objects will be 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 11.

7 is a view showing a driving apparatus of a plasma display panel according to an embodiment of the present invention.

Referring to FIG. 7, a driving apparatus of a plasma display panel according to an exemplary embodiment of the present invention includes a video signal control circuit (VSC) 122 through which a video signal is input, and a VSC 122. ), The first inverse gamma correction unit 102A, the halftone processing unit 106, the subfield mapping unit 108 and the data alignment unit 110 connected between the plasma display panel 120 and the reset pulse and the sustain pulse. A waveform generator 118 for supplying a timing control signal including the waveform to the plasma display panel 120, a second inverse gamma correction unit 102B connected between the VSC 122 and the waveform generator 118, and An average picture level (hereinafter referred to as "APL") detection unit 112 is included. Here, the halftone processing unit 106 applies a halftone method of determining a coefficient from a lookup table and performing error diffusion.

The VSC 122 samples and digitizes the analog video signal according to the clock signal.

The first and second inverse gamma correction units 102A and 102B inversely gamma correct the digital video signal from the VSC 122 to linearly convert the luminance value according to the gray value of the video signal.

The APL detector 112 detects an average luminance, that is, APL, on a frame-by-frame basis with respect to data input from the second inverse gamma correction unit 102B. The APL detected by the APL detector 112 is divided into 256 steps from 0 to 255 according to the luminance value when the input image data is assumed to be 8 bits, and in case of 16 bits, 1024 steps from 0 to 1023 according to the luminance value. Divided into

The halftone processor 106 applies a halftone method of determining a coefficient from a lookup table and applying error diffusion. The halftone processing unit 106 will be described later in detail with reference to FIG. 8.

The subfield mapping unit 108 maps the data input from the halftone processing unit 106 to prestored subfields and supplies the data to the data alignment unit 110 for each subfield.

The data alignment unit 110 supplies the image data input from the subfield mapping unit 108 to a data driving integrated circuit (hereinafter, referred to as "IC") of the plasma display panel 120. The data driving IC is connected to the data electrodes of the plasma display panel 120 to latch data input from the data alignment unit 110 by one horizontal line, and then supply the latched data to the data electrodes in units of one horizontal period. do.

The waveform generator 118 generates a timing control signal for driving the plasma display panel 120 in response to a signal input from the APL detector 112, and converts the timing control signal into a data driver IC, a scan driver IC, and a sustain signal. Supply to drive IC. The scan driving IC is connected to the scan electrodes of the plasma display panel 120 orthogonal to the data electrodes to sequentially supply scan pulses to the scan electrodes in response to a timing control signal input from the waveform generator 118. During the sustain period, sustain pulses are simultaneously supplied to the scan electrodes. The sustain driving IC supplies sustain pulses to the sustain electrodes formed on the plasma display panel 120 to be in parallel with the scan electrodes and to be paired with the scan electrodes.

8 is a diagram illustrating in detail the halftone processing unit 106 according to an embodiment of the present invention.

Referring to FIG. 8, the halftone processor 106 according to an exemplary embodiment of the present invention may generate an error extractor 130, an error value, and randomly generate an error value from an input image signal R, G, or B. FIG. An error diffusion block 140 generating a carry with an error diffusion coefficient corresponding to the sum of the noises, and image signals R ', G', and B 'extracted from the carry and error values generated from the error diffusion block 140; And a signal generator 150 to remove the error diffusion pattern of the still image.

The error extractor 130 separates error values from the input image signals R, G, and B.

Since the error diffusion block 140 generates each image signal R, G, and B in the same manner, only the R signal will be described in detail with reference to FIG. 9. Referring to FIG. 9, the error diffusion block 140 may generate random noise and an error generated by the random generator 142 and the random generator 142 to generate random noise in a predetermined range according to a change in brightness of a video signal. An error from the lookup table 146 and the lookup table 146 which prestore the error diffusion coefficient corresponding to the result value from the adder 144, the adder 144 adding the error value from the extractor 130 And a carry generator 148 that calculates a carry based on the diffusion coefficients a, b, c, and d and the error value.

