KR100599659B1 - Plasma display device and image processing method thereof - Google Patents

Abstract

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

The image processing method of the plasma display device according to the present invention reduces the gradation distortion by diffusing the fractional error of the number of sustain pulses in each subfield during the predetermined frame when a predetermined frame or more is a still image.

Sustain Pulse, Fractional Error, Frame, Image Processing, Gradation

Description

Plasma display device and image processing method {PLASMA DISPLAY DEVICE AND IMAGE PROCESSING METHOD THEREOF}

1 is a timing diagram illustrating a method of driving a general plasma display device.

2 illustrates an example of the number of sustain pulses of each subfield in a typical plasma display device.

3 is a schematic plan view of a plasma display device according to an exemplary embodiment of the present invention.

4 is a block diagram schematically illustrating a plasma display device controller according to an exemplary embodiment of the present invention.

5 is a block diagram schematically illustrating a method of reducing gradation distortion of an image in a still image according to an exemplary embodiment of the present invention.

6 is an example of a method of reducing grayscale distortion of an image in a still image according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma display device and an image processing method thereof. More particularly, the present invention relates to a plasma display device and a method for processing the same, which reduce distortion of a gray level caused by a minority error of the number of sustain pulses in each subfield in a still image. .

Plasma display devices are flat display devices that display characters or images using plasma generated by gas discharge, and dozens to millions or more of pixels are arranged in a matrix form according to their size.

1 is a timing diagram illustrating a method of driving a general plasma display device.

Referring to the drawing, a unit frame is divided into eight subfields SF1-SF8 for time division gray scale display. Each subfield SF1-SF8 is divided into a reset period, an address period A1-A8, and a sustain period S1-S8.

The reset period is a period for initializing the state of each discharge cell to smoothly perform the addressing operation on the discharge cell, and the address period is a discharge cell that is turned on to select a discharge cell that is turned on and a discharge cell that is not turned on. Is a period in which wall charges are accumulated by applying an address voltage to the discharge cells. The sustain period is a period in which discharge for actually displaying an image is performed on the addressed discharge cells by applying a sustain pulse.

In the figure, the total length of the sustain periods S1-S8 in the unit frame is 255 T (T is the unit time). At this time, a time corresponding to 2 ^n-1 T (T is unit time) is set in the sustain period Sn of the nth subfield SFn, respectively. The n-th subfield has a weight value proportional to the length of the sustain period of the corresponding subfield, and the weight is proportional to the number of sustain pulses applied to the discharge cells. Accordingly, it is understood that when the subfield to discharge the discharge cells is appropriately selected from the eight subfields, display of 256 gray levels can be performed in all subfields including 0 (zero) gray that does not discharge the discharge cells. Can be.

Here, a considerable amount of power is consumed when discharging by applying a sustain pulse to the discharge cell. In particular, when displaying a bright image, the discharge is continuously generated according to the number of sustain pulses applied during the sustain period, at which time a lot of power is consumed.

Accordingly, when the image is bright, the sustain pulse is not continuously applied during the sustain period, and the number of sustain pulses applied to each subfield is adjusted according to the brightness of the image. In general, the brightness of the image is calculated by averaging the grayscale values of all discharge cells, and calculating the Automatic Power Control (APC) level using the average grayscale value. When the APC level is high, the number of sustain pulses in units of frames is reduced. On the contrary, when the APC level is low, the number of sustain pulses in units of frames is increased.

2 shows an example of the number of sustain pulses in units of frames determined according to the APC level and the number of sustain pulses of each subfield calculated according to the weight of each subfield.

When the number of sustain pulses in the frame unit is determined, the number of sustain pulses in each subfield is calculated according to the number of sustain pulses in the frame unit. The number of sustain pulses in each subfield may be calculated by first dividing the number of sustain pulses in a frame unit by the sum of all subfield weights and multiplying the value by the weights of the respective subfields. However, the number of sustain pulses of each subfield calculated as shown in FIG. 2 has a fractional part together with an integer part. Since the number of sustain pulses is output only by the integer part, the fractional part is discarded or rounded. In this case, an error by the fractional part occurs in the gradation representation.

