Background Art As a display apparatus for an image display, a plasma display apparatus has become popular. As a principle of the display operation by the plasma display, as is well-known, two glass substrates are oppositely provided to form a space in between, for example, and a certain gas is sealed into the space. Then, by applying a certain voltage to this space filled with the gas, vacuum discharge is generated. Consequently, within the space of the two glass substrates, the gas is ionized to be a plasma state, and then, ultraviolet rays are radiated. Here, if a fluorescent substance layer is formed within the space of the two glass substrates, the above mentioned ultraviolet rays are irradiated on this fluorescent substance layer, and then the fluorescent substance layer radiates visible lights of a predetermined color.

As such fluorescent substance layers, those corresponding to three colors of R (red), G (green), and B (blue) are formed, for example, so as to obtain light emitting phenomenon based on the above mentioned vacuum discharge for each display cell formed in a matrix. Hence, the plasma display apparatus which is able to

carry out the color image display is thus configured.

Further, as a method of driving the above mentioned plasma display apparatus, so-called a sub-field method is known. The sub-field method is a drive method where one field is divided into a plurality of sub-fields, and a light emitting period of a display cell is controlled for each sub-field, thereby a gradation (luminance) of each display cell is expressed. At this time, by controlling the gradations of respective display cells for R, G and B constituting one pixel, not only the gradation balance of an entire screen but also the color reproduction for each pixel is performed. In short, it is possible to reproduce the color image.

As mentioned above, the image displayed on the plasma display apparatus is obtained through the visible light radiated from the fluorescent substance layer. However, it is known that this fluorescent substance layer is deteriorated correspondingly to usage elapse. Such deterioration in the fluorescent substance is caused by the factors of bombardment by the ultraviolet rays radiated by the vacuum discharge, by ions generated within the vacuum space, and the like.

Thus, the deterioration in the fluorescent substances is further intensified as the accumulation time of light emissions is longer.

Further, in the actual display, each of light emission accumulation time of the fluorescent substances corresponding to the respective display cell is not uniform, thereby inducing variation on the basis of the images displayed until that time.

In short, the variation is induced in the degree of the deterioration in the fluorescent substances among the display cells.

The deterioration in the fluorescent substance appears as

lowering in the light emission luminance. Further, as mentioned above, the fact that the variation is induced in the deteriorations in the fluorescent substances corresponding to the respective display cells leads to the variation in the light emission luminance of the fluorescent substance. Also, for example, if the variation in the light emission luminance is induced among the fluorescent substances of R, G and B constituting one pixel, white balance is also disturbed.

Consequently, even from the consideration of the entire display screen, it may be observed such that the portion where the deterioration is intensified with regard to a region to be originally displayed at the same luminance and coloration is displayed at luminance and coloration which are different from those of the periphery. This is said to be so-called a burn-in. If the burn-in occurs, the region in which the fluorescent substance is deteriorated is displayed, for example, as a fixed pattern so as to overlap with the original image. Thus, as the factor of deteriorating the displayed image quality, this is deemed to be a problem from before.

As the actual example of the burn-in, for example, based on the relation between a screen size and an aspect ratio of a displayed image, there is a case in which black portions are frequently displayed on upper and lower sections or left and right sections of a image portion. As compared with the fluorescent substance of the image portion displayed as the black portion, the fluorescent substance of the image portion has a longer light emission accumulation time. Consequently, the degree of the deterioration in the fluorescent substance is greatly different between the displayed region as the image portion and the

displayed region as the black portion, which brings about the burn-in where the boundary between the image portion and the black portion is evidently viewed.

Also, for example, if a video source such as a movie and the like is displayed frequently, for example, a portion where caption is displayed in white has longer light emission accumulation time of the fluorescent substance than those of the other displayed portions, and such portion is viewed based on the burn-in as the fixed pattern.

As one of countermeasures against the burn-in as mentioned above, it is known to employ a method referred to as a so-called pixel shift wherein the display positions of images are shifted a bit at the time of displaying the image. If the image display is carried out by using such pixel shift method, for example, the positions of the display cells producing the image portion at a high luminance are shifted. Thus, it is possible to suppress the progress of the deterioration only in the fluorescent substance corresponding to the particular display cells. In short, this carries out the image display while protecting the display cells from the burn-in. Also, as the burn-in protection countermeasure, it is known to carry out the displaying while suppressing entirely the luminance of the displayed image.

However, the protective measure by means of such pixel shift and low luminance in the displayed image and the like can not be considered to be perfect, for example, in view the case that the image portion of the high luminance is displayed as substantially fixed pattern, such as the cases that the picture portion and the black portion are displayed, and that the captions are displayed, as mentioned above. In short, in the case of employing the

method of the pixel shift, the portion in which the pixel shift is performed on the screen is narrow. Thus, even if the pixel shift is carried out, there is a high possibility in that the display cell area displaying at the high luminance exists, and the burn-in is easily induced in such area. Also, for example, once the burn-in becomes outstanding, even by using this method of the pixel shift, it is difficult to conceal this burn-in.

Also, even if the method is employed to suppress the luminance level of the displayed image entirely, the burn-in is caused by the light emission time difference accumulated over a long time, and the luminance of the displayed image is lowered. Thus, this is disadvantageous in view of contrast and the like, and it is difficult to display the displayed image with high quality. Also, even if this method is used, it is difficult to conceal the burn-in that is already formed.

Also, a method is known in which, for example, if the burn-in becomes outstanding, lights are emitted from the entire screen for a certain period at substantially the maximum luminance level so that a fluorescent substance layer is intentionally deteriorated over the entire displayed area, thereby making the degree of the deterioration among the display cells as regular as possible. This is referred to as, for example, full white burning.

However, in the case of this full white burning, since the once-induced burn-in can not be sufficiently modified, it is not practically effective.

Accordingly, as the countermeasure against the burn-in, such configuration is known that calculates an accumulation value of light emission times for each display cell on the basis of a luminance value of a video signal, and corrects the video signal so

that the luminance irregularity caused by the burn-in is not visually recognized on the basis of this calculated accumulation value of the light emission times, and then carries out a display drive (for example, refer to a Japanese Laid Open Patent Application JP-Heisei, 10-149133).

In this case, the accumulation value of the light emission times for each display cell is treated as the component corresponding to the degree of the deterioration in the fluorescent substance corresponding to the display cell. In short, the deterioration degree in the luminance of the fluorescent substance is correlated with the accumulation value of the light emission times for each display cell. Further, the luminance lowering in each display cell is estimated on the basis of such accumulation value of the light emission times for each display cell. Then, the display with correction for the burn-in is executed so as to cancel this estimated luminance lowering.

In the case of such configuration, even once the burn-in is induced, the image display is carried out such that this burn-in is not recognized. Also, it is possible to carry out the display drive by considering the proper luminance and white balance on the basis of the luminance lowering based on the fluorescent substance deterioration. Thus, it is possible to suppress the lowering in the quality of the displayed image.

In case of the configuration for carrying out the display correction on the basis of the accumulation value of the light emission times for the display cell as mentioned above, the calculation of the accumulation value of the light emission times of the display cell (the deterioration degree in the fluorescent substance for each display cell) is carried out based on the

luminance level of the video signal. This is based on the fact that, in the light emission control based on the sub-field method, for example, each display cell is controlled to emit the lights in accordance with the accumulation time within one field period corresponding to the luminance level of the video signal corresponding to one field.

However, when the display drive for the plasma display apparatus is considered in the actual usage, there may be the case that the light emission time of the display cell does not always correspond to the luminance level indicated by the video signal itself. As one of specific examples, the following cases are listed. As the configuration for the display drive in the plasma display apparatus, there is a system which is configured by combining a luminance control referred to as a PLE (Peak Luminance Enhancement) control with the sub-field method.