The random generator 142 generates random noise according to the brightness change of the pixel. Here, the jumping weight has a predetermined value, for example, a value in the range of 0 to 5, and the random generator 142 generates noise (+ w to -w) according to the brightness change.

The adder 144 generates an index by adding the random noise generated from the random generator 142 and the error value separated from the error extractor 130.

The lookup table 146 stores the error diffusion coefficient corresponding to the index of the adder 144 in advance. For example, in the driving apparatus that adds and expresses the gray level generated by the 8-bit error diffusion coefficient to the 10-bit actual gray scale, the lookup table 146 displays 4 as shown in FIG. 10 when the error value of the input signal is 10. FIG. You will have a coefficient table. Here, each coefficient value has experimental values for optimizing an image pattern pattern.

The carry generator 148 calculates a carry using an error diffusion coefficient from the lookup table 146.

The signal generator 150 adds the input video signals R ', G', and B 'from which the carry and error values are excluded from the carry generator 148 to add new image signals R', G ', and B'. Will be reproduced ”.

Looking at the driving method of the driving apparatus of the plasma display panel according to the embodiment of the present invention having such a structure, the driving method according to the embodiment of the present invention, first, while extracting an error value from the input image signal, Random error of the predetermined range is generated using the error diffusion block 140 according to the brightness change.

Thereafter, the error diffusion block 140 designates an error diffusion coefficient corresponding to the sum of the error value and the random noise from the lookup table 146.

Next, the error diffusion block 140 generates a carry using the error diffusion coefficient from the specified lookup table 146 and adds the generated carry and the input image signal from which the error value is removed to stop the error diffusion pattern. Will be removed.

Here, in the driving method of the plasma display panel according to an exemplary embodiment of the present invention, as the random noise value increases, the degree of change of the error diffusion pattern changes.

As described above, the driving apparatus and method of the plasma display panel according to the present invention can remove the stationary error diffusion pattern by adding a random error to the error value by using the error diffusion pattern lookup table as a stationary error diffusion pattern. The method of adding noise to an input video signal can solve the distortion problem of the video signal. Therefore, the halftone processing unit and the driving apparatus and method of the plasma display panel according to the present invention using the same can improve the gray scale expression.

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 (6)

A video signal control circuit unit to which a video signal is input; A first inverse gamma correction unit, a halftone processing unit, a subfield mapping unit, and a data alignment unit connected between the image signal control circuit unit and the plasma display panel; A waveform generator for supplying a timing control signal to the plasma display panel; A second inverse gamma correction unit and an average image level detection unit connected between the image signal control circuit unit and the waveform generation unit; The halftone processing unit extracts an error value from the image signal, an error extracting unit, an error diffusion block generating a carry with an error diffusion coefficient corresponding to a sum of a randomly generated noise, and the error value, the carry and the error value And a signal generator for generating a signal by adding the extracted image signal. The method of claim 1, The error diffusion block A random generator for generating random noise; An adder for adding the random noise and an error value; A look-up table which previously stores an error diffusion coefficient corresponding to a result value from the adder; And And a carry generator for calculating a carry based on the error diffusion coefficient and the error value. The method of claim 2, The random generator And driving the random noise according to a change in brightness. The method of claim 3, wherein The brightness change is a driving device of the plasma display panel, characterized in that it has a value in the range of 0 to 5. The method of claim 2, The lookup table And a 4x256 coefficient table for an 8-bit error diffusion coefficient. Extracting an error value from an image signal and generating random noise in a predetermined range according to a brightness change; Designating an error diffusion coefficient corresponding to the sum of the error value and the random noise; Generating a carry using the error diffusion coefficient and the error value; And And adding an image signal from which the carry and the error value are removed.

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