JP2014235209A - Gamma adjustment method, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a display with almost uniform gradation irrespective of a pixel position within a screen with respect to the same input gradation without increase in circuit size or adjustment time.SOLUTION: A gamma adjustment method is configured to: perform a gamma adjustment to predetermined reference coordinates included in M×N sets of coordinates set to a screen, and measure a maximum luminance value and an intermediate luminance value as to each set of the M×N sets of coordinates (S3 and S4); calculate a luminance normalization value obtained by dividing an intermediate luminance value measured in the S4 by the maximum luminance value measured in the S4 as to each set of the M×N sets of coordinates (S5); calculate a luminance deviation indicated by a difference between the luminance normalization value of the reference coordinates and the luminance normalization value of each set of the M×N sets of coordinates, for each set of the M×N sets of coordinates, on the basis of the calculated normalization value (S6); determine a gamma correction value for each set of the M×N sets of coordinates from a plurality of preliminarily determined correction values on the basis of the luminance deviation in the calculated intermediate gradation for each set of the respective M×N sets of coordinates (S7); and cause a display device to store the gamma correction value in association with each set of the M×N sets of coordinates (S8).

Description

  The present invention relates to a gamma adjustment method and a display device, and more particularly to a gamma adjustment method for adjusting gamma of a display device and a display device that is gamma adjusted by the method.

  Conventionally, gamma adjustment is performed in a production line of a liquid crystal television which is one of thin display devices. In general, the gamma (γ) of a liquid crystal television is adjusted to 2.2, which is the same as that of a CRT. In normal gamma adjustment, the gamma value is adjusted for a plurality of gradations (for example, about 10 gradations) at the center of the screen of the liquid crystal panel, and the gamma value is set as the gamma value for the entire screen.

  The above gamma adjustment method will be briefly described. First, a predetermined measuring instrument is set at the center of the screen of the liquid crystal panel, and the luminance (and chromaticity) at the center of the screen of the liquid crystal panel is measured for a predetermined input gradation of the video signal. Then, the gamma is adjusted so that the measured value becomes the target value, and an LUT (Look Up Table) for gamma conversion is created.

For example, as shown in FIG. 11A, the screen luminance (cd / m ² ) for a plurality of gradations (0 to 255: 1 point, 2 points, 3 points,..., S point) of the video signal. ) Is adjusted so that the measured value becomes the target value. At this time, in order to increase the accuracy of the gamma adjustment, it is only necessary to increase the input gradation for gamma adjustment and increase the number of measurement points. Between input gradations that have been gamma adjusted in this manner, an intermediate value is set by a method such as linear interpolation, and a gamma curve indicating input / output characteristics is determined.

  For example, as shown in FIG. 11B, the conversion using the gamma curve is realized by using LUTs independently for each of RGB. The LUT is stored in a ROM (Read Only Memory) or a RAM (Random Access Memory) of the liquid crystal television, and converts the input gradation (Rin, Gin, Bin) into an output gradation (Rout, Gout, Bout). That is, the LUT is referred to using the input gradations of RGB as addresses, and the output gradation (gradation after gamma adjustment) is determined.

  On the other hand, in the liquid crystal panel, the input gradation of the video signal (0 to 255 in the case of 8 bits) is converted from digital to analog, the inclination of the liquid crystal element is controlled by the voltage value, and the light quantity is adjusted. However, display elements such as liquid crystals have different characteristics such as TFTs (Thin Film Transistors) constituting pixels even in the same liquid crystal panel due to the manufacturing process. For this reason, even if the same voltage is applied, the inclination of the liquid crystal element is different, which causes a difference in the amount of transmitted light. In other words, in the case of pixels having the same input gradation and different positions, the amount of light is not the same depending on the pixel position because the inclination of the liquid crystal element varies. That is, although the input gradation is the same, the amount of light varies depending on the pixel position in the liquid crystal panel, resulting in a non-uniform display.

  On the other hand, for example, Patent Document 1 discloses a technique in which a screen is divided into a plurality of M × N areas, and correction is performed with different gamma characteristics in each area. Specifically, the screen is divided into a plurality of M × N areas, a gamma adjustment point is provided for each M × N, and the gamma characteristic of each area is calculated. Then, the display device manages the coordinates of the video signal to be displayed, determines which region of M × N corresponds to the coordinate, selects the gamma characteristic of the determined region, and performs processing. Thereby, uniform display output can be performed for the same input gradation regardless of the pixel position in the screen.

JP 2000-298450 A

  However, in the technique described in Patent Document 1, an LUT is required for each M × N area. Therefore, if the adjustment area is increased, the circuit scale is increased accordingly. For example, if there are nine adjustment areas, a total of nine LUTs must be prepared, one for each adjustment area. If the number of input gradation adjustment points is S, it is necessary to adjust M × N × S. However, in order to perform gamma adjustment with higher accuracy, increase M, N, and S. As a result, the adjustment time may increase accordingly.

  The present invention has been made in view of the above-described circumstances. For the same input gradation, a substantially uniform gradation regardless of the pixel position in the screen without increasing the circuit scale and the adjustment time. It is an object of the present invention to provide a gamma adjustment method that enables display with a gender and a display device that is gamma adjusted by the method.

In order to solve the above-mentioned problem, a first technical means of the present invention is a gamma adjustment method for adjusting gamma of a display device, wherein a coordinate setting for setting a plurality of adjustment target coordinates on the screen of the display device is provided. A gamma adjustment step for performing gamma adjustment on predetermined reference coordinates and determining a reference gamma value of the display device;
A maximum luminance value measurement step for measuring a maximum luminance value of the adjustment target coordinates when a maximum gradation image signal is input for the plurality of adjustment target coordinates; and an intermediate gradation image signal for the plurality of adjustment target coordinates. An intermediate luminance value measuring step for measuring an intermediate luminance value of the adjustment target coordinates when input, and an intermediate luminance value measured in the intermediate luminance value measuring step for the plurality of adjustment target coordinates in the maximum luminance value measuring step. Based on the brightness normalized value calculated in the brightness normalized value calculating step and the brightness normalized value calculated in the brightness normalized value calculating step, for each of the plurality of adjustment target coordinates, A luminance deviation calculating step of calculating a luminance deviation indicated by a difference or a ratio between a luminance normalized value of the reference coordinates and a luminance normalized value for each of the plurality of adjustment target coordinates; Gamma correction for each of the plurality of adjustment target coordinates from among a plurality of gamma correction difference values determined in advance based on the luminance shift in the intermediate gradation for each of the plurality of adjustment target coordinates calculated in the shift calculation step. A gamma correction difference value determining step for determining a difference value, and a gamma correction difference value stored in the display device in association with each of the plurality of adjustment target coordinates, the gamma correction difference value determined in the gamma correction difference value determining step. And a storing step.

