KR100612516B1 - Image processing device and method for plasma display panel - Google Patents

Abstract

The present invention relates to a plasma display panel, and more particularly, to an image processing apparatus and method for a plasma display panel capable of removing a specific pattern displayed during driving of a plasma display panel and increasing gray scale expression.

An image processing apparatus of a plasma display panel for processing an image signal to implement an image, the apparatus comprising: an inverse gamma correction unit configured to gamma correct the image signal with pre-stored gamma data; When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal is less than or equal to a predetermined threshold, an error component of the image signal of the previous frame is added to the image signal of the current frame. A half toning unit for diffusing; And subfield mapping for mapping an image signal input from the half-toning unit to a subfield mapping table.

Description

Image Processing Device and Method for Plasma Display Panel

1 illustrates a structure of a general plasma display panel.

2 is a diagram illustrating a method of implementing an image of a conventional plasma display panel.

3 is a graph comparing luminance characteristics of a plasma display panel and a cathode ray tube.

4 is a graph illustrating inverse gamma correction in a conventional plasma display panel.

5A and 5B illustrate dithering methods of a conventional plasma display panel.

6 is a diagram illustrating an error diffusion method of a conventional plasma display panel.

7 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

8 is a block diagram illustrating an operation characteristic of a half toning unit according to an embodiment of the present invention.

9 is a schematic diagram for explaining error diffusion according to an embodiment of the present invention.

***** Explanation of symbols for main parts of drawing *****

710; Inverse gamma correction unit 720; Gain control

730, 800; Half toning unit 740; Subfield Mapping Section

810; A frame memory unit 820; Error Diffusion Determination Unit

830; Error Diffusion Execution Unit

The present invention relates to a plasma display panel, and more particularly, to an image processing apparatus and method for a plasma display panel capable of removing a specific pattern displayed during driving of a plasma display panel and increasing gray scale expression.

In general, a plasma display panel (Plasma Display Panel) is a partition wall formed between the front substrate and the rear substrate to form a unit cell, each of the neon (Ne), helium (He) or a mixture of neon and helium ( The main discharge gas such as Ne + He) and an inert gas containing a small amount of xenon are filled. When discharged by a high frequency voltage, the inert gas generates vacuum ultraviolet rays and emits phosphors formed between the partition walls to realize an image. Such a plasma display panel has been spotlighted as a next generation display device because of its thin and light configuration.

1 illustrates a structure of a general plasma display panel.

As shown in FIG. 1, a plasma display panel includes a front substrate in which a plurality of sustain electrode pairs formed by pairing a scan electrode 102 and a sustain electrode 103 are formed on a front glass 101, which is a display surface on which an image is displayed. The rear substrate 110 having the plurality of address electrodes 113 arranged to intersect the plurality of sustain electrode pairs on the back glass 111 forming the back surface 100 and the rear surface is coupled in parallel with a predetermined distance therebetween. .

The front substrate 100 may include a scan electrode 102 and a sustain electrode 103, that is, a transparent electrode a made of a transparent indium thin oxide (ITO) material for mutual discharge in one discharge cell and maintaining light emission of the cell. It is covered by one or more dielectric layers 104 which limit the discharge current of the scan electrode and the sustain electrode 103 provided with the bus electrode b made of a metal material and insulate the electrode pairs. A protective layer 105 in which magnesium oxide (MgO) is deposited is formed on the entire surface of the dielectric layer 104 to facilitate discharge conditions.

The rear substrate 110 is arranged in such a manner that a plurality of discharge spaces, that is, barrier ribs 112 of a stripe type (or well type) for forming discharge cells are maintained in parallel. In addition, a plurality of address electrodes 113 which perform address discharge to generate vacuum ultraviolet rays are arranged in parallel with the partition wall 112. On the upper side of the rear substrate 110, R, G, and B phosphors 114 which emit visible light for image display during address discharge are coated. A dielectric layer 115 is formed between the address electrode 113 and the phosphor 114 to protect the address electrode 113.

2 is a diagram illustrating a method of implementing an image of a conventional plasma display panel.

As shown in FIG. 2, the plasma display panel divides one frame period into a plurality of subfields having different discharge times, and emits the plasma display panel in a subfield period corresponding to a gray value of an input image signal. An image is implemented.

