JP4415156B2 - Brightness correction method and display system - Google Patents

Description

  The present invention corrects each pixel value of a display image using a plurality of specific pixel values and correction values corresponding to a plurality of specific pixel positions, and reduces luminance unevenness when the display image is displayed on the display panel. The present invention relates to a correction method and a display system.

  In a display device having a display panel such as an LCD (Liquid Crystal Display), a CRT (Cathode Ray Tube), or a PDP (Plasma Display Panel), or a display device that projects a display image such as a projector, an image display There is a problem that uneven brightness occurs in the region. For example, in the case of an LCD, the luminance unevenness occurs due to variations in the thickness of the liquid crystal layer, variations in the operating characteristics of the liquid crystal driving transistor, variations in the light emission distribution of the backlight, and the like.

  FIGS. 10A and 10B and FIGS. 11A and 11B are conceptual diagrams showing examples of image display of the display device. The display device 20 includes a display panel 22 such as an LCD, and an image processing unit 62 that corrects an image displayed on the display panel 22. A computer 60 is connected to the display device 20. In the example of FIG. 10A, the display image received from the computer 60 by the image processing unit 62 is displayed on the display panel 22, and the display image is divided into 4 blocks in the horizontal direction and 3 blocks in the vertical direction. The brightness of the upper left and lower right blocks is lower than that of the other blocks, resulting in uneven brightness.

  As a method of reducing the luminance unevenness, there is a method of correcting the luminance of a region where the luminance unevenness has occurred in the image processing unit 62 (see, for example, Patent Document 1). In the case of the example of FIG. 10A, as shown in FIG. 10B, the image processing unit 62 corrects the gradation (pixel value) of the upper left and lower right portions of the display image to increase the luminance. Can be considered. The brightness increase in the image processing unit 62 and the brightness decrease in the display panel 22 for the upper left and lower right portions are offset, and brightness unevenness is reduced.

In the example of FIG. 10B, correction is performed so as to increase the luminance in the region where the luminance decreases. However, in many display panels, it is easier to decrease the luminance than to increase the luminance. In many cases, the correction is made so that the value falls. For example, as shown in FIG. 11A, when the brightness of the upper left and lower right portions of the image display area of the display panel 22 is lower than the other portions, as shown in FIG. Reduce the brightness by correcting the gradation except for the lower right. Luminance is balanced and luminance unevenness is reduced by the luminance reduction in the image correction unit 62 for the portions other than the upper left and lower right, and the upper left and lower right luminance reduction in the display panel 22.
JP-A-8-223519

  10 and 11, the display image is divided into 4 × 3 blocks. However, in order to reduce the luminance unevenness more finely, it is necessary to divide the display image into smaller blocks. However, when the block is divided finely, there arises a problem that the circuit scale of the image processing unit 62 increases. Also, the luminance unevenness distribution differs for each input gradation, and in order to reduce the brightness unevenness more precisely, the brightness unevenness distribution at multiple input gradations is measured and corrected according to the input gradation. Need to do. However, when the correction according to the input gradation is performed, there is a problem that the circuit scale of the image processing unit 62 increases.

  On the other hand, the display panel of the display device has gradation characteristics called gamma characteristics. The gradation characteristics indicate the relationship between the input signal to the display panel and the actual brightness on the display panel (but not the proportional relationship). For example, the brightness on the display panel is input to the liquid crystal panel. Some are proportional to the 2.2 power of the signal. For this reason, when correction is performed without considering the gradation characteristics of the display panel, there is a problem in that the correction level becomes excessive or insufficient, and the uneven luminance portion becomes extremely bright or dark.

  The present invention has been made in view of such circumstances, and by calculating a correction value based on the target luminance, the measured luminance stored in advance and the gradation characteristics of the display panel, luminance unevenness can be reduced without excess or deficiency. An object of the present invention is to provide a luminance correction method and a display system that can be eliminated.

  Further, the present invention determines a target luminance for any of a plurality of specific pixel values, and calculates a target luminance for other specific pixel values based on the determined target luminance and the gradation characteristics of the display panel. Another object of the present invention is to provide a brightness correction method and a display system that eliminate the need to determine target brightness for all specific pixel values.

  Further, the present invention is configured to perform interpolation of the correction value corresponding to the pixel position of the correction target pixel using the correction value corresponding to the specific pixel value of the peripheral position of the pixel position of the correction target pixel. Another object of the present invention is to provide a display system capable of reducing the storage capacity necessary for storing correction values.

