KR20070073154A - Plasma display device and image processing method thereof - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device, and more particularly, to a plasma display device and an image processing method thereof capable of improving an image processing speed and improving a gradation expression power.

The plasma display apparatus according to the present invention includes an inverse gamma correction unit that inversely gamma corrects an image signal input from an external device, and a half that spreads an arbitrary predetermined error value between adjacent pixels on the same line among data of the inverse gamma corrected image signal. It includes a tonal part.

Description

Plasma Display Apparatus and Image Processing Method Thereof

1 is a view showing a method for implementing an image of a conventional plasma display device.

2A is a graph comparing luminance characteristics of a plasma display device and a cathode ray tube.

2B is a graph showing inverse gamma correction in a conventional plasma display device.

3A and 3B illustrate a dithering method of a conventional plasma display panel.

4A and 4B illustrate an error diffusion method of a conventional plasma display panel.

Fig. 5 shows an example of the plasma display device of the present invention.

6 is a diagram showing a first embodiment of an error diffusion method according to the present invention;

7 is a view for explaining the error diffusion method in accordance with the present invention in time.

8 is a view for explaining a second embodiment of the error diffusion method according to the present invention.

9 is a view for explaining a third embodiment of the error diffusion method according to the present invention.

10 is a view for explaining a fourth embodiment of the error diffusion method according to the present invention;

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

500: reverse gamma correction unit 510: gain control unit

520: halftone unit 530: subfield mapping unit

540: APL calculation unit 550: sustain number control unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device, and more particularly, to a plasma display device and an image processing method thereof capable of improving an image processing speed and improving gray scale expression.

In general, a plasma display panel is a partition wall formed between a front panel and a rear panel to form a unit discharge cell, and each cell includes neon (Ne), helium (He), or a mixture of neon and helium (Ne + He). An inert gas containing a main discharge gas such as and a small amount of xenon is filled. A plurality of unit discharge cells described above are gathered to form one pixel. For example, a red (R) cell, a green (G) cell, and a blue (B) cell may form one pixel. When a high frequency voltage is applied to such a unit discharge cell to discharge, an inert gas generates vacuum ultra violet rays and emits phosphors formed between the partition walls to realize an image. Such a plasma display panel has a spotlight as a next generation display device because of its thin and light configuration.

1 is a view showing a method for implementing an image of a conventional plasma display device.

As shown in FIG. 1, the plasma display apparatus divides one frame period into a plurality of subfields having different discharge times, and emits a 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 a rate of 2n (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.

The brightness characteristics of the plasma display according to this are as shown in FIG. 2B.

2A is a graph comparing luminance characteristics of a plasma display device and a cathode ray tube.

As shown in FIG. 2A, a cathode-ray tube (CRT) and a liquid crystal display (LCD) express a desired gray level by controlling the displayed light in an analog manner with respect to an input video signal. , Typically has nonlinear luminance characteristics. In contrast, since the plasma display device expresses gray scales by modulating the number of light pulses using a matrix array of discharge cells that can be turned on / off, the plasma display apparatus has a linear luminance characteristic. The gray scale expression method of the plasma display device is called a PWM (Pulse Width Modulation) method.

In this case, the display device, such as a cathode ray tube (CRT), because the brightness characteristics compared to the display current is proportional to 2.2 multipliers, the input external video signal such as a broadcast signal transmits a signal corresponding to the inverse of the 2.2 multiplier. Therefore, the plasma display apparatus having the linear brightness characteristic needs to perform inverse gamma correction on an image signal input from the outside. This inverse gamma correction will be described with reference to FIG. 2B.

2B is a graph illustrating inverse gamma correction in a conventional plasma display apparatus.

In FIG. 2B, the target luminance represents an ideal inverse gamma result to be corrected, the actual luminance is a measured luminance value as a result after the inverse gamma correction, and the PDP luminance is less than or equal to the measured luminance value 3 in the absence of inverse gamma correction. It is shown.

 As shown in FIG. 2B, the target luminance is expressed as luminance values having different levels of 61 gray levels from '0' to '60'. 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 apparatus, there is a problem in that it is impossible to express enough gray scales in a dark area, thereby generating a contour noise in which images are aggregated.

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

First, the dithering method will be described with reference to FIG. 3.

3A and 3B illustrate dithering methods of a conventional plasma display panel. 3A is a conventional 2 × 2 dither mask, and FIG. 3B is a dither mask pattern by a 2 × 2 dither mask.

As shown in FIGS. 3A and 3B, 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 310. . At this time, it is intended to increase the gray scale expression power that is insufficient by turning on the off-pixel and turning off the off-pixel. In addition, the dithering method is a method that adds an 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 PDP has been repeatedly used.

