JP2015138439A - Image processing apparatus, image processing method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that can reduce luminance unevenness through image processing and suppress a reduction in a dynamic range due to the image processing.SOLUTION: An image processing apparatus of the present invention is an image processing apparatus that can perform image processing to reduce luminance unevenness on a screen of a display device, and includes: determination means for determining, on the basis of input image data, a representative gradation value that represents a gradation value of the input image data; first correction means for correcting the input image data by increasing gradation values of pixels of the input image data at a rate of increase based on the representative gradation value; and image processing means for performing the image processing on the image data after the correction by the first correction means.

Description

  The present invention relates to an image processing apparatus, an image processing method, and a program.

  In a display device such as a liquid crystal display or a plasma display, display unevenness (brightness or color unevenness on the screen) due to a member of the display device occurs. For example, in a liquid crystal display, display unevenness occurs due to uneven thickness of a liquid crystal layer or a color filter and unevenness of light emitted from a backlight. Further, in the plasma display, display unevenness due to variation in light emission characteristics between plasma elements occurs.

  Further, in the liquid crystal display, in addition to display unevenness due to the members, display unevenness due to the internal structure occurs. In a liquid crystal display, an image is displayed on a screen when light from a backlight passes through a liquid crystal element. Here, of the light from the backlight, the light transmitted through the liquid crystal element at the edge of the screen is weakened by reflection and diffusion on the inner wall provided along the edge of the screen. As a result, luminance unevenness occurs where the luminance at the edge of the screen is lower than that at the center of the screen.

  By using a plurality of light sources as the light source of the backlight and increasing the light emission luminance of the light source provided near the edge of the screen, the above-described luminance unevenness can be reduced. However, it is difficult to sufficiently reduce the luminance unevenness by controlling only the light emission luminance of the light source, and the luminance unevenness cannot be sufficiently reduced by controlling only the light emission luminance of the light source. For example, since combined light of light from a plurality of light sources enters the liquid crystal element, it is necessary to consider light from all the light sources in order to reduce luminance unevenness. For this reason, it is difficult to sufficiently reduce the luminance unevenness by controlling only the light emission luminance of the light source, and the luminance unevenness cannot be sufficiently reduced by controlling only the light emission luminance of the light source. In order to sufficiently reduce the luminance unevenness, it is necessary to correct the image data to be displayed.

  Image processing for reducing luminance unevenness is disclosed in Patent Document 1, for example. In the technique disclosed in Patent Document 1, display brightness is measured in advance when image data having a uniform gradation value is displayed for each of a plurality of divided areas constituting a screen area. In addition, a correction rate for reducing luminance unevenness is prepared in advance for each divided region. Then, for each divided area, the gradation value of the image data to be displayed in the divided area is corrected with the correction rate of the divided area.

  As disclosed in Patent Document 1, in the conventional technique, luminance unevenness is reduced by reducing the gradation value of a region where the display luminance is high in accordance with a region where the display luminance (luminance on the screen) is low. The Therefore, the dynamic range of the image data is lowered in the area where the gradation value is reduced. Such a decrease in dynamic range is not preferable.

JP 2007-114427 A

  An object of the present invention is to provide a technique that can reduce luminance unevenness by image processing and can suppress a decrease in dynamic range due to image processing.

The first aspect of the present invention is:
An image processing apparatus capable of executing image processing for reducing luminance unevenness on a screen of a display device,
Determining means for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
First correction means for correcting the input image data by increasing the gradation value of each pixel of the input image data at an increase rate based on the representative gradation value;
Image processing means for performing the image processing on the image data corrected by the first correction means;
An image processing apparatus comprising:

The second aspect of the present invention is:
An image processing apparatus capable of executing image processing for reducing luminance unevenness on a screen of a display device,
Determining means for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
Image processing means for performing the image processing on the input image data;
Correction means for correcting the image data by increasing the gradation value of each pixel of the image data after the image processing at an increase rate based on the representative gradation value;
An image processing apparatus comprising:

The third aspect of the present invention is:
An image processing method capable of executing image processing for reducing luminance unevenness on a screen of a display device,
A determination step for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
A first correction step of correcting the input image data by increasing the gradation value of each pixel of the input image data at an increase rate based on the representative gradation value;
An image processing step of performing the image processing on the image data corrected by the first correction step;
An image processing method characterized by comprising:

The fourth aspect of the present invention is:
An image processing method capable of executing image processing for reducing luminance unevenness on a screen of a display device,
A determination step for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
An image processing step for performing the image processing on the input image data;
A correction step of correcting the image data by increasing the gradation value of each pixel of the image data after the image processing at an increase rate based on the representative gradation value;
An image processing method characterized by comprising:

  According to a fifth aspect of the present invention, there is provided a program that causes a computer to execute each step of the above-described image processing method.

  According to the present invention, it is possible to reduce luminance unevenness by image processing and to suppress a decrease in dynamic range due to image processing.

