KR20070072123A - Plasma display apparatus and image processing method there of - Google Patents

Abstract

A plasma display and an image processing method thereof are provided to improve gray level reproducing performance and to prevent decrease in the number of sustain pulses by saturating output value at high gray level and thus increasing the number of subfields. In a plasma display, there is provided a plasma display panel(360). An inverse gamma correcting unit(300) performs inverse gamma correction on an image signal input from the outside such that an output gray level output according to an input gray level of the image signal becomes saturated as the number of subfields increases. A subfield mapping unit(330) performs a subfield mapping on the image signal output from the inverse gamma correcting unit.

Description

Plasma Display Apparatus and Image Processing Method Thereof

1 is a diagram showing an example of a general plasma display panel structure.

2 is a diagram showing a method of implementing an image of a conventional plasma display panel.

3 is a block diagram showing an image processing unit of the plasma display device of the present invention.

4A and 4B are graphs showing the relationship between the number of sustain pulses according to the APL value used in the plasma display device of the present invention.

5A to 5B are graphs showing the relationship between luminance per gray level according to the number of subfields according to an embodiment of the present invention.

6 is a graph showing the relationship between the output gray scale according to the input gray scale according to another embodiment of the present invention.

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

300: reverse gamma correction unit 310: gain control unit

320: halftone part 330: subfield mapping part

340: APL calculation unit 350: sustain pulse number control unit

The present invention relates to a plasma display device, and more particularly, to a plasma display device and an image processing method thereof capable of preventing image quality deterioration.

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

1 is a diagram illustrating a general plasma display panel structure.

As shown in FIG. 1, a conventional plasma display panel includes a plurality of scan electrodes 102 and Y and sustain electrodes 103 and Z formed on a front substrate 101 that is an image display surface. The front panel 100 in which the storage electrode pairs are arranged, and the rear panel 110 in which the plurality of data electrodes 113 and X are arranged so as to intersect the plurality of storage electrode pairs described above on the rear substrate 111 forming the rear surface are constant. Combined in parallel with a distance between them.

The front panel 100 is, for example, a scan electrode 102 and Y and a sustain electrode 103 and Z for mutual discharge in one discharge cell and maintaining light emission of the cell, that is, a transparent electrode formed of a transparent ITO material. And a pair of scan electrodes 102 and Y and sustain electrodes 103 and Z provided as a bus electrode b made of a metal material. Scan electrodes 102 and Y and sustain electrodes 103 and Z are covered by one or more upper dielectric layers 104 that limit the discharge current and insulate the electrode pairs, and discharge on top of upper dielectric layer 104. In order to facilitate the condition, a protective layer 105 on which magnesium oxide (MgO) is deposited is formed.

For example, the rear panel 110 may be arranged such that a plurality of discharge spaces, that is, partitions 112 of a stripe type (or well type) for forming the discharge cells are parallel to each other. In addition, a plurality of data electrodes 113 and X for performing address discharge to generate vacuum ultraviolet rays are disposed in parallel with the partition wall 112. On the upper side of the rear panel 110, R, G, and B phosphors 114 which emit visible light for image display during address discharge are coated. A lower dielectric layer 115 is formed between the data electrodes 113 and X and the phosphor 114 to protect the data electrodes 113 and X.

The front panel 100 and the rear panel 110 formed as described above are bonded to each other through a sealing process to form a plasma display panel. In addition, a plasma display panel is provided with a driving unit for driving electrodes such as scan electrodes 102 and Y, sustain electrodes 103 and Z, and data electrodes 113 and X. Make up the device.

The above-described driving unit generates a discharge by supplying a predetermined driving voltage to the plurality of electrodes to display an image. A method of implementing such an image of the plasma display apparatus is shown in FIG. 2.

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

As shown in FIG. 2, the plasma display panel divides one frame period into a plurality of subfields having different discharge times, and emits the 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, gray levels of an image can be realized according to the weight of the sustain period of each subfield.

Here, the gray scale expression power is improved as the number of subfields forming one frame is increased. That is, as the number of subfields increases, the number of values of "N" of 2 ⁿ representing the aforementioned sustain period increases. As the number of " N " increases, the number of gray scale values that can be expressed increases, thereby improving gray scale expression power.