Each subfield is divided into a reset period for uniformly generating a discharge, an address period for selecting a discharge cell, and a sustain period for implementing gray scale according to the number of discharges. For example, when the image is to be displayed with 256 gray levels, the frame period (16.67 ms) corresponding to 1/60 second is divided into eight subfields.

In addition, each of the eight subfields is divided into a reset period, an address period, and a sustain period. Here, the sustain period is increased at the ratio of 2 ⁿ (n = 0,1,2,3,4,5,6,7) in each subfield. As described above, since the sustain period is changed in each subfield, gray levels of an image can be realized.

3 is a graph comparing luminance characteristics of a plasma display panel and a cathode ray tube.

As shown in FIG. 3, a cathode-ray tube and a liquid crystal display display a desired gray scale by controlling the displayed light in an analog manner with respect to an input video signal. It has a luminance characteristic of. In contrast, the plasma display panel modulates the number of light pulses using a matrix array of discharge cells that can be turned on and off, thereby expressing gray scale, and thus has a linear luminance characteristic.

The gray scale expression method of the plasma display panel is called a PWM (pulse width modulation) method. The luminance of the plasma display panel changes linearly with the number of pulses, but since the degree of perception of our vision is nonlinear, noise is generated when the gray scale is expressed in the low gray scale region. Therefore, in order to solve the above problem, the plasma display panel inversely gamma corrects the input image signal data as shown in FIG. 4.

4 is a graph illustrating inverse gamma correction in a conventional plasma display panel.

In Fig. 4, the target luminance is an ideal inverse gamma result to be corrected, and the actual luminance is a measured luminance value as a result after inverse gamma correction, and the plasma display panel luminance is a luminance value measured in the absence of inverse gamma correction. 3 or less is shown.

As shown in FIG. 4, the target luminance is expressed as luminance values having different gray levels of 61 to 0 to 60, respectively. In contrast, the actual luminance is expressed by only eight luminance values of 61 gray levels from 0 to 60. Therefore, when the inverse gamma correction is performed in the plasma display panel, sufficient gray scale expression cannot be expressed in a dark area, resulting in a contour noise in which images are aggregated.

In order to express the insufficient gray level of the plasma display panel, a half tone method such as a dithering method and an error diffusion method is conventionally used.

First, the dithering method will be described with reference to FIGS. 5A and 5B.

5A and 5B illustrate dithering methods of a conventional plasma display panel. 5A is a conventional 2x2 dither mask, and FIG. 5B is a dither mask pattern by a 2x2 dither mask.

As illustrated in FIGS. 5A and 5B, the dithering method is a method of determining whether a carry occurs by comparing a gray value of each pixel with a specific threshold value of the dither mask. In this case, the expression power of the insufficient gradation is enhanced by turning on the pixel in which the digitization has occurred and turning off the pixel in which the digitization has occurred.

In addition, the dithering method is a method that adds appropriate noise so that the pseudo contour is not visible. Conventionally, a three-dimensional dither mask pattern corresponding to a plurality of frames, a plurality of lines, and a plurality of columns of a plasma display panel is repeatedly used.

However, the dithering method has a problem in that dithering noise, which reduces image quality, occurs at a specific gray level. In addition, there is a problem that an error indicating how large or small than a threshold value is not considered at all when generating a lift.

An error diffusion method, which is another method, is described with reference to FIG. 6.

6 is a diagram illustrating an error diffusion method of a conventional plasma display panel.

As shown in FIG. 6, the error diffusion method is a method for spatially correcting an error that is discarded by causing an error generated when the corresponding pixel is quantized to affect adjacent pixels.

Here, the error diffusion method multiplies each error value generated in the image signals a, b, c, and d of adjacent pixels by a specific coefficient. Thereafter, error values obtained by multiplying the coefficients are added to the i value, and then quantized. Thereafter, the error value generated by the quantization is stored in the line memory again and repeated for every pixel.

On the other hand, in the error diffusion method, the error diffusion coefficient is set constant for neighboring pixels. In low gradation, an error diffusion pattern is generated due to a constant error diffusion coefficient repeated every line and every frame.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an image processing apparatus and method for a plasma display panel that can improve gray scale expression by improving the image processing apparatus and method for a plasma display panel.

Another object of the present invention is to provide an image processing apparatus and method for a plasma display panel capable of suppressing a specific pattern generated when expressing insufficient gray scale.

In addition, another object of the present invention is to provide an image processing apparatus and method for a plasma display panel that can ensure the reliability of gradation representation.

