1. Field of the Invention
The present invention relates to an image display apparatus having a plurality of display devices and a manufacturing method thereof.
2. Description of the Related Art
In image display apparatuses which form images using a plurality of display devices, variation in luminance of the display devices causes a deterioration in image quality.
Japanese Patent Application Laid-Open No. 2004-325565 (FIG. 2) discloses a method for obtaining a deterioration quantity of luminance based on previously measured luminance deterioration characteristics of RGB and accumulated lighting time of the display devices so as to correct luminance balance of RGB in EL displays.
The characteristics of time variation in luminance of the display devices, however, vary according to not only colors but also devices. For this reason, when the characteristics of variation with time varies in the plurality of display devices composing the image display apparatus, even if the correction in JP-A No. 2004-325565 is applied, luminance unevenness among the display devices cannot be sufficiently corrected.
The present invention solves the above problem, and its object is to provide an image display apparatus which can reduce the luminance unevenness caused by the time variation in luminance and can display images with high quality for a long period, and a manufacturing method thereof.
According to a first aspect of the present invention, there is provided an image display apparatus, including:
a plurality of display devices; and
a correction circuit which corrects image data in order to reduce luminance unevenness among the plurality of display devices,
wherein the correction circuit includes:
a first storing unit which stores first characteristic data of each of the display devices which represent variation characteristics of luminance with respect to drive time;
a second storing unit which stores drive time data which represent values correlated with the drive time of the display devices and are updated when the display devices are driven; and
a calculation unit which calculates correction values corresponding to each of the display devices based on the first characteristic data and the drive time data.
According to a second aspect of the present invention, there is provided a method for manufacturing an image display apparatus having a plurality of display devices, including the steps of:
measuring luminance or physical quantities correlated with the luminance of the display devices at the time of driving the display devices for a predetermined measuring period;
calculating first characteristic data of each of the display devices which represent variation characteristics of luminance with respect to drive time based on measured values obtained at the measuring step; and
storing the calculated first characteristic data in a storing unit of the image display apparatus.
According to the present invention, the image display apparatus, which reduces the luminance unevenness due to the time variation in the luminance and can display images with high quality for a long period, can be provided.
Preferred embodiments of the present invention are described in detail below with reference to the drawings.
The present invention is preferably applied to a self-luminous image display apparatus. Examples of this kind of image display apparatuses include image display apparatuses using electron-emitting devices (cold cathode electron-emitting devices), EL displays, LED displays and PDPs. The present invention is preferably applied to the image display apparatus using the electron-emitting devices in all of them because variation in emission current-voltage characteristics with time varies among the electron-emitting devices.
In the image display apparatus using electron-emitting devices, an electron-emitting device and phosphor (illuminant) opposed to the electron-emitting device compose a display device. Examples of the electron-emitting devices include field-emission devices (FE devices), surface-conduction emission devices (SCE devices), and metal/insulation/metal devices (MIM devices).
A first embodiment is described with reference to the block diagram of
As shown in
The first storing unit 1 stores luminance variation characteristic data (first characteristic data) showing luminance variation characteristic with respect to drive time (hereinafter, simply “luminance variation characteristic”) therein. Since the luminance variation characteristic can be specific to the respective display devices, the first storing unit 1 stores luminance variation characteristic data about each of the plurality of display devices 4 respectively therein. The luminance variation characteristic data are stored in the first storing unit 1 at a step of manufacturing the image display apparatus.
The “variation in luminance with respect to the drive time” includes a case where as the drive time of the display devices becomes longer, the luminance becomes lower (deteriorated), and a case where as the drive time becomes longer, the luminance becomes higher (improved). Hereinafter, the “variation in luminance with respect to the drive time” is also simply described as “variation in luminance with time”.