FIG. 1 is a block diagram illustrating an example of a functional configuration of a display device according to a first embodiment. FIG. 10 is a diagram illustrating an example of luminance unevenness according to the first embodiment. FIG. 10 is a diagram illustrating an example of image data before unevenness reduction processing according to the first embodiment. The figure which shows an example of the process information which concerns on Example 1. FIG. 7 is a flowchart illustrating an example of the operation of the display device according to the first embodiment. FIG. 6 is a block diagram illustrating an example of a functional configuration of a display device according to a second embodiment. 10 is a flowchart illustrating an example of the operation of the display device according to the second embodiment. FIG. 10 is a diagram illustrating an example of input image data according to the second embodiment. The figure which shows an example of the histogram of the input image data which concerns on Example 1,2.

<Example 1>
Hereinafter, an image processing apparatus and an image processing method according to Embodiment 1 of the present invention will be described. The image processing apparatus according to the present embodiment is an apparatus that can execute image processing that reduces luminance unevenness on the screen of the display device.
In this embodiment, an example in which luminance unevenness is reduced only by image processing will be described, but the present invention is not limited to this. For example, when the display device is a liquid crystal display device (liquid crystal display), luminance unevenness may be reduced by image processing and processing for controlling the light emission luminance of the backlight.
In this embodiment, an example in which the display device includes an image processing device will be described. However, the image processing device may be a separate device from the display device.
In this embodiment, an example in which a process for reducing brightness unevenness is performed as a process for reducing display unevenness will be described. However, a process for reducing both brightness unevenness and color unevenness may be performed.

FIG. 1 is a block diagram illustrating an example of a functional configuration of the display device 10 according to the present embodiment.
In the storage unit 100, processing information indicating the values of processing parameters used in image processing (unevenness reduction processing) for reducing luminance unevenness is recorded in advance. As the storage unit 100, a semiconductor memory, an optical disk, a magnetic disk, or the like can be used.
The representative determining unit 101 determines a representative gradation value that represents the gradation value of the input image data based on the input image data (image data input to the display device 10).
The correction unit 102 corrects the input image data by increasing the gradation value of each pixel of the input image data at an increase rate based on the representative gradation value determined by the representative determination unit 101. In this embodiment, the increase rate is determined using the representative gradation value and the processing information.
The image processing unit 103 performs unevenness reduction processing on the image data corrected by the correction unit 102. In this embodiment, unevenness reduction processing is performed using processing information.
The display unit 104 displays the image data after the unevenness reduction processing by the image processing unit 103. As the display unit 104, a liquid crystal display panel, a plasma display panel, an organic EL display panel, or the like can be used.

  In this embodiment, unevenness reduction processing is performed in the image processing unit 103. Thereby, luminance unevenness can be reduced. In this embodiment, the gradation value of the input image data is increased. Thereby, a higher value can be obtained as a gradation value after unevenness reduction processing (after image processing) than when the gradation value of input image data is not increased. As a result, a decrease in dynamic range due to unevenness reduction processing can be suppressed. Further, in this embodiment, the gradation value of the input image data is increased at an increase rate based on the representative gradation value determined by the representative determination unit 101. Thereby, a preferable value can be obtained as the gradation value after the unevenness reduction process, and a decrease in the dynamic range can be suppressed with high accuracy.

When the image processing apparatus according to the present embodiment is a separate apparatus from the display apparatus, the display unit 104 is provided in the display apparatus.
The storage unit 100 may be a storage medium that is not removable from the image processing apparatus, or may be a storage medium that is removable from the image processing apparatus.

FIG. 2 is a diagram illustrating an example of luminance unevenness according to the present embodiment. FIG. 2 shows an example of a display image (image displayed on the screen) when image data with uniform gradation values is displayed.
In this embodiment, as shown in FIG. 2, it is assumed that luminance unevenness 105 in which the luminance increases from the edge of the screen toward the center occurs. That is, in this embodiment, it is assumed that the luminance unevenness 105 in which the luminance decreases as it goes from the center of the screen toward the edge occurs.
The brightness unevenness is not limited to the brightness unevenness 105 shown in FIG. Any luminance unevenness may occur, and the state of the luminance unevenness is not particularly limited.

In this embodiment, it is assumed that unevenness reduction processing is performed to reduce the gradation value of a region with a high display luminance in accordance with a region with a low display luminance.
FIG. 3 shows an example of image data before unevenness reduction processing (before image processing). In the image data 106 of FIG. 3, the gradation value of the area A at the center of the screen is 192, and the gradation value of the other area B is 0. When the above-described unevenness reduction processing is performed on the image data shown in FIG. 3, the amount of decrease in the gradation value and the amount of decrease in the dynamic range are maximized at the center of the screen.
Note that the method of unevenness reduction processing is not limited to the above method. For example, the unevenness reduction processing may be image processing that increases the gradation value in a region with low display luminance and reduces the gradation value in a region with high display luminance.

