JP2012058516A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that white balance is deviated from initial setting when a display device is continuously used.SOLUTION: The display device includes a display section including light emission elements emitting light in mutually different colors, a luminance control unit that image signals are input, multiplies a gray scale level of each color in the image signals by a coefficient irrespective of colors and outputs the result to the display unit, and a statistical processing unit that statistically processes an aggregate of the image signals constituting the image displayed by the display unit, determines a color representing the image, and outputs it to the luminance control unit. The faster the luminance degrading rate, the smaller the coefficients are set by the luminance control unit according to the color representing the image.

Description

  The present invention relates to a display device, and particularly relates to a display device using a self-luminous element such as an organic EL element.

  In recent years, self-luminous display devices using self-luminous elements such as organic electroluminescence elements (hereinafter referred to as “organic EL elements”) and plasma elements have been widely used. In order to perform color display, a pixel is formed by combining a plurality of self-light emitting elements that emit light of different colors. Generally, a red light emitting element, a green light emitting element, and a blue light emitting element are used as one pixel.

  However, when self-luminous elements emit light continuously for a long time, there is a problem that the luminance decreases due to changes in the elements or deterioration of phosphors. Self-luminous elements that emit light of different colors are made of different light-emitting materials and have a layer structure that matches each emission wavelength, and therefore the deterioration speed is also different. For this reason, if the display device is continuously used for a long time, not only the luminance is lowered as a whole, but also the white balance is changed from the initial setting due to the difference in the deterioration characteristics of the respective colors.

  FIG. 15 is an example of luminance reduction of a red (R) light emitting element, a green (G) light emitting element, and a blue (B) light emitting element. It shows a change in relative luminance with respect to the initial luminance with respect to the elapsed time from the start of light emission. In this example, the deterioration of the blue (B) light emitting element progresses the fastest. Therefore, when white is continuously displayed, the white balance is shifted in the red direction. A decrease in relative luminance per unit time is called a deterioration rate. In FIG. 15, the luminance decreases as an exponential function of time, the degradation rate of each color is substantially constant, the degradation rate of B is the fastest, and the degradation rate of R is the slowest. G is in between.

  Patent Document 1 discloses an organic EL display device in which the light emitting area of each light emitting element is made different to suppress deterioration. By changing the light emitting area, the amount of current (current density) per light emitting area required to obtain the same luminance is changed. The larger the amount of current per light emitting area, the faster the brightness decreases, so by adjusting the respective light emitting areas so that the light emitting elements that are slow to deteriorate are larger than the light emitting elements that are rapidly deteriorated. The deterioration rate of each light emitting element can be made close, and the change in white balance described above is suppressed.

  Patent Document 2 proposes a plasma display device that suppresses deterioration by reducing the display luminance corresponding to each color of the phosphor at different ratios. The speed of deterioration of the phosphor depends on the intensity of the emitted light, and the deterioration can be suppressed by reducing the intensity. Therefore, when the average luminance level of the entire screen or each small area is detected and it is determined that the same image is displayed for a long time, the luminance of each color is decreased at a different ratio. At that time, the luminance reduction rate is set to be larger for the color corresponding to the phosphor that is rapidly deteriorated. The progress of the deterioration of the phosphor that is rapidly deteriorated can be suppressed, and as a result, the amount of deterioration of each color can be made comparable. By detecting the luminance level for each color, the luminance reduction rate can be set more accurately.

JP 2001-290441 A JP 2001-014914 A

  In Patent Document 1, since the ratio of deterioration rates of the light emitting elements of the respective colors is not changed, it is replaced with the aperture ratio. Therefore, when the deterioration characteristics change in a complicated manner with time, it is appropriate for a long period. The effect cannot be obtained.

  In the method of Patent Document 2, the luminance reduction rate of the display image is set to be larger for the color corresponding to the phosphor that is rapidly deteriorated. For this reason, although the progress of the deterioration is delayed, the brightness is lowered at a different reduction rate, so that the white balance is lost and the hue changes.

