KR100593069B1 - Image Processing Apparatus and Method for Plasma Display Panel - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus and method for a plasma display panel that performs halftone correction using different halftones according to the gradation level of an image displayed on a screen. This has the effect of improving the picture quality.

In order to achieve the above object, the present invention provides an inverse gamma correction unit which inversely gamma corrects a gray level of an image signal input from the outside, and a decimal bit (Bit) of the gray level of the inverse gamma corrected image by the inverse gamma correction unit. And a subfield mapping unit for subfield mapping the halftone-corrected image signal by the halftone correction unit and the halftone correction unit for halftone correction in different halftones according to the grayscale value of the gamma-corrected image signal. It is done.

Plasma Display Panel, Image Processing, Dithering, Error Diffusion, Carry, Fractional Bits

Description

Image Processing Apparatus and Method for Plasma Display Panel

1 is a view showing the structure of a typical plasma display panel.

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

3 is a diagram comparing luminance characteristics of a plasma display panel and a CRT.

4 illustrates reverse gamma correction in a conventional plasma display panel.

5 is a diagram showing an image processing apparatus of a conventional plasma display panel.

6 is a view for explaining a conventional halftone method.

7 shows an image processing apparatus of the plasma display panel of the present invention.

FIG. 8 illustrates the structure of the random dither mask generator of FIG. 7 in more detail. FIG.

9 illustrates an image processing method of the plasma display panel of the present invention.

FIG. 10 is a diagram conceptually illustrating an example in which error diffusion and dithering are applied in operation S920 of generating a plurality of carryes of FIG. 9; FIG.

FIG. 11 is a view illustrating the S930 stage of selecting the carry of FIG. 9 in more detail; FIG.

12 is a diagram for explaining an example of error diffusion.

13A to 13B are diagrams for explaining an example of dithering.

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

70: reverse gamma correction unit 71: halftone correction unit

72: subfield mapping unit 700: carry generation unit

701: halftone path selector 702: carry selector

703: Mixer 704: Random Dither Mask Generator

705, 706. 707, 708, 709: halftone calculation means

The present invention relates to a plasma display panel, and more particularly, by performing halftone correction using a different halftone method according to the gradation level of an image displayed on a screen, suppressing noise generation, An image processing apparatus and method for a plasma display panel for improving image quality.

In general, a plasma display panel is a partition wall formed between a front substrate and a rear substrate to form a unit cell, and each cell includes neon (Ne), helium (He), or a mixture of neon and helium (Ne + He) and The same main discharge gas and an inert gas containing a small amount of xenon (Xe) 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.

1 illustrates a structure of a general plasma display panel. As shown, the plasma display panel includes a front substrate 10 in which a plurality of sustain electrode pairs formed by pairing a scan electrode 101 and a sustain electrode 102 on a front glass 100 that is a display surface on which an image is displayed. And a rear substrate 11 having a plurality of address electrodes 112 arranged on the rear glass 110 forming the rear surface so as to intersect with the plurality of sustain electrode pairs described above.

The front substrate 10 is made of a scan electrode 101 and a sustain electrode 102, that is, a transparent electrode (a) formed of a transparent ITO material and a metal material to mutually discharge and maintain light emission of the cells in one discharge cell. The scan electrode 101 and the sustain electrode 102 provided as the bus electrode b are included in pairs. The scan electrode 101 and the sustain electrode 102 are covered by one or more dielectric layers 103 which limit the discharge current and insulate the electrode pairs, and the magnesium oxide top surface of the dielectric layer 103 to facilitate the discharge conditions. A protective layer 104 on which (MgO) is deposited is formed.

The rear substrate 11 is arranged in such a manner that a plurality of discharge spaces, that is, barrier ribs 111 of a stripe type (or well type) for forming discharge cells are maintained in parallel. In addition, a plurality of address electrodes 112 which perform address discharge to generate vacuum ultraviolet rays are arranged in parallel with the partition wall 111. On the upper side of the rear substrate 11, R, G, and B phosphor layers 113 emitting visible light for image display during address discharge are formed. A white dielectric 114 is formed between the address electrode 112 and the phosphor layer 113 to protect the address electrode 112 and reflect visible light emitted from the phosphor layer 113 to the front substrate 10.

A method of expressing an image gray level of a plasma display panel having such a structure will be described with reference to FIG. 2.

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

As shown in FIG. 2, in the conventional method of expressing a gray level in a plasma display panel, a frame is divided into several subfields having different number of emission times, and each subfield is again configured as a reset period (RPD) for initializing all cells. ) Is divided into an address period APD for selecting a cell to be discharged and a sustain period SPD for implementing gradation 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 SF1 to SF8 as shown in FIG. 2, and eight subfields. Each of the SFs SF1 to SF8 is divided into a reset period, an address period, and a sustain period.