In order to achieve the above object, an image processing apparatus of a plasma display panel for processing an image signal of the present invention to implement an image, comprising: an inverse gamma correction unit for gamma correcting the image signal with pre-stored gamma data; When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal is less than or equal to a predetermined threshold, an error component of the image signal of the previous frame is added to the image signal of the current frame. A half toning unit for diffusing; And subfield mapping for mapping an image signal input from the half-toning unit to a subfield mapping table.

The half toning unit of the present invention includes a frame memory unit for storing the inverse gamma corrected image signal in units of frames; An error diffusion determining unit determining whether an error is diffused by comparing a difference between gray levels between a previous frame and a current frame of the video signal with the predetermined threshold; And an error diffusion execution unit for diffusing an error component of an image signal in time according to the information input from the error diffusion determination unit.

Error diffusion of the present invention is characterized in that it is made in units of pixels.

Error components of the video signal of the error-diffused current frame of the present invention are accumulated.

The present invention is characterized in that the accumulated error component is erased when the gradation value difference of the video signal exceeds the predetermined threshold.

The predetermined threshold of the present invention is characterized by one.

An image processing method of a plasma display panel for processing an image signal according to an embodiment of the present invention, comprising: an inverse gamma correction step of gamma correcting the image signal with pre-stored gamma data; When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal is less than or equal to a predetermined threshold, an error component of the image signal of the previous frame is added to the image signal of the current frame. Diffusion halftone step; And a subfield mapping step of mapping an image signal input from the halftoning step to a subfield mapping table.

The half toning step of the present invention includes a frame memory step of storing the inverse gamma corrected image signal in units of frames; An error spreading determining step of determining whether or not an error spreads by comparing a difference between gray levels of a previous frame and a current frame of the video signal with the predetermined threshold value; And an error diffusion step of diffusing an error component of an image signal in time according to the information input from the error diffusion determination step.

According to an aspect of the present invention, in order to increase the gradation expression power of the inverse gamma corrected image signal and to improve the gradation linearity, an error diffusion is performed, and a temporal error diffusion that accumulates and displays error components of an input image signal in units of frames Do this. In this case, the image signal having the gray level difference is erased so that the error of the previous frame is not affected by the error component of the previous frame. As a result, the gray scale expressing power can be increased, and specific patterns generated when the plasma display panel is driven can be removed.

Hereinafter, with reference to the accompanying drawings, a specific embodiment according to the present invention will be described.

7 is a block diagram schematically illustrating an image processing apparatus of a plasma display panel according to an embodiment of the present invention.

As illustrated in FIG. 7, an image processing apparatus of a plasma display panel according to an exemplary embodiment of the present invention may include an inverse gamma correction unit 710, a gain control unit 720, a half toning unit 730, and a subfield mapping unit ( 740.

The inverse gamma correction unit 710 gamma-corrects an input image signal through pre-stored gamma data, and linearly converts a displayed luminance value according to a gray value of the input image signal.

The gain controller 720 may be adjusted by a user or a set maker with respect to the red, green, and blue image signals corrected by the inverse gamma correction unit 710. Adjust the gain by red, green and blue by multiplying the gain values. At this time, the user or set maker may set the desired color temperature by the gain control unit 720. In one embodiment of the present invention further includes a gain control unit 720 for performing such a function.

The half toning unit 730 may improve the gradation expression power by finely adjusting the luminance value displayed according to the gradation value by diffusing an error component with respect to the image signal input from the gain control unit 720. Such a method is called an error diffusion method, and in addition to error diffusion, the lower toning unit may use the dithering method described with reference to FIGS. 5A and 5B.

In performing the error diffusion, the half-toning unit 730 according to an embodiment of the present invention has a threshold that is a difference between the gray level value of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal. When the value is less than or equal to the threshold, temporal error spreading is performed to spread the error component of the video signal of the previous frame to the video signal of the current frame. The description thereof will be described later in more detail.

The subfield mapping unit 740 maps the image signal input from the half toning unit 730 to a preset subfield mapping table.

The data sorter 750 sorts the spatially sorted subfield mapping data input from the subfield mapper 740 into temporal data.

The data driver 760 receives the data aligned in time by the data aligner 750, and supplies an address driving pulse to an address electrode (not shown) of the plasma display panel, thereby realizing an image of the plasma display panel. Here, the half toning unit according to an embodiment of the present invention will be described in detail with reference to FIG. 8.