  An object of the present invention is to provide a display device having a long lifetime by preventing deterioration of a light emitting element without changing the white balance from the initial setting.

The present invention
A display unit including light emitting elements that emit light of different colors;
A luminance control unit that receives an image signal, multiplies the gradation level of each color indicated by the image signal by a coefficient independent of color, and outputs the result to the display unit; and
A statistical processing unit that statistically processes the set of image signals constituting the image displayed on the display unit, determines a color representative of the image, and outputs the color to the luminance control unit;
A display device comprising:
The luminance control unit is configured to set the coefficient in a descending order of the luminance deterioration rate when the light emitting element continuously emits light according to a color representing the image.

  According to the present invention, even when the display device is continuously used for a long time, the deterioration between the light emitting elements having different colors can be made equal to each other, and the change in hue can be suppressed. Moreover, since the white balance of the display image does not change due to the brightness adjustment, the user does not feel uncomfortable.

It is a schematic diagram of the display apparatus of this invention. It is a block diagram which shows the structure of the display apparatus of this invention. It is a figure which shows the time change of the gain adjusted by a brightness | luminance control part. It is a block diagram which shows the structure of a statistics process part. It is an example of a histogram. It is a block diagram which shows the structure of a brightness | luminance control part. It is a block diagram which shows the structure of another brightness | luminance control part. It is a flowchart which shows the procedure which determines the representative color of an image. It is a figure which shows the time change of another gain. It is a modification of the time change of a gain. It is another modification of the time change of a gain. It is a figure which shows the display apparatus of this invention attached to the digital camera. It is a figure which shows the time-dependent change of a brightness | luminance. It is a figure which shows the time change of the gain of an Example. It is a figure which illustrates the time-dependent change of a brightness | luminance. It is a figure which illustrates another time-dependent change of a brightness | luminance. Furthermore, it is a figure which illustrates the time-dependent change of a brightness | luminance.

  FIG. 1A is a diagram showing an embodiment of the display device 11 of the present invention. In the display unit 12, pixels formed of light emitting elements 13 of red (R), green (G), and blue (B) shown in FIG. 1B are arranged in a matrix, and an image is displayed. In general, a pixel includes light emitting elements of different colors, and may include colors other than R, G, and B. Examples of the light emitting element 13 used in the self-luminous display device 11 include an organic EL element and a plasma display element that excites a phosphor with plasma.

  The display device 11 may be a display device that operates alone, such as a television receiver that receives and displays broadcast waves, or may be a display device that is incorporated inside another device such as a camera.

  FIG. 2 is a block diagram for explaining the configuration of the display device 11. The display device 11 of the present invention includes a statistical processing unit 21 and a luminance control unit 24 in addition to the display unit 12 described above.

  The image signal 22 input to the statistical processing unit 21 and the luminance control unit 24 is a digital or analog signal that includes gradation data corresponding to each light emitting element of the display unit 12 in time series. In the case of a digital signal, it consists of 2 bits for identifying the color and 8 bits representing the gradation level, and after being classified by color, it becomes an 8-bit gradation data signal. In the case of an analog signal, the image signal 22 is a RGB parallel voltage signal, and the amplitude of the voltage is gradation data.

  The luminance control unit 24 receives the image signal 22 and the determination result 23 of the statistical processing unit 21 and performs adjustment to apply a certain coefficient (also referred to as gain) to the image signal 22. This coefficient, that is, the gain is a positive number of 1 or less, and is a common value that does not depend on the color of the image signal. By multiplying this by the gradation level indicated by the image signal 22, a signal 25 in which the gradation level is reduced to the low luminance side at a constant rate is generated and output to the display unit 12. In response to this, in the display unit 12, the brightness of the displayed image as a whole decreases at a reduction rate equal to the above gain.

  An image of one frame displayed on the display unit 12 is composed of the entire image signal transmitted in time series during one frame period. The statistical processing unit 21 determines how many representative colors of one image are. In the present embodiment, among the light emitting elements of different colors, the color of the light emitting element that emits light with the highest brightness when viewed as an entire image is a color that represents the image (hereinafter referred to as a representative color). As determined. When the image displayed on the display unit 12 is viewed, the most dominant color that characterizes the image is the representative color of the image.