The reset period and the address period of each subfield are the same for each subfield. The address discharge for selecting the cell to be discharged is caused by the voltage difference between the address electrode and the transparent electrode which is the scan electrode. The sustain period is increased at a rate of 2 ⁿ ( ^where n = 0, 1, 2, 3, 4, 5, 6, 7) in each subfield. In this way, since the sustain period is different in each subfield, the gray scale of the image is expressed by adjusting the sustain period of each subfield, that is, the number of sustain discharges.

The plasma display panel displaying an image in this manner is easy to manufacture because the structure is simpler than that of the cathode ray tube (CRT), which has been mainly used as the main display means. In addition, such a plasma display panel has a thinner feature than a cathode ray tube, and is currently being spotlighted as a next generation display device.

3 is a diagram comparing luminance characteristics of a plasma display panel and a CRT. As shown in the figure, the CRT expresses a desired gray level by controlling the displayed light in an analog manner with respect to an input image signal, and thus has a nonlinear luminance characteristic. 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 human vision is nonlinear, noise is generated when the gray scale is expressed in a low gray scale region. Accordingly, in order to solve the problem of noise generation, the plasma display panel inversely gamma corrects the input image data as shown in FIG. 4.

4 is a diagram illustrating inverse gamma correction in a conventional plasma display panel. As shown, the target luminance represents the ideal inverse gamma result to be corrected, the actual luminance is the measured luminance value as a result after the inverse gamma correction, and the luminance of the plasma display panel is measured in the absence of inverse gamma correction. The luminance value 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 0-60, 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, it is impossible to express enough grayscale in a dark area, thereby generating a contour noise in which the images are aggregated.

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

Here, the above-described halftone will be described in more detail. First, the error diffusion method attempts to spatially correct an error that is discarded by causing an error occurring when the corresponding pixel is quantized to affect the neighboring pixels. Way. This error diffusion method has a problem in that an error diffusion pattern is generated at a uniform gray level due to a constant error diffusion coefficient as the error diffusion coefficient for a neighboring pixel is set to be constant and repeated for each line and every frame.

Next, 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. Insufficient gray scale expression power is increased by turning on a pixel where a spot has occurred and turning off a pixel that does not.

Plasma display panels generally use error diffusion and dithering when using the above-mentioned error diffusion and dithering methods to express a large number of gray levels with a small number of real grays. Use it.

An image processing apparatus of a conventional plasma display panel for realizing an image using a halftone method that uses such error diffusion and dithering will be described with reference to FIG. 5.

5 is a diagram illustrating a part of an image processing apparatus of a conventional plasma display panel. As shown, an image processing apparatus of a conventional plasma display panel includes an inverse gamma correction unit 50 that performs inverse gamma correction on R (Red), G (Green), and B (Blue) image signals, and inverse gamma correction. A halftone unit 51 for improving the expressive power of the image signal, a mixer 52, and a subfield mapping unit 53 for mapping the subfields to the halftone-adjusted image signal. .

Here, it is well known that an image signal passed through the inverse gamma correction unit 50 includes an integer part and a decimal part, that is, an integer bit and a decimal bit. The halftone unit 51 corrects the fractional bits of the image signal output by the inverse gamma correction unit 50 through error diffusion and dithering to generate a predetermined carry, and thus the halftone unit 51 The mixer 52 adds the predetermined carry generated by the and the integer bits of the video signal output by the inverse gamma correction unit 50 to the subfield mapping unit 53. Then, the subfield mapping unit 53 maps the video signal received from the mixer 52 according to the subfield.

Referring to the structure of the halftone unit 51 of the conventional image processing apparatus in more detail, the halftone unit 51 of the conventional image processing apparatus includes one A-bit error diffusion unit 500 and one (NA) bit dithering unit. 501 and a (NA) bit random dither mask generator 502. For example, it includes a 4-bit error diffusion unit and a 3-bit dithering unit. The halftone unit 51 of such a conventional image processing apparatus uses an error diffusion method up to the lowest specific bit of the number of decimal places and a dithering method for the decimal places other than the specific bit. The operation of the halftone unit 51 will now be described with reference to FIG. 6.

Assuming that all of the fractional parts of the image signal output by the inverse gamma correction unit 50 have seven bits, the A bit, for example, the least three bits, of the fractional parts may have an error. The carry is corrected by a diffusion method to generate a predetermined carry, and the carried carry is transferred to the next three bits after the lower three bits. In addition, assuming that the bits (7-A) bits, for example, A bits, other than the lowest A bits, which are incorrectly spread out of seven decimal bits, are assumed to be 4 bits, NA) The bit dithering unit 501 corrects using the dithering method to generate a predetermined carry and adds the carry generated with the integer portion generated by the inverse gamma correction unit 50. As a result, various gradation expressions are possible using only integer gradation values.