  In the present invention, correction is performed by interpolating a correction value corresponding to the pixel value of the correction target pixel using correction values corresponding to specific pixel values above and below the pixel value of the correction target pixel. Another object of the present invention is to provide a display system capable of reducing the storage capacity necessary for storing values.

In the luminance correction method according to the first aspect of the invention, each pixel value of the display image is corrected using a plurality of specific pixel values and correction values corresponding to the plurality of specific pixel positions, and the display image is displayed on the display panel. In the luminance correction method for reducing the luminance unevenness, the measurement luminance of each specific pixel position obtained by displaying the display image of each specific pixel value on the display panel and performing the measurement is stored in advance, and each stored specific pixel value is stored. Based on the measured luminance at each specific pixel position, a target luminance for each specific pixel value is set from the measured luminance distribution in the display image when the display image of each specific pixel value is displayed, and the target for each specific pixel value The error of the measured luminance with respect to the luminance is calculated for each specific pixel position, and the correction value for correcting the error of each specific pixel position for each calculated specific pixel value is the input pixel value and output luminance in the display panel. Based on the gradation characteristics indicating the relationship, calculation is performed in correspondence with each specific pixel position in each specific pixel value, and when the image is displayed, the specific value corresponding to the pixel value for each pixel position in the image is displayed. Correction is performed using a pixel value and a correction value calculated for a specific pixel position corresponding to the pixel position.

  The brightness correction method according to a second aspect of the present invention is the brightness correction method according to the first aspect, wherein the target brightness for any one of the specific pixel values is determined, and the other specific pixel values are determined based on the determined target brightness and the gradation characteristics of the display panel. A target luminance is calculated, and the correction value is calculated using the determined or calculated target luminance.

The display system according to the third aspect of the present invention corrects each pixel value of the display image using a plurality of specific pixel values and correction values corresponding to the plurality of specific pixel positions, and brightness when the display image is displayed on the display panel. In a display system that reduces unevenness, a luminance storage unit that stores the measurement luminance of each specific pixel position obtained by displaying a display image of each specific pixel value on the display panel and performing measurement, and for each stored specific pixel value Based on the measured luminance at each specific pixel position, means for setting a target luminance at each specific pixel value from the measured luminance distribution in the display image when the display image of each specific pixel value is displayed, and for each specific pixel value Means for calculating the error of the measured luminance with respect to the target luminance for each specific pixel position and a correction value for correcting the error of each specific pixel position for each calculated specific pixel value are input to the display panel. Correction value calculating means for calculating a value corresponding to each specific pixel position in each specific pixel value based on gradation characteristics indicating a relationship between the pixel value and the output luminance, and when displaying the image, each pixel position of the image The pixel value is corrected using the correction value calculated by the correction value calculation means for the specific pixel value corresponding to the pixel value and the specific pixel position corresponding to the pixel position. It is characterized by.

  A display system according to a fourth invention is the display system according to the third invention, based on the determining means for determining the target brightness for any specific pixel value, the target brightness determined by the determining means and the gradation characteristics of the display panel, Target luminance calculating means for calculating target luminance for other specific pixel values, and the correction value calculating means calculates the correction value using the target luminance determined or calculated by the determining means or the target luminance calculating means. It is comprised by these.

  The display system according to a fifth aspect of the present invention is the display system according to the third or fourth aspect, wherein the correction value corresponding to the specific pixel value at the peripheral position of the pixel position of the correction target pixel is used to correct the pixel position of the correction target pixel. A pixel position interpolating means for interpolating values is provided.

  The display system according to a sixth aspect of the present invention is the display system according to any of the third to fifth aspects, wherein the correction value corresponding to the pixel value of the correction target pixel is determined using correction values corresponding to the specific pixel values above and below the pixel value of the correction target pixel. It is characterized by comprising pixel value interpolation means for performing the above interpolation.

  In the first and third inventions, the correction value is calculated based on the target luminance, the measured luminance stored in advance, and the gradation characteristics of the display panel, and the pixel value such as the gradation is calculated using the calculated correction value. Since the correction is performed, the luminance of the display panel is corrected to the target luminance. Since the correction is performed in consideration of the gradation characteristics of the display panel, the luminance unevenness can be corrected without excess or deficiency.

  In the second and fourth inventions, a target brightness for any one of a plurality of specific pixel values is determined, and a target brightness for another specific pixel value is calculated based on the determined target brightness and the gradation characteristics of the display panel. Therefore, it is not necessary to determine the target luminance for all the specific pixel values, and it is only necessary to determine for any specific pixel value.

