Method of displaying gray scales of plasma display panel, and plasma display device

A method of expressing gray scales of a plasma panel display using the sum of weights assigned to subfields, including extracting a first gray scale arrangement including gray scale n using (k−1) subfields to gray scale m using k subfields from a second gray scale arrangement including gray scale 1 to gray scale m using k subfields between the 1st and the jth subfields when the number of subfields used for gray scale (i+1) is the same or greater than the number of subfields used for gray scale i, and generating a third gray scale arrangement including gray scales (n+p) to (m+p) by adding a weight p of the (j+1)th subfield to the first gray subfield arrangement including the gray scales n to m.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0037296, filed on May 25, 2004, which is hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of displaying gray scales of a plasma display panel (PDP), and more particularly, relates to a method and apparatus for more accurately expressing gray scales.

2. Description of the Background

Generally, a plasma display device displays characters or images using a PDP, which generates plasma by gas discharge. The PDP may include hundreds of thousands to millions of pixels (discharge cells) arranged in a matrix. PDPs may be direct current (DC) types or alternating current (AC) types according to driving voltage waveform patterns and discharge cell structures.

In a general AC PDP, a single field (1 TV field) may be divided into a plurality of subfields. Each subfield is assigned a weight, and a total of the weights respectively assigned to the plurality of subfields represents gray scales. Examples of a method representing gray scales will be described hereinafter. Assume that a single field is divided into eight subfields SF1to SF8and weights assigned to the subfields are 1, 2, 4, 8, 16, 32, 64, and 128, respectively.

In this case, when a discharge cell represents gray scale1, the discharge cell is turned on in the first subfield SF1and is turned off in the remaining subfields SF2to SF8. If a discharge cell represents gray scale27, the discharge cell is turned on in the first, second, fourth, and fifth subfields SF1, SF2, SF4, and SF5(1+2+8+16=27). Further, gray scale255is represented by turning on the discharge cell from the first subfield to the eighth subfield SF1to SF8. The gray scale is represented by adding up weights assigned to the subfields having the discharge cells selected to be turned on.

Each subfield of the PDP may include a reset period, an address period, and a sustain period. The address period selects discharge cells to be turned on in a corresponding subfield, and the sustain period sustain-discharges the selected discharge cells during a period corresponding to a weight assigned to the corresponding subfield. Herein, the duration of the sustain period, in other words, the amount of light emitted due to the sustain-discharge during the sustain period, determines weight values. Substantially, the amount of light emission within a single subfield is the sum of the amount of light emitted due to the sustain discharge and an address discharge. For instance, in the case that the amount of light emitted due to the address discharge and the first occurrence of a sustain-discharge is set to be 2 (cd/m2) and the amount of light emitted due to a sustain pulse of one period is set to be 1.4, the amount of light emission for each gray scale is shown inFIG. 1.

Referring toFIG. 1, the amount of light emission for gray scale7and gray scale8are almost identical, and the amount of light emission for gray scale15is greater than the amount of light emission for gray scale16. When representing gray scale7, the address discharge occurs three times because the discharge cell is turned on in the first, second, and third subfields, whereas the address discharge occurs once for gray scale8because the discharge cell is turned on only in the fourth subfield to represent gray scale8. However, according to the foregoing assumption, two emissions of the amount of light emitted from the address discharge (1.2) is almost identical to the amount of light emitted due to the sustain discharge (1.4), and therefore gray scales7and8are represented as almost the same. In like manner, the address discharge occurs four times for gray scale15, whereas the address discharge occurs once for gray scale16. Accordingly, the amount of light emission for gray scale15is greater than the amount of light emission for gray scale16, thereby resulting in a reverse gray scale.

Accordingly, in a conventional subfield structure, a gray scale to be displayed on the screen may not always be represented as it is supposed to be when actually displayed on the screen.

SUMMARY OF THE INVENTION

The present invention provides a method of expressing gray scales of a PDP where input gray scales may match output gray scales.

