KR20070072121A - Plasma display apparatus and image processing method thereof - Google Patents

Abstract

A plasma display and an image processing method thereof are provided to optimize inverse gamma correction by converting the first output gradation value exceeding an integer among output gradation values having an integer and a decimal into an integer. A plasma display includes an inverse gamma correcting unit(510) for performing inverse correction on an input gradation value of an image signal input from the outside, and an integer converting unit(530) for converting the first output gradation value exceeding an integer among output gradation values of the inverse gamma corrected image signal having an integer and a decimal into an integer. The integer converting unit converts the first output gradation value exceeding the integer among the output gradation values with respect to all or a part of the input gradation values.

Description

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

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

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

3 is a graph illustrating a relationship between the number of sustain pulses according to an APL value used in a conventional plasma display apparatus.

4 is a graph illustrating an inverse gamma correction curve of a conventional plasma display device.

5 is a block diagram illustrating a plasma display device according to an embodiment of the present invention.

6 is a diagram illustrating an inverse gamma correction curve according to the present invention.

The present invention relates to a plasma display device and an image processing method thereof, and more particularly, to a plasma display device and an image processing method thereof capable of reducing noise displayed on a screen when the plasma display device is driven.

In general, a plasma display device includes a plasma display panel in which a space partitioned by a partition formed between a front substrate and a rear substrate forms one unit cell, and each cell includes neon and helium (Ne). He) or an inert gas containing a small amount of xenon and a main discharge gas such as a mixed gas of Ne and Helium (Ne + He). When discharged by a high frequency voltage, the inert gas generates vacuum ultraviolet rays and emits phosphors formed between the partition walls to realize an image. Such a plasma display device has been spotlighted as a next generation display device because of its thin and light configuration.

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

As shown in FIG. 1, the plasma display apparatus divides one frame period into a plurality of subfields having different discharge times, and emits a plasma display panel in a subfield period corresponding to a gray value of an input image signal. An image is implemented.

Each subfield is divided into a reset period for uniformly generating a discharge, an address period for selecting a discharge cell, and a sustain period for implementing gray scale according to the number of discharges. For example, when the image is to be displayed with 256 gray levels, the frame period (16.67 ms) corresponding to 1/60 second is divided into eight subfields. In addition, each of the eight subfields is divided into a reset period, an address period, and a sustain period. Here, the sustain period is increased at 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 graph comparing luminance characteristics of a plasma display device and a cathode ray tube.

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

At this time, the display device such as the cathode ray tube is because the brightness characteristics compared to the display current is proportional to the 2.2 multiplier, the input external video signal such as a broadcast signal transmits a signal corresponding to the inverse of the 2.2 multiplier. Therefore, a plasma display device having a linear brightness characteristic needs to inversely gamma correct an image signal input from the outside.

The inverse gamma correction curve generated when the inverse gamma correction of an image signal input from the outside is determined according to the subfield mapping method and the number of sustain pulses.

First, the subfield mapping determines a weight of the subfield, and thus selects a mapping code that minimizes false contour noise among the subfield mapping codes. Table 1 below is an example of a subfield mapping method using 10 subfields and 256 real gray scales created by the above method. Here, the real gray refers to a gray level which is displayed as a combination of subfields having different gray weights, not a gray level displayed through image processing such as half-toning, and refers to a gray level as a reference for image processing.

Next, as shown in FIG. 3, the number of sustain pulses is determined according to an APL (Average Picture Level) value and a weight of a subfield.

3 is a graph illustrating a relationship between the number of sustain pulses according to an APL value used in a conventional plasma display apparatus.

As shown in FIG. 3, the conventional plasma display apparatus includes an APL unit (not shown) and differently assigns a weight of the number of sustain pulses applied to the sustain period according to the APL value.

In a typical plasma display apparatus, cells emit light by sustain pulses alternately applied to scan electrodes and sustain electrodes, thereby displaying an image signal input from the outside. At this time, the applied sustain pulse is a high voltage, the magnitude of the voltage is 180V to 220V power consumption is large.

In order to reduce power consumption, in the conventional plasma display apparatus, the maximum number of sustain pulses is allocated to the sustain period at an APL value of 20% APL or less, and the number of sustain pulses allocated to the sustain period is gradually reduced at an APL value of 20% APL or more. To do that. Accordingly, the power consumption of the plasma display device gradually increases before an APL value of less than 20% APL, but the power consumption of the plasma display device remains constant after an APL value of more than 20% APL.

As such, the number of sustain pulses allocated to each subfield according to the APL value is determined according to Equation 1 in order to realize an optimal picture quality.

(1 ^a -1) + (2 ^a -1) + (4 ^a -1) + (7 ^a -1) + (12 ^a -1) + (19 ^a -1) + (30 ^a -1) + ( 43 ^a -1) + (59 ^a -1) + (78 ^a -1) = S _total

Here, S _total is the _total number of sustain pulses for one frame preset according to each APL value. Thus, the number of sustain pulses for each subfield is obtained according to a value calculated by (SF weight) ^a in Equation 1 as shown in Table 2 below.

