Method and apparatus for controlling the gray scale of plasma display device

Abstract

A method of controlling the gray scale of a plasma display device has a forming step of forming a frame for an image by a plurality of subframes each having a different brightness, a setting step of setting the number of sustain emissions of each subframe in an anti-geometrical progression corresponding to the brightness of each subframe, and a displaying step of displaying the image on the plasma display device by a gray scale display having a specific brightness. The number of sustain emissions in each subframe is set individually by the each subframe, and this establishes a linear relation between the gray level and the corresponding brightness Therefore, an enhancement of display quality of the plasma display device can be realized. A method of controlling the gray scale of a plasma display device has a forming step of forming a frame for an image by a plurality of subframes each having a different brightness, a setting step of setting the number of sustain emissions of each subframe in an anti-geometrical progression corresponding to the brightness of each subframe, and a displaying step of displaying the image on the plasma display device by a gray scale display having a specific brightness. The number of sustain emission in each subframe is set individually by the each subframe, and this establishes a linear relation between the gray level and the corresponding brightness. Therefore, an enhancement of display quality of the plasma display device can be realized.

Description

B=f₂(K)  (2)
ƒ₁(P3)=2׃₁(P2)=4׃₁(P1)  (3)
P1<P2<P3  (4)
b₁=ƒ₁(P1)−ƒ₂(1)  (5)
b₂=ƒ₁(P2)−ƒ₂(2)  (6)
b₃=ƒ₁(P1+P2)−ƒ₂(3)  (7)
b₄=ƒ₁(P3)−ƒ₂(4)  (8)
b₅=ƒ₁(P1 P3)−ƒ₂(5)  (9)
b₆=ƒ₁(P2+P3)−ƒ₂(6)  (10)
b₇=ƒ₁(P1+P2+P3)−ƒ₂(7)  (11)
$\begin{array}{cc}B=f_1\left(P\right)& \left(1\right)\\ B=f_2\left(K\right)& \left(2\right)\\ f_1\left(\mathrm{P3}\right)=2\times f_1\left(\mathrm{P2}\right)=4\times f_1\left(\mathrm{P1}\right)& \left(3\right)\\ \mathrm{P1}<\mathrm{P2}<\mathrm{P3}& \left(4\right)\\ b_1=f_1\left(P1\right)-f_2\left(1\right)& \left(5\right)\\ b_2=f_1\left(P2\right)-f_2\left(2\right)& \left(6\right)\\ b_3=f_1\left(P1+\mathrm{P2}\right)-f_2\left(3\right)& \left(7\right)\\ b_4=f_1\left(P3\right)-f_2\left(4\right)& \left(8\right)\\ b_5=f_1\left(P1P3\right)-f_2\left(5\right)& \left(9\right)\\ b_6=f_1\left(P2+\mathrm{P3}\right)-f_2\left(6\right)& \left(10\right)\\ b_7=f_1\left(P1+\mathrm{P2}+\mathrm{P3}\right)-f_2\left(7\right)& \left(11\right)\\ \mathrm{bS1}=\sum _{k=1}^7\left(b_1^2\right)& \left(12\right)\\ \mathrm{bS2}=\sum _{k=1}^7❘b_k❘& \left(13\right)\\ \mathrm{Pn}>\sum _{k=1}^{n-1}\mathrm{Pk}& \left(14\right)\end{array}$

First, the brightness B of a panel is measured for some numbers P of sustain discharge pulses to get actually measured values in a gray scale-brightness characteristic as shown in FIG. 7, and the resultant curve is made B=f1(P) of the equation (1). In the prior art, the number of sustain emissions in each subframe is so set that the number of pulses in an arbitrary subframe is two times the number of pulses in the subframe next brighter than the former. However, in this embodiment, the number of sustain emissions in each subframe is so set that the brightness of an arbitrary subframe is two times the brightness of the subframe next brighter than the former.

A case of optimization according to the embodiment will be shown exemplifying the actually measured values in the gray scale-brightness characteristic shown in FIG. 7. Assuming the brightness of subframe SP3 to be 60 cd/m×m, the brightness of subframe SF2 is half of 60. 30 cd/m×m, the brightness of subframe SF1 is half of 30. 15 cd/m×m. In this case the numbers of sustain discharge pulses for each gray level are as set forth in Table 1 below.

TABLE 1
GRAY LEVEL	0	1	2	3	4	5	6	7
BRIGHTNESS Cd/m2	0	15	30	43	60	66	71	76
NUMBER-OF SUSTAIN	0	15	30	45	80	95	110	125
DISCHARGE PULSES

In FIG. 8, a dashed line indicates the relation before the optimization, a fine solid line indicates the relation after the optimization, and a thick solid line indicates an ideal line.

