KR100639033B1 - Subfield Mapping Apparatus and Method for Reducing Halftone Noise - Google Patents

Abstract

The present invention relates to a subfield mapping apparatus and method for reducing halftone noise, comprising: checking subfield mapping data when noise is present when a plasma display panel is driven; If there is a mapping section having a large difference in weighted sums in adjacent mapping sections of the subfield mapping data, the method includes inserting mapping data capable of reducing the difference in weighted sums between mapping sections having a large difference in weighted sums. .

Accordingly, in the present invention, by inserting mapping data that can reduce the difference in weighted sums into a mapping section having a large difference in weighted sums, halftone noise can be reduced by reducing real grayscale differences, thereby improving image quality of the plasma display panel. It works.

Halftone, noise, subfield, mapping, weighting, sum

Description

Apparatus and method of subfield mapping for decreasing halftone noise}

1 is a perspective view showing a discharge cell of a three-electrode AC surface discharge type PDP;

2 is a block diagram of a driving apparatus of a general plasma display panel.

3 is a block diagram of a plasma display panel driving apparatus according to the present invention;

4 is a flowchart of a subfield mapping method capable of reducing halftone noise according to the present invention.

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

10,20: first and second reverse gamma adjustment unit 11: gain adjustment unit

12: error diffusion unit 13 subfield mapping unit

14: data alignment unit 21: APL calculation unit

22: timing controller 30: display and selection unit

31: memory

The present invention relates to a subfield mapping apparatus for reducing halftone noise. More particularly, the present invention relates to a subfield mapping apparatus for reducing halftone noise. More particularly, the present invention relates to a subfield mapping apparatus. The present invention relates to a subfield mapping apparatus and method for reducing halftone noise that can reduce noise and improve image quality of a plasma display panel.

In general, a plasma display panel (hereinafter referred to as a 'PDP') displays an image using visible light generated from a phosphor when ultraviolet rays generated by gas discharge excite the phosphor.

The PDP is thinner and lighter than the cathode ray tube (CRT), which has been mainly used for display means, and has the advantage of enabling high definition / large screen.

1 is a perspective view showing a discharge cell of a three-electrode alternating surface discharge type PDP, wherein the discharge cell of the three-electrode alternating surface discharge type PDP includes a scan electrode 12Y and a sustain electrode 12Z formed on the upper substrate 10, and a lower portion thereof. An address electrode 20X formed on the substrate 18 is provided.

The upper dielectric layer 14 and the passivation layer 16 are stacked on the upper substrate 10 having the scan electrode 12Y and the sustain electrode 12Z side by side.

Wall charges generated during plasma discharge are accumulated in the upper dielectric layer 14.

In addition, 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 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 electrode 12Y and the sustain electrode 12Z.

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.

In addition, the phosphor 26 is excited by ultraviolet rays generated during plasma discharge to generate visible light of any one of red, green, and blue.

Inert gas for gas discharge is injected into the discharge space provided between the upper and lower plates and the partition wall.

The cell of the plasma display panel having such a structure is selected by the counter discharge between the address electrode 20X and the scan electrode 12Y, and then sustains the discharge by the surface discharge between the sustain electrode pairs 12Y and 12Z.

In the cell of the plasma display panel, the fluorescent material 26 emits light by ultraviolet rays generated during sustain discharge, so that visible light is emitted outside the cell.

As a result, the plasma display panel having the cells displays an image.

In this case, the plasma display panel adjusts the discharge sustain period of the cell, that is, the number of sustain discharges, according to the video data, thereby implementing gray scale for displaying an image.

On the other hand, the address is performed in units of subfields to express each subfield on or off.

2 is a block diagram of a driving apparatus of a general plasma display panel, wherein the driving apparatus 100 of the plasma display panel includes a gain adjusting unit 11 connected between the first inverse gamma adjusting unit 10 and the data arranging unit 14; An error diffusion unit 12 and a subfield mapping unit 13 are provided, and an APL (Average Picture Level) calculation unit 21 is provided between the second inverse gamma adjustment unit 20 and the timing controller 22.

The first and second inverse gamma correction units 10 and 20 perform inverse gamma correction on digital video data RGB from an input line to linearly convert luminance of a gray level of an image signal.