  In the fifth aspect of the invention, the correction values corresponding to the specific pixel values around the pixel position of the correction target pixel are used to interpolate the correction values corresponding to the pixel position of the correction target pixel. It is not necessary to store the correction value corresponding to, and it is only necessary to store the correction values corresponding to some specific pixel positions. Therefore, the storage capacity necessary for storing correction values can be reduced.

  In the sixth aspect of the invention, the correction values corresponding to the pixel values of the correction target pixel are interpolated using the correction values corresponding to the specific pixel values above and below the pixel value of the correction target pixel. It is not necessary to store the correction values corresponding to, but only store the correction values corresponding to some specific pixel values. Therefore, the storage capacity necessary for storing correction values can be reduced.

  According to the first and third inventions, it is possible to correct luminance unevenness without excess or deficiency.

  According to the second and fourth inventions, it is not necessary to determine the target luminance for all specific pixel values.

  According to the fifth and sixth inventions, it is possible to reduce the storage capacity of the correction value storage unit in which the correction value is stored. The cost and size of the correction circuit portion can be reduced.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. In the following description, as shown in FIG. 11B, in a display device that is connected to a computer 60 and includes an image processing unit 62 that corrects a display image and the display panel 22 such as an LCD, A description will be given by taking as an example a case where luminance unevenness is reduced by lowering.

  FIG. 1 is a block diagram showing a configuration example of a display system according to the present invention. The display system includes a computer 60 and a display device 20 connected to the computer 60. The computer 60 is connected to a hard disk drive (hereinafter referred to as a hard disk) 12 in which a measurement brightness table (to be described later) is stored, and is connected to the hard disk 12 to determine a target brightness (to be described later) and calculate a correction coefficient (to be described later). And a RAM (Random Access Memory) 14 that is connected to the calculation unit 10 and stores temporary data used for calculation of correction coefficients.

  For example, as shown in FIG. 11, the display device 20 includes an image processing unit 62 and a display panel (LCD) 22, and the image processing unit 62 is connected to the calculation unit 10 and stores the calculated correction coefficient. A coefficient memory 16 is provided. The computer 60 and the display device 20 include a USB (Universal Serial Bus) port or a serial port, and are connected to each other by a USB cable or a serial cable. Therefore, for example, data can be transferred from the calculation unit 10 of the computer 60 to the correction coefficient memory 16 of the display device 20. A display cable that outputs a display image signal is also connected between the computer 60 and the display device 20.

  The display panel 22 of the display device 20 is a liquid crystal panel having, for example, 1600 pixels in the horizontal direction (horizontal direction, hereinafter referred to as H direction) and 1200 pixels in the vertical direction (vertical direction, hereinafter referred to as V direction). For example, the pixel can output 256 gradations of black and white or 256 gradations of R (red), G (green), and B (blue). Hereinafter, description will be made by taking 256 gray scales as an example.

  The display panel 22 should output the luminance corresponding to the gradation (pixel value) of each pixel of the display image, but an error occurs between the luminance to be output and the luminance that is actually output. And uneven brightness occurs. The actually output luminance can be measured with a luminance measuring device. FIG. 2 is a perspective view showing an outline of the luminance measurement of the image display area of the display panel 22 using the luminance measuring device. A luminance measuring device 28 is disposed in front of the display panel 22 and the luminance distribution of the entire image display area of the display panel 22 is measured. Here, since the luminance distribution varies depending on the gradation of the display image, the luminance distribution when each display image having a plurality of gradations is displayed is measured. For example, the luminance distribution is measured when a display image having specific gradations (specific pixel values) of 32, 96, 160, and 224 among 0 to 255 gradations is displayed.

  In the measured luminance distribution, the measured luminance of the entire image display area is not stored in the measured luminance table, but only the measured luminance at a specific coordinate (specific pixel position) is stored in the measured luminance table. For example, the entire image display area is divided into a plurality of blocks, and the measured luminance of the central coordinates of each block is stored in the measured luminance table. FIG. 3A is a schematic diagram illustrating an example of specific coordinates. In the example of FIG. 3A, the H direction is divided into 4 blocks and the V direction is divided into 3 blocks. The method of dividing the block is arbitrary. For example, the V direction can be divided into 16 blocks and the H direction can be divided into 16 blocks with respect to the central square area excluding both ends of the image display area. . The measurement brightness table stores the measurement brightness of the center coordinates (specific coordinates) of the block. Each coordinate in the image display area of the display panel 22 and each coordinate in the display image have a correspondence relationship.

