JP2009145780A - Correcting method, display apparatus and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a correcting method with which a gamma correction can be made easily, speedily, and accurately in each display apparatus, and to provide a display apparatus and a computer program for carrying out the correction method. <P>SOLUTION: In an LUP in a pre-stage for inputting an image signal to a display section, a gradation value included in an image signal is corrected. In this case, a non-linear portion of a gamma value distribution relative to an input gradation value representing a gradation characteristic is corrected by a first correction value, by which the gradation characteristics of the display section of the display apparatus used as a reference have a constant prescribed gamma value (e.g., &gamma;=2.2). The gamma value is measured or calculated for a minimum input gradation value used to specify a function representing the characteristic of the gamma value distribution after the correction. The function is specified by the measured or calculated gamma value. A second correction value to be corrected so that the gamma value may be constant is calculated. The LUT corrects a gradation value for an image signal inputted using the calculated second correction value. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a correction method for correcting the intensity in accordance with the gradation characteristics of each display device, and in particular, a correction method capable of performing correction in each display device simply and quickly with high accuracy, and the correction method are implemented. The present invention relates to a computer program that causes a display device and a computer to function as the display device.

  Display devices such as LCD (Liquid Crystal Display) monitors, PDP (Plasma Display Panel) monitors, organic EL (Electro Luminescence) monitors, CRT (Cathode Ray Tube) monitors, electronic papers, etc. In the case of a PDP monitor, it has characteristics of various parts such as a light emission characteristic for each element and a characteristic of a circuit for generating a voltage applied to each panel. Due to the characteristics of the parts, the change in luminance in the actually displayed image may not be smooth, whereas the change in the intensity of each color component included in the image signal input to the display device is smooth.

  The luminance characteristic with respect to the intensity of each color component included in the input image signal is called a gradation characteristic (or gamma characteristic). When the intensity included in the input image signal is changed smoothly, the correspondence between the input intensity and the luminance is corrected so that a smooth gradation expression is realized in the display image. This is called gamma correction because various changes are corrected so as to draw a gamma curve, and various methods have been proposed for gamma correction.

  Patent Document 1 includes a storage unit that stores a voltage value corresponding to the intensity of each color component included in an input image signal, and the voltage value can be adjusted from the outside so that the liquid crystal A gamma correction technique capable of adjusting a voltage value according to a gradation characteristic in a panel is disclosed.

  Patent Document 2 relates to a D / A converter that converts the intensity of each color component represented by an input image signal into an analog voltage value applied to each element of a liquid crystal panel or PDP, and is included in the D / A converter. A gamma correction technique is disclosed in which the voltage value to be applied can be adjusted according to the characteristics of each panel by making the resistance value of the ladder resistor for voltage division variable and adjustable.

Patent Document 3 discloses a gamma correction technique in which correction is performed using correction amounts corresponding to component data resulting from a difference in gradation characteristics in a liquid crystal panel, for example, a cell gap in a liquid crystal panel to be used, and I / V characteristics of a transistor. Is disclosed.
JP 2005-049418 A JP 2007-241235 A JP 2006-227453 A

  With the techniques disclosed in Patent Documents 1 and 2, gamma correction according to the characteristics of each display device is possible. However, when correcting each display device, it takes time to perform detailed measurement of each component, adjustment to change the resistance value included in each circuit, and the like. In view of securing the production volume and costs in the manufacturing process, it is desirable to reduce the time required for adjustment performed for each display device.

  In the technique disclosed in Patent Document 3, the whole is adjusted with a correction amount determined according to the characteristics of each liquid crystal panel measured in advance without performing adjustment based on the actual measurement of the gradation characteristics at the time of manufacture. By correcting, the manufacturing time can be reduced. However, when high-precision gamma correction is required, in the configuration in which each intensity is uniformly corrected with a correction amount determined according to the characteristics of a specific component, individual gradations caused by various elements There is a possibility that the characteristics cannot be corrected with high accuracy.

  In addition, in this case, the correction amount for gamma correction based on the gradation characteristics actually measured on the reference display device can be corrected by applying the correction amount uniformly to other devices. There is a possibility that characteristics that are different in each device cannot be corrected with high accuracy.

  The present invention has been made in view of such circumstances, and the gradation characteristics of individual display devices are attributed to characteristics common to the individual display devices, and different elements of the individual display devices. The gamma correction according to the characteristics of each display device can be performed more accurately and quickly with a simple configuration. It is an object of the present invention to provide a correction method that can be performed, a display device that implements the correction method, and a computer program.

  Another object of the present invention is to extract a display device having gradation characteristics, which is a median value among a plurality of display devices, as a reference display device, thereby improving the accuracy of correction and displaying the display device. It is an object of the present invention to provide a correction method capable of performing gamma correction according to individual characteristics with a simple configuration.

  Another object of the present invention is to increase the accuracy of correction by calculating the correction amount based on actual measurement when calculating the correction amount according to the characteristics of the reference display device. An object of the present invention is to provide a correction method capable of performing gamma correction according to characteristics with a simple configuration.

  Another object of the present invention is that a characteristic caused by a different element in each display device after correction according to a characteristic caused by a common element in each display device is expressed by a linear function such as a linear function. By making use of this relationship, it is possible to perform correction by measuring at least two intensities, thereby performing gamma correction according to the characteristics of each display device more accurately and quickly with a simple configuration. It is an object of the present invention to provide a correction method that can be used.

  In the correction method according to the first aspect of the present invention, when inputting an image signal to the display means for displaying an image, the correction signal stored for each one or a plurality of color components included in the image signal input to the display means is used. In the correction method for correcting the intensity, a first correction amount for correcting the intensity for each color component included in the input image signal is stored so that the gradation characteristic of an arbitrary display means exhibits a predetermined gradation characteristic. When the image signal including the intensity corrected using the first correction amount is input to the display means, the relationship between the output intensity and the input intensity in the display image displayed by the display means is specified and specified. Based on the relationship, a second correction amount for correcting the intensity for each color component included in the image signal input to the display means is calculated, the calculated second correction amount is stored, and the image signal is stored in the display means. If you enter And correcting by using the intensity of each color component included in the image signal with the second correction amount.