At this time, the (N-A) bit dithering unit 501 uses a dither mask generated by the (N-A) bit random dither mask generation unit 502.

That is, the halftone unit 51 of the conventional image processing apparatus predetermines the number of bits of the fractional part to dither the fractional bits of the inverse gamma corrected video signal and the number of bits of the fractional part to be error-diffused, and adjusts the number of bits according to the determined number As described above, the fractional part of the inverse gamma corrected image signal is dithered and error diffused to realize an image. For example, regardless of the gray value of the input image signal, the fractional bits of all the inversely gamma-corrected image data are used for the lower 4 bits and the error diffusion method is applied to the upper 3 bits.

However, in the conventional image processing apparatus using such an image processing method, a relatively low gray level image signal, a relatively high gray level image signal, or a relatively low gray level are used because all of the same dithering and error diffusion methods are used after inverse gamma correction. Image quality is lowered at the time of the display and at a relatively high gradation. That is, the error diffusion method reduces the halftone noise more effectively at low gray levels, and the dithering method reduces the halftone noise more effectively at high gray levels. The conventional image processing apparatus of the plasma display panel has a problem in that halftone noise increases in an image of a specific gray scale and image quality deteriorates.

The present invention for solving this problem, the plasma display to reduce the noise of the image displayed on the screen using a different halftone method according to the grayscale value of the input image signal is inverse gamma correction, and improve the image quality It is an object of the present invention to provide an image processing apparatus and method for a panel.

In order to achieve the above object, the present invention relates to an inverse gamma correction unit which inversely gamma corrects a gray level of an image signal input from the outside, and to a decimal bit (Bit) of the gray level of the inverse gamma corrected image by the inverse gamma correction unit. And a subfield mapping unit for subfield mapping the halftone-corrected video signal by the halftone correction unit and the halftone correction unit for halftone correction in different halftones according to the grayscale value of the inverse gamma corrected image signal. It features.

The halftone correction unit halftones the fractional bits of the gray level of the image signal corrected by the inverse gamma correction unit using a plurality of different halftone calculation means to correct a plurality of carry along each path. After the generation, one carry is selected from among a plurality of carry in accordance with the gray level of the video signal, and is summed with the integer bits of the gray level of the inverse gamma corrected video signal.

The half-tone correcting unit is a carry generator which half-tones the fractional bits of the gray level of the image signal corrected by the inverse gamma correction unit by a plurality of different halftone calculating means to generate a plurality of carry; A halftone path selector for selecting a halftone path corresponding to the gradation level of the video signal by comparing a gray level of a signal with a preset carry selection criterion, and selecting the halftone path among a plurality of carry generated by the carry generator A carry selection unit for selecting a carry of the halftone calculation means corresponding to the half-tone path selected by the addition and an integer bit of the gray level of the image signal inversely gamma corrected by the inverse gamma correction unit and a mixer selected by the carry selection unit Characterized in that it comprises a.

The carry generation unit generates a random dither mask generation unit generating random dither masks as many as the number of bits of the decimal bits of the image signal inversely gamma corrected by the inverse gamma correction unit, and random bits generated by the random dither mask generation unit. And a plurality of halftone calculation means for generating a predetermined carry by halftone correcting the fractional bits of the inverse gamma corrected image signal through dithering or error diffusion using a dither mask.

The random dither mask generation unit includes a bit number determination unit that determines the number of bits of the fractional bits of the gray level of the video signal, a random coefficient generation unit that generates a predetermined number of random coefficients according to the number of bits determined by the bit number determination unit; And a random dither mask generation unit for each bit number that generates a plurality of random dither masks by using the random coefficients generated by the random coefficient generator.

The random number dither mask generation unit for each bit number may select N random dither masks, ranging from 1-bit random dither masks to N-bit random dither masks, when the fractional bits of the image signal inversely gamma corrected by the inverse gamma correction unit are N bits. It is characterized by generating.

One of the halftone calculating means may generate a predetermined carry by halftone correcting all fractional bits of the inverse gamma corrected video signal through error diffusion.

One of the halftone calculating means may generate a predetermined carry by halftone correcting all the decimal bits of the inverse gamma corrected video signal through dithering.

The halftone calculation means for halftone correcting all the fractional bits of the inverse gamma corrected image signal by dithering is random random dither when the fractional bits of the inverse gamma corrected image signal by the inverse gamma correction unit are N bits. The dithering is performed using an N-bit random dither mask generated by the mask generator.

At least one of the halftone calculating means is error diffusion and dithering the fractional bits of the inverse gamma corrected image signal when the fractional bits of the inverse gamma corrected image signal by the inverse gamma correction unit are two or more bits. Half-tone correction using all of the above to generate a predetermined carry.

