JP2017134361A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device capable of accurately correcting a secular change of gamma characteristics even when a state of the light source of an image forming device and the like changes.SOLUTION: An image forming device is constituted of including: a display element for displaying an image; a measurement part for performing a measurement relating to the gamma characteristics during the driving of the display element; a storage part for storing first measurement data acquired by the measurement part when making the display element driven based on the predetermined gamma characteristics display the predetermined measurement pattern; a pattern change part for changing the measurement pattern, and the first measurement data; and a correction part for correcting the gamma characteristics based on the second measurement data acquired by the measurement part when making the measurement pattern different from the predetermined measurement pattern by the pattern change part display.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image display device such as a liquid crystal projector that displays an image using a liquid crystal display element.

  An image display device using a liquid crystal display element may change with time in gamma characteristics with long-term use. For example, in a liquid crystal projector, the gamma characteristic of a liquid crystal display element may fluctuate due to strong light irradiation on the liquid crystal layer or moisture penetration from the outside. When the gamma characteristic changes with time, the monitor gamma value, which is the color of the display image, deviates from a predetermined standard value (for example, sRGB standard γ = 2.2), and the image quality deteriorates.

  When a color image is displayed by modulating different colors with a plurality of liquid crystal display elements, such as a three-plate liquid crystal projector, the achromatic color may be colored due to the difference in the amount of gamma fluctuation between the liquid crystal display elements. The image quality is also degraded.

  Patent Document 1 discloses a technique for measuring a time-dependent change in gamma characteristics of an image display device by a light detection unit in the image display device, calculating a time-dependent change amount of the gamma characteristics from the measurement result, and performing correction. ing.

JP 2013-228577 A

  However, the conventional techniques disclosed in the above-mentioned patent documents do not consider that the correction accuracy decreases when the light amount of the light source decreases due to the deterioration of the light source of the image display device.

  Accordingly, the present invention is to provide an image display device capable of accurately correcting a change with time in gamma characteristics even when the state of a light source or the like of the image display device changes.

  In order to achieve the above object, the present invention provides a display element for displaying an image, a measurement unit for measuring gamma characteristics when driving the display element, and the display element driven based on a predetermined gamma characteristic. A storage unit that stores the first measurement data acquired by the measurement unit when displaying a predetermined measurement pattern, a pattern change unit that changes the measurement pattern, the first measurement data, A correction unit that corrects gamma characteristics based on second measurement data acquired by the measurement unit when a measurement pattern different from the predetermined measurement pattern is displayed by the pattern change unit. Features.

  According to the present invention, it is possible to provide an image display device capable of accurately correcting a change with time in gamma characteristics even when the state of a light source or the like of the image display device changes.

The figure which shows the structure of a liquid crystal projector. The figure which shows the structure of the optical system of a liquid crystal projector. The figure regarding the characteristic of a display element. The figure which shows an example of a gamma conversion table. The figure which shows an example of a time-dependent change of a gamma characteristic. The flowchart of the pre-processing for gamma conversion table correction | amendment. Flow chart of real gamma measurement. The figure which shows an example of the measurement pattern of each gradation used for an initial real gamma measurement. The figure which showed the relationship between the actual gamma characteristic and the correction amount of a gamma conversion table. Explanatory drawing of the predetermined gradation and background measured value by light quantity. Explanatory drawing of the gamma characteristic before and after a light quantity fall. FIG. 12 is an enlarged view near the 100th gradation in FIG. 11. The figure which normalized FIG. 8 with the maximum value. FIG. 14 is an enlarged view near the 100th gradation in FIG. 13. The flowchart of a gamma conversion table correction process. The figure which shows an example of the measurement pattern of each gradation used for the real gamma measurement after time passage. FIG. 10 is a diagram illustrating an example of a measurement pattern for each gradation used for initial actual gamma measurement in the second embodiment. The figure which shows the measurement pattern of each gradation used for the real gamma measurement after time-lapse in Example 2. FIG.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  Hereinafter, a liquid crystal projector according to a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 2 is a block diagram showing the configuration of the optical system 200 of the liquid crystal projector 100.