  The correction method according to the second invention is characterized in that the arbitrary display means is extracted from a plurality of display means, the display means having a gradation characteristic that is a median value.

  The correction method according to a third aspect of the present invention is to measure a gradation characteristic of the arbitrary display means and calculate the first correction amount based on a comparison between the measured gradation characteristic and the predetermined gradation characteristic. It is characterized by.

  In the correction method according to a fourth aspect of the present invention, the relationship is represented by a linear function having a logarithm of the output intensity with the input intensity as a base and the input intensity as a variable, and an image signal including at least two different input intensity The output intensity in the display image displayed by the display means when input is acquired, the linear function is specified from the two different input intensities and the acquired output intensity, and the second correction amount is determined from the specified linear function. It is characterized by calculating.

  According to a fifth aspect of the present invention, there is provided a display device for displaying an image, and a correction unit for correcting the intensity for each of one or a plurality of color components included in an image signal input to the display unit using a stored correction amount. In the display device having the above, correction is performed using the first correction amount for correcting the intensity for each color component included in the input image signal so that the gradation characteristic of an arbitrary display unit exhibits a predetermined gradation characteristic. For each color component included in the image signal input to the display means based on the relationship between the output intensity in the display image displayed by the display means when the image signal including the intensity is input to the display means. Means for calculating a second correction amount for correcting the intensity of the image and means for storing the second correction amount, and when the correction means inputs an image signal to its own display means, Included colors Wherein the intensity of each minute are to be corrected by using the second correction amount.

  According to a sixth aspect of the present invention, there is provided a computer program including one or a plurality of image signals that are input to the display unit using a correction amount stored in a computer that includes a unit that inputs an image signal to a display unit that displays an image. In a computer program for executing the step of correcting the intensity for each color component, the intensity for each color component included in the input image signal is set so that the gradation characteristic of an arbitrary display means shows a predetermined gradation characteristic. The step of correcting the intensity using the first correction amount stored to correct the image, the step of inputting an image signal including the corrected intensity to the display means, and the display means when input to the display means A step of specifying a relationship between an output intensity and an input intensity in the displayed display image; and input to the display means based on the specified relationship. Calculating a second correction amount for correcting the intensity of each color component included in the image signal, and when inputting the image signal to the display means, the intensity of each color component included in the input image signal The correction step is performed using the first correction amount and the second correction amount.

  In the present invention, as the first stage, correction is performed using a first correction amount that corrects the gradation characteristics of an arbitrary display means so as to exhibit predetermined gradation characteristics. As a result, the correction is made so as to absorb the gradation characteristic due to the cause common to the respective display means. In the second-stage correction, correction is performed to absorb the gradation characteristics caused by different elements that remain after the first-stage correction. The gradation characteristics remaining after the first stage correction are expressed by a function that can be specified with respect to a change in intensity included in each image signal input to each display means. Therefore, the output intensity in the display image with respect to a plurality of input intensities is obtained by measurement, simulation, or the like to specify the relationship, and the second correction amount is calculated using the relationship. Then, the second correction amount is corrected so as to absorb the characteristics due to different causes in each display means.

  In the present invention, the arbitrary display means serving as a reference for calculating the first correction amount may be a display means provided in another display device that is not the display device to be corrected, or the display device itself to be corrected is Display means provided may be used. Furthermore, a virtual display unit having standard gradation characteristics using an average value, a median value, or the like in a plurality of display units may be used as a reference display unit. Further, the gradation characteristics of the reference display means may be gradation characteristics in a partial region such as a central portion in an image displayed on the display means in consideration of spatial unevenness. In addition, by using a display device having gradation characteristics as the median value as the reference display means, the amount corrected in the first stage is reduced, and the correction error due to variations in the characteristics of the individual display devices is reduced. Is expected to do.

  In the present invention, the first correction amount is calculated based on a comparison between the actually measured gradation characteristic and the predetermined gradation characteristic by measuring the gradation characteristic of the other display means serving as a reference or its own display means. The

  Further, in the present invention, when each intensity is corrected using the first correction amount that corrects the gradation characteristic of an arbitrary display means serving as a reference so as to exhibit a predetermined gradation characteristic, the gradation characteristic is compared with the input intensity. It is expressed as a function. In this function, the logarithm of the output intensity in the display image based on the input intensity is represented by a linear function having the input intensity as a variable, and at least two different intensities are corrected and input using the first correction amount. The linear function can be specified from the output intensity in the display image in this case. Then, the second correction amount is calculated from the identified linear function.

  In the case of the present invention, the first correction amount in which the gradation characteristic of the reference display means becomes a predetermined gradation characteristic in the first stage correction is also applied to each display means. Detailed measurement and calculation are not required. In the second-stage correction, the gradation characteristics caused by elements different from the reference display means in each display means are corrected. In this case, the gradation characteristics after the first-stage correction are the input intensity. Has an identifiable relationship to change. Therefore, the second correction amount can be calculated by performing the minimum measurement that can specify the relationship. Therefore, it is possible to perform correction that absorbs different characteristics while reducing the number of times of measurement and the time required for adjustment, and gamma correction according to the characteristics of each display device can be performed more accurately and quickly with a simple configuration. Can be done.

  According to the present invention, the gradation characteristic of the reference display means is set to the median value of the gradation characteristics of the plurality of display means, so that the error in the first-stage correction can be further reduced and the characteristics of each display device can be reduced. The gamma correction according to the above can be performed with a simple configuration and with higher accuracy.

  According to the present invention, the gradation characteristic of the reference display means is measured, and compared with a predetermined gradation characteristic, the first correction amount is calculated. Since the gradation characteristics as a result of integrating the characteristics of the elements such as circuits, elements, and panels constituting the display means are actually measured, it is possible to calculate the first correction amount that comprehensively corrects the respective characteristics. Become. Thereby, the correction can be performed with high accuracy by comparing the actual gradation characteristic with a predetermined ideal gradation characteristic.

