JP2003116042A - Uneven sensitivity remover, image pickup device, and uneven display testing system of display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily remove uneven sensitivity in an image pickup device without preparing a special light source. SOLUTION: In a state of focused on a subject 5, a light source 6 having a light-emitting plane is carried in between an image pickup device 14 and a subject 5 to image the light from the light-emitting plane of the light source 6. Based on imaging data of the light source 6 thus-obtained, uneven sensitivity of an imaging lens 1 and an image pickup element 2 of the image pickup device 14 is computed by a computation part 10 and is stored in an uneven sensitivity storage part 4. Subsequently, the imaging data of the subject 5 is acquired by imaging the subject 5 from carrying out the light source 6, and the uneven sensitivity stored in the uneven sensitivity storage part 4 is removed from this imaging data by the computation part 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensitivity unevenness removing device, an imaging device, and a display unevenness inspection system for a display device, and more particularly to an inspection system for inspecting display unevenness of a display device by an imaging device such as a digital camera.

[0002]

2. Description of the Related Art Conventionally, unevenness in sensitivity or uneven display may occur in an image pickup device of an image pickup device such as a CCD camera or a display device of a display device such as a monitor of a television or a personal computer.

FIG. 5 is a diagram showing sensitivity unevenness of a conventional image pickup device and display unevenness of a display device. FIG. 5A shows the level of image pickup data output from a part of the image pickup element and the display element. FIG. 5B shows the average of the levels of image pickup data output from all the image pickup elements and display elements.

One of the sensitivity unevenness of the conventional image pickup device is caused by the sensitivity variation of individual pixels constituting the image pickup element. As shown in FIG. It is a high-frequency unevenness in which the level of the output imaging data fluctuates.

Another type of sensitivity unevenness of conventional image pickup devices is caused by an image pickup lens and an optical system such as a microlens arranged above pixels, as shown in FIG. 5B. The unevenness of the frequency is low such that the output of the pixels located in the central part of the image pickup surface is high and the output of the pixels located in the peripheral part is low. This phenomenon is called shading.

[0006] Here, for example, when manufacturing a display device, it is inspected whether or not the display unevenness falls within a predetermined range. This inspection may be performed visually, but may also be performed based on an image captured by an imaging device such as a CCD camera in order to perform the inspection with high stability and reliability.

When inspecting the display unevenness of the display device by using a CCD camera or the like, the following steps are roughly performed.
First, display a single color patch on the display device, and
Take an image with a camera. Next, the unevenness of sensitivity of the image pickup device is removed from the imaged data of the display device to extract the display unevenness of the display device. Then, it is determined whether or not the display unevenness is within a predetermined threshold value.

For example, Japanese Unexamined Patent Publication No. 10-260109 discloses a method for correcting sensitivity unevenness of an image pickup device. The method described in this publication is
A white light source is prepared, the light source is imaged by an image pickup device, and Rc, Gc, and Bc which are R, G, and B output values output from a pixel located in the center among pixels arranged in the image pickup device.
And an output value that represents the positions of pixels arranged at other positions by the coordinates (i, j) of the imaging system, the position (i,
j) the correction factor of the RGB image sensor is R (i, j) / R
c, G (i, j) / Gc, B (i, j) / Bc are calculated, and the output of the CCD camera is divided by this correction coefficient to eliminate the sensitivity unevenness of the image pickup apparatus.

When the white light source has some unevenness in brightness and color, the image pickup device of the image pickup apparatus is based on the image pickup data obtained by picking up an image of the white light source with the image pickup lens removed from the CCD camera. The sensitivity unevenness can be corrected.

[0010]

However, in the conventional technique, it is necessary that the light source to be prepared has ideally uniform in-plane chromaticity and luminance and is large in size of about 1 m × 1 m. To be done. In addition, it is troublesome because the imaging needs to be performed twice, that is, with the lens removed and with the lens attached. Furthermore, since it is necessary to measure multiple points such as 4 × 5 grid points using a colorimeter as a light source, it takes time to measure the sensitivity unevenness, and data at points other than the measurement points by the colorimeter are interpolated. Since it is obtained by processing, there is also a problem that an error occurs due to interpolation at this time.

Therefore, it is an object of the present invention to easily remove the sensitivity unevenness of the image pickup device without preparing a special light source.