In this embodiment, information indicating the relationship between the gradation value before unevenness reduction processing and the degree of decrease in gradation value due to unevenness reduction processing is prepared as processing information.
FIG. 4 is a diagram illustrating an example of processing information according to the present embodiment. The processing information 107 in FIG. 4 indicates the degree of decrease for all pixel positions and for all gradation values that can be taken by the image data before unevenness reduction processing. The processing information in FIG. 4 includes a reduction amount added to the gradation value in the unevenness reduction processing as the reduction degree. In the present embodiment, the gradation values are an R value, a G value, and a B value. Therefore, in this embodiment, as shown in FIG. 4, the amount of decrease in R value is shown for each combination of pixel position and R value (R value before unevenness reduction processing), and G is set for each combination of pixel position and G value. Processing information indicating the amount of decrease in the value and indicating the amount of decrease in the B value is prepared for each combination of the pixel position and the B value.
In FIG. 4, the pixel position (horizontal position, vertical position) = (1, 1) is the pixel position of the upper left corner of the screen, and the pixel position (m ÷ 2, n ÷ 2) is the pixel at the center of the screen. The pixel position (m, n) is the pixel position at the lower right corner of the screen. m and n are integers of 3 or more. When the screen size (resolution) is the FHD size, m = 1920 and n = 1080. The processing information in FIG. 4 includes a reduction amount of m × n × number of gradation values that can be taken by image data before unevenness reduction processing × number of types of gradation values.

  For example, the amount of decrease is calculated in advance based on display luminance measured in a state where image data with uniform gradation values is displayed. Specifically, the amount of decrease for each pixel position is calculated based on the display luminance for each pixel position. Then, by performing the above processing while changing the gradation value from the minimum value to the maximum value that can be taken, the amount of decrease for each combination of the pixel position and the gradation value is calculated. When the gradation value of the image data can take an integer of 0 or more and 255 or less, for example, the pixel value (R value, G value, B value) = (0, 0, 0) image data, pixel value (255 , 0, 0) image data, pixel value (0, 255, 0) image data, pixel value (0, 0, 255) image data, pixel value (128, 128, 128) image data, pixel value (255, 255, 255) image data, etc. are displayed.

Note that the gradation value is not limited to the R value, the G value, and the B value. For example, the gradation value may be a Y value (luminance value).
As the processing information, the table shown in FIG. 4 may be prepared, or a function indicating the relationship shown in FIG. 4 may be prepared.
The processing information is not limited to the information shown in FIG. For example, the processing information may include a reduction rate by which the gradation value is multiplied in the unevenness reduction processing, instead of the reduction amount. Further, the processing information may include a gradation value after the unevenness reduction processing instead of the degree of decrease.
In the processing information of FIG. 4, the degree of decrease is shown for all pixel positions and all gradation values, but the processing information is not limited to this. In the processing information, the degree of decrease may be indicated for some pixel positions and some gradation values. In the unevenness reduction process, a degree of reduction corresponding to a combination of a pixel position and a gradation value that is not indicated by the processing information may be calculated. The degree of decrease corresponding to the combination of the pixel position and the gradation value not shown in the processing information can be calculated by interpolation, for example.

The representative determining unit 101 acquires the degree of reduction (a reduction amount) corresponding to the representative gradation value from the processing information. Then, the representative determining unit 101 calculates the gradation value after the unevenness reduction processing when the representative gradation value is the gradation value before the unevenness reduction processing, using the acquired reduction amount. Specifically, the gradation value after unevenness reduction processing when the representative gradation value is the gradation value before unevenness reduction processing is calculated by adding the acquired decrease amount to the representative gradation value. . In this embodiment, the amount of decrease is maximized at the center pixel position (m, n). Then, the representative determining unit 101 acquires the reduction amount of the pixel position (m, n) among the plurality of reduction amounts corresponding to the representative gradation value. Therefore, the representative determination unit 101 calculates the minimum value of the gradation value after the unevenness reduction process when the representative gradation value is the gradation value before the unevenness reduction process.
Then, the representative determination unit 101 calculates a value obtained by dividing the representative gradation value by the calculated gradation as an increase rate.

In this embodiment, the maximum tone value of the input image data is determined as the representative tone value. When the input image data is the image data shown in FIG. 3, the representative gradation value is 192, and −18 is acquired as the amount of decrease corresponding to the representative gradation value (the amount of decrease in pixel position (m, n)). The Then, the increase rate is calculated using the following Equation 1. When the representative gradation value is 192 and the amount of decrease is −18, 1.1 is calculated as the increase rate.

Increase rate = representative gradation value ÷ (representative gradation value + decrease amount) (Equation 1)

The representative gradation value is not limited to the maximum gradation value of the input image data. For example, the representative gradation value may be a minimum value, a mode value, an intermediate value, an average value, etc. of the gradation values of the input image data.
The method for calculating the increase rate is not limited to the above method. For example, the increase rate may be calculated using the decrease amount of the pixel position other than the pixel position where the decrease amount is maximum. Further, when the gradation value after unevenness reduction processing is indicated by the processing information, the gradation value after the unevenness reduction processing (representative gradation value + decrease amount) is acquired from the processing information, not the amount of decrease. May be used.
However, if the maximum gradation value of the input image data is used as the representative gradation value and the reduction of the gradation value at the pixel position where the reduction amount is maximum is considered, the dynamic range is assumed to be the lowest. The rate of increase can be determined. Then, by using such an increase rate, it is possible to suppress a decrease in dynamic range with higher accuracy.
Processing for determining the representative gradation value, processing for calculating the gradation value after the unevenness reduction processing when the representative gradation value is the gradation value before the unevenness reduction processing, and processing for calculating the increase rate May be performed by different functional units.

The correction unit 102 multiplies the gradation value of each pixel of the input image data by the increase rate calculated by the representative determination unit 101 as shown in Equation 2 below. In Equation 2, LK is a gradation value after being multiplied by the increase rate. Then, the correction unit 102 outputs the image data after being multiplied by the increase rate to the image processing unit 103.