  According to the present invention, the gradation characteristics remaining after the first stage correction using the first correction amount are expressed by a linear function in which the logarithm of the output intensity in the display image with the input intensity as the base uses the intensity before correction as a variable. Identify by relationship. Therefore, it is possible to specify the linear function by measuring the output intensity in the display image when at least two input intensities are corrected using the first correction amount and input to the display means. Thereby, the first correction amount calculated in advance in the first stage may be used, and the second correction amount may be calculated by measuring the output intensity when an image signal including at least two intensities is input in the second stage, Gamma correction according to the characteristics of each display device can be performed with higher accuracy and speed with a simple configuration.

  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 a display device according to the present invention. The display device 1 includes an input unit 11 that is an interface that receives an input of an image signal from an image signal output device 2 described later, and a conversion that appropriately converts a gradation value indicating the intensity of each color component included in the input image signal. Unit 12, unevenness correction unit 13 that corrects luminance unevenness and color unevenness, LUT (Look Up Table) 14 that performs gamma correction that absorbs the gradation characteristics of display unit 16, and display the corrected gradation values 16, an output unit 15 that outputs to 16, and a display unit 16 including a panel such as an LCD panel and a PDP and a drive circuit that drives the panel. The conversion unit 12, the unevenness correction unit 13, the LUT 14, and the output unit 15 are configured by an ASIC (Application Specific Integrated Circuit). The conversion unit 12, the unevenness correction unit 13, the LUT 14, and the output unit 15 are not limited to ASICs, but may be configured by an FPGA (Field Programmable Gate Array), and may be configured by individual circuits. Also good.

  The image signal output device 2 is a device that outputs image signals of a PC (Personal Computer), a TV tuner, a DVD (Digital Versatile Disc) player, a game machine, and the like.

  The display device 1 receives the image signal output from the image signal output device 2 by the input unit 11, and displays the color component of each pixel included in the image signal or the gradation value representing the intensity of luminance and color difference based on the display unit. The image signal corresponding to 16 is output by the output unit 15, and the image is displayed on the display unit 16.

  The conversion unit 12 represents the color component of each pixel constituting the image displayed on the display unit 16 by R (Red: red component) G (Green: green component) B (Blue: blue component), and for each of the RGB An input of a 24-bit RGB signal representing a gradation value indicating the intensity of the color component in 8 bits, that is, 256 levels from 0 to 255, is received. Therefore, the input unit 11 may have an analog / digital conversion function, a function of converting to an RGB signal, or the like depending on the type of image signal received by the input unit 11. The image signal received by the conversion unit 12 is not limited to the 24-bit RGB signal as described above, and may include a signal including other color components. Further, depending on the conversion process, for example, each color component may be 10 bits, 14 bits, or the like. The image signal represented by

  The conversion unit 12 appropriately converts the gradation value for each color component input via the input unit 11 and outputs the result. The conversion unit 12 stores a coefficient for conversion, for example, a color matrix according to the setting of the color space, or a coefficient for converting the intensity ratio according to the setting of the color temperature. The conversion unit 12 converts the input gradation value of each color component using a coefficient and outputs the converted value.

  The LUT 14 outputs an output from the unevenness correction unit 13 so as to absorb the gradation characteristic indicating the correspondence between the input gradation value and the output luminance in the display unit 16 in order to realize a smooth gradation display on the display unit 16 in the subsequent stage. Gamma correction is performed on the gradation value for each color component, and the corrected image signal is input to the display unit 16 via the output unit 15.

FIG. 2 is an explanatory diagram showing an outline of gamma correction. FIG. 2A shows an example of the gradation characteristic of the display unit 16, and FIG. 2B shows an ideal gradation characteristic. In the case of the ideal gradation characteristics shown in FIG. 2B, the relationship (gamma curve) in which the luminance y of the displayed image is x to the γ power (y = x ^γ ) with respect to the input gradation value x. To be output. Here, γ is called a gamma value, and the gamma value γ is a gradation ratio obtained by normalizing the input gradation value x from the minimum gradation value to the maximum gradation value between 0 and 1. The logarithm is obtained by dividing the logarithm of the luminance ratio normalized to a numerical value between zero and 1 from the luminance corresponding to the minimum gradation value to the luminance corresponding to the maximum gradation value (Equation 1). The gamma value γ is generally good when γ = 2.2 or γ = 1.8.

  γ = log (luminance ratio) / log (gradation ratio) (1)

  The LUT 14 corrects and outputs the gradation value for each color component output from the unevenness correction unit 13 so that the gamma value γ = 2.2 or γ = 1.8 over all gradation values. FIG. 2C shows an example in which the gradation value is corrected by the LUT 14. The horizontal axis in FIG. 2C is the gradation value input from the unevenness correction unit 13 in the previous stage of the LUT 14, and the vertical axis in FIG. 2C is output by the gradation value correction in the LUT 14. It is a gradation value. As shown in FIG. 2C, in the LUT 14, the gradation value output for each input gradation value is associated. Specifically, the corrected gradation value is stored in the memory constituting the LUT 14 so as to be rewritable for each input gradation value, and the LUT 14 is the corrected gradation value corresponding to the input gradation value. Is configured to output. The gradation value after the gradation value is corrected by the LUT 14 is input from the unevenness correction unit 13 by being input to the display unit 16 having the gradation characteristics shown in FIG. For the tone value of each color component, the luminance of the image displayed on the display unit 16 has the tone characteristics shown in FIG.

  The number of data stored in the LUT 14 is finite. For example, when the gradation value is represented by 8 bits, that is, 256 gradations for each color component, the correspondence between the input gradation value and the output gradation value is 256. It is. Therefore, although the curve shown in FIG. 2C is actually a discrete graph (scatter diagram), it is represented as a curve for convenience. In the present embodiment, the gradation characteristics and the distribution of the gamma values with respect to the gradation values are treated as curves, but in reality, they are similarly discrete graphs.