However, increasing the number of subfields thus encounters a time limit. For example, the margin of the driving time decreases as the address period increases in the single scan method. Problems caused by the reduction of the driving time margin may be described as follows.

That is, a problem arises that the number of subfields that can be used overall decreases due to an increase in the address period. Accordingly, there is a problem that the image quality deterioration phenomenon is intensified, such as not only the number of real gray scales that can be expressed but also strong halftone noise appear.

On the other hand, in order to maintain the number of subfields, the weight of the sustain pulses assigned to each gray level in each sustain period, that is, the number of sustain pulses, must be reduced, which not only lowers the brightness and reduces the sharpness. There is a problem.

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

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

Further, another object of the present invention is to provide a plasma display device and an image processing method thereof capable of preventing a decrease in luminance while increasing the number of subfields.

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

The plasma display device according to the present invention for achieving the above object is a plasma display panel, an inverse gamma correction unit and the inverse gamma correction unit to saturate as the number of subfields is increased according to the input gray level of the external image signal And a subfield mapping unit for subfield mapping the image signal output from the gamma correction unit.

The plasma display panel may be driven by a single scan method.

The output gradation according to the input gradation when the number of subfields is N is equal to the output gradation according to the input gradation when the number of subfields is N-1 below a predetermined threshold gradation value.

In addition, the output gradation value according to the input gradation when the number of the subfields is N is saturated above a predetermined threshold gradation value.

The maximum value of the output grayscale according to the input grayscale when the number of subfields is N is the same as the maximum value of the output grayscale according to the input grayscale when the number of subfields is N-1.

In addition, the plasma display apparatus according to the present invention for achieving the above object is a sustain pulse number control unit so that the output luminance output according to the input gray level of the plasma display panel and the external image signal is saturated as the number of subfields increases. And a driving unit which applies a sustain pulse according to the output of the sustain pulse number control unit.

The plasma display panel may be driven by a single scan method.

The output luminance according to the input grayscale when the number of the subfields is N is equal to the output luminance according to the input grayscale when the number of the subfields is N-1 below a predetermined threshold grayscale value.

The output luminance value according to the input gray level when the number of the subfields is N is saturated above a predetermined threshold gray value.

The maximum value of the output luminance according to the input grayscale when the number of subfields is N is the same as the maximum value of the output luminance according to the input grayscale when the number of subfields is N-1.

In the image processing method of the plasma display apparatus according to the present invention for achieving the above object, an inverse gamma correction step of causing an output gray level to be saturated according to an input gray level of an external image signal, as the number of subfields is increased, the inverse gamma And a subfield mapping step of subfield mapping the image signal output in the correction step.

In addition, the method of driving the plasma display device may be a single scan method.

The output gradation according to the input gradation when the number of subfields is N is equal to the output gradation according to the input gradation when the number of subfields is N-1 below a predetermined threshold gradation value.

In addition, the output gradation value according to the input gradation when the number of the subfields is N is saturated above a predetermined threshold gradation value.

The maximum value of the output grayscale according to the input grayscale when the number of subfields is N is the same as the maximum value of the output grayscale according to the input grayscale when the number of subfields is N-1.

In addition, the image processing method of the plasma display apparatus according to the present invention for achieving the above object is a sustain pulse number control step of causing the output luminance output according to the input gray level of the external image signal to be saturated as the number of subfields increases And applying a sustain pulse according to the output of the sustain pulse number control unit.

In addition, the method of driving the plasma display device may be a single scan method.

The output luminance according to the input grayscale when the number of subfields is N may be equal to the output luminance according to the input grayscale when the number of subfields is N-1 below a predetermined threshold grayscale value.

The output luminance value according to the input gray level when the number of the subfields is N is saturated above a predetermined threshold gray value.

The maximum value of the output luminance according to the input grayscale when the number of subfields is N is the same as the maximum value of the output luminance according to the input grayscale when the number of subfields is N-1.

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

3 is a block diagram showing an image processing unit of the plasma display device of the present invention.

As shown in FIG. 3, the plasma display apparatus according to an exemplary embodiment of the present invention includes an inverse gamma correction unit 300, a gain control unit 310, a halftone unit 320, a subfield mapping unit 330, and an APL ( An average picture level calculator 340, a sustain pulse number controller 350, and a plasma display panel 360.

The inverse gamma correction unit 300 linearly converts the displayed luminance value by correcting the output gray value according to the gray value of the image signal input through the prestored gamma data.