The halftone calculating means using both error diffusion and dithering among the halftone calculating means generates a predetermined carry of the predetermined number of lower fractional bits among the fractional bits of the inverse gamma corrected image signal through error diffusion to generate a predetermined carry. Each of the fractional bits is summed up, and the summed fractional bits are halftone-corrected through dithering to generate a predetermined carry.

Among the halftone calculation means, the halftone calculation means using both error diffusion and dithering has N bits, and the lower fractional bits to which error diffusion is applied are A bits. In this case, the random dither mask generation unit performs dithering with a random dither mask of (NA) bits.

Among the halftone calculation means, the number of halftone calculation means using both error diffusion and dithering is N-bit when the fractional bits of the video signal inversely gamma corrected by the inverse gamma correction unit are N bits. It is characterized by being a dog.

The carry selection criterion is characterized in that as the gray level of the input image signal is lower, the number of lower decimal bits to which error diffusion is applied among the decimal bits of the gray level of the inverse gamma corrected image signal is increased.

The present invention also provides an inverse gamma correction step of inversely gamma correcting a gray level of an image signal input from an external source, and a fractional bit of the inverse gamma correction image signal in the inverse gamma correction step. A carry generation step of generating a plurality of carry by halftone correction by a plurality of different halftone calculation means according to the level, and selecting a carry corresponding to the gradation level of the video signal from the plurality of carry generated in the carry generation step An output for outputting a carry selection step, a summing step in which the carry selected in the carry selection step and an integer bit of an inverse gamma corrected image signal in the inverse gamma correction step, and a result obtained in the summing step are output to the subfield mapping unit Characterized in that it comprises a step.

In the carry generation step, when the number of fractional bits of the inverse gamma corrected video signal in the inverse gamma correction step is N and A is an integer greater than or equal to 0, the inverse gamma corrected video signal in the inverse gamma correction step It generates a plurality of carry by generating a predetermined carry through the error diffusion of the lower (NA) bits of the minority bits and each of the remaining upper A bits, and half-tone correction of the summed values through dithering. .

The carry selection step may include selecting a carry corresponding to the gradation level of the image signal by comparing the gradation level of the image signal with a preset carry selection criterion.

Hereinafter, an image processing apparatus and a method of a plasma display panel of the present invention will be described in detail with reference to the accompanying drawings.

7 is a view showing an image processing apparatus of the plasma display panel of the present invention. As illustrated, the image processing apparatus of the plasma display panel of the present invention includes an inverse gamma correction unit 70, a halftone correction unit 71, and a subfield mapping unit 72.

The inverse gamma correction unit 70 corrects the inverse gamma of the gray level of the image signal input from the outside for each of R, G, and B. The inverse gamma corrected video signal includes an integer bit (an integer part) and a decimal bit (a fractional part).

The halftone correcting unit 71 performs halftone correction using a different halftone method according to the grayscale value of the inverse gamma corrected image signal. The halftone correcting unit 71 is inverse gamma corrected by the inverse gamma correcting unit 70. After a few bits of the gray level of the corrected video signal are halftone corrected by a plurality of different halftone means to generate a plurality of carry along each path, a plurality of carry signals are generated according to the gray level of the video signal. One carry is selected from the carry and summed with the integer bits of the gray level of the inverse gamma corrected video signal to be output. That is, a plurality of carry is generated by a plurality of different methods, and a carry corresponding to the gray level of the inverse gamma corrected video signal is selected from the generated carry, and the carry is summed with integer bits.

The subfield mapping unit 72 subfield maps the video signal halftone corrected by the halftone correction unit 71.

The structure of the halftone correcting unit 71 described above in the image processing apparatus of the plasma display panel according to the present invention having the above structure will be described in more detail as follows.

The halftone corrector 71 includes a carry generator 700, a halftone path selector 701, a carry selector 702, and a mixer 703.

The carry generator 700 half-tones the fractional bits of the gray level of the image signal inversely gamma corrected by the inverse gamma corrector 70 by using a plurality of different halftone means to generate a plurality of carry.

The halftone path selector 701 selects a halftone path corresponding to the gray level of the video signal by comparing the gray level of the video signal with a preset carry selection criterion. The above-mentioned carry selection criteria are set in advance according to the interval of the gradation level. For example, the gradation level of the video signal is in the range of 0 to 255, and the number of decimal bits of the video signal that is inversely gamma corrected by the inverse gamma correction unit 70 is seven. Select the path where the tone calculating means is located, and select the path where the halftone calculating means with the sign 706 is located in the 40 to 75 grayscale section. In this way, the halftone calculating means with the sign 709 is selected in the 215 to 255 grayscale section. It may be set to select a path to be located. The ranges of the gradation sections presented here are set arbitrarily for convenience of explanation, and are not limited to the ranges of the gradation sections. And the halftone calculation means described above with reference numerals 705, 706 and 709 will be described in more detail in the following description.

