KR100844817B1 - Plasma Display Apparatus and Image Processing Method thereof - Google Patents

Abstract

The present invention is a plasma display device and an image processing method thereof.

The plasma display device and the image processing method thereof according to the present invention detect an average brightness level of a video signal when mapping a weight of a subfield according to an average brightness level of an image signal input from the outside, and the subfield if the average brightness level is lower than a threshold value. The gray scale weight is adjusted to increase exponentially, and when the average brightness level is higher than the threshold, the gray scale weight of the subfield is adjusted to increase logarithmically.

Description

Plasma Display Apparatus and Image Processing Method {Plasma Display Apparatus and Image Processing Method}

1 is a diagram illustrating a method of implementing an image of a conventional plasma display apparatus.

2 is a diagram illustrating a mapping table of subfields according to a conventional grayscale.

3 is a view for explaining a plasma display device according to an embodiment of the present invention.

4 is a diagram for describing an operation characteristic of a subfield mapping memory unit according to an exemplary embodiment of the present invention.

5A to 5D are diagrams illustrating a subfield mapping table according to an embodiment of the present invention.

FIG. 6 is a graph showing gray scale weights for respective subfields at an average image level at which the video signal data has a low or high threshold according to an embodiment of the present invention.

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

110; A frame memory unit 130; Gamma Correction Unit

150; Halftone portion 170; APL detector

190; An SFM memory unit 210; Plasma Display Panel (PDP)

The present invention is a plasma display device and an image processing method thereof capable of reducing a luminance step of real gray.

In general, the plasma display apparatus includes a plasma display panel in which a partition wall formed between the front substrate and the rear substrate forms one unit cell and a driving unit for driving the plasma display panel. Each cell of the plasma display panel is filled with a main discharge gas such as neon (Ne), helium (He), or a mixture of neon and helium (Ne + He) and an inert gas containing a small amount of xenon. 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.

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 levels according to the number of discharges. For example, when displaying an image with 256 gray levels, a frame period (16.67 ms) corresponding to 1/60 second is divided into eight subfields by being given a weight.

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.

2 is a diagram illustrating a mapping table of subfields according to a conventional grayscale.

Referring to FIG. 2, the conventional subfield mapping table has a format in which the weight is small in the low order subfield SF1 and the weight is high in the high order subfield SF10.

Looking at the conventional subfield mapping table in detail, in general, as the grayscale value increases, the sum of the weights of all subfields increases proportionally, but any interval in which the grayscale value increases (for example, the grayscale value 15- -> 16, 21-> 22, 28-> 29, 36-> 37), the sum of the weights of the subfields increases rapidly, resulting in a luminance difference of real gray in the image where the actual image is reproduced. .

This phenomenon is caused by a further difference in the sum of the weights of the subfields in the high interval (36-> 37) where the gray value is increased than in the low interval (15-> 16) where the gray value is increased, resulting in a luminance step of the actual gray level. Appears badly.

Such real-tone luminance step generates halftone noise such as dither noise or error diffusion noise during image processing of externally input image data, and especially in video, pseudo contour This can cause (contour noise).

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma display device and an image processing method thereof capable of reducing halftone noise by compensating for steps between real grays.

Another object of the present invention is to provide a plasma display apparatus and an image processing method thereof capable of suppressing moving image pseudo contours in an image implemented when a plasma display panel is driven.

In order to achieve the above object, the plasma display device and the image processing method thereof according to an embodiment of the present invention, the average brightness level of the video signal when mapping the weight of the subfield according to the average brightness level of the video signal input from the outside If the average brightness level is lower than the threshold, the gray scale weight of the subfield is adjusted exponentially. If the average brightness level is higher than the threshold, the gray scale weight of the subfield is adjusted logarithmically. .

In the subfields corresponding to less than the threshold of the average brightness level (low APL), a weight step between neighboring subfield gradations corresponding to more than the gradation threshold (High gradation) is increased.