Here, the inverse gamma correction unit 300 according to an embodiment of the present invention saturates the output gray level output according to the input gray level of the external image signal as the number of subfields increases. It will be described later.

The gain controller 310 may be adjusted by a user or a set maker for the red, green, and blue image signals corrected by the inverse gamma correction unit 300. Adjust the gain by red, green and blue by multiplying the gain values. In this case, the gain controller 310 may set a color temperature desired by the user or the set maker.

The halftone unit 320 quantizes an image signal input from the gain control unit 310 and diffuses an error component generated therebetween to adjacent pixels, thereby finely adjusting the luminance value displayed according to the gray scale value to adjust the gray scale expression power. Improve. Such a method is called an error diffusion method, and in addition, the halftone unit 320 may be half-toned by using a dithering method through a dither mask.

The subfield mapping unit 330 maps an image signal input from the halftone unit 320 to a preset subfield mapping table and outputs the mapping. Thereafter, the data alignment unit (not shown) aligns the data mapped by the subfield mapping unit 330 into temporal data and supplies the plasma display panel 360 to the plasma display panel 360 through a driving device to implement an image.

The APL calculator 340 calculates an average picture level (APL) value for one frame of an externally input image signal. The weight of the sustain pulse number, that is, the luminance value for one frame is determined according to the calculated APL value. Information of the APL value is provided to the sustain pulse number control unit 350, and the sustain pulse number control unit 350 maintains constant power consumption by adjusting the number of sustains of the entire screen every frame.

In addition, in another embodiment of the present invention, the sustain pulse number control unit 350 may cause the output luminance output according to the input gray level of the external image signal to be saturated as the number of subfields increases. It will be described in detail with reference to.

Meanwhile, the plasma display apparatus of the present invention achieves a technical problem of increasing the number of subfields by saturating an output value in high gradation to improve the gradation expression power and preventing the decrease of the number of sustain pulses. In order to clarify the construction and operation of the present invention, the concept of APL (Average Picture Level) is as follows.

4A and 4B are graphs showing the relationship between the number of sustain pulses according to the APL value used in the plasma display device of the present invention.

As illustrated in FIG. 4A, the plasma display apparatus includes an average picture level (APL) calculator 340 described above with reference to FIG. 3 to differently assign the weight of the number of sustain pulses applied to the sustain period according to the APL value.

That is, by adjusting the number of sustain pulses according to the average picture level (APL), power consumption can be kept constant as shown in the graph of FIG. 4A. More specifically, the plasma display apparatus is configured to allocate the maximum number of sustain pulses per gray level at an APL value of 20% APL or less, and to gradually reduce the number of sustain pulses allocated per gray level at an APL value of 20% APL or more. 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.

In addition, the adjustment according to the APL has the effect of realizing the sharper picture quality by improving the contrast on the dark screen while considering the characteristic that the human eye is not sensitive even when the overall brightness is relatively lower on the bright screen. .

Here, as shown in FIG. 4B, in a bright screen, for example, a screen having a high APL (Average Picture Level), since a large number of discharge cells are turned on, a weight of the number of sustain pulses allocated per gray level may be lowered to lower the maximum brightness. That is, as the APL increases, the weight of the number of sustain pulses allocated per gray level decreases, so that the luminance curve per gray level increases with a low slope.

On the contrary, in a dark screen, for example, a screen having a low Average Picture Level (APL), since the discharge cells are relatively small, the maximum brightness may be increased by increasing the weight of the number of sustain pulses allocated per gray level. That is, as shown in FIG. 4B, as the APL becomes smaller, the weight of the number of sustain pulses allocated per gray level increases, so that the slope of the luminance curve per gray level becomes higher. Accordingly, the number of sustain pulses becomes the maximum at the maximum gray value when APL is low. It can be seen that. In other words, it can also be seen that the maximum number of sustain pulses available under such conditions is limited.

Meanwhile, in the configuration for increasing the number of subfields used in one frame of the present invention, such an APL concept may be considered as an example.

That is, the number of subfields that can be used in one frame is closely correlated with the number of sustain pulses that are applied in the sustain period. More specifically, the number of usable subfields in one frame may be low. You are limited by the total number of sustain pulses used in dark scenes. That is, the number of subfields should be adjusted in consideration of the region where the APL to which the largest number of sustain pulses is allocated is low.