[0012]

In order to solve the above-mentioned problems, the present invention is a sensitivity unevenness removing device for removing the sensitivity unevenness of the imaging device from the imaging data of the object imaged by the imaging device, A light source having a light emitting surface arranged at a distance different from the distance between the imaging device and the subject, and a light source obtained by imaging light from the light emitting surface of the light source under a condition of focusing on the subject. And an arithmetic unit for calculating the sensitivity unevenness of the image pickup apparatus based on the image pickup data and removing the sensitivity unevenness from the image pickup data of the subject.

Further, the present invention is a sensitivity unevenness removing device for removing sensitivity unevenness of the image pickup device from image pickup data of the object picked up by the image pickup device, the sensitivity unevenness remover being arranged between the image pickup device and the object. The unevenness of sensitivity of the imaging device is calculated based on the diffuser that diffuses the light from the subject and the imaging data obtained by capturing the light diffused by the diffuser under the condition of focusing on the subject. And an arithmetic unit that removes the sensitivity unevenness from the imaged data of the subject.

Further, the image pickup apparatus of the present invention comprises an image pickup device having pixels arranged two-dimensionally, an optical system for collecting light from a subject to the image pickup device, and a gap between the optical system and the subject. A light source capable of transporting a light emitting surface, and the image pickup device and the image pickup device based on image pickup data of the light source obtained by picking up light from the light emitting surface of the light source under a condition in which a subject is focused by the optical system. And a calculation unit that calculates the sensitivity unevenness of the optical system and removes the sensitivity unevenness from the imaging data of the subject.

Furthermore, the image pickup device of the present invention comprises an image pickup device having pixels arranged two-dimensionally, an optical system for collecting light from a subject to the image pickup device, and the optical system and the subject. The image sensor and the optical system based on image data of a subject obtained by capturing the light diffused by the diffuser under a condition in which the subject is focused by the optical system and a diffuser that can be conveyed in between. And a calculation unit that removes the sensitivity unevenness from the imaging data of the subject.

Furthermore, the inspection system for a display device of the present invention includes an image pickup device for picking up light from the display device, a light source which can be conveyed on a line connecting the display device and the image pickup device, and the display device. The sensitivity unevenness of the imaging device is calculated based on the imaging data of the light source obtained by imaging the light from the light emitting surface of the light source under the focused condition, and the sensitivity unevenness of the imaging device is calculated from the imaging data of the subject. And a discriminating device for discriminating whether or not the image pickup data of the display device from which the sensitivity unevenness is eliminated by the arithmetic device falls within a predetermined threshold value.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment> [Description of Configuration] FIG. 1 is a schematic configuration diagram of a sensitivity unevenness removing apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is an imaging lens, 2 is an image sensor, 3 is a black level storage unit, 4 is sensitivity unevenness storage unit, 5 is a subject, 6 is a light source, 7 is a light source transporting unit, 8 is a brightness adjusting unit, and 9 is A computer, 10 is a calculation unit, and 14 is an imaging device.

The image pickup lens 1 is a standard lens having a focus adjusting function and a diaphragm, and an ND filter or the like in place of the diaphragm so that the amount of light can be adjusted.

The image pickup device 2 is formed by arranging pixels such as a CCD image pickup device and a MOS type image pickup device in a matrix, a honeycomb, and a delta, and a microlens is provided on the image pickup lens 1 side.

The black level storage unit 3 is a writing / reading memory for storing the black level of the image pickup device 2 calculated by the calculation unit 10 based on the image pickup data obtained by picking up the image of the light source 6.

The uneven sensitivity storage unit 4 is a writing / reading memory that stores the uneven sensitivity of the image pickup lens 1 and the image pickup device 2 calculated by the calculation unit 10 based on the image pickup data obtained by picking up the image of the light source 6.

The subject 5 is a display such as an LCD, PDP, CRT, or a paper such as a printed matter.

The light source 6 has a flat light emitting surface,
There may be some uneven brightness and uneven color. here,
The light source 6 includes a plurality of fluorescent lamps and a transmissive white diffuser plate in front of the fluorescent lamps, and has a size of 20 cm in length × 20 cm in width.

The light source transport section 7 includes an image pickup lens 1 and an object 5.
The light source 6 is carried in between the image pickup lens 1 and the subject 5
The light source 6 is carried out from between.