In such a case, the fractional part error is not so much a problem in a moving picture, but there is a problem in that a subtle difference such as color in the still picture is generated.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a plasma display device and a method for processing the same, which reduce distortion of a gray level caused by a minority error of the number of sustain pulses in each subfield in a still image.

In accordance with an aspect of the present invention, there is provided an image processing method of a plasma display device. The plasma display device divides an input image signal into a plurality of subfields and displays a gray level according to a combination of the plurality of subfields. In the image processing method of

determining whether the input video signal is the same video signal by a predetermined number of frames or more;

(b) calculating the number of sustain pulses of each subfield according to the video signal; And

(c) If it is determined in step (a) that the same video signal is input for a predetermined number of frames or more, and if a fractional part exists in the number of sustain pulses of each subfield calculated in step (b), Determining the number of sustain pulses as an integer part of the sustain pulse number + 1 in a predetermined frame, and determining the number of sustain pulses as an integer part + 0 in the predetermined frame.

Plasma display device according to another aspect of the present invention

A plasma panel in which discharge cells are formed in an area where a plurality of address electrodes, a plurality of scan electrodes, and a sustain electrode cross each other;

If it is determined that the same video signal is inputted by a predetermined number of frames or more from the input video signal, and the number of sustain pulses of each subfield is calculated according to the video signal, and a fractional part exists, the number of sustain pulses of each subfield is determined. In the frame of, the integer part of the sustain pulse number + 1 is determined, and in the predetermined frame, the integer part of the sustain pulse number + 0 is determined.

A controller configured to generate a control signal for applying the determined number of sustain pulses of each subfield; And

And a scan / hold electrode driver for driving the scan / hold electrode in accordance with a control signal generated by the controller.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

A plasma display device and an image processing method thereof according to an embodiment of the present invention will now be described in detail with reference to FIGS. 3 to 6.

3 is a schematic plan view of a plasma display device according to an exemplary embodiment of the present invention.

As shown in FIG. 3, a plasma display device according to an exemplary embodiment of the present invention includes a plasma panel 100, an address driver 200, a scan / hold driver 300, and a controller 400.

The plasma panel 100 includes a plurality of electrodes. The electrodes are arranged in a matrix of m × n. Specifically, address electrodes (hereinafter referred to as 'A electrodes') A1-Am are arranged in a column direction, and n rows of scan electrodes are arranged in a row direction. Hereinafter, the Y electrodes (Y1-Yn) and the sustain electrodes (hereinafter referred to as 'X electrodes') (X1-Xn) are arranged in a zigzag. Here, the discharge space at the intersection of the A electrodes A1-Am and the X and Y electrodes X1-Xn and Y1-Yn forms a discharge cell.

The address driver 200 receives an address drive control signal from the controller 400 and applies an address pulse for selecting a discharge cell to be displayed to each address electrode A1-Am.

The scan and sustain driver 300 receives a control signal from the controller 400 and alternately applies a sustain pulse to the scan electrodes Y1-Yn and the sustain electrodes X1-Xn to perform sustain discharge for the selected discharge cell. do.

The controller 400 receives R, G, and B image signals and a synchronization signal from the outside, divides one frame into several subfields, and divides each subfield into a reset period, an address period, and a sustain period to drive the plasma display device. Generate a control signal. The controller 400 generates a control signal for applying an address pulse and supplies the control signal to the address driver 200. In addition, the controller 400 obtains the number of sustain pulses applied in the sustain period of each subfield, generates a control signal corresponding thereto, and supplies the generated control signal to the scan / maintenance driver 300.

The controller 400 first calculates an average gray value of all the discharge cells, and calculates an APC level using the average gray value. The number of sustain pulses in units of frames is determined according to the APC level. When the APC level is high, the number of sustain pulses in units of frames is reduced. On the contrary, when the APC level is low, the number of sustain pulses in units of frames is increased. In addition, the controller 400 obtains the number of sustain pulses in each subfield according to the number of sustain pulses in the frame unit and the weight of each subfield.