In the subfields corresponding to the threshold brightness level higher than the average brightness level (high APL), the weight step between neighboring subfield grayscales corresponding to the grayscale threshold value or higher (High grayscale) is reduced.

In the subfields corresponding to the threshold of the average brightness level (lower APL), the weight difference between neighboring subfields of the gray scale below the threshold (Low gradation) is reduced.

In the subfields corresponding to the threshold brightness level higher than the average brightness level (high APL), a weight step between neighboring subfield gray levels corresponding to the gray level threshold value or higher (low gray level) is increased.

The threshold of the average brightness level is preferably 10% of the maximum average brightness level.

The gray scale threshold of the subfield preferably has a gray scale value of the middle subfield substantially in the gray scale weight order of all the subfields.

In addition, the plasma display apparatus according to an embodiment of the present invention includes a frame memory unit for storing an image signal input from the outside, a gamma correction unit for gamma-correcting the image signal stored in the frame memory unit, and a gamma-corrected image signal in units of frames. An average brightness level detector (APL unit) for detecting the average brightness level, and a subfield mapping memory unit for adjusting the gray scale weight of the subfield according to the average brightness level, wherein the subfield mapping memory unit corresponds to the average brightness level It includes a plurality of subfield mapping table for adjusting the gray scale weight.

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

3 is a view for explaining a plasma display device according to an embodiment of the present invention.

As shown in FIG. 3, the plasma display apparatus according to the exemplary embodiment of the present invention includes a frame memory unit 110, a gamma adjusting unit 130, a halftone unit 150, an average image level (APL) detector 170, A subfield mapping (SFM) memory unit 190 is included.

The frame memory unit 110 stores R, G, and B image signals input from the outside in units of frames.

The gamma correction unit 130 gamma-corrects an image signal stored in units of frames. The plasma display device is characterized in that the luminance value actually displayed with respect to the gray value of the image signal forms a linear curve. On the other hand, since the luminance value of the image signal input from the outside has a gamma characteristic, in the exemplary embodiment of the present invention, the gamma correction unit 130 is provided to gamma-correct the external image signal, thereby providing a plasma display apparatus. The screen actually implemented has a linear luminance value with respect to the gray scale value.

The halftone unit 150 halftons the gamma corrected image signal. The gamma corrected video signal is reduced in gray scale expression in the signal processing. In order to compensate for this, in an embodiment of the present invention, the halftone unit 150 is provided to improve the reduced gray scale expressive power and to ensure gray scale linearity. Such half-toning methods include dithering and error diffusion methods. Use a dithering method and error diffusion method, or a combination of both.

An example of an error diffusion method divides an image signal data into integer and fractional parts, multiplies the fractional part by a coefficient such as Floyd-Steinberg, and spreads the error component to adjacent cells.

The average image level detector (APL detector) 170 detects average brightness per frame of the image signal data input from the gamma correction unit 130. In this case, the average image level detector 170 may detect the average brightness level by the predetermined threshold value. For example, when the average image level is set to 0 to 1023, when the average image level threshold is set to 1/3, the average image level detector 170 performs three steps (APL 1: 0) on the image signal data. ~ 341, APL 2: 342 ~ 682, APL 3: 683 ~ 1023) to detect the average image brightness leveled. The threshold value of the arbitrarily set average image level may vary depending on the discharge characteristics of the plasma display panel.

In this case, it is preferable that the threshold of the average brightness level is substantially 10% (APL: 0 to 102) of the maximum average brightness level.

The subfield mapping memory unit 190 adjusts the weight value according to the gray level of the subfield in response to the average image level of the video signal. In more detail, the subfield mapping memory unit 190 corresponds to the grayscale threshold of the subfield (for example, when the total grayscale value of the subfield is 256 grayscales) in response to the average image brightness leveled to an arbitrary threshold. If you set the threshold to 1/3 of the total gray level, any gray level threshold can be in the range of 0 to 86, 87 to 172, and 173 to 255.) The weight step between the gray levels is adjusted.