The carry selector 702 selects a carry of the halftone calculating means corresponding to the halftone path selected by the halftone path selector 701 from the plurality of carry generated by the carry generator 700 described above.

The mixer 703 adds the integer bits of the gray level of the image signal inversely gamma corrected by the inverse gamma correction unit 70 and the carry selected by the carry selection unit 702.

The carry generator 700 of the halftone corrector 71 is positioned on different paths between the random dither mask generator 704 and the inverse gamma corrector 70 and the carry selector 702, respectively. It includes a plurality of different halftone calculation means (705, 706, 707, 708, 709).

Here, the random dither mask generator 704 generates a random dither mask for each bit number according to the number of bits of the decimal bits of the image signal inversely gamma corrected by the inverse gamma correction unit 70. The generation unit 704 will be described in more detail with reference to FIG. 8 as follows.

Referring to FIG. 8, the random dither mask generation unit 704 includes a bit number determination unit 800 that determines the number of bits of the fractional bits of the gray level of the image signal, and a predetermined number of random coefficients according to the number of bits determined by the bit number determination unit. And a random number generator 802 for each bit number that generates at least one random dither mask using the random coefficients generated by the random coefficient generator 801.

Referring to the operation of the random dither mask generation unit 704, if a decimal bit, for example, N bits of the inverse gamma corrected image signal is input, the bit number determination unit 800 determines how much the aforementioned N value is. . For example, when the fractional bits of the inverse gamma corrected video signal are 7 bits, the bit number determination unit 800 determines N as 7. Then, the random coefficient generator 801 generates an appropriate number of random coefficients according to the number of bits determined by the bit number determination unit 800. Then, the random number dither mask generator 802 for each bit number generates a plurality of random dither masks using random coefficients. That is, a total of seven random dither masks are generated, ranging from a 1-bit random dither mask to a 7-bit random dither mask.

The halftone calculation means 705, 706, 707, 708, and 709 are error spread or the random dither mask generator 704 generates the fractional bits of the image signal inversely gamma corrected by the inverse gamma correction unit 70. Halftone correction is performed through dithering using a predetermined random dither mask to generate a predetermined carry. Although the number of halftone calculation means 705, 706, 707, 708, and 709 is shown as five in FIG. 7, the halftone calculation means 705, 706, 707, 708, and 709 is not limited to five. It is determined according to the number of bits of all the decimal bits of the inverse gamma corrected video signal. For example, assuming that the number of bits of all the decimal bits of the inverse gamma corrected video signal is seven, the number of halftone calculation means is six. Such halftone calculating means will become more apparent from the following description.

Here, any one of the plurality of halftone calculating means 705, 706, 707, 708, 709 generates half of the bit by correcting all the fractional bits of the inverse gamma corrected video signal through error diffusion to generate a predetermined carry. For example, as illustrated in FIG. 7, the halftone operation means having a sign 705 half-tone corrects all fractional bits of the inverse gamma corrected video signal through error diffusion to generate a predetermined carry. The half-tone calculating means of this code 705 includes an N-bit error diffusion unit (unsigned). For example, assuming that the number of bits of the fractional bits of the inverse gamma corrected video signal is 7 bits, the halftone calculation means 705 includes a seven-bit error spreader, and the seven-bit error spreader includes seven bits of the inverse gamma corrected video signal. Inverse gamma correction is performed on the fractional bits of the bit through error diffusion to generate a predetermined carry. The error diffusion method applied here includes a random error diffusion method or a normal error diffusion method. The error diffusion is as follows. As an example of such error diffusion, quantization error data of digital video data is calculated using a Floyd-Steinberg error diffusion filter, and the calculated error data are spread to adjacent pixels with different weights. . For example, in the case of performing an error diffusion operation on the current P5 pixel as shown in FIG. 12, the error diffusion method has a weight of 1/16 for P1 adjacent to the P5 pixel, a weight of 5/16 for P2, and 3 for P3. The weight of / 16 is weighted to P4 and 7/16 to calculate the error diffusion coefficient for each of the P1 to P4 pixels. Subsequently, the calculated error diffusion coefficients are added to generate a carry signal to be added to the current P5 pixel data. Through this process, a predetermined carry is generated.