  The statistical processing unit 21 statistically processes the gradation data included in the image signal using a set of all image signals constituting the image of the display unit 12 as a population, and a statistical amount such as an average value or an intermediate value of the gradation level Is calculated. The statistic for different colors is compared to determine the brightest color and determine the representative color of the image. Further, the representative color may be determined by comparing two or more statistics as required. Since the representative color is determined statistically, the color that characterizes the entire image is determined as the representative color regardless of the brightness of the individual light emitting elements.

  In the case where the color representing the image is a color with a rapid luminance deterioration, the deterioration proceeds rapidly if the same image continues to be displayed as it is. Therefore, the brightness of the display unit on which the image is displayed is quickly lowered to slow down the progress of deterioration. When the representative color of the image is a color other than the color whose luminance is deteriorated rapidly, the deterioration does not proceed so much, so that the luminance of the displayed image is maintained as it is or only the luminance is lowered slightly.

  In this way, by determining the representative color of the image and reducing the brightness of the image displayed according to the color, the progress of the fast-degrading color is slowed and the progress of the degradation of all the colors is made comparable. Can be aligned. As a result, it is possible to prevent the white balance from deviating rapidly due to the color having a high deterioration rate. Further, since the brightness is lowered uniformly for each color regardless of the color, the white color is not reddish and the hue of the natural image does not change.

  The brightness adjustment is performed by appropriately selecting a coefficient to be multiplied by the gradation data according to the display image. As many coefficients as the number of colors are prepared in the luminance control unit 24, and the coefficients have a size corresponding to the deterioration rate of each color. That is, the coefficient is set smaller as the color has a faster deterioration rate. In response to the determination of the representative color of the image, the luminance control unit selects a coefficient of that color from the prepared colors, and uses this as a coefficient to be multiplied with the gradation data.

  FIG. 3 is a diagram illustrating how the brightness of the displayed image is adjusted. The coefficient multiplied by the gradation data, that is, the gain gradually decreases with the display time.

  The rate of decrease per time varies depending on the representative color of the image, and the rate of decrease is greater for colors with a higher deterioration rate. When the representative color coincides with the color with the fastest deterioration, the luminance is greatly reduced as indicated by the gain 51. When the representative color of the displayed image is the second most rapidly deteriorated color, as shown by the gain 52, the color is lowered more slowly than that. When the representative color of the displayed image is the color with the slowest deterioration, the color is lowered most slowly as indicated by the gain 53. The magnitude of the gain reduction rate is determined by the deterioration rate.

  As shown in FIG. 3, the gain is set to 1 when image display is started, and is decreased according to time as long as the same image display continues. For this reason, it is preferable that the luminance control unit 24 includes a counter that counts the time from the start of image display, and further stores a gain table for obtaining a gain from the output of the counter and the output of the statistical processing unit. . When the image is switched, the gain is reset to 1.

  In FIG. 3, the gain is decreased linearly with time, but it may be changed with time in a stepwise manner as shown in FIG. Alternatively, as shown in FIG. 11, the luminance adjustment start timing may be made different. When the gain is set when the determined display time comes, and thereafter the gain is maintained until it is set next, it becomes stepwise as shown in FIG. Since the deterioration hardly progresses when the luminance is low, the gain setting can be performed only once and the gain can be maintained thereafter. However, it is preferable to reduce the width of the reduction in one step so that the reduction in luminance is not recognized by the user and uncomfortable.

(Statistics processing department)
FIG. 4 is a diagram showing the inside of the statistical processing unit 21.
The statistical processing unit 21 includes a histogram creation unit 31 and a histogram comparison unit 33. The histogram creation unit 31 decomposes an input image signal into color components and creates a histogram (shown by R, G, and B in the figure) of gradation data included in one frame of the image signal for each color. . Also, a combined histogram (indicated by RGB in the figure) is created by adding together the RGB histograms.

