JP2014002325A - Image display device, image display system, measurement method and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device, an image display system, a measurement method and a computer program that enhance a display quality by being provided with two look up tables (LUT), and can perform calibration accurately and quickly.SOLUTION: An image display device 1 is configured to: convert an input image signal by a first LUT 21; perform an image signal process to the converted image signal by an image signal process part 14; and convert an image signal after subjected to the image signal process by a second LUT 22 and display the converted image signal on a display panel 15. For the calibration and the like, when an output physical amount of the display panel 15 is measured by a sensor 16, the image display device 1 is configured to change the first LUT 21 to a measurement LUT 23 stored in a storage part 12 and measure the output physical amount by displaying an image signal converted by the measurement LUT 23 and the second LUT 22 on the display panel 15.

Description

  The present invention relates to an image display apparatus, an image display system, a measurement method, and a computer program for measuring characteristics of a display device when performing calibration or the like.

  An image display apparatus having a display device such as a liquid crystal panel or a PDP (Plasma Display Panel) performs a process of correcting a gradation characteristic of an input image signal in accordance with the gradation characteristic of the display device, a so-called γ correction process. . In the γ correction processing of the image display device, an LUT (Look Up Table) in which the gradation value of the input image signal and the gradation value of the corrected output image signal are associated with each other is used. The LUT is realized by using a memory element such as SRAM (Static Random Access Memory), for example, and associates the gradation value of the input image signal with the address of the SRAM, and outputs the gradation value of the output image signal to each address. Remember as.

  A conventional image display device includes one LUT as described above, and after performing correction processing using the LUT on an input image signal from a PC (Personal Computer) or the like, the image signal processing unit performs color correction or the like. Various image signal processing is performed to display an image on a display device. There is also an image display device including two LUTs (see, for example, FIG. 11 of Patent Document 1). Such an image display device performs a correction process using the first LUT on an input image signal. The image signal processing unit performs various image signal processing such as color correction, and performs correction processing using the second LUT on the image signal after the image signal processing to display an image on the display device. An image display device having two LUTs has an advantage that advanced color control can be performed as compared with an image display device having one LUT.

  In the image display apparatus, the gradation characteristics of the display device may change due to changes over time. When a secular change occurs, the image display apparatus preferably performs a process (so-called calibration) for updating various characteristics related to the image display, so that a high-quality image display can be maintained. In calibration, for example, the brightness or chromaticity of an image displayed on a display device is measured using a sensor or the like, and an LUT value that can offset the influence of secular change is calculated based on the measurement result. Process to update the value. In the image display device having two LUTs as described above, the first LUT is updated by, for example, calibration (however, the second LUT may be updated).

JP 2011-95285 A

  In an image display apparatus having one LUT, when the calibration is performed, the gradation characteristic of the display device is measured without performing the correction process using the LUT that is the update target, so that the display device itself (or close to it) is measured. Since characteristics can be measured, accurate calibration can be performed. On the other hand, in the image display apparatus having two LUTs, even if the gradation characteristics of the display device are measured without performing the correction process using the first LUT to be updated, the second LUT is used. Since the correction process is performed, there is a problem that the characteristics of the display device itself cannot be measured and the calibration accuracy is low. In addition, since the characteristics of the display device itself cannot be measured, for example, in the case of a configuration in which a plurality of first LUTs are stored in advance and the first LUT is switched according to the image quality setting of the user, each first LUT There is a problem that it is necessary to perform a calibration process for the, and the calibration time is increased.

  That is, the conventional image display apparatus has a feature that, in the case of a configuration having one LUT, advanced color control cannot be performed, but calibration can be performed with high accuracy and high speed. The configuration having two LUTs is characterized by high display image quality but low calibration accuracy and time. For example, by performing conversion with the display device having a characteristic of γ = 1.0 in the second LUT, the image signal processing unit can perform image signal processing by assuming that the display device has a linear characteristic. It is possible to perform high-precision image signal processing at high speed using processing such as interpolation.

  The present invention has been made in view of such circumstances. An object of the present invention is to provide two LUTs to improve display image quality and to perform calibration with high accuracy and at high speed. A display device, an image display system, a measurement method, and a computer program are provided.

  An image display apparatus according to the present invention includes a first lookup table for converting a gradation value of an input image signal, and an image signal processing unit that performs image signal processing on the image signal converted by the first lookup table. A second look-up table for converting the gradation value of the image signal processed by the image signal processing unit, and a display device for displaying an image related to the image signal converted by the second look-up table A third look-up table storing the correspondence between the input tone value and the output tone value that cancels the conversion by the second look-up table, and measuring the output physical quantity of the display device And a table switch for switching the first look-up table to the third look-up table when the measuring means performs measurement. Characterized in that it comprises a stage.