When the controller 400 obtains the number of sustain pulses applied to the sustain period of each subfield in the still image, the control unit 400 spreads the generated fractional error to subfields having the same weight of other frames. Tone distortion of the display image is reduced.

If the controller 400 defines an image that is the same as at least 10 frames as a still image, and determines that the currently displayed image is a still image, the controller 400 rounds the number of sustain pulses of each subfield to a second decimal place. Then, the number of sustain pulses of each subfield in the first to tenth frames is determined by using the numbers of the rounded decimals 0 to 9.

That is, the controller 400 sets the number of sustain pulses of the corresponding subfield to an integer part of the number of sustain pulses of the corresponding subfield in the frame of the number of 0 to 9 which is the rounded decimal number among 10 frames of the still image. In the remaining frames, the number of sustain pulses of the corresponding subfield is an integer part of the number of sustain pulses of the corresponding subfield.

For example, when the number of sustain pulses in one subfield is 17.6, the fractional part error is 0.6. Accordingly, the number of sustain pulses is determined to be 18 in six frames among the ten frames of the still image, and the number of sustain pulses is determined to be 17 in the remaining four frames. Thus, the decimal point of the number of sustain pulses of each subfield in the ten frames is spread to the subfields having the same weight of the other frames.

That is, if the control unit 400 according to the embodiment of the present invention recognizes that the same image signal is input for a predetermined number of frames or more from the input image signal, the control unit 400 performs a fractional part of the number of sustain pulses of each subfield calculated from the input image signal. Is classified into one of fractions having the predetermined number as a denominator.

Further, in the frame of the number of the molecular part of the fraction whose denominator is the predetermined number among the predetermined number frames, the number of sustain pulses of the corresponding subfield is set as an integer part of the number of sustain pulses of the corresponding subfield + 1, In the remaining frames, the number of sustain pulses of the corresponding subfield is determined as an integer part of the number of sustain pulses of the corresponding subfield.

In other words, when the same video signal is input for 10 or more frames, when the number of sustain pulses in one subfield is 17.6, the fractional error 0.6 of the number of sustain pulses in the corresponding subfield may be expressed as a fraction of 6/10. . Here, the number of sustain pulses of the corresponding subfield of the 10 frames is determined in consideration of the fraction 6/10. That is, in 6 frames out of 10 frames, 6/10 fractions are calculated as 1 to determine the number of sustain pulses as 18, and in 4 frames out of 10 frames, 6/10 fractions are calculated as 0 and sustain is calculated. The number of pulses is determined to be 17.

4 is a block diagram schematically illustrating a plasma display device controller 400 according to an exemplary embodiment of the present invention.

The control unit 400 includes an inverse gamma correction unit 410, an error diffusion unit 420, a memory control unit 430, an APC unit 440, and a scan / hold driver 450.

The inverse gamma correction unit 410 maps the n-bit R, G, and B image input data currently input to the inverse gamma curve and corrects the m-bit (m≥n) image signal. In a typical plasma display device, n is 8 and m is 10 or 12.

The error diffusion unit 420 error spreads the lower m-n bit image signal to the surrounding pixels from the m-bit image signal inversely gamma corrected by the inverse gamma correction unit 410. The error diffusion is a method of displaying an image by separating an image signal for a lower bit and spreading it to adjacent pixels. A detailed description thereof is described in Korean Laid-Open Patent Publication No. 2002-0014766.

The memory controller 430 generates subfield data corresponding to the gray level of the image signal output from the error diffusion unit 420, and then rearranges the subfield data into address data for driving the plasma display device. In this case, the memory controller 430 transmits address data for all discharge cells to the address driver 200 for each subfield.

The APC unit 440 calculates an average gray value of the image signal output from the inverse gamma correction unit 420, calculates an APC level according to the average gray value, and maintains the number of sustain pulses in the frame unit corresponding to the APC level ( Number of sustain discharge pulses).

In addition, the APC unit 440 calculates the number of sustain pulses in each subfield using the number of sustain pulses in the frame unit. For example, the number of sustain pulses in a frame unit is 1120, and the weights of the first to eighth subfields SF1-SF8 are 1, 2, 4, 8, 16, 32, 64, and 128, respectively. The number of sustain pulses of the eighth subfield may be obtained by using Equation 1.