In Table 2, the APL value is divided into 32 steps from 0 to 31. APL 0 has the smallest APL value and the largest sum of the number of sustain pulses. In addition, APL 31 has the largest APL value and the smallest sum of the number of sustain pulses.

When the above-described subfield mapping method and the number of sustain pulses are determined, the luminance value of the image displayed on the screen is obtained according to each subfield mapping code. That is, the luminance value corresponding to each real gradation value is measured. The grayscale values between neighboring real grayscale values are filled by linear interpolation using the measured luminance values. Thus, the final inverse gamma correction curve may be generated as shown in FIG. 4 through the measured luminance values.

FIG. 4 is a luminance curve showing luminance values according to real grayscale values of a conventional plasma display device, and an inverse gamma correction curve illustrating inverse gamma corrected output grayscale values with respect to input grayscale values using information on luminance curves.

As shown in FIG. 4, in the conventional plasma display apparatus, the luminance value of the large APL value APL 31 increases linearly, but the luminance value of the small APL value APL 0 increases when the subfield mapping code increases. In the middle, a luminance step occurs.

The reason for this is that the number of sustain pulses is determined according to Equation 1, so that the number of sustain pulses increases exponentially as the subfield increases at a small APL value (APL 0). In particular, the portion where the luminance step occurs occurs when the number of subfields used in the subfield mapping code increases. Since the luminance step is reflected in the image, there is a problem that noise is generated.

On the other hand, the number of real grays used is an important factor in the image implementation of the plasma display device. In other words, when the number of actual gradations is large, pseudo contour noise is generated. When the number of actual gradations is small, halftone noise is increased. In this case, the degree of generation of pseudo contour noise and halftone noise also varies depending on the inverse gamma correction method even for the subfield mapping code using the same number of real gray scales.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a plasma display apparatus and an image processing method thereof capable of optimizing inverse gamma correction, which is essential for implementing an image of the plasma display apparatus.

Another object of the present invention is to provide a plasma display device and an image processing method thereof capable of reducing pseudo contour noise and halftone noise displayed on a screen.

According to an aspect of the present invention, there is provided a plasma display apparatus including an inverse gamma correction unit configured to reverse gamma correct an input gray value of an image signal input from an external device, and an inverse gamma corrected integer and a decimal point. And an integer conversion unit for converting the first output gray level value exceeding the integer among the output gray level values of the video signal to the integer.

The integer converting unit converts the first output gray level value exceeding the integer among the output gray level values to all the input gray level values to the integer.

The integer conversion unit may convert a first output gray level value exceeding the integer among the output gray level values into a part of the input gray level value.

An image processing method of a plasma display apparatus according to an embodiment of the present invention includes an inverse gamma correction step of inverse gamma correction of an input gray level value of an image signal input from an outside, and an inverse gamma correction of an image signal including integers and decimals. And an integer conversion step of converting the first output gradation value exceeding the integer among the output gradation values into the integer.

In the integer conversion step, the first output gray level value exceeding the integer among the output gray level values for all of the input gray level values is converted into the integer.

In the integer conversion step, the first output gray level value exceeding the integer among the output gray value values is converted into the integer for a part of the input gray value.

 Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the present invention;

<Example>

5 is a block diagram illustrating a plasma display device according to an embodiment of the present invention.

As shown in FIG. 5, the plasma display apparatus according to an exemplary embodiment of the present invention includes an inverse gamma correction unit 510, a gain control unit 520, an integer converter 530, a half toning unit 540, and a subfield. A mapping unit 550, a data alignment unit 560, and a data driver 570 are provided.

The inverse gamma correction unit 510 inversely gammas the input gray value of the image signal so that the luminance value displayed with respect to the input gray value of the image signal has a linear value when the image signal input from the outside is displayed on the plasma display panel. Correct it.

The gain controller 520 may be adjusted by a user or a set maker with respect to the red, green, and blue image signals corrected by the inverse gamma correction unit 510. Adjust the gain for each of the red, green, and blue multiplications by multiplying the gain values. In this case, the gain controller 520 may set a color temperature desired by the user or the set maker.

The integer converting unit 530 is inverse gamma corrected to convert the first output gray value exceeding an integer among the output gray values of the video signal including the integer and the decimal to an integer. The function of the integer conversion unit 530 will be described by taking a mapping using 255 real tones as an example.

First, the inverse gamma correction unit 510 performs inverse gamma correction on the input gray value in the manner as shown in Table 3, and outputs the output gray value.

               (a) (b)

(A) of Table 3 is a mathematically calculated value, and (b) is an actual algorithm applied value, the fractional part of the output gradation value rounded off based on 1/128 units.