The brightness adjusting section 8 adjusts the brightness of the light source 6 based on the image pickup data from the image pickup device 2. In the present embodiment, the brightness can be adjusted in a plurality of steps by changing the number of emitted light of the fluorescent lamp of the light source 6. It should be noted that the brightness of the light-emitting body may be directly adjusted, or a light-reducing film or the like may be placed on the front surface.

The computer 9 performs processing for controlling the light emission of the light source 6, the driving of the light source transport section 7, the driving of the brightness adjusting section 8, and the like. It should be noted that the computer 9 may store the black level and the unevenness in sensitivity, or may perform an operation for removing them from the imaged data of the subject 5.

The calculation unit 10 calculates the black level and sensitivity unevenness of the image pickup device 2 based on the image pickup data obtained by picking up the image of the light source 6, and the black level storage unit from the image pickup data obtained by picking up the image of the subject 5. The black level stored in 3 and the sensitivity unevenness stored in the sensitivity unevenness storage unit 4 are removed.

The image pickup device 14 includes an image pickup lens 1, an image pickup device 2, a black level storage unit 3, a sensitivity unevenness storage unit 4, and a calculation unit 1.
It is a monochrome camera or a color camera having 0.

[Explanation of Operation] Hereinafter, the operation of FIG. 1 will be described by taking as an example the case where the black level and sensitivity unevenness of the image pickup lens 1 and the image pickup element 2 are removed and the display unevenness of the display which is the object 5 is corrected. Will be described.

First, a cap (not shown) is attached to the image pickup lens 1 so that light is not incident on the image pickup device 2 and an image is picked up by the image pickup device 14. In general, the image sensor 2 has a characteristic of outputting image data of a certain pattern even without input light. Such an output is called a black level.

The black level output from the image pickup device 2 is stored in the black level storage unit 3 via the arithmetic unit 10. Since the black level does not change due to the imaging conditions such as focus and aperture, once the black level is imaged and stored, it need not be acquired again. The black level may be acquired at the manufacturing stage or may be acquired by the user of the imaging device 14.

On the other hand, the sensitivity unevenness calculated based on the image pickup data obtained by picking up the image of the light source 6 changes each time the image pickup conditions such as the focus and the diaphragm of the image pickup lens 1 are changed. This is because, due to the shading of the image pickup lens 1, the amount of light gathered in the central portion of the image pickup element 2 and the amount of light gathered in the peripheral portion of the image pickup element 2 are different.

Next, as shown in FIG. 1, the image pickup device 14 is arranged so that the subject 5 can be picked up, and the entire surface of the subject 5 is displayed with the same brightness, for example, white. Then, the focus of the imaging lens 1 is adjusted, the aperture is adjusted, an ND filter is attached if necessary, and the subject 5 is focused.

Here, the distance between the imaging lens 1 and the subject 5, that is, the working distance is set to 3 m, for example.

Next, the light source 6 is carried between the image pickup lens 1 and the subject 5 by the light source transport section 7. At this time, the light emitting surface of the light source 6 and the image pickup device 2 are arranged to face each other. The distance between the imaging lens 1 and the light source 6 is, for example, 3c.
m.

Then, under the condition of focusing on the subject 5,
The image pickup device 14 takes an image with the light source 6 emitting light. Then, the imaging data obtained by the imaging device 2 is output to the computer 9. In the computer 9, the image obtained by this imaging data is too bright and saturated,
Determine if it is too dark and the gradation is not flattened.

As a result of the determination, if the brightness of the light source 6 is not required, the brightness adjusting unit 8 is instructed to adjust the brightness of the light source 6. The brightness adjusting unit 8 adjusts the brightness of the light source 6 according to an instruction from the computer 9. The image capturing device 14 captures images of the light source 6 several times until the adjustment is completed.

Specifically, first, the light source 6 is turned on at a predetermined brightness according to an instruction from the brightness adjusting section 8. The level of the imaging data of the light source 6 is taken into the computer 9 and the average value of the levels is obtained. Imaging and brightness adjustment of the light source 6 are repeated until this value falls within a predetermined range.