In addition, any one of the plurality of halftone calculating means 705, 706, 707, 708, 709 generates half the halftone correction by dithering all the decimal bits of the inverse gamma corrected video signal. For example, as illustrated in FIG. 7, the halftone calculation unit 709 signifies halftone correction of all fractional bits of an inverse gamma corrected video signal to generate a predetermined carry. The half-tone calculating means of this code 709 includes an N-bit dithering unit (unsigned). For example, assuming that the number of bits of the fractional bits of the inverse gamma corrected video signal is four bits, the halftone calculation means 709 includes a four bit dithering portion, and the four bit dithering portion of the four bits of the inverse gamma corrected video signal. Inverse gamma correction is performed through dithering the decimal bits to generate a predetermined carry. At this time, the 4-bit dithering unit performs dithering using the 4-bit random dither mask generated by the random dither mask generation unit 704 described above. That is, the specific dither noise is removed by using the generated random dither mask pattern. As an example of dithering using the random dither mask, when the input data value is '0111' as shown in FIG. 13A, eight random coefficients of 0000, 0011, 0101, 1010, 1100, 1101, 1110, and 1111 are generated. do. In FIG. 13A, a position of a cell that is turned on is randomly selected. Therefore, different dither masks are repeatedly applied to each cell according to data.

In addition, at least one of the plurality of halftone calculating means 705, 706, 707, 708, and 709 may half-correct the fractional bits of the inverse gamma corrected image signal using both error diffusion and dithering to carry a predetermined carry. Generates. For example, as shown in FIG. 7, the halftone calculation means 706, 707, and 708 use halftone correction on the fractional bits of the inverse gamma corrected video signal using both error diffusion and dithering to generate a predetermined carry. That is, a predetermined carry of a predetermined number of lower fractional bits among the fractional bits of the inverse gamma corrected video signal is generated through error diffusion, and the sum is added to the remaining fractional bits of the upper portion, and the summed fractional bits are halftone corrected through dithering. To generate a predetermined carry. Here, if the number of decimal bits of the inverse gamma corrected video signal is N and A is 0 or more and N or less, the halftone calculation means of codes 706, 707, and 708 are A bit error spreading unit (unsigned) and (NA), respectively. And a bit dithering unit (unsigned).

Referring to the halftone calculation means 706, 707, and 708 for halftone correction using both error diffusion and dithering, for example, the halftone calculation means of 707 is referred to as (N-2). A bit error spreader (unsigned) and a 2-bit dithering unit (unsigned) are included. For example, assuming that the number of bits of the fractional bits of the inverse gamma corrected image signal is 7 bits, the halftone calculating means of code 707 includes a 5-bit error diffusion unit and a 2-bit dithering unit, and the 5-bit error diffusion unit includes an inverse gamma correction unit. The lower 5 bits of the fractional bits of the formed shape signal are generated through error diffusion, and the predetermined carry is added to the fractional bits of the remaining upper 2 bits. Thereafter, the 2 bit dithering unit reverse-gamma corrects the upper 2 bits of the decimal bits obtained by adding the carry generated through error diffusion to generate a predetermined carry. Here, even when the aforementioned 2-bit dithering unit dithers the upper fractional bits of 2 bits, dithering is performed using the 2-bit random dither mask generated by the random dither mask generation unit 704 described above. In the dithering performed by using the aforementioned 2-bit random dither mask, for example, as shown in FIG. 13B, when the input data value is '01', one random coefficient of 0000 occurs. The location of the cells that are turned on here in FIG. 13B is randomly selected.

Among the halftone calculation means 705, 706, 707, 708, 709, the number of halftone calculation means 706, 707, 708 that uses both error diffusion and dithering is inverse gamma corrected by the inverse gamma correction unit. When the fractional bits of a signal are N bits, they are (N-1).

The image processing apparatus of the plasma display panel of the present invention having such a structure generates a plurality of carry by halftone-correcting the fractional bits of the gray level of the inverse gamma corrected image signal by a plurality of different methods, and then inverts the plurality of carry. By selecting a carry optimized for the gradation level of the gamma-corrected image signal, the generation of noise of the image is reduced and the image quality is improved. The image processing method applied to the image processing apparatus of the plasma display panel of the present invention is shown in FIG. Looking at the following.

9 is a view showing an image processing method of the plasma display panel of the present invention. As shown, the image processing method of the plasma display panel according to the present invention includes an inverse gamma correction step (S900), an integer bit, a fractional bit separation step (S910), a carry generation step (S920), a carry selection step (S930), and a carry; An integer bit summing step S940 and a subfield mapping unit output step S950 are included.

That is, the inverse gamma correction unit 70 corrects the gray level of the image signal input from the outside (S900).

Subsequently, in step S900, the gray level of the image signal, which is inverse gamma corrected by the inverse gamma correction unit 70, is divided into integer bits and decimal bits (S910).

Halftone correction by the plurality of halftone calculating means 705, 706, 707, 708, and 709 located on a plurality of different halftone paths according to the gray level of the video signal according to the above-described step S910 By generating a plurality of carry (S920). In step S920, the N-bit error diffusion step (S921), (N-1) bit error diffusion and 1-bit dithering step (S922), (N-2) error diffusion step, and 2-bit dithering step (S923), 1 bit Error diffusion and (N-1) bit dithering step S924 and N-bit dithering step S925 are included. In other words, assuming that the number of fractional bits of the inverse gamma corrected image signal in step S900, that is, the number of fractional bits separated in step S910 is N and A is an integer greater than or equal to 0, the lower (NA) bits of the fractional bits. To generate a predetermined carry through error diffusion, and add each of the remaining upper A bits, and half-correct the A-bit random dither mask generated by the random dither mask generation unit 704 through dithering. Generates.