  FIG. 3B is a diagram showing an outline of the measured luminance table stored in the hard disk (luminance storage unit) 12. The measurement luminance table stores the measurement luminance of specific coordinates (center coordinates of each block of 4 × 3) in each of the specific gradations 32, 96, 160, and 224. The measurement brightness stored in the measurement brightness table can be measured by a method similar to the conventional method. In addition, the measurement brightness table is measured by an external storage device such as a CD (Compact Disk) -ROM provided in the computer 60 or a communication device such as a LAN (Local Area Network) card, as in the case of a device driver or application software. Can be received and stored in the hard disk 12. 2 may be connected to the computer 60 with a USB cable or a serial cable, and the measured value may be sent to the computer and stored in the hard disk 12 as a measured luminance table.

The calculation unit (determination unit) 10 determines a target luminance for any one of the specific gradations. For example, among the specific gradations, the target luminance of 224 having the highest gradation is determined. The target luminance (224) can be determined by the calculation unit (determination unit) 10 based on the measured luminance table. For example, it is possible to determine the target luminance (224) so that the ratio of the area (correction target) that is equal to or higher than a certain luminance value in the measured luminance becomes a predetermined value or more. For example, when the predetermined value is set to 94%, when the ratio of the measured luminance of 123 cd / m ² or more is 94% or more and the ratio of the measured luminance of 124 cd / m ² or more is less than 94%, the target luminance ( 224) is determined to be 123 cd / m ² .

  The calculation unit (target luminance calculation means) 10 calculates target luminances of other specific gradations 32, 96, and 160 based on the determined target luminance (224). Normally, the tone characteristics unique to the display panel are indicated by a gamma function.

It is possible to calculate more. Here, the exponent γ in the above equation is the gamma value of the display device, and the following description will be given taking an example where the gamma value is 2.2. Information such as a gamma value relating to gradation characteristics is stored in the hard disk 12, for example. The target brightness 1.7, 19.1, 58.7 of each specific gradation 32, 96, 160 is calculated by the calculation unit 10 using the above equation. FIG. 4A is a diagram showing the relationship between the gradation and the calculated target luminance. The received target brightness and the calculated target brightness are stored in the RAM 14 by the calculation unit 10. However, the target luminance setting method is not limited to the above method. For example, the target luminance of the specific gradation 224 is provisionally determined to be 123 cd / m ² by the above method. At that time, when the distribution ratio of the calculated target luminance of 1.7 cd / m ² at the specific gradation 32 is 80%, which is significantly lower than the ratio of 94% at the specific gradation 224, the uneven luminance correction at the specific gradation 32 is corrected. Since the area is reduced, a method of resetting the luminance such that the ratio becomes 94% in this gradation to the target luminance and recalculating the target luminance of the other specific gradation using the above formula can be considered.

The calculation unit (correction value calculation means) 10 calculates a correction coefficient (correction value) for gradation (pixel value) based on the error between the target luminance and the measured luminance. As described above, the target luminance of the specific gradation 224 is determined to be 123 cd / m ² , but there are many cases where an error (brightness unevenness) occurs between the specific luminance and the measured luminance. FIG. 4B is a diagram illustrating an example of a luminance error. Respect gradation 224, if the measured brightness of a particular coordinate of 146cd / m ^2, for ² high 23 cd / m than the target luminance 123cd / m ^2, the operating section 10 calculates a correction coefficient luminance 23 cd / m ² lowered To do. In this case, in consideration of the gamma function (gamma value = 2.2) indicated by the broken line in the figure, when the gradation at which the luminance is 123 cd / m ² is x,
123 = (x / 224) ^2.2 × 146
x = (123/146) ^{1 / 2.2} × 224≈207
And the correction coefficient is (123/146) ^{1 / 2.2} . Further, by multiplying the gradation 224 by the correction coefficient (123/146) ^{1 / 2.2} , the gradation 207 for obtaining the target luminance 123 cd / m ² is obtained.

The calculation unit 10 calculates correction coefficient = (target luminance / measured luminance) ^{1 / 2.2} for each specific gradation and each measured luminance of the specific luminance table, and temporarily stores the calculated correction coefficient in the RAM 14. After that, it is stored in the correction coefficient memory 16. The correction coefficient memory 16 stores a correction coefficient for each specific coordinate in each specific gradation, similarly to the measured luminance shown in FIG. In the case of RGB gradation, a measurement luminance table corresponding to each of R, G, and B is stored in the hard disk 12.