Considering the above, the implementation luminance per gray level according to the number of subfields is as follows.

5A to 5B are graphs showing the relationship between luminance per gray level according to the number of subfields according to an embodiment of the present invention.

In FIG. 5A, a relationship between weights of output luminances (number of sustain pulses) implemented per gray level is illustrated. In other words, as the number of sustain pulses per gray level is allocated, a steep rise curve such as curve A appears.

However, if the number of subfields is increased here, i.e., if the number of subfields forming a frame is increased from N-1 to N, the time that can be allocated to the sustain period is reduced, and thus the available sustain is possible. The number of pulses is also reduced so that the output luminance characteristic per gray level is represented by curve B. FIG.

As the subfield is increased in this manner, the curve gradually decreases from B to C and from C to D, so that the number of sustain pulses allocated per gray level decreases, thereby decreasing luminance. The configuration and operation of the present invention for preventing the luminance deterioration phenomenon caused by increasing the number of subfields in order to increase the gray scale expression power are as follows.

As shown in FIG. 5B, for example, as the number of subfields is increased from N-1 to N, the output luminance curve per gray level is changed from A to B. In the present invention, the output luminance curve per gray level is thus lowered. Can be prevented.

That is, even if the number of subfields is increased from N-1 to N, for example, the saturation of the maximum sustain pulses that can be used in the high gradation region, ie, the maximum value of the corresponding curve B, is maintained so that the output luminance curve per gradation remains mostly A. You can.

More specifically, a predetermined threshold gray value G may be set to control and saturate the output luminance according to the input gray level only in a high gray level region over the threshold gray value.

Such a function may be performed by the sustain pulse number control unit described above with reference to FIG. 3. That is, the sustain pulse number control unit can saturate the luminance value corresponding to the maximum number of sustain pulses available by controlling the number of sustain pulses allocated per input gray level in the high gray level region having a value equal to or greater than a predetermined threshold gray level value (G). It is.

As described above, according to the present invention, it is possible to provide a plasma display device capable of improving the gray scale expression power by preventing the deterioration of image quality and realizing a higher quality image.

In addition, not only the number of subfields can be increased, but also the luminance reduction caused by the saturation of the high gradation region can be prevented.

In other words, the area where the APL is small and the high gradation is not affected by the human eye even if the gradation is saturated to some degree, and the area where the APL is small and the high gradation is the luminance value corresponding to the limited number of sustain pulses. In the other areas, the output luminance characteristic can be kept high as the subfield increases. Accordingly, the practical image can compensate for the luminance deterioration caused by the increased subfield while eliminating output characteristic distortion.

In addition, the structure of this invention is not limited to this. That is, it is considered that the present invention is considered to be included in the present invention as long as it increases the number of subfields and saturates a high gradation region in which the number of sustain pulses is limited, thereby preventing a decrease in luminance.

Such a function of the present invention may be performed by the inverse gamma correction unit of FIG. 3 according to another embodiment.

6 is a graph showing the relationship between the output gray scale according to the input gray scale according to another embodiment of the present invention.

As shown in FIG. 6, the inverse gamma correction unit corrects an output gray value according to a gray value of an input image signal by using prestored gamma data to display a gamma characteristic of a curve such as A. FIG.

Here, the inverse gamma correction unit may convert an output grayscale value with respect to an input grayscale in a high grayscale region having a value equal to or greater than a predetermined threshold grayscale value G. For example, above the threshold gray value G, the gray scale value itself may be converted into a gray scale value corresponding to the saturated luminance value from the output gray scale value according to the input gray scale value as shown in the curve B. FIG. In this way, the object of the present invention can be achieved by varying the gamma characteristic so as to convert the gray value itself so as to saturate the luminance value of the maximum number of sustain pulses allowed in the high gray level.

As described above, the plasma display apparatus of the present invention can not only deteriorate the halftone noise and the image quality by increasing the number of subfields, thereby realizing a high quality image, but also improving the luminance and clarity, which are opposite effects. It works. In addition, the present invention may be referred to as a practical technology corresponding to high quality and low price in the market of plasma display apparatuses, in which demand is gradually increased and popularized.

The present invention can use both the dual scan method and the single scan method for driving the data electrodes separately, but can be used more efficiently in the single scan method.