  According to a second technical means, in the first technical means, the gamma correction difference value determining step includes a value of a luminance deviation in an intermediate gradation for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculating step, and By comparing the correction luminance deviation value in the intermediate gradation region for each of the plurality of predetermined gamma correction difference values, a correction luminance deviation corresponding to the luminance deviation is determined, and the determined correction luminance deviation is determined. A corresponding gamma correction difference value is determined, and the correction luminance deviation in the intermediate gradation region for each of the plurality of gamma correction difference values is determined by calculating a correction gamma value from a difference between each of the plurality of gamma correction difference values and the reference gamma value. A corrected brightness that calculates a corrected brightness normalized value for a gradation normalized value obtained by dividing an input gradation value of at least the intermediate gradation range of the video signal by the maximum gradation value for each calculated corrected gamma value. Based on the normalized value calculation step and the corrected luminance normalized value calculated in the corrected luminance normalized value calculating step, the corrected luminance normalized value at the reference gamma value and each of the respective gamma correction difference values It is characterized in that it is obtained by a corrected luminance deviation calculating step for calculating a corrected luminance deviation indicated by a difference or ratio between the corrected gamma value and the corrected luminance normalized value.

  According to a third technical means, in the second technical means, the value of the corrected luminance deviation in the intermediate gradation range includes a peak value of the corrected luminance deviation, and the gamma correction difference value determining step includes the calculation of the luminance deviation. The luminance deviation value in the intermediate gradation for each of the plurality of adjustment target coordinates calculated in the step, and the correction luminance deviation peak in the intermediate gradation area for each of the gamma correction difference values calculated in the correction luminance deviation calculation step. The correction brightness shift having a peak value closest to the brightness shift value is determined as a correction brightness shift corresponding to the brightness shift.

  A fourth technical means is a display device that is gamma-adjusted by the gamma adjustment method in any one of the first to third technical means, wherein the gamma correction is performed for each of the reference gamma value and the plurality of adjustment target coordinates. A storage unit that stores a difference value, and a gamma adjustment unit that performs gamma adjustment using the reference gamma value stored in the storage unit and a gamma correction difference value of each of the plurality of adjustment target coordinates. It is what.

  According to a fifth technical means, in the fourth technical means, the gamma adjustment unit obtains coordinates of a display pixel when displaying a video signal on the display device, and coordinates of the display pixel and the plurality of adjustments. Calculating a distance to peripheral coordinates located around the coordinates of the display pixel among the target coordinates, and weighting a gamma correction difference value of the peripheral coordinates stored in the storage unit based on the calculated distance Thus, the gamma correction difference value of the display pixel is calculated.

  According to the present invention, the same input gradation can be displayed with substantially uniform gradation regardless of the pixel position in the screen without increasing the circuit scale and adjustment time.

It is a block diagram which shows the structural example of the display apparatus and gamma adjustment apparatus which concern on this invention. It is a figure which shows an example of the coordinate set with respect to the screen of a display apparatus. It is a figure which shows an example of the luminance measurement result with respect to the screen of FIG. It is a figure which shows an example of the measurement data after normalizing with respect to the measurement result of FIG. It is a figure which shows an example of the theoretical calculation result when it is assumed that the gamma characteristic shifted | deviated. It is a flowchart for demonstrating an example of the gamma adjustment method by this invention. It is a figure for demonstrating the other specific example of the gamma adjustment method by the display apparatus and gamma adjustment apparatus of FIG. It is a figure for demonstrating an example of the gamma adjustment process of the display apparatus by this invention. It is a figure for demonstrating an example of the gamma adjustment process of the display apparatus by this invention. It is a figure for demonstrating an example of the gamma adjustment process of the display apparatus by this invention. It is a figure for demonstrating a prior art.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a gamma adjustment method of the present invention and a display device that is gamma adjusted by the method will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration example of a display device and a gamma adjustment device according to the present invention, in which 10 denotes a display device and 50 denotes a gamma adjustment device. The display device 10 can be exemplified as a television receiver, for example, and will be described as the television receiver 10 below. The television receiver 10 receives video / audio data transmitted by terrestrial digital broadcasting and video / audio data transmitted by satellite broadcasting. In order to receive each video / audio data, a digital terrestrial broadcasting antenna 32 and a satellite broadcasting antenna 33 are provided outside the television receiver 10.

  Video / audio data transmitted by terrestrial digital broadcasting is supplied from the terrestrial digital broadcasting antenna 32 to the terrestrial digital broadcasting tuner 11. The terrestrial digital broadcast tuner 11 selects a channel designated by the user from a plurality of channels in the terrestrial digital broadcast, and supplies video / audio data of the channel to the selector 14.

  Video / audio data transmitted by satellite broadcasting is supplied from the satellite broadcasting antenna 33 to the satellite broadcasting tuner 12. The satellite broadcast tuner 12 selects a channel designated by the user from a plurality of channels in the satellite broadcast, and supplies video / audio data of the channel to the selector 14.

  The television receiver 10 may further include an external input terminal 13. The external input terminal 13 is an interface for connecting external devices such as an HD (Hard Disk) recorder and a BD (Blu-ray (registered trademark) Disk) to the television receiver 10. The interface is one in which the television receiver 10 receives video / audio data from the external device, and conforms to a standard capable of connecting the television receiver 10 and the external device. It is. Examples of such interface standards include HDMI (registered trademark) (High-Definition Multimedia Interface) and HDV (High-Definition Video: IEEE1394). When an external device is connected to the television receiver 10, video / audio data recorded in the external device is supplied to the selector 14 via the external input terminal 13.

  The user can select a video / audio data supply source to be viewed via the remote control 31 or an operation panel (not shown). An operation signal output from the remote controller 31 when operated by the user is supplied to the control unit 22 via the infrared light receiving unit 21. The control unit 22 controls the selector 14 based on the operation signal. For example, when the user selects viewing of the terrestrial digital broadcast using the remote controller 31, the remote controller 31 outputs an operation signal corresponding to the operation. Upon receiving the operation signal, the control unit 22 controls the selector 14 so that the selector 14 selects the terrestrial digital broadcast tuner 11 as an input source of video / audio data.

  The selector 14 supplies the audio / video data from the terrestrial digital broadcast tuner 11 selected as the input source to the decoding unit 15. The decoding unit 15 first separates the supplied video / audio data into video data, audio data, and character information data. The character information data includes EPG (Electronic Program Guide) and OSD (On Screen Display) display data. Next, the decoding unit 15 decodes the video data and the audio data. The audio data decoded by the decoding unit 15 is output as audio from the speaker 17 via the audio signal processing unit 16.