According to the above mentioned PLE control, the display luminance level is controlled so as to be increased in a region where an average luminance level of input video signals is low and decreased in a region where an electric power consumption is large and the average luminance level is high. Consequently, relatively high peak luminance level can be obtained while the electric power consumption is suppressed in a case where a display area is large and the average luminance level is high.

And, the above mentioned PLE control is carried out such that the time length as the display period (the light emission period) in each sub-field is dynamically varied on the basis of the average luminance level of the input video signals.

Based on this fact, in the case of the display drive in which the PLE control is combined, even if a certain display cell has the

same luminance level, the actual light emission time length is changed correspondingly to the difference of the average luminance level at that time. In short, in the case of the display drive in which the PLE control is combined, it is understood that the light emission time length can not be singly determined from the luminance level of the video signal given to one display cell.

Thus, in such a case, if the configuration of carrying out the display correction on the basis of the accumulation value of the light emission times of the display cells as mentioned above is employed as the countermeasure against the burn-in, the accumulation value of the light emission times of the display cells is not always accurate, because the luminance level of the video signal is defined as the base. If the accuracy is lowered, the effect of the image correction for the burn-in is reduced correspondingly. In the actual condition, the countermeasure having higher reliability against the burn-in is requested.

Disclosure of Invention Accordingly, the present invention will be configured as a display apparatus as follows by considering the above mentioned problems. In short, it is provided with : a display panel unit formed such that since an application of an effective pulse for discharge which is a pulse voltage effective for the discharge in a display cell is carried out, a fluorescent substance positioned at the display cell is excited, thereby radiating a displaying light of a visible light ; a driving means for driving the display panel unit so as to select the display cell from which the displaying light is radiated, and carry out the application of the effective pulse for the discharge in this selected display cell ; a number of

accumulative pulses measuring means for measuring a number of accumulative pulses that is an accumulative value of an application number of the effective pulses for the discharges, for each display cell, and obtaining this measured result as the number information of accumulative pulses and a controlling means for carrying out a control so that the application of the effective pulse for the discharge is carried out by the driving means, so as to correct a difference of a luminance level among respective cells which is estimated on the basis of the number information of the accumulative pulses obtained by this number of accumulative pulses measuring means.

Also, as a driving method of a display apparatus, it is designed so as to execute : a driving procedure for driving a display panel unit formed such that since an application of an effective pulse for discharge which is a pulse voltage effective for discharge in a display cell is carried out, a fluorescent substance positioned at the display cell is excited, thereby radiating a displaying light of a visible light, and driving the display panel unit so as to select the display cell from which the display light is radiated, and carry out the application of the effective pulse for the discharge in this selected display cell ; a number of accumulative pulses measuring procedure for measuring the number of accumulative pulses that is an accumulative value of an application number of the effective pulses for the discharges for each display cell, and obtaining this measured result as number information of the accumulative pulses and a controlling procedure for carrying out a control so that the application of the effective pulse for the discharge is carried out by the driving procedure, so as to correct a difference of a luminance level among respective cells which is

estimated on the basis of the number information of accumulative pulses obtained by this number of accumulative pulses measuring procedure.

According to the above mentioned respective configurations, as the display apparatus based on the present invention, the display panel unit is configured such that since the fluorescent substance positioned for each display cell is excited by the discharge, the visible light is radiated from the fluorescent substance, thereby carrying out the display. In addition, the present invention is designed so as to measure and obtain the accumulative value (the number of accumulative pulses) of the application number of the effective pulses for the discharge in order to generate the above mentioned discharge for each display cell, and the application of the effective pulse for the discharge as mentioned above is carried out so as to correct the difference of the luminance level among the respective cells, which is estimated on the basis of the number information of the accumulative pulses for each this display cell.

Under such configuration, if the deterioration intensification degree in the fluorescent substance can be considered to depend on the application number of the effective pulses for the discharges, the deterioration intensification degree in the fluorescent substance for each display cell, in short, the lowering degree in the light emission luminance level of the visible light can be estimated at the high precision, on the basis of the application number of the effective pulses for the discharges.

And, the excellent correction result can be expected by carrying out the control so as to attain the necessary application operation of the effective pulses for the discharges, in such a way that the light emission luminance level difference (in short, the

deterioration degree difference) among the cells is canceled (corrected) on the basis of the thus-estimated lowering degree of the light emission luminance level in the fluorescent substance.

Brief Description of Drawings Fig. 1 is a perspective view showing a structure of a display panel of a plasma display apparatus as an embodiment of the present invention ; Fig. 2 is a view showing the configuration of the plasma display apparatus of the embodiment, by means of an electrode driver and an electrode ; Fig. 3 is a view showing a relation among R, G and B cells in the display panel of the embodiment, and pixels ; Fig. 4 is a view showing an example of a sub-field pattern applied in the embodiment ; Fig. 5 is a timing chart showing a timing for applying a voltage to drive an electrode in a sub-field method ; Fig. 6 is a sectional view of the display panel, to explain a displaying principle in the display panel of the embodiment ; Fig. 7 is a block diagram showing an operational function corresponding to a correction display of the embodiment; Fig. 8 is a block diagram showing a hardware configuration corresponding to the correction display, as the plasma display apparatus of the embodiment ; Figs. 9A and 9B are charts conceptually showing a mapping structure of number information of accumulative effective pulses after startup or number information of accumulative effective pulses before correction held in RAM or EEPROM, in the embodiment ;

Fig. 10 is a flowchart showing a processing operation example to execute a correction display through a burning based on a user operation, as the embodiment ; Fig. 11 is a flowchart showing a processing operation example to automatically execute the correction display by the burning, as the embodiment and Fig. 12 is a flowchart showing a flow of operations to execute the correction display based on an image display control, as the embodiment.

Best Mode for Carrying out the Invention Fig. 1 shows a structure of a display panel of a plasma display apparatus that is a display apparatus as an embodiment of the present invention. By the way, as the plasma display apparatus of this embodiment, an AC type (an alternating current type) is cited as an example. As the display panel, the configuration of a surface discharge type is employed based on a three-electrode structure.

As shown in Fig. 1, a transparent front glass substrate 101 is placed on a forefront surface of the display panel. Further, a sustain electrode 102 including an electrode X 102A and an electrode Y 102B as a pair is placed on a rear side of this front glass substrate 101. The electrode X 102A and the electrode Y 102B are placed parallel to each other with a predetermined interval in-between, for example, as shown in Fig. 1. The sustain electrode 102 composed of the electrode X 102A and the electrode Y 102B as the pair forms a line as one column. Also, each of the electrode X 102A and the electrode Y 102B is formed by combining a transparent conductive film 102a and a metal film

(bus conductor) 102b, respectively.

On the rear side of the front glass substrate 101, a dielectric layer 103 made of, for example, low melting point glass is further placed in addition to the sustain electrode 102 including the electrode X 102A and the electrode Y 102B as mentioned above.

Then, a protective film 104 made of, for example, MgO and the like is formed on the rear side of this dielectric layer 103.

Further on a front side of a rear glass substrate 105, an address electrode 107 is placed in a direction orthogonal to the sustain electrode 102 including the electrode X 102A and the electrode Y 102B. The address electrode 107 forms a line as a row. In addition, a separation wall 106 is formed between the address electrodes 107 adjacent to each other. Then, so as to cover a top surface of the rear glass substrate 105 on which the respective address electrode 107 is placed and the side wall sections of the separation walls 106 on both sides thereof, fluorescent substance layers 108R, 108G and 108B for the respective colors R, G and B are formed so as to be sequentially arrayed.