The luminance variation characteristic data does not have to represent variation in a luminance value of the display devices, and may represent variation in value of “physical quantity correlated with the luminance”. In the case of a cold cathode electron-emitting device, the physical quantity correlated with the luminance includes an electric current (drive current) which is applied between a cathode electrode and a gate electrode of the electron-emitting device, an electric current (emission current) which is applied from an electron-emitting device to an anode electrode, and an electron emission efficiency.
The luminance variation characteristic data is calculated based on the luminance of the respective display devices or measured values of the physical quantity correlated with the luminance, or is calculated based on a database of the luminance of the display devices or the physical quantity correlated with the luminance. Precisely, since the luminance variation characteristic varies in each display device, actual measured values are preferably used in order to improve correction accuracy. That is to say, the individual display devices of the image display apparatus are actually driven, the luminance or the physical quantity correlated with the luminance is measured, and the data about the luminance variation characteristics of the individual display devices is calculated based on the obtained measured values. The luminance may be measured directly by using a luminance meter, or the driving current or the emission current may be measured by using an electrical measuring system. The measuring device for measuring the luminance or the physical quantity correlated with the luminance can be installed into the image display apparatus. If the image display apparatus has the measuring device, the data about the luminance variation characteristic can be suitably updated.
The format of the luminance variation characteristic data may be coefficients (parameters) representing an approximate curve of the luminance variation characteristics, or a look-up table. From a viewpoint of reducing a storage region, it is preferable that the luminance variation characteristic data is retained in the former coefficient format. The approximate curve of the luminance variation characteristics can be expressed by a function of time composed of one or a plurality of coefficients. For example, the approximation curve is expressed by a logarithmic approximation formula in Formula 1:
Li=ai×Log(Ti)+bi (Formula 1)
In the Formula 1, Li denotes prediction luminance, and Ti denotes accumulated drive time. Coefficients ai and bi denote the luminance variation characteristic data, and they are parameters which do not depend on the time. i denotes a number of a display device.
At an initial driving stage, the characteristics of the display devices may greatly fluctuate due to an influence of emitted gas or the like. For this reason, preliminary drive time referred to as aging is occasionally set at the initial stage. When such aging period is set, offset time T0 corresponding to the aging period may be introduced like a Formula 2.
Li=ai×Log(Ti−T0)+bi (Formula 2)
The formula which expresses the luminance variation characteristic varies according to a type of the devices, a manufacturing method of the devices and a driving condition. For example, the characteristic is expressed by a linear formula like a Formula 3. Any formulas may be adopted as long as the formulas are expressed by the function of time having one or a plurality of coefficients.
Li=ai+bi×Ti (Formula 3)
The second storing unit 2 stores drive time data which represent values correlated to the drive time of the display devices therein. The value of the drive time data is zero at an initial stage, and when the display devices are driven, the drive time data are updated.
“The value correlated with the drive time” (hereinafter, simply “drive time correlated value”) is an accumulated total of the drive time of the display devices, or an accumulated total of values obtained by adjusting the drive time of the display devices according to gradation values. The latter value can be called also as an accumulated total of values obtained by weighing the drive time of the display devices according to the gradation values.
When a driving signal is a simple pulse width modulated signal, the former value (namely, the total value of the pulse widths of the driving signal) is preferable. When the driving signal is an amplitude modulated signal or a combined signal of the pulse width modulation and the amplitude modulation, the latter value is preferable. For example, in the case of the amplitude modulated signal, the pulse width is constant regardless of the gradation value, and the luminance of the devices varies according to the level of the amplitude. Therefore, in the case of the driving for one hour with maximum gradation (maximum amplitude), “1 hour” is added to the drive time data, but in the case of the driving for 1 hour with 50% of the maximum gradation, only “0.5 hour” is added. That is to say, not the time of actually applying signals is accumulated but corresponding values at the time when signals with maximum gradation (maximum amplitude) are supposed to be applied is accumulated. In other words, values corresponding to time integration of the amplitudes of the driving signals are accumulated. The same holds for the case of a signal where the pulse width modulation and the amplitude modulation are combined (a signal which obtains a plurality of amplitude values in one driving signal waveform).