LK = tone value of input image data × increase rate (Expression 2)

The image processing unit 103 performs unevenness reduction processing on the image data output from the correction unit 102 using the processing information stored in the storage unit 100. Then, the image processing unit 103 outputs the image data after the luminance unevenness reduction process to the display unit 104. In the present embodiment, the amount of decrease corresponding to the gradation value of the image data output from the correction unit 102 (the gradation value after being multiplied by the increase rate) is acquired from the processing information. Then, as shown in Expression 3 below, the acquired reduction amount is added to the gradation value LK of the image data output from the correction unit 102. In the image processing unit 103, such processing is performed on each pixel of the image data output from the correction unit 102. In Equation 3, HK is a gradation value after luminance unevenness reduction processing.

HK = LK + reduction amount (Equation 3)

  Hereinafter, the operation of the display device 10 according to the present embodiment will be described with reference to the flowchart of FIG. Hereinafter, an example will be described in which the luminance unevenness illustrated in FIG. 2 occurs, the image data illustrated in FIG. 3 is input as the input image data, and the processing information illustrated in FIG. 4 is prepared in advance.

  First, the representative determining unit 101 determines a representative gradation value of input image data (S100). Specifically, the representative gradation value is determined for each of the R value, the G value, and the B value. That is, the R representative gradation value representing the R value of the input image data, the G representative gradation value representing the G value, and the B representative gradation value representing the B value are determined. Here, for simplicity, only the R value is focused. When the image data shown in FIG. 3 is input as the input image data, 192 is acquired as the R representative gradation value.

  Next, the representative determining unit 101 acquires a reduction amount corresponding to the representative gradation value determined in S100 from the storage unit 100 (S101). Specifically, an R decrease amount that is a decrease amount corresponding to the R representative gradation value (R value decrease amount), and a G decrease amount that is a decrease amount corresponding to the G representative gradation value (G value decrease amount). , And a B decrease amount that is a decrease amount corresponding to the B representative gradation value (a decrease amount of the B value). When 192 is acquired as the R representative gradation value, −18 is acquired as the R decrease amount.

Then, the representative determination unit 101 determines an increase rate from the representative gradation value determined in S100 and the decrease amount acquired in S101 (S102). Specifically, an R increase rate that is an increase rate of the R value is determined from the R representative gradation value and the R decrease amount, and a G increase rate that is the increase rate of the G value is determined from the G representative gradation value and the G decrease amount. The B increase rate, which is the increase rate of the B value, is determined from the B representative gradation value and the B decrease amount. When 192 is acquired as the R representative gradation value and −18 is acquired as the R decrease amount, 1.1 (= 192 ÷ (192-18)) is acquired as the R increase rate.
The representative determining unit 101 outputs the determined increase rate to the correcting unit 102.

Next, the correction unit 102 increases the gradation value of each pixel of the input image data at the increase rate determined in S102 (S103). Specifically, the R value of each pixel of the input image data is multiplied by the R increase rate, the G value of each pixel of the input image data is multiplied by the G increase rate, and the B value of each pixel of the input image data is B Multiply by the rate of increase. In the image data shown in FIG. 3, the R value of the pixel at the upper left corner is 0, and the R value of the center pixel is 192. Therefore, when the R increase rate of 1.1 is acquired and the image data shown in FIG. 3 is input as the input image data, the R value of the pixel at the upper left corner is the R value as shown in Equation 4 below. It is corrected to LK1, and the R value of the center pixel is corrected to the R value LK2.

LK1 = R value at the upper left corner × R increase rate = 0 × 1.1 = 0
LK2 = R value at center × R increase rate = 192 × 1.1 = 211
... (Formula 4)

The correction unit 102 outputs the image data multiplied by the increase rate to the image processing unit 103.

The image processing unit 103 performs unevenness reduction processing on the image data output from the correction unit 102 using the processing information stored in the storage unit 100 (S104). Specifically, for each pixel of the image data output from the correction unit 102, processing for obtaining the R correction amount corresponding to the R value and adding the R correction amount to the R value is performed. For each pixel of the image data output from the correction unit 102, processing for obtaining a G correction amount corresponding to the G value and adding the G correction amount to the G value is performed. Then, for each pixel of the image data output from the correction unit 102, a process of acquiring a B correction amount corresponding to the B value and adding the B correction amount to the B value is performed.
The image processing unit 103 outputs the image data after the luminance unevenness reduction process to the display unit 104.

For example, for the pixel at the upper left corner, R reduction amount = 0 corresponding to the combination of the pixel position at the upper left corner and the R value LK1 = 0 is acquired, and for the center pixel, the center pixel position and the R value LK2 = R reduction amount corresponding to the combination with 211 = −20 is acquired. Then, as shown in Expression 5 below, the R value LK1 = 0 of the pixel in the upper left corner is corrected to the R value HK1, and the R value LK2 = 211 of the center pixel is corrected to the R value HK2.