  Next, correction of luminance unevenness using a correction coefficient will be described. FIG. 5 is a block diagram illustrating a configuration example of a part of the image processing unit 62 included in the display device according to the present invention. The image processing unit 62 is connected to the correction coefficient memory 16, the gradation level selection unit 46 that is connected to the correction coefficient memory 16 and receives a pixel signal of a display image to be displayed on the display panel 22, a display image synchronization signal, and a clock An address counter 30 to which a signal is input, a block address generator 32 connected between the address counter 30 and the correction coefficient memory 16, buffers 34 and 36 connected to the correction coefficient memory 16, and each of the buffers 34 and 36 The H direction interpolation units 38 and 40 connected to each other, the V direction interpolation units 42 and 44 connected to the H direction interpolation units 38 and 40, and the V direction interpolation units 42 and 44, respectively, and a delay circuit The level direction interpolation unit 52 connected to the gradation level selection unit 46 via 48, and is connected to the level direction interpolation unit 52 and the address counter 30. Rutotomoni, and a luminance correcting portion 56 connected to the gradation level selector 46 via a delay circuit 50.

  The buffer 34 includes four buffers 34a, 34b, 34c, and 34d, the buffer 36 includes four buffers 36a, 36b, 36c, and 36d, and the H direction interpolation unit 38 includes two H direction interpolation units 38a and 38b. The H direction interpolation unit 40 includes two H direction interpolation units 40a and 40b. The buffers 34a and 34b are connected to the H direction interpolation unit 38a, the buffers 34c and 34d are connected to the H direction interpolation unit 38b, the buffers 36a and 36b are connected to the H direction interpolation unit 40a, and the buffers 36c and 36d are H direction interpolation. It is connected to the part 40b. The H direction interpolation units 38 a and 38 b are connected to the V direction interpolation unit 42, and the H direction interpolation units 40 a and 40 b are connected to the V direction interpolation unit 44.

  The address counter 30 counts pixel addresses representing pixel coordinates (pixel positions) in the display image based on the synchronization signal and the clock signal. In many cases, the count is performed from the upper left to the upper right of the display image, and from the lower left to the lower right while sequentially moving downward. Counting for one image is completed at the lower right of the display image, and counting is started again from the upper left. The pixel address is sent to the H direction interpolation units 38 and 40 and the V direction interpolation units 42 and 44, and the synchronization signal is sent to the luminance correction unit 56.

  The block address generator 32 generates addresses of blocks that divide the display image. As described above, the correction coefficient memory 16 stores correction coefficients corresponding to the center coordinates of the blocks that divide the display image or the image display area of the display panel 22 as shown in FIG. The block address generator 32 provides the correction coefficient memory 16 with the block address corresponding to the pixel address.

  The gradation level selection unit 46 selects a gradation level based on the pixel signal. As described above, the correction coefficient memory 16 stores correction coefficients for a plurality of specific gradations as shown in FIG. The gradation level selection unit 46 selects a gradation level corresponding to the gradation of the pixel. For example, level 0: 0 ≦ gradation ≦ 32, level 1:32 <gradation ≦ 96, level 2:96 <gradation ≦ 160, level 3: 160 <gradation ≦ 224, level 4: 224 <gradation ≦ Any one of 255 is selected, and the selection result (selected gradation level) is given to the correction coefficient memory 16. For example, when the gradation of the pixel is 200, level 3 is selected. Further, gradation level information including the gradation of the pixel and the upper and lower limits of the selected gradation level is provided to the level direction interpolation unit 52 via the delay circuit 48. Further, the pixel signal is given to the luminance correction unit 56 via the delay circuit 50.

  The correction coefficient memory 16 outputs correction coefficients corresponding to the received block address and selected gradation level to the buffers 34 and 36. More specifically, the correction coefficients in the upper level and lower level specific gradations including the gradation of the pixel are output separately to the buffer 34 (upper level) and the buffer 36 (lower level). For example, when the gradation of the pixel is 200 and the selected gradation level is level 3, the correction coefficient at the upper specific gradation 224 is output from the correction coefficient memory 16 to the buffer 34, and the correction at the lower gradation specific gradation 160 is performed. The coefficient is output from the correction coefficient memory 16 to the buffer 36.