  In the image display device according to the present invention, the second look-up table stores a conversion value that causes the display device to have a γ characteristic of γ = 1.0 when viewed from the image signal processing unit. And

  In the image display device according to the present invention, the third lookup table stores correspondences between input gradation values and output gradation values corresponding to γ characteristics of the display device, and the second lookup table The table stores a correspondence between input gradation values and output gradation values corresponding to an inverse function of the γ characteristic of the display device.

  The image display device according to the present invention further includes update means for updating the first lookup table or the second lookup table in accordance with a measurement result of the measurement means.

  An image display system according to the present invention includes an image display device having a display device that displays an image, and an image signal output device that outputs an image signal related to an image displayed on the image display device. A first look-up table for converting a gradation value of the image signal output from the image signal output device, and an image signal processing unit for performing image signal processing on the image signal converted by the first look-up table A second lookup table for converting the gradation value of the image signal processed by the image signal processing unit, and an input gradation value and an output gradation value that cancel the conversion by the second lookup table A third look-up table that stores the correspondence between the display device, a measurement unit that measures the output physical quantity of the display device, and the measurement unit Table switching means for switching the look-up table to the third look-up table, and the first look-up table, the image signal processing unit, the second look-up table, and the measuring means are the image display device or the Provided in an image signal output device, wherein the third look-up table and the table switching means are provided in the image display device or the image signal output device provided with the first look-up table. To do.

  The measurement method according to the present invention includes a first lookup table for converting a gradation value of an input image signal, and image signal processing for performing image signal processing on the image signal converted by the first lookup table. , A second look-up table for converting the gradation value of the image signal processed by the image signal processing unit, and a display for displaying an image related to the image signal converted by the second look-up table A measurement method for measuring an output physical quantity of a display device in an image display system comprising a device, wherein a correspondence between an input tone value and an output tone value that cancels conversion by the second lookup table is stored A third lookup table is provided, the first lookup table is switched to the third lookup table, and the output of the display device is changed. And measuring a physical quantity.

  The computer program according to the present invention also includes a first lookup table for converting a gradation value of an input image signal, and an image signal processing for performing image signal processing on the image signal converted by the first lookup table. , A second look-up table for converting the gradation value of the image signal processed by the image signal processing unit, and a display for displaying an image related to the image signal converted by the second look-up table A computer program that causes a computer included in an image display system including a device to measure an output physical quantity of the display device, and that corresponds to an input tone value and an output tone value that cancel the conversion by the second lookup table Is stored in the third lookup table, and the first lookup table is stored in the computer. A step to switch the Buru in the third look-up table, characterized in that and a step of causing the process of measuring the output physical quantity of said display device.

In the present invention, the input image is converted by the first lookup table, the image processing for the converted image is performed by the image processing unit, and the image after the image processing is converted by the second lookup table and converted. Display the image on the display device. The processing by the first lookup table, the image processing unit, and the second lookup table may be performed by the image display device or may be performed by an external device such as a PC connected to the image display device.
When measuring an output physical quantity (for example, luminance or chromaticity of a display image) of the display device for calibration or the like, the first lookup table is switched to the third lookup table, and the third lookup table and the third lookup table 2. Measurement is performed on the display image that has been converted by the lookup table. The third look-up table is a look-up table that stores a value that cancels the conversion by the second look-up table. As a result, since the conversion of the third lookup table and the second lookup table is canceled at the time of measurement, the output physical quantity of the display device when the first lookup table and the second lookup table do not exist (that is, the display device) The output physical quantity by (or close to) itself can be measured.
Since the output physical quantity of the display device itself can be measured, accurate measurement can be performed, and various calibrations can be performed using the measurement result. In addition, when performing normal image display, an appropriate value of each first lookup table is calculated from the output physical quantity of the display device itself even if the configuration is such that a plurality of first lookup tables are switched according to user settings. Therefore, it is not necessary to perform measurement for each first lookup table, and calibration can be performed in a short time.

  In the present invention, the second look-up table stores a conversion value that makes the display device a γ characteristic of γ = 1.0 when viewed from the image processing unit. Accordingly, the image processing unit can perform image processing by regarding the γ characteristic of the display device as γ = 1.0, that is, a linear characteristic. For example, the image processing unit can perform high-accuracy image processing using processing such as linear interpolation. It can be performed at high speed.

In the present invention, a value corresponding to the γ characteristic of the display device is stored in the third lookup table. For example, in the manufacturing process of the image display device, the gamma characteristic of the display device alone can be measured, and the measurement result can be stored in the third lookup table. On the other hand, a value corresponding to an inverse function of the γ characteristic of the display device is stored in the second lookup table. For example, the inverse function can be calculated from the γ characteristic of the display device alone measured in the manufacturing process of the image display device, and the calculation result can be stored in the second lookup table.
Thereby, during the normal operation of the image display device, the γ characteristic of the display device can be canceled by conversion of the second look-up table, and the γ characteristic of the display device can be set to γ = 1.0 as viewed from the image processing unit. . Further, at the time of measurement, the conversion of the third lookup table and the conversion of the second lookup table can be canceled and the γ characteristic of the display device can be measured.