HK1 = LK1 + R decrease amount = 0-0 = 0
HK2 = LK2 + R decrease amount = 211-20 = 191
... (Formula 5)

In the conventional method, a reduction amount corresponding to the gradation value of the input image data is acquired. Then, a value obtained by adding the reduction amount to the gradation value of the input image data is output as the gradation value after the unevenness reduction processing. Therefore, for the center pixel, an R decrease amount −18 corresponding to the combination of the center pixel position and the R value 192 of the input image data is acquired. Then, as shown in Equation 6 below, the R value 192 of the center pixel is corrected to the R value HK3.

HK3 = R value at the center−R decrease amount = 192-18 = 174 (Expression 6)

As described above, in the conventional method, a gradation value lower than the gradation value of the input image data is obtained as the gradation value after the unevenness reduction processing. Specifically, the gradation value 192 decreases to the gradation value 174 at the center of the screen. As a result, the dynamic range decreases. In the present embodiment, as shown in Expression 5, the gradation value after the unevenness reduction process can be obtained as a value substantially equal to the gradation value of the input image data, and the dynamic range can be prevented from being lowered. Specifically, in the center of the screen, a gradation value 191 that is substantially equal to the gradation value 192 of the input image data is obtained as the gradation value after the unevenness reduction processing.

  Next, the display unit 104 displays the image data output from the image processing unit 103 (S105).

  As described above, according to the present embodiment, it is possible to reduce brightness unevenness by performing unevenness reduction processing. Further, according to the present embodiment, before the unevenness reduction process, the gradation value of each pixel of the input image data is increased at an increase rate based on the representative gradation value of the input image data (level expansion process). As a result, a decrease in gradation value due to unevenness reduction processing (a decrease from the gradation value of input image data) can be suppressed with high accuracy, and a decrease in dynamic range due to unevenness reduction processing can be suppressed with high accuracy. it can.

  In this embodiment, the example in which the level expansion process is performed before the unevenness reduction process has been described. However, the level expansion process may be performed after the unevenness reduction process. Specifically, the unevenness reduction process may be performed on the input image data, and the gradation value of each pixel of the image data after the unevenness reduction process may be increased at an increase rate based on the representative gradation value of the input image data. In such a configuration, as the image data after the level expansion process, an image in which a decrease in gradation value due to the unevenness reduction process is suppressed with high accuracy, and a decrease in dynamic range due to the unevenness reduction process is suppressed with high accuracy. Data can be obtained.

<Example 2>
Hereinafter, an image processing apparatus and an image processing method according to Embodiment 2 of the present invention will be described. In Example 1, when the gradation value of the input image data is close to the upper limit value (255), the gradation value after multiplying by the increase rate may exceed the upper limit value. In such a case, the gradation value is limited to the upper limit value, and the dynamic range may not be effectively reduced. In this embodiment, a description will be given of a configuration that can effectively suppress a decrease in dynamic range even when the gradation value of input image data is close to the upper limit value (255).

FIG. 6 is a block diagram illustrating an example of a functional configuration of the display device 20 according to the present embodiment.
In addition, the same code | symbol is attached | subjected to the same function part as Example 1 (FIG. 1), and the description is abbreviate | omitted.

The first correction unit 201 multiplies the gradation value of each pixel of the input image data by the set first increase rate. Then, the first correction unit 201 outputs the image data after being multiplied by the first increase rate to the image processing unit 103.
The second correction unit 202 multiplies the gradation value of each pixel of the image data output from the image processing unit 103 by the set second increase rate. Then, the second correction unit 202 outputs the image data after being multiplied by the second increase rate to the display unit 104.

The representative determining unit 200 calculates the increase rate by the same process as in the first embodiment. Hereinafter, the increase rate calculated by the same processing as in the first embodiment is referred to as “calculated increase rate”.
Then, the representative determining unit 200 determines whether or not the input image data has a gradation value equal to or greater than a threshold value, and sets an increase rate in the first correction unit 201 and the second correction unit 202 according to the determination result. . In the present embodiment, as in the first embodiment, the maximum tone value of the input image data is acquired as the representative tone value. Then, the representative determining unit 200 performs a process of determining whether or not the representative gradation value is equal to or greater than the threshold value as a process of determining whether or not the input image data has a gradation value equal to or greater than the threshold value.
The threshold value may be a fixed value determined in advance by a manufacturer or the like, or may be a value that can be changed by the user.

When the input image data has a gradation value equal to or higher than the threshold value (when the representative gradation value is equal to or higher than the threshold value), a value obtained by multiplying the gradation value of the input image data by the calculated increase rate has an upper limit value. There is a high possibility of exceeding. Therefore, in such a case, the representative determination unit 200 sets the first increase rate A = 1 for the first correction unit 201 and the second increase rate B = calculation increase for the second correction unit 202. Set the rate. Therefore, in this case, input image data is output from the first correction unit 201. Then, the image processing unit 103 performs unevenness reduction processing on the input image data. That is, the image processing unit 103 uses input image data as corrected image data. Thereafter, the second correction unit 202 increases the gradation value of the image data after the unevenness reduction processing.
By setting the calculated increase rate for the second correction unit 202, it is possible to suppress the gradation value from being limited to the upper limit value, and even when the gradation value of the input image data is close to the upper limit value. It is possible to effectively suppress a decrease in dynamic range.