In this case, it is preferable that the gray scale threshold of the subfield has the gray scale values (87 to 172 gray scale values) of the intermediate subfield substantially in the gray weight order of all the subfields.

The subfield mapping memory 190 may independently adjust the weight according to the grayscale value of the subfield and the number of sustain pulses corresponding thereto, but may adjust the number of sustain pulses so as to correspond one-to-one with the weight according to the subfield grayscale value. have.

4 is a diagram for describing an operation characteristic of a subfield mapping memory unit according to an exemplary embodiment of the present invention.

As shown in FIG. 4, the subfield mapping memory unit 190 includes a sustain pulse setting table 191 and a subfield mapping table 193.

The sustain pulse setting table 191 is formed in plural, and each sustain pulse setting table corresponds to the average brightness values APL1, APL2, and APL3 leveled according to the average brightness threshold detected by the average image level detector 170. The number of sustain pulses can be set. Alternatively, the number of sustain pulses may be set corresponding to the gray scale weights of the subfields set in the plurality of subfield mapping tables 193 to be described later.

 The subfield mapping table 193 also includes a plurality of subfield mapping tables 193, and each subfield mapping table corresponds to average brightness values leveled according to the average brightness threshold detected by the average image level detector 170, so that the gray scale weights of the subfields are different. Is set.

The information set in the sustain pulse setting table and the subfield mapping table as described above is provided to a timing controller (not shown), and the timing controller controls the circuit that generates the sustain pulse in hardware to supply the sustain pulse to the plasma display panel. do.

5 (a) to 5 (d) are diagrams illustrating a subfield mapping table according to an embodiment of the present invention.

As illustrated, the subfield mapping table may have different gray level weights of the subfields corresponding to the average brightness values leveled according to the average brightness threshold.

That is, as shown in FIG. 5A, when the average image level threshold of the image signal data is low, for example, when the subfield mapping table has a range of 0 to 341 for a total of 0 to 1023 of the average image level, Hereinafter, a low average image level (low APL) threshold.) A range of 172 to 256 for a high gray level threshold value of the subfield corresponding to the low average image level, for example, a total gray level value 256 gray levels of the subfield. It can be set to have a weight step between neighboring gray scales in the range (hereinafter, referred to as a threshold of high sub-field gray scale (High gray scale)) larger than a step between gray scale weights of other video signal data,

As shown in FIG. 5B, when the average image level threshold of the image signal data is high, for example, when the subfield mapping table has a range of 683 to 1023 for a total of 0 to 1023 of the average image level, A high average image level (high APL) threshold is referred to as a high average image level (high APL) threshold. Can be set to be smaller than the step between gradation weights,

As shown in (c) of FIG. 5, the subfield mapping table has a low gray level threshold value, for example, a total gray level of a subfield, when the video signal data has a low average picture level threshold. When the value is in the range of 0 to 86 for 256 gray levels (hereinafter referred to as the threshold of low sub-field gray level), the weight step between neighboring gray levels is greater than the step between gray level weights of other video signal data. Can be set to be small,

Also, as shown in (d) of FIG. 5, the subfield mapping table includes neighboring grayscales in a low grayscale threshold range of a low subfield corresponding to the high averaged image level when the image signal data has a high average image level threshold. The weight step of the camera may be set to be larger than the step between the gray scale weights of the other video signal data.

The average image level thresholds of the video signal data and the gray level thresholds of the subfields described with reference to FIG. 5 are merely an example for understanding the present disclosure. That is, the average image level threshold of the image signal data or the gray level threshold of the subfield may be adjusted according to various characteristics such as discharge characteristics of the plasma display panel.

FIG. 6 is a graph showing gray scale weights for respective subfields at an average image level at which the video signal data has a low or high threshold according to an embodiment of the present invention.

As shown in (a) of FIG. 6, it can be seen that the subfield gray scale weight is exponentially increased at a low average image level of the image signal data. As shown in (b) of FIG. It can be seen that the subfield gray scale weight is increased logarithmically at a high average image level.