After such structure is established, the front end sections of the separation walls 106 are actually combined so as to come in contact with the protective film 104. Due to such structure, a discharging space 109 is formed in which the fluorescent substance layers 108R, 108G and 108B are formed. After this discharging space 109 is made vacuum, a gas, for example, such as Neon (Ne), Xenon (Xe), Helium (He) or the like is sealed in it.

Further, within the discharging space 109 in which this gas is sealed, the surface discharge is generated between the electrode X 102A and the electrode Y 102B. Consequently, the ultraviolet rays are radiated. Those ultraviolet rays cause the fluorescent

substance layers 108 to be excited, thereby radiating display lights serving as visible lights.

Fig. 2 shows the configuration of a driving circuit system designed for the structure of the above mentioned display panel.

For example, when viewed as the entire display panel, the electrodes X 102A as the sustain electrode 102 are horizontally arrayed as electrodes XI to Xn from the upper direction to the lower direction. Similarly, the electrodes Y 102B are horizontally arrayed as electrodes Y1 to Yn from the upper direction to the lower direction. Further, each set of the electrode XI and electrode Y1, the electrode X2 and electrode Y2, ... and the electrode Xn and electrode Yn forms a line in one column direction. Also, an address electrode A 107 forms a line in a row direction by being arranged, for example, as address electrodes Al to Am vertically from the left direction to the right direction. Further, each of crossing points of the column direction lines composed of the sustain electrodes 102 (the electrodes XI to Xn and the electrodes Y1 to Yn) serving as the pairs and the row direction lines as the address electrodes 107 (Al to Am) is formed as one cell (a display cell) 30.

The cell 30 in this case indicates the structured portion of the display panel constituted by the position at which the sustain electrode 102 (the electrode X, the electrode Y) and the address electrode A 107 is crossing, as mentioned above. Further, in this cell 30, according to the structure of the display panel shown in Fig. 1 and Fig. 3, a cell 30R of R (red), a cell 30G of G (green) and a cell 30B of B (blue) are obtained correspondingly to the colors of the correspondingly placed fluorescent substance layers 108. In this case, one pixel 31 that enables a color representation is

formed by the set of the cells 30R, 30G and 30B of R, G and B which are arrayed adjacently in the horizontal direction.

Now, the display drive for the display panel as the plasma display apparatus based on the above mentioned structure is explained. This embodiment is designed so as to carry out the image display based on the so-called sub-field method. The sub-field method divides a period corresponding to one filed (= 16.

7 ms) into a plurality of sub-fields, as shown in Fig. 4. In Fig. 4, the one field period is divided into 8 sub-fields SF1 to SF8. Here, each sub-field period is composed of a reset period Trs, an address period Tad, and a sustaining period Ts as shown in Fig. 4. The operations of the respective periods will be described later.

If one field period is divided into 8 sub-fields, binary weightings are set such that the relative ratios of the luminance to be represented by the respective sub-fields SF1 to SF8 become 1: 2: 4: 8 : 16: 32: 64: 128. And, the luminance levels to be represented by the respective sub-fields SF1 to SF8 are set correspondingly to these set weightings. This luminance setting is actually set on the basis of the number of sustain pulses applied to the electrode X and the electrode Y in order to generate the surface discharge in the sustain period Ts. Here, a pulse output cycle is constant when the sustain pulses are applied.

Thus, as the luminance weighting becomes greater, the sustain period Ts becomes longer. On the contrary, the lengths of the reset period Trs and the address period Tad are determined by the total number n of lines in the column direction and become constant irrespectively of the luminance weighting. And, depending on the combination of light emission/non light emission in which such sub-fields SF1 to SF8 are used, gradations

of 256 steps can be represented for each cell of R, G and B.

The waveform view of Fig. 5 shows a display drive timing in one sub-field period. At first, the reset period Trs that becomes the first period in the one sub-field period is the period in which wall charges of a horizontal line (sustain electrodes) group are removed in order to cancel the effect of the light emission condition in the immediately preceding sub-field period. To do so, for example, a write pulse Pw is simultaneously applied to the sustain electrodes XI to Xn. Since this write pulse Pw rises up to a positive potential Vr, the strong surface discharge is generated, and a large number of wall charges are accumulated in the dielectric layer 103. And, in response to the trailing of the write pulse Pw, the self-discharge caused by the wall charges accumulated at the time of the rising is generated, thereby removing the wall charges in the dielectric layer 103. By the way, in Fig. 5, a positive pulse Paw resulting from a potential Vaw is applied to the address electrodes Al to Am at the same output timing as the write pulse Pw. This application of the pulse Paw suppresses the charging of the inner wall surface on the rear of the display panel.

In the next address period Tad, addressing is carried out on the basis of a line sequential manner, and the light emission/non-light emission is set for each cell 30 in this sub-field period. In short, the address period Tad is the period to select the cell 30 from which the light is to be emitted in the one sub-field period. For this reason, here, by continuously applying a positive potential Vax with respect to a ground potential (0V) to the sustain electrode X, it is arranged to obtain the condition biased by this potential Vax. In addition, the sustain electrode Y

side is biased by a negative potential Vsc.

And, under this condition, a negative scanning pulse Py is sequentially applied to the sustain electrodes Y1 to Yn. In short, for the horizontal line, selection is carried out so as to sequentially scan, for example, from the upper direction to the lower direction. And, within the period where the line selection is carried out by applying the scanning pulse Py, a positive addressing pulse Pa having a potential Va is applied to the address electrode A corresponding to a cell from which light is emitted in the selected line among the address electrodes Al to Am.

In the selected horizontal line to which the scanning pulse Py is applied, at the cell 30 to which the addressing pulse Pa is applied, opposite discharge is generated between the sustain electrode Y and the addressing electrode A, thereby generating the wall charges. However, at this time, since the sustain electrode X is biased to the potential of the same polarity as the addressing pulse Pa, it is biased to the potential of the same polarity as the addressing pulse Pa. For this reason, the addressing pulse Pa is removed from the sustain electrode X, and the discharge is not generated between the sustain electrode X and the address electrode A.

The next sustaining period Ts is the period to maintain the light emission condition to the cell 30 set as the component from which light is emitted by the addressing in the above mentioned address period Tad. To do so, at first, a sustain pulse Ps having a predetermined pulse width having a positive potential Vs is simultaneously applied to the sustain electrodes Y1 to Yn. And, after the completion of the application of the sustain pulse to

those sustain electrodes Y1 to Yn, similarly, the sustain pulse Ps having the predetermined pulse width having the positive potential Vs is simultaneously applied to the sustain electrodes XI to Xn. After the completion of the application of the sustain pulse to those sustain electrodes XI to Xn, similarly, the sustain pulse Ps is alternately applied to the sustain electrodes Y1 to Yn and the sustain electrodes X1 to Xn. For each application of the sustain pulse Ps, in the cell 30 set so as to emit the light in the previous address period Tad, namely, in the cell 30 in which the accumulation of the wall charges is done, the surface discharge is generated between the sustain electrode X and the sustain electrode Y.

Here, Fig. 6 explains the light emitting operation of the plasma display apparatus that employs the display panel structure as this embodiment. In Fig. 6, in the display panel of the structure as this embodiment, the unit corresponding to one cell 30 is shown by a sectional view. By the way, in Fig. 6, the same symbols are given to the same portions as Fig. 1, and their explanations are omitted. As mentioned above, in the cell 30 in which the wall charges are accumulated by the application of the addressing pulse Pa in the address period Tad, in the sustaining period Ts, the surface discharge is generated correspondingly to the alternate application of the sustain pulse Ps to the sustain electrode 102 (the electrode X and the electrode Y). This surface discharge is the plasma discharge in which the gas sealed in the discharging space 109 is at the plasma state. Consequently, the ultraviolet rays are radiated within the discharging space 109.