The gain adjusting unit 11 adjusts the gain of the digital video data RGB corrected by the first inverse gamma correction unit 10 by the effective gain.

In addition, the error diffusion unit 12 finely adjusts the luminance value by diffusing the quantization error of the digital video data RGB input from the gain adjustment unit 11 to adjacent cells.

To this end, the error diffusion unit 12 divides the data into integer and fractional parts, and multiplies the fractional part by Floid-Steinberg coefficients.

The subfield mapping unit 13 maps the data input from the error diffusion unit 12 to a prestored subfield pattern and supplies the mapping data to the data alignment unit 14.

In addition, the data aligning unit 14 supplies the digital video data input from the subfield mapping unit 13 to the data driver 110 of the PDP.

The data driver 110 is connected to the data electrodes of the PDP to latch data input from the data alignment unit 14 by one horizontal line, and then supply the latched data to the data electrodes of the PDP in units of one horizontal period. do.

Meanwhile, the APL calculator 21 detects an APL on a frame basis with respect to the digital video data RGB input from the second inverse gamma correction unit 20 and determines the number of sustain pulses corresponding to the detected APL. Will output a signal for

The timing controller 22 receives a signal from the APL calculator 21 and generates a control signal for controlling the data driver, the scan / sustain driver, and the common sustain driver of the PDP.

The driving apparatus of the plasma display panel performs time division driving by dividing one frame into several subfields having different emission counts in order to realize gray levels of an image.

That is, the number of sustains is distributed to each subfield according to a certain principle, and then the gray level is expressed by the sum of the number of sustains of the subfields turned on by turning on and off each subfield.

Subfield mapping to express 0 to 255 gradations has a myriad of methods depending on the number of subfields used and the number of real gradations.

For example, when 12 subfields are used, a total of 212 mappings are possible, and the final subfield mapping is completed by drawing mappings corresponding to the actual tone numbers according to the desired actual tone numbers among the mappings.

In general, the more the number of subfields is used within the range that satisfies the timing margin, the better the image quality of the plasma display panel.

However, if the number of real gradations is large, false contour noise is generated, and if less, halftone noise is generated, a compensation problem occurs.

On the other hand, the plasma display module (Module) has a gray scale expressing power capable of expressing a gray level of 8 to 10 bits each of R, G, and B, and expresses 28 to 210 gray levels of each of R, G, and B.

However, in order to express 28 to 210 gray scales, a plasma display module control technology capable of controlling 28 to 210 gray scales is required.

Theoretically enough, but due to problems such as increased memory size, it actually uses halftone technology to produce 28 to 210 gradations.

There are a myriad of methods for halftones and related technologies, each with different advantages and disadvantages.

There are three typical techniques for halftones described later.

First is patterning. In this technique, patterns that are typically used are generated repeatedly, one cell is set at a constant brightness level, and a setting is performed at all higher brightness levels.

Second, an error diffusion technique is a technique for representing a color image or a black and white image with a smaller amount of bits / pixels.

That is, a technique of estimating one value, calculating an error between the actual value and the estimated value, and distributing it to neighboring pixels.

Third is the dithering technique.

By thresholding one image with one dither matrix, an output dot corresponding thereto is generated wherever the image pixel is larger than the value of the dither matrix.

The gray level described above is expressed as the sum of the number of sustains of subfields that are turned on by distributing the number of sustains to each subfield according to a certain principle, and then turning each subfield on and off.

Table 1 below shows an example of subfield mapping.

In Table 1, the gray level is expressed according to the value size of the portion indicated by the sum of the rightmost weights of the subfield mappings.

For example, in the case of expressing 28 gray levels, 28 gray level mapping is required to express all of them as real grays.

However, when the halftone technique is used, 256 gray levels can be represented with 62 real gray numbers smaller than 256 as shown below.

62 are represented as actual gray scales, and the remaining 256 to 62 = 194 gray scales can be generated using the halftone technique based on 62 real gray scales.

In general, when a large number of real tones are used in the subfield mapping, the degree of dependency on halftones is reduced, and thus, the halftone noise of each halftone technique is also reduced.