Looking at the step S920 for generating such a carry in more detail with reference to Figure 10a to Figure 10c as follows.

For example, assuming that the fractional bits of the inverse gamma corrected grayscale, ie, N, are seven, the fractional bits of the seven bits of the grayscale of the inverse gamma corrected video signal are halftone-corrected through error diffusion to perform a predetermined carry. Generates.

In addition, a predetermined carry is generated through error diffusion of the lower 6 bits of the decimal bits of the gray level of the grayscale of the image signal that has been inversely gamma corrected in step S922, and the predetermined carry generated as described above is left over. One-bit fractional bits are summed, and the summed one-bit fractional bits are half-tone corrected by dithering using a one-bit dither mask generated by the random dither mask generator 704 to generate a predetermined carry.

In addition, in step S923, as shown in FIG. 10C, half-tone correction is performed through error diffusion of 5 bits and dithering of 2 bits to generate a predetermined carry.

In addition, in step S924, as shown in FIG. 10B, halftone correction is performed through error diffusion of 4 bits and dithering of 3 bits to generate a predetermined carry.

Although not shown in FIG. 9, a concept of generating a predetermined carry by performing halftone through 3-bit error diffusion and 4-bit dithering is illustrated in FIG. 10A.

Here, in the descriptions of steps S923 and S924, steps S923 and S924 are repeated since the halftone correction is performed through the same process except that the bits of the fractional bits to which error diffusion or dithering are applied differ from the above-described step S922. The description is omitted.

In addition, a predetermined carry is generated by performing halftone correction on the 7-bit fractional bits of the gray level of the inverse gamma corrected image signal in step S925 through dithering.

As described above, in step S920, a plurality of carry is output through a plurality of different methods as described above.

After the operation S920 of generating the plurality of carry, one carry corresponding to the gradation level of the image signal is selected from the plurality of carry (S930).

Herein, step S930 of selecting the carry will be described in more detail with reference to FIG. 11. In step S930, first, the gray level of the input image signal is compared with a preset carry selection criterion to select from among (N + 1) paths. A path corresponding to the gradation level of the image signal described above is selected (S1100). Thereafter, the carry corresponding to the selected path is output (S1101).

For example, when the number of bits of the fractional bits of the gray level of the inverse gamma corrected video signal is seven, and the gray level of the input video signal is between 0 and 40 levels, the path where the halftone calculating means 705 is located is located. In the case where the selection is made in advance, when a video signal having a gradation level of 30 is input, the halftone path selector 701 detects that the gradation level of the input video signal is 30, and causes the carry selector 702 to detect the gradation level of 30. A predetermined control signal is applied to select the path where the halftone calculating means 705 is located. The carry selector 702 then selects a carry generated by the halftone calculating means 705.

After the operation S930 of selecting one carry among the plurality of carry, the carry selected in operation S930 is summed with the integer bits separated in operation S910 (S940).

In operation S950, the value summed up in operation S940 is output to the subfield mapping unit.

Subsequently, the subfield mapping unit performs subfield mapping on the sum of the input values.

As such, it will be understood by those skilled in the art that the above-described technical configuration of 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 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 in detail above, the present invention has the effect of suppressing noise and improving image quality by applying halftone correction by applying different halftone methods according to the gradation level of the video signal.

Claims (17)