The drive time data are preferably updated and stored individually for all the display devices 4. This is because the correcting accuracy is improved.
From a viewpoint of reducing the storage region, the common drive time data may be used for two or more display devices. The value represented by this data is a central value of the drive time correlated values of two or more display devices. Examples of such a central value include an average value of the drive time correlated values of all the display devices and the drive time corrected values of the plurality of display devices Further, the drive time correlated value of a certain display device, such as a display device at the center of an image area, may be used as the central value. Further, a general average value according to an output object may be used. In the case of a TV video, since average luminance is 20% to 30% of the maximum luminance, 20% to 30% of the actual drive time may be used as a central value of the drive time correlated value.
The correction value calculation unit 3 refers to the first storing unit 1 and the second storing unit 2 so as to obtain a variation amount in the luminance of the respective display devices with time (decrease amount or increase amount) based on the luminance variation characteristic data specific to the display devices and the drive time data. The correction value calculation unit 3 determines a correction target value based on the variation amount in the luminance of all the display devices with time. The correction value calculation unit 3 obtains a correction value for correcting an input signal (input image data) so that the display devices have luminance of the correction target values.
A concrete correcting method is described with reference to
The luminance fluctuation (broken line) shown in
The logarithmic approximation formula of the Formula 1 is fitted to the luminance fluctuation shown in
When a unit of the time Ti in the Formula 1 is set to hour, and a unit of the prediction luminance Li is set to cd/m2, the coefficient ai roughly takes a value of −250 to 250, and the coefficient bi roughly takes a value of 250 to 2000. When the coefficient ai takes a positive value, as the drive time Ti becomes longer, the prediction luminance Li becomes longer (improved).
In the first embodiment, the coefficients ai and bi which are the luminance variation characteristic data are obtained by fitting the logarithmic approximation formula of the Formula 1 to the luminance fluctuation for the initial drive time of 0 to 100 hours. As shown in
In the example of
A correcting example at certain drive time t1 is described below with reference to
The correction value calculation unit 3 reads the coefficients ai and bi from the first storing unit 1, and reads the drive time Ti (=t1) from the second storing unit 2. The prediction luminance L1 to L3 of the display devices 1 to 3 at the drive time t1 is calculated according to the Formula 1. The correction target values are determined based on the calculated prediction luminance L1 to L3 of all the display devices. The correction values to be applied to the display devices 1 to 3 are obtained from the correction target values. In the example of
When such a correction is made, luminance unevenness among the display devices which is caused by a difference in the luminance variation characteristics can be reduced. The luminance unevenness can be evaluated by a value “σ (standard deviation) of the luminance/average value” in the case where signals with uniform gradation are input into all the display devices.
As the correction target value is set to be smaller, the luminance unevenness is reduced. As shown in
The luminance of all the display devices does not necessarily have to be uniform. The luminance unevenness may be not more than an acceptability limit of audiences of the image display apparatus. Concretely, when “σ of the luminance/average value” is about 1% to 3%, the luminance unevenness is not noticeable. Therefore, the correction target value may be set to a value of luminance unevenness which is not more than the acceptability limit of audience of the image display apparatus.
When the correction target value is set to a value larger than the minimum value of the prediction luminance of all the devices, image data after the correction possibly exceeds the maximum gradation. Therefore, a limiter is preferably provided and limits the value of the image data after the correction so that the value does not exceed the maximum gradation. In another manner, a gain is applied to the image data, so that the value of the image data after the correction may be adjusted so as not to exceed the maximum gradation. In yet another manner, it is preferable that a length of one horizontal scanning period of each scanning line is suitably changed according to a value range of the image data after the correction.
The image data are corrected by using the correction values obtained in the above correcting method, and display devices 4 are driven by the corrected image data. As a result, the luminance unevenness of the image display apparatus is reduced.