The embodiment shown in FIG. 8 has an advantage that it does not need complex calculations, but lacks linearity in higher gray levels when the linearity of the brightness B of the pane with respect to the number P of sustain discharge pulses is low. Namely, the numbers of sustain emissions of each subframe are like a geometric series (1, 2, 4, 8, . . .) in the conventional gray scale controlling method, whereas the numbers of sustain emissions of each subframe is set on the basis of the brightness of the each subframe in the inventive gray scale controlling method for the plasma display device. Therefore, the numbers of sustain emissions of each subframe are not like a geometric series in the inventive gray scale controlling method for a plasma display device. Namely, the number of sustain emissions in each subframe is set in an anti-geometrical progression, or the number of sustain emissions in each subframe is not determined in accordance with any mathematical relationship.

FIG. 9 shows another embodiment of a gray scale controlling method for a plasma display device in accordance with the invention, and FIG. 10 is a diagram for explaining still another embodiment of a gray scale controlling method for a plasma display device in accordance with the invention. In FIGS. 9 and 10, the axis of ordinates indicates the brightness B |cd/m×m|, the axis of abscissas indicates the gray level.

As shown in FIG. 9, in this embodiment the target line of the brightness B for gray levels is set to B=f2(K) of the equation (2). Note that, assuming the difference between a calculated brightness and a target brightness in a certain gray level X in a certain sustain pulse number ratio to be bx, it is possible to find the numbers (P1, P2, P3) of sustain pluses of each subframe, for examples in the 8 gray scales in the following procedure.

The optimum numbers of sustain pulses are such, P1, P2, and P3, as to minimize bS1 in the equation (12) which satisfies the conditions of the equations (4) to (11) when the equation (1) is obtained first by actual measurement and the equation (2) is set. In other words, in order to make the relation between the gray level and the corresponding brightness a linear relation, the numbers of sustain emissions of each subframe in the case when the sum of the squares of errors in each gray level with respect to the ideal values becomes minimum is calculated on the basis of data of the brightness actually measured for the numbers of sustain emissions. In the embodiment shown in FIG. 9, the calculations are complex as compared with the embodiment shown in FIG. 8, but a result very close to optimum can be found.

It should be noted that though the numbers of sustain emissions of each subframe in the case when the sum of the squares of errors in each gray level with respect to the ideal values becomes minimum is calculated in the equation (12), by using the equation (13) instead of the equation (12), it is possible to calculate the numbers of sustain emissions of each subframe in the case when the sum of the absolute values of errors in each gray level with respect to the ideal values becomes minimum. In other words, in order to make the relation between the gray level and the corresponding brightness a linear relation, the numbers of sustain emissions of each subframe in the case when the sum of the absolute values of errors in each gray level with respect to the ideal values becomes minimum is calculated on the basis of data of the brightness actually measured for the numbers of sustain emissions.

When the equation (12) or (13) is used, there is the possibility of bringing about the situation in which for the brightness of an arbitrary gray level, the brightness of the gray level next larger than the former exceeds that of the former. In order to avoid this, the condition of equation (14) is added. The equation (14) indicate that the number of pulses of an arbitrary subframe exceeds the sum of the numbers of the pulses of the subframes which have less pulses than the former subframe. That is, it is possible to make such arrangement that for the brightness of the first subframe with an arbitrary gray levels the brightness of the second subframe which has a next larger gray level than the first subframe never exceeds that of the first subframe.

Further, in order to obtain higher brightness, the number of sustain pulses of each subframe may be increased. However, the number of sustain pulses which can be included in a limited time within a vertical synchronous period has a limitation. Thus, if the sum (P1+P2+P3) of the numbers of pulses within a vertical synchronous signal or the number (P3) of pulses of the highest level subframe is first set, and then, P1, P2 and P3 in the case when bS1 of the equation (12) or bS2 of the equation (13) which satisfies the conditions of the equations (4) to (11) becomes minimum are found, then they are the optimum number of sustain pulses. In this case there is no need for setting B=f2(K) of the equation (2). Note that the number of pulses of SF3 is set for 60 in the embodiment in FIG. 9. That is, an arrangement may be so made that the sum of the numbers of sustain emissions of one or two subframes in a plurality of subframes, or the sum of the numbers of sustain emissions of two or three subframes is specified. Note that, when the number of the subframes is increased, the number of the subframes to be specified is increased.

Next if there is a sufficiently long vertical synchronous period as shown in FIG. 10 and the target maximum brightness needs to be set, the maximum brightness f1(P1+P2+P3) is first set, and then P1, P2 and P3 in the case when bS1 of the equation (12) or bS2 of the equation (13) which satisfies the conditions of the equations (3) to (10) becomes minimum are found, the resultant values being the optimum number of sustain pulses. In this case, B=f2(K) of the equation (2) need not be set. Note that, in the embodiment of FIG. 10, the brightness of the gray level 7 is set for 140 cd/m×m. Namely, an arrangement may be so made that the brightness of the subframe with the maximum gray level is specified.