8 is a block diagram illustrating an operation characteristic of a half toning unit according to an embodiment of the present invention.

As shown in FIG. 8, the half toning unit 800 according to an embodiment of the present invention includes a frame memory unit 810, an error diffusion determining unit 820, and an error diffusion performing unit 830.

The frame memory unit 810 stores the inverse gamma corrected image signal in units of lines. In addition, the frame memory unit 810 stores the gray scale value of the image signal which has been subjected to the error diffusion, and repeats it every pixel. In the exemplary embodiment of the present invention, the frame memory unit 810 is included in the half toning unit 800, but generally, the frame memory unit included in the plasma display panel may be used. That is, the frame memory unit may be located outside the half toning unit.

The error diffusion determining unit 820 obtains a difference between the gray level values of the image signal of the previous frame N-1 input from the frame memory unit 810 and the image signal of the current frame N input after the inverse gamma correction. Thereafter, the difference value of the grayscale value and a predetermined threshold value are compared to determine whether the error is spread.

The error spreading unit 830 spreads the error component of the image signal in time according to the information input from the error diffusion determining unit 820.

In an embodiment of the present invention, the gray level values of the image signals of the previous frame and the current frame are compared in pixel units, and error diffusion is performed.

At this time, error components of the video signal of the error-spread current frame are accumulated. That is, the error component of the previous frame N-1 is received from the current frame N to affect the current frame, and the error of the current frame is accumulated. By accumulating the error of the current frame affects the next frame (N + 1) again, it is possible to suppress the loss of the gradation representation due to the quantization of the image signal. Here, the difference between the gray level value of each of the previous frame and the current frame, the current frame, and the next frame must satisfy a predetermined threshold value or less.

When the difference in the gray value of the image signal according to an embodiment of the present invention exceeds a predetermined threshold, the accumulated error component is erased. That is, since the human eye accumulates light in time and feels its brightness, when the gray level difference of the image signal exceeds a predetermined threshold, diffusion of an error component adversely affects the implemented image. Therefore, in an exemplary embodiment of the present invention, when the gray value difference of the video signal exceeds a predetermined threshold value, the error component that accumulates is eliminated, so that the gray level value of the frame in which the gray value difference occurs is not affected.

At this time, the predetermined threshold value according to an embodiment of the present invention is characterized in that 1. After inverse gamma correction, the video signal has a gray value having an integer part and a fractional part. Accordingly, the image signal having a gradation difference greater than or equal to 1 does not perform error diffusion by a threshold value, and the image signal having a gradation difference less than or equal to 1 performs error diffusion by a threshold value.

As a result, it is possible to exclude an image signal of a frame adversely affected by the error spreading and to perform a more reliable error spreading.

The image processing method of the plasma display panel according to the exemplary embodiment of the present invention includes the following steps.

First, the video signal is gamma-corrected with pre-stored gamma data.

Subsequently, when the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal is less than or equal to a predetermined threshold, an error component of the image signal of the previous frame is spread to the image signal of the current frame. Let's do it.

Subsequently, subfield mapping is performed to map the half-toned video signal to a subfield mapping table.

At this time, the half-toning method is performed according to the following steps.

First, the inverse gamma corrected image signal is stored in units of frames.

Thereafter, the difference between the gray level value of the previous frame and the current frame of the image signal is compared with a predetermined threshold value to determine whether the error is spread.

Then, the error component of the video signal is spread in time according to the information input by the error diffusion determination.

At this time, error components of the video signal of the error-spread current frame are accumulated. In addition, when the gray value difference of the video signal exceeds a predetermined threshold, the accumulated error component is erased and initialized. The predetermined threshold value is one.

9 is a schematic diagram illustrating an error diffusion method according to an embodiment of the present invention. The operation of the block of FIG. 9 may be represented by Equations 1, 2, and 3 below.

9 and the parameters of Equations 1, 2 and 3 are defined as follows.

D is an error diffusion determining block that determines whether or not an error is spread.

Q is a quantization block that quantizes the inverse gamma corrected video signal.

Z is an error component delay block that delays the error components in time.

n represents the current frame.

n-1 represents the previous frame.

F (i, j) represents the input image signal after inverse gamma correction. In this case, i and j are coordinates representing pixel positions of the video signal.