Here, Nsf (n) is the number of sustain pulses in the nth subfield, and Nfr is the number of sustain pulses in units of frames. Wsf (n) is a weight of the nth subfield, and nmax is a total number of subfields, which is 8 in this embodiment.

When the number of sustain pulses in the frame unit is 1120, the number of sustain pulses of the first to eighth subfields calculated using Equation 1 is 4.39, 8.78, 17.56, 35.13, 70.27, 140.54, 281.09, and 562.19, respectively. The number of sustain pulses of each subfield thus calculated is composed of an integer part and a fractional part. In this case, since the output of the sustain pulse number is only an integer output, the APC unit 440 converts the fractional part to an integer.

However, when the currently displayed image is a still image, the APC unit 440 spreads the fractional error to subfields having the same weight of other frames to reduce the gradation distortion of the display image.

That is, when the APC unit 440 analyzes the image signal and determines that 10 or more frames of the image are the same, the APC unit 440 rounds the number of sustain pulses of each subfield to the second decimal place, and then rounds the decimal number from 0 to 0. A number of nine is used to determine the number of sustain pulses in each subfield of the first to tenth frames.

That is, the APC unit 440 converts the number of sustain pulses of the corresponding subfield into an integer part of the number of sustain pulses of the corresponding subfield in the frame of the number of 0 to 9 which is the rounded decimal number among 10 frames of the still image. In the remaining frames, the number of sustain pulses of the corresponding subfield is an integer part of the number of sustain pulses of the corresponding subfield.

For example, when the number of sustain pulses in one subfield is 17.6, the fractional part error is 0.6. Accordingly, the number of sustain pulses is determined to be 18 in six frames among the ten frames of the still image, and the number of sustain pulses is determined to be 17 in the remaining four frames. Thus, the decimal point of the number of sustain pulses of each subfield in the ten frames is spread to the subfields having the same weight of the other frames.

In addition, the APC unit 440 may adjust the number of sustain pulses in each subfield so that the overall luminance is constant when the gray level distortion is reduced in this manner. For example, when sustain discharge occurs in all subfields in a discharge cell, when the number of sustain pulses is 17.6, 18 sustain pulses generate an error of +0.4 in the corresponding frame. If you set 17 to, you get -0.6 error in the frame. In this case, the error of the luminance can be reduced by making the error of the number of sustain pulses in the unit of frame close to zero in one frame in the APC unit 440.

The method of reducing the error of the luminance in the APC unit 440 is as follows.

When the fractional part error is rounded to two decimal places, a number of 0.0, 0.1, and 0.2 to 0.9 is generated. In addition, the frequency of occurrence of these ten types of numbers is similar. Accordingly, the APC unit 440 according to an embodiment of the present invention divides the number of sustain pulses of each subfield into a case where the fractional part error is less than 0.50 and a case where it is 0.50 or more.

For example, when the number of sustain pulses is 17.6, the fractional part error is 0.6. Since 0.6 is 0.50 or more, in this case, the number of sustain pulses is 18 in the first to sixth frames, and the number of sustain pulses is 17 in the seventh to tenth frames. In the case where the number of sustain pulses is 17.4, the fractional part error is 0.4. Since 0.4 is less than 0.50, in this case, the number of sustain pulses is 16 in the first to sixth frames, and the number of sustain pulses is 17 in the seventh to tenth frames.

As a result, the APC unit 440 may reduce the error of luminance while reducing the distortion of the gray level in the still image.

The scan and sustain drive control unit 450 generates a control signal corresponding to the number of sustain pulses of each subfield calculated by the APC unit 440 and transmits the control signal to the scan and sustain drive unit 300.

5 is a block diagram schematically illustrating a method of reducing gradation distortion of an image in a still image according to an exemplary embodiment of the present invention.

A method of reducing grayscale distortion of an image in a still image is as follows. First, the received video signal is analyzed first to determine whether the product signal is equal to or greater than 10 frames (S100). The average gray value of the video signal is calculated, an APC level is calculated according to the average gray value, and the number of sustain pulses in units of frames corresponding to the APC level is determined (S110-S130). Next, the number of sustain pulses in each subfield SF is calculated by using the number of sustain pulses in the frame unit and the equation (1) (S140).

