JP2015043091A - Image display device and image display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology about image display using a liquid crystal panel.SOLUTION: An image display device includes: a liquid crystal panel which includes a plurality of liquid crystal cells, where each liquid crystal cell is controlled on the basis of display characteristics defined as change in optical characteristics to an input signal, thereby the image display device displays an image; a characteristic relaxation section which receives input of a gray-scale signal having characteristics whose rate of change is reduced compared with the rate of change of inclination of display characteristics specific to each liquid crystal cell, generates driving voltage adapted to the rate of change of the inclination of the display characteristics specific to each liquid crystal cell, and inputs the driving voltage into the liquid crystal panel as an input signal; and an unevenness correction processing circuit which, in order to suppress occurrence of unevenness caused by variation of the display characteristics in a panel face, refers to a characteristic value indicating the display characteristics whose rate of change of the liquid crystal cells is reduced, generates an unevenness correction image signal by correcting the gamma corrected gray-scale data corresponding to image data, inputs the unevenness correction image signal into the characteristic relaxation section as the gray-scale signal, and generates driving voltage.

Description

  The present invention relates to a technique for image display using a liquid crystal panel.

  A display device using a liquid crystal panel, for example, a 3LCD type liquid crystal projector, is not uniform in characteristics of each liquid crystal panel such as transmittance or reflectance (hereinafter also referred to as display characteristics) and spectral irradiation intensity from the light source to the liquid crystal panel. And uneven brightness may occur. Variation in characteristics for each primary color (red, green, blue), that is, for each liquid crystal panel, particularly variation in display characteristics within the liquid crystal panel surface, results in “color unevenness” in the projected color image. In order to reduce such color unevenness, a projector equipped with a color unevenness correction circuit is known (Patent Document 1 below).

JP 2005-115400 A

  Such a color unevenness correction circuit is a circuit that corrects variations in display characteristics (hereinafter also referred to as “characteristic unevenness”) within the plane of each liquid crystal panel (red, green, and blue), and is an image signal input to a liquid crystal projector. In accordance with the above, in the process of generating a signal for driving each liquid crystal panel, a correction value related to the position of each liquid crystal cell constituting the liquid crystal panel is added to the data value corresponding to the gradation included in the image signal. By doing so, the reduction in characteristic unevenness is realized. The color unevenness correction circuit has correction value data (hereinafter also referred to as correction data) for each specific gradation value of the image signal. When the gradation value of the input image signal (hereinafter also referred to as input gradation value) is a value other than the specific gradation value, correction of two specific gradation values sandwiching the input gradation value A correction value corresponding to the input gradation value is calculated by linearly interpolating the values. Then, the gradation value data corrected based on the calculated correction value is converted into the value of the voltage applied to each liquid crystal cell and input to the liquid crystal panel.

  However, the “applied voltage-transmittance characteristics (hereinafter also referred to as VT characteristics)” of each liquid crystal cell constituting the liquid crystal panel is not a straight line, but an S-shaped curve having a point where the slope changes abruptly. When the input gradation value is corrected using a correction value obtained by performing linear interpolation between specific gradation values, an error may occur in the correction value, and in some cases, it may appear as color unevenness. It was pointed out.

  In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.

[Application Example 1]
An image display device that displays an image based on input image data, and is composed of a plurality of liquid crystal cells, and each liquid crystal cell is controlled based on display characteristics defined as changes in optical characteristics with respect to an input signal. Accordingly, a gradation signal having a characteristic in which the change rate is reduced as compared with the change rate of the inclination of the display characteristic specific to each liquid crystal cell and the liquid crystal panel for displaying an image is input. A characteristic relaxation unit that generates a driving voltage suitable for the change rate of the inclination of the display characteristic inherent to the cell and inputs it to the liquid crystal panel as the input signal, and suppresses occurrence of unevenness due to variations in display characteristics within the panel surface Therefore, a characteristic value representing a display characteristic in which the liquid crystal cell at a predetermined position in the plane of the liquid crystal panel is specified and prepared, and the rate of change of the specified liquid crystal cell is reduced A non-uniformity correction processing circuit that generates a non-uniformity correction image signal obtained by correcting gamma-corrected grayscale data corresponding to the image data, inputs the grayscale signal to the characteristic relaxation unit, and generates the drive voltage; An image display device comprising:

  The image display device includes a characteristic relaxation unit. When the display characteristics of the liquid crystal cell are evaluated through the characteristic relaxation unit, it can be evaluated as a display characteristic having a change rate lower than the change rate of the inclination of the actual display characteristic of the liquid crystal cell. Therefore, by providing the characteristic relaxation unit in the previous stage of the liquid crystal panel, it can be controlled as a liquid crystal panel including a liquid crystal cell exhibiting display characteristics with a low change rate of inclination. Here, the “gradient” of the display characteristic is, for example, “change in transmittance (T) with respect to the applied voltage (V) in the VT characteristic (applied voltage-transmittance characteristic) of the liquid crystal cell which is one of the display characteristics. Say "Rate". That is, in this example, the “inclination change rate” corresponds to a twice-differentiated value based on the applied voltage (V) in the VT characteristic. The unevenness correction processing circuit can be regarded as a liquid crystal panel having such characteristics, and can suppress the occurrence of unevenness due to variations in display characteristics of the liquid crystal cell within the panel surface. In addition, as a display characteristic, the transmittance | permeability and the reflectance with respect to the applied voltage of a liquid crystal cell are mentioned, for example.