The present invention discloses a method of expressing gray scales of a plasma display panel representing the gray scales using a sum of weights assigned to a plurality of subfields having discharge cells selected to be turned on, the method including extracting a first gray scale arrangement, including a gray scale n using (k−1) subfields to a gray scale m using k subfields (n<m, n is an integer), from a second gray scale arrangement, including a gray scale I to the gray scale m using k subfields between a 1st subfield and a jth subfield, when a number of subfields used for representing gray scale (i+1) (1≦i≦(m−1)) is the same or greater than a number of subfields used for representing gray scale i; generating a third gray scale arrangement including a gray scale (n+p) to a gray scale (m+p) by adding a weight p assigned to a (j+1)th subfield to the first gray scale arrangement including the gray scale n to the gray scale m; and generating a fourth gray scale arrangement including the gray scale1to the gray scale (m+p) by selecting the second gray scale arrangement in a range from gray scale1to a gray scale (n+p−1) and selecting the third gray scale arrangement in a range from the gray scale (n+p) to the gray scale (m+p).

The present invention also discloses a plasma display including a plasma display panel having a plurality of discharge cells, and expressing gray scales by a sum of weights assigned to subfields of a discharge cell selected to be turned on among a plurality of subfields having respective weights, and a controller selecting subfields of the discharge cell selected to be turned on according to an input gray scale. The controller sets a number of subfields used to represent input gray scale (i+1) to be the same or greater than a number of subfields used to represent input gray scale i.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

The following detailed description shows and describes only certain exemplary embodiments of 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. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive. There may be parts shown in the drawings, or parts not shown in the drawings, that are not discussed in the specification as they are not essential to a complete understanding of the invention. Like reference numerals designate like elements.

FIG. 2schematically illustrates a plasma display device according to an exemplary embodiment of the present invention.

Referring toFIG. 2, the plasma display device according to an exemplary embodiment of the present invention may include a PDP100, a controller200, an address electrode driver300, a sustain electrode driver, and a scan electrode driver500.

The PDP100includes address electrodes A1to Amarranged in columns, and sustain electrodes X1to Xnand scan electrodes Y1to Ynarranged in rows. The sustain electrodes X1to Xncorrespond to the respective scan electrodes Y1to Yn, and sustain electrode ends are coupled to each other. Additionally, the PDP100includes a front substrate (not shown) on which the sustain electrodes and the scan electrodes (X1to Xnand Y1to Yn) are arranged, and a rear substrate (not shown) on which the address electrodes (A1to Am) are arranged. The front and rear substrates may be made of, for example, glass, and they are sealed together with a discharge space therebetween. The address electrodes A1to Ammay be substantially orthogonal to the scan electrodes Y1to Ynand the sustain electrodes X1to Xn. An intersection between each of the address electrodes A1to Amand the scan and sustain electrode X1to Xnand Y1to Ynpairs forms a discharge cell.

The controller200selects one or more subfields of a discharge cell selected to be turned on, and generates an address driving control signal, a sustain electrode driving control signal, and a scan electrode driving control signal. Further, the controller200adjusts the number of subfields representing gray scale (i+1) to be the same or larger than that of subfields representing gray scale (i).

The address driver300, the X electrode driver400, and the Y electrode driver500receive a driving control signal from the controller200, and respectively apply the driving control signal to the address electrodes A1to Am, the sustain electrodes X1to Xn, and the scan electrode Y1to Ynin the respective subfields.

A method of forming subfields by the controller200according to an exemplary embodiment of the present invention will be described hereinafter, referring toFIG. 3A,FIG. 3BandFIG. 3C, as well asFIG. 4A,FIG. 4B,FIG. 4C,FIG. 4D,FIG. 4EandFIG. 4F.

Generally, an address discharge occurs in the address period when positive voltages are applied to the address electrodes of discharge cells selected to be turned on and negative voltages are applied to the scan electrodes of the discharge cells. Herein, un-selected scan electrodes may be biased with positive voltages. Accordingly, positive wall charges may form on the scan electrodes and negative wall charges may form on the sustain electrodes of the discharge cells in which the address discharge occurs. Sustain pulses, alternately having a high level voltage and a low level voltage, are alternately applied to the scan electrodes and the sustain electrodes. Herein, phases of the sustain pulse applied to the scan electrode and the sustain electrode are opposite to each other. During the sustain period, applying the high level voltage to the scan electrodes causes a sustain discharge, and then sustain pulses may be repeatedly applied corresponding to weights assigned to the respective subfields, thereby causing the sustain discharge to occur repeatedly. The final sustain discharge may occur in a state that application of the high level voltage to the scan electrode has already proceeded. Here, one period of the sustain pulse is a period during which the sustain pulse applied to the scan electrode (or sustain electrode) has the low level voltage and the high level voltage once. That is, the sustain period comprises a high level voltage applied to the scan electrode and n periods of the sustain pulse (where, n is a positive integer or zero).