Using the optimum number of sustain discharge pulses found through each method as described above, the driving operation described below will be carried out.

FIGS. 11A and 11B are block diagrams showing an embodiment of a plasma display device to which the inventive gray scale controlling method for a plasma display device is applied. In FIGS. 11A and 11B (FIG. 11B), reference numeral 10 denotes a control circuit, 11 denotes a display data controller, 12 denotes a frame memory, 13 denotes a panel drive controller, 14 denotes a scan driver controller, and 15 denotes a common driver controller. Further, reference numeral 21 denotes an address driver, 22 denotes a X driver, 23 denotes a Y scan driver, and 30 denotes a plasma display panel (PDP). These components are identical to those shown in FIG. 3, so explanations will be omitted.

In FIGS. 11A and 11B, reference numeral 41 denotes a high-tension input for driving, 42 denotes a consumed current detecting circuit, 43 denotes an A/D converters and 44 denotes an automatic power controller (APC). Further, reference numeral 51 denotes a brightness controller, 52 denotes an A/D converter, 53 denotes a number-of-sustain-pulse pattern selection signal external input section, 54 denotes a number-of-sustain-pulse pattern selection adder, 55 denotes a ROM (read only memory), and 56 denotes a number-of-sustain-pulse-by-SF external input section. Also, reference marks SW1 and SW2 denote selection switches.

The data of the numbers of sustain discharge pulses which are calculated through the above described gray scale controlling method for a plasma display device (the optimum number-of-sustain-emission calculating method) are stored in ROM 55. The data of the number of sustain discharge pulses which are output from ROM 55 are supplied to the common driver controller 15 in the control circuit 10, which output control signals for sustain discharge pulses of each subframe by a specified number from ROM 55 in a prescribed timing to the X driver 22 and Y driver 24. The X driver 22 and Y driver 24 output high-tension panel driving pulses on the basis of the control signals supplied from the control circuit 10. That is, the numbers of sustain emissions in each subframe are set in ROM 55 and are read therefrom as the occasion demands.

In this case, making good use of a vacant area in ROM which had been used for driving waveforms, instead of adding new ROM, will contribute to cost reduction and saving of the mounting area. In other words, a memory for setting and storing the numbers of sustain emissions in each subframe can be constituted by the vacant area of the driving waveform memory device 55 in the plasma display device.

Furthermore, if the data of the numbers of sustain discharge pulses are calculated and set not only in one kind of pattern but in a plurality of kinds of patterns different in relative brightness using the equations (12) and (13), it becomes possible to adjust the brightness keeping a constant gray scale display. Brightness information set by the brightness controller 51 is converted by the A/D converter 52 into a digital signal, which serves as ROM address signal and selects number-of-sustain-emission data. That is, an arrangement can be so made that one piece is selected by the brightness controller 51 out of information about the numbers of sustain emissions of each subframe which is set in ROM. This enables the user to adjust the brightness to the operating circumstance of the device.

In this case, by shifting the points of contact of the selection switch SW1 from (1) to (2), information from an external device instead of information by the brightness controller 51 can be let in via a number-of-sustain-pulse pattern selection signal external input section 53. Further, information on the number of sustain emissions of a frame may be set as a plurality of combinations in ROM 55, and any one among the plurality of combinations may be selected by means of selection signals supplied from outside of the plasma display device. This enables the remote control of brightness adjustment and so forth.

Further, in the present plasma display device, since the consumed current varies greatly depending on brightness and a display rate, the power supplying route is provided with a consumed current detecting circuit 42 using well known technology, so that the consumed current is controlled and limited to below the set value by limiting the brightness when the consumed current exceeds a prescribed value because of the increase of a display rate and the like. By adding the output of automatic power controller (consumed current controller means) 44 for controlling the consumed current in the number-of-sustain-pulse pattern selecting adder and writing the result in ROM 55, it becomes possible to achieve smooth gray scale control limiting the consumed current to below a certain value. Namely, it is possible to make the consumed power constant regardless of the change of a display rate.

The above described plasma display device is so arranged that each control is achieved on the basis of information in ROM (55) provided within the main body of the plasma display device. By the way, the life span of a plasma display device is generally defined as halving of brightness. For example, when it is desirable to do higher level gray scale control from the outside of the unit in order to cope with such a phenomenon, shifting the points of contact of the selection switch SW2 from side (1) to side (2) enables the external input of the number of sustain pulses by subframe (or subfield), and eventually enables real-time alteration of the number of sustain discharge pulses.