  On the other hand, when the input image data does not have a gradation value equal to or higher than the threshold value (when the representative gradation value is less than the threshold value), the gradation value of the input image data is multiplied by the calculated increase rate. It is unlikely that the value will exceed the upper limit. Therefore, in such a case, the representative determination unit 200 sets the first increase rate A = calculated increase rate for the first correction unit 201 and the second increase rate B = for the second correction unit 202. 1 is set. In this case, the same processing as that of the correction unit 102 of the first embodiment is performed in the first correction unit 201. In the image processing unit 103, the same processing as that in the first embodiment is performed. The second correction unit 202 outputs the same image data as the image data after the unevenness reduction process.

In this embodiment, the example in which the increase rate is set in both the first correction unit 201 and the second correction unit 202 has been described. However, the calculated increase rate is set in one of the first correction unit 201 and the second correction unit 202. May be set, and an increase rate may not be set for the other. In such a configuration, the process of multiplying the gradation value by the increase rate may be omitted in the correction unit for which the increase rate was desired to be set. Then, the same image data as the image data input to the correction unit may be output from the correction unit for which the increase rate was not set.
Also, first to fourth paths may be provided as image data transmission paths. The first path is a path for inputting the input image data to the image processing unit 103 via the first correction unit 201, and the second path is the image processing unit 103 that bypasses the first correction unit 201 for the input image data. It is a route to input. The third path is a path for inputting the image data after the unevenness reduction process to the display unit 104 via the second correction unit 202, and the fourth path is the image data after the unevenness reduction process is input to the second correction unit 202. This is a route that is bypassed and input to the display unit 104. The second route and the third route are used when the representative gradation value is equal to or greater than the threshold value, and the first route and the fourth route are used when the representative gradation value is less than the threshold value. The transmission path to be switched may be switched.

Hereinafter, the operation of the display device 20 according to the present embodiment will be described with reference to the flowchart of FIG. In the display device 20 according to the present embodiment, the processes of S101 and S102 in FIG. Thereafter, S200 to S205 in FIG. 7 are performed instead of the processes in S103 and S104 in FIG. And the process of S105 of FIG. 5 is performed.
Note that the processing in S101, S102, and S105 in FIG. 5 is the same as that in the first embodiment, and a description thereof will be omitted.

  Hereinafter, an example in which the image data 203 shown in FIG. 8 is input as input image data, the processing information shown in FIG. 4 is prepared in advance, and 225 is set as the threshold value of the representative gradation value will be described. . In the input image data 203 of FIG. 8, the gradation value of the area A at the center of the screen is 255, and the gradation value of the other area B is 0. Therefore, -30 is acquired as the amount of decrease corresponding to the representative gradation value 255, and 1.13 (= 255 / (255-30)) is calculated as the calculated increase rate.

  In S200, the representative determination unit 200 determines whether the representative gradation value is equal to or greater than a threshold value. If the representative gradation value is greater than or equal to the threshold value, the process proceeds to S201. If the representative gradation value is less than the threshold value, the process proceeds to S202. When 225 is set as the threshold value and the input image data shown in FIG. 8 is input, a value 255 larger than the threshold value 225 is acquired as the representative gradation value, and the process proceeds to S201. When 225 is set as the threshold value and the image data shown in FIG. 3 is input as the input image data, a value 192 smaller than the threshold value 225 is acquired as the representative gradation value, and the process proceeds to S202. .

  In S <b> 201, the representative determining unit 200 sets the first increase rate A = 1 for the first correction unit 201 and sets the second increase rate B = calculated increase rate for the second correction unit 202. When the input image data shown in FIG. 8 is input, the second increase rate B = 1.13 is set.

  In S <b> 202, the representative determining unit 200 sets the first increase rate A = calculated increase rate for the first correction unit 201 and sets the second increase rate B = 1 for the second correction unit 202. When the image data shown in FIG. 3 is input as the input image data, the calculation increase rate = 1.1 is calculated as described in the first embodiment. Therefore, the first increase rate A = 1.1 is set.

Specifically, the processing of S200 to S202 is executed for each of the R value, the G value, and the B value.
That is, in S200, it is determined whether or not the R representative gradation value is greater than or equal to a threshold, whether or not the G representative gradation value is greater than or equal to the threshold, and whether or not the B representative gradation value is greater than or equal to the threshold. The threshold value compared with the R representative gradation value, the threshold value compared with the G representative gradation value, and the threshold value compared with the B representative gradation value may be the same or different.
If the R representative gradation value is greater than or equal to the threshold value, the first R increase rate Ar = 1 is set for the first correction unit 201 and the second correction unit 202 is set to the second value in S201. R increase rate Br = calculated R increase rate is set. If the R representative gradation value is less than the threshold value, the first R increase rate Ar = calculated R increase rate is set for the first correction unit 201 and the second correction unit 202 is An R increase rate Br = 1 of 2 is set. The calculated R increase rate is an R increase rate calculated by the same method as in the first embodiment.
Similarly, a first G increase rate, a second G increase rate, a first B increase rate, and a second B increase rate are set.