  The light emitted from the light source 201 is converted into polarized light having a uniform polarization direction by the illumination optical system 202, and the intensity distribution is made uniform. The light emitted from the illumination optical system 202 is separated into G light and RB light by the dichroic mirror 203. Here, the G light is Green light and is abbreviated as “G light”. Similarly, Red light is abbreviated as “R light”, Blue light as “B light”, and Red light and Blue light are collectively abbreviated as “RB light”.

  The G light transmitted through the dichroic mirror 203 is reflected by a PBS (polarization beam splitter) 204 and enters the G liquid crystal display element 207G. The G light modulated by the G liquid crystal display element 207G passes through the PBS 204, is reflected by the PBS 206, and travels toward the projection optical system 208. Of the RB light reflected by the dichroic mirror 203, the B light has its polarization direction rotated 90 degrees by a wavelength-selective polarizing plate (not shown), passes through the PBS 205, and enters the B liquid crystal display element 207B. The B light modulated by the B liquid crystal display element 207B is reflected by the PBS 205, passes through the PBS 206, and travels toward the projection optical system 208.

  On the other hand, of the RB light reflected by the dichroic mirror 203, the R light is reflected by the PBS 205 and enters the R liquid crystal display element 207R. The R light modulated by the R liquid crystal display element 207R passes through the PBS 205 and the PBS 206 and travels toward the projection optical system 208.

  The G light, B light, and R light that form the projected image are combined by the PBS 206 and projected onto a screen (not shown) or the like by the projection optical system 208.

  An optical sensor 209 is disposed on the surface of the PBS 206 that does not transmit any of the G light, R light, and B light (hereinafter also referred to as display light) toward the projection optical system 208. The optical sensor 209 (measurement unit) measures the light amount of the leaked light by using the characteristic that the PBS 206 generates a certain amount of leaked light with respect to the RGB display light. By measuring the amount of leakage light, the light intensity (luminance) of the projected image can be indirectly measured.

  As described above, the liquid crystal projector 100 forms a projected image by modulating the light from the light source 201 by the liquid crystal display element 207 in accordance with the image signal.

  FIG. 1 is a block diagram showing the configuration of the liquid crystal projector 100.

  An image signal is input to the image processing unit 101 via a video cable (not shown) from a video player (not shown) which is an external image supply device. The image signal input to the image processing unit 101 is subjected to various image processing such as brightness correction, contrast correction, and color conversion processing, and is converted into an image signal suitable for driving the liquid crystal display element 207. The converted image signal is input to the gamma conversion circuit 102.

  The optical system 200 is the optical system described with reference to FIG. As the liquid crystal display element 207, the RGB liquid crystal display elements 207R, 207G, and 207B are collectively shown as the liquid crystal display element 207.

  When a liquid crystal driving voltage proportional to the gradation (input gradation) of the image signal is applied, the liquid crystal display element 207 follows a non-linear voltage-transmission (or reflection) characteristic (VT characteristic) as shown in FIG. The display light with a sufficient amount of light is emitted.

  The gamma conversion circuit 102 performs a gradation conversion process on the image signal using a gamma conversion table (gamma data) as shown in FIG. 4, and a gamma characteristic indicating the relationship between the input gradation and the display light (output gradation). Is an appropriate gamma value (for example, sRGB standard γ = 2.2).

  The storage unit 106 includes a nonvolatile memory, and stores a plurality of gamma conversion tables (LUTs) 107 and initial measurement luminance data 108 (measurement value memory) obtained by an optical sensor 209 described later.

  The image signal subjected to gamma conversion by the gamma conversion circuit 102 is input to the liquid crystal driving unit 103. The liquid crystal driving unit 103 generates a liquid crystal driving voltage corresponding to the gradation (input gradation) of the image signal and applies it to the liquid crystal display element 207 to drive the liquid crystal display element 207.

  The optical sensor 209 photoelectrically converts the above-described leakage light and outputs an electrical signal having a value corresponding to the amount of the leakage light. An electrical signal as an analog signal output from the optical sensor 209 is converted into a digital signal by the AD converter 104 and input to the CPU 105.

  The CPU 105 controls each operation of the liquid crystal projector 100, and performs luminance measurement by the optical sensor 209, calculation of a gamma conversion table, and table setting in a gamma correction table, which will be described later. The CPU 105 also serves as a pattern changing unit that changes the measurement pattern for correcting the gamma conversion table and a correction unit that corrects the gamma conversion table.