  In the present invention, the value of the first lookup table or the second lookup table is updated according to the measurement result of the display device. Since the characteristics of the display device itself can be measured by performing the measurement as described above, for example, the first lookup is performed so that the deviation of the measurement characteristic from the target characteristic is calculated and the deviation can be offset. One or both of the table or the second lookup table can be updated. By performing such an update, the display quality of the image display apparatus can be maintained.

  In the case of the present invention, display with high image quality can be performed by providing the first lookup table and the second lookup table. Further, during calibration or the like, the output of the display device itself is output by switching the first lookup table to the third lookup table that cancels the conversion of the second lookup table and measuring the output physical quantity of the display device. Physical quantities can be measured with high accuracy, and calibration can be performed in a short time.

It is a block diagram which shows the structure of the image display system which concerns on this Embodiment. It is a schematic diagram for demonstrating the conversion process by a 1st LUT and a 2nd LUT. It is a schematic diagram for demonstrating the measurement process of a display panel. It is a flowchart which shows the procedure of the calibration process which an image display apparatus performs. It is a graph which shows the verification result of calibration accuracy. It is a graph which shows the example of 1 characteristic of the display panel of a measuring object. It is a schematic diagram for demonstrating the measurement process in the conventional image display apparatus. It is a schematic diagram for demonstrating the measurement process in the image display apparatus which concerns on this invention. It is a block diagram which shows the structure of the image display system which concerns on a modification.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof. FIG. 1 is a block diagram showing a configuration of an image display system according to the present embodiment. In the figure, reference numeral 1 denotes an image display device that displays an image on the display panel 15 in accordance with an input image signal from the PC 5. The image display apparatus 1 includes a control unit 11, a storage unit 12, an operation unit 13, an image signal processing unit 14, a display panel 15, a sensor 16, a first LUT 21, a second LUT 22, and the like.

  The PC 5 is a general-purpose computer, and generates and outputs an image signal related to an image to be displayed on the image display device 1 in accordance with a user operation or the like. The image display device 1 and the PC 5 are connected via a signal cable for transmitting and receiving an image signal. The image signal output from the PC 5 is input to the image display device 1 as, for example, an RGB image signal. The input image signal input to the image display device 1 is given to the first LUT 21.

  The first LUT 21 is for converting the gradation value of the input image signal, and stores the correspondence between the gradation value of the input image signal and the gradation value of the output image signal (converted image signal). ing. The first LUT 21 is realized by using a memory element such as SRAM, for example, by associating the gradation value of the input image signal with the address of the SRAM and storing the gradation value of the output image signal as data for each address. it can. Note that three first LUTs 21 for R, G, and B are provided for the RGB signals of the input image signal (however, these three are collectively shown as the first LUT 21 in FIG. 1). ). The first LUT 21 converts the gradation value of the input image signal and supplies the converted image signal to the image signal processing unit 14.

  The first LUT 21 stores the gradation value of the output image signal as data of 10 bits (or more bits) when the gradation value of the input image signal is represented by 8 bits for each color of RGB, for example. doing. As a result, the 8-bit input image signal is expanded to a 10-bit image signal by the first LUT 21 and provided to the image signal processing unit 14 (however, the first LUT 21 outputs an image signal having the same number of bits as the input image signal). May be). As the output tone value of the first LUT 21, for example, an appropriate value is calculated in the manufacturing process of the image display device 1, and stored in advance (factory shipment state). Further, the output gradation value of the first LUT 21 is updated to an appropriate value in consideration of a desired target value or a secular change by performing calibration thereafter.

  The image signal processing unit 14 performs various image signal processing on the image signal given from the first LUT 21, and gives the processed image signal to the second LUT 22. In the present embodiment, any image signal processing performed by the image signal processing unit 14 may be used. For example, the image signal processing unit 14 can perform image signal processing such as color space conversion or color temperature adjustment by performing a predetermined matrix operation on the input RGB gradation values. Since the image signal processing unit 14 performs the calculation with the number of bits expanded by the first LUT 21, it can perform high-accuracy image signal processing.

  Similar to the first LUT 21, the second LUT 22 is for converting the gradation value of the input image signal, and stores the correspondence between the gradation value of the input image signal and the gradation value of the output image signal. Yes. The second LUT 22 is realized by using, for example, a memory element such as SRAM, associating the gradation value of the input image signal with the address of the SRAM, and storing the gradation value of the output image signal as data for each address. it can. The second LUT 22 includes three R, G, and B signals for each RGB signal of the input image signal (however, these three are collectively shown as the second LUT 22 in FIG. 1). ). The second LUT 22 converts the gradation value of the image signal given from the image signal processing unit 14 and gives the converted image signal to the display panel 15.