Following S201 or S202, the first correction unit 201 increases the gradation value of each pixel of the input image data at the set first increase rate (S203). Specifically, the R value of each pixel of the input image data is multiplied by the first R increase rate, the G value of each pixel of the input image data is multiplied by the first G increase rate, and each of the input image data The B value of the pixel is multiplied by the first B increase rate. In the input image data shown in FIG. 8, the R value of the pixel at the upper left corner is 0, and the R value of the center pixel is 255. When the image data shown in FIG. 8 is input as the input image data, 1 is set as the first R increase rate. Therefore, when the image data shown in FIG. 8 is input as the input image data, the R value of the pixel at the upper left corner is corrected to the R value LK1 as shown in the following Expression 7, and the R value of the center pixel is corrected. Is corrected to the R value LK2. That is, the same image data as the input image data is obtained as the image data after being multiplied by the first increase rate.

LK1 = R value at upper left corner × first R increase rate = 0 × 1 = 0
LK2 = center R value × first R increase rate = 255 × 1 = 255
... (Formula 7)

The first correction unit 201 outputs the image data after being multiplied by the first increase rate to the image processing unit 103.

Then, the image processing unit 103 performs unevenness reduction processing on the image data output from the first correction unit 201 using the processing information stored in the storage unit 100 (S204).
The image processing unit 103 outputs the image data after the luminance unevenness reduction process to the second correction unit 202.

The method of unevenness reduction processing is the same as that in the first embodiment.
For example, for the pixel at the upper left corner, R reduction amount = 0 corresponding to the combination of the pixel position at the upper left corner and the R value LK1 = 0 is acquired, and for the center pixel, the center pixel position and the R value LK2 = R reduction amount corresponding to the combination with 255 = −30 is acquired. Then, as shown in Equation 8 below, the R value LK1 = 0 of the pixel in the upper left corner is corrected to the R value HK1, and the R value LK2 = 255 of the center pixel is corrected to the R value HK2.

HK1 = LK1 + R decrease amount = 0-0 = 0
HK2 = LK2 + R decrease amount = 255-30 = 225
... (Formula 8)

Next, the second correction unit 201 increases the gradation value of each pixel of the input image data at the set second increase rate (S205). Specifically, the R value of each pixel of the input image data is multiplied by the second R increase rate, the G value of each pixel of the input image data is multiplied by the second G increase rate, and each of the input image data The B value of the pixel is multiplied by the second B increase rate. When the input image data shown in FIG. 8 is input, 255 is acquired as the R representative gradation value, and 1.13 is calculated as the calculated R increase rate. Then, 1.13 (calculated R increase rate) is set as the second R increase rate. Therefore, when the image data shown in FIG. 8 is input as the input image data, the R value HK1 of the pixel at the upper left corner is corrected to the R value LK3 as shown in Equation 9 below, and the R value of the center pixel is corrected. The value HK2 is corrected to the R value LK4.

LK3 = HK1 × second R increase rate = 0 × 1.13 = 0
LK4 = HK2 × second R increase rate = 225 × 1.13 = 254
... (Formula 9)

The second correction unit 201 outputs the image data after being multiplied by the second increase rate to the display unit 104.

  From Equation 9, it can be seen that when the gradation value of the input image data is close to or equal to the upper limit value, the gradation value is suppressed from being limited to the upper limit value, and the decrease in the dynamic range is effectively suppressed. .

  As described above, according to the present embodiment, when the input image data has a gradation value equal to or greater than the threshold value, the unevenness reduction process is performed on the input image data. Then, the gradation value of the image data after the unevenness reduction process is increased at an increase rate. Thereby, even when the gradation value of the input image data is close to or equal to the upper limit value, it is possible to effectively suppress a decrease in the dynamic range.

  In the first and second embodiments, the image processing apparatus may include a determination unit that determines whether or not the gradation value of the input image data varies based on the input image data. When it is determined that the gradation value of the input image data does not vary, 1 may be used as the increase rate (calculated increase rate). The variation in the gradation values of the input image data means that the input image data is complex image data. That the gradation value of the input image data does not vary means that the input image data is flat image data. With such a configuration, it is possible to prioritize the reduction of luminance unevenness when the input image data is flat image data, and when the input image data is complex image data, the dynamic range and gradation Priority can be given to maintaining sex.

Whether or not the gradation values of the input image data vary can be determined using, for example, a histogram of gradation values of the input image data. Specifically, it is determined that the gradation value of the input image data varies when the number of peaks in the histogram is greater than or equal to the peak threshold, and the gradation of the input image data when the number of peaks in the histogram is less than the peak threshold. It can be determined that the values do not vary.
An example of a histogram is shown in FIGS. Here, 2 is used as the peak threshold value.
Each of the histogram 300 in FIG. 9A and the histogram 301 in FIG. 9B has two peaks. Therefore, when the histogram 300 or the histogram 301 is obtained, it is determined that the gradation values of the input image data are varied, and processing giving priority to the dynamic range and gradation is performed. Specifically, the calculated increase rate obtained by the method described in the first and second embodiments is used.
There is only one peak in the histogram 302 of FIG. Therefore, when the histogram 302 is obtained, it is determined that the gradation value of the input image data does not vary, and processing giving priority to the reduction of luminance unevenness is performed. Specifically, 1 is used as the calculated increase rate.
The peak threshold value may be a fixed value determined in advance by a manufacturer or the like, or may be a value that can be changed by the user.

  Note that the degree of variation in the gradation value of the input image data (for example, the number of peaks in the histogram) may be acquired based on the input image data. The calculated increase rate may be corrected to a value closer to 1 as the degree of variation is lower, and the corrected calculated increase rate may be used.