And, the reaction to this irradiation of the ultraviolet rays causes the visible light to be radiated from the fluorescent

substance layer 108. This visible light is radiated at any color of R, G and B, correspondingly to the fact that the actual fluorescent substance layer is any one of an R fluorescent substance layer 108R, a G fluorescent substance layer 108G and a B fluorescent substance layer 108B. And, this visible light is reflected by the fluorescent substance layer 108, transmitted through the protective film 104, the dielectric layer 103 and the front glass substrate 101, and irradiated as the display light to the front side.

As mentioned above, in each cell 30, its light emission is controlled such that it is lighted by the principle explained in Fig.

6 as mentioned above. And, such a lighting operation is carried out by the display drive based on the sub-field method already explained in Fig. 4 and Fig. 5. Thus, in each cell 30, its light emission is controlled such that the necessary luminance in the range of the 256 gradation steps is obtained in the one field period.

By the way, the fluorescent substance layer 108 is deteriorated with time by carrying out the image display. The deterioration in the fluorescent substance layer 108 appears as lowering in the luminance level. Thus, as for the fluorescent substance layer 108 in a certain fixed display region, if its deterioration is intensified over the other regions, the difference of the luminance is generated between this region and the peripheral display regions, which brings about the phenomenon referred to as the so-called burn-in. If the burn-in is induced, for example, that burn-in portion seems to overlap with the displayed image as a fixed pattern. Hence, this is undesirable because the quality of the displayed image is damaged thereby.

Accordingly, as the plasma display apparatus, for example, it is necessary to employ the configuration that can solve the deterioration caused by such burn-in in the displayed image quality. Here, the main factor of the deterioration in the fluorescent substance layer 108 results from the ultraviolet rays irradiated by the surface discharge within the discharging space 109 and the impulse of the ionized gas, as explained in the conventional technique. This namely means that the deterioration is further intensified in the fluorescent substance layer 108 of the cell 30 in which the number of the surface discharges is greater within a certain unit time. And, the surface discharge is generated for each application of the sustain pulse Ps, in the sustaining period Ts within each sub-field period.

By the way, for the sake of verification, as evident from the explanations up to the present, the sustain pulse Ps itself is applied to all of the cells 30 in each sub-field period. And, as for a certain cell 30, the effective sub-field, in which the surface discharge is carried out by the sustain pulse Ps and the fluorescent substance layer 108 is excited, is only the sub-field to which the addressing pulse Pa is applied in the immediate preceding address period Tad. In short, the sustain pulse Ps is effective in generating the surface discharge, only for the cell 30 to which the addressing pulse Pa is applied in the immediate preceding address period Tad.

Accordingly, hereafter, the sustain pulse that becomes effective for the surface discharge is referred to as an effective sustain pulse. Or, it is also abbreviated as an effective pulse. Also, for example, if one field period is considered to be a unit time, the number of effective sustain pulse for each cell 30 in this unit time

is the total number of the sustain pulses obtained by the combination of the sub-fields (to which the addressing pulse Pa is applied) that is made effective, in order to emit the light from the fluorescent substance layer 108. And, as the total number of the effective sustain pulses in this one field period becomes greater, the luminance level of the cell 30 from which the light is emitted in that field image becomes higher.

The deterioration in the fluorescent substance layer 108 is thought to be further intensified as the light is emitted from the fluorescent substance at a higher luminance for a longer time.

However, from the above mentioned explanation, the fact that the light is emitted from the fluorescent substance layer 108 at the higher luminance for the longer time may be considered that the effective sustain pulses are applied by a large number of times within the unit time.

Then, in this embodiment, the deterioration degree in the fluorescent substance layer 108 is assumed to be the accumulation number of the effective sustain pulses within the unit time. And, it is designed so as to carry out the correction for the burn-in in the displayed image, on the basis of this accumulation number of the effective sustain pulses. The configuration for this design will be described below.

Fig. 7 shows an operational function of the correction for the burn-in in the plasma display apparatus of the present embodiment as a block diagram. A display state judging unit 1 judges whether or not a display unit 5 is presently executing an image display. The display unit 5 in this case is provided with, a plasma display panel and respective electrode drivers (an address electrode driver 21, an electrode X driver 22 and an electrode Y

driver 23), for example, which are shown in Fig. 1 and Fig. 2. In this case, if the image display is being executed, a pulse counting unit 2 measures the number of effective sustain pulses, for the respective cells 30 constituting the plasma display panel serving as the display unit 5. The number of effective sustain pulses measured by the pulse counting unit 2 as mentioned above are added, for example, sequentially and accumulatively, and they are then held. In this way, the number of accumulative effective sustain pulses which is the accumulation value of the effective sustain pulses until that time is always obtained.

A correction judging unit 3 is the unit for judging whether or not the correction display of the correction for the burn-in is executed. For example, as the plasma display apparatus in this embodiment, if the display for the burn-in correction referred to as so-called burning can be executed by the operation of a user, whether or not the burn-in correction display is instructed by this user operation is judged, thereby judging whether or not the correction display is executed. Also, the judgment as to whether or not the correction display is executed is considered to be automatically executed. For example, by referring to the number of accumulative effective sustain pulses obtained by the above mentioned pulse counting unit 2 at a predetermined timing, if the magnitude of the number of accumulative effective sustain pulses of each cell 30 satisfies a certain predetermined condition, it is judged that the burn-in correction is necessary. Then, the judgment on the execution of the correction display is carried out.

A correction display controlling unit 4 carries out the control so that the correction display for the correction for the luminance irregularity caused by the burn-in is executed by the display unit

5, in response to the fact that the judged result indicating the execution of the correction display is obtained from the correction judging unit 3.

As the correction display in this case, two methods are roughly considered. As one of the two methods, the deterioration degree in the fluorescent substance layer 108 of the cell 30 in which the deterioration is not intensified is adjusted to the fluorescent substance layer 108 of the cell 30 in which the deterioration is intensified by applying a so-called burning to the fluorescent substance layer 108 in order to physically emit light.

Consequently, after the correction, the difference of the luminance level among the cells 30 is canceled, thereby carrying out the image display without any burn-in phenomenon.

As the other method, when the actual execution of the image display based on the input video signal is carried out, the luminance level of each cell 30 (in short, the light emission luminance of the fluorescent substance layer 108) is dynamically adjusted so that the luminance irregularity and color irregularity caused by the burn-in are corrected based on this display control.

And, in any of the above mentioned correction displays, this embodiment is designed so as to set the burning on the basis of the number of accumulative effective sustain pulses of the respective cells 30, which are held as mentioned above, or the luminance pattern for the image display (the combination pattern of the sub-fields), and execute the image display based on this set luminance pattern.

Fig. 8 shows the units mainly related to the display correction, as the hardware configuration of the plasma display apparatus in this embodiment. Also, Fig. 8 collectively shows the

correspondence to the respective functional units shown in Fig. 7 as mentioned above, by using dashed lines. With reference to Fig. 8, the operations as the above mentioned respective functional units are described in detail on the basis of the operations as the hardware.

At first, the basic operation of the image display corresponding to the input video signal is described with reference to Fig. 8.

The video signal is inputted to a panel driver 12. The panel driver 12 decodes the input video signal, and generates a display data indicative of the luminance levels in the respective R, G and B cells, for example, for each field image unit, and then outputs these display data to a PLE unit 14 of a display unit 5.

The PLE unit 14 executes the luminance control referred to as a PLE (Peak Luminance Enhancement) control, on the basis of the input display data. As the PLE control, an average luminance level is calculated from the input display data, for example, per each field image. And, on the basis of the calculated average luminance level of the video signal, the luminance level is converted on the basis of a previously determined PLE property.