In the above description, a surface-discharge AC plasma display device with a three-electrode structure has been described in detail as an example to which the inventive gray scale controlling method for a plasma display device is applied. However, it should be noted that in addition to the three-electrode surface-discharge AC plasma display device (with reference to FIGS. 1A and 1B), the present invention can be applied to, for example, a two-electrode facing-discharge plasma display device (with reference to FIGS. 2A and 2B) and other plasma display devices.

As described above, according to a gray scale controlling method for a plasma display device of the present invention, the number of sustain emissions in each subframe is set individually by each subframe. This establishes a linear relation between the gray level and the corresponding brightness and enables the enhancement of display quality of the plasma display device.

Many different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention, and it should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.

Claims

1. A method of controlling the a gray scale of a plasma display device, wherein said method comprises the steps of:

forming a frame for an image by a plurality of subframes each having a specific weight value;

calculating numbers of sustain emissions of said plurality of subframes so as to make a ratio of brightness of said plurality of subframes so as to substantially correspond with equal a ratio of the specific weight values of said plurality of subframes, wherein a ratio of numbers of sustain emissions of said plurality of subframes does not equal the ratio of the specific weight values of said plurality of subframes; and

displaying the image on said plasma display device by optionally combining said subframes each having the calculated number of the sustain emissions.

2. A method of controlling the a gray scale of plasma display device as claimed in claim 1, wherein the number of sustain emissions of said each subframes is so calculated, that the brightness obtained by one subframe of said plurality of subframes having an arbitrary brightness is twice the brightness obtained by another subframe of said plurality of subframes having a brightness next to that of said one subframe.

3. A plasma display device comprising at least one pair of electrodes for carrying out a discharge operation, wherein:

said plasma display device is driven by separating address periods in which display data are written in a common period for each display line in the screen, said display data is so as to accumulate wall charges necessary for sustain discharge from sustain discharge periods in which sustain discharge for light emission is repeated in a common period for each display line, one frame forming an image is constituted by a plurality of subframes each having a specific weight value, numbers of sustain emissions of said plurality of subframes are calculated so at to make a ratio of brightness of said plurality of subframes is calculated so as to substantially correspond with equal a ratio of the specific weight values of said plurality of subframes, wherein a ratio of numbers of sustain emissions of said plurality of subframes does not equal to the ratio of the specific weight values of said plurality of subframes, and the image is displayed on said plasma display device by optionally combining said subframes each having the calculated number of the sustain emissions.

4. A plasma display device as claimed in claim 3, wherein said plasma display device is a three-electrode plasma display device.

5. A plasma display device as claimed in claim 4, wherein said three-electrode plasma display device is a three-electrode surface discharge AC plasma display device.

6. A plasma display device as claimed in claim 4, wherein said three-electrode plasma display device comprises:

first and second electrodes arranged in parallel with each other; and

third electrodes orthogonal to said first and second electrodes, said first electrode being commonly connected together, and said second electrodes being arranged for display lines, respectively, wherein said display device has a surface discharge structure employing wall charges as memory media.

7. A plasma display device as claimed in claim 6, wherein said three-electrode plasma display device further comprises:

a first substrate, and said first and second electrodes being arranged in parallel with each other on said first substrate and paired for respective display lines;

a second substrate spaced apart from and facing said first substrate, and said third electrodes being arranged on said second substrate away from and orthogonal to said first and second electrodes;

a wall charge accumulating dielectric layer covering the surfaces of said first and second electrodes and said first substrate;

a phosphor formed over said third electrodes and said second substrate;

a discharge gas sealed in a cavity defined between said first and second substrates; and

cells formed at intersections where said first and second electrodes cross said third electrodes.

8. A plasma display device as claimed in claim 3, wherein said plasma display device is a two-electrode plasma display device.

9. A plasma display device as claimed in claim 8, wherein said two-electrode plasma display device is a two-electrode facing-discharge AC-driven plasma display panel.

10. A plasma display device as claimed in claim 8, wherein said two-electrode plasma display device comprises:

a plurality of first electrodes; and

a plurality of second electrodes orthogonal to said first electrodes, and said first electrodes being arranged for display lines, respectively wherein said display device has a surface discharge structure employing wall charges as memory media.

11. A plasma display device as claimed in claim 10, wherein said two-electrode plasma display device further comprises:

a first substrate, and said first electrodes being arranged in parallel on said first substrate;

a second substrate spaced apart from and facing said first substrate, and said second substrate being arranged on said second substrate away from and orthogonal to said first electrodes;

a wall charge accumulating dielectric layer covering the surfaces of said first electrodes and said first substrate;

a phosphor formed over said second electrodes and said second substrate;

a discharge gas sealed in a cavity defined between said first and second substrates; and

cells formed at intersections where said first electrodes cross said second electrodes.

12. A plasma display device as claimed in claim 3, wherein said plasma display device further comprises a memory for setting and storing the number of sustain emissions in each subframe, and information on the number of sustain emissions in said search subframe is read at any time from said memory.