  Here, the liquid crystal projector 100 may change with time in the VT characteristics of the liquid crystal display element 207 with long-term use. For example, the VT characteristics fluctuate due to intense light irradiation on the liquid crystal layer or moisture penetration from the outside. If the gamma conversion table is used as it is when the VT characteristic fluctuates, the gamma characteristic changes as a result, deviating from an appropriate gamma value (for example, sRGB standard γ = 2.2), and the image quality deteriorates. .

  FIG. 5 shows an example of the change with time of the gamma characteristic. Reference numeral 501 denotes a gamma characteristic set to γ = 2.2 by gamma adjustment in the production process of the liquid crystal projector. On the other hand, reference numeral 502 denotes a gamma characteristic in which the halftone becomes brighter because the VT characteristic fluctuates due to a change with time but the gamma conversion table is not changed.

  Therefore, in this embodiment, the gamma characteristic that has changed with time is measured, a gamma conversion table that takes into account the change from the gamma characteristic adjusted in the production process is calculated, and is set in the gamma conversion circuit 102. Here, the actual gamma characteristic actually obtained with the liquid crystal display element 207 (that is, the liquid crystal projector) is changed from the gamma characteristic before the start of user use (gamma characteristic adjusted in the production process) to the time-dependent change with use. A case of changing to a bright gamma characteristic will be described. However, even when the actual gamma characteristic changes from the gamma characteristic before the start of user use to a gamma characteristic that becomes darker, the following gamma conversion table correction processing can be similarly applied.

  First, the flowchart of FIG. 6 shows a pre-processing procedure for gamma conversion table correction performed in the production process of the liquid crystal projector of this embodiment. The entire correction processing including this pre-processing is executed by the CPU 105 as the pattern changing unit and the correcting unit in accordance with the computer program.

  In STEP 601, the CPU 105 performs gamma adjustment, and determines a setting value for the gamma conversion circuit 102 so that the gamma characteristic becomes a predetermined gamma characteristic (for example, γ = 2.2). For example, the amount of light from the liquid crystal display element 207 is measured using an external luminance meter (not shown) or the like, and a set value for the gamma conversion circuit 102 so that a predetermined gamma characteristic is obtained based on the measurement result. To decide.

  Next, in STEP 602, the CPU 105 writes the setting value for the gamma conversion circuit 102 determined in STEP 601 into the storage unit 106 as an initial gamma conversion table.

  Next, in STEP 603, the CPU 105 drives the liquid crystal display element using the initial gamma conversion table set in STEP 601, and measures the actual gamma characteristic at that time by the optical sensor 209.

  The flowchart in FIG. 7 is a detailed procedure of STEP 603.

  In STEP 701, the CPU 105 determines a liquid crystal display element for measuring the actual gamma characteristic from among RGB.

  Next, in STEP 702, the CPU 105 displays an image with a predetermined gradation on the liquid crystal display element to be measured.

  Next, in STEP 703, when the CPU 105 displays an image of a predetermined gradation in STEP 702, the optical sensor 209 measures the luminance of the leaked light.

  Next, in STEP 704, the CPU 105 determines whether or not measurement for a predetermined gradation has been completed. When the measurement for the predetermined gradation is not completed, the process returns to STEP 702 again. When measurement for a predetermined gradation is completed, the process proceeds to STEP 705.

  In this embodiment, the luminance is measured with seven gradations, the characteristics of gradation and luminance are acquired, and the actual gamma characteristic is measured. FIG. 8 shows a measurement pattern to be displayed on the liquid crystal display element when the luminance of the seven gradations is measured by the optical sensor. Here, the number of pixels of the measurement pattern to be displayed is S0 (area indicated by 802), and the number of effective pixels of the liquid crystal display element is Sa (area indicated by 801 including 802). A solid line 901 in FIG. 9A shows an example of the measured actual gamma characteristic (gradation-luminance characteristic), and almost coincides with the gamma characteristic 501.

  Next, in STEP 705, the CPU 105 determines whether or not the measurement of the RGB liquid crystal display elements is finished. If the measurement of the liquid crystal display elements for RGB has not been completed, the process returns to STEP 701 again. When the measurement of each of the liquid crystal display elements for RGB is completed, the process ends.