  The correction value used for obtaining the corrected gradation value stored in the LUT 14 is different for each display device 1 because the gradation characteristic is different for each display unit 16. As shown in FIG. 2B, the gradation characteristic, that is, the output luminance for each gradation value is measured for each display unit 16 of each display device 1, and the gradation characteristic of the display unit 16 is absorbed. The processing for calculating the correction value for correcting the gradation characteristics so as to obtain a proper gradation characteristic for all the gradation values for each display device 1 and calculating and storing the corrected gradation value from the correction value is long. It takes time.

  FIG. 3 is a graph illustrating an example of gradation characteristics that differ depending on the display unit 16 included in each display device 1. The horizontal axis of the graph of FIG. 3 indicates the gradation value input to the display unit 16, and the vertical axis indicates the image displayed on the display unit 16 with the gradation value as a base relative to the input gradation value. The logarithm of the luminance of the light, that is, the gamma value γ. In the graph of FIG. 3, curves A, B, and C representing the gradation characteristics of the display unit 16 of each of the three display devices 1 are shown. In an ideal gradation characteristic, as indicated by a broken line in FIG. 3, the gamma value γ is a constant value such as γ = 2.2, γ = 1.8, etc. over all input gradation values. However, as represented by the curves A, B, and C in the graph of FIG. 3, the input due to various causes such as the characteristics of the constituent elements in the drive circuit of the display unit 16 and the characteristics of the panel used for the display unit 16. The gamma value γ with respect to the gradation value is not a constant value.

  When referring to the graph of FIG. 3, the curves A, B, and C can be regarded as combined curves of the nonlinear part and the linear part. The non-periodic curve portions seen on the low gradation value side and the high gradation value side in each of the curves A, B, and C in the graph of FIG. 3, that is, the non-linear portions are caused by the circuit characteristics in the display unit 16. When the display unit 16 uses a liquid crystal panel, the linear portion is presumed to be caused by variations in the gap between the electrodes sandwiching the liquid crystal layer. For example, a correction value for correcting the gradation value input to the display unit 16 having the gradation characteristic of one of the curves A, B, and C so as to make the curve B linear is calculated. When an image signal in which the gradation value is corrected using the correction value is input to the display unit 16 corresponding to the other curves A and C, the distribution of the gamma value with respect to the gradation value is almost linear, that is, the curves B and C Can be estimated from the fact that is almost linear.

  If the drive circuit included in the display unit 16 has the same configuration, the characteristics of the elements constituting the circuit are almost the same. The characteristics resulting from the circuit mechanism are the same in the display units 16 of the respective display devices 1 using the circuit having the same configuration. Therefore, when correction for absorbing characteristics due to circuit characteristics is performed, the distribution of the gamma value with respect to the gradation value is almost linear. On the other hand, the gap between electrodes varies even with liquid crystal panels of the same type and the same size. The variation in the gap between the electrodes is caused by the variation in the gradient of the distribution of the gamma value with respect to the gradation value.

  FIG. 4 is an explanatory diagram showing a correspondence example between the gradation value input to the digital / analog (D / A) converter constituting the drive circuit of the display unit 16 and the output voltage value. In the example of the display unit 16 illustrated in the explanatory diagram of FIG. 4, the gradation value is represented by 64 bits.

  When the liquid crystal panel is used, a plurality of reference voltages V1, V2, V3, V4,... Are generated by the D / A converter and applied to the electrodes of each element of the liquid crystal panel, and this is divided by the ladder resistance. Create by. In the display unit 16, a voltage created corresponding to the input gradation value is selected and output to the element corresponding to each pixel. As shown in the explanatory diagram of FIG. 4, there is a point where the reference voltages (V2, V3, V4) used when generating the voltage are switched. This switching point causes non-linearity in the relationship between the input gradation value and the output voltage value.

  FIG. 5 is a graph showing an example of the correspondence between the gradation value input to the D / A converter and the output voltage value. The horizontal axis of the graph of FIG. 5 indicates the input gradation value, and the vertical axis indicates the voltage value created for each gradation value.

  As shown in the graph of FIG. 5, the voltage value applied to the electrodes of the liquid crystal panel corresponding to the input gradation value has a plurality of non-smooth sharp portions, that is, a steep slope with respect to the gradation value. The curve has a point (point) that changes to. Circles represented by broken lines in FIG. 5 indicate cusps. These cusps correspond to the switching points of the reference voltages (V2, V3, V4) in the explanatory diagram of FIG. The non-linear portions of the curves A, B, and C shown in the graph of FIG. 3 are near the cusps of the curve indicating the relationship between the gradation value of the input digital signal and the reference voltage shown in the graph of FIG. The analysis shows that the distortion is caused.

  In view of this, the LUT 14 according to the present embodiment uses the display unit 16 of the display device 1 serving as a reference for the portion corresponding to the non-linear part of the distribution of the gamma values with respect to the input gradation values shown in the graph of FIG. Is corrected using the first correction value for setting the gamma value to γ = 2.2 over all gradation values. The LUT 14 further provides a second correction value for correcting the gradation characteristics of the individual display units 16 corresponding to the linear portions so that the gamma value approaches γ = 2.2 over all gradation values. It is configured to calculate and correct the gradation value included in the input image signal using this.

  First, calculation of the first correction value for correcting the portion corresponding to the nonlinear portion will be described. The reference gradation characteristics may be obtained by, for example, extracting an arbitrary display device 1 and measuring the gradation characteristics of the display unit 16 included in the display device 1. A plurality of display devices 1 may be extracted in advance, the gradation characteristics of each display unit 16 may be measured, and the gradation characteristic that becomes the median value from the measured gradation characteristics may be used as a reference. Further, an average of gradation characteristics measured by several display devices 1 may be calculated, and the average may be used as a reference gradation characteristic. In addition to obtaining the reference gradation characteristics by actual measurement, the gradation characteristics are calculated by calculation formulas or simulations from the components of the drive circuit constituting the display unit 16 included in each display device 1, and the gradation characteristics are calculated. It may be based on characteristics.