  The histogram is a distribution diagram in which the number of appearances of each gradation level is counted using the gradation data of all the pixels of the display unit 12 constituting one image as a population. FIG. 5 is a histogram created for one color of an image when the image signal is 256 gradation data. The horizontal axis represents gradation levels from 0 to 255, and the vertical axis represents the number of appearances of each gradation level.

  The histogram comparison unit 33 receives the created histogram information 32, extracts a statistic from the histogram, and compares the statistic of different colors to determine a color representing the image. Here, an average value or an intermediate value is considered as a statistic. The average value is the value of the gradation level that is averaged by weighting the number of appearances, and the intermediate value is the gradation level of the image signal that is in the middle when the image signals are arranged in order from the highest gradation level. It is. The average value of the histogram shown in FIG.

(Brightness control unit)
FIG. 6 is a block diagram showing an internal configuration of the luminance control unit 24. The luminance control unit 24 includes at least a gain multiplication unit 41, a gain storage unit 42, and a display time counter unit 43.

  The gain storage unit 42 holds a gain table (hereinafter referred to as a table) that records gains for each display time when the representative color is R, G, or B. The relationship between the display time and the gain held in the table matches the time change of the gain shown in FIG. That is, the gain values of R, G, and B described in the table are in the order of deterioration speed when viewed in one display time, and the gain value is smaller for a color with a faster deterioration speed. Gain values with the same deterioration rate are equal.

  This table is recorded in the ROM before product shipment. Instead of the table, a gain calculation circuit that calculates and outputs a gain when a color and a display time are input may be provided. When the gain reduction rate is constant as shown in FIG. 3, the calculation is simpler.

  The gain multiplication unit 41 sends the result 23 of determining the representative color of the input image to the gain storage unit 42. The display time counter unit 43 starts counting from the start of image display, counts the time during which the same display continues, and sends it to the gain storage unit 42. The gain storage unit 42 reads the gain value corresponding to the representative color indicated by the sent determination result 23 in the display time from the table, and sends it back to the gain multiplication unit 41. The gain multiplication unit 41 multiplies the returned value by the image signal 22 and transmits the resulting signal 25 to the display unit 12.

  The display time counter unit 43 may count the time after an external reset signal (not shown) is input. When the display device 11 is incorporated in a digital camera, a signal obtained by pressing the shutter button may be input to the display time counter unit 43 and the time from that time may be counted. When the display device is a television receiver, scene switching may be detected from the image signal 22 and the time from that point may be counted.

  The deterioration characteristics are measured in advance as shown in FIG. 15, and the speed of deterioration of each color is known.

  Although the deterioration rate is constant in FIG. 15, the deterioration rate may change depending on the light emitting element, for example, the progress of deterioration becomes slow after a certain time. FIG. 16 shows the deterioration characteristics of the organic EL element in which the initial deterioration rate is in the order of R> B> G, but after 200 hours, the deterioration rate of R decreases. Thus, when the deterioration rate changes as the usage time of the display device elapses, the accumulated usage time is measured, and the relationship between the degradation rate stored in the display device and the accumulated usage time is used occasionally. It is preferable to cope with the change in the deterioration rate.

  FIG. 7 is a block diagram showing a configuration of the luminance control unit 24 different from that in FIG. The same parts as those in FIG.

  The brightness control unit 24 of FIG. 7 is different from that of FIG. 6 in that the brightness control unit 24 includes an integrated usage time counter 44 that measures an integrated value of usage time since the display device is shipped, that is, integrated usage time. When the accumulated usage time data is sent from the accumulated usage time counter 44 to the gain storage unit 42, a table corresponding to the data is sent to the gain multiplication unit. As shown in FIG. 17, even when the deterioration characteristics of each light emitting element greatly change from the initial stage depending on the display time of integration, the table is updated to another table when the integration display time reaches a certain time t. By doing so, the effect is obtained continuously.