  Next, in STEP 604, the CPU 105 performs the luminance measurement of the optical sensor 209 and the background measurement (for example, measurement data of a gradation of 0) in the measurement pattern shown in FIG. This is done for each display element. As shown in FIG. 10, the measured value measured at a predetermined gradation by the optical sensor 209 is L0 (1001), and the background of the optical sensor 209 is BK0 (1002).

  In this embodiment, the measurement by the optical sensor 209 is performed at the predetermined gradation (1001) shown in FIG. 10, but the measurement may be performed at a gradation different from the gradation shown in FIG. The measurement pattern displayed on the liquid crystal display element may be a measurement pattern other than that shown in FIG. The actual gamma characteristic result measured in STEP 703 can also be used.

  Next, in STEP 605, the CPU 105 measures the measured data of the actual gamma characteristics in the production process (first measured data that is the initial actual gamma characteristics), the luminance value of the optical sensor 209 at a predetermined gradation, and the back. The ground luminance is stored in the storage unit 106. Further, the CPU 105 sets an initial gamma conversion table as a gamma table used for driving the liquid crystal display element after the start of use by the user. Then, the preprocessing for gamma conversion table correction ends.

  Thereafter, when the gamma characteristic changes with time as the user uses the liquid crystal projector, the gamma conversion table is corrected. When performing the correction process, the state of the light source or the like may change with use by the user, and the amount of light may decrease. If correction processing is performed in a state where the amount of light is reduced, the correction accuracy decreases.

  The correction accuracy when the light amount decreases will be described with reference to FIGS.

  In FIG. 11, 1101 indicates an actual gamma characteristic measured by the optical sensor 209 in the production process, and 1102 indicates an actual gamma characteristic when measured using the measurement pattern used in the production process when the amount of light decreases. .

  FIG. 12 is an enlarged view of the vicinity of 100 gradations in FIG. 11, assuming that the light amount is not reduced 1101, the light amount is reduced 1102, and noise is superimposed on each specific gradation (1201, 1202). FIG.

  FIG. 13 is a diagram illustrating the actual gamma characteristics obtained by normalizing the actual gamma characteristics of FIG. 11 with respective luminance maximum values. FIG. 14 is an enlarged view around the 100th gradation in FIG. When the amount of light decreases, the dynamic range decreases and the measurement resolution decreases. Therefore, when the same noise is applied to a specific gradation, as shown by 1201 and 1202 in FIG. 14, the influence of noise increases when the amount of light decreases. When a correction error occurs due to the influence of such noise when correction is performed, fluctuations near some gradations increase, and image quality such as color misregistration deteriorates.

  Therefore, in this embodiment, the light amount is detected by the optical sensor, and the measurement pattern to be displayed is changed according to the light amount, so that the light amount input to the optical sensor can be controlled and the change with time can be corrected accurately. I have to.

  The flowchart of FIG. 15 shows the procedure of the correction process when the gamma characteristic changes with time as the liquid crystal projector of this embodiment is used by the user.

  In STEP1501, the CPU 105 measures the measurement value L0 and the background BK0 in the pre-processing, and similarly measures the measurement value L1 (1003 in FIG. 10) and the background as BK1 (1004 in FIG. 10). (Third measurement data) is performed.

Next, in STEP 1502, based on the measurement result of STEP 1501 and the measurement result in the preprocessing, the CPU 105 calculates the number of pixels S1 after changing the measurement pattern when used for the measurement of the actual gamma characteristic by the following formula. To do.
S1 = (L0−BK0) / (L1−BK1) × S0 (1)
L0: Initial measured value of predetermined gradation
BK0: Background measurement at the time of L0 acquisition
L1: Measurement value of a predetermined gradation after time
BK1: Background measurement at the time of L1 acquisition
S0: Number of pixels at the time of initial measurement data acquisition However, if S1 ≧ Sa, S1 = Sa

  That is, the number of display pixels used in the measurement pattern is calculated after the time according to the ratio of the measurement data of the initial predetermined gradation and the measurement data of the predetermined gradation after the time.