<Other examples>
The present invention can also be implemented by a system (or a device such as a CPU or MPU) of a system or apparatus that implements the functions of the above-described embodiments by reading and executing a program recorded in a storage device. The present invention can also be implemented by a method comprising steps executed by a computer of a system or apparatus that implements the functions of the above-described embodiments by reading and executing a program recorded in a storage device, for example. . For this purpose, the program is stored in the computer from, for example, various types of recording media that can serve as the storage device (ie, computer-readable recording media that holds data non-temporarily). Provided to. Therefore, the computer (including devices such as CPU and MPU), the method, the program (including program code and program product), and the computer-readable recording medium that holds the program non-temporarily are all present. It is included in the category of the invention.

101 representative determination unit 102 correction unit 103 image processing unit

Claims (19)

An image processing apparatus capable of executing image processing for reducing luminance unevenness on a screen of a display device,
Determining means for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
First correction means for correcting the input image data by increasing the gradation value of each pixel of the input image data at an increase rate based on the representative gradation value;
Image processing means for performing the image processing on the image data corrected by the first correction means;
An image processing apparatus comprising: An image processing apparatus capable of executing image processing for reducing luminance unevenness on a screen of a display device,
Determining means for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
Image processing means for performing the image processing on the input image data;
Correction means for correcting the image data by increasing the gradation value of each pixel of the image data after the image processing at an increase rate based on the representative gradation value;
An image processing apparatus comprising: Second correction means for correcting the image data by increasing the gradation value of each pixel of the image data after the image processing at the increase rate when the input image data has a gradation value equal to or greater than a threshold value; In addition,
The image processing apparatus according to claim 1, wherein the image processing unit uses the input image data as the corrected image data when the input image data has a gradation value equal to or greater than the threshold value. . The increase rate is a value obtained by dividing the representative gradation value by a gradation value after the image processing when the representative gradation value is a gradation value before the image processing. Item 4. The image processing device according to any one of Items 1 to 3. The increase rate is a value obtained by dividing the representative gradation value by the minimum value of the gradation value after the image processing when the representative gradation value is the gradation value before the image processing. The image processing apparatus according to any one of claims 1 to 4. Processing information indicating the relationship between the gradation value before the image processing and the degree of decrease in the gradation value due to the image processing is prepared in advance,
Using the degree of decrease corresponding to the representative gradation value in the processing information, the gradation value after the image processing when the representative gradation value is the gradation value before the image processing is determined. The image processing apparatus according to claim 4, wherein: Based on the input image data, further comprising a determination means for determining whether or not the gradation value of the input image data varies;
7. The method according to claim 1, wherein when the determination unit determines that the gradation value of the input image data does not vary, 1 is used as the increase rate. Image processing device. The image processing apparatus according to claim 7, wherein the determination unit determines whether or not the gradation value of the input image data varies based on a histogram of gradation values of the input image data. . The image processing apparatus according to claim 1, wherein the representative gradation value is a maximum gradation value of the input image data. An image processing method capable of executing image processing for reducing luminance unevenness on a screen of a display device,
A determination step for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
A first correction step of correcting the input image data by increasing the gradation value of each pixel of the input image data at an increase rate based on the representative gradation value;
An image processing step of performing the image processing on the image data corrected by the first correction step;
An image processing method comprising: An image processing method capable of executing image processing for reducing luminance unevenness on a screen of a display device,
A determination step for determining a representative gradation value representing the gradation value of the input image data based on the input image data;
An image processing step for performing the image processing on the input image data;
A correction step of correcting the image data by increasing the gradation value of each pixel of the image data after the image processing at an increase rate based on the representative gradation value;
An image processing method comprising: A second correction step of correcting the image data by increasing the gradation value of each pixel of the image data after the image processing at the increase rate when the input image data has a gradation value equal to or greater than a threshold; In addition,
The image processing method according to claim 10, wherein, when the input image data has a gradation value equal to or greater than the threshold value, the input image data is used as the corrected image data in the image processing step. . The increase rate is a value obtained by dividing the representative gradation value by a gradation value after the image processing when the representative gradation value is a gradation value before the image processing. Item 13. The image processing method according to any one of Items 10 to 12. The increase rate is a value obtained by dividing the representative gradation value by the minimum value of the gradation value after the image processing when the representative gradation value is the gradation value before the image processing. The image processing method according to any one of claims 10 to 13. Processing information indicating the relationship between the gradation value before the image processing and the degree of decrease in the gradation value due to the image processing is prepared in advance,
Using the degree of decrease corresponding to the representative gradation value in the processing information, the gradation value after the image processing when the representative gradation value is the gradation value before the image processing is determined. The image processing method according to claim 13 or 14, A determination step of determining whether or not gradation values of the input image data vary based on the input image data;
16. The method according to claim 10, wherein 1 is used as the increase rate when it is determined that the gradation value of the input image data does not vary in the determination step. Image processing method. The image processing method according to claim 16, wherein in the determination step, it is determined whether or not the gradation value of the input image data varies based on a histogram of gradation values of the input image data. . The image processing method according to claim 10, wherein the representative gradation value is a maximum gradation value of the input image data.   A program causing a computer to execute each step of the image processing method according to any one of claims 10 to 18.

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