In the first embodiment, the luminance variation characteristic data is calculated by using the Formulas 1 to 3 based on measured results of the luminance for 100 hours at the initial driving stage (or physical quantity correlated with the luminance). That is to say, long-period luminance variation characteristics specific to the display devices can be estimated only by measuring the initial variation in the luminance with time, and the parameters to be stored in the first storing unit 1 can be determined.
In the first embodiment, 100 hour from the start of driving is set to predetermined measuring time, but the measuring period is not limited to this. This is because the tendency in the luminance variation with time varies according to types, shapes and materials of the display devices. For example, the variation characteristics of the current-voltage characteristics of an electron-emitting device with respect to time vary among FE devices, SCE devices and MIM devices, and vary even in the FE devices according to their shapes and materials. Therefore, it is desirable to suitably determine the measuring period according to the characteristics of display devices to be used so that the luminance variation characteristic data obtained from the luminance fluctuation at the measuring period will well predict the luminance fluctuation after the measuring period.
Modulation of a driving signal (modulation signal) to be given to the display devices is described with reference to
The modulating method includes a pulse width modulating system shown in
Reference numerals d1 to d5 in
In order to obtain the luminance variation characteristic data from the measured value, the image data d1 for measurement is firstly input. In order to display images suitable for measurement, the correction data d2, if necessary, is transmitted from the correction value calculation unit 103 to the multiplier 106. The multiplier 106 operates the data d1 and d2 so as to convert them into corrected image data d3 for displaying images suitable for the measurement. The data d3 is transmitted to the modulating circuit 108. When the multiplier 106 does not perform an operation on the data d1 and d2, the image data d1 is transmitted as the corrected image data d3 to the modulating circuit 108.
A synchronous signal d4 of the image data d1 is transmitted to the scanning circuit 109. The modulating circuit 108 and the scanning circuit 109 transmit signals to the display devices 104 via the column-direction wiring 110 and the row-direction wiring 111, so that the display devices 104 are driven. At this time, the display devices 104 may be driven one by one, or they may be driven simultaneously. As a result, an image for measuring luminance unevenness is displayed. The unevenness measuring unit 112 measures the luminance of the display devices 104 (or the physical quantity such as device currents correlated with the luminance). Data measured by the unevenness measuring unit 112 is transmitted to the operating unit 113. The operating unit 113 calculates luminance variation characteristic data (coefficients ai and bi) of each display device 104 based on the measured data.
When the luminance variation characteristic data is calculated from the database (not shown), the operating unit 113 calculates the coefficients ai and bi from the data read from the database, and allows the values to be stored in the first storing unit 101.
The correction for reducing the luminance unevenness is carried out in the following manner. The correction value calculation unit 103 calculates correction values corresponding to the display devices 104 based on the luminance variation characteristic data in the first storing unit 101 and the drive time data in the second storing unit 102. The calculated correction values are sent as the correction data d2 to the multiplier 106. The multiplier 106 generates the corrected image data d3 based on the image data d1 input into the correction circuit 100 and the corrected data d2. The modulating circuit 108 generates a driving signal (modulating signal) from the corrected image data d3 so as to output the driving signal to the column-direction wiring 110. As a result, the image whose luminance unevenness is reduced is displayed.
The drive time data stored in the second storing unit 102 is updated according to driving of the display devices. In the constitution of
The driving of the image display apparatus is carried out by a simple matrix system or an active matrix system. The simple matrix system is describe below with reference to
A certain row of the display panel 107 is selected for one horizontal scanning period of an image. A scanning signal is applied from the scanning circuit 109 to the row-direction wiring 111 on the selected row. As a result, the scanning signal is applied to the display device connected to the selected row.
On the other hand, the modulating circuit 108 simultaneously outputs information signals (modulating signals) for each of the display devices on the selected row for selected one horizontal scanning period. The information signals are supplied to the display devices via the column-direction wirings 110.