  The luminance control unit 24 and the statistical processing unit 21 may be inside the display device 11 as shown in FIG. 2, but when the display device 11 is incorporated in a digital camera or the like, the luminance control unit 24 or the statistical processing is performed. The unit 21 may be installed outside the display device 11 as part of the signal processing circuit of the digital camera. Alternatively, only the histogram creation unit 31 may be installed outside the display device 11, and the histogram comparison unit 33 may be in the display device 11.

(Representative color judgment procedure)
Hereinafter, a procedure for determining a representative color of an image will be described with an example.

[Example 1]
FIG. 8A is a flowchart showing a procedure for determining image features using intermediate values, and FIG. 8B is a flowchart showing a procedure for determining image features using average values. In FIG. 8A, the intermediate values of the red, green, and blue histograms are R, G, and B, and in FIG. 8B, the average values are r, g, and b. The procedure for determination using the intermediate value will be described below, but the same applies to the case where the average value is used.

First, it is determined whether R> G. If it is Y (Yes), it is next determined whether or not RG> X, and if it is N (No), it is next determined whether or not GR> X. X is a number representing the degree of discreteness of the two values, and in this embodiment, X = 30. If this determination is N (No), a result “R is equivalent to G: R to G” is output, and if Y (Yes), “R is greater than G: R> G”. Alternatively, the result “R is less than G: R <G” is output.
R and B, and G and B are compared in the same procedure.

As a result, the luminance magnitude relationship is (1) R>G> B,
(2) R>B> G,
(3) R> G to B
(4) G>R> B
(5) G>B> R
(6) G> R to B
(7) B>R> G
(8) B>G> R
(9) B> R to G
(10) R to G> B
(11) G-B> R
(12) R to B> G
(13) R to G to B
It will be one of 13 ways. Note that the symbol “˜” indicates that the luminance is approximately the same.

  In the case of (1)-(3), R is determined as the representative color, in the case of (4)-(6), G is determined as the representative color, and in the case of (7)-(9), B is the representative color. It is determined.

  In the case of (10)-(13), there are a plurality of representative color candidates and determination cannot be made. In this case, however, both colors are sent to the luminance control unit 24 as they are, assuming that both colors are representative colors. When the determination result that there are a plurality of representative colors is obtained as in (10) to (13), the luminance control unit 24 that receives the determination results from the deterioration rate data of the three colors stored in advance. The faster color (the fastest color when there are three or more) is selected, and the corresponding gain is selected assuming that the color is the representative color.

  As described above, since the color characterizing the image is determined and the luminance of the three colors is uniformly reduced based on the determined color, it is possible to effectively suppress the progress of deterioration without destroying the white balance.

[Example 2]
Looking at the degradation characteristics of FIG. 15, the degradation rate of R is far apart and slow, and the degradation rates of G and B are considerably faster than R. The deterioration rates of G and B are close to each other.

  In such a case, only the determination of whether or not the representative color of the image is R is performed according to the procedure of FIG. When Y (Yes), the representative color is R (determination result A). At this time, since the image degradation is expected to be small, the gain 52 is gradually lowered.

  In the case of N (No), the representative color is G or B, or a plurality of colors (determination result B). Even in the case of a plurality of colors, since at least one of G and B is included therein, it is expected that the image is rapidly deteriorated. Therefore, the gain 51 is quickly reduced. Since the degradation rates of R and G are almost equal, luminance adjustment using the same gain is sufficient regardless of which is the representative color of the image. Therefore, only two gain adjustments are possible including the case of Yes. Determination of which of G and B is the representative color can also be omitted.

[Example 3]
FIG. 9 is a diagram showing a state of brightness adjustment of the organic EL display device having the deterioration characteristics shown in FIG. 17, which is different from FIGS. 15 and 16. This deterioration characteristic is fast because the deterioration rate of B is far away, and the deterioration rates of R and G are considerably slower than B. The deterioration rates of R and G are about the same.

  In such a case, only the determination of whether or not the representative color of the image is B is performed in the same procedure as in FIG. 8A, and when it is Y (Yes), the gain 51 is suddenly decreased and the gain 51 is set. Decrease promptly. When it is N (No), the gain reduction is moderated and the gain 52 is not lowered much. In the latter case, since the degradation rates of R and G are almost equal, luminance adjustment using the same gain is sufficient regardless of which is the representative color of the image. Therefore, only two types of gain adjustment are required. The determination of which of R and G is the representative color can also be omitted.