The fractional error in the calculated number of sustain pulses of each subfield is spread to subfields having the same weight of other frames to reduce the gradation distortion of the display image. First, the number of sustain pulses of each subfield is rounded to two decimal places, and then the number of sustain pulses of each subfield of the first to tenth frames is determined using the rounded decimal numbers 0 to 9. do.

That is, the number of sustain pulses of the corresponding subfield is set as an integer part of the number of sustain pulses of the corresponding subfield + 1 in the frame of the rounded decimal number 0 to 9 of the 10 frames of the still image. The number of sustain pulses of the field is made an integer part of the number of sustain pulses of the corresponding subfield (S150).

For example, when the number of sustain pulses in one subfield is 17.6, the fractional part error is 0.6. Accordingly, the number of sustain pulses is determined to be 18 in six frames among the ten frames of the still image, and the number of sustain pulses is determined to be 17 in the remaining four frames. Thus, the decimal point of the number of sustain pulses of each subfield in the ten frames is spread to the subfields having the same weight of the other frames.

In addition, the number of sustain pulses of each subfield may be divided into a case where the fractional part error is less than 0.50 and a case where the number is 0.50 or more.

For example, when the number of sustain pulses is 17.6, the fractional part error is 0.6. Since 0.6 is 0.50 or more, in this case, the number of sustain pulses is 18 in the first to sixth frames, and the number of sustain pulses is 17 in the seventh to tenth frames. In the case where the number of sustain pulses is 17.4, the fractional part error is 0.4. Since 0.4 is less than 0.50, in this case, the number of sustain pulses is 16 in the first to sixth frames, and the number of sustain pulses is 17 in the seventh to tenth frames.

That is, the method of reducing the distortion of the gray scale in the still image according to the embodiment of the present invention,

When it is recognized that the same video signal is inputted by a predetermined number of frames or more from the input video signal, the fractional part of the sustain pulse number of each subfield calculated from the input video signal is classified into one of the fractions having the predetermined number as the denominator.

Then, in the frame of the number of the molecular part of the fraction whose denominator is the predetermined number among the predetermined number frames, the number of sustain pulses of the corresponding subfield is + an integer part of the number of sustain pulses of the corresponding subfield + 1, In the remaining frames, the number of sustain pulses of the corresponding subfield is determined as an integer part of the number of sustain pulses of the corresponding subfield.

Accordingly, the method according to the embodiment of the present invention can reduce the error of luminance while reducing the distortion of the gray scale in the still image.

Referring to FIG. 6, an example of a method of reducing grayscale distortion of an image in a still image according to an exemplary embodiment of the present invention will be described.

An example of the case where the APC level is 160 is shown here. That is, when the APC level of the still image currently displayed is 160, the number of sustain pulses in the corresponding frame unit is 1120.

When the number of sustain pulses in the frame unit is substituted into Equation 1, the number of sustain pulses in the first to eighth subfields is 4.39, 8.78, 17.56, 35.13, 70.27, 140.54, 281.09, and 562.19, respectively. When rounded to the second decimal place, the number of sustain pulses in the first to eighth subfields is 4.4, 8.8, 17.6, 35.1, 70.3, 140.5, 281.1, and 562.2, respectively.

Herein, the number of sustain pulses of the corresponding subfield is set to the integer part of the number of sustain pulses of the corresponding subfield + 1 in the frame of the number 0 to 9, which is the rounded decimal number, and the number of sustain pulses of the corresponding subfield in the remaining frames. Let it be an integer part of the number of sustain pulses in the subfield.

In addition, in order to reduce the luminance error while reducing the gradation distortion in the still image, the number of sustain pulses of each subfield is divided into a case where the fractional error is less than 0.50 and more than 0.50.

therefore. As shown in FIG. 6, since the number of sustain pulses of the first subfield is 4.4 and the fractional part error of 4.4 is 0.50 or less, the number of sustain pulses of the first to sixth subfields is 4, and the number of the seventh to tenth subfields is shown. The number of sustain pulses is five. In addition, since the number of sustain pulses of the second subfield is 8.8 and the fractional part error of 8.8 is 0.50 or more, the number of sustain pulses of the first to eighth subfields is 9, and the number of sustain pulses of the ninth and tenth subfields. Is 8.