However, the dithering method has a problem in that dither patterns are visible for still images or regions having a uniform value. In addition, there is a problem that an error indicating how large or less than a threshold value is not considered at all when generating a digitization.

An error diffusion method, which is another method, is described with reference to FIG. 4.

4A and 4B illustrate an error diffusion method of a conventional plasma display panel. 4A is a diagram for describing a conventional spatial error diffusion method, and FIG. 4B is a block diagram for performing the error diffusion of FIG. 4A.

As shown in FIG. 4A, 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 neighboring pixels.

Here, the error diffusion method multiplies each error value generated in neighboring pixels, that is, three pixels (a, b, c) of the previous line and the immediately adjacent pixel (d) by a specific coefficient. Subsequently, error values obtained by multiplying the coefficients are added to the center cell (i) and then quantized.

Thereafter, the error value generated by the quantization is stored in the line memory again and repeated for every pixel.

As shown in FIG. 4B, the error diffusion block maps and outputs the luminance value closest to the target luminance by repeatedly performing a spatial feedback routine.

In addition, in FIG. 4B, the operation may be expressed by Equations 1 and 2 below.

Here, the parameters of Equation 1, Equation 2 and FIG. 4B are defined as follows.

n represents the current frame.

F (i, j) is a gray level value input after the inverse gamma correction.

Q block is a quantization block.

B (i, j) is the quantized grayscale value.

E (i, j) is the error that occurs in quantization.

f (i, j) is a value obtained by adding a quantization error value to an input grayscale value after inverse gamma correction.

That is, f (i, j) is a value obtained by multiplying the error value of the pixel neighboring F (i, j) in the current frame by the error diffusion coefficient h (i, j) in the H block.

However, this error diffusion method is difficult in time. For example, spreading the error of the pixel d immediately adjacent to the center cell i causes a problem that is difficult to implement in hardware.

In other words, in processing data in the order of incoming data, all the above steps are done in hardware because the error of the pixel immediately after the calculation of the error of the next pixel is finished should be used in the error calculation of the current pixel. It becomes difficult to perform in the clock.

Moreover, the temporal problem of error diffusion is intensified in integer error diffusion and multichannel mode. This not only causes the problem of error diffusion, but also causes the screen to break.

SUMMARY OF THE INVENTION In order to solve such a problem, an object of the present invention is to provide a plasma display device and an image processing method thereof capable of improving the speed of image processing.

Further, another object of the present invention is to provide a plasma display device and an image processing method thereof capable of improving gray scale expression.

The technical problem of the present invention is not limited to the above-mentioned thing, and another technical problem to be achieved by the present invention will be clearly understood by those skilled in the art by the effect of the configuration of the present invention.

The plasma display device according to the present invention for achieving the above object is a predetermined gamma correction unit between the inverse gamma correction unit for performing an inverse gamma correction of the image signal input from the outside and the adjacent pixels of the same line among the data of the inverse gamma corrected image signal It includes a halftone portion for diffusing the error value of.

In addition, the error value is characterized in that "0".

In addition, the error value is characterized in that the random.

In addition, the halftone unit is characterized in that the integer error diffusion.

In addition, the plasma display apparatus uses a multi-channel mode in which image signal data corresponding to at least two or more neighboring pixels are divided into at least two channels, and the channels are synchronized with one clock signal and output. Shall be.

The halftone unit may be configured to diffuse an error value of a previous line into a pixel of a current line.

The halftone unit may spread an error value of at least two pixels before pixels of the same line to pixels of the current line.

The plasma display apparatus according to the present invention for achieving the above object does not spread the error between adjacent pixels on the same line among the inverse gamma correction unit for inverse gamma correction of the image signal input from the outside and the data of the inverse gamma corrected image signal It does not include a halftone portion.

The image processing method of the plasma display apparatus according to the present invention for achieving the above object is an inverse gamma correction step of inverse gamma correction of an image signal input from the outside and adjacent pixels of the same line among the data of the inverse gamma corrected image signal. The liver includes a halftone step of spreading a predetermined random error value.

In addition, the error value is characterized in that "0".

In addition, the error value is characterized in that the random.

In addition, it is characterized in that the integer error diffusion in the halftone step.

In addition, in the image processing method of the plasma display apparatus, a multi-channel mode is used in which image signal data corresponding to at least two or more neighboring pixels are divided into at least two channels, and the channels are synchronized with one clock signal and output. Characterized in that.