[Application Example 2]
The image display device according to Application Example 1, wherein the characteristic relaxation unit generates the drive voltage to be output to the liquid crystal panel in response to the unevenness correction image signal input from the unevenness correction processing circuit. An image display device including a lookup table to be referred to.

  According to this image processing display device, since the characteristic relaxation unit includes the lookup table, the processing can be performed at a higher speed than when all processing is performed by calculation.

[Application Example 3]
The image display device according to Application Example 1 or Application Example 2, wherein the unevenness correction processing circuit stores the characteristic value corresponding to a specific gradation value of the gradation data and inputs the gradation When the data is not the specific gradation value, the image display device uses the gradation interpolation characteristic value, which is a value calculated by an interpolation calculation referring to the characteristic value, as the characteristic value.

  According to this image display apparatus, since the unevenness correction processing circuit stores only the characteristic values corresponding to the specific gradation values, the memory of the storage unit is compared with the case of storing the characteristic values for all the gradation values. Capacity can be reduced.

[Application Example 4]
4. The image display device according to any one of application examples 1 to 3, wherein the unevenness correction processing circuit includes the gradation data corresponding to a liquid crystal cell other than the liquid crystal cell at the predetermined position in the surface of the liquid crystal panel. When performing the correction on the image display device, an in-plane interpolation characteristic value, which is a value calculated by an interpolation calculation referring to the characteristic value corresponding to the liquid crystal cell at the predetermined location, is referred to as the characteristic value.

  According to this image display device, when correcting gradation data corresponding to a liquid crystal cell other than a liquid crystal cell at a predetermined position in the plane of the liquid crystal panel, the characteristic value corresponding to the liquid crystal cell at the predetermined position is referred to. Since the calculation is performed by the interpolation calculation, the correction can be performed with higher accuracy than the case where the correction is performed by referring to the characteristic value corresponding to the liquid crystal cell at a predetermined location as it is.

[Application Example 5]
The image display device according to any one of Application Examples 1 to 4, wherein the input image data includes three gradation data components of R, G, and B, and the characteristic relaxation unit includes the R , G, and B, an image display device that performs the different correction on the gradation data.

  The display characteristics of the liquid crystal cell are generally different for each of R, G, and B light. According to this image display device, the characteristic relaxation unit performs different corrections on the respective R, G, and B gradation data, and therefore the same processing is performed on each of the R, G, and B gradation data. Compared with the case where correction is performed, correction with higher accuracy can be performed.

[Application Example 6]
The image display device according to Application Example 1 to Application Example 5, wherein the input image data includes three gradation data components of R, G, and B, and the unevenness correction processing circuit includes the R, G , B are provided with different look-up tables for the gradation data.

  According to this image display apparatus, the unevenness correction processing circuit corrects each of the R, G, and B tone data using different look-up tables. Therefore, the three tone data of R, G, and B are used. As compared with the case where correction is performed using the same lookup table, correction with higher accuracy can be performed.

[Application Example 7]
The image display device according to any one of application examples 1 to 6, wherein the image display device is a projector that projects and displays a display image based on the image data.

[Application Example 8]
It is composed of a plurality of liquid crystal cells, and each liquid crystal cell is controlled based on display characteristics defined as a change in optical characteristics with respect to an input signal. An image display method for displaying an image based on the input of a gradation signal having a characteristic in which the change rate is reduced as compared to a change rate in inclination of a display characteristic unique to each liquid crystal cell, A drive voltage suitable for the rate of change in the slope of the display characteristics inherent to the liquid crystal cell is generated and input to the liquid crystal panel as the input signal. Prior to the generation of the drive signal, the display characteristics vary within the panel surface. In order to suppress the occurrence of unevenness, the display is a value prepared by specifying a liquid crystal cell at a predetermined position in the surface of the liquid crystal panel, and the rate of change of the specified liquid crystal cell is reduced. And generating a non-uniformity corrected image signal obtained by correcting the gamma-corrected gradation data corresponding to the image data, and using the generated non-uniformity corrected image signal as the gradation signal to generate the driving voltage. The image display method to generate.

  According to this image display method, the display characteristics of the liquid crystal cell can be handled as display characteristics having a change rate lower than the change rate of the inclination of the actual display characteristic of the liquid crystal cell, and the occurrence of unevenness can be suppressed.

  Note that the present invention can be realized in various modes. For example, the present invention can be realized in the form of a data conversion method and apparatus, a data processing system, an integrated circuit for realizing the functions of the method or apparatus, a computer program, a recording medium on which the computer program is recorded, and the like.