  On the other hand, the video data decoded by the decoding unit 15 is supplied to the video signal processing unit 18. The video signal processing unit 18 appropriately performs A / D conversion processing, YI separation processing, IP conversion processing, matrix conversion processing, and other video processing on the supplied video data as necessary. As a result, the video signal processing unit 18 supplies the RGB signal converted from the video data to the image quality adjustment unit 19.

  The image quality adjustment unit 19 performs gamma adjustment (also referred to as gamma correction) by adjusting the gains of the RGB color signals supplied from the video signal processing unit 18. The image quality adjustment unit 19 may also be configured to execute white balance (WB) adjustment. In general gamma adjustment, the image quality adjustment unit 19 refers to the gamma adjustment value when performing gamma adjustment on the supplied RGB signal. The gamma adjustment value is stored in, for example, the nonvolatile memory 23.

  The gamma adjustment value defines the gain of each of the R, G, and B signals according to the input gradation of the RGB signal supplied to the image quality adjustment unit 19. The image quality adjustment unit 19 refers to, for example, a look-up table (LUT) as an association between input gradations of supplied RGB signals and gains of R, G, and B signals. Hereinafter, this LUT is referred to as a gamma adjustment LUT. Note that the location where the gamma adjustment LUT is stored is not limited to the memory 23, and the image quality adjustment unit 19 may include a unique nonvolatile memory.

  The RGB signal whose gamma has been adjusted by the image quality adjustment unit 19 is supplied to the LCD module 20, and the LCD module 20 displays an image corresponding to the RGB signal whose gamma has been adjusted.

  Each television receiver 10 is adjusted in gamma by using the gamma adjustment method according to the embodiment of the present invention before being shipped from the manufacturing factory. That is, the gamma adjustment method is executed as one of the manufacturing processes of the television receiver 10. By adjusting the gamma, the gamma adjustment value is stored in the non-volatile memory 23 as a gamma adjustment LUT. For example, when the television receiver 10 reaches the user's hand, the user may want to adjust the gamma to obtain the desired gradation. Therefore, the gamma of the television receiver 10 may be configured to be adjustable by the user via the remote controller 31 or the operation panel. At this time, the gamma adjustment value customized by the user may be stored in the nonvolatile memory 23 as a separate gamma adjustment LUT.

  The television receiver 10 includes an LCD module 20 as display means for displaying video. The LCD module 20 includes a liquid crystal panel and a backlight. The liquid crystal panel drives the liquid crystal included in each sub-pixel according to the RGB signals supplied from the image quality adjustment unit 19. Thus, the luminance of the color displayed by each sub-pixel is determined, and as a result, an image is displayed on the LCD module 20. As the backlight, a cold cathode fluorescent lamp (CCFL) or an LED can be used. Moreover, it can also be set as a backlight by using CCFL and LED together.

  Next, a configuration example of the gamma adjustment device 50 used when adjusting the gamma of the television receiver 10 will be described below with reference to FIG. The gamma adjustment device 50 includes a light detection unit 51, a control unit 52, a memory 53, and an output unit 54.

  As the light detection unit 51, a device generally called a color meter can be used. This color meter is roughly classified into a spectroscopic type and a stimulus value direct reading type based on the measurement principle. The spectroscopic colorimeter can measure the luminance and chromaticity with high accuracy, but has the disadvantage that the time required for the measurement is long. On the other hand, the stimulus value direct-reading type colorimeter is inferior to the spectroscopic method in terms of accuracy, but has an advantage of being able to measure luminance and chromaticity in a short time. In order to improve the manufacturing efficiency of the television receiver 10, it is preferable to use a stimulus value direct-reading color meter as the light detection unit 51.

  The light detection unit 51 is disposed at a position facing a predetermined region in the LCD module 20. The light detection unit 51 detects the light emitted from the LCD module 20 and supplies light intensity at predetermined wavelengths R, G, and B to the control unit 52 as a signal. In the control unit 52, the reference gamma value and the gamma correction difference value are determined by the gamma adjustment method described below. The reference gamma value and the gamma correction difference value determined by the control unit 52 are supplied to the output unit 54, and the output unit 54 converts the reference gamma value and the gamma correction difference value supplied from the control unit 52 to the adjustment terminal 24. The reference gamma value and the gamma correction difference value are stored in the memory 23.

2 to 5 are views for explaining the concept of the gamma adjustment method according to the present invention. In the example of FIG. 2, the luminance value for the input gradation (0 to 255) is measured at points P1 to P9 on the screen. It is assumed that the liquid crystal panel at this time is adjusted with, for example, gamma 2.2 at point P5. Then, the difference between the measured luminance value of the point P5 located at the center of the screen (the maximum luminance value at this time is 120 cd / m ² ) and the measured luminance values of the points P1 to P9 (hereinafter referred to as “screen luminance difference”). What was taken is shown in FIG. In FIG. 3, the horizontal axis represents the input gradation (8 bits: 0 to 255) of the video signal, and the vertical axis represents the screen luminance difference (cd / m ² ). The functions f1 to f9 correspond to the points P1 to P9. Since the function f5 corresponds to the point P5, the screen brightness difference is 0 for all input gradations.

  According to the measurement result of FIG. 3, when gamma adjustment is performed only at the point P5 in the center of the screen, the screen brightness is not constant at the other points P1 to P4 and P6 to P9 for the same input gradation. As described above, this is caused by variations in the characteristics of the display elements, and it can be seen that the gamma value is not constant depending on the position on the screen.

FIG. 4 is a diagram illustrating an example of measurement data after normalization is performed on the measurement result of FIG. 3. In the figure, the horizontal axis represents the input gradation (8 bits: 0 to 255) of the video signal, and the vertical axis represents the normalized measurement difference. The measurement data of FIG. 4 will be specifically described based on the example of FIG. First, in the example of FIG. 2, a value obtained by dividing the luminance value of each input gradation by the maximum luminance value at points P1 to P9 is set as a normalized measurement value. That means
Normalized measurement value = luminance value of each input gradation (cd / m ² ) / maximum luminance value (cd / m ² ) (1)
It becomes. Note that the maximum luminance values are considered to be equal at points P1 to P9.

  And based on the normalized measurement value of the points P1-P9, the difference of the normalized measurement value of the point P5 located in the center of a screen and each normalized measurement value of the points P1-P9 is taken. This difference corresponds to the normalized measurement difference in FIG. In FIG. 4, the functions f1 to f9 correspond to the points P1 to P9 as in the measurement result of FIG. Since the function f5 corresponds to the point P5, the normalized measurement difference is 0 for all input gradations.