13. A plasma display device as claimed in claim 12, wherein said memory is constituted by a vacant area of a driving wave-form memory device in said plasma display device, and the information on the number of sustain emissions in said each subframe is set in the vacant area of said driving wave-form memory device.

14. A plasma display device as claimed in claim 12, wherein said plasma display device further comprises a brightness controller for adjusting the brightness, and aid brightness controller selects one piece from the information on the number of sustain emissions in said each subframe set in said memory.

15. A plasma display device as claimed in claim 12, wherein the number of sustain emissions in said each subframe is set as a plurality of combinations in said memory, and an arbitrary one of said plurality of combinations is selected by selection signals supplied from the outside of said plasma display device.

16. A plasma display device as claimed in claim 12, wherein said plasma display device further comprises a consumed current controller for controlling and keeping the consumed current below a predetermined value, the number of sustain emissions in said each subframe is set as a plurality of combinations in said memory, an arbitrary one of said plurality of combinations is selected in response to the output from said consumed current controllers and thereby the power consumption is keep constant regardless of the change of display rate.

17. A plasma display device as claimed in claim 12, wherein the information on the number of sustain emissions in said each subframe is supplied from the outside of said plasma display device.

18. A method of controlling the a gray scale of a plasma display device, wherein said method comprises the steps of:

forming a frame for an image by a plurality of subframes each having a specific weight value; and

displaying the image on said plasma display device by optionally combining gray levels of said plurality of subframes, wherein each gray level numbers of sustain emissions of said plurality of subframes are calculated so as to make a ratio of brightnesses of each gray level said plurality of subframes is calculated so at to substantially correspond with equal a ratio of the specific weight values of each gray level the specific weight values of said plurality of subframes and a ratio of numbers of sustain emissions of each gray level said plurality of subframes does not equal the ratio of the specific weight values of each gray level the specific weight values of said plurality of subframes.

19. A method of controlling the a gray scale of a plasma display device as claimed in claim 18, wherein the number of sustain emissions of said each subframe is so calculated, that the a sum of the squares of errors with the ideal values in said each gray level becomes a minimum, in order to make the a relation between the said each gray level and the corresponding brightness linear.

20. A method of controlling the a gray scale of a plasma display device as claimed in claim 19, wherein the a brightness of one subframe of said plurality of subframes having a next larger gray level than that of another subframe of said plurality of subframes does not exceed the a brightness of said another subframe, for the brightness of said another subframe having said arbitrary gray level.

21. A method of controlling the a gray scale of a plasma display device as claimed in claim 19, wherein the a sum of the numbers of sustain emissions of several subframes in said plurality of subframes is specified.

22. A method of controlling the a gray scale of a plasma display device as claimed in claim 19, wherein the a brightness of an optional subframe is specified in said plurality of subframes.

23. A method of controlling the a gray scale of a plasma display device as claimed in claim 18, wherein the a number of sustain emissions of said each subframe is so calculated, that the a sum of the absolute values of errors with the ideal values in said each gray level becomes a minimum, in order to make the a relation between the said each gray level and the corresponding brightness linear.

24. A method of controlling the a gray scale of a plasma display device as claimed in claim 23, wherein the a brightness of one subframe of said plurality of subframes having a next larger gray level than that of another subframe of said plurality of subframes does not exceed the a brightness of said another subframe, for the brightness of said another subframe having said arbitrary gray level.

25. A method of controlling the a gray scale of a plasma display device as claimed in claim 23, wherein the a sum of the numbers of sustain emissions of several subframes in said plurality of subframes is specified.

26. A method of controlling the a gray scale of a plasma display device as claimed in claim 23, wherein the a brightness of an optional subframe is specified in said plurality of subframes.

27. A plasma display device comprising at least one pair of electrodes for carrying out a discharge operation, wherein:

said plasma display device is driven by separating address periods in which display data are written in a common period for each display line in the a screen, said display data is so as to accumulate wall charges necessary for sustain discharge from sustain discharge periods in which sustain discharge for light emission is repeated in a common period for each display line, one frame forming an image is constituted by a plurality of subframes each having a specific weight value, and an image on said plasma display device is displayed by optionally combining gray levels of said plurality of subframes, wherein each gray level numbers of sustain emissions of said plurality of subframes are calculated so as to make a ratio of brightness of each gray level is calculated so as to said plurality of subframes substantially correspond with equal a ratio of the specific weight values ofeach gray scale the specific weight values of said plurality of subframes, and a ratio of numbers of sustain emissions of each gray level said plurality of subframes does not equal the ratio of the specific weight values of each gray level the specific weight values of said plurality of subframes.