  Next, in STEP 1503, the CPU 105 changes the measurement pattern based on S <b> 1 calculated in STEP 1502 for the number of pixels of the measurement pattern to be used for measuring the actual gamma characteristic.

  FIG. 16 shows an example of the changed measurement pattern. As indicated by 1602, the number of display pixels of the measurement pattern (display area on the display element) is changed so as to be within a predetermined range with the calculated pixel number S1 as the center. As a result, the measurement data when the predetermined gradation is displayed with the initial measurement pattern in the initial state and the measurement data when the measurement pattern is changed and the predetermined gradation is displayed after the change with time are substantially matched. Can do.

  Therefore, the decrease in the amount of light can be compensated for by changing the measurement pattern, the measurement resolution can be made substantially coincident with the initial state, and the change with time can be corrected with high accuracy.

  Next, in STEP 1504, the CPU 105 measures the actual gamma characteristic in the same manner as the measurement of the actual gamma characteristic in the preprocessing, using the measurement pattern changed in STEP 1503, according to the flowchart of FIG. (Second measurement data)

  Next, in STEP 1505, the CPU 105 determines a liquid crystal display element for performing gamma conversion table correction from among RGB.

  Next, in STEP 1506, the CPU 105 performs initial real gamma characteristics (first measurement data) stored in the storage unit 106 and real gamma characteristics after the lapse (second measurement) for the liquid crystal display element to be corrected. The amount of change in a certain gradation is calculated from the difference in the measurement data. Using this change amount, an amount for correcting the gamma conversion table is calculated.

  The measurement value at 80 gradations in FIG. 9A will be described as an example. Assume that the actual gamma characteristic 2002 after the lapse of time is measured with respect to the initial actual gamma characteristic 2001. The amount of change over time is 2003.

  On the other hand, as the correction amount of the gamma conversion table shown in FIG. 9B, the correction amount is calculated so as to correct the change amount 2003 over time in 80 gradations with respect to the initial gamma conversion table 904. That is, by calculating the correction amount 2006 so that the set value 2007 of 80 gradations becomes the set value 2008 as the correction amount of the gamma conversion table, it is possible to correct the change with time of the gamma characteristic.

  STEP 1507 determines whether or not measurement for a predetermined gradation has been completed. If the measurement for the predetermined gradation has not been completed, the process returns to STEP 1506 again. When measurement for a predetermined gradation is completed, the process proceeds to STEP 2209.

  After calculating the correction amount at each measurement point according to the flow of STEP 1506 and STEP 1507, the gamma conversion table is corrected by performing interpolation calculation from these correction amounts, and a new gamma conversion table 905 is obtained. Thereby, the difference between the initial gamma characteristic and the gamma characteristic after change with time can be made equal to or less than a predetermined threshold value, and the initial gamma characteristic and the gamma characteristic after time can be substantially matched.

  Next, in STEP 1508, the CPU 105 determines whether or not the correction of the RGB liquid crystal display elements is finished. If correction of the liquid crystal display elements for RGB has not been completed, the process returns to STEP 1505 again. When the correction of the liquid crystal display elements for RGB is completed, the process ends.

  As explained above, even when the actual gamma measurement after lapse of time, the amount of light decreases and the amount of light received by the optical sensor decreases, the amount of light received by the optical sensor is corrected by changing the measurement pattern of the actual gamma measurement, The gamma conversion table can be corrected with high accuracy.

  A liquid crystal projector according to the second embodiment of the present invention will be described below with reference to FIGS.

  Since the configuration of the liquid crystal projector 100 of the present embodiment is the same as that of the first embodiment, description thereof is omitted.

  The flowchart in this embodiment is the same as that in the first embodiment. The difference from the first embodiment is that two types of measurement patterns are used when measuring the actual gamma characteristics.

  FIG. 17 shows an example of a measurement pattern used when measuring the actual gamma characteristic in the preprocessing. In this embodiment, the measurement pattern 1701 from the intermediate gradation to the low gradation side and the measurement pattern 1702 from the intermediate gradation to the high gradation side are changed.