2 is an explanatory diagram illustrating a configuration of a projector. FIG. It is a block diagram explaining the flow of a data conversion process. It is explanatory drawing explaining the process in a color nonuniformity correction circuit. It is explanatory drawing explaining VT relaxation LUT. It is explanatory drawing explaining VT relaxation LUT. It is explanatory drawing explaining the modification 1. FIG. It is explanatory drawing explaining the modification 2. FIG.

Next, embodiments of the present invention will be described based on examples.
A. First embodiment:
(A1) System configuration:
FIG. 1 is an explanatory diagram showing the configuration of a projector 10 as a first embodiment of the invention. The projector 10 is a 3LCD type liquid crystal projector. The projector 10 includes an input interface (input IF) 20, a color conversion circuit 30, a gamma correction circuit 40, a color unevenness correction circuit 50, a VT characteristic relaxation circuit 60, a liquid crystal panel drive unit 70, liquid crystal panels 91 to 93, a control unit 110, A memory 120 is provided.

  The color conversion circuit 30, the gamma correction circuit 40, the color unevenness correction circuit 50, and the VT characteristic relaxation circuit 60 are provided in an image processing unit 100 provided exclusively for image processing. The image processing unit 100 is a processor dedicated to image processing, and for example, a DSP (Digital Signal Processor) can be used. The projector 10 also includes an illumination optical system 80 for illuminating the liquid crystal panels 91 to 93. The illumination optical system 80 splits the illumination light emitted from the light source 81 and the light source 81 into R, G, and B illumination light. And a spectroscopic optical system 82. Further, the projector 10 includes a dichroic prism 94 and a lens unit that synthesizes image light modulated by the liquid crystal panels 91, 92, and 93 with the three lights (R, G, and B) dispersed by the spectroscopic optical system 82. 95. The image light synthesized by the dichroic prism 94 and the lens unit 95 is projected and displayed as a display image on the screen SC. The liquid crystal panels 91 to 93 are also simply referred to as a liquid crystal panel 90.

  The input IF 20 is a processing unit for inputting image data input from an image data output device such as a personal computer or a DVD playback device to the projector 10. In this embodiment, the input IF 20 inputs image data (hereinafter also referred to as YUV data) expressed in a color space of Y (lightness) U (color difference) V (color difference) as image data.

  The color conversion circuit 30 converts image data (YUV data) input from the input IF 20 into gradation data Da (hereinafter also referred to as RGB data Da) expressed in 10-bit RGB that can be processed by the projector 10. It is. The gamma correction circuit 40 is a circuit that performs gamma correction on the RGB data input to the liquid crystal panel 90. Specifically, considering the VT characteristic (applied voltage-transmittance characteristic) of the liquid crystal panel 90 so that the transmittance (T) of the liquid crystal panel 90 becomes a predetermined characteristic with respect to the gradation data Da, This is a circuit for correcting the gradation data Da. Note that the gradation data after gamma correction is referred to as gradation data Db.

  The color unevenness correction circuit 50 corrects the gradation data Db after the gamma correction in the gamma correction circuit 40 so as to control the color unevenness generated in the image displayed on the screen SC. “Color unevenness” is caused by the non-uniform thickness of the liquid crystal layer of the liquid crystal panel or the operational characteristics of the TFTs corresponding to each liquid crystal cell varying within the liquid crystal panel surface. This is a variation in the display characteristics in the key direction. Therefore, the color unevenness correction circuit 50 corrects the gradation data Db in the in-plane direction and the gradation direction of the liquid crystal panel to reduce the color unevenness.

  The VT relaxation circuit 60 is a circuit that relaxes the VT characteristics of the liquid crystal cells constituting the liquid crystal panel 90. Hereinafter, the VT characteristic of the liquid crystal cell constituting the liquid crystal panel 90 is also simply referred to as the VT characteristic of the liquid crystal panel 90. As described later with reference to FIG. 4B, the VT characteristic of the liquid crystal panel 90 is an S-shaped curve having a point at which the slope changes rapidly, and a local gradation region (applied voltage region). Therefore, the transmittance (T) or the rate of change in reflectance (hereinafter also referred to as “slope”) increases. In other words, the VT characteristic curve (hereinafter also referred to as VT curve) has a shape having a portion where the curvature (or the second-order differential value of the transmittance (T) by the applied voltage (V)) is large. ing. The VT mitigation circuit is relative to the color unevenness correction circuit 50 so that the color unevenness correction circuit 50 treats the curve of the VT curve as a gentle shape and can accurately perform color unevenness correction in the gradation direction of the gradation data Db. The VT curve of the VT characteristic of the liquid crystal panel 90 seen in FIG. Actually, the VT characteristic is relaxed by performing data conversion on the gradation data Dc subjected to the color unevenness correction by the color unevenness correction circuit 50. The data after data conversion in the VT relaxation circuit 60 is referred to as gradation data Dd. The liquid crystal panel driving unit 70 applies a voltage corresponding to the gradation data Dd to the liquid crystal panel, and forms an image on the liquid crystal panel 90 (91 to 93). The control unit 110 includes a CPU, and has a function of reading a driver program for the projector 10 stored in the memory 120 and controlling the operation of the projector 10.