Depending on this PLE property, the properties of the display luminance levels of the respective R, G and B cells are set in such a way that in a region where the average luminance level of the video signal is low, the display luminance is increased by a predetermined amount on the basis of that level, and in a region having a large electric power consumption where the average luminance level is high, the display luminance is decreased by a predetermined amount so as to reduce the electric power consumption on the basis of that level.

Then, the luminance to be displayed by the actual light

emission control is determined for the respective R, G and B cells, on the basis of the thus-set properties of the luminance levels.

For example, if the gradation representation method of 256 steps shown in Fig. 4 is employed as the sub-field method, any luminance among the gradations of 0 and 255 is set for each of the R, G and B cells. In this way, setting the luminance of the respective R, G and B cells sets the luminance patterns within one field period (the combination of the sub-field periods on which the light emission control should be performed), with regard to the respective R, G and B cells.

Further, a display controller 13 of the display unit 5 controls the display drive onto a plasma display panel 17, on the basis of the thus-determined luminance pattern. In short, for example, in such a way that the respective electrode drivers (the address electrode driver 21, the electrode X driver 22 and the electrode Y driver 23) shown in Fig. 2 carry out the voltage applications at the necessary timings to the target electrodes, it executes the operational controls of those electrode drivers. Since such an operation is executed for each field period, the image corresponding to the input video signal is displayed on the plasma display panel in the display unit 5. Also, the image displayed at this time is displayed by the cell group whose luminance is set by the PLE control. And, the contrast is further improved as the image displayed by the PLE control as mentioned above.

And, the configuration for the burn-in correction of this embodiment is combined with the above mentioned basic image display operation as which will be described below. At first, the function as the display state judging unit 1 shown in Fig. 2 is carried out by judging the presence or absence of the video signal

inputted to the panel driver 12 with a main controller 10. In this case, the main controller 10 is composed of, for example, a micro computer and the like, and executes the entire operation control in the plasma display apparatus in this embodiment. An EEPROM (Electrically Erasable Programmable ROM) 11 is connected to this main controller 10, where the EEPROM 11 is able to rewrite data and to hold the stored content even if the power source supply is stopped. In this case, this EEPROM 11 holds and stores the number of accumulative effective sustain pulses for each cell 30, in which the number of effective sustain pulses measured by the operation as the pulse counting unit 2 are accumulated. By the way, in this case, the number of accumulative effective sustain pulses stored in the EEPROM 11 is defined as the number of accumulative effective sustain pulses before correction, and it is discriminated from the number of accumulative effective sustain pulses after startup, which is the effective sustain pulse number that is temporary held in a RAM 16 during starting-up of the power source as described later.

The operation as the pulse counting unit 2 is performed, for example, when a display controller 13 included by the display unit 5 uses a ROM 15 for a number of pulses reference table and the RAM 16 as shown in the drawings. The display controller 13 in this embodiment accumulatively measures the numbers of effective sustain pulses applied to each cell 30, for example, for the image display executed up to the present after the latest startup of the power source, and writes the measured values as the number of accumulative effective sustain pulses after startup to the RAM 16, and holds it.

Here, on the plasma display apparatus of this embodiment, the

image that is PLE-controlled on the basis of the average luminance level of the input video signal is displayed, as mentioned above. In short, in accordance with a predetermined PLE property, the luminance levels of the respective R, G and B cells designated by the input video signal are dynamically converted, and then carried out the image display. This indicates the following possible case. That is, for example, even if the input video signal indicates the same luminance level with regard to a certain cell at the same position, the luminance level actually set for the display is different on the basis of the average luminance level in that field. Thus, in the display controller 13, it is necessary to measure the number of effective sustain pulses based on the luminance level of each cell set on the basis of this PLE control result. For this reason, when measuring the number of effective sustain pulses, the display controller 13 refers to the ROM 15 for the number of pulses reference table 15.

According to the previous explanation of the PLE unit 14, the luminance levels actually set for the respective R, G and B cells, namely, the combinations of the sub-fields effective for the light emission control are determined, for example, on the basis of the average luminance level calculated for each one field period.

The ROM 15 for number of pulses reference table stores the information in which the luminance levels of the respective R, G and B cells, for example, indicated by the input video signal are correlated with the number of effective sustain pulses corresponding to the actual display luminance levels of the respective R, G and B cells determined by the preset PLE property.

The number of effective sustain pulses stored in this ROM 15 for the number of pulses reference table is the total number of the

effective sustain pulses, which is determined on the basis of the combination of the sub-fields where the surface discharges are effective within one field period, for example, set corresponding to the luminance level.

The display controller 13 obtains the information of the luminance levels of the respective R, G and B cells indicated by the input video signal, from the display data inputted to the PLE unit 14. And, it reads out the number of effective sustain pulses correlated with this obtained information of the luminance levels, and adds to the number of effective sustain pulses for each cell position written to the RAM 16 as the number of accumulative effective pulses after startup up to the present. And, it executes the process for rewriting the number of effective sustain pulses for each cell position obtained by this adding process, as a new number of accumulative effective pulses after startup, to the RAM 16.

This number of accumulative effective pulses after startup is held in the RAM 16, for example, through the structure shown in Figs. 9A and 9B. At first, the screen image formed on the plasma display panel through the structure shown in Fig. 1 is such that the cells 30 are arrayed in the shape of a matrix, as shown in Fig.

9A. And, when the lines in the column direction composed of line numbers n are referred to as LI to Ln from the upper side to the lower side and the lines in the row direction composed of line numbers m are referred to as Cl to Cm from the left side to the right side, the position of each cell 30 is represented by the combination of LI to Ln and Cl to Cm. For example, the cell 30 at the position of a first column and a first row is represented by (L1, C1). Also, the cell 30 at the position of a third column and a

second row is represented by (L3, C2).

And, in the RAM 16, for example, as shown in Fig. 9B, the values as the accumulative effective pulse number after startup in those cells are stored and held so as to be correlated with the cell positions (L1, C1), (L1, C2),... (Ln, Cm-1), (Ln, Cm).

Also, the value as the number of accumulative effective pulses after startup to be stored in the RAM 16 shown in Fig. 9B as mentioned above may be held by counting the actual accumulation value for each cell position. However, this embodiment is assumed to set the particular cell 30 having a standard value, as the actual number of accumulative effective pulses after startup to be stored in this RAM 16. For example, here, as the condition to specify the cell 30 which should have the standard value, the number of accumulative effective sustain pulses is assumed to be the maximum value. In this case, for example, for the cell 30 in which the number of accumulative effective sustain pulses is maximum, a value 0 is assumed to be stored as the standard value. Also, with regard to the other cells 30, an operation for calculating a differential value from the number of accumulative effective sustain pulses that becomes maximum as mentioned above, with regard to the number of accumulative effective sustain pulses, is carried out to then treat this differential value as the number of accumulative effective sustain pulses to be stored.

The number of accumulative effective sustain pulses of this embodiment is used for the display correction. At this time, the correction corresponding to the relative difference of the accumulative degree in the fluorescent substance layer 108 among the cells is carried out. In short, this results in the

correction corresponding to the difference of the number of accumulative effective sustain pulses. Thus, as mentioned above, even if the information as the difference of the number of accumulative effective sustain pulses is treated and stored as the number of accumulative effective pulses after startup, there is no trouble in the correcting operation while referring to this information.

Also, as compared with the case of merely storing the actual accumulation value as the number of accumulative effective pulses after startup in the RAM 16, for example, the number of bits (data size) to represent the number of accumulative effective pulses for each cell position can be reduced, thereby using the memory capacity of the RAM 16 while saving.