  In addition, the correction coefficients of four (2 × 2) blocks around the pixel are output to the buffers 34a to 34d and the buffers 36a to 36d. FIG. 6 is a diagram showing an example of pixel coordinates and block center coordinates (specific coordinates). In FIG. 6, P is a pixel, P0 to P3 are the centers of the respective blocks, and the pixel P is surrounded by the centers P0 to P3 of the blocks. Of the four blocks around the pixel P, the correction coefficient corresponding to the upper left (P0) block is output to the buffers 34a and 36a, the correction coefficient corresponding to the upper right (P1) is output to the buffers 34b and 36b, and the lower left ( The correction coefficient corresponding to P2) is output to the buffers 34c and 36c, and the correction coefficient corresponding to the lower right (P3) is output to the buffers 34d and 36d. For example, when the pixel is in the vicinity of the outer periphery of the display image as in P ′ of FIG. 6, the pixel P ′ cannot be surrounded by the center of the block, but in this case, 2 × 2 in the vicinity of the pixel P ′. Select the block. Thereafter, processing similar to that for the pixel P is performed.

  The H direction interpolation unit (pixel position interpolation means) 38 performs interpolation in the H direction on the correction coefficients in the blocks arranged in the H direction, and obtains correction coefficients in the H direction coordinates of the pixels. More specifically, the H direction interpolation unit 38a performs interpolation in the H direction using the correction coefficients corresponding to P0 and P1 in FIG. 6 stored in the buffers 34a and 34b and the pixel address received from the address counter. Then, a correction coefficient corresponding to the H direction coordinate P01 of the pixel is obtained. Similarly, the H direction interpolation unit 38b performs interpolation in the H direction using the correction coefficients corresponding to P2 and P3 in FIG. 6 stored in the buffers 34c and 34d and the pixel address received from the address counter, A correction coefficient corresponding to the H direction coordinate P23 of the pixel is obtained. The obtained correction coefficient is sent to the V-direction interpolation unit 42.

  The V direction interpolation unit (pixel position interpolation means) 42 performs interpolation in the V direction on the correction coefficients in the blocks arranged in the V direction, and obtains the correction coefficient in the V direction coordinates of the pixel. More specifically, the V direction interpolation unit 42 performs interpolation in the V direction using the correction coefficients corresponding to P01 and P23 of FIG. 6 received from the H direction interpolation units 38a and 38b and the pixel address received from the address counter. The correction coefficient corresponding to the pixel coordinate P is obtained. The obtained correction coefficient is sent to the level direction interpolation unit 52. The operations of the H direction interpolation unit (pixel position interpolation unit) 40 and the V direction interpolation unit (pixel position interpolation unit) 44 are the same as those of the H direction interpolation unit 38 and the V direction interpolation unit 42 described above, and the buffers 36a to 36b. Interpolation in the H direction and the V direction is performed on the correction coefficient stored in 36d.

  The level direction interpolation unit (pixel value interpolation unit) 52 uses the upper level and lower level correction coefficients received from the V direction interpolation units 42 and 44 and the gradation level information received from the delay circuit 48 to Interpolation in the level direction is performed to obtain a correction coefficient corresponding to the gradation of the pixel. For example, the correction coefficient in the gradation 200 of the pixel is interpolated using the correction coefficient in the specific gradation 224 at the upper level and the correction coefficient in the specific gradation 160 at the lower level. The level direction interpolation can be performed in the same manner as the H direction interpolation and the V direction interpolation. The obtained correction coefficient is sent to the luminance correction unit 56.

  The luminance correction unit 56 multiplies the pixel signal received from the delay circuit 50 by a correction coefficient. The luminance correction unit 56 also performs processing such as rounding the lower bits of the correction coefficient using a dither method. A display image based on the pixel signal multiplied by the correction coefficient is output to the display panel 22.

  FIG. 7 is a flowchart showing an example of a procedure for calculating a correction coefficient for each specific coordinate in each specific gradation. The arithmetic unit 10 acquires the target luminance of the specific gradation 224 (S10) and stores it in the RAM 14, and also determines other specific gradations (based on the target luminance of the specific gradation 224 and the gradation characteristics of the display panel). 160, 96, and 32) are calculated (S12) and stored in the RAM. Thereafter, the arithmetic unit 10 calculates a correction coefficient corresponding to each specific coordinate based on the target luminance, each measured luminance, and the gradation characteristic of the display panel at each specific gradation (S14), and stores it in the RAM 14. The correction coefficient stored in the RAM 14 is stored in the correction coefficient memory 16 (S16).