(A2) Data conversion process:
Next, data conversion processing performed through the gamma correction circuit 40, the color unevenness correction circuit 50, and the VT characteristic relaxation circuit 60 of the projector 10 will be described. FIG. 2 is a block diagram illustrating a data flow until YUV data input via the input IF 20 is input to the liquid crystal panels 91 to 93 by data conversion processing. As described above, the YUV data is converted into the gradation data Da which is RGB data via the color conversion circuit 30. The red component data of the gradation data Da is called gradation data Dar, the green component data is called gradation data Dag, and the blue component data is called gradation data Dab. It should be noted that data whose gradation data code endings are “r”, “g”, and “b” described below indicate red component data, green component data, and blue component data, respectively. Hereinafter, in the present description, the data conversion process will be described using the red component gradation data.

  As shown in FIG. 2, the color conversion circuit 30 performs color conversion (YUV → RGB) on the YUV data and outputs 10-bit RGB data. The gradation data Dar is 10-bit data of the red component of RGB data. The color conversion circuit 30 inputs the gradation data Dar generated by the color conversion to the gamma correction circuit 40. The gamma correction circuit 40 includes a gamma LUT 41, a gamma LUT 42, and a gamma LUT 43, which are lookup tables used for gamma correction. The gamma LUT 41 stores a 12-bit gradation value (gamma correction value) after the gamma correction for the gradation data Dar. The gamma correction circuit 40 stores a gamma correction value for each gradation value of the gradation data Dar, designates an address according to the gradation value of the gradation data Dar, and sets the gamma correction value of the gamma LUT 41. This is read and input to the color unevenness correction circuit 50 as 12-bit gradation data Dbr.

  The color unevenness correction circuit 50 includes a color unevenness correction LUT 51, a color unevenness correction LUT52, and a color unevenness correction LUT53, which are look-up tables used for color unevenness correction. Each of the color unevenness correction LUTs 51 to 53 stores a color unevenness correction value Dh to be added to the gradation data Db as color unevenness correction. The color unevenness correction LUT 51 stores a color unevenness correction value Dhr to be added to the gradation data Dbr. FIG. 3 is an explanatory diagram for explaining processing of gradation data Dbr in the color unevenness correction circuit. The central grid point in FIG. 3 represents the color unevenness correction LUT 51. The color unevenness correction LUT 51 stores color unevenness correction values Dhr for a plurality of specific liquid crystal cells of the liquid crystal panel 91. Hereinafter, the grid position of the color unevenness correction LUT 51 corresponding to the cell positions of the plurality of specific liquid crystal cells is also referred to as a specific position. Further, the color unevenness correction LUT 51 stores a color unevenness correction value Dhr for each specific 8 gradation values according to the gradation range of the gradation data Dbr input corresponding to one specific position. . Hereinafter, the lattice plane of the color unevenness correction LUT 51 corresponding to the specific eight gradation values is also referred to as specific gradation values 1 to 8. That is, the color unevenness correction LUT 51 is a three-dimensional lookup table (hereinafter referred to as 3D-LUT) that stores the color unevenness correction value Dhr for each specific gradation value at each specific position. The gradation data Dbr corresponding to the specific gradation value at the specific position where the color unevenness correction value Dhr is stored is also referred to as stored value gradation data.

  When the input gradation data Dbr is gradation data corresponding to a specific gradation value at a specific position on the liquid crystal panel 91, that is, stored value gradation data, the color unevenness correction circuit 50 corresponds to the corresponding color unevenness. The correction value Dhr is added to the read gradation data Dbr and input to the VT characteristic relaxation circuit 60 as gradation data Dcr. On the other hand, when the input gradation data Dbr is gradation data Dbr other than the stored value gradation data, eight stored value gradations adjacent to the liquid crystal in-plane direction and the gradation direction of the input gradation data Dbr. The color unevenness correction value Dhr of the data is read out. Then, for each of two specific gradation values sandwiching the gradation data Dbr, an interpolation operation is performed using the four color unevenness correction values Dhr in each surface in the direction in the liquid crystal panel surface, and two interpolation operation values α1 and α2 are obtained. calculate. In the case of the specific example of FIG. 3, the input gradation data Dbr is a gradation value sandwiched between the specific gradation value 1 and the specific gradation value 2, and the specific positions 1, 2, and 2 in the liquid crystal panel surface. The gradation data corresponds to the position of the liquid crystal panel surrounded by 3 and 4. Therefore, in the in-plane direction of the liquid crystal panel at the specific gradation value 1, the interpolation calculation value α1 is calculated by weighted average using the color unevenness correction values Dhr1 to D4 stored in the respective stored value gradation data 1 to 4. The weighted average is, for example, an area ratio of areas divided by points on the liquid crystal panel corresponding to the input gradation data Dbr (hereinafter also referred to as input data points) and specific positions 1, 2, 3, and 4. Is used as a weighting coefficient, or a weighted average using the distance between the input data point and four specific positions as a weighting coefficient is used. Next, in the in-plane direction of the liquid crystal panel at the specific gradation value 2, the interpolation calculation value α2 is calculated by weighted average using the color unevenness correction values Dhr5 to 8 stored in the respective stored value gradation data 5 to 8. .