In addition, in the halftone step, the error value of the previous line is diffused to the pixel of the current line.

In addition, in the halftone step, an error value of at least two pixels before the pixels of the same line is diffused to the pixels of the current line.

The image processing method of the plasma display apparatus according to the present invention for achieving the above object is an inverse gamma correction step of inverse gamma correction of an image signal input from the outside and adjacent pixels of the same line among the data of the inverse gamma corrected image signal. The liver includes a halftone step of error diffusion.

Hereinafter, with reference to the accompanying drawings will be described in more detail the configuration of the plasma display panel according to the present invention.

5 is a view showing an example of the plasma display device of the present invention.

As shown in FIG. 5, the plasma display apparatus according to an exemplary embodiment of the present invention includes an inverse gamma correction unit 500, a gain control unit 510, a halftone unit 520, a subfield mapping unit 530, and an APL ( An average picture level calculator 540, a sustain pulse number controller 550, and a plasma display panel 560.

The inverse gamma correction unit 500 linearly converts the displayed luminance value by correcting the output gray value according to the gray value of the image signal input through the prestored gamma data.

The gain controller 510 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 500. Adjust the gain by red, green and blue by multiplying the gain values. In this case, the gain controller 510 may set a color temperature desired by the user or the set maker.

The halftone unit 520 quantizes an image signal input from the gain control unit 510 and diffuses an error component generated therein into adjacent pixels, thereby finely adjusting the luminance value displayed according to the gray scale value to adjust the gray scale expression power. Improve. Such a method is referred to as an error diffusion method, and in addition, the halftone unit 520 may be half-toned by using a dithering method through a dither mask.

Here, the halftone unit 520 according to the present invention may improve the speed of error diffusion by diffusing an arbitrary error value that is not preset or spreading a predetermined error value between adjacent pixels of the same line, differently from the conventional art. It will be described in detail below 6.

The subfield mapping unit 530 maps and outputs the video signal input from the halftone unit 520 to a preset subfield mapping table. Subsequently, the data alignment unit (not shown) aligns the data mapped by the subfield mapping unit 530 into temporal data and supplies the data to the plasma display panel 560 through a driving device to implement an image.

The APL calculator 540 calculates an average picture level (APL) value for one frame of an externally input image signal. The weight of the sustain pulse number, that is, the luminance value for one frame is determined according to the calculated APL value. Information of the APL value is provided to the sustain pulse number control unit 550, and the sustain pulse number control unit 550 adjusts the sustain number of the entire screen every frame to maintain constant power consumption at all times.

Herein, the function and effect of the halftone part having the features of the present invention will be described in more detail.

6 is a diagram illustrating a first embodiment of an error diffusion method according to the present invention.

As shown in FIG. 6, the error diffusion method according to the embodiment of the present invention is different from the conventional method, and does not perform error diffusion between adjacent pixels on the same line. That is, when the error of adjacent cells is diffused to the center cell i, the error of the next pixel among the cells of the same line is not diffused. For example, error diffusion may be performed by adding one more pixel d of the previous line instead of the error value of the pixel next to the current line.

That is, by multiplying the error values generated in the four pixels (a, b, c, d) of the previous line by the predetermined coefficients, these values are added to the center cell (i), and then quantized, and the error spreads to the next cell again. To do it. There is an effect that the speed of image processing can be improved by not diffusing the error of the immediately adjacent pixel, as shown in FIG.

7 is a view for explaining the error diffusion method according to the present invention in time.

As shown in FIG. 7, error diffusion processes data in the order in which the pixels enter. That is, the calculation of the error may be performed according to the clock signal Clock.

For example, the error corresponding to the unit pixel by calculating an error (eg, Error1 * 7/16) of adjacent pixels with respect to the center pixel and calculating their sum (eg, Error Sum2) in accordance with one clock signal as shown in FIG. 7. A diffusion step can be performed.

However, in order to calculate Error Sum3 when calculating the error for each center cell, previous data, that is, the calculation of Error2, must be pre-arranged. Again, in order to calculate Error Sum4, previous data, that is, the calculation of Error3, should be calculated in advance.

As described above, the error diffusion method according to the embodiment of the present invention can solve the time delay problem caused by the sequential calculation as described above by not error diffusion the next pixel.

The present invention is not limited to the above-described first embodiment, but can be variously implemented. The second embodiment will be described with reference to FIG. 8.

8 is a view for explaining a second embodiment of the error diffusion method according to the present invention.