  FIG. 8 is a flowchart showing an example of a procedure for correcting the gradation of each pixel using the correction coefficient stored in the correction coefficient memory 16. The gradation level selection unit 46 selects gradation levels corresponding to the gradation of the pixel (specific gradations corresponding to the upper and lower sides of the pixel gradation) (S20), and the selected gradation level is stored in the correction coefficient memory 16. give. Further, the correction coefficient memory 16 selects specific coordinates corresponding to the upper, lower, left, and right of the pixel coordinates based on the block address received from the block address generator 32 (S22), and selects 2 based on the gradation level. For each specific gradation, the correction coefficients of the selected four specific coordinates are read out to the buffers 34 and 36 (S24).

  Next, the H direction interpolation units 38 and 40 interpolate correction coefficients in the H direction (S26) at specific coordinates arranged in the left and right (H direction) for each of the two selected specific gradations, and also in the V direction. The correction coefficients are interpolated in the V direction (S28) at the specific coordinates arranged vertically (V direction) for each of the two specific gradations selected by the interpolation units 42 and 44, and further selected by the level interpolation unit 52 The correction coefficient is interpolated in the level direction at each of the two specific gradations (S30). The luminance correction unit 56 corrects the gradation of the pixel using the interpolated correction coefficient (S32). A display image in which the gradation of each pixel is corrected is displayed on the display panel 22. The correction is performed using a correction coefficient based on the target luminance.

  Note that even if the gradation is 0, the luminance of the display panel 22 may not be 0. In this case, there is a tendency that excessive correction is performed on a display image having a generally low gradation. Therefore, it is preferable to correct the luminance unevenness in consideration of the luminance when the gradation is 0. For example, when the correction coefficient is calculated, the luminance value at the time of gradation 0 is used as an offset and subtracted from the measured luminance.

In the above-described embodiment, the luminance unevenness is reduced by reducing the luminance. Therefore, the correction is not performed when the correction coefficient is 1 or more, and the correction can be performed when the correction coefficient is less than 1. It is. Further, the correction is not performed when the gradation of the pixel is less than 32 or greater than 224, and the correction can be performed when the gradation of the pixel is 32 or more and 224 or less. Further, in the above-described embodiment, the luminance correction unit 56 multiplies the pixel gradation by the correction coefficient. However, the pixel gradation is x, and the specific gradations above and below the pixel gradation are x1, x2. The correction coefficients corresponding to the gradations x1 and x2 are C1 and C2, and the corrected gradation x ′ is x ′ = {x · C2 · (| x−x1 |) + x · C1 · (| x−x2 | )}
÷ (| x1-x2 |)
It is also possible to calculate more.

In each of the embodiments described above, the luminance unevenness is reduced by lowering the luminance. However, it is also possible to reduce the luminance unevenness by increasing the luminance. FIG. 9 is a diagram showing another example of luminance error. Respect gradation 224, if the measured brightness of a particular coordinate of 100 cd / m ^2, for 23 cd / m ² lower than the target luminance 123cd / m ^2, the operating section 10 calculates a correction coefficient to increase 23 cd / m ² brightness To do. In this case, in consideration of the gradation characteristic (gamma value = 2.2) inherent to the display panel indicated by the broken line in the figure, when the gradation at which the luminance is 123 cd / m ² is x,
123 = (x / 224) ^2.2 × 100
x = (123/100) ^{1 / 2.2} × 224≈246
And the correction coefficient is (123/100) ^{1 / 2.2} . In addition, the gradation 246 for obtaining the target luminance 123 is obtained by multiplying the gradation 224 by the correction coefficient (123/100) ^{1 / 2.2} .

  In each of the above-described embodiments, the LCD has been described as an example. However, the present invention is not limited to the LCD, and the present invention is applied to correction of luminance unevenness such as a CRT or a PDP, or is applied to correction of uneven luminance of a projector. The invention can be applied. In addition, each of the embodiments described above is configured by a computer and a display device. However, the components according to the present invention of the computer 60 shown in FIG. 1 are provided inside the display device, and the present invention is realized by the display device alone. It is also possible to do.