  In the present embodiment, the gradation characteristics of the display unit 16 of each of the three display devices 1 are measured, the display device 1 having the gradation characteristic as the median value is extracted, and the display unit 16 of the extracted display device is extracted. The gradation characteristics are set as a reference. In the example shown in the graph of FIG. 3, the gradation characteristic represented by the curve B is a median value and is set as a reference.

  FIG. 6 is a graph showing an example in which the reference gradation characteristic is corrected. The horizontal axis of the graph of FIG. 6 indicates the gradation value input to the display unit 16, and the vertical axis indicates the gamma value γ with respect to the input gradation value. A broken line in FIG. 6 indicates a gradation characteristic specific to the display unit 16 of the display device 1 set as a reference, and is equal to the curve B in FIG. A solid line in FIG. 6 indicates the gradation characteristic after the reference gradation characteristic is corrected by the first correction value. Further, the alternate long and short dash line in FIG. 6 indicates a straight line with a gamma value γ = 2.2.

First, the first correction value is calculated in advance for each input gradation value so that the gradation characteristic set as a reference is γ = 2.2 over all gradations. Specifically, the first correction value = γ _target / γ _{ref x} , γ _target = target gamma value (for example, 2.2), and γ _{ref x} = gamma value at the input gradation value x in the reference gradation characteristic. is there. For example, when the gamma value for one input gradation value x1 in the reference gradation characteristic is γ _{ref x1} = 2.3, the first correction value for the input gradation value x1 is (2.2 / 2.3). ) Is calculated. When the gamma value for the other input tone value x2 in the reference tone characteristic is γ _{ref x2} = 2.5, the first correction value for the input tone value x2 is (2.2 / 2.5). ) Is calculated. In the LUT 14, the gradation value x in the following expression 2 and the gradation value x ′ after correction using the first correction value are stored in association with each other. The LUT 14 outputs the corrected gradation value x ′ stored in association with the gradation value x included in the input image signal.

Tone value after correction x ′ = x ^α , α (first correction value) = γ _target / γ _{ref x} (2)

As a result, the gamma value γ is the target gamma value γ = 2.2 over all gradations in the reference gradation characteristics. For example, when the LUT 14 inputs an image signal to the display unit 16 and the gradation value included in the image signal input from the unevenness correction unit 13 to the LUT 14 is x1, the LUT 14 is associated with the gradation value x1, Since x1 ′ = x1 ^{(2.2 / 2.3)} corrected using the first correction value α = (2.2 / ^2.3) is stored, x1 ′ is output. Similarly, when the gradation value included in the image signal input from the unevenness correction unit 13 to the LUT 14 is x2, the LUT 14 sets x2 ′ = x2 ^{(2.2 / 2.5)} stored in association with the gradation value x2. Output.

  Due to the correction using the first correction value α in the LUT 14 described above, the gradation characteristic of the display unit 16 represented by the broken line in FIG. 6 is compared with the gradation value included in the image signal input to the LUT 14. As shown by the solid line in FIG. 6, it is a substantially linear function with γ = 2.2.

  Next, the first correction value α is used so that the reference gradation characteristic is γ = 2.2 over all gradations, and the first stage of the display unit 16 of the display device 1 having individually different gradation characteristics is used. A case where correction is performed by the LUT 14 will be described.

  FIG. 7 is a graph showing an example of gradation characteristics in the display unit 16 of each display device 1 when correction is performed by the LUT. FIG. 7A is a graph showing an example of gradation characteristics when the LUT 14 performs correction using the first correction value α calculated based on the reference gradation characteristics. In the graph of FIG. 7A, the horizontal axis indicates the gradation value input to the LUT 14, and the vertical axis indicates the gamma value for the input gradation value. The gradation value on the horizontal axis is the gradation value x before correction according to Equation 2. A broken line in FIG. 7A indicates a gradation characteristic specific to the display unit 16 for comparison, and is equal to the curve C in FIG. Also, the alternate long and short dash line in FIG. 7 indicates a straight line with a gamma value γ = 2.2.

  When the gradation value x for each color component output from the unevenness correction unit 13 is corrected by the expression 2 in the LUT 14 of each display device 1, as shown in the graph of FIG. The non-linear part in the distribution is eliminated and converted into a substantially linear shape. However, in the correction using the first correction value α, as shown in the graph of FIG. 7A, the gamma value γ is not 2.2 over all gradations.

  Therefore, in this embodiment, the distribution of the gamma value with respect to the input gradation value after correction using the first correction value α is treated as a linear function, and the slope and intercept are specified. For this reason, first, output luminances at two input tone values are measured with respect to a linear function distribution of the corrected gamma value using the first correction value α, and the inherent gamma in the display unit 16 of each display device 1 is measured. Obtained by calculating the value. The x mark in FIG. 7A indicates a specific gamma value for two input gradation values. As a result, the slope and intercept of the linear function shown in the graph of FIG. Then, a second correction value for calculating a linear function distribution of the gamma value as a gamma value γ = constant distribution is calculated from the specified slope and intercept, and a gradation value to be corrected by taking the second correction value into account is obtained. It is stored in the LUT 14 in association with the input gradation value. A specific example of the method for calculating the second correction value will be described later in detail.

  The graph of FIG. 7B is a distribution of gamma values when correction using the second correction value calculated based on the specified linear function is performed. In the graph of FIG. 7B, the horizontal axis indicates the gradation value input to the LUT 14, and the vertical axis indicates the gamma value for the input gradation value. The gradation value on the horizontal axis is the gradation value x before correction according to Equation 2. For comparison, the broken line in FIG. 7B shows the distribution of the gamma value with respect to the input gradation value after correction using the first correction value α, and is equal to the solid line in FIG. 7A. Further, the alternate long and short dash line in FIG. 7B shows a straight line with a gamma value γ = 2.2.

  As shown in the graph of FIG. 7B, the correction using the first correction value α and the second correction value causes the gamma value to be substantially equal to the entire gradation value with respect to the input gradation value. It becomes a constant value. By this correction, the gradation characteristics of each display unit 16 are absorbed, and smooth gradation expression can be realized on the display unit 16 by the gradation value for each color component of the image signal output from the unevenness correction unit 12. it can.