B (i, j) is a video signal quantized by a Q block.

E (i, j) is the temporal error component of the video signal. That is, the quantization error component generated in the previous frame.

f (i, j) is the error spread video signal. That is, f (i, j) is an image signal obtained by accumulating an error component delayed by one frame through Z blocks in the previous frame to F (i, j) in the current frame.

Referring to FIG. 9 and Equation 1, Equation 2, and Equation 3, first, the error diffusion is performed by comparing the difference of gray values with a predetermined threshold value and determining whether or not the error spreads. In FIG. 9, it is determined whether an error spreads in the D block.

At this time, in one embodiment of the present invention, when the difference between the grayscale value of the previous frame and the current frame is less than or equal to a predetermined threshold, error diffusion is performed so that the f (i, j) value has the value shown in Equation (2).

In addition, when the difference between the gray level value of the previous frame and the current frame exceeds a predetermined threshold, the error component is erased and initialized, so that the f (i, j) value output from the D block is F (i) as shown in Equation 3 below. , j).

As a result, the gray scale expressing power can be increased, and a specific pattern generated during error diffusion can be suppressed.

As such, the technical configuration of the present invention described above can be understood by those skilled in the art that the present invention can be implemented in other specific forms without changing the technical spirit or essential features of the present invention.

Therefore, the above-described embodiments are to be understood as illustrative and not restrictive in all respects, and the scope of the present invention is indicated by the appended claims rather than the foregoing description, and the meanings of the claims and All changes or modifications derived from the scope and the equivalent concept should be construed as being included in the scope of the present invention.

As described above, the present invention improves the gray scale expression by improving the image processing apparatus and method of the plasma display panel.

In addition, the present invention has the effect of suppressing a specific pattern generated when expressing insufficient gradation.

In addition, the present invention has the effect of ensuring the reliability of the gradation representation.

Claims (12)

An image processing apparatus of a plasma display panel for processing an image signal to implement an image, An inverse gamma correction unit configured to gamma correct the image signal with pre-stored gamma data; When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal is less than or equal to a predetermined threshold, an error component of the image signal of the previous frame is added to the image signal of the current frame. A half toning unit for diffusing; And A subfield mapping unit for mapping an image signal input from the half toning unit to a subfield mapping table; An image processing apparatus of a plasma display panel comprising a. The method of claim 1, The half toning unit A frame memory unit for storing the inverse gamma corrected image signal in units of frames; An error diffusion determining unit determining whether an error is diffused by comparing a difference between gray levels between a previous frame and a current frame of the video signal with the predetermined threshold; And An error diffusion execution unit for diffusing an error component of an image signal in time according to the information input from the error diffusion determination unit; An image processing apparatus of a plasma display panel comprising a. The method according to claim 1 or 2, And the error diffusion is performed in pixel units. The method according to claim 1 or 2, And error components of the video signal of the error-diffused current frame are accumulated. The method of claim 4, wherein And the accumulated error component is erased when the gray value difference of the video signal exceeds the predetermined threshold value. The method according to claim 1 or 2, And said predetermined threshold is one. An image processing method of a plasma display panel for processing an image signal to implement an image, An inverse gamma correction step of gamma correcting the image signal with pre-stored gamma data; When the difference between the grayscale values of the previous frame N-1 and the current frame N of the inverse gamma corrected image signal is less than or equal to a predetermined threshold, an error component of the image signal of the previous frame is added to the image signal of the current frame. Diffusion halftone step; And A subfield mapping step of mapping an image signal input from the halftoning step to a subfield mapping table; Image processing method of a plasma display panel comprising a. The method of claim 7, wherein The half toning step A frame memory step of storing the inverse gamma corrected image signal in units of frames; An error spreading determining step of determining whether or not an error spreads by comparing a difference between gray levels of a previous frame and a current frame of the video signal with the predetermined threshold value; And An error diffusion step of diffusing an error component of an image signal in time according to information input from the error diffusion determination step; Image processing method of a plasma display panel comprising a. The method according to any one of claims 7 to 8, And the error diffusion is performed in pixel units. The method according to any one of claims 7 to 8, And error components of the video signal of the error-diffused current frame are accumulated. The method of claim 10, And the accumulated error component is erased when the gray value difference of the video signal exceeds the predetermined threshold. The method according to any one of claims 7 to 8, And said predetermined threshold is one.

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