  The input gradation data Dbr is obtained by performing linear interpolation in the gradation direction between the specific gradation value 1 and the specific gradation value 2 using the interpolation calculation values α1 and α2 calculated in this way. An interpolation calculation value α0 for is calculated. Thereafter, the interpolation calculation value α0 is added to the gradation data Dbr, and is input to the VT characteristic relaxation circuit 60 as 12-bit gradation data Dcr. In this way, the color unevenness correction circuit 50 performs color unevenness correction on the gradation data Dbr. The interpolation calculation value α0 may be calculated by calculation using a bicubic method using eight lattice points (in this embodiment, color unevenness correction values Dhr1 to Dhr8).

  Next, the VT characteristic relaxation circuit 60 will be described. The VT characteristic relaxation circuit 60 substantially corrects the gradation value data corresponding to the applied voltage input to the liquid crystal panel 90 before it is input to the liquid crystal panel, so that the VT characteristic relaxation circuit 60 substantially subtracts the VT characteristic curve ( This is a circuit for making the (VT curve) gentle. In other words, this is a circuit for reducing the rate of change in the slope of the VT curve. The VT characteristic relaxation circuit 60 includes VT relaxation LUTs 61 to 63 that are lookup tables for data conversion, and each has gradation data Dcr that is red component data, gradation data Dcg that is green component data, and blue component. Is used for the data conversion of the gradation data Dcb, which is the above data.

In this description, the VT relaxation LUT 61 will be described. 4A shows a relaxed VT characteristic which is a VT characteristic relaxed from the VT characteristic of the liquid crystal panel 90, FIG. 4B shows a characteristic of the VT relaxed LUT, and FIG. 4C shows the liquid crystal panel. The VT characteristic is shown. In this description as well, the description will be made using gradation data of the red component. The gradation data Dbr input to the color unevenness correction circuit 50 is processed in the order of processing until it is converted to the transmittance T (%) of the liquid crystal panel 91 via the VT characteristic relaxation circuit 60 and the liquid crystal panel 91. explain. The 12-bit gradation data Dbr input from the VT characteristic relaxation circuit 60 to the color unevenness correction circuit 50 is converted into 12-bit gradation data Dcr as shown in FIG. The gradation data Dcr is input to the VT characteristic relaxation circuit 60 and converted into 12-bit gradation data Ddr as shown in FIG.
The gradation data Ddr is input to the drive circuit 71. The drive circuit 71 converts the input gradation data Ddr into a voltage Vdr and inputs it to the liquid crystal panel 91. In the liquid crystal panel 91 having VT characteristics shown in FIG. 4C, the transmittance of the cell to which the input voltage Vdr is applied is set to T (%).

  When the above processing is graphed with respect to the relationship between the gradation data Db and the gradation data Dc, the relaxation VT characteristic shown in FIG. 4A is obtained. Further, the gradation data Dc is replaced with the gradation data Dd based on the characteristics shown in FIG. 4B, and finally the transmittance T is set based on the VT characteristics of the liquid crystal panel shown in FIG. Converted. In other words, the VT characteristic of the liquid crystal panel in FIG. 4C can be viewed as the VT characteristic shown in FIG. FIG. 5 is an explanatory diagram for conceptually explaining these relationships. As can be seen from FIG. 5, the gradation data Dbr is converted into gradation data Dcr based on the curve of the relaxation VT characteristic, converted into gradation data Ddr with reference to the VT relaxation LUT, and then D / D (not shown). The voltage is converted to the voltage Vdr by the A converter and input to the liquid crystal panel 91, and finally the transmittance T is obtained.

  As a result, when comparing the VT characteristics and relaxed VT characteristics of the liquid crystal panel while paying attention to the respective VT curves, the relaxed VT characteristics of the VT curve are more gradual than the VT curves of the liquid crystal panel. Yes. That is, it can be seen that the rate of change in the slope of the VT characteristic is reduced. That is, the VT relaxation LUT is a LUT indicating a conversion function of gradation data generated by comparing the VT characteristics of the liquid crystal panel with the ideal relaxation VT characteristics.

  The gradation data Dcr is converted into gradation data Ddr through the VT relaxation LUT 61 (see FIG. 2), and the voltage Vdr corresponding to the gradation data Ddr is transmitted through the drive circuit 71 for driving the liquid crystal panel 91. Is applied to the liquid crystal panel 91, a series of data conversion processing ends. By performing such a series of data conversion processing on the gradation data of the R, G, and B color components, the projector 10 reduces color unevenness on the display image. That is, the color unevenness correction LUT 51, the color unevenness correction LUT52, and the color unevenness correction LUT53 store different color unevenness correction values Dh. In addition, the liquid crystal panels 91 to 93 corresponding to R, G, and B have different VT characteristics of the liquid crystals depending on the color components of R, G, and B. The values stored in the VT relaxation LUT 61, the VT relaxation LUT 62, and the VT relaxation LUT 63 included in the VT characteristic relaxation circuit are also different depending on each VT characteristic. That is, the shape of the characteristics of the VT relaxation LUT shown in FIG. 4A is different for each color component.