FIG. 5 is a diagram illustrating an example of a theoretical calculation result when it is assumed that the gamma characteristic is shifted. In the figure, the horizontal axis represents the input gradation (8 bits: 0 to 255) of the video signal, and the vertical axis represents the normalized theoretical difference. First, in the case of the example of FIG. 2, gamma adjustment is performed at the point P5 located at the center of the screen by the following equation.
Y (IN) = (IN / Ymax) ^γ Expression (2)
However, IN is the input gradation value (0 to 255) of the video signal, Ymax is the maximum gradation value (255) of the video signal, and γ is the reference gamma value. That is, Y (IN) is a corrected luminance normalized value when the gamma adjustment is performed with the reference gamma value γ with respect to the gradation normalized value IN / Ymax obtained by dividing the input gradation value IN by the maximum gradation value Ymax. is there.

Here, the reference gamma value γ is set to 2.2, for example, and the predetermined gamma correction difference value S is set to 0.08, 0.06, 0.04, 0.0 in ± 0.02 units, for example. In the case of 02, 0, −0.02, −0.04, −0.06, −0.08, the corrected gamma value γ−S, which is the difference between each gamma correction differential value S and the reference gamma value γ, is 2.12, 2.14, 2.16, 2.18, 2.20, 2.22, 2.24, 2.26, 2.28. Then, for each corrected gamma value γ-S, a corrected luminance normalized value is calculated for a gradation normalized value obtained by dividing the input gradation value of the video signal by the maximum gradation value. This can be calculated by modifying the above equation (2) as follows.
Y (IN) = (IN / Ymax) ^γ-S (3)
Where IN is the input gradation value (0 to 255) of the video signal, Ymax is the maximum gradation value (255) of the video signal, γ is the reference gamma value, S is the gamma correction difference value, and γ-S is the correction gamma value. It is. That is, Y (IN) is a correction luminance normalization when gamma adjustment is performed with a correction gamma value γ−S with respect to a gradation normalization value IN / Ymax obtained by dividing the input gradation value IN by the maximum gradation value Ymax. Value.

  Then, based on the corrected brightness normalization value Y (IN) calculated as described above, the corrected brightness normalization value Y ((gamma = 2.2) for each predetermined gamma correction difference value S ( IN) and each corrected gamma value (γ-S = 2.12, 2.14, 2.16, 2.18, 2.2, 2.22, 2.24, 2.26, 2.28). The difference from the corrected luminance normalization value Y (IN) is obtained. This difference corresponds to the normalized theoretical difference in FIG. The function γ1 corresponds to the gamma correction difference value S = 0.08. Hereinafter, the functions γ2, γ3, γ4, γ5, γ6, γ7, γ8, and γ9 are the gamma correction difference values S = 0.06, 0.04, 0.02, 0, -0.02, -0.04, respectively. Corresponds to -0.06, -0.08. In these functions γ1 to γ9, the gamma correction difference value is calculated as ± 0.02 unit. However, for example, ± 0.01 unit may be used. In this case, a value between each function is obtained by interpolation. Can do.

  In the example of FIG. 5, the gradation normalization value obtained by dividing all the input gradation values of the video signal by the maximum gradation value is calculated, but the input gradation value of the intermediate gradation range to be compared is the maximum gradation value. It is only necessary to calculate the gradation normalization value divided by. The range of the intermediate gradation range is not particularly limited, but for example, an input gradation value in the range of 128 ± 50 can be considered.

  In the above, the functions f1 to f9 in FIG. 4 show the relationship between the input gradation of the video signal and the normalized measurement difference obtained by measuring the actual luminance at the points P1 to P9. On the other hand, the functions γ1 to γ9 in FIG. 5 show the relationship between the input gray level of the video signal and the theoretical normalization theoretical difference obtained by calculation using Equation (3). Here, the normalized measurement difference can be regarded as a luminance deviation in measurement (actual measurement) at points P1 to P9, and the normalized theoretical difference is a calculation luminance deviation (hereinafter, this is assumed when the gamma characteristic is deviated). Can be regarded as a corrected luminance shift). In addition, the luminance deviation and the corrected luminance deviation may use a ratio instead of the difference, but here, a case where the difference is used will be described as an example.

  The functions f1 to f9 in FIG. 4 are obtained by measuring the actual luminance deviation with respect to the input gradation (0 to 255) of the video signal, and it can be seen that a peak appears in the vicinity of the intermediate gradation. In addition, it can be seen that the functions γ1 to γ9 in FIG. 5 also have peaks in the vicinity of the intermediate gradation with respect to the input gradation (0 to 255) of the video signal. That is, it is considered that the characteristics in the vicinity of the intermediate gradation of the functions f1 to f9 in FIG. 4 and the characteristics in the vicinity of the intermediate gradation of the functions γ1 to γ9 in FIG. In the present embodiment, paying attention to this point, a process for assigning an optimal gamma correction difference value for the points P1 to P9 is performed by comparing the characteristics in the vicinity of the intermediate gradation between the two. Note that among the functions f1 to f9 in FIG. 4, the functions f2, f9, etc. have no peak near the intermediate gradation, but the difference between the peak luminance difference and the intermediate gradation luminance difference is small, or FIG. Since the purpose is to specify an approximation from the functions γ1 to γ9, it is also determined based on the characteristics near the intermediate gradation.

  Specifically, the gamma adjustment device 50 has the maximum luminance value when the maximum gradation video signal is input to the display device 10 and the intermediate gradation image on the display device 10 for each point P1 to P9. The intermediate luminance value when the signal is input is measured, and the luminance deviation value in FIG. 4 (that is, the value of the normalized measurement difference) is obtained from these measurement results. That is, the luminance deviation value is uniquely determined by the maximum luminance value and the intermediate luminance value, but the intermediate gradation video signal to be input to the display device 10 is not limited to 128, but around 128. For example, 150 may be used.

  It is conceivable that the functions γ1 to γ9 in FIG. 5 are stored in advance in the memory 53 of the gamma adjustment device 50 as table data for each predetermined gamma correction difference value. Note that the functions γ1 to γ9 in FIG. 5 also have a corrected luminance shift peak value in the vicinity of the intermediate gradation, and therefore correspond to the intermediate gradation range (for example, 128 ± 50) so as to include this peak value. Only the corrected luminance deviation value to be performed (that is, the value of the normalized theoretical difference) may be stored.