By the way, as the condition of the cell 30 having the standard value, it is defined that the cell 30 has the maximum value as the number of accumulative effective sustain pulses, however, this is only one example. For example, on the contrary, the number of accumulative effective sustain pulses may have the minimum value. Also, assuming that the cell located at the particular position is the cell 30 having the standard value, the differential value from the standard value set for the cell 30 at this particular position may be stored with regard to the cells at the other positions. This point is similar with regard to the number information of the accumulative effective pulses before correction that is stored and held in the EEPROM 11, which will be described later.

Here, it is assumed that the power source is switched to an off-state after stating up the present power source, for example.

At the timing when the power source is turned off, the display

controller 13 reads out the number information of the accumulative effective pulses after startup held in the RAM 16 up to the present, and transfers to the main controller 10.

The EEPROM 11 is connected to the main controller 10, as mentioned above, and this EEPROM 11 stores the information of the number of accumulative effective pulses before correction.

The number information of the accumulative effective pulses before corrections stored in this EEPROM 11 includes, as the number of accumulative effective pulses for each cell, the value in which the number of effective sustain pulses for each cell after the final execution of the display correction by the burning are accumulated. As the number information of the accumulative effective pulses before correction stored in this EEPROM 11, it may be the information to be stored, for example, through the structure explained in Figs. 9A and 9B. Also, even as the value of the number of accumulative effective pulses before correction to be stored correspondingly to each cell position, similar to the number of accumulative effective pulses after startup held in the RAM 16, the value of the cell in which the number of accumulative effective pulses before correction becomes maximum is used as the standard value (for example, 0). As for the other cells, the value indicative of the difference from this maximum value may be stored.

And, the main controller 10 executes the process for generating the information of a new number of accumulative effective pulses before correction, including the process for adding the information of the transferred number of accumulative effective pulses after startup to the number information of the accumulative effective pulses before correction already stored in

the EEPROM 11. By the way, at this time, for example, the cell position is at first specified in which the number of accumulative effective pulses before correction becomes maximum, based on the result of the above mentioned adding process, and the standard value is set for the number of accumulative effective pulses before correction at this cell position. And, as the value to be stored in the other cell position, the differential value from this maximum value is newly calculated, for each cell position. Then, those new standard values and differential values are correlated for each cell position, and the number information of the accumulative effective pulses before correction in the EEPROM 11 is rewritten.

In this way, as the number information of the accumulative effective pulses before correction in the EEPROM 11, the number information of the accumulative effective sustain pulses of each cell obtained by the image display during the previous starting up of the power source after the correction display for the final burning, is always stored. By the way, for example, in response to the execution of the correction display by the burning, the number information of the accumulative effective pulses before correction with regard to all of the cells stored in this EEPROM 11 are reset to the initial value. Also, the number information of the accumulative effective pulses after startup held in the RAM 16 as mentioned above are also reset in response to the execution of the correction display by the burning.

In addition, the main controller 10 has the function as the correction judging unit 3. In short, for example, in response to the operation of the display correction instruction through the user, or a display correction execution command automatically

generated on the basis of the correction judgment process result in the main controller 10 and the like, the main controller 10 judges, for example, that the correction display by the burning should be executed.

In succession, under the configuration of the plasma display apparatus in this embodiment shown in Fig. 8 as mentioned above, the processing operation example for the correction display by the burning will be described below with reference to a flowchart of Fig. 10. By the way, as the processing operation shown in Fig. 10, the case is exemplified in which the instruction of the correction display execution is carried out by the operation of the user.

Also, the process shown in Fig. 10 is assumed to be executed under the linkage between the main controller 10 and the display controller 13, if it is the case of Fig. 8.

At first, at step S101, after the present power source state is recognized, it is judged whether or not a main power source is on.

And, as long as the main power source is on, an affirmation result is obtained in this case, and the flow of the flowchart proceeds to step S102.

At step S102, it is judged whether or not a setup operation to be executed at a time of a main power source start is completed.

However, since the process shown in Fig. 10 is related to the correction display, the setup operation to be judged in this case is limited to the operation for reading the number information of the accumulative effective pulses before corrections from the EEPROM 11. At step S102, as the setup operation, if the judgment result of a rejection is obtained because the reading of the number information of the accumulative effective pulses before corrections from the EEPROM 11 is not completed, the flow

of the flowchart proceeds to step S103. Then, the number information of the accumulative effective pulses before correction is read from the EEPROM 11. For example, after the process for storing in the RAM inside the main controller 10 is executed, the flow of the flowchart proceeds to a process at step S104. By the way, the number information of the accumulative effective pulses before corrections read from the EEPROM 11 may be written to the RAM 16 and held therein. On the contrary, at step S102, if the setup operation is completed and the reading of the number information of the accumulative effective pulse before corrections is also completed, the affirmation result is obtained, and the flow of the flowchart proceeds to step S104, in its original state.

At step S104, it is judged whether or not an image is presently displayed on the display unit 5. This process corresponds to the operation as the display state judging unit 1 in Fig. 7 and Fig. 8.

Here, if the rejection result is obtained because the image is not displayed, the flow of the flowchart returns back to the process at step S101. On the contrary, if the affirmation result is obtained because of the image display state, the flow of the flowchart proceeds to the process at step S105.

At step S105, in response to the fact that the image is presently displayed and outputted, the process is executed for measuring the number of accumulative effective pulses after startup and for holding this measured result in the RAM 16. This process at step S105 becomes the process as the pulse counting unit 2 explained in Fig. 8.

At next step S106, it is judged whether or not a correction display execution command is generated. This process at step S106 becomes the process as the correction judging unit 3. Thus,

as shown in Fig. 8, when the main controller 10 enters the correction display execution command, it is judged that the correction display should be executed. For example, in this case, unless the user especially carries out the operation for the correction display execution, the correction display execution command is not generated. Thus, at this step S106, the rejection result is obtained, thereby making the flow of the flowchart returning back to the process at step S101. By the way, the routine in which the flow of the flowchart returns from this step S106 to step S101 is carried out at a timing for each vertical blanking signal of the input video signal, namely, a field cycle.

Also, at step S101, for example, assuming that the main power source is switched from the on-state to the off-state, if the judgment result of the rejection is obtained at step S101, the flow of the flowchart proceeds to a process at step S113. At step S113, as already explained in Fig. 8, the number information of the new accumulative effective pulses before corrections is calculated from the number information of the accumulative effective pulses after startups that is written and held in the RAM 16 until that time, and the number information of the accumulative effective pulses before correction which is the number information of the accumulative effective pulses before the present power source start that is presently read in the main controller 10. And, the writing process to the EEPROM 11 is executed at next step S114 so as to change the number information of the past accumulative effective pulses before corrections stored in the EEPROM 11 into the number information of the new accumulative effective pulses before corrections obtained as mentioned above.

And, since the user carries out the operation for the display

correction execution, if the display correction execution is generated, the affirmation result is obtained at step S106, and the flow of the flowchart proceeds to processes on and after step S107. The processes at step S107 to step S112 correspond to the operation as the correction display unit 5.

At step S107, at first, it executes a controlling process for stopping the image display executed up to the present. To do so, for example, it stops the video signal input to the panel driver 12, and stops the driving operation for the display on the display unit 5. And, at next step S108, a process for calculating the number of correction sustain pulses to be applied to each cell is executed for the correction display by the burning.