That is, the single scan method for driving all the data electrodes with one driving unit is spotlighted as a reduction in manufacturing cost. In such a single scan method, the margin of driving time is reduced. That is, the address period for addressing all electrodes becomes long, so that the above-mentioned sustain period is shortened, which reduces the practicality of driving.

As a result, the problem of decreasing the number of subfields or the number of sustain pulses is a technical problem to be solved by the single scan method. The present invention can compensate for luminance and sharpness falling while increasing the number of subfields. By presenting a configuration that can solve the above technical problem.

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

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

As described above, the plasma display device and the image processing method thereof of the present invention have the effect of preventing image quality deterioration.

In addition, the plasma display device and the image processing method thereof of the present invention have the effect of improving the margin of the driving time.

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

In addition, the plasma display device and the image processing method thereof of the present invention have an effect of improving the brightness and the sharpness.

Claims (20)

A plasma display panel; An inverse gamma correction unit configured to saturate the output grayscale output according to the input grayscale of the external video signal as the number of subfields increases; And A subfield mapping unit for subfield mapping the image signal output from the inverse gamma correction unit; Plasma display device comprising a. The method of claim 1, And a method of driving the plasma display panel is a single scan method. Which drives the scan electrode with one scan driver The method of claim 1, And an output gradation according to an input gradation when the number of subfields is N is equal to an output gradation according to an input gradation when the number of subfields is N-1 below a predetermined threshold gradation value. . The method of claim 3, wherein And an output gradation value corresponding to an input gradation when the number of subfields is N is saturated above a predetermined threshold gradation value. The method of claim 4, wherein And a maximum value of an output gradation according to an input gradation when the number of subfields is N is the same as a maximum value of an output gradation according to an input gradation when the number of subfields is N-1. A plasma display panel; A sustain pulse number controller configured to saturate an output luminance output according to an input gray level of an external video signal as the number of subfields increases; And A driver for applying a sustain pulse according to the output of the sustain pulse number control unit; Plasma display device comprising a. The method of claim 6, And a method of driving the plasma display panel is a single scan method. The method of claim 6, An output luminance according to an input gradation when the number of subfields is N, equal to an output luminance according to an input gradation when the number of subfields is N-1 below a predetermined threshold gradation value . The method of claim 8, And an output luminance value corresponding to an input gradation when the number of subfields is N is saturated above a predetermined threshold gradation value. The method of claim 9, And the maximum value of the output luminance according to the input grayscale when the number of subfields is N is the same as the maximum value of the output luminance according to the input grayscale when the number of subfields is N-1. In the image processing method of the plasma display device, An inverse gamma correction step of causing an output gray level output according to an input gray level of an external video signal to be saturated as the number of subfields increases; A subfield mapping step of subfield mapping the image signal output in the inverse gamma correction step; Image processing method of the plasma display device comprising a. The method of claim 11, And the method of driving the plasma display device is a single scan method. The method of claim 11, And an output gradation according to an input gradation when the number of subfields is N is equal to an output gradation according to an input gradation when the number of subfields is N-1 below a predetermined threshold gradation value. Image processing method. The method of claim 13, And an output gradation value corresponding to an input gradation when the number of subfields is N is saturated above a predetermined threshold gradation value. The method of claim 14, The maximum value of the output gradation according to the input gradation when the number of subfields is N is the same as the maximum value of the output gradation according to the input gradation when the number of subfields is N-1. Treatment method. In the image processing method of the plasma display device, A sustain pulse number control step of causing the output luminance output according to an input gray level of an external video signal to be saturated as the number of subfields increases; Applying a sustain pulse according to the output of the sustain pulse number control unit; Image processing method of the plasma display device comprising a. The method of claim 16, And the method of driving the plasma display device is a single scan method. The method of claim 16, An output luminance according to an input gradation when the number of subfields is N, equal to an output luminance according to an input gradation when the number of subfields is N-1 below a predetermined threshold gradation value Image processing method. The method of claim 18, And an output luminance value corresponding to an input gradation when the number of subfields is N is saturated above a predetermined threshold gradation value. The method of claim 19, The maximum value of the output luminance according to the input gradation when the number of subfields is N is the same as the maximum value of the output luminance according to the input gradation when the number of subfields is N-1. Treatment method.

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