  The second LUT 22 stores the gradation value of the output image signal as 8-bit (or more bits) data when the gradation value of the input image signal is represented by 10 bits for each color of RGB, for example. doing. As a result, the gradation value of each color given from the image signal processing unit 14 is reduced to an 8-bit image signal that can be processed by the display panel 15 by conversion, and is given to the display panel 15 by the conversion ( However, when the display panel 15 can process, the second LUT 22 may be configured to output an image signal having the same number of bits as the input image signal).

  The display panel 15 is configured using a display device such as a liquid crystal panel or a PDP. The display panel 15 performs image display based on the image signal given from the second LUT 22 (an image signal in which the pixel value of each color is 8 bits).

  The operation unit 13 is one or a plurality of buttons or switches provided on the lower front surface or the side surface of the housing of the image display device 1, and performs various setting operations (for example, brightness, contrast, color temperature, etc.) by the user. Accept settings). The operation unit 13 notifies the control unit 11 of the accepted operation.

  The storage unit 12 is configured by a non-volatile rewritable memory element such as an EEPROM (Electrically Erasable Programmable Read Only Memory) or a flash memory. The storage unit 12 stores, in addition to the measurement LUT 23 described later, one or a plurality of data set by switching to the first LUT 21 and initial values (factory default values) of the first LUT 21 and the second LUT 22. Yes. The control unit 11 can read out the data stored in the storage unit 12 and rewrite the data.

  The control unit 11 is configured using an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and each of the units such as the first LUT 21, the image signal processing unit 14, and the second LUT 22 in the image display device 1. Control the behavior. For example, the control unit 11 switches the data of the first LUT 21 (the gradation value of the output image signal) to another data stored in the storage unit 12 according to the user's setting operation received by the operation unit 13, or Processing such as changing the conditions of the image signal processing performed by the image signal processing unit 14 is performed, and the operation of each unit is controlled to perform image display according to the setting. The control unit 11 receives a control signal from the PC 5 and controls the operation of each unit in accordance with the control signal. Further, the control unit 11 performs a calibration process for updating the data of the first LUT 21 or the second LUT 22 based on information given from the sensor 16.

  The sensor 16 detects an output physical quantity such as luminance and / or chromaticity when the display panel 15 displays an image, and gives a detection result to the control unit 11. For example, the sensor 16 is provided in a frame-like portion surrounding the display panel 15 of the housing of the image display device 1. The sensor 16 is configured to move in and out on the display surface of the display panel 15 from the inside of the housing according to the operation of an actuator or a motor. The control unit 11 moves the sensor 16 on the display surface when performing a calibration process. Move to and measure. Further, for example, the sensor 16 is configured to be detachably connected to the image display device 1 through a signal line or the like, and when performing a calibration process, the user mounts the sensor 16 on the display surface of the display panel 15, The line may be connected to the image display apparatus 1. The sensor 16 gives the detection result to the control unit 11 as data such as RGB or XYZ.

  FIG. 2 is a schematic diagram for explaining conversion processing by the first LUT 21 and the second LUT 22. During the normal operation in which the image display device 1 displays an input image from the PC 5, data corresponding to the user setting is set in the first LUT 21. The storage unit 12 stores a plurality of γ characteristic data corresponding to γ values such as γ = 1.8, 2.2,. The control unit 11 reads any one data from the storage unit 12 according to the setting received by the operation unit 13 and sets it in the first LUT 21. By adopting a configuration in which the data of the first LUT 21 is switched in this way, it is possible to easily change display characteristics in accordance with user settings.

  In the second LUT 22, γ characteristic data that cancels the γ characteristic of the display panel 15 is set. That is, when the γ characteristic is measured with the display panel 15 alone and a γ characteristic of γ = a is obtained, data of the γ characteristic of γ = 1 / a corresponding to the inverse function is set in the second LUT 22. As a result, the combined γ characteristic of the second LUT 22 and the display panel 15 is γ = 1.0. Therefore, the image signal processing unit 14 can perform processing by assuming that the display panel 15 has a linear characteristic, and can perform high-precision and high-speed processing using operations such as linear interpolation. The image display apparatus 1 displays an image with γ characteristics of γ = 1.8, 2.2,... Set in the first LUT 21.

  FIG. 3 is a schematic diagram for explaining the measurement process of the display panel 15. When the image display apparatus 1 measures the output physical quantity of the display panel 15 with the sensor 16 prior to the calibration process or the like, the control unit 11 switches the first LUT 21 to the measurement LUT 23. Note that switching refers to reading the data of the measurement LUT 23 stored in the storage unit 12 and setting the data of the measurement LUT 23 in a memory element such as SRAM in which the data of the first LUT 21 has been set. The memory element in which this data is set is called a measurement LUT 23. That is, the first LUT 21 and the measurement LUT 23 are configured by physically setting different data in the same memory element (however, different memory elements may be used).