To do so, the number information of the accumulative effective pulses before corrections read from the EEPROM 11 by the setup operation at the time of the present main power source start and the number information of the accumulative effective pulse after startup held in the RAM 16 up to the present are used. In short, the number of accumulative effective pulses after startup are added to the number of accumulative effective pulses before corrections, for each cell. From this addition result, for example, at first, the cell in which the number of accumulative effective sustain pulses becomes the maximum value at this time is recognized, and the standard value is set for this cell. And, for the other cells, a calculating process is carried out for converting the value obtained from the above mentioned addition result into the differential value from the standard value. The value of each cell obtained as mentioned above, namely, becomes the value corresponding to the number of correction sustain pulses. And, the number of correction sustain pulses for each cell obtained as

mentioned above correspond to the number of times to excite the fluorescent substance layer of each cell, in such a way that with regard to the fluorescent substance layer of the cell where the deterioration degree is intensified most violently, the light emission luminance of the fluorescent substance layers of the other respective cells becomes equivalent to the light emission luminance level corresponding to that deterioration degree.

However, as described in this embodiment, under the configuration having the respective fluorescent substance layers 108 of R, G and B for full-color image display, it is known that the deterioration properties (the intensification degree of the deterioration and the lowering amount in the light emission luminance level based on the deterioration degree) are different, for example, on the basis of the materials, for each fluorescent substance layer of R, G and B. In short, even in the case of the same number of accumulative sustain pulses, the lowering amounts in the light emission luminance of the respective fluorescent substance layers of R, G and B are not the same degree. Also, this implies that as the deterioration is further intensified, the white balance becomes unsuitable at a higher probability.

Thus, irrespectively of the R, G and B cells, the number of correction sustain pulses is determined by simply defining the number of accumulative effective pulses as the standard.

Consequently, even if the correction display by the burning is done, although there is no difference among the numbers of sustain pulses in the respective cells after the correction, since the proper white balance is not actually set, the color irregularity is induced. In short, this is imperfect as the correction for the

burn-in image.

So, this embodiment is designed such that the actual differential value is calculated by considering the deterioration properties of the fluorescent substance layers for each R, G and B cells, when executing the operating process for converting into the differential value from the standard value at step S108. The deterioration properties of the respective fluorescent substance layers of R, G and B are determined, for example, by the materials used in the fluorescent substance layer, as mentioned above. Thus, the deterioration tendency based on the number of sustain pulses can be known from an experiment and the like.

And, the RGB balance correction value to be considered for each of the R, G and B cells is stored on the basis of the deterioration tendency based on this number of sustain pulses, and the configuration to execute the operating process for the differential value at step S106 is employed from this RGB balance correction value.

Depending on the thus set number of sustain pulses, the deterioration degree in the fluorescent substance layer 108 is adjusted, for example, so as to correct the luminance difference among the R, G and B cells in one field. Consequently, the color representation under the proper white balance setting is carried out for each pixel. Moreover, together with this, the deterioration degree in the cell 30 is also adjusted so as to correct the luminance level difference among the pixels. Thus, the luminance irregularity and the color irregularity are canceled also as the entire image.

At next step S109, a correcting luminance pattern for each cell is set on the basis of the number of correction sustain pulses. As

the number of correction sustain pulses in this case, for example, it may be determined with the display drive based on the sub-field method shown in Fig. 4 as a preamble. And, the correction display is executed at next step S110. In short, in accordance with the correcting luminance pattern obtained at step S109, the respective electrode drivers (the address electrode driver 2, the electrode X driver 22 and the electrode Y driver 23) in the display unit 5 are controlled so as to drive the respective electrodes in accordance with the necessary pattern. And, at the stage when this correction display is ended, the necessary number of effective sustain pulses based on the correction are applied to each cell.

Then, the deterioration degree in the fluorescent substance layer among respective cells is adjusted, thereby canceling the luminance irregularity and the color irregularity.

Then, when the correction display at step S110 is ended, at next step Slll, the number information of the accumulative effective pulses after startup held in the RAM 16 up to the present is reset to the original value. Also, at next step S112, the number information of the accumulative effective pulses before corrections that is stored and held in the EEPROM 11 up to the present is reset to the original value, and the flow of the flowchart returns back to the process at step S101.

However, as the actual process at step S112, at this stage, only the number information of the accumulative effective pulses before corrections read in the main controller 10 is reset, and the number information of the accumulative effective pulses before correction in the EEPROM 11 may not be reset. Tentatively, after the present process at step S112, even if the correction display should be again executed before the main power source is

turned off, at this time, as explained at step S108, the number information of the accumulative effective pulses after startup held in the inner RAM of the display controller 13 is used for the calculation of the number of correction sustain pulses, and the number information of the accumulative effective pulses after startup in the EEPROM 11 is not used. And, when the main power source is finally turned off as described later, the number information of the accumulative effective pulses before correction in the EEPROM 11 is rewritten on the basis of the number information of the accumulative effective pulses after startup held in the RAM 16 at this time. At this time, the number information of the accumulative effective pulses before corrections in the EEPROM 11 has the proper content.

In the processing operation shown in Fig. 10 as mentioned above, the trigger of the correction display execution is defined as the correction display instruction through the user operation.

However, as the trigger of the correction display in this embodiment, it may be configured to automatically judge whether or not the correction display is executed, on the basis of the number information of the present accumulative effective pulses, and automatically execute the correction display in accordance with this judgment result, other than the instruction through the user operation, as the operation of the correction judging unit 3, as mentioned above.

Fig. 11 shows the processing operation for this configuration.

This process shown in Fig. 11 is also executed under the linkage between the main controller 10 and the display controller 13. In this process shown in Fig. 11, at first, a process at step S201 reads the number information of the accumulative effective

pulses before correction from the EEPROM 11 at a predetermined timing.

Here, in the plasma display apparatus of this embodiment, as shown in Fig. 1 and Fig. 3, for example, one pixel 31 is constituted by the set of the R, G and B cells (30R, 30G and 30B) arranged adjacently in the column direction. In short, the color reproduction as full color is carried out for each pixel 31. Thus, as the magnitude relation among the numbers of accumulative effective pulses for each R, G and B cells for each pixel 31, an offset value is given in which the deterioration properties of the respective fluorescent substance layers (108R, 108G and 108B) of R, G and B are considered. Then, if the difference equal to or greater than a preset threshold occurs, it is possible to deem that the burn-in is induced.

At step S202, the magnitude relation of the number of accumulative effective pulses among the R, G and B cells for each pixel unit targeted for the comparison among the above mentioned thresholds is recognized. As the concrete process, for example, basically, the differential values of the numbers of accumulative effective pulses among the R, G and B cells are assumed to be R-G = a, R-B = b and G-B = c. Then, the values of those a, b and c are calculated. By the way, as mentioned above, as for the respective values of the actual a, b and c, the offset values should be given in which the deterioration properties of the respective fluorescent substance layers of R, G and B are considered.

And, at next step S203, with regard to the respective differential values (a, b and c) of the numbers of accumulative effective pulses among the R, G and B cells for each pixel obtained

at step S202 as mentioned above, it is judged whether or not there is the pixel exceeding the threshold. By the way, instead of the consideration of the deterioration properties in the respective fluorescent substance layers of R, G and B when the above mentioned differential values a, b and c are calculated, even if this threshold is assumed to be the value set by considering the deterioration properties in the respective fluorescent substance layers of R, G and B, the proper judgment result is obtained at step S203. Here, for example, if the rejection result is obtained at step S203, there is no pixel in which the improper white balance and the luminance irregularity especially caused by the burn-in occur. In this case, the processing routine shown in this figure is once ended.

On the contrary, if the affirmation result is obtained at step S203, there is the pixel in which the luminance irregularity caused by the burn-in occurs. So, in this case, the correction display is executed as the process at step S204. As the correction display at this step S204, for example, the previous processes from step S107 to step S112 in Fig. 10 may be executed.