As shown in FIG. 8, the error diffusion method according to the second embodiment of the present invention is characterized in that error diffusion is not performed between adjacent pixels on the same line. That is, when the error of adjacent cells is diffused to the center cell i, the error of the next pixel among the cells of the same line is not diffused. For example, the error diffusion may be performed by adding one more pixel (a) before at least two pixels among the pixels on the same line instead of the error value of the pixel immediately adjacent to the current line.

That is, by multiplying the error value generated in the three pixels (b, c, d) of the previous line by the pixel (a) at least two pixels before the same line, and adding these values to the center cell (i), Quantization is performed to allow error diffusion to the next cell. In this way, the error diffusion method can be used without the error diffusion of the immediately adjacent pixel, thereby improving the speed of image processing. In addition, since the error diffusion method is not limited in time, the hardware can be easily implemented in hardware, thereby contributing more to the precision of image processing.

On the other hand, the error diffusion method of the present invention can be more usefully used in integer error diffusion and multi-channel mode, for example, the hardware implementation of error diffusion is more difficult. That is, the present invention, for example, improves the speed of error diffusion to enable unit error diffusion in one clock signal during integer error diffusion.

In another example, an error diffusion method is possible in a multi-channel mode in which image signal data corresponding to at least two or more neighboring pixels are divided into at least two channels, and the channels are synchronized with one clock signal and output. An embodiment thereof will be described with reference to FIG. 9.

9 is a view for explaining a third embodiment of the error diffusion method according to the present invention.

9A is a diagram illustrating a method of error diffusion by distinguishing each channel in a two-channel mode, and FIG. 9B is a diagram illustrating a method of error diffusion without distinguishing each channel in a two-channel mode.

As shown in FIG. 9A, the error diffusion method according to the third embodiment of the present invention can prevent the error diffusion between adjacent pixels of the same line from the conventional method. The error value can be set to "0".

It is also possible to set the coefficient C4 of the pixel immediately next to the center pixel of the same line to "0" so as not to spread the error.

That is, when the error of adjacent cells is diffused to the center cell (i), the error of the next pixel among the cells of the same line is not spread so that the speed of error diffusion is improved. It can be implemented.

In this case, the error diffusion in the two channel mode may be performed by dividing the pixel into which each data is input for each channel as shown in FIG. 9A, and processing may be performed without distinguishing the channel as shown in FIG. 9B. Can be.

That is, in 9a, data can be supplied by dividing each channel, that is, a discharge cell into a channel consisting of a cells and c cells, and a channel consisting of b cells and d cells, for example. In this case, error diffusion may be performed for each channel. For example, a channel consisting of a and c cells is as follows.

That is, the coefficients (C1, C2, C3) defined for the error value generated at the three pixels (a2, a3, a4) of the previous line among the pixels of the same channel consisting of a cell and c cell with c3 as the center pixel (i). Multiply these values by adding them to the center cell (i), and then quantize the cells to allow error diffusion to the next cell. Here, the pixel c2 immediately adjacent to the same channel may set the coefficient C4 to “0” so as not to substantially spread an error.

In addition, other values may be applied to the coefficients C1, C2, and C3 of the previous line, for example, using information stored in one or more tables, for example, APL or error level.

In addition, in the exemplary embodiment of the present invention, an error application direction is illustrated from the upper line to the lower line, but the diffusion of the error line from the lower line to the upper line may be applied using, for example, a memory control block.

On the other hand, by using the error diffusion method of the present invention, in the multi-channel mode as shown in Figure 9b it is possible to spread the error without distinguishing the channel in particular.

That is, as shown in FIG. 9B, with d2 as the center pixel i and multiplying the error values generated at three adjacent pixels a2, b2 and a3 of the previous line without distinguishing the channel, the predetermined coefficients C1, C2 and C3 are multiplied. These values are added to the center cell (i) and then quantized to allow error diffusion to the next cell. Here, the pixel c2 immediately adjacent to the same line may set the coefficient C4 to "0" so as not to substantially spread an error.

As described above, according to another exemplary embodiment of the present invention, which does not diffuse the error of the pixel immediately adjacent to the same line or improves the speed of error diffusion by spreading a predetermined random error value, randomly sets an error value applied between adjacent pixels. The error diffusion is as follows.

10 is a view for explaining a fourth embodiment of the error diffusion method according to the present invention.

FIG. 10A is a diagram illustrating a method of error diffusion by distinguishing each channel in a two channel mode, and FIG. 10B is a diagram illustrating a method of error diffusion without distinguishing each channel in a two channel mode.

As shown in FIG. 10A, the error diffusion method according to the fourth embodiment of the present invention performs error diffusion between adjacent pixels on the same line differently from the conventional method, and randomly sets an applied error value regardless of the memory unit. It can solve the time problem that occurs during error diffusion.