  The measurement LUT 23 cancels gradation value conversion by the second LUT 22, and data corresponding to the inverse function of the data set in the second LUT 22 is set. That is, when γ characteristics data of γ = 1 / a is set in the second LUT 22, γ characteristics data of γ = a is set in the measurement LUT 23. As described above, since data corresponding to the inverse function of the γ characteristic of the display panel 15 is set in the second LUT 22, data corresponding to the γ characteristic of the display panel 15 is set in the measurement LUT 23. Therefore, the γ characteristic of the display panel 15 alone is measured in the manufacturing process of the image display device 1, the measurement result itself is stored in the storage unit 12 as the measurement LUT 23, and data corresponding to the inverse function of the measured γ characteristic is stored. What is necessary is just to calculate and set to 2nd LUT22.

  By setting such data, the conversion of the measurement LUT 23 and the conversion of the second LUT 22 are canceled out, and the image display device 1 performs display with the γ characteristic (γ = a) of the display panel 15 alone. By measuring the display panel 15 with the sensor 16 in this state, it is possible to obtain the same measurement result as when an image is displayed on the display panel 15 without performing conversion by the first LUT 21 and the second LUT 22.

  For example, when each color of RGB is represented by 8 bits, the control unit 11 changes the gradation of one color (for example, R) one by one from 0 to 255, and the gradation of another color (for example, GB). Is fixed to 0, and the output physical quantity of the display panel 15 by the sensor 16 is measured. The control unit 11 performs this measurement in the same manner for each color of RGB, and can obtain a correspondence relationship between the input gradation and the output gradation in the case of performing monochromatic display. Further, for example, the control unit 11 changes the gradation of each color of RGB with the same value (R = G = B) by one gradation from 0 to 255, and measures the output physical quantity of the display panel 15 by the sensor 16. Also good. In addition, you may perform the measurement of the display panel 15 using the sensor 16 by methods other than these.

  After the measurement by the sensor 16 is completed, the control unit 11 performs a process of updating the value of the first LUT 21 based on the measurement result. For example, the control unit 11 calculates the deviation of the measurement result with respect to the ideal γ characteristic (for example, the characteristic of γ = 2.2) of the display panel 15 and updates the value of the first LUT 21 so as to cancel this deviation. Further, for example, the control unit 11 may update the value of the first LUT 21 by calculating a deviation (that is, secular change) of the measurement result with respect to the previous characteristic of the display panel 15 (characteristic of the measurement LUT 23). When a plurality of values of the first LUT 21 are stored in the storage unit 12, the control unit 11 updates all of them.

  For example, the control unit 11 may update the value of the second LUT 22 based on the measurement result of the sensor 16. The control unit 11 calculates a value that cancels the measurement result (a value corresponding to an inverse function of the measurement result) and sets the value in the second LUT 22. In this case, the control unit 11 stores a new LUT obtained from the measurement result in the storage unit 12 as the measurement LUT 23, and performs measurement using the measurement LUT 23 in the next measurement.

  FIG. 4 is a flowchart showing the procedure of the calibration process performed by the image display apparatus 1. For example, when an instruction to start calibration processing is given by an operation on the operation unit 13, the control unit 11 first moves the sensor 16 from a position accommodated in the housing to a measurement position on the display panel 15 (step S1). . Next, the control unit 11 switches the first LUT 21 to the measurement LUT 23 (step S2), and sets the gradation of the input image to R = G = B = 0 (step S3).

  Next, the control unit 11 sets any one color of RGB as the measurement target color, and after repeating the processes of steps S4 to S7 for this color, changes the measurement target color, and the sensor 16 for all colors. Measure. In detail, the control part 11 measures the output physical quantity with respect to the display image of the display panel 15 with the sensor 16 (step S4), and memorize | stores a measurement result in the memory | storage part 12 (step S5). The control unit 11 determines whether or not the gradation of the measurement target color at the time of measurement is the maximum gradation (255 in the case of 8 bits) (step S6). When the gradation is not the maximum gradation (S6: NO), the control unit 11 increases the gradation of the measurement target color by one gradation (step S7), returns the process to step S4, and repeats the measurement.

  When the gradation of the measurement target color is the maximum gradation (S6: YES), the control unit 11 determines whether the measurement has been completed for all the RGB colors (step S8). When the measurement of all colors has not been completed (S8: NO), the control unit 11 returns the process to step S3 and performs the same measurement using another unmeasured color as the measurement target color. When the measurement of all colors is completed (S8: YES), the control unit 11 moves the sensor 16 from the measurement position on the display panel 15 to the accommodation position in the housing (step S9).