By the way, the judging process at step S203 as mentioned above may be designed such that the affirmation result is obtained if there is a single pixel exceeding the threshold with regard to the respective differential values (a, b and c) of the numbers of accumulative effective pulses among the R, G and B cells. However, for example, in this case, even under the condition that the luminance irregularity and color irregularity on the displayed image are not substantially visually recognized, the correction display is considered to be executed frequently and automatically. There may a case that such condition is not

suitable, for example, in the case when the electric power consumption and the convenience of the user are considered. So, for example, the judging process at step S203 may be designed such that the affirmation result is obtained if there are a certain plurality of pixels exceeding the threshold with regard to the respective differential values (a, b and c) of the numbers of accumulative effective pulses among the R, G and B cells.

Moreover, it may be considered that the affirmation result is obtained if the number of such pixels is judged to be equal to or greater than a certain number in a range of a region size, to a degree that the burn-in is estimated to be outstanding. In short, the standard of the judging process at step S203 may be suitably changed, depending on the condition in which the burn-in needs to be actually corrected.

By the way, there may be considered several chances and timings when the process shown in Fig. 11 as mentioned above is actually executed. For example, the automatic execution after a certain time after the main power source is turned off is considered to be reasonable. In short, the execution under the condition that the main power source is off is desirable. In short, the burning is automatically executed in this case. Thus, if the execution is possible when the main power source is on, the display screen based on the input video signal is suddenly disappeared. Instead of it, the image by the burning is displayed, which may lead to an undesirable case.

Of course, the process shown in Fig. 11 can be designed such that it can be executed, for example, while the image is displayed.

In this case, the processes at steps S201 to S202 are desirable because the accurate result is obtained, if they are designed as

follows. That is, they obtain the number information of the accumulative effective pulses before correction already read by the main controller 10 and the number information of the accumulative effective pulses after starting up held in the RAM 16 at this time, and calculate the differential values of the numbers of accumulative effective pulses among the R, G and B cells for each pixel, on the basis of those information.

Here, both of the display corrections explained in Fig. 10 and Fig. 11 are the correction so that due to the display referred to as the burning, the deterioration in the necessary fluorescent substance layer is positively intensified, thereby making the deterioration in the fluorescent substance layer regular as the entire display panel. However, as the correction display in this embodiment based on the number information of the accumulative effective pulses, other than the above mentioned burning, for example, it is possible to execute the display image correction for controlling the gradation of the luminance of each cell, so as not to induce the luminance irregularity and the color irregularity, if the image display is actually executed.

The operational procedure for this execution is shown as a flowchart in Fig. 12. By the way, the configuration of the plasma display apparatus in this embodiment corresponding to Fig. 12 may be basically similar to that of Fig. 8. However, in this case, the configuration as the correction judging unit 3 for judging whether or not the correction display by the burning is executed is not especially required.

Here, if the image display is started, the plasma display apparatus executes the operation at step S301. By the way, at the stage when the operation at step S301 is firstly started, it is

supposed that the reading of the number information of the accumulative effective pulses before corrections to the main controller 10 from the EEPROM 11 as the setup at the time of the start is completed. Then, at step S301, the differential value of the number of accumulative effective pulses among the respective cells at this time is calculated on the basis of the number information of the accumulative effective pulses before correction read in the main controller 10 as mentioned above and the number of accumulative effective pulse after startup held in the RAM 16 at this time. In short, the accurate number of accumulative effective sustain pulses for each cell at this time can be obtained by adding the number information of the accumulative effective pulses before correction for each cell and the present number of accumulative effective pulses after startup.

And, the differential value of the number of accumulative effective pulses among respective cells at this time is calculated on the basis of this number of accumulative effective sustain pulse. As the process for calculating this differential value, it can be basically calculated, for example, by obtaining the differential value of the number of accumulative effective pulses of the other cell, with respect to the standard value of the number of accumulative effective pulses of the cell that is the standard.

And, at next step S302, the actual luminance level corresponding to one field to be set in each cell is set on the basis of the calculation result obtained at step S301 as mentioned above. The luminance level set at this time is set, for example, in such a way that the light is emitted from each cell at the original luminance level, so as to cancel the difference of this luminance level, correspondingly to the difference of the

luminance level for each cell, which is estimated in accordance with the calculation result obtained at step S301. Also, at this time, the luminance level setting which considers the display through the proper white balance (the coloration) is carried out by considering the deterioration properties in the respective fluorescent substance layers of R, G and B. Thus, the setting of the luminance level for each cell should be done, for example, so as to cancel the luminance difference among the R, G and B cells constituting one pixel and further cancel the luminance level difference among the pixels. And, the correcting luminance pattern corresponding to one field (the combination of the sub-field patterns) is set on the basis of the thus set luminance level of each cell. In short, the setting of the cell is done from which the light is emitted in each sub-field.

At next step S303, a control is executed for displaying the image corresponding to one field based on the correcting luminance pattern generated as mentioned above. And, in association with the display of this field image, as shown as a process at next step S304, through the present display of the field image, so as to add the number of effective sustain pulses applied to each cell to the number of accumulative effective pulses after startup up to the present, the number of accumulative effective pulses after startup held in the RAM 16 is updated. And, if this process is ended, the flow of the flowchart returns back to the process at step S301. Since such processes at steps S301 to S304 are repeated, for example, for each field cycle, the field image displayed each time becomes the image in which the luminance level difference of R, G and B in the pixel and the luminance level difference among the pixels are canceled. As a result, the image

in which the luminance irregularity and coloration irregularity caused by the burn-in are corrected is stably displayed.

As mentioned above, in this embodiment, irrespectively of the fact that the operation as the correction display is the burning or the image display control in real time, the correction display is executed on the basis of the number of effective sustain pulses of each cell. Here, as a comparison, a configuration is conventionally known for determining the accumulative light emission time of the fluorescent substance layer of each cell on the basis of the luminance level indicated by the input video signal and executing the correction display for the burn-in correction on the basis of this accumulative light emission time.

However, as mentioned above, for example, if the PLE control and the like are done, there is discrepancy between the luminance level indicated by the video signal and the actual accumulative light emission time. Thus, the correction display for the accurate burn-in correction can not be always executed. On the contrary, in this embodiment, the correction display is executed on the basis of the number of effective sustain pulses actually applied to the cell. For this reason, for example, even in the same luminance level indicated by the video signal by the PLE control, even if the actually set luminance level (the light emission time) is converted, since the number of effective sustain pulses is basic, it is possible to obtain the information corresponding to the accumulative light emission time of each cell, which is always accurate. For this reason, the burn-in correction display is carried out at the high faithfulness, corresponding to the actual burn-in degree.

Also, as compared with the pixel shift, the displaying through

the luminance suppression and the full white burning which are the other conventional burn-in countermeasures and the like, the correction display as this embodiment has no lowering in the display quality and has no trouble in which the modification of the luminance irregularity is insufficient as the result of the burning.

By the way, this embodiment may be designed, for example, so as to execute any of the correction display as the burnings shown in Fig. 10 and Fig. 11 and the correction display as the displayed image correction shown in Fig. 12 or may be designed so as to be able to execute both of them. Also, as the present invention, if the effective sustain pulse number for each cell is basic, a method other than the methods explained by using the flowcharts and the like up to the present may be used for the process for generating the luminance level for the correction using this number of effective sustain pulses.

Also, the present invention can be applied to the display apparatus having the features that the display at the cell unit urges the light emission from the fluorescent substance resulting from the pulse application and that the fluorescent substance is deteriorated by the ultraviolet rays irradiation in association with this pulse application and the ion impulse, and any factor other than the above mentioned two items if it is associated with the application of pulses.