[Example 4]
When the histogram of any color has a shape distributed almost symmetrically around one center, the average value and the intermediate value are approximately the same. In that case, it does not change even if it determines using either an intermediate value or an average value.

  On the other hand, when the histogram has two peaks, the average value is between the two peaks, but the average value is far from the average value, such that the intermediate value is in one of the peaks. May be a value. When there are many such images, it is preferable to determine using both the intermediate value and the average value. That is, the comparison of FIG. 8A and FIG. 8B is performed in parallel and adopted when both give the same result.

  When R> G in the intermediate value comparison but r <g in the average value comparison, both colors are determined as characteristic colors, and the result is sent to the luminance control unit 24 as a result. Send. In the luminance control unit, the larger deterioration rate is determined as the representative color, and a gain corresponding to the representative color is selected.

  The determination procedure described above may be performed by selecting a representative value and a determination condition that are expected to have the greatest effect each time in comparison with the deterioration characteristics of the display device. In a display device in which an image to be displayed is assumed in advance, the determination procedure can be determined in consideration of that.

  When an input image signal of R, G, B is generally high and an image close to full white lighting is displayed, the user can easily recognize that the gain is reduced. In order to prevent this, a threshold value Z for determining close to white display is set for all of Examples 1 to 4, and whether or not R> Z and G> Z and B> Z is satisfied in the histogram comparison unit 33. This determination may be performed with priority. The display image determined as Y (Yes) in this determination has a gain magnitude (close to 1) larger than that of the display image determined as N (No). The gain at that time is less likely to be perceived by the user by setting the luminance reduction rate to 3% or less per step, and is hardly perceived by setting the gain to 1.5% or less per step.

  When the same pattern is always displayed in the same place as a display image, such as a telop or broadcast station mark during TV broadcasting, or various information displayed on the monitor of a digital camera, the deterioration of a specific light emitting element will progress There is. Considering this point, the luminance control unit 24 may vary the gain for the input signal for each location. This will be described below.

  FIG. 12 shows a display device 11 attached to a digital camera. The information 103 such as the shooting date and time and the shooting conditions displayed semi-fixedly on the monitor screen which is the display unit 12 is often arranged in the peripheral region 102 of the display unit 12, so that the light emitting elements in the peripheral region 102 are deteriorated. Is particularly easy to progress. In such a case, the magnitude of the gain / gain of the gradation data of the image signal 22 corresponding to the light emitting elements in the peripheral region 102 is made smaller than that in the central region 101. As a result, the luminance of the peripheral region 102 is significantly reduced from the central region 101 as the display time elapses, and the difference in the in-plane deterioration speed of the display region can be suppressed.

Depending on the position of the fixed display information, on the contrary, the gain to be multiplied in the peripheral area 102 may be larger than that in the central area 101, and the location is not necessarily classified as the central area and the peripheral area. The classification is not limited to the upper half, the lower half, and the left and right divisions.
Hereinafter, specific examples of the organic EL display device of the present invention will be described.

  This example is an organic EL display device having the configuration of FIG. The statistical processing unit 21 has the configuration shown in FIG. 4 and determines the representative color using the determination procedure of Example 1. The luminance control unit 24 has a configuration shown in FIG. 7 and stores deterioration rate data up to 1500 hours and a gain table.

The display device 11 includes organic EL elements of red, green, and blue colors, and the color is red in the CIExy coordinates: (x, y) = (0.67, 0.33),
Green: (x, y) = (0.25, 0.69),
Blue: (x, y) = (0.14, 0.08)
The luminous efficiency with respect to the current is red: 18 cd / A,
Green: 21 cd / A,
Blue: 2.9cd / A
It is.