  The control unit 11 calculates the difference between the measurement result stored in the storage unit 12 and the ideal characteristic of the display panel 15 (step S10), and updates the value of the first LUT 21 based on the calculated difference (step S11). Note that the control unit 11 performs the processing of steps S10 and S11 for each color of RGB. When the first LUT 21 is switchable, the control unit 11 updates all the first LUTs 21. Thereafter, the control unit 11 switches the measurement LUT 23 to the first LUT 21 (step S12) and ends the process.

  FIG. 5 is a graph showing a calibration accuracy verification result. In the image display device 1, the first LUT 21 is switched to the measurement LUT 23 as described above, the display panel 15 is measured, and the first LUT 21 is updated using the measurement result, and then an image having a gradation value of 0 to 255 is input. Then, the output gradation when displaying on the display panel 15 was measured, and the difference from the theoretical value was calculated to verify the calibration accuracy. In the illustrated graph, the horizontal axis represents the input gradation, and the vertical axis represents the error rate [%] from the theoretical value of the output gradation. The error rate in the image display apparatus 1 according to the present invention is indicated by a solid line (invention method) in the figure. For comparison, the error rate when the first LUT 21 is displayed and measured using the first LUT 21 and the first LUT 21 is updated using the measurement result is indicated by a broken line (conventional method) in the figure. is there.

  As shown in the graph, when the measurement is performed by the method of the present invention, the error rate is improved as compared with the case where the measurement is performed by the conventional method. In particular, a wide improvement effect is obtained in the range of input gradations 64 to 255, and a remarkable improvement effect is obtained around the input gradation 128. When the average error rate is calculated, the error rate is 0.75% in the conventional method, whereas it is reduced to 0.38% in the method of the present invention. Note that the improvement effect depends on the original gradation characteristics of the display panel 15 and is particularly effective when there is a gradation collapse. The effect also varies depending on the target gradation characteristics.

  Next, details of the measurement processing performed by the image display device 1 will be described with reference to specific examples. FIG. 6 is a graph showing an example of the characteristics of the display panel 15 to be measured, and the characteristics are illustrated by limiting the input gradation to a range of 14-22. FIG. 7 is a schematic diagram for explaining the measurement processing in the conventional image display device. The input gradation, the input / output value of the first LUT 21, the input / output value of the second LUT 22, and the display panel 15 are input. Are shown in order from the top. In the figure, 8-bit data is represented by an integer value, and data expanded to 9 bits or more is represented by a real value up to the first decimal place.

  In this example, it is assumed that a characteristic value of γ = 1.0 is set in the first LUT 21 and a characteristic value that cancels the characteristic shown in FIG. 6 is set in the second LUT 22. In the measurement processing of the conventional image display device shown in FIG. 7, for example, when the input gradation is 15, 15.0 is output by the first LUT 21 and 16.3 is output by the second LUT 22, On the other hand, the gradation value 16.3 (or gradation value 16 if this is converted to 8 bits) is input to the display panel 15. Similarly, a gradation value 14.0 is input to the display panel 15 for the input gradation 14, and a gradation value 18.0 is input to the display panel 15 for the input gradation 16. Therefore, the gradation values 15.0, 16.0, and 17.0 are not input to the display panel 15, and the output physical quantity of the display panel 15 corresponding to these gradation values cannot be measured.

  For example, when the output physical quantity of the display panel 15 corresponding to the input gradation 16 cannot be measured, the output gradation value for the input gradation value 16 is easily calculated when the value of the first LUT 21 is updated based on the measurement result. I can't. For example, the output physical quantity of the display panel 15 corresponding to the gradation value 16.0 is calculated from the output physical quantity of the display panel 15 corresponding to the measured gradation values 14.0 and 16.3 by interpolation or the like, and the calculation result The first LUT 21 is updated using. Since the value obtained by the interpolation process or the like includes an error, there is a possibility that the update accuracy is lowered.

  FIG. 8 is a schematic diagram for explaining measurement processing in the image display device 1 according to the present invention. In the image display apparatus 1 according to the present invention, a measurement LUT 23 is used instead of the first LUT 21 when the display panel 15 is measured. The measurement LUT 23 is set to a value that cancels the conversion of the second LUT 22. In the measurement processing of the image display device 1 shown in FIG. 8, for example, when the input gradation is 15, 14.3 is output by the measurement LUT 23 and 15.0 is output by the second LUT 22, On the other hand, a gradation value of 15.0 is input to the display panel 15. Similarly, the same gradation value of 14.0 to 22.0 is input to the display panel 15 regardless of the input gradation of 14 to 22. Therefore, the conversion of the first LUT 21 and the second LUT 22 is not performed on the input gradation, and the output physical quantity when the input gradation is directly input to the display panel 15 can be measured by the sensor 16.