However, when a lot of real gradations are used, a problem arises in that a large number of false contours occur.

Therefore, subfield mapping according to the actual number of real numbers is necessary.

In the case of subfield mapping, the number of real gradations is determined through appropriate compensation between false contour and halftone noise.

Appropriate compensation standards can be different for each person and company, and the appropriate number of real gradations is determined by which weight is added.

Table 1 shows an example of using 62 real gray scales, and using 62 halftones produces 256 gray scales (of course, more than 256 gray scales can be expressed).

At this time, when the number of actual gray scales is determined, optimal subfield mapping is performed accordingly.

After the subfield mapping for the image quality optimization is completed, it is possible to confirm whether 256 (or more) gray scales are well represented by using a pattern generator.

At this time, 62 of the gradations from 0 to 255 are real gradations, so they can be expressed clearly.

However, since the remaining 194 are grayscales produced by the halftone technique, the unique halftone noise generated by the halftone technique used is generated.

For example, when a dither technique is used, dither noise due to a dither mask is generated.

Dither noise occurs at the part where the real tone difference is large.

When subfield mapping is performed, subfield mapping is performed to prevent a large gap between real gray scales, and halftone noise may be severely generated even by a relatively small gray scale difference.

At this time, in the case of a dither mask, the mask used by the gray level is different, but when the dither mask is very irregularly turned on and off, dither noise appears severely in the gray level using the mask.

Of course, when manufacturing a dither mask, this is taken into consideration and optimized, but dither noise will be severe in QA test environments such as low and high temperatures.

In order to solve the problems described above, by inserting mapping data that can reduce the difference in weighted sum in a mapping section having a large difference in weighted sum, the halftone noise can be reduced by reducing the real grayscale difference so that the plasma display can be reduced. An object of the present invention is to provide a subfield mapping apparatus and method for reducing halftone noise, which can improve the image quality of a panel.

A preferred aspect for achieving the objects of the present invention described above is a look up table by mapping the digital video data RGB with inverse gamma corrected and gain-adjusted to subfield patterns. A subfield mapping unit for generating subfield mapping data and outputting the mapping data;

A memory for storing a look up table generated by the subfield mapping unit;

Display the subfield mapping data and select mapping data that can reduce the difference in weighted sums from a lookup table stored in the memory between mapping periods having a large difference in weighted sums in adjacent mapping periods of the subfield mapping data. A subfield mapping apparatus for reducing halftone noise, comprising a display and a selectable portion, is provided.

Another preferred aspect for achieving the above object of the present invention is the step of checking the subfield mapping data, if there is noise when driving the plasma display panel;

If there is a mapping section having a large difference in weighted sum in adjacent mapping sections of the subfield mapping data, inserting mapping data capable of reducing a difference in weighted sum between mapping sections having a large difference in weighted sum is included; A subfield mapping method is provided that reduces tone noise.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

3 is a block diagram of a plasma display panel driving apparatus according to an embodiment of the present invention, in which gamma-corrected and gain-adjusted, error-diffused digital video data (RGB) is mapped to a subfield pattern to look up table. A subfield mapping unit 13 for generating subfield mapping data and outputting the mapping data; A memory 31 for storing a look up table generated by the subfield mapping unit 13; A mapping capable of displaying the subfield mapping data and reducing a difference in weighted sums in a lookup table stored in the memory 31 between mapping periods having a large difference in weighted sums in adjacent mapping sections of the subfield mapping data. The display and selector 30 capable of selecting data is a device for reducing halftone noise according to the present invention.

The lookup table is mapping data in which 256 subfields are mapped, and the subfield mapping data is mapping data in which fewer than 256 subfields are mapped.

The first and second inverse gamma adjustment units 10 and 20, the gain adjustment unit 11, the error diffusion unit 12, the data alignment unit 14, and the APL calculation unit 21 included in the plasma display panel driving apparatus are included. The timing controller 22 is omitted since it has been described in the prior art, and '300' in FIG. 3 is a PDP.

Therefore, the apparatus for reducing such halftone noise is inverse gamma corrected in the first inverse gamma adjustment unit 10 and gain is adjusted in the gain adjustment unit 11, so that the error diffusion unit 12 spreads the digital video data ( RGB) is mapped to the subfield pattern by the subfield mapping unit 13 and the mapping data is output to the data alignment unit 14.