  As described above, by providing the VT relaxation LUT, the VT characteristic of a liquid crystal panel (liquid crystal cell) having a steep curve can be handled as a liquid crystal panel having the VT characteristic of the gentle curve shown in the relaxation VT characteristic. it can. In particular, the relaxation VT characteristic is within a voltage interval corresponding to each interval (hereinafter also referred to as a gradation interval) of gradation values composed of specific gradation values stored in the color unevenness correction LUTs 51 to 53 of each color unevenness correction circuit 50. If the VT characteristic relaxation circuit 60 performs data conversion so that the curve becomes a linear curve, the accuracy of calculation of the interpolation calculation value α0 in the color unevenness correction circuit 50 is improved. For example, in this embodiment, the interpolation calculation value α0 is calculated by performing linear interpolation in the gradation direction between the specific gradation value 1 and the specific gradation value 2 using the interpolation calculation values α1 and α2. To do. The interpolation calculation value α0, which is a value calculated by linear interpolation in the gradation direction, is later reflected in the applied voltage Vd corresponding to the gradation data Ddr. At this time, an error due to the interpolation calculation in the gradation direction becomes an error of the transmittance T, but the transmittance T due to the error in the interpolation calculation becomes closer to a linear relationship between the applied voltage Vd and the transmittance T between the specific gradation values. The error can be reduced. As a result, the accuracy of color unevenness correction is improved.

  As a correspondence relationship with the claims, the color unevenness correction circuit 50 corresponds to the unevenness correction processing circuit described in the claims, and the VT characteristic relaxation circuit 60 corresponds to the characteristic relaxation unit described in the claims. The gradation data Dc corresponds to the unevenness correction image signal described in the claims, the gradation data Dd corresponds to the input signal described in the claims, and the color unevenness correction value Dh corresponds to the claims. It corresponds to the characteristic value described in.

B. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

(B1) Modification 1:
In the above embodiment, as shown in FIG. 2, the gradation data Dcr output from the color unevenness correction circuit 50 is 12-bit gradation data. The number of bits of Dcr may be increased. For example, as shown in FIG. 6A, when the gradation data Dcr is 14 bits, the VT characteristics viewed through the gamma correction circuit 40 to the VT characteristic relaxation circuit 60 have the accuracy shown in FIG. The VT characteristic of “2.2 power curve” can be obtained. For comparison, FIG. 6B shows the VT characteristic viewed through the gamma correction circuit 40 to the VT characteristic relaxation circuit 60 in the case of the first embodiment. It can be seen that the accuracy of the output value with respect to the input value is improved in the VT characteristic of the “2.2 power curve” of Modification 1. Also in this way, the same effect as in the above embodiment can be obtained.

(B2) Modification 2:
As a second modification, a data conversion process as shown in FIG. The projector in Modification 2 includes an error diffusion processing unit 65 in addition to the configuration of the first embodiment. Further, the number of bits of the gradation data is set larger than the gradation value that can be expressed by the liquid crystal panel driving unit 70. In the case of the modification 2, as shown in FIG. 7, the gradation data Dc is 14 bits, the gradation data Dd is 14 bits, and the gradation data De output from the error diffusion processing unit 65 is 12 bits. Other gradation data Da and Db are the same as in the first embodiment.

  The error diffusion processing unit 65 outputs gradation data Dd sequentially input in 14 bits as 12-bit gradation data De, and at this time, rounds the data value from 14 bits to 12 bits. Specifically, the rounding process is performed on the lower 2 bits of the 14-bit data. At this time, the information of the lower 2 bits subjected to rounding is diffused in the time axis direction to the 12-bit data value after the rounding process, and added to the 12-bit data value sequentially input and rounded. In other words, in order to express the fine gradation expression that can be expressed by the lower 2 bits subjected to rounding with the 12-bit gradation data after rounding, the gradation values corresponding to the lower 2 bits are sequentially output. Distribution to a gradation value of gradation data to be performed at a predetermined ratio. In this way, the visual afterimage effect makes it possible to perform a gradation expression that is substantially finer than the gradation expression that is simply truncated and expressed as 12-bit gradation data. Also in this way, the same effect as in the above embodiment can be obtained.

(B3) Modification 3:
In the above embodiment, the data conversion process is applied to the liquid crystal projector. Thus, the present invention can be applied to an image display device that displays an image.