  The image display device 1 having the above configuration converts the input image signal by the first LUT 21, performs image signal processing on the converted image signal by the image signal processing unit 14, and converts the processed image signal by the second LUT 22. And displayed on the display panel 15. The second LUT 22 stores a conversion value (output gradation value with respect to the input gradation value) for setting the γ characteristic of the display panel 15 to γ = 1.0, as viewed from the first LUT 21 and the image signal processing unit 14. As a result, the image signal processing unit 14 can perform image signal processing on the assumption that the display panel 15 has a characteristic of γ = 1.0, that is, a linear characteristic. Image signal processing can be performed at high speed.

  The image display device 1 switches the first LUT 21 to the measurement LUT 23 stored in the storage unit 12 when measuring the output physical quantity (luminance or chromaticity, etc.) of the display panel 15 with the sensor 16 for calibration or the like. The input image signal converted by the measurement LUT 23 and the second LUT 22 is displayed on the display panel 15 for measurement. The measurement LUT 23 stores a conversion value that cancels the conversion by the second LUT 22. Thereby, at the time of measurement, since the conversion of the first LUT 21 and the second LUT 22 is canceled, the output physical quantity of the display panel 15 (that is, the characteristics of the display panel 15 itself) when the first LUT 21 and the second LUT 22 are not present can be measured. . As a result, calibration processing such as updating of the first LUT 21 or the second LUT 22 can be accurately performed using the measurement result. Even in a configuration in which a plurality of first LUTs 21 are switched, an appropriate value of each first LUT 21 can be accurately calculated from the measurement result of the display panel 15 itself, so that it is not necessary to perform measurement for each first LUT 21 and calibration is performed. Can be performed in a short time.

  For example, the characteristics of the display panel 15 alone are measured in the manufacturing process of the image display device 1, and the measurement result is stored in the storage unit 12 as the measurement LUT 23, and the value corresponding to the inverse function of the measurement result is used as the second LUT 22. Can be set. Thereby, during the normal operation of the image display device 1, the characteristic of the display panel 15 can be canceled by the second LUT 22, and the γ characteristic of the display panel 15 can be set to γ = 1.0 as viewed from the image signal processing unit 14. At the time of measurement, the conversion of the second LUT 22 can be canceled by the measurement LUT 23, and the characteristics of the display panel 15 itself can be measured by the sensor 16.

  In the present embodiment, the image display device 1 includes the sensor 16, but the present invention is not limited to this. For example, it is good also as a structure which provides a sensor in PC5 and performs a measurement and transmits a measurement result to the control part 11 of the image display apparatus 1. FIG. Further, although the image display device 1 is configured to perform color display, it may be configured to perform monochrome display.

  Further, the image display device 1 performs measurement by increasing the input gradation from 0 to 255 one by one in RGB single color display, and outputs the display panel 15 by the sensor 16 in the procedure of performing this measurement for all colors. Although the physical quantity was measured, this procedure is an example, and the measurement may be performed by any other procedure. Further, instead of measuring all the gray levels from 0 to 255, it may be configured to measure only some of the necessary gray levels. The calibration method (update of the first LUT 21 or the second LUT 22) performed by the image display apparatus 1 may be any method. Therefore, the measurement by the sensor 16 may be performed by a method suitable for the calibration method.

  The second LUT 22 has a configuration in which a conversion value that sets the display panel 15 to have a characteristic of γ = 1.0 as viewed from the image signal processing unit 14 is set, but the present invention is not limited to this. For example, a conversion value that makes the display panel 15 have a characteristic such as γ = 2.0 when viewed from the image signal processing unit 14 may be set in the second LUT 22. Even in this case, the original characteristic of the display panel 15 (γ = 2.2 in many cases), the processing of the image signal processing unit 14 can be facilitated.

(Modification)
FIG. 9 is a block diagram illustrating a configuration of an image display system according to a modification. The image display system according to the modification is configured such that the PC 205 includes the first LUT 21, the image signal processing unit 14, and the second LUT 22. The PC 205 stores an image display program 210 in the storage unit 12. The control unit 211 of the PC 205 reads the image display program 210 from the storage unit 12 and executes it, whereby the image generation unit 217, the first LUT 21, the image signal processing unit 14, and the second LUT 22 are realized as software functional blocks. The PC 205 generates an image signal related to an image for display by the image generation unit 217 in response to an operation by a user or the like, converts the generated image signal by the first LUT 21, performs image signal processing by the image signal processing unit 14, and Conversion by the second LUT 22 is performed, and the image signal after these processes is input to the image display device 201. The image display device 201 performs image display according to the input image signal.

  When performing calibration, the user attaches the sensor 16 connected to the PC 205 to the display surface of the image display apparatus 201. The PC 205 stores the measurement LUT 23 in the storage unit 12, and the control unit 211 performs measurement by the sensor 16 by switching the first LUT 21 to the measurement LUT 23. Thereafter, the control unit 211 updates the first LUT 21 or the second LUT 22 based on the measurement result.