  The gamma adjustment device 50 obtains the luminance deviation value (FIG. 4) in the intermediate gradation for each coordinate of the points P1 to P9 and the corrected luminance deviation value (FIG. 5) in the intermediate gradation area for each gamma correction difference value. By comparing, the correction luminance shift of FIG. 5 corresponding to the luminance shift of FIG. 4 is determined, and a gamma correction difference value corresponding to the determined correction luminance shift is determined. When there are a plurality of corrected luminance deviation values for each gamma correction difference value in the intermediate gradation region of FIG. 5, each of them is compared with the luminance deviation value of FIG. 4 and has a value closest to this luminance deviation value. Select the correction brightness deviation. More preferably, as shown in FIG. 5, since the value of the corrected luminance deviation in the intermediate gradation range includes the peak value of the corrected luminance deviation, the luminance deviation in the intermediate gradation for each coordinate of the points P1 to P9. The value (FIG. 4) is compared with the peak value of the corrected luminance deviation (FIG. 5) in the intermediate gradation region for each gamma correction difference value, and the corrected luminance deviation having the peak value closest to this luminance deviation value is You may make it determine with the correction | amendment luminance shift corresponding to this luminance shift. According to this, since the gamma correction difference value can be determined only by comparison with the peak value, the adjustment time can be further shortened.

  Specifically, in FIG. 4, when the input gradation is 128, for example, the values of the luminance shifts (normalized measurement differences) of the functions f3 and f6 can be regarded as substantially the same. Then, referring to the peak value of the corrected luminance deviation (normalized theoretical difference) in the intermediate gradation range of the functions γ1 to γ9 in FIG. 5 based on the luminance deviation value, the luminance deviation values of the functions f3 and f6 are the function It can be seen that it is closest to the peak value of γ3 (corrected gamma value: 2.16, gamma correction difference value: 0.04). Thus, the points P3 and P6 corresponding to the functions f3 and f6 can be determined as the correction gamma value “2.16” and the gamma correction difference value “0.04”. The gamma correction difference value is stored in the display device 10 in association with the points P3 and P6. For other functions f1 (point P1), f2 (point P2), f4 (point P4), and f7 (point P7) to f9 (point P9), gamma correction difference values can be determined in the same procedure. Note that the function f5 (point P5) has already been adjusted with the reference gamma and does not need to be corrected, so it is excluded.

In the above description, the gammas of the points P3 and P6 mean that the reference gamma of point P5 is shifted to 2.16. Accordingly, in order to adjust the gamma of the points P3 and P6 to the reference gamma 2.2, the display device 10 performs gamma adjustment by the following equation.
Yout (IN) = (IN / Ymax) ^γ−S · (IN / Ymax) ^S (4)
However, IN is the input gradation value (0 to 255) of the video signal, Ymax is the maximum gradation value (255) of the video signal, γ is the reference gamma value (2.2 here), and S is the gamma correction difference value ( Here, 0.04), γ-S is a corrected gamma value (here 2.16).

  The above processing is also executed for points P1, P2, P4, P7 to P9 other than points P3, P5, and P6, and gamma adjustment is performed using the respective gamma correction difference values for each point. Note that gamma adjustment is performed for the point P5 using the reference gamma value. On the display device side, it is only necessary to store the reference gamma value (gamma adjustment LUT) adjusted at the point P5 in the center of the screen and the gamma correction difference value of each point, and it is necessary to provide a gamma adjustment LUT for each point. There is no. As a result, it is possible to display with substantially uniform brightness regardless of the pixel position in the screen for the same input gradation without increasing the circuit scale and adjustment time.

  FIG. 6 is a flowchart for explaining an example of the gamma adjustment method according to the present invention. In this example, a case where gamma adjustment of the display device 10 is performed using a gamma adjustment device 50 as shown in FIG. 1 will be described. First, the gamma adjustment device 50 sets M × N coordinates on the screen of the display device 10 (step S1). For example, as shown in FIG. 2, 3 × 3 coordinates (points P1 to P9) are set on the screen of the display device 10. The coordinate information at this time is stored in the display device 10 and the gamma adjustment device 50, respectively. Then, the gamma adjustment device 50 performs gamma adjustment on predetermined reference coordinates included in the M × N coordinates and determines the reference gamma value of the display device 10 (step S2). In the case of the example in FIG. 2, for example, gamma adjustment is performed at the point P5 located at the center of the screen as the reference coordinates, and the adjusted gamma value is set as the reference gamma value of the display device 10. In this example, the reference gamma value is adjusted to “2.2”.

  In the above description, the M × N matrix coordinates are an example of a plurality of adjustment target coordinates according to the present invention, and may be any other coordinates. Setting can be facilitated and gamma adjustment can be performed more efficiently. In addition, although the coordinates of the point P5 located at the center of the screen are shown as an example of the predetermined reference coordinates of the present invention, other arbitrary coordinates may be used.

  Next, the gamma adjustment device 50 measures the maximum luminance value of each coordinate when the video signal of the maximum gradation is input for each of the M × N coordinates (step S3). In the case of the example of FIG. 2, the video signal of (255, 255, 255) is input to the display device 10 as the video signal of the maximum gradation, and this video signal is displayed on the screen after being corrected by gamma 2.2. To do. The gamma adjustment device 50 measures the maximum luminance value on the screen at this time for the points P1 to P9.

  Next, the gamma adjustment device 50 measures the intermediate luminance value of each coordinate when an intermediate gray scale video signal is input for each M × N coordinate (step S4). In the case of the example in FIG. 2, the display device 10 receives, for example, a video signal of (128, 128, 128) as an intermediate grayscale video signal, and outputs this video signal on the screen after correction with gamma 2.2. To do. The gamma adjusting device 50 measures the intermediate luminance values at this time for the points P1 to P9. Note that the intermediate gradation video signal is not limited to the above (128, 128, 128), and may be any video signal included in the vicinity of the intermediate gradation.

Next, the gamma adjustment apparatus 50 calculates a luminance normalized value obtained by dividing the intermediate luminance value measured in step S4 by the maximum luminance value measured in step S3 for each of M × N coordinates (step S5). In the case of the example in FIG. 2, the gamma adjustment device 50 calculates the luminance normalized value for each of the points P1 to P9. This process is executed by the control unit 52. If the processing in step S5 is shown by a calculation formula,
Luminance normalization value = intermediate luminance value (cd / m ² ) / maximum luminance value (cd / m ² ) (5)
It becomes.

  Next, the gamma adjustment apparatus 50 determines the normalized luminance value of the reference coordinate and the normalized luminance value of each M × N coordinate for each M × N coordinate based on the normalized luminance value calculated in step S5. The luminance deviation indicated by the difference or ratio is calculated (step S6). In the case of the example of FIG. 2, since the reference coordinate is the point P5 in the center of the screen, the difference or ratio between the luminance normalized value at the point P5 and the luminance normalized values at the points P1 to P9 is obtained. This process is executed by the control unit 52.