The subfield mapping unit 13 generates a look up table in which subfields are mapped to 256 real gray scales and subfield mapping data in which subfields are mapped to 256 real grayscales.

In addition, when the noise occurs in the plasma display panel, the display and selector 30 performs a function of allowing a user to check mapping data and select mapping data that can reduce a difference in weight sum from a lookup table. do.

FIG. 4 is a flowchart of a subfield mapping method capable of reducing halftone noise according to the present invention. When the plasma display panel is driven as in step S10, it is checked whether noise is present.

Thereafter, in step S20, if noise exists, the subfield mapping data is checked (step S30).

Next, if there is a mapping section having a large difference in weighted sum in adjacent mapping sections of the subfield mapping data, mapping data for reducing the difference in weighted sum is inserted between mapping sections having a large difference in weighted sum. And step S50)

The mapping data to be inserted may be extracted and inserted from mapping data having a greater number of subfields than the subfield mapping data, and the mapping data having a greater number of subfields than the subfield mapping data may be stored in the previously stored subfield. It is preferably mapping data.

The number of subfields of the mapping data having a greater number of subfields than the subfield mapping data is 256, and the subfield mapping data has a number of subfields smaller than 256.

Here, as shown in Table 2 below, it can be seen that the sum of weights is larger between the 16th and 17th mapping sections than in the other mapping sections (ie, 52-37 = 15).

Table 3 below shows a look up table in which subfields are mapped to 256 real gray scales (0 to 255).

In step S50 of the flowchart of FIG. 4, mapping data for reducing the difference of weight sums (ie, real gradations) is extracted from the lookup table in which subfields are mapped to 256 real gradations shown in Table 3, and inserted.

That is, as shown in Table 4 below, the real gradation 45 corresponding to the median weight value of the 16th and 17th mapping periods is inserted.

The lookup table in which subfields are mapped to the 256 real gray scales is stored and used in a memory.

As described above, according to the present invention, halftone noise is reduced by inserting mapping data capable of reducing the difference of weighted sums between adjacent real grays having a large difference in real grays, that is, a mapping interval having a large difference in weighted sums. There is an advantage that can be reduced.

As described above, the present invention inserts mapping data capable of reducing the difference in weighted sums into a mapping section having a large difference in weighted sums, thereby reducing halftone noise by reducing real grayscale differences, thereby improving image quality of the plasma display panel. There is an excellent effect that can be improved.

Although the invention has been described in detail only with respect to specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

Claims (6)

Inverse gamma-corrected and gain-adjusted subfield mapping for mapping the diffused digital video data (RGB) to a subfield pattern to generate a look up table and subfield mapping data and output the mapping data Wealth; A memory for storing a look up table generated by the subfield mapping unit; Display the subfield mapping data and select mapping data that can reduce the difference in weighted sums from a lookup table stored in the memory between mapping periods having a large difference in weighted sums in adjacent mapping periods of the subfield mapping data. A subfield mapping apparatus for reducing halftone noise comprising a display and a selectable portion. The method of claim 1, The lookup table is mapping data in which 256 subfields are mapped. And the subfield mapping data is mapping data in which less than 256 subfields are mapped. Checking subfield mapping data when noise is present when the plasma display panel is driven; If there is a mapping section having a large difference in weighted sum in adjacent mapping sections of the subfield mapping data, inserting mapping data capable of reducing a difference in weighted sum between mapping sections having a large difference in weighted sum is included; Subfield mapping method to reduce tone noise. The method of claim 3, wherein The inserted mapping data is, The subfield mapping method of reducing halftone noise, characterized in that the subfield mapping data is extracted and inserted from mapping data having a larger number of subfields than the subfield mapping data. The method of claim 4, wherein Mapping data having a greater number of subfields than the subfield mapping data, Subfield mapping method for reducing halftone noise, characterized in that the pre-stored subfield mapping data. The method according to claim 4 or 5, The subfield mapping method of reducing halftone noise, wherein the number of subfields of the mapping data is larger than the subfield mapping data.

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