In addition, it is also possible to randomly set the coefficient C4 of the pixel immediately next to the center pixel of the same line to spread the error.

That is, when the error of adjacent cells is diffused to the center cell (i), the error value of the next pixel among the cells of the same line is diffused to a random value (C4) to improve the speed of error diffusion and to increase the integer error. The channel mode, for example, can be implemented in the two-channel mode as shown in FIG. 10A.

As described above, the error diffusion in the two-channel mode may be performed by dividing an error diffusion by dividing the pixel into which each data is input for each channel as shown in FIG. 10A. As shown in FIG. You can make it possible.

That is, in 10a, data may be supplied for each channel, that is, for example, by dividing the discharge cells into channels consisting of a cells and c cells and channels consisting of b cells and d cells. At this time, channel error error diffusion can be performed. For example, a channel consisting of a and c cells is as follows.

That is, the coefficients (C1, C2, C3) defined for the error value generated at the three pixels (a2, a3, a4) of the previous line among the pixels of the same channel consisting of cells a and c, with c3 as the center pixel (i). Multiply these values by adding them to the center cell (i), and then quantize the cells to allow error diffusion to the next cell. Here, the pixel c2 immediately adjacent to the same channel may randomly set the coefficient C4 so that the error diffusion rate is not substantially delayed. In addition, a random error diffusion pixel may be set to a3 cell and c2 cell to facilitate implementation in hardware, or may be variously implemented.

In addition, other values may be applied to the coefficients C1, C2, and C3 of the previous line, for example, using information stored in one or more tables, for example, APL or error level.

In addition, in the exemplary embodiment of the present invention, an error application direction is illustrated from the upper line to the lower line, but the diffusion of the error line from the lower line to the upper line may be applied using, for example, a memory control block.

On the other hand, by using the error diffusion method of the present invention, as shown in FIG.

That is, as shown in FIG. 10B, with d2 as the center pixel i and multiplying the error values generated at three adjacent pixels a2, b2, and a3 of the previous line without distinguishing the channel, the coefficients C1, C2, and C3 are determined. These values are added to the center cell (i) and then quantized to allow error diffusion to the next cell. Here, the pixel c2 immediately adjacent to the same line may randomly set the coefficient C4 so that the error diffusion rate is not substantially delayed.

As such, the present invention can improve the error diffusion speed to solve the speed problem occurring in hardware implementation. In addition, it is possible to prevent the pattern noise by performing variously, such as random error diffusion.

In addition, since the accuracy of error diffusion can be improved, there is an effect that the gray scale expression power is improved.

Such a configuration of the present invention is not limited to the above embodiment. In other words, if the configuration can be prevented from being temporally bound by the error value of the immediately adjacent pixel, it is considered to be included in the present invention.

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 exemplary embodiments described above are to be understood as illustrative and not restrictive in all aspects, and the scope of the present invention is indicated by the following claims rather than the detailed description, and the meaning and scope of the claims and All changes or modifications derived from the equivalent concept should be interpreted as being included in the scope of the present invention.

As described above, the plasma display device and the image processing method thereof of the present invention have the effect of improving the speed of image processing.

In addition, the plasma display device and the image processing method thereof of the present invention have the effect of preventing the pattern noise appearing on the screen.

In addition, the plasma display device and the image processing method thereof of the present invention have an effect of improving the gray scale expression power.

In addition, the plasma display device and the image processing method thereof of the present invention have the effect of increasing the accuracy of error diffusion.

Claims (8)

An inverse gamma correction unit configured to inversely gamma correct an image signal input from the outside; And A halftone unit configured to diffuse an arbitrary predetermined error value between adjacent pixels of the same line among data of the inverse gamma corrected image signal; Plasma display device comprising a. The method of claim 1, And the error value is "0". The method of claim 1, And the error value is random. The method of claim 1, And the halftone unit is an integer error diffusion. The method of claim 1, The plasma display apparatus uses a multi-channel mode in which image signal data corresponding to at least two or more neighboring pixels are divided into at least two channels, and the channels are synchronized with one clock signal and output. Display device. The method of claim 2, And the halftone unit diffuses the error value of the previous line to the pixels of the current line. The method of claim 2, And the halftone unit spreads an error value of at least two pixels before pixels of the same line to pixels of the current line. An inverse gamma correction unit configured to inversely gamma correct an image signal input from the outside; And A halftone unit which does not spread an error between adjacent pixels of the same line among data of the inverse gamma corrected image signal; Plasma display device comprising a.

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