The display devices emit light only when the scanning signals and the information signals are applied simultaneously. As a result, the display devices on the selected rows emit light with desired luminance according to a pulse width or an amplitude of the information signals. The selected rows are sequentially switched during one vertical scanning period, so that an image can be displayed.
According to the above constitution, the luminance unevenness due to the variation in the luminance with time is reduced, so that images with high quality can be displayed for a long period. Further, since the luminance variation characteristic data specific to the devices are used so that the correction is carried out, even if devices with different characteristics are mixed, sufficient luminance unevenness reducing effect can be obtained.
A second embodiment is described with reference to the block diagram of
As shown in
The first storing unit 11 stores luminance variation characteristic data of the display devices 14 therein. In the second embodiment, not the variation in the luminance with time but the variation in device currents with time as the physical quantity correlated with the luminance is used as the luminance variation characteristic data. An emission current which is emitted from electron-emitting devices is defined as the device current here, but another electric current (for example, a driving current) correlated with the emission current may be defined as the device current.
A constitution of the second storing unit 12 is similar to that in the first embodiment (the second storing unit 2 in
The third storing unit 15 stores phosphor deterioration characteristic data (second characteristic data) representing deterioration characteristics of the phosphors with respect to drive time (hereinafter, simply “phosphor deterioration characteristic”) therein. The phosphor deterioration characteristics are expressed by Formula 4.
A denotes luminance efficiency of the phosphors, A0 denotes initial luminance efficiency of the phosphors, A/A0 denotes deterioration rate of the phosphors, Q[C/cm2] denotes a total electric charge injection amount, and Q50% [C/cm2] denotes a total electric charge injection amount where the luminance efficiency of the phosphors is deteriorated to 50%. The third storing unit 15 stores a value of Q50% which is measured in advance therein.
The correction value calculation unit 13 refers to the first storing unit 11 and the second storing unit 12 so as to obtain the variation amount in the device currents of the display devices with time (decrease amount or increase amount) based on the luminance variation characteristic data specific to the respective display devices and the drive time data. The correction value calculation unit 13 refers to the third storing unit 15 and the second storing unit 12 so as to obtain deterioration rate of each of the phosphors of the display devices based on the phosphor deterioration characteristic data and the drive time data. The correction value calculation unit 13 calculates the variation amount in the luminance of the display devices with time based on the variation amount in the device currents with time and the deterioration rate of the phosphors. The correction value calculation unit 13, then determines a correction target value based on the variation amount in the luminance of the entire display devices with time. The correction value calculation unit 13 obtains correction valued for correcting input signals (input image data) so that the display devices have luminance of the correction target values.
A correcting method in the second embodiment is described with reference to
A fluctuation (broken line) of the emission current in
Ii=ci×Log(Ti)+di (Formula 5)
Ii denotes a prediction device current, and Ti denotes accumulated drive time. The coefficients ci and di are parameters which do not depend on time. In the second embodiment, the coefficients ci and di are stored as the luminance variation characteristic data in the first storing unit 11. When a unit of the time Ti in the Formula 5 is hour (time) and a unit of the prediction device current Ii is μA, the coefficient ci roughly obtains a value of −15 to 15, and the coefficient di roughly obtains a value of 3 to 10.
Similarly to the first embodiment, also in the second embodiment, the coefficients ci and di are obtained by fitting the Formula 5 to the fluctuation in the device current up to 100 hours at the initial driving stage. As shown in
The fluctuation in the device current in
The drive time data is stored in the second storing unit 12 as shown in
A correction example is described. The correction value calculation unit 13 reads the coefficients ci and di from the first storing unit 11, and reads the drive time Ti from the second storing unit 12. The prediction device currents Ii of the display devices at the drive time Ti are calculated by the Formula 5. The correction value calculation unit 13 reads the deterioration characteristics Q50% of the phosphors with respective colors from the third storing unit 15, and converts the drive time Ti into the total electric charge injection amount Q, so as to calculate the luminance efficiency A of the phosphors according to the Formula 4. The value of the initial luminance efficiency A0 is known.