White white in CIExy coordinates: (x, y) = ( 0.313,0.329), when the luminance 500 cd / ^{m 2,} a maximum luminance of each color, red 132cd / ^{m 2,} green 315cd / ^{m 2} , Blue is 53 cd / m ² , and the ratio of currents flowing through the colors is red: green: blue≈1: 2: 2.5.

In addition, as an example of the display image, an image largely classified into a red-based image, a green-based image, a blue-based image, and a white-based image is displayed in this order for 30 seconds, and is repeated for a total of 1500 hours. Assumed. On average, the deterioration characteristics are the same as when the entire surface is lit white, displayed with chromaticity (x, y) = (0.313, 0.329), and luminance of 500 cd / m ² .

  FIG. 13 shows the luminance deterioration characteristics when each image is kept lit for 30 seconds without changing the gain.

  At the time when 200 hours passed, the red luminance decreased by 0.5%, the green luminance decreased by 2.5%, and the blue luminance decreased by 3%. The change in white balance is Δxy = 0.0002. When 1500 hours passed, the luminance was reduced by 1% for red, 12% for green, and 7% for blue. The change in white balance is Δxy = 0.0089.

  As a result of determining the display image by the histogram comparison unit, the representative color of each image is red (determination result A) for a red image, green (determination result B) for a green image, and blue (determination result) for a blue image. As a result B), the white image was white (determination result C) because of the determination to determine white.

  Based on this, the gain was adjusted as shown in FIG. That is, in the case of the determination result A, the representative color is red and its deterioration rate is small, so that the decrease in gain is moderated. In the case of the determination result B, the representative color is green or blue, and both of them have a fast deterioration rate, so that the gain is quickly reduced. When the determination result is C, the luminance decrease is most gradual.

  When such adjustment was performed, after 200 hours, the red luminance decreased by 0.9%, the green luminance decreased by 1.9%, and the blue luminance decreased by 2.2%. The change in white balance is Δxy = 0.0009.

  After 1500 hours, the luminance decreased by 2.5% for red, 9.2% for green, and 5.9% for blue. The change in white balance is Δxy = 0.0005.

  From the above, at both time points of 200 hours and 1500 hours, the amount of change in white balance is smaller than when luminance adjustment is not performed. That is, the white balance shift is suppressed by adjusting the luminance.

DESCRIPTION OF SYMBOLS 11 Display apparatus 12 Display part 13 Light emitting element 21 Statistical processing part 22 Image signal 23 Determination result 24 Luminance control part 41 Gain multiplication part 42 Gain memory | storage part 43 Display time counter 44 Integrated use time counter 101 Center area | region 102 of a display part Surrounding area 103 Date display

Claims (6)

A display unit including light emitting elements that emit light of different colors;
A luminance control unit that receives an image signal, multiplies the gradation level of each color indicated by the image signal by a coefficient independent of color, and outputs the result to the display unit; and
A statistical processing unit that statistically processes the set of image signals constituting the image displayed on the display unit, determines a color representative of the image, and outputs the color to the luminance control unit;
A display device comprising:
The luminance control unit is configured to set the coefficient in a descending order of the luminance deterioration rate when the light emitting element continuously emits light according to a color representing the image.   The statistical processing unit calculates an intermediate value or average value of gradation levels of the image signal for each color, compares the intermediate value or average value of different colors, and determines the color having the highest intermediate value or average value. The display device according to claim 1, wherein the display device has a color representative of the image.   The brightness control unit includes a display time counter that measures the display time of the image, and the coefficient is set to decrease as the display time output from the display time counter increases. Item 3. The display device according to Item 1 or 2.   The display device according to claim 3, wherein the luminance control unit includes a table that associates outputs of the statistical processing unit and the display time counter with the coefficients.   The luminance control unit includes an integrated usage time counter that measures an integrated value of time using the display unit, and updates the table when an output of the integrated usage time counter reaches a predetermined value. The display device according to claim 4.   The luminance control unit sets the coefficient that multiplies the gradation level of the image signal corresponding to the peripheral region of the display unit to be smaller than the coefficient that multiplies the gradation level of the image signal corresponding to the center region of the display unit. The display device according to claim 1, wherein the display device is a display device.

Images