  A specific example of a second correction value calculation method for correcting the gradation value by specifying the slope and intercept of the linear function shown in the graph of FIG. 7A will be described in detail below.

First, an image signal including one input gradation value after correction using the first correction value α, for example, x = 64, is input, and output luminance corresponding to the input gradation value is measured. Then, a gamma value γ ₆₄ for x = ₆₄ is acquired from the output luminance. When the gamma value when the input gradation value included in the image signal input to the LUT 14 is x = 64 is γ ₆₄ = 2.3, the gamma value γ ₆₄ = 2.3 is set over all gradation values. Conversion is performed so that γ _target = 2.2 which is a target gamma value. That is, the gradation value x ′ corrected by Expression 2 is converted by Expression 3 shown below.

Tone value x ″ = x ′ ^β after correction, converted value β = (γ _{ref 64} / γ ₆₄ ) (3)

  Equation 3 is converted into Equation 4 shown below.

Gradation value after correction ^{x'' = x δ = (x α} ) β = x α * β, δ = (γ target / γ ref x) * (γ ref 64 / γ 64), γ ref 64 = criteria Gamma value at gradation value x = 64 in the gradation characteristic, unique gamma value acquired when γ ₆₄ = x = 64 (4)

By inputting an image signal including the corrected gradation value x ″ to the display unit 16, the gamma value for the gradation value x = 64 becomes γ = 2.2. When the specific gamma value γ ₆₄ = 2.3 of the display unit 16 with the gradation value x ″ = 64 input to the display unit 16, the output luminance is x ″ ^2.3 = (x ^δ ) ^2.3 = x ^{δ * 2.3} . Here, the index δ * 2.3 of x is {(2.2) / (2.3) * (2.3) /2.3} = 2.2 (γ = 2.2).

  The linear function indicated by the solid line in the graph of FIG. 7A by the correction of Expression 4 is translated as indicated by the two-dot chain line in the graph of FIG. 7A, and the gradation value is x = 64, a linear function passing through a point where the gamma value is γ = 2.2. This makes it possible to calculate the slope without obtaining an intercept. In this case, when the slope of the linear function is a, the linear function is expressed by the following formula 5.

  (Γ−2.2) = a (x−64) (5)

  In order to correct the linear gradation characteristic as shown in FIG. 7A to an ideal gradation characteristic, that is, to make the gamma value constant, the following expression is obtained by adding Expression 5 = zero to the gamma value. The correction formula f (x) represented by 6 is required.

  f (x) = − a (x−64) (6)

  In order to specify the inclination a, a gamma value at another gradation value is required. Here, as an example, the gamma value at x = 192 is acquired. Thereby, the inclination a can be calculated by the following equation 7.

a = (γ ₁₉₂ −γ ₆₄ ) / (192-64), γ ₁₉₂ = (specific gamma value acquired when x = 192), γ ₆₄ = (specific value acquired when x = 64) Gamma value) (7)

  By combining Equations 4, 6, and 7, the gamma value representing the gradation characteristic at the display unit 16 is constant at γ = 2.2 with respect to the gradation value input to the LUT 14 in each display device 1. In order to achieve this, correction is performed by the following equation (8).

Tone value after correction x ′ ″ = x ^ε , ε = (γ _target / γ _{ref x} ) * (γ _{ref 64} / γ ₆₄ ) + f (x) = [(γ _target / γ _{ref x} ) * (γ _{ref 64} / γ ₆₄ ) − {(γ ₁₉₂ −γ ₆₄ ) / (192-64)} * (x−64)] = (8)

  The corrected gradation value x ″ ″ is stored in the LUT 14 in association with the gradation value x. The LUT 14 outputs the corrected gradation value x ′ ″ stored in association with the gradation value x for each color component included in the image signal output from the unevenness correction unit 13. As a result, the LUT 14 is configured to perform correction using ε in Equation 8 described above as the second correction value.

The LUT 14 has a corrected level obtained by using the first correction value α = (γ _target / γ _{ref x} ) = (target gamma value / gamma value at the gradation value x in the reference gradation characteristic). The tone value is stored in association with the input tone value x. The second LUT 14 includes a second LUT, and the second LUT 14 has a corrected level using ζ1 = (γ _{ref 64} / γ ₆₄ ), ζ2 = slope a, and ζ3 = 64 as the second correction values. The tone value may be stored in association with the input tone value. In this case, using the first correction value α and the second correction values ζ1, ζ2, and ζ3, ε in Expression 8 can be transformed as shown in Expression 9 below.

  ε = {α * ζ1-ζ2 (x−ζ3)} (9)

  By inputting the gradation value x ′ ″ thus corrected to the display unit 16, the solid line in the graph of FIG. 7B with respect to the gradation value input to the LUT 14 in each display device 1. As shown in FIG. 5, the gradation characteristic can be made constant with the gamma value γ = 2.2 over the entire gradation value.

  In the above description, x = 64 and x = 192 are given as an example of the two gradation values, but it goes without saying that other gradation values may be used. When calculating the inclination, if the inclination is zero in a part of the gradation value range of the reference gradation characteristics, the gradation value in the gradation value range may be used. Thereby, it is possible to calculate the inclination a of the linear portion in the display unit 16 of each display device 1 more easily.

Next, the above process will be described with reference to a flowchart. Note that the processing shown in the flowchart of FIG. 8 is performed in advance by a correction device connected to store the first correction value and the second correction value in the LUT 14 in the manufacturing process. Here, the correction device is, for example, an adjustment personal computer installed in the production line.
When each display device 1 receives an image signal from the image signal output device 2 and inputs the image signal to the display unit 16, the gradation value for each color component included in the received image signal is obtained by the LUT 14 in the previous stage of the display unit 16. The correction is performed using the first correction value and the second correction value.