Table 4 shows mapping codes for mapping using 255 real tones.

The mapping code used in the gradation representation is determined through the output gradation values in Table 3 (b) and Table 4.

For example, an output gray scale value corresponding to the input gray scale value 665 is 49.1875, and this output gray scale value is expressed by adding a halftone region between mapping codes 49 and 50 of Table 4.

In order to reduce such a halftone use area, the integer conversion unit 530 of the present invention, as shown in Table 5, the first output gradation value exceeding the integer among the output gradation values including an integer and a decimal number is the integer. By converting to, the halftone area used to express the fractional part is reduced to reduce the halftone noise.

Table 5 shows the integer conversion method of the integer conversion unit 530 of the present invention.

         (a) conventional method (b) method of the present invention

For example, in the case of the input gradation value 660, the halftone region between mapping codes 47 and 48 is used because the output gradation value is 47.140625. Only output gradation value is expressed. Therefore, unlike the conventional method shown in Table 5 (a), the input gradation value 660 is gradation expressed as an output gradation value having only real gradation values as shown in Table 5 (b), thereby expressing gradation without using a halftone region. , Halftone noise is reduced.

6 is a diagram illustrating an inverse gamma correction curve according to the present invention.

As shown in FIG. 6, it can be seen that the inverse gamma correction curve according to the present invention has no significant difference compared with the conventional inverse gamma correction curve. Therefore, the halftone noise is reduced by minimizing the halftone use area while maintaining the advantages of the conventional inverse gamma correction curve such as gray scale linearity.

The integer converting unit 530 preferably converts the first output gray value exceeding the integer among the output gray value values including integers and decimals to all integers. In this way, the use of the halftone region can be minimized.

The integer conversion unit 530 preferably converts the first output gray level value exceeding an integer among the output gray value values including integers and decimals for a part of the input gray level values into integers. In this way, the existing inverse gamma correction curve is used as it is in the area where the halftone area is not minimized, and in the area where the halftone area needs to be reduced, the integer conversion is performed as described above and the halftone noise and pseudo contour Reduce noise to an appropriate level at the same time.

The half toning unit 540 half-tons the image signal input from the integer converter 530 by at least one method of error diffusion or dithering. The image signal input to the half toning unit 540 includes grayscale data consisting of integer and decimal data. At this time, the decimal data is halftoned to be reflected in the integer data, and whether the integer data is mapped to the selected subfield mapping table is determined. As a result, the total gray value of the input video signal is determined, and the gray linearity and the gray scale expressing power of the displayed image can be secured.

The subfield mapping unit 550 maps an image signal input from the half toning unit 540 to a preset subfield mapping table.

The data arranging unit 560 sorts the spatially aligned subfield mapping data input from the subfield mapping unit 550 into temporal data.

The data driver 570 receives the time-aligned data by the data aligning unit 560 and supplies an address driving pulse to an address electrode (not shown) of the plasma display panel, thereby realizing an image of the plasma display apparatus. .

As described in detail above, according to the present invention, there is an effect capable of optimizing inverse gamma correction which is essential in realizing an image of the plasma display apparatus. In addition, it is possible to reduce pseudo contour noise and halftone noise displayed on the screen.

Since the image processing method according to an exemplary embodiment of the present invention processes the image under the same principle as the plasma display apparatus according to the exemplary embodiment of the present invention described in detail above, the description of the plasma display apparatus according to the exemplary embodiment of the present invention will be described. Replace with

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

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

As described in detail above, according to the present invention, there is an effect capable of optimizing inverse gamma correction which is essential in realizing an image of the plasma display apparatus.

In addition, it is possible to reduce pseudo contour noise and halftone noise displayed on the screen.

Claims (6)

An inverse gamma correction unit configured to inverse gamma correct an input gray value of an image signal input from the outside; And An integer conversion unit for converting the first output gray level value exceeding the integer among the output gray level values of the video signal including the inverse gamma corrected integer and a decimal number to the integer Plasma display device comprising a. The method of claim 1, The integer conversion unit And a first output gradation value exceeding the integer among the output gradation values for all of the input gradation values is converted into the integer. The method of claim 1, The integer conversion unit And a first output gradation value exceeding the integer among the output gradation values with respect to a part of the input gradation value to the integer. An inverse gamma correction step of inversely gamma correcting an input gray level value of an image signal input from the outside; And An integer conversion step of converting the first output gray level value exceeding the integer among the output gray level values of the video signal including the inverse gamma corrected integer and a decimal number to the integer Image processing method of the plasma display device comprising a. The method of claim 4, wherein In the integer conversion step And the first output gradation value exceeding the integer among the output gradation values is converted to the integer with respect to all the input gradation values. The method of claim 4, wherein In the integer conversion step And the first output gradation value exceeding the integer among the output gradation values is converted to the integer with respect to a part of the input gradation value.

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