For instance, brightness x of a subfield having weight1is obtained by adding the brightness by an address discharge and the first sustain discharge, the brightness (x+y) of a subfield having weight2is obtained by adding brightness y by the sustain discharges that have occurred during one period of the sustain pulse and the brightness x by the address discharge and the first sustain discharge. Brightness of a subfield having weight4is obtained by adding brightness3yby the sustain discharges that have occurred during three periods of the sustain pulse and the brightness x. Therefore, brightness of a subfield having weight j is obtained by adding the brightness x and brightness [(j−1)*y)] by the sustain discharges that have occurred during (j−1) periods of the sustain pulse.

Brightness [L(i)] of gray scale i and brightness [(L(i+1))] of gray scale (i+1) vary depending on weights and the number of associated subfields used to represent gray scales i and (i+1), as known from Equations 1 and 2.
L(i)=ax+byEquation 1

where x is the brightness by an address discharge and the first sustain discharge, y is brightness by a sustain pulse of one period, a is the number of subfields used to represent gray scale i, and b is the total periods of the sustain pulse in the subfields used to represent gray scale i.
L(i+1)=cx+dyEquation 2

where c is the number of subfields used to represent gray scale (i+1), and d is the total periods of the sustain pulse in the subfields used to represent gray scale (i+1).

Equation 3 provides the brightness difference between gray scales (i+1) and i. Equation 3 may be calculated as Equation 4 when (a+b) is smaller than (c+d).
L(i+1)−L(i)=(c−a)x+(d−b)yEquation 3
L(i+1)−L(i)=(c−a)x+(a−c+e)y=(c−a)(x−y)−eyEquation 4

where e is (c+d)−(a−b), which becomes greater than 0.

When brightness of x and y are the same, a difference between L(i+1) and L(i) becomes a positive number, and thus gray scales are not reversed. However, when a large difference exists between the brightness of x and y, a value of (c−a) may cause gray scales to be reversed. Thus, the value of (c−a) may be set as shown in Equation 5 to prevent gray scales from being reversed.
c−a=0, orc−a=1  Equation 5

Referring toFIG. 3A,FIG. 3BandFIG. 3C, a method of determining weights of subfields to satisfy Equation 5 will be described in detail.

As shown inFIG. 3A, firstly, weights assigned to the first subfield SF1and the second subfield SF2are set to be1and2, respectively. Assume that the weight of the third subfield is set to be4. In this case, one subfield (subfield SF3) is turned on to represent the gray scale4, whereas two subfields (subfields SF1and SF2) are turned on to represent the gray scale3. Accordingly, this assumption does not satisfy Equation 5. Therefore, the weight of the third subfield is set to be3.

Further, assume that the weight assigned to the fourth subfield SF4is set to be6. However, this assumption also does not satisfy Equation 5 because the gray scale6uses the subfields from the first to the third SF1to SF3whereas the gray scale7uses the first subfield SF1and the fourth subfield SF4. Therefore, the weight of the fourth subfield SF4may be set to be4or5. Herein, when the weight of the fourth subfield SF4is set to be4, the weight of the fifth subfield SF5may be set to be6or7. Alternatively, when the weight of the fourth subfield SF4is set to be5, the weight of the fifth subfield SF5may be set to be7or8.

For instance, when the weight of the fourth subfield SF4is set to be5, gray scales0to11can be represented by incrementing the number of subfields using the first subfield SF1to the fourth subfield SF4. However, the number of subfields representing gray scale11increases by 1 as compared to the number of subfields representing gray scale10, and thus weight of the fifth subfield SF5is set to represent gray scale11using three subfields with combinations of the first to the fourth subfields SF1to SF4and the fifth subfield SF5. Herein, gray scales11to18can be represented by respectively adding 8 to the gray scales3to10since the gray scales3to10use two or three subfields. In other words, the weight of the fifth subfield SF5is set to be8, and the gray scales11to18are represented by the combination of the subfields used to represent the gray scales3to10and the fifth subfield SF5. According to the foregoing method, gray scales0to18can be represented without reducing the number of subfields.