Prediction luminance L is obtained based on the prediction device currents I and the deterioration rate of the phosphors by Formula 6. In the Formula 6, A denotes the luminance efficiency of the phosphors, and γ is a gamma coefficient. The value of the gamma coefficient γ is known.
L=A×I
γ (Formula 6)
After the prediction luminance of all the display devices is calculated according to the Formula 6, correction values of the devices are calculated by the method similar to that in the first embodiment. The input image data is corrected by using the calculated correction values so that the luminance unevenness is reduced.
In the above description, the logarithmic approximation formula like the Formula 5 is used, but similarly to the first embodiment, the coefficients ci and di may be obtained by using an approximation formula such as a Formula 7 where an aging period is taken into consideration or a linear formula such as a Formula 8. T0 in the Formula 7 is offset time corresponding to the aging period.
Ii=ci×Log(Ti−T0)+di (Formula 7)
Ii=ci+di×Ti (Formula 8)
(Measuring Period of Variation with Time)
In the second embodiment, luminance variation characteristic data is calculated by using the Formula 5, 7 or 8 based on the measured results of the device currents for 100 hours at the initial driving stage. That is to say, long-term luminance variation characteristics specific to the devices can be estimated only by measuring the initial variation in the device currents with time, and the parameters to be stored in the first storing unit 11 can be determined. The measuring period is not limited to 100 hours, and it can be suitably determined according to the characteristics of the devices to be used.
As shown in
A modulating method is similar to that in the first embodiment.
The image display apparatus in
According to the above constitution, both the variation characteristic in the electron-emitting devices with time and the variation characteristic in the phosphors with time are taken into consideration, so that the correction of the luminance unevenness with high accuracy can be realized.
A third embodiment of the present invention is described.
The basic constitution in the third embodiment is similar to that in the second embodiment. In the second embodiment, the values representing the variation in the device currents specific to the display devices with time are stored in the first storing unit, but in the third embodiment, values representing the variation in the luminance specific to the display devices with time obtained from the measured values of the luminance are stored in the first storing unit.
Also in the third embodiment, the values representing the deterioration of the phosphors are stored in the third storing unit similarly to the second embodiment.
The luminance of the display devices depends on not only the levels of the device currents but also the luminance efficiency of the phosphors. Considering this, when the values obtained from the measured values of the luminance are used as the parameters (luminance variation characteristic data) to be stored in the first storing unit, one might think that the fluctuation in the luminance due to the deterioration of the phosphors is corrected excessively (doubly). However, as shown in
The third embodiment can be applied suitably and particularly to a case where the measurement of the luminance is easier than the measurement of the device currents, or a case where measurement accuracy of the luminance is better than that of the device currents, or a case where the measurement time of the luminance is shorter than that of the device currents.
A basic constitution of the image display apparatus of Examples is described below.
An electron source in the Examples has a plurality of electron-emitting devices, and a plurality of row-direction wirings and a plurality of column-direction wirings, which connect the electron-emitting devices into a matrix pattern, on a substrate.
A surface-conduction electron-emitting device (“SCE device”) is an example of the electron-emitting devices composing the electron source, and its constitutional example is schematically shown in
A method for manufacturing an SCE device shown in
One example of the image display apparatus using the electron source where the electron-emitting devices shown in
In
In order to improve the strength against atmospheric pressure, a supporter, not shown, which is called a spacer is preferably provided between the face plate 1418 and the electron source substrate 1411.
Further, in order to maintain the degree of vacuum in the sealed envelope, a getter process is preferably executed before and the after the sealing.