It is a block diagram which shows the structural example of the display system which concerns on this invention. It is a perspective view which shows the outline | summary of the brightness | luminance measurement of the image display area of the display panel using a brightness | luminance measuring device. (A) is the schematic which shows the example of a specific coordinate, (b) is a figure which shows the outline | summary of the measurement brightness | luminance table memorize | stored in the hard disk. (A) is a figure which shows the relationship between a gradation and the calculated target brightness | luminance, (b) is a figure which shows the example of the error of a brightness | luminance. It is a block diagram which shows the example of a structure of a part of image processing part with which the display apparatus which concerns on this invention is provided. It is a figure which shows the example of the coordinate of a pixel, and the center coordinate of a block. It is a flowchart which shows the example of the calculation procedure of the correction coefficient of each specific coordinate in each specific gradation. It is a flowchart which shows the example of the correction procedure of the gradation of each pixel using the correction coefficient memorize | stored in the correction coefficient memory. It is a figure which shows the other example of the difference | error of a brightness | luminance. It is a conceptual diagram which shows the example of the image display of a display apparatus. It is a conceptual diagram which shows the example of the image display of a display apparatus.

Explanation of symbols

10 Arithmetic unit 12 Hard disk 14 RAM
16 Correction coefficient memory 20 Display device 22 Display panel 28 Luminance measuring device 30 Address counter 32 Block address generator 34, 36 Buffer 38, 40 H direction interpolation unit 42, 44 V direction interpolation unit 46 Gradation level selection unit 48, 50 Delay Circuit 52 Level direction interpolation unit 56 Brightness correction unit 60 Computer 62 Image processing unit

Claims (6)

In a luminance correction method for correcting each pixel value of a display image using correction values corresponding to a plurality of specific pixel values and a plurality of specific pixel positions to reduce luminance unevenness when a display image is displayed on a display panel,
The measurement brightness of each specific pixel position obtained by displaying a display image of each specific pixel value on the display panel and performing measurement is stored in advance.
Based on the measured luminance at each specific pixel position for each specific pixel value stored, set the target luminance at each specific pixel value from the measured luminance distribution in the display image when displaying the display image of each specific pixel value,
The error of the measured luminance relative to the target luminance before Symbol each specific pixel value, calculated for each particular pixel location,
A correction value for correcting an error of each specific pixel position for each calculated specific pixel value is set to each specific pixel position in each specific pixel value based on a gradation characteristic indicating a relationship between the input pixel value and the output luminance in the display panel. Correspondingly calculated,
When displaying an image, the pixel value at each pixel position of the image is corrected using a specific pixel value corresponding to the pixel value and a correction value calculated for the specific pixel position corresponding to the pixel position. A brightness correction method characterized by performing. Determine the target brightness for any particular pixel value,
The target luminance for another specific pixel value is calculated based on the determined target luminance and the gradation characteristics of the display panel, and the correction value is calculated using the determined or calculated target luminance. The luminance correction method according to 1. In a display system that corrects each pixel value of a display image using correction values corresponding to a plurality of specific pixel values and a plurality of specific pixel positions, and reduces luminance unevenness when the display image is displayed on the display panel.
A luminance storage unit for storing the measurement luminance of each specific pixel position obtained by displaying a display image of each specific pixel value on the display panel and performing measurement;
Means for setting a target luminance at each specific pixel value from a measured luminance distribution in the display image when a display image of each specific pixel value is displayed based on the measured luminance at each specific pixel position for each specific pixel value stored; ,
The error of the measured luminance relative to the target luminance before Symbol each specific pixel value, means for calculating for each particular pixel location,
A correction value for correcting an error of each specific pixel position for each calculated specific pixel value is set to each specific pixel position in each specific pixel value based on a gradation characteristic indicating a relationship between the input pixel value and the output luminance in the display panel. Correction value calculating means for calculating the pixel value, and when displaying an image, for the pixel value at each pixel position of the image, a specific pixel value corresponding to the pixel value and a specific pixel corresponding to the pixel position A display system, wherein the position is corrected using the correction value calculated by the correction value calculation means. Determining means for determining a target luminance for any particular pixel value;
Target luminance calculating means for calculating target luminance for other specific pixel values based on the target luminance determined by the determining means and the gradation characteristics of the display panel, the correction value calculating means comprising: 4. The display system according to claim 3, wherein the correction value is calculated using the target luminance determined or calculated by the luminance calculating means.   A pixel position interpolation unit that performs interpolation of a correction value corresponding to a pixel position of the correction target pixel using a correction value corresponding to a specific pixel value at a peripheral position of the pixel position of the correction target pixel. Item 5. The display system according to Item 3 or 4.   The pixel value interpolation means for interpolating the correction value corresponding to the pixel value of the correction target pixel using correction values corresponding to the specific pixel values above and below the pixel value of the correction target pixel. The display system according to any one of 3 to 5.

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