As described above, according to the present invention, by adjusting the subfield gray scale weight according to the average image level of the image signal data, the actual gray level difference of the image reproduced on the actual plasma display panel can be reduced, resulting in suppression of noise such as halftone or pseudo contour. can do.

On the other hand, the technical configuration of the present invention described above will 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 present invention improves the plasma display apparatus and the image processing method thereof, thereby reducing halftone noise by reducing a real gray level according to an image signal input from the outside.

In addition, the present invention has the effect of suppressing the moving image pseudo contour in the image to be implemented by improving the plasma display device and the image processing method thereof.

Claims (15)

A frame memory unit which stores an image signal input from the outside; A gamma correction unit configured to gamma correct an image signal stored in the frame memory unit; An average brightness level detector (APL unit) for detecting an average brightness level of the gamma-corrected video signal in units of frames; And A subfield mapping memory unit configured to adjust a gray scale weight of the subfield according to the average brightness level, When the average brightness level is lower than a threshold, the gray scale weight of the subfield increases exponentially, And when the average brightness level is higher than the threshold, the gray scale weight of the subfield increases logarithmically. The method of claim 1, And the subfield mapping memory unit includes a plurality of subfield mapping tables that adjust gray level weights of the subfields corresponding to the average brightness level. The method of claim 1, The subfield mapping memory unit And increasing a weight step between neighboring subfield gradations corresponding to a gradation threshold or higher (high gradation) in subfields corresponding to the threshold value of the average brightness level below (low APL). The method of claim 1, The subfield mapping memory unit And reducing a weight step between neighboring subfield gradations corresponding to a gradation threshold or higher (High gradation) in subfields corresponding to the threshold brightness level or higher (high APL) of the average brightness level. The method of claim 1, The subfield mapping memory unit And reducing a weight step between neighboring subfield grayscales corresponding to a gray scale threshold (low gray scale) in subfields corresponding to the threshold brightness level (low APL) below the average brightness level. The method of claim 1, The subfield mapping memory unit And increasing a weight step between neighboring subfield gradations corresponding to a gradation threshold or higher (Low gradation) in subfields corresponding to the threshold brightness level or higher (high APL) of the average brightness level. The method according to any one of claims 3 to 6, The threshold of the average brightness level is substantially 10% of the maximum average brightness level. The method according to any one of claims 3 to 6, And the gradation threshold of the subfield is a gradation value of the middle subfield substantially in the gradation weight order of all the subfields. In the image processing method of the plasma display device for mapping the weight of the subfield according to the average brightness level of the video signal input from the outside, Detecting an average brightness level of the video signal; And Adjusting the gray scale weight of the subfield according to the average image level, When the average brightness level is lower than a threshold, the gray scale weight of the subfield increases exponentially, And the gray scale weight of the subfield is increased logarithmically when the average brightness level is higher than the threshold value. The method of claim 9, The image processing of the plasma display apparatus, characterized by increasing the weight step between neighboring subfield gradations corresponding to the gradation threshold value or higher (High gradation) in subfields corresponding to the threshold value of the average brightness level below (low APL). Way. The method of claim 9, And reducing a weight step between neighboring subfield gradations corresponding to a gradation threshold or higher (High gradation) in subfields corresponding to the threshold brightness level or higher (high APL) of the average brightness level. The method of claim 9, Image processing of the plasma display apparatus characterized in that the weight difference between the subfields of the subfields corresponding to less than the threshold of the average brightness level (low APL) is less than the threshold of gray (Low gradation). Way. The method of claim 9, The image processing of the plasma display apparatus is characterized by increasing a weight step between neighboring subfield gradations corresponding to a gradation threshold or higher (Low gradation) in subfields corresponding to the threshold brightness level or higher (high APL). Way. The method according to any one of claims 10 to 13, And the threshold of the average brightness level is substantially 10% of the maximum average brightness level. The method according to any one of claims 10 to 13, And the gradation threshold of the subfield is substantially the gradation value of the intermediate subfield in the gradation weighting order of all the subfields.

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