28. A method of controlling a gray scale of a plasma display device, wherein said method comprises:

forming a frame for an image by a plurality of subframes having respective, predetermined brightnesses;

setting a number of sustain emissions, individually for and corresponding to the predetermined brightness of each individual subframe, numbers of sustain emissions of different subframes bearing a non-linear relationship to the different, predetermined brightnesses of the respective, different subframes; and

displaying the image on said plasma display device in accordance with selected subframes to produce a gray scale display of a specific brightness.

29. A method of controlling a gray scale of a plasma display device as claimed in claim 28, further comprising:

setting numbers of sustain emissions for respective subframes to establish a linear relationship between respective gray levels and corresponding brightnesses of different subframes.

30. A method of controlling a gray scale of a plasma display device as claimed in claim 28, further comprising:

setting the number of sustain emissions for respective subframes in a pattern in a memory accessible by a brightness controller.

31. A method of controlling a gray scale of a plasma display device as claimed in claim 30, further comprising:

setting plural said patterns having respective, different relative brightnesses in the memory accessible by the brightness controller; and

selecting among the patterns to thereby adjust the brightness of the display of the image.

32. A method of controlling a gray scale of a plasma display device as claimed in claim 28, wherein the setting is performed by a calculation whereby the brightness obtained by one subframe of the plurality of subframes having an arbitrary brightness is twice the brightness obtained by another subframe of the plurality of subframes having a brightness next to that of the one subframe.

33. A method of controlling a gray scale of a plasma display device as claimed in claim 28, further comprising:

setting the number of sustain emissions of each subframe such that the sum of the squares of errors with ideal values in each gray level becomes a minimum and thereby to make the relation between the gray level and the corresponding brightness linear.

34. A method of controlling a gray scale of a plasma display device as claimed in claim 28, wherein the number of sustain emissions is set so that the brightness of one subframe of the plurality of subframes having a next larger gray level than that of another subframe of the plurality of subframes does not exceed the brightness of the another subframe, for the brightness of the another subframe having the arbitrary gray level.

35. A method of controlling a gray scale of a plasma display device as claimed in claim 28, further comprising:

setting the number of sustain emissions of each subframe such that the sum of the absolute values of errors with the ideal values in each gray level becomes a minimum in order to make the relation between the gray level and the corresponding brightness linear.

36. A method of controlling a gray scale of a plasma display device as claimed in claim 28, wherein the number of sustain emissions of each subframe is set in an anti-geometrical progression corresponding to the predetermined brightness of each subframe of the plurality of subframes.

37. An apparatus controlling a gray scale of a plasma display device in which a frame for an image is formed by a plurality of subframes having respective, predetermined brightnesses, comprising:

a memory having set therein a number of sustain emissions individually for, and corresponding to, the predetermined brightness of each individual subframe, numbers of sustain emissions of different subframes bearing a non-linear relationship to the different predetermined brightnesses of the respective, different subframes; and

a controller displaying the image on said plasma display device in accordance with selected subframes to produce a gray scale display of a specific brightness.

38. The apparatus as claimed in claim 37, further comprising:

the memory having set therein numbers of sustain emissions for respective subframes to establish a linear relationship between the respective gray levels and corresponding brightnesses of the different subframes.

39. The apparatus as claimed in claim 37, further comprising:

the memory having set therein the number of sustain emissions for respective subframes in a pattern in a memory accessible by a brightness controller.

40. The apparatus as claimed in claim 39, further comprising:

the memory having set therein plural said patterns having respective, different relative brightnesses in the memory accessible by the brightness controller; and

the controller selecting among the patterns to thereby adjust the brightness of the display of the image.

41. The apparatus as claimed in claim 37, wherein the setting is performed by a calculation whereby the brightness obtained by one subframe of the plurality of subframes having an arbitrary brightness is twice the brightness obtained by another subframe of the plurality of subframes having a brightness next to that of the one subframe.

42. The apparatus as claimed in claim 37, further comprising:

the memory having set therein the number of sustain emissions of each subframe such that the sum of the squares of errors with ideal values in each gray level becomes a minimum and thereby to make the relation between the gray level and the corresponding brightness linear.

43. The apparatus as claimed in claim 37, further comprising:

the memory having set therein the number of sustain emissions so that the brightness of one subframe of the plurality of subframes having a next larger gray level than that of another subframe of the plurality of subframes does not exceed the brightness of the another subframe, for the brightness of the another subframe having the arbitrary gray level.

44. The apparatus as claimed in claim 37, further comprising:

the memory having set therein the number of sustain emissions of each subframe such that the sum of the absolute values of errors with the ideal values in each gray level becomes a minimum in order to make the relation between the gray level and the corresponding brightness linear.

45. The apparatus as claimed in claim 37, further comprising:

the memory having set therein the number of sustain emissions of each subframe is set in an anti-geometrical progression corresponding to the predetermined brightness of each subframe of the plurality of subframes.