(B4) Modification 4:
In the above embodiment, the specific configuration and processing of the image display device have been described. However, the image display device may have the following characteristics. That is, an image display device that displays an image based on input image data is composed of a plurality of liquid crystal cells, and each liquid crystal cell is controlled based on display characteristics defined as changes in optical characteristics with respect to an input signal. A liquid crystal panel for displaying an image, and a characteristic relaxation unit interposed in a front stage of the liquid crystal panel, wherein a change in the inclination of the display characteristic of the liquid crystal cell of the liquid crystal panel via the characteristic relaxation unit A characteristic of generating a relaxation signal that is a signal corrected so that the rate is a rate of change reduced compared to the rate of change of the slope of the display characteristic unique to each liquid crystal cell, and inputting the relaxation signal to the liquid crystal panel as the input signal In order to suppress the occurrence of unevenness due to variations in the display characteristics of the liquid crystal cell and the relaxation part, a liquid crystal cell at a predetermined position in the surface of the liquid crystal panel is specified and prepared. And generating a non-uniformity-corrected image signal obtained by correcting the gamma-corrected gradation data corresponding to the image data with reference to the characteristic value representing the display characteristic of the specified liquid crystal cell with the reduced rate of change. And a non-uniformity correction processing circuit that inputs the characteristic mitigation unit and generates the mitigation signal based on the non-uniformity correction image signal. The characteristic relaxation unit includes a relaxation lookup table that is a lookup table for storing the relaxation signal output to the liquid crystal panel in response to the unevenness correction image signal input from the unevenness correction processing circuit. It is good.

DESCRIPTION OF SYMBOLS 10 ... Projector 30 ... Color conversion circuit 40 ... Gamma correction circuit 50 ... Color unevenness correction circuit 60 ... VT characteristic relaxation circuit 61 ... VT relaxation LUT
65 ... Error diffusion processing unit 70 ... Liquid crystal panel drive unit 71 ... Drive circuit 80 ... Illumination optical system 81 ... Light source 82 ... Spectral optical system 90 ... Liquid crystal panel 91 ... Liquid crystal panel 94 ... Dichroic prism 95 ... Lens unit 100 ... Image processing unit 110 ... Control unit 120 ... Memory 41-43 ... Gamma LUT
51-53 ... Color unevenness correction LUT
Dh: Color unevenness correction value T: Transmittance Da to Dd: Gradation data Vd: Voltage

In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.
According to an aspect of the present invention, an image display device that displays an image based on input image data is provided. The image display device includes a plurality of liquid crystal cells, and each liquid crystal cell is controlled based on display characteristics defined as changes in optical characteristics with respect to an input signal, thereby displaying an image; and A gamma correction circuit that performs gamma correction on the image data, and a liquid crystal cell at a predetermined location in the surface of the liquid crystal panel is specified in order to suppress unevenness due to variations in display characteristics in the panel surface. A non-uniformity correction image obtained by correcting a gamma-corrected gradation data corresponding to the image data with reference to a characteristic value representing a display characteristic of the specified liquid crystal cell in which the rate of change is reduced. Compared to the unevenness correction processing circuit that generates a signal and inputs it to the characteristic relaxation unit as the gradation signal, the change rate is reduced compared to the change rate of the inclination of the display characteristic specific to each liquid crystal cell. A characteristic relaxation unit that receives a grayscale signal having the above-described characteristics, generates a drive voltage that conforms to the rate of change in the slope of display characteristics unique to each liquid crystal cell, and inputs the drive voltage to the liquid crystal panel as the input signal; Prepare. The image display device includes a characteristic relaxation unit. When the display characteristics of the liquid crystal cell are evaluated through the characteristic relaxation unit, it can be evaluated as a display characteristic having a change rate lower than the change rate of the inclination of the actual display characteristic of the liquid crystal cell. Therefore, by providing the characteristic relaxation unit in the previous stage of the liquid crystal panel, it can be controlled as a liquid crystal panel including a liquid crystal cell exhibiting display characteristics with a low change rate of inclination. Here, the “gradient” of the display characteristic is, for example, “change in transmittance (T) with respect to the applied voltage (V) in the VT characteristic (applied voltage-transmittance characteristic) of the liquid crystal cell which is one of the display characteristics. Say "Rate". That is, in this example, the “inclination change rate” corresponds to a twice-differentiated value based on the applied voltage (V) in the VT characteristic. The unevenness correction processing circuit can be regarded as a liquid crystal panel having such characteristics, and can suppress the occurrence of unevenness due to variations in display characteristics of the liquid crystal cell within the panel surface. In addition, as a display characteristic, the transmittance | permeability and the reflectance with respect to the applied voltage of a liquid crystal cell are mentioned, for example.