Gray scale19can also be represented by adding the weight assigned to the sixth subfield SF6to gray scales using three subfields to represent the gray scale instead of using five subfields SF1to SF5. In other words, as shown inFIG. 3B, gray scales19to29can be represented by adding 11 to the gray scales that use three or four subfields (gray scales8to18). Thus, setting the weight of the sixth subfield SF6to11may prevent reverse gray scales.

On the other hand, as shown inFIG. 3C, gray scales16to27can be represented by removing the gray scales using four subfields inFIG. 3A(gray scales16to18), and adding 12 to gray scales using two or three subfields (gray scales4to15), and thereby to represent gray scales16to27using three or four subfields. In other words, the weight assigned to the sixth subfield SF6can be set to be12.

In a like manner, further gray scales also can be represented by setting weights for subfields without reducing the number of subfields to be used.

FIG. 4A,FIG. 4B,FIG. 4C,FIG. 4D,FIG. 4EandFIG. 4Fshow an exemplarily subfield arrangement according to an embodiment of the present invention. Shaded portions of the Figures show gray scales that are represented by a weight assigned to a newly added subfield and previous subfields, but these gray scales therein are not substantially used.

Referring toFIGS. 4A to 4F, weights of the first to third subfields SF1to SF3are respectively set to be1,2, and3, and the weight assigned to the fourth subfield SF4, which is 5, is added to the gray scales1to5to represent gray scales6to10. Gray scales11to18are represented by adding weight8to the gray scales3to10using two or three subfields, and gray scales16to18using four subfields are removed. Then, weight13is added to the gray scales3to15using two or three subfields to represent the gray scales16to18. Then, the weight13is added again to the gray scales3to15using two or three subfields so as to represent gray scales16to28. Weight20is added to the gray scales9to28using three or four subfields to represent gray scales29to48, and the gray scales41to48using five subfields are removed. Weight32is added to the gray scales9to40using three or four subfields so as to represent gray scales41to72.

Gray scales73to117are represented by adding weight45to the gray scales28to72using four or five subfields, and gray scales118to174are represented by adding weight57to the gray scales61to117using five or six subfields. Weight69is added to the gray scales106to174using six or seven subfields to represent gray scales175to243, and gray scales244to255are represented by using the remaining subfields.

To satisfy Equation 5, the following rule may be applied to represent weights and gray scales of each subfield according to an embodiment of the embodiment of the present invention.

First, assume that there is a first gray scale arrangement with1to k subfields that does not decrement the number of subfields although levels of gray scales increase. In other words, gray scales0to f are represented by1to k subfields, and the number of subfields used to represent gray scale (i+1) is the same as, or one greater than, the number of subfields used to represent gray scale i.

Herein, when a range of gray scale levels extends by adding a (k+1)thsubfield, gray scales (a range of gray scales g to f, where g is smaller than f, and the gray scale f is represented using less than (k−1) subfields) beyond a predetermined gray scale level using less than k subfields in the first gray scale arrangement are selected as a second gray scale arrangement. A third gray scale arrangement ranges from gray scales (g+h) to (f+h) by adding the weight h assigned to an additional subfield. For instance, the gray scales29to48inFIG. 4are represented by adding the weight20to the gray scales9to28(herein, h is set to be20, g to be9, and f to be28).

Herein, the number of subfields used to represent gray scale (g+h) may be reduced when the gray scale (g+h) uses two more subfields than gray scale g so that the gray scale (g+h) may use one more subfield than the gray scale g. Therefore, the weight assigned to the additional subfields may be the same or smaller than the total number of gray scales using the same number of subfields as the gray scale g and gray scales using one more subfield compared to the gray scale g in the second gray scale arrangement. In other words, assume that a total number of gray scales using the same number of subfields as the gray scale g within a range of gray scales g to f, is set to be N1, and a total number of gray scales using one more subfield than the gray scale g is set to be N2. In this case, weight h assigned to the additional subfields must satisfy Equation 6.
h<N1+N2  Equation 6

The third gray scale arrangement including the gray scale (g+h) to (f+h) is joined to the first gray scale arrangement. Herein, when the gray scale (g+h) is included in the first gray scale arrangement, a new arrangement of gray scales may be generated from the gray scale (g+h) by applying the third gray scale arrangement thereto.

By repeating the foregoing methods, gray scale levels can be increased without reducing the number of subfields to be used to represent the gray scale levels.

According to the present invention, input gray scales and output gray scales are matched with each other to prevent reverse gray scales.