46. A method of controlling a gray scale of a plasma display device, wherein said method comprises the steps of:

forming a frame for an image by a plurality of subframes each having a specific weight value, each of said subframes including an address period and a sustain discharge period, said address period being a common period to carry out address discharge on each selected display line so as to selectively accumulate wall charges for cells formed on said each selected display line, said sustain discharge period being a common period to carry out sustain emissions on said each selected display line, the sustain emissions on said each selected display line being carried out in said sustain discharge period;

calculating numbers of sustain emissions of said plurality of subframes so as to make a ratio of brightnesses of said plurality of subframes substantially equal a ratio of the specific weight values of said plurality of subframes, wherein a ratio of numbers of sustain emissions of said plurality of subframes does not equal the ratio of the specific weight values of said plurality of subframes; and

displaying the image on said plasma display device by optionally combining said subframes each having the calculated number of the sustain emissions, and thereby a brightness-drop caused in accordance with increasing the number of sustain emissions is compensated.

47. A method of controlling a gray scale of a plasma display device as claimed in claim 46, wherein the number of sustain emissions of said each subframe is so calculated, that the brightness obtained by one subframe of said plurality of subframes having an arbitrary brightness is twice the brightness obtained by another subframe of said plurality of subframes having a brightness next to that of said one subframe.

48. A plasma display device comprising at least one pair of electrodes for carrying out a discharge operation, wherein:

said plasma display device is driven by separating address periods in which display data are written in a common period for each display line in the screen so as to accumulate wall charges necessary for sustain discharge from sustain discharge periods in which sustain discharge for light emission is repeated in a common period for each display line, one frame forming an image is constituted by a plurality of subframes each having a specific weight value, numbers of sustain emissions of said plurality of subframes are calculated so as to make a ratio of brightnesses of said plurality of subframes substantially equal a ratio of the specific weight values of said plurality of subframes, wherein a ratio of numbers of sustain emissions of said plurality of subframes does not equal the ratio of the specific weight values of said plurality of subframes, and the image is displayed on said plasma display device by optionally combining said subframes each having the calculated number of the sustain emissions, and thereby a brightness-drop caused in accordance with increasing the number of sustain emissions is compensated.

49. A plasma display device as claimed in claim 48, wherein said plasma display device is a three-electrode plasma display device.

50. A plasma display device as claimed in claim 49, wherein said three-electrode plasma display device is a three-electrode surface discharge AC plasma display device.

51. A plasma display device as claimed in claim 49, wherein said three-electrode plasma display device comprises:

first and second electrodes arranged in parallel with each other; and

third electrodes orthogonal to said first and second electrodes, said first electrode being commonly connected together, and said second electrodes being arranged for display lines, respectively, wherein said display device has a surface discharge structure employing wall charges as memory media.

52. A plasma display device as claimed in claim 51, wherein said three-electrode plasma display device further comprises:

a first substrate, and said first and second electrodes being arranged in parallel with each other on said first substrate and paired for respective display lines;

a second substrate spaced apart from and facing said first substrate, and said third electrodes being arranged on said second substrate away from and orthogonal to said first and second electrodes;

a wall charge accumulating dielectric layer covering the surfaces of said first and second electrodes and said first substrate;

a phosphor formed over said third electrodes and said second substrate;

a discharge gas sealed in a cavity defined between said first and second substrates; and

cells formed at intersections where said first and second electrodes cross said third electrodes.

53. A plasma display device as claimed in claim 48, wherein said plasma display device is a two-electrode plasma display device.

54. A plasma display device as claimed in claim 53, wherein said two-electrode plasma display device is a two-electrode facing-discharge AC-driven plasma display panel.

55. A plasma display device as claimed in claim 53, wherein said two-electrode plasma display device comprises:

a plurality of first electrodes; and a plurality of second electrodes orthogonal to said first electrodes, and said first electrodes being arranged for display lines, respectively wherein said display device has a surface discharge structure employing wall charges as memory media.

56. A plasma display device as claimed in claim 55, wherein said two-electrode plasma display device further comprises:

a first substrate, and said first electrodes being arranged in parallel on said first substrate;

a second substrate spaced apart from and facing said first substrate, and said second electrodes being arranged on said second substrate away from and orthogonal to said first electrodes; a wall charge accumulating dielectric layer covering the surfaces of said first electrodes and said first substrate;

a phosphor formed over said second electrodes and said second substrate; a discharge gas sealed in a cavity defined between said first and second substrates; and cells formed at intersections where said first electrodes cross said second electrodes.

57. A plasma display device as claimed in claim 48, wherein said plasma display device further comprises a memory for setting and storing the number of sustain emissions in each subframe, and information on the number of sustain emissions in said each subframe is read at any time from said memory.