Since the number of sustain pulses of the sixth subfield is 140.5, the number of sustain pulses before rounding to the second decimal place is 140.54. Since the fractional part error of 140.54 is 0.50 or more, the number of sustain pulses of the first to fifth subfields is 141. And the number of sustain pulses of the sixth to tenth subfields is 140.

As described above, when the number of sustain pulses of each subfield is divided into a case where the fractional part error is less than 0.50 and a case of 0.50 or more, as shown in FIG. 6, the number of sustain pulses in units of frames is 1118, 1119, and 1121 in the first to tenth frames. Appears. Therefore, the error of the overall luminance is also reduced.

In the exemplary embodiment of the present invention, the criterion for determining that the currently displayed image is a still image is the same image by 10 frames or more, but the present invention is not limited to the number of the frames.

In the embodiment of the present invention, the number of subfields is shown as eight, but the present invention is not limited thereto.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

As described above, according to the present invention, the gradation distortion of the display image may be reduced by spreading the fractional part error in the number of sustain pulses of each subfield to subfields having the same weight of other frames.

The number of sustain pulses of each subfield is divided into a case where the fractional error is less than 0.50 and a case where the fractional error is 0.50 or more, thereby reducing the luminance error while reducing the distortion of the gray scale in the still image.

Claims (5)

An image processing method of a plasma display device, which divides an input video signal into a plurality of subfields and displays a gray scale according to a combination of the plurality of subfields. (a) determining whether K (K is a natural number) or more identical video signals in the input video signal; (b) calculating the number of sustain pulses of each subfield according to the video signal; And (c) If it is determined in step (a) that the same video signal is input for at least K frames, and a fractional part exists in the number of sustain pulses of each subfield calculated in step (b), the sustain of each subfield is performed. Determining the number of pulses by a part of the K frames as an integer part of the corresponding sustain pulse + 1, and determining the remainder of the K frames as an integer part of the corresponding sustain pulse number + 0. Way. The method of claim 1, Step (c) is, (d) If it is determined in step (a) that the same video signal is equal to or greater than the K frames, the fractional part of the number of sustain pulses of each subfield calculated in step (b) is the fraction of the number K as the denominator. Classifying them as one; And (e) In the frame of the number of the molecular part of the fraction of which K is the denominator among the K frames, the number of sustain pulses of the corresponding subfield is + an integer part of the number of sustain pulses of the corresponding subfield + 1, and the rest And determining the number of sustain pulses of the corresponding subfield as an integer part of the number of sustain pulses of the corresponding subfield in the frame. The method of claim 2, K is 10, and the fractional part is the first decimal place. A plasma panel in which discharge cells are formed in an area where a plurality of address electrodes, a plurality of scan electrodes, and a sustain electrode cross each other; If it is determined that the same video signal is inputted by more than K frames from the input video signal, and the number of sustain pulses of each subfield is calculated according to the video signal, if a fractional part exists, the number of sustain pulses of each subfield is determined by the K. Some of the frames are determined by the integer part of the sustain pulse number + 1, the rest of the K frames are determined by the integer part + 0 of the sustain pulse number, and the control signal to apply the sustain pulse number of each determined sub-field A control unit for generating a; And And a scan / hold electrode driver for driving the scan / hold electrode in accordance with a control signal generated by the controller. The method of claim 4, wherein The control unit, If it is determined that the same video signal equal to or greater than K frames is input from the input video signal, the fractional part of the number of sustain pulses of each subfield calculated from the input video signal is classified into one of the fractions with K as the denominator. The number of sustain pulses of the corresponding subfield is set to the integer part of the number of sustain pulses of the corresponding subfield + 1 in the frame of the number of the molecular part of the fraction having the classified K as the denominator among the K frames. And determining the number of sustain pulses of the field as an integer part of the number of sustain pulses of the corresponding subfield.

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