An Example 1 of the image display apparatus is described with reference to
At the manufacturing process for the image display apparatus, the luminance of the respective display devices is measured. The display devices are driven by driving signals corresponding to the maximum gradation, and a fluctuation in the luminance for 100 hours is recorded. CCD cameras are used for measuring the luminance. Concretely, all the display devices are allowed to emit light by the same image data, and the entire display surface is divided to be measured by a plurality of CCD cameras. One example of the measured luminance is shown in
The approximation curve in the Formula 1 was fitted to the luminance measured results of the display devices, so that the coefficients ai and bi of each display device were obtained. The coefficients ai and bi were stored in the first storing unit 101.
The second storing unit 102 stores the drive time data of the display devices therein (see
A luminance unevenness evaluating method for checking an effect due to the carrying-out of the present invention is described below.
A test image signal is used for evaluating luminance unevenness. Pulse width modulation was used as the modulating method. The gradation at each time was set to random values according to normal distribution having an average of 50% of the maximum gradation and a standard deviation of 15%. A driving voltage was set to 16V, a driving voltage pulse width at the time of maximum gradation was set to 5 μsec, and the devices were driven at 60 Hz.
The values in the first storing unit 101 and the second storing unit 102 were used, so that the variation amount in the luminance with time (prediction luminance Li) was calculated by the correction value calculation unit 103. Correction target values were determined based on the prediction luminance of all the devices, and the correction values of the devices were obtained from the correction target values. And, the test image signals input into the display devices were corrected.
A correction example for 100 hours after the starting of the luminance unevenness evaluation is concretely described. The corrected results of the nine devices are described for simple description.
In the Example 1, the correction was carried out by using the luminance variation characteristics specific to the display devices (coefficients ai and bi) On the contrary, in the comparative example, the correction is carried out by using coefficients a0 and b0 which are uniform in all the display devices. The coefficients a0 and b0 in the comparative example were obtained by fitting the approximation curve in the Formula 1 to the measured result of the luminance of a certain representative device.
As shown in
Test image signals were used for evaluating the luminance unevenness similarly to the Example 1.
The prediction luminance was calculated by using the values shown in
A broken line of
In the Example 2, in order to reduce a storage region of the second storing unit, a central value of the accumulated drive time (see
Test image signals similarly to the Example 1 were used for evaluating the luminance unevenness.
An Example 3 of the image display apparatus is described with reference to
A fluctuation in the luminance for 100 hours at the initial driving state was measured by the method similar to that in the Example 1. The measured luminance was converted into the device currents by the Formula 6. At this time, 0.7 was used as γ in the Formula 6, an initial values of the luminance efficiency of the phosphors were used as A.
The approximation curve in the Formula 5 was fitted to the fluctuation in the device currents of the display devices, so that the coefficients ci and di of the display devices were obtained. The coefficients ci and di were stored in the first storing unit 201. The range of the coefficient ci became −2 to −4, and the range of the coefficient di became 4 to 6. The drive time data of the display devices (corresponding values assuming that devices were driven at maximum gradation) is stored in the second storing unit 202 (see
Test image signals similarly to the Example 1 were used for evaluating the luminance unevenness.
The correction value calculation unit 203 obtained variation amount in the device currents with time (prediction device currents Ii) based on the value in the first storing unit 201 and the value in the second storing unit 202. The deterioration rates of the phosphors were obtained by using the values in the second storing unit 202 and the values in the third storing unit 205. The variation amount in the luminance of the display devices with time were calculated based on the variation amount in the device currents with time and the deterioration rates of the phosphors. Correction target values were determined based on the variation amount in the luminance of the devices with time, and the correction values of the devices were obtained from the correction target values. And, the test image signals input into the devices, respectively, were corrected using the correction values.
The luminance unevenness was evaluated similarly to the Example 1.
In the Example 4, in order to reduce the storage region in the second storing unit, a central value of the accumulated drive time (see
Test image signals similar to that in the Example 1 were used for evaluating the luminance unevenness.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2007-168486, filed Jun. 27, 2007 which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2007-168486 | Jun 2007 | JP | national |