  As described above, the processing by the first LUT 21, the image signal processing unit 14, and the second LUT 22 may be performed by any of the PC and the image display device. For example, the first LUT 21 may be processed by a PC, and the image display device 14 and the second LUT 22 may be processed by the image display device. Further, when some or all of the first LUT 21, the image signal processing unit 14, and the second LUT 22 are provided in the PC, these parts or all may be realized in the control unit 211 as software functional blocks as shown in FIG. 9. Alternatively, it may be realized as a hardware functional block outside the control unit 211. Similarly, in the image display apparatus 1 shown in FIG. 1, the first LUT 21, the image signal processing unit 14, and the second LUT 22 are implemented as hardware functional blocks, but some or all of these are implemented as software functional blocks. You may implement | achieve in the control part 11. FIG. In this case, an image display program similar to that shown in FIG. 9 is stored in the storage unit 12 of the image display device 1, and the control unit 11 reads and executes the image display program, whereby the first LUT 21, the image signal processing unit 14, and The function of the second LUT 22 is realized. In any configuration, when measuring the display panel 15 using the sensor 16, the measurement LUT 23 is used instead of the first LUT 21.

1 image display device 5 PC (image signal output device, computer)
11 Control unit (table switching means, updating means)
12 storage unit 13 operation unit 14 image signal processing unit 15 display panel (display device)
16 Sensor (measuring means)
21 First LUT (first lookup table)
22 Second LUT (second lookup table)
23 LUT for measurement (third lookup table)
201 Image display device 205 PC (image signal output device, computer)
210 Image display program (computer program)
211 control unit (table switching means, update means)
217 Image generation unit

Claims (7)

A first look-up table for converting the gradation value of the input image signal, an image signal processing unit for performing image signal processing on the image signal converted by the first look-up table, and processing performed by the image signal processing unit An image display apparatus comprising: a second look-up table for converting a gradation value of an image signal subjected to the image signal; and a display device for displaying an image related to the image signal converted by the second look-up table. ,
A third lookup table storing the correspondence between the input gradation value and the output gradation value that cancels the conversion by the second lookup table;
Measuring means for measuring an output physical quantity of the display device;
An image display device comprising: table switching means for switching the first lookup table to the third lookup table when the measurement means performs measurement. 2. The image display device according to claim 1, wherein the second look-up table stores a conversion value that causes the display device to have a γ characteristic of γ = 1.0 when viewed from the image signal processing unit. . The third look-up table stores correspondences between input gradation values and output gradation values corresponding to the γ characteristics of the display device,
The second look-up table stores a correspondence between an input gradation value and an output gradation value corresponding to an inverse function of the γ characteristic of the display device. Image display device. The update means which updates the said 1st lookup table or the said 2nd lookup table according to the measurement result of the said measurement means is further provided. The Claim 1 thru | or 3 characterized by the above-mentioned. Image display device. In an image display system comprising an image display device having a display device for displaying an image, and an image signal output device for outputting an image signal related to an image displayed on the image display device,
A first lookup table for converting a gradation value of an image signal output from the image signal output device;
An image signal processing unit that performs image signal processing on the image signal converted by the first lookup table;
A second lookup table for converting the gradation value of the image signal processed by the image signal processing unit;
A third lookup table storing the correspondence between the input gradation value and the output gradation value that cancels the conversion by the second lookup table;
Measuring means for measuring an output physical quantity of the display device;
Table switching means for switching the first lookup table to the third lookup table when the measurement means performs measurement, and
The first look-up table, the image signal processing unit, the second look-up table, and the measurement unit are provided in the image display device or the image signal output device,
The image display system, wherein the third look-up table and the table switching means are provided in the image display device or the image signal output device provided with the first look-up table. A first look-up table for converting the gradation value of the input image signal, an image signal processing unit for performing image signal processing on the image signal converted by the first look-up table, and processing performed by the image signal processing unit In an image display system comprising: a second look-up table for converting the gradation value of the image signal that has been performed; and a display device that displays an image related to the image signal converted by the second look-up table, A measurement method for measuring an output physical quantity of the display device,
A third lookup table storing the correspondence between the input gradation value and the output gradation value that cancels the conversion by the second lookup table;
Switching the first lookup table to the third lookup table and measuring the output physical quantity of the display device. A first look-up table for converting the gradation value of the input image signal, an image signal processing unit for performing image signal processing on the image signal converted by the first look-up table, and processing performed by the image signal processing unit The image display system includes a second look-up table for converting the gradation value of the image signal subjected to the image processing, and a display device that displays an image related to the image signal converted by the second look-up table. A computer program for causing a computer to measure an output physical quantity of the display device,
Storing a third look-up table storing the correspondence between the input tone value and the output tone value that cancels the conversion by the second look-up table;
In the computer,
Switching the first lookup table to the third lookup table;
And executing a process of measuring an output physical quantity of the display device.

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