An inverse gamma correction unit that inversely gamma corrects a gray level of an image signal input from the outside; A halftone correction unit configured to halftone correct a decimal bit (Bit) of the gray level of the inverse gamma corrected image signal by the inverse gamma corrector in a different halftone method according to the gray value of the inverse gamma corrected image signal; And A subfield mapping unit for subfield mapping the halftone corrected image signal by the halftone correction unit; Image processing apparatus of the plasma display panel comprising a. The method of claim 1, The halftone correction unit After the half-bit correction of the fractional bits of the gray level of the image signal corrected by the inverse gamma correction unit by a plurality of different halftone calculation means to generate a plurality of carry along each path And selecting one carry among a plurality of carry according to the gray level of the video signal, and adding the carry to the integer bit of the gray level of the inverse gamma corrected video signal to output the sum. The method according to claim 1 or 2, The halftone correction unit A carry generator for half-tone correcting the fractional bits of the gray level of the image signal corrected by the inverse gamma correction unit by using a plurality of different halftone calculation means to generate a plurality of carry; A halftone path selector configured to select a halftone path corresponding to the gray level of the video signal by comparing the gray level of the video signal with a preset carry selection criterion; A carry selector for selecting a carry of a halftone calculating means corresponding to a halftone path selected by the halftone path selector from among a plurality of carry generated by the carry generator; And A mixer for adding the integer bits of the gray level of the video signal corrected by the inverse gamma correction unit and the carry selected by the carry selection unit; An image processing apparatus of a plasma display panel comprising a. The method of claim 3, wherein The carry generation unit A random dither mask generation unit generating random dither masks as many as the number of bits of the fractional bits of the image signal inversely gamma corrected by the inverse gamma correction unit; A plurality of halftone calculation means for generating a predetermined carry by halftone correcting the fractional bits of the inverse gamma corrected image signal through dithering or error diffusion using a random dither mask of a predetermined bit generated by the random dither mask generator; An image processing apparatus of a plasma display panel comprising a. The method of claim 4, wherein The random dither mask generator A bit number discriminating unit for discriminating the number of bits of the fractional bits of the gray level of the video signal; A random coefficient generator for generating a predetermined number of random coefficients according to the number of bits determined by the bit number discriminator; And A random number dither mask generator for each bit number that generates a plurality of random dither masks using random coefficients generated by the random coefficient generator An image processing apparatus of a plasma display panel comprising a. The method of claim 5, The random number dither mask generation unit for each bit number When the fractional bits of the video signal corrected by the inverse gamma correction unit are N bits, An image processing apparatus of a plasma display panel, characterized by generating N random dither masks from 1-bit random dither masks to N-bit random dither masks. The method of claim 4, wherein One of the plurality of halftone calculating means And half-tone correction of all fractional bits of the inverse gamma corrected image signal through error diffusion to generate a predetermined carry. The method of claim 4, wherein One of the plurality of halftone calculating means And half-tone correction of all fractional bits of the inverse gamma corrected image signal through dithering to generate a predetermined carry. The method of claim 8, Halftone calculation means for halftone correction of all the fractional bits of the inverse gamma corrected video signal by dithering When the fractional bits of the video signal corrected by the inverse gamma correction unit are N bits, And dithering with the N-bit random dither mask generated by the random dither mask generator. The method of claim 4, wherein At least one of the plurality of halftone calculating means When the fractional bits of the video signal corrected by the inverse gamma correction unit are two or more bits, And performing a half carry on the fractional bits of the inverse gamma corrected image signal using both error diffusion and dithering to generate a predetermined carry. The method of claim 10, Halftone calculation means using both error diffusion and dithering of the plurality of halftone calculation means A predetermined number of lower fractional bits among the fractional bits of the inverse gamma corrected image signal are generated through error diffusion, and a predetermined carry is added to each of the upper fractional bits, and the summed fractional bits are halftone corrected through dithering. An image processing apparatus for a plasma display panel, characterized by generating a predetermined carry. The method of claim 11, Halftone calculation means using both error diffusion and dithering of the plurality of halftone calculation means When the fractional bits of the image signal corrected by the inverse gamma correction unit are N bits and the lower fractional bits to which the error diffusion is applied are A bits, And dithering the random dither mask of the (N-A) bit generated by the random dither mask generator. The method of claim 11, Among the plurality of halftone calculation means, the number of halftone calculation means using both error diffusion and dithering is When the fractional bits of the video signal corrected by the inverse gamma correction unit are N bits, (N-1) plasma display panel image processing apparatuses. The method of claim 3, wherein The carry selection criteria is And the number of lower fractional bits to which error diffusion is applied among the fractional bits of the grayscale of the inverse gamma corrected image signal increases as the grayscale level of the input image signal is lower. An inverse gamma correction step of inversely gamma correcting a gray level of an image signal input from the outside; A carry generation step of generating a plurality of carry by halftone correcting the fractional bits of the image signal corrected in the reverse gamma correction by a plurality of different halftone calculating means according to the gray level of the image signal; A carry selection step of selecting a carry corresponding to the gradation level of the video signal among a plurality of carry generated in the carry generation step; A summing step of adding the carry selected in the carry selection step and the integer bits of the inverse gamma corrected video signal in the inverse gamma correction step; And An output step of outputting a result summed in the adding step to a subfield mapping unit; Image processing method of a plasma display panel comprising a. The method of claim 15, In the carry generation step In the inverse gamma correction step, when the number of decimal bits of the inverse gamma corrected video signal is N and A is an integer of 0 or more and N or less, In the inverse gamma correction step, the lower (NA) bit of the decimal bits of the inverse gamma corrected image signal is generated through error diffusion, and a predetermined carry is added to each of the remaining upper A bits, and each half is summed through dithering. An image processing method of a plasma display panel, characterized by generating a plurality of carry by tone correction. The method of claim 15, In the carry selection step And selecting a carry corresponding to the gradation level of the image signal by comparing the gradation level of the image signal with a preset carry selection criterion.

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