  Next, the gamma adjustment device 50 calculates M × N from a plurality of predetermined gamma correction difference values based on the luminance shift in the intermediate gradation for each M × N coordinate calculated in step S6. A gamma correction difference value for each coordinate is determined (step S7). The gamma adjustment device 50 stores the gamma correction difference value determined in step S7 in the display device 10 in association with each M × N coordinate (step S8).

  The process of step S7 will be specifically described. As described above, the gamma adjustment device 50 stores in advance the corrected luminance deviation value in the intermediate gradation range of the functions γ1 to γ9 in FIG. 5 in the memory 53 for each gamma correction difference value. The gamma adjustment device 50 calculates the luminance deviation value in the intermediate gradation for each M × N coordinate calculated in step S 6 and the corrected luminance deviation in the intermediate gradation area for each gamma correction difference value stored in the memory 53. The correction brightness shift having a value closest to the brightness shift value is determined as a correction brightness shift corresponding to the brightness shift. Then, a gamma correction difference value corresponding to the determined corrected luminance deviation is determined.

  For example, in the example of FIG. 4 described above, when the input gradation is 128, the values of the luminance shifts (normalized measurement differences) of the functions f3 and f6 can be regarded as substantially the same. Then, referring to the peak value of the corrected luminance deviation (normalized theoretical difference) in the intermediate gradation range of the functions γ1 to γ9 in FIG. 5 based on the luminance deviation value, the luminance deviation values of the functions f3 and f6 are the function It can be seen that it is closest to the peak value of γ3 (corrected gamma value: 2.16, gamma correction difference value: 0.04). Thus, the points P3 and P6 corresponding to the functions f3 and f6 can be determined as the correction gamma value “2.16” and the gamma correction difference value “0.04”. For other functions f1 (point P1), f2 (point P2), f4 (point P4), and f7 (point P7) to f9 (point P9), gamma correction difference values can be determined in the same procedure. Note that the function f5 (point P5) has already been adjusted with the reference gamma and does not need to be corrected, and thus is excluded.

  Next, another specific example of the gamma adjustment method by the display device 10 and the gamma adjustment device 50 of FIG. 1 will be described with reference to FIG. In the example of FIG. 7, 5 × 3 coordinates are set on the screen of the display device 10. This 5 × 3 coordinate is represented by P (x, y), and gamma adjustment is performed at P (3, 2) which is the center point. The number of bits of the input gradation is 8 bits from 0 to 255.

  First, gamma adjustment is performed for a plurality of input gradations at P (3, 2). Next, with respect to the input gradation of (255, 255, 255), the maximum luminance value at each point of P (1, 1) to P (5, 3) is measured, and this is calculated as Ymax (x, y). And Further, with respect to the input gradation of (128, 128, 128), an intermediate luminance value at each point of P (1, 1) to P (5, 3) is measured, and this is expressed as Ymid (x, y). To do.

  Next, at each point of P (1,1) to P (5,3), Ymid (x, y) / Ymax (x, y) −Ymid (3,2) / Ymax (3,2) Calculate the brightness deviation value. Then, based on the luminance deviation value, the correction luminance deviation value (FIG. 5) in the intermediate gradation region for each predetermined gamma correction difference value is referred to, and the corrected luminance having a value closest to the luminance deviation value The deviation is determined as a corrected luminance deviation corresponding to the luminance deviation. If the corrected luminance deviation is determined, the gamma correction difference value is uniquely determined. Hereinafter, this gamma correction difference value is assumed to be k (x, y). The gamma correction difference value k (x, y) is stored in the display device 10 in association with P (1, 1) to P (5, 3).

  FIGS. 8-10 is a figure for demonstrating an example of the gamma adjustment process of the display apparatus 10 by this invention. In this example, description will be made based on the configuration examples of FIGS. The display device 10 includes a memory 23 corresponding to a storage unit that stores a reference gamma value γ and a gamma correction difference value k (x, y) for each coordinate of 5 × 3, and a reference gamma value γ stored in the memory 23. And an image quality adjustment unit 19 corresponding to a gamma adjustment unit that performs gamma adjustment using the gamma correction difference value k (x, y) of each coordinate of 5 × 3.

  In the above, the display device 10 associates the gamma correction difference value k (x, y) with the measurement point P (x, y) in FIG. 7, that is, the points P (1, 1) to P (5, 3). y) is held in the memory 23. Further, a reference gamma value (for example, 2.2) when gamma adjustment is performed with P (3, 2) is also held in the memory 23. The display device 10 can recognize the coordinates (Px, Py) of the display pixel and display the coordinates (Px, Py) of the display pixel and the measurement point P (1, 1) when displaying the video signal. To the peripheral coordinates P (x, y), P (x + 1, y), P (x, y + 1), and P (x + 1, y + 1) located around the coordinates of the display pixel among P (5, 3) (That is, the number of pixels) can be recognized. Further, the gamma correction difference value kp (x, y) of the coordinates (Px, Py) of the display pixel is the peripheral coordinates P (x, y), P (x + 1, y), P (x, y + 1), P ( x + 1, y + 1) and the gamma correction difference values k (x, y), k (x + 1, y), k (x, y + 1), k (x + 1, y + 1) of each peripheral coordinate. it can.

  As shown in FIG. 8, the image quality adjustment unit 19 processes RGB independently. Since the gamma adjustment is performed by luminance, the image quality adjusting unit 19 temporarily converts the input gradations (0 to 255) of R, G, and B to luminance values Lv (R), Lv (G), and Lv (B). Conversion is performed (S11). For example, conversion can be performed using a luminance conversion table common to RGB as shown in FIG. The luminance data is obtained by measuring the luminance level after gamma adjustment at the gamma adjustment point P (3, 2). At this time, the luminance level may be measured for all input gradations, or only a specific gradation may be measured and an interpolation process may be performed between them. Alternatively, a theoretical value of gamma 2.2 obtained from the maximum luminance value may be used. It is desirable to use the value of the adjustment point P (3, 2) as the maximum luminance value at this time.

Next, the gamma correction difference value kp (x, y) of the display pixel is a distance from the peripheral coordinates P (x, y), P (x + 1, y), P (x, y + 1), P (x + 1, y + 1). It is determined based on the weight and gamma correction difference values k (x, y), k (x + 1, y), k (x, y + 1), k (x + 1, y + 1) of the peripheral coordinates (S12). When the coordinates (Px, Py) of the display pixel have a relationship as shown in FIG. 10, for example, the gamma correction difference value kp (x, y) of the display pixel can be obtained by the following equation.
K1 = {b · k (x, y) + a · k (x + 1, y)} / (a + b)
K2 = {b · k (x, y + 1) + a · k (x + 1, y + 1)} / (a + b) (6)
kp (x, y) = {d · K1 + c · K2} / (c + d)
However, a, b, c, d are the coordinates (Px, Py) of the display pixel and the peripheral coordinates P (x, y), P (x + 1, y), P (x, y + 1), P (x + 1, y + 1). (The number of pixels).