For example, if the output of the image pickup device 14 can express 4096 gradations, the upper limit is previously set to 3000 gradations, for example.
The lower limit is set to, for example, 1000 gradations when the imaging device 14 is manufactured. In a certain image pickup, if the average value of the level of the image pickup data of the light source 6 exceeds the upper limit of 3000,
If the brightness of the light source 6 is lowered by one level, and conversely, if it is below the lower limit 1000, the process of increasing the brightness of the light source 6 by one level is repeated.

Then, the average value of the levels of the imaged data is 1
When it enters between 000 and 3000, the brightness adjustment of the light source 6 is completed. The last level of the image pickup data at the time of this brightness adjustment becomes a level C (i, j) described later.

Since the object 5 is still focused, the image of the light source 6 formed on the image pickup device 2 is in a blurred state. Therefore, it is possible to obtain imaging data of the light source 6 that is not caused by uneven brightness or uneven color. In the arithmetic unit 10,
The sensitivity unevenness of the image sensor 2 is calculated based on the imaged data, and the calculation result is stored in the sensitivity unevenness storage unit 3.

According to the verification by the inventor, when the object 5 which is about 3 m away is in focus, if the working distance is within 5 cm and the light source 6 is imaged, the image on the image sensor 2 is ideal. It was found that it can be approximated to a uniform light source image. After that, further verification,
It has been found that the distance between the image pickup lens 1 and the light source 6 may be set in the first half of the distance between the image pickup lens 1 and the subject 5.

Next, the light source transport unit 7 stops the light emission of the light source 6, and the light source 6 is carried out between the imaging lens 1 and the subject 5. Then, the subject 5 is imaged by the imaging device 14 in a state where the entire surface of the display, which is the subject 5, is displayed in white with the same brightness.

Then, as described below, the calculation unit 10 removes the black level stored in the black level storage unit 3 from the imaged data of the subject 5 and stores it in the sensitivity unevenness storage unit 4. Eliminate unevenness in sensitivity.

The image pickup data of the subject 5 from which the black level and the unevenness of sensitivity are removed are sent to the computer 9 where the display unevenness of the display of the subject 5 is analyzed. Then, based on the analysis result, it is inspected whether the display unevenness falls within a predetermined threshold value.

Next, the calculation method of the calculation unit 10 will be described.

The position of each pixel of the image sensor 2 is represented by the coordinates (i, j) of the image pickup system, the level of the image pickup data of the object 5 is V (i, j), the black level is K (i, j), If the level of the image pickup data of the light source 6 is C (i, j), the black level K (i, j) of the level V (i, j) of the image pickup data of the subject 5
The level V ′ (i, j) of the data after the removal is represented by the formula (1)
Can be calculated using V '(i, j) = V (i, j) -K (i, j) (1)

Further, the level C'of the image data C (i, j) of the light source 6 after the black level K (i, j) is removed.
(I, j) can be calculated using the equation (2). C '(i, j) = C (i, j) -K (i, j) (2)

If the level of the data obtained by removing the black level from the level of the image data output from the pixel located at the center of the image sensor 2 when the light source 6 is imaged is C1c, the image sensor 2 will be described. The sensitivity unevenness correction coefficient C ″ (i, j) can be calculated using Equation (3). C ″ (i, j) = C1c / C ′ (i, j) (3)

Next, as shown in the mathematical expression (4), the image pickup data V of the object 5 in which the sensitivity unevenness is corrected by multiplying V ′ (i, j) by the correction coefficient C ″ (i, j). ”
(I, j) can be obtained. V ″ (i, j) = V ′ (i, j) × C ″ (i, j) (4)

By performing such a calculation, not only the black level of the image sensor 2 but also the sensitivity unevenness including shading can be removed.

Note that, as shown in FIG. 2, the subject transporting section 11 for transporting the subject 5 is provided, and the subject 5 placed at a position, for example, 5 cm away from the image sensing device 14 is focused and then the image sensing device. By arranging the light source 6 at a position away from 14 by, for example, 10 cm, it is possible to perform imaging without focusing on the light source 6.

As described above, in the present embodiment, the light source 6 is imaged prior to the imaging of the subject 5, and the image pickup lens 1 and the image pickup element 2 are taken.
The case where the sensitivity unevenness of the subject 5 is acquired has been described as an example.
The image of the light source 6 may be taken after the image of is taken.

<Second Embodiment> FIG. 3 is a schematic configuration diagram of an image pickup apparatus according to a second embodiment of the present invention. In FIG.