  On the low gradation side, since the brightness to be displayed is dark, the amount of leakage light that can be measured by the optical sensor 209 is also reduced. Therefore, by increasing the number of pixels in the measurement pattern on the low gradation side than the number of pixels in the measurement pattern on the high gradation side, the amount of leakage light that can be measured by the optical sensor 209 can be increased, and the dynamics on the low gradation side can be increased. The range can be increased.

  However, in the case of the same number of pixels in the measurement pattern as that on the low gradation side, the amount of leakage light that can be measured by the optical sensor 209 may be saturated particularly on the high gradation side. The number is smaller than the number of pixels in the measurement pattern on the key side.

  In addition, the luminance of the optical sensor 209 at a predetermined gradation is measured by setting a specific gradation for each of the two measurement patterns.

  In the actual gamma measurement after the change with time, the measurement pattern is changed in the same manner as in Example 1 for each of the two measurement patterns. FIG. 18 shows an example of a changed measurement pattern.

  Using the changed measurement pattern 1801 on the low gradation side and measurement pattern 1802 on the high gradation side, respectively, the gamma conversion table is corrected as in the first embodiment.

  As described above, by using two types of measurement patterns for actual gamma measurement, the dynamic range on the low gradation side can be further expanded. Furthermore, even if the amount of light decreases during the actual gamma measurement after lapse of time and the amount of light received by the optical sensor decreases, the amount of light received by the optical sensor is corrected by changing each of the two types of measurement patterns of actual gamma measurement, The gamma conversion table can be corrected with high accuracy.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  For example, in addition to the rectangular measurement pattern, the measurement pattern may be displayed in a checkered pattern, or a vertical line pattern, a horizontal line pattern, or the like may be used.

  In the second embodiment, two measurement patterns are used. However, two or more measurement patterns may be used.

  The present invention is effective in changing the gamma characteristic of an image display device.

DESCRIPTION OF SYMBOLS 100 Liquid crystal projector 207 Liquid crystal display element 209 Optical sensor 105 CPU
106 Storage unit

Claims (8)

A display element for displaying an image;
A measurement unit for measuring gamma characteristics when driving the display element;
A storage unit for storing first measurement data acquired by the measurement unit when a predetermined measurement pattern is displayed on the display element driven based on a predetermined gamma characteristic;
A pattern change unit that changes the measurement pattern, the first measurement data, and a second measurement acquired by the measurement unit when a measurement pattern different from the predetermined measurement pattern is displayed by the pattern change unit. A correction unit for correcting gamma characteristics based on the data;
An image display device comprising: The pattern changing unit includes measurement data at a predetermined gradation among the stored first measurement data,
With the use of the image display device, a third acquired by the measurement unit at the predetermined gradation when the predetermined measurement pattern is displayed on the display element driven based on the predetermined gamma characteristic. Measurement data and
The image display apparatus according to claim 1, wherein the measurement pattern is changed based on the parameter.   3. The pattern changing unit changes the measurement pattern according to a ratio between measurement data at a predetermined gradation of the first measurement data and the third measurement data. The image display device described in 1. 4. The correction unit according to claim 1, wherein the correction unit corrects the gamma characteristic so that the first measurement data matches the second measurement data. 5. Image display device.   The image display apparatus according to claim 1, wherein the pattern changing unit changes a display area of the measurement pattern on the display element. The pattern changing unit
As the first measurement data, the measurement value L0 at a predetermined gradation, the background measurement value at the time of acquiring the L0 is BK0, and as the third measurement data, the measurement value L1 at the predetermined gradation, at the time of acquiring the L1. When the background measurement value is BK1, the display pixel number of the measurement pattern at the time of obtaining the first measurement data is S0, and the changed display pixel number is S1,
S1 = (L0−BK0) / (L1−BK0) × S0
The image display apparatus according to claim 2, wherein the number of display pixels on the display element of the measurement pattern is changed based on S <b> 1. The storage unit includes first gamma data for driving the display element based on the predetermined gamma characteristic, and a second gamma data for driving the display element based on a gamma characteristic different from the predetermined gamma characteristic. Store the gamma data of
The correction unit rewrites the second gamma data so that the first measurement data matches the second measurement data acquired by using the first gamma data. Item 7. The image display device according to any one of Items 1 to 6.   The image display apparatus according to claim 1, wherein the pattern changing unit includes a plurality of types of measurement patterns.