58. A plasma display device as claimed in claim 57, wherein said memory is constituted by a vacant area of a driving wave-form memory device in said plasma display device, and the information on the number of sustain emissions in said each subframe is set in the vacant area of said driving wave-form memory device.

59. A plasma display device as claimed in claim 57, wherein said plasma display device further comprises a brightness controller for adjusting the brightness, and said brightness controller selects one piece from the information on the number of sustain emissions in said each subframe set in said memory.

60. A plasma display device as claimed in claim 57, wherein the number of sustain emissions in said each subframe is set as a plurality of combinations in said memory, and an arbitrary one of said plurality of combinations is selected by selection signals supplied from the outside of said plasma display device.

61. A plasma display device as claimed in claim 57, wherein said plasma display device further comprises a consumed current controller for controlling and keeping the consumed current below a predetermined value, the number of sustain emissions in said each subframe is set as a plurality of combinations in said memory, an arbitrary one of said plurality of combinations is selected in response to the output from said consumed current controllers and thereby the power consumption is kept constant regardless of the change of displayed rate.

62. A plasma display device as claimed in claim 57, wherein the information on the number of sustain emissions in said each subframe is supplied from the outside of said plasma display device.

63. A method of controlling a gray scale of a plasma display device, wherein said method comprises:

forming a frame for an image by a plurality of subframes each having a specific weight value, each of said subframes including an address period and a sustain discharge period, said address period being a common period to carry out address discharge on each selected display line so as to selectively accumulate wall charges for cells formed on said each selected display line, said sustain discharge period being a common period to carry out sustain emissions on said each selected display line, the sustain emissions on said each selected display line being carried out in said sustain discharge period; and

displaying the image on said plasma display device by optionally combining gray levels of said plurality of subframes, wherein numbers of sustain emissions of said plurality of subframes are calculated so as to make a ratio of brightnesses of said plurality of subframes substantially equal a ratio of the specific weight values of said plurality of subframes and a ratio of numbers of sustain emissions of said plurality of subframes does not equal the ratio of the specific weight values of said plurality of subframes, and thereby a brightness-drop caused in accordance with increasing the number of sustain emissions is compensated.

64. A method of controlling a gray scale of a plasma display device as claimed in claim 63, wherein the number of sustain emissions of said each subframe is so calculated, that a sum of the squares of errors with ideal values in said each gray level becomes a minimum, in order to make a relation between said each gray level and corresponding brightness linear.

65. A method of controlling a gray scale of a plasma display device as claimed in claim 64, wherein a brightness of one subframe of said plurality of subframes having a next larger gray level than that of another subframe of said plurality of subframes does not exceed a brightness of said another subframe, for the brightness of said another subframe having said arbitrary gray level.

66. A method of controlling a gray scale of a plasma display device as claimed in claim 64, wherein a sum of the numbers of sustain emissions of several subframes in said plurality of subframes is specified.

67. A method of controlling a gray scale of a plasma display device as claimed in claim 64, wherein a brightness of an optional subframe is specified in said plurality of subframes.

68. A method of controlling a gray scale of a plasma display device as claimed in claim 63, wherein a number of sustain emissions of said each subframe is so calculated, that a sum of the absolute values of errors with ideal values in said each gray level becomes a minimum, in order to make a relation between said each gray level and corresponding brightness linear.

69. A method of controlling a gray scale of a plasma display device as claimed in claim 68, wherein a brightness of one subframe of said plurality of subframes having a next larger gray level than that of another subframe of said plurality of subframes does not exceed a brightness of said another subframe, for the brightness of said another subframe having said arbitrary gray level.

70. A method of controlling a gray scale of a plasma display device as claimed in claim 68, wherein a sum of the numbers of sustain emissions of several subframes in said plurality of subframes is specified.

71. A method of controlling a gray scale of a plasma display device as claimed in claim 68, wherein a brightness of an optional subframe is specified in said plurality of subframes.

72. A plasma display device comprising at least one pair of electrodes for carrying out a discharge operation, wherein:

said plasma display device is driven by separating address periods in which display data are written in a common period for each display line in a screen so as to accumulate wall charges necessary for sustain discharge from sustain discharge periods in which sustain discharge for light emission is repeated in a common period for each display line, one frame forming an image is constituted by a plurality of subframes each having a specific weight value, and an image on said plasma display device is displayed by optionally combining gray levels of said plurality of subframes, wherein numbers of sustain emissions of said plurality of subframes are calculated so as to make a ratio of brightnesses of said plurality of subframes substantially equal a ratio of the specific weight values of said plurality of subframes, and a ratio of numbers of sustain emissions of said plurality of subframes does not equal the ratio of the specific weight values of said plurality of subframes, and thereby a brightness-drop caused in accordance with increasing the number of sustain emissions is compensated.