  FIG. 8 is a flowchart illustrating an example of a processing procedure for calculating the first correction value in the present embodiment. The correction device calculates the reference gradation characteristics by actually measuring with one display device 1 or taking a median value based on the measurement results of the plurality of display devices 1 (step S11). Then, the first correction value is calculated so that the reference gradation characteristic is a predetermined gradation characteristic, that is, a gradation characteristic that is constant at a gamma value γ = 2.2 (step S12). Then, the correction device stores the corrected gradation value using the calculated first correction value in the storage area of the correction device itself (step S13), and ends the process.

  FIG. 9 is a flowchart illustrating an example of a processing procedure for calculating the second correction value in the present embodiment. The processing shown in the flowchart of FIG. 9 is configured to be performed on each display device 1. Note that each display device 1 here is a display device 1 to be corrected, which is different from the display device 1 that is a target of measurement of the gradation characteristics serving as a reference in the flowchart of FIG. In each of the display devices 1 to be corrected, the test pattern is sequentially input over all gradation values, and the process shown in the flowchart of FIG. 9 is performed.

  The LUT 14 of the display device 1 stores the corrected output gradation value calculated using the first correction value stored in the correction device in association with the input gradation value ( Step S21). In the display device 1, each gradation value included in the image signal input to the LUT 14 is corrected by the LUT 14, and the LUT 14 inputs an image signal including the corrected gradation value to the display unit 16 (step S22). The display device 1 calculates and acquires a gamma value from the output luminance for one gradation value in the display unit 16 (step S23). Here, the measurement of the output luminance in the display unit 16 is performed by a measuring device connected in the manufacturing process, and the display device 1 acquires the output luminance or the gamma value from the measuring device. Then, the display device 1 stores the corrected gradation value obtained by the above equation 4 in the LUT 14 based on the acquired gamma value, and the gamma value in the one gradation value is a predetermined gamma value γ = 2. 2 is corrected (step S24).

  Next, the display device 1 calculates and acquires a gamma value from the output luminance for the other gradation value after the correction in step S24 (step S25). The display device 1 calculates the slope and intercept of the linear function of the distribution of the gamma value with respect to the gradation value from the gamma value with respect to the two gradation values acquired in step S23 and step S25 (step S26), and calculates the first slope from the calculated inclination. 2 correction values are calculated (step S27), and the corrected gradation value using the first correction value stored in the LUT 14 is rewritten to the corrected gradation value using the second correction value (step S28). ), The calculation and storage processing of the second correction value is terminated.

  In the processing procedure shown in the flowchart of FIG. 9, the linear function is corrected so that it passes through the gamma value γ = 2.2 in one gradation value by the processing in step S24. Therefore, for the slope calculated in step S26 in the processing procedure shown in the flowchart of FIG. 9 and the intercept in the intercept, it is only necessary to calculate the slope using the gamma value γ = 2.2. As a result, the calculation can be simplified, but it is of course possible to omit the processing in step S23 and calculate the slope and intercept from the gamma values of the two input gradation values.

  The corrected gradation value using the second correction value calculated by the processing procedure described above is written in the LUT 14 in association with the input gradation value. Thereafter, the LUT 14 outputs the gradation value corrected by Expression 8 using the second correction value for the gradation value for each color component included in the image signal output from the unevenness correction unit 13, and the output unit 15. Is input to the display unit 16.

  When the correction method shown in the present embodiment is used, information to be measured for calculating the second correction value may be the following information. For example, the maximum luminance and chromaticity of each color of R, G, B, and W on the display unit 16, and the luminance for the minimum two input gradation values (gradation values at x = 64 before correction, at x = 64) (Gradation value at x = 192 after correction so that γ = 2.2). In this way, by reducing the amount of information to be measured in advance and making the correction possible with a simple configuration, gamma correction can be performed quickly, as shown in FIG. 7B. It is possible to correct the gradation characteristics in the display unit 16 to be constant with high accuracy.

  In the present embodiment, the distribution of gamma values with respect to input gradation values remaining when correction is performed using the first correction value calculated from the reference gradation characteristics is treated as a linear function, and the gamma values for two gradation values are calculated. It was set as the structure which calculates | requires the inclination and intercept for acquiring by measurement and specifying a linear function. However, the present invention is not limited to this, and the gamma value distribution treated as a linear part is treated as a predetermined high-order function, and a gamma value for several gradation values for specifying this is obtained by measurement. Also good.

  In the present embodiment, the corrected gradation value using the first correction value stored in the LUT 14 in association with each gradation value is changed to the corrected gradation value using the second correction value. The configuration was rewritten. However, it may be configured to include two LUTs that individually store gradation values to be corrected using the first correction value and the second correction value.

  In this embodiment, correction for gradation values of a plurality of color components is taken as an example. However, the present invention may be applied to correction for gradation values in a monochrome image signal.

  In the description of the processing procedure shown in the flowcharts of FIG. 8 and FIG. 9 described above, in the manufacturing process of each display device 1, the correction characteristic is measured as a reference gradation characteristic, and the first correction value is calculated. Then, the correspondence between the input gradation value and the corrected gradation value is stored, and the input gradation value using the first correction value and the corrected gradation value are determined by each display device 1 to be corrected. Is stored and the second correction value is calculated. The processing procedure shown in the flowchart of FIG. 9 can be performed not only during the manufacturing process but also during operation as the display device 1. In other words, the first correction value calculated from the reference gradation characteristics is not stored in the LUT 14 but separately stored in a non-rewritable storage area, and the display apparatus 1 itself uses the first correction value for the LUT 14 after correction. After the second tone value is stored again, the subsequent processing (processing from step S22 to step S28) is performed to recalculate the second correction value. At this time, the measurement of the output luminance in the display unit 16 in step S25 may be configured such that the user can measure and input to the display device 1 using the measuring device.

  As described above, the display device 1 itself has an excellent effect in that it can correct the gradation characteristics that have changed due to aging not only by the manufacturing process but also by the years of use. In addition, the display device 1 keeps the number of years of use, and the display device 1 autonomously corrects the gradation characteristics, that is, recalculates the second correction value when the number of years of use passes a predetermined period. It is good.