  That is, the image quality adjustment unit 19 acquires the coordinates of the display pixel when displaying the video signal on the display device 10, and the coordinates of the display pixel among the coordinates (Px, Py) of the display pixel and the coordinates of 5 × 3. The distances between the peripheral coordinates P (x, y), P (x + 1, y), P (x, y + 1), and P (x + 1, y + 1) located in the periphery are calculated, and the memory 23 is based on the calculated distance. Gamma correction difference values of display pixels are weighted by weighting the stored gamma correction difference values k (x, y), k (x + 1, y), k (x, y + 1), and k (x + 1, y + 1). kp (x, y) is calculated.

Using the gamma correction difference value kp (x, y) obtained in this way, the luminance value is converted by the following equation. The luminance values Lv (R), Lv (G), and Lv (B) before conversion are input from the previous stage (S11).
Lv (R) ′ = Lv (R) × (R / 255) ^{kp (x, y)}
Lv (G) ′ = Lv (G) × (G / 255) ^{kp (x, y)} (7)
Lv (B) ′ = Lv (B) × (B / 255) ^{kp (x, y)}

Here, there are 256 types of R / 255, G / 255, and B / 255, respectively, but it is not realistic to take an unlimited range for correction with the gamma correction difference value kp (x, y). For this reason, the range of correction is limited, for example, limited to +0.2 to −0.2, and has a fixed value in increments of 0.02 (R / 255) ^{kp (x, y)} , (G / 255) ^{kp (x, y)} , (B / 255) ^{kp (x, y)} can be ROMized, and a small circuit configuration can be obtained.

  Next, the luminance value Lv ′ converted in S12 is returned to the RGB gradation code (S13). More specifically, the result of gamma adjustment performed at the gamma adjustment point P (3, 2) is inversely converted. That is, the reverse process of S11 is performed. For example, if RGB is 8 bits, it is possible by performing 256 comparisons. More realistically, since the luminance value to be corrected does not take the entire range, the luminance value Lv and the RGB gradation code are acquired for several points before and after the converted gradation code at the time of RGB → Lv conversion in S11. In addition, the inverse transformation may be performed by comparing with the acquired data. Thereby, it can be set as a small circuit structure.

  Next, the normal gamma LUT is referred to based on the RGB tone codes R ′, G ′, and B ′ inversely converted in S13, and thus the normal inverse based on the reference gamma value (eg, 2.2). Gamma processing is performed (S14). The normal gamma LUT is composed of, for example, a RAM, and data adjusted at the gamma adjustment point P (3, 2) is written therein.

  As described above, according to the present invention, gamma adjustment can be performed using one normal gamma LUT based on the reference gamma value and the gamma correction difference value for each measurement point, thereby increasing the circuit scale and adjustment time. Accordingly, it is possible to realize substantially uniform luminance characteristics for the same input gradation regardless of the pixel position.

  As described above, the gamma adjustment method according to the present invention is a gamma adjustment method for adjusting gamma of a display device, and a coordinate setting step for setting a plurality of adjustment target coordinates on the screen of the display device; A gamma adjustment step for performing gamma adjustment on a predetermined reference coordinate to determine a reference gamma value of the display device, and a maximum luminance value of the adjustment target coordinate when a video signal having a maximum gradation is input for the plurality of adjustment target coordinates A maximum luminance value measuring step for measuring the intermediate luminance value, an intermediate luminance value measuring step for measuring an intermediate luminance value of the adjustment target coordinate when an intermediate gradation video signal is input for the plurality of adjustment target coordinates, and the plurality of adjustments Luminance normalization obtained by dividing the intermediate luminance value measured in the intermediate luminance value measurement step for the target coordinate by the maximum luminance value measured in the maximum luminance value measurement step. A brightness normalized value calculating step for calculating the reference coordinate and the brightness normalized value of the reference coordinate and the plurality of the adjusted coordinates for each of the plurality of adjustment target coordinates based on the brightness normalized value calculated in the brightness normalized value calculating step. A luminance deviation calculating step for calculating a luminance deviation indicated by a difference or a ratio from the luminance normalized value for each of the adjustment target coordinates, and an intermediate gradation for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculating step. A gamma correction difference value determining step for determining a gamma correction difference value for each of the plurality of adjustment target coordinates from a plurality of predetermined gamma correction difference values based on a luminance shift in A gamma correction difference value storage step for storing the gamma correction difference value determined in the determination step in the display device in association with each of the plurality of adjustment target coordinates. Those were. According to this, it is possible to display the same input gradation with substantially uniform gradation regardless of the pixel position in the screen without increasing the circuit scale and adjustment time. Furthermore, if the maximum luminance of the panel can be made uniform, the same input gradation can be displayed with substantially uniform luminance regardless of the pixel position in the screen.

  Further, the gamma correction difference value determining step includes a luminance deviation value in an intermediate gradation for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculation step, and a plurality of predetermined gamma correction difference values. A correction luminance deviation corresponding to the luminance deviation is determined, and a gamma correction difference value corresponding to the determined correction luminance deviation is determined. The correction luminance shift in the intermediate gradation region for each gamma correction difference value of the calculated gamma correction value from the difference between each of the plurality of gamma correction difference values and the reference gamma value, for each of the calculated correction gamma values, A corrected luminance normalized value calculating step for calculating a corrected luminance normalized value with respect to a gradation normalized value obtained by dividing at least an input gradation value of an intermediate gradation region of a video signal by a maximum gradation value; and the corrected luminance Based on the corrected luminance normalized value calculated in the normalized value calculating step, the corrected luminance normalized value at the reference gamma value and the corrected luminance normalized value at each corrected gamma value for each gamma correction difference value It is desirable that the correction brightness shift calculation step for calculating the correction brightness shift indicated by the difference or ratio with According to this, similarly to the above, it is possible to display the same input gradation with substantially uniform gradation regardless of the pixel position in the screen without increasing the circuit scale and adjustment time. . Furthermore, if the maximum luminance of the panel can be made uniform, the same input gradation can be displayed with substantially uniform luminance regardless of the pixel position in the screen.

  In addition, the value of the corrected luminance deviation in the intermediate gradation range includes a peak value of the corrected luminance deviation, and the gamma correction difference value determining step is performed for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculating step. And the peak value of the corrected luminance deviation in the intermediate gradation region for each of the gamma correction difference values calculated in the corrected luminance deviation calculating step. It is desirable to determine the corrected luminance deviation having the closest peak value as the corrected luminance deviation corresponding to the luminance deviation. According to this, since the gamma correction difference value can be determined only by comparison with the peak value, the adjustment time can be further shortened.