In order to solve at least a part of the problems described above, the present invention can take the following forms or application examples.
According to an aspect of the present invention, an image display device that displays an image based on input image data is provided. This image display device is a liquid crystal cell of multiple, respective liquid crystal cell, by being controlled based on the display characteristics defined as a change in optical properties with respect to the input signal, and a liquid crystal panel for displaying an image A gamma correction circuit that performs gamma correction on the image data, and a liquid crystal cell at a predetermined position in the surface of the liquid crystal panel is specified in order to suppress unevenness due to variations in display characteristics in the panel surface. A gamma value corresponding to the image data with reference to a characteristic value representing a display characteristic with a reduced rate of change in inclination of the display characteristic specific to each liquid crystal cell of the specified liquid crystal cell. A non-uniformity correction processing circuit that generates a non-uniformity correction image signal obtained by correcting the corrected gradation data and inputs the non-uniformity correction image signal to the characteristic relaxation unit as the gradation signal, and an inclination of display characteristics specific to each liquid crystal cell A gradation signal having a characteristic in which the rate of change is reduced compared to the rate of change is input, and a driving voltage suitable for the rate of change in the slope of the display characteristic specific to each liquid crystal cell is generated, and the input signal is used as the input signal. And a characteristic relaxation unit that inputs to the liquid crystal panel. The image display device includes a characteristic relaxation unit. When the display characteristics of the liquid crystal cell are evaluated through the characteristic relaxation unit, it can be evaluated as a display characteristic having a change rate lower than the change rate of the inclination of the actual display characteristic of the liquid crystal cell. Therefore, by providing the characteristic relaxation unit in the previous stage of the liquid crystal panel, it can be controlled as a liquid crystal panel including a liquid crystal cell exhibiting display characteristics with a low change rate of inclination. Here, the “gradient” of the display characteristic is, for example, “change in transmittance (T) with respect to the applied voltage (V) in the VT characteristic (applied voltage-transmittance characteristic) of the liquid crystal cell which is one of the display characteristics. Say "Rate". That is, in this example, the “inclination change rate” corresponds to a twice-differentiated value based on the applied voltage (V) in the VT characteristic. The unevenness correction processing circuit can be regarded as a liquid crystal panel having such characteristics, and can suppress the occurrence of unevenness due to variations in display characteristics of the liquid crystal cell within the panel surface. In addition, as a display characteristic, the transmittance | permeability and the reflectance with respect to the applied voltage of a liquid crystal cell are mentioned, for example.

Claims (8)

An image display device that displays an image based on input image data,
A plurality of liquid crystal cells, each of which is controlled based on display characteristics defined as a change in optical characteristics with respect to an input signal, thereby displaying an image; and
A gradation signal having a characteristic in which the change rate is reduced compared to the change rate of the display characteristic slope inherent to each liquid crystal cell is input, and the change rate of the display characteristic slope unique to each liquid crystal cell is input. A characteristic relaxation unit that generates a suitable drive voltage and inputs the input signal to the liquid crystal panel;
In order to suppress the occurrence of unevenness due to variations in display characteristics within the panel surface, the liquid crystal cell is a value prepared by identifying a liquid crystal cell at a predetermined location within the surface of the liquid crystal panel, and the liquid crystal cell of the identified liquid crystal cell Referring to a characteristic value representing a display characteristic with a reduced rate of change, a non-uniformity corrected image signal is generated by correcting the gamma-corrected gradation data corresponding to the image data, and input to the characteristic relaxation unit as the gradation signal And an unevenness correction processing circuit for generating the drive voltage. The image display device according to claim 1,
The image display apparatus includes a look-up table that is referred to when the drive voltage to be output to the liquid crystal panel is generated in response to the unevenness correction image signal input from the unevenness correction processing circuit. The image display device according to claim 1 or 2,
The unevenness correction processing circuit stores the characteristic value corresponding to a specific gradation value of the gradation data, and if the input gradation data is not the specific gradation value, the characteristic value An image display device using a gradation interpolation characteristic value, which is a value calculated by an interpolation calculation referring to, as the characteristic value. The image display device according to any one of claims 1 to 3,
The unevenness correction processing circuit includes:
When performing the correction on the gradation data corresponding to the liquid crystal cell other than the liquid crystal cell at the predetermined location in the surface of the liquid crystal panel,
An image display device that refers to an in-plane interpolation characteristic value, which is a value calculated by an interpolation calculation referring to the characteristic value corresponding to the liquid crystal cell at the predetermined location, as the characteristic value. The image display device according to any one of claims 1 to 4,
The input image data includes three gradation data components of R, G, and B,
The image display device, wherein the characteristic relaxation unit performs the different correction on the gradation data of each of the R, G, and B. The image display device according to claim 1, wherein:
The input image data includes three gradation data components of R, G, and B,
The non-uniformity correction processing circuit includes the different look-up tables for the gradation data of R, G, and B, respectively.   The image display device according to claim 1, wherein the image display device is a projector that projects and displays a display image based on the image data. It is composed of a plurality of liquid crystal cells, and each liquid crystal cell is controlled based on display characteristics defined as a change in optical characteristics with respect to an input signal. An image display method for displaying an image based on:
A gradation signal having a characteristic in which the change rate is reduced as compared to the change rate of the display characteristic inclination unique to each liquid crystal cell is input, and the change rate of the display characteristic inclination unique to each liquid crystal cell is input. A suitable drive voltage is generated and input to the liquid crystal panel as the input signal,
Prior to the generation of the drive signal, in order to suppress the occurrence of unevenness due to variations in display characteristics within the panel surface, the value is a value prepared by identifying a liquid crystal cell at a predetermined location within the surface of the liquid crystal panel. And generating a non-uniformity-corrected image signal by correcting the gamma-corrected gradation data corresponding to the image data, with reference to a characteristic value representing a display characteristic of the specified change rate of the liquid crystal cell reduced, An image display method for generating the drive voltage using the generated unevenness-corrected image signal as the gradation signal.

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