  In the present embodiment, the conversion unit 12, the unevenness correction unit 13, and the LUT 14 are each required to increase the processing speed. Therefore, the configuration is realized by each module configuring the ASIC and the FPGA provided in the display device. did. However, the computer apparatus may be configured to perform gamma correction of an image displayed on a monitor connected to the computer apparatus by causing the computer apparatus to execute a computer program for executing the correction method according to the present invention. FIG. 10 is a block diagram showing a configuration when the correction method according to the present invention is implemented by a computer apparatus. In this case, the computer apparatus 3 includes a control unit 30 such as a CPU and an MPU, a storage unit 31 such as a hard disk (Hard Disk), an EEPROM (Electronically Erasable and Programmable Read Only Memory), and the corrected image signal to the monitor 4. And an output unit 32 for outputting.

  The storage unit 31 stores a control program 3P for causing the computer apparatus 3 to perform the correction method according to the present invention on the image signal received via the input unit 32. The control program 3P includes a conversion unit 33, an unevenness correction unit 34, and a gamma correction unit 35, which are modules for causing the control unit 30 to function as the conversion unit 12, the unevenness correction unit 13, and the LUT 14 in the display device 1 described above. ing. The control program 3P stored in the storage unit 31 is recorded on a portable recording medium such as a DVD or CD-ROM (not shown), and the control unit 30 includes an auxiliary storage unit (not shown) such as a DVD / CD drive. ), The control program 3P recorded on the portable recording medium may be stored in the storage unit 31.

  The control unit 30 of the computer device 3 having such a configuration reads and executes the control program 3P from the storage unit 31, and the input unit 32 from the image signal output device 2 by the function of the gamma correction unit 35 included in the control program 3P. The gradation value of each color component represented by the image signal received via the image signal is converted by the function of the conversion unit 33, and the luminance unevenness and the color unevenness are corrected by the function of the unevenness correction unit. The control unit 30 can further perform gamma correction for smoothing the gradation characteristics of the connected monitor 4 by the function of the gamma correction unit 35.

It is a block diagram which shows the structure of the display apparatus which concerns on this invention. It is explanatory drawing which shows the outline | summary of a gamma correction. It is a graph which shows the example of the gradation characteristic which changes with the display parts with which each display apparatus is provided. It is explanatory drawing which shows the example of a response | compatibility with the gradation value input into the digital / analog (D / A) converter which comprises the drive circuit of a display part, and the output voltage value. It is the graph which showed the example of the correspondence of the gradation value input into a D / A converter, and the output voltage value. It is a graph which shows the example by which the reference | standard gradation characteristic is correct | amended. It is a graph which shows the example of the gradation characteristic in the display part of each display apparatus at the time of correct | amending by LUT. It is a flowchart which shows an example of the process sequence in which a 1st correction value is calculated in this Embodiment. It is a flowchart which shows an example of the process sequence in which a 2nd correction value is calculated in this Embodiment. It is a block diagram which shows the structure in the case of implementing the correction method which concerns on this invention with a computer apparatus.

Explanation of symbols

1 Display device 14 LUT (correction means)
16 Display section (display means)
2 Image signal output device 30 Control unit 34 Gamma correction unit (correction means)
3P control program

Claims (6)

In the correction method for correcting the intensity for each of one or a plurality of color components included in the image signal to be input to the display means using the stored correction amount when inputting the image signal to the display means for displaying an image,
A first correction amount for correcting the intensity of each color component included in the input image signal is stored so that the gradation characteristic of an arbitrary display means shows a predetermined gradation characteristic,
When an image signal including the intensity corrected using the first correction amount is input to the display unit, the relationship between the output intensity in the display image displayed by the display unit and the input intensity is specified,
Based on the identified relationship, a second correction amount for correcting the intensity of each color component included in the image signal input to the display means is calculated,
Store the calculated second correction amount,
When an image signal is input to the display unit, the intensity for each color component included in the input image signal is corrected using the second correction amount. The arbitrary display means includes
The correction method according to claim 1, wherein display means having a gradation characteristic that is a median value is extracted from the plurality of display means. Measuring the gradation characteristics of the arbitrary display means,
The correction method according to claim 1, wherein the first correction amount is calculated based on a comparison between the measured gradation characteristic and the predetermined gradation characteristic. The relationship is expressed by a linear function in which the logarithm of the output intensity based on the input intensity is a variable of the input intensity,
Obtaining an output intensity in a display image displayed by the display means when an image signal including at least two different input intensities is input;
Identifying the linear function from the two different input intensities and the acquired output intensities;
The correction method according to claim 1, wherein the second correction amount is calculated from the identified linear function. In a display device comprising: display means for displaying an image; and correction means for correcting the intensity for each of one or a plurality of color components included in an image signal input to the display means using a stored correction amount;
The image signal including the intensity corrected by using the first correction amount for correcting the intensity of each color component included in the input image signal so that the gradation characteristic of an arbitrary display means shows the predetermined gradation characteristic. A second correction unit that corrects the intensity of each color component included in the image signal input to the display unit based on the relationship between the output intensity of the display image displayed by the display unit and the input intensity when input to the display unit. Means for calculating a correction amount;
Means for storing the second correction amount;
The correction means, when inputting an image signal to its own display means, corrects the intensity of each color component included in the input image signal using the second correction amount. apparatus. A step of correcting the intensity for each of one or a plurality of color components included in the image signal input to the display means using a correction amount stored in a computer having means for inputting the image signal to display means for displaying an image. In a computer program that executes
On the computer,
The intensity is corrected using the first correction amount stored for correcting the intensity of each color component included in the input image signal so that the gradation characteristic of an arbitrary display means shows a predetermined gradation characteristic. Step to do,
Inputting an image signal including the corrected intensity to the display means;
Identifying the relationship of the output intensity in the display image displayed by the display means when input to the display means to the input intensity;
Calculating a second correction amount for correcting the intensity of each color component included in the image signal input to the display means based on the identified relationship; and
When inputting an image signal to the display means, a computer program for executing the step of correcting the intensity of each color component included in the input image signal using the first correction amount and the second correction amount .

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