  A display device that is gamma adjusted by the above gamma adjustment method, the storage unit storing the reference gamma value and the gamma correction difference value for each of the plurality of adjustment target coordinates, and the reference stored in the storage unit And a gamma adjustment unit that performs gamma adjustment using a gamma value and a gamma correction difference value of each of the plurality of adjustment target coordinates. According to this, similarly to the above, it is possible to display the same input gradation with substantially uniform gradation regardless of the pixel position in the screen without increasing the circuit scale and adjustment time. . Furthermore, if the maximum luminance of the panel can be made uniform, the same input gradation can be displayed with substantially uniform luminance regardless of the pixel position in the screen.

  In addition, the gamma adjustment unit acquires the coordinates of the display pixels when the video signal is displayed on the display device, and the coordinates of the display pixels and the plurality of adjustment target coordinates By calculating the distance from the peripheral coordinates located around the coordinates of the display pixel and weighting the gamma correction difference value of the peripheral coordinates stored in the storage unit based on the calculated distance, It is desirable to calculate a gamma correction difference value. According to this, similarly to the above, it is possible to display the same input gradation with substantially uniform gradation regardless of the pixel position in the screen without increasing the circuit scale and adjustment time. . Furthermore, if the maximum luminance of the panel can be made uniform, the same input gradation can be displayed with substantially uniform luminance regardless of the pixel position in the screen.

  The plurality of adjustment target coordinates are preferably M × N matrix coordinates. According to this, coordinate setting can be facilitated and gamma adjustment can be performed more efficiently.

DESCRIPTION OF SYMBOLS 10 ... Display apparatus (television receiver), 11 ... Digital terrestrial broadcast tuner, 12 ... Satellite broadcast tuner, 13 ... External input terminal, 14 ... Selector, 15 ... Decoding part, 16 ... Audio signal processing part, 17 ... Speaker, DESCRIPTION OF SYMBOLS 18 ... Video signal processing part, 19 ... Image quality adjustment part, 20 ... LCD module, 21 ... Infrared light-receiving part, 22 ... Control part, 23 ... Memory, 24 ... Adjustment terminal, 31 ... Remote control, 32 ... Terrestrial digital broadcasting antenna 33 ... Satellite broadcasting antenna, 50 ... Gamma adjustment device, 51 ... Light detection unit, 52 ... Control unit, 53 ... Memory, 54 ... Output unit.

Claims (5)

A gamma adjustment method for adjusting gamma of a display device,
A coordinate setting step for setting a plurality of adjustment target coordinates on the screen of the display device;
A gamma adjustment step for performing gamma adjustment on predetermined reference coordinates and determining a reference gamma value of the display device;
A maximum luminance value measuring step for measuring the maximum luminance value of the adjustment target coordinates when a video signal of the maximum gradation is input for the plurality of adjustment target coordinates;
An intermediate luminance value measuring step for measuring an intermediate luminance value of the adjustment target coordinates when an image signal of intermediate gradation is input for the plurality of adjustment target coordinates;
A luminance normalized value calculating step for calculating a luminance normalized value obtained by dividing the intermediate luminance value measured in the intermediate luminance value measuring step for the plurality of adjustment target coordinates by the maximum luminance value measured in the maximum luminance value measuring step;
Based on the luminance normalized value calculated in the luminance normalized value calculating step, for each of the plurality of adjustment target coordinates, the luminance normalized value of the reference coordinate and the luminance normalized value of each of the plurality of adjustment target coordinates A luminance deviation calculating step for calculating a luminance deviation indicated by a difference or ratio with
Based on the luminance deviation in the intermediate gradation for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculation step, among the plurality of predetermined gamma correction difference values, for each of the plurality of adjustment target coordinates. A gamma correction difference value determination step for determining a gamma correction difference value;
A gamma correction difference value storing step for storing the gamma correction difference value determined in the gamma correction difference value determining step in the display device in association with the plurality of adjustment target coordinates. Method. The gamma correction difference value determination step includes a luminance deviation value in an intermediate gradation for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculation step, and an intermediate value for each of the plurality of predetermined gamma correction difference values. By comparing the value of the correction luminance deviation in the gradation range, the correction luminance deviation corresponding to the luminance deviation is determined, and a gamma correction difference value corresponding to the determined correction luminance deviation is determined.
The correction luminance shift in the intermediate gradation region for each of the plurality of gamma correction difference values is calculated by calculating a correction gamma value from the difference between each of the plurality of gamma correction difference values and the reference gamma value. A corrected luminance normalized value calculating step for calculating a corrected luminance normalized value for a gradation normalized value obtained by dividing the input gradation value of at least the intermediate gradation region of the video signal by the maximum gradation value;
Based on the corrected luminance normalized value calculated in the corrected luminance normalized value calculating step, the corrected luminance normalized value at the reference gamma value and the corrected luminance at the corrected gamma value are calculated for each gamma correction difference value. The gamma adjustment method according to claim 1, wherein the gamma adjustment method is obtained by a corrected luminance deviation calculating step of calculating a corrected luminance deviation indicated by a difference or a ratio from the normalized value. The correction luminance deviation value in the intermediate gradation range includes a peak value of the correction luminance deviation,
The gamma correction difference value determination step includes a luminance deviation value in an intermediate gradation for each of the plurality of adjustment target coordinates calculated in the luminance deviation calculation step, and each gamma correction difference calculated in the correction luminance deviation calculation step. Comparing with the peak value of the corrected luminance deviation in the intermediate gradation area for each value, and determining the corrected luminance deviation having the peak value closest to the luminance deviation value as the corrected luminance deviation corresponding to the luminance deviation The gamma adjustment method according to claim 2, wherein A display device that is gamma adjusted by the gamma adjustment method according to claim 1,
A storage unit that stores the reference gamma value and a gamma correction difference value for each of the plurality of adjustment target coordinates; and the reference gamma value stored in the storage unit and the gamma correction difference value of each of the plurality of adjustment target coordinates. And a gamma adjustment unit that performs gamma adjustment using the display device.   The gamma adjustment unit acquires the coordinates of a display pixel when displaying a video signal on the display device, and is located around the coordinates of the display pixel among the coordinates of the display pixel and the plurality of adjustment target coordinates. Calculating a gamma correction difference value of the display pixel by calculating a distance from the peripheral coordinates and weighting a gamma correction difference value of the peripheral coordinates stored in the storage unit based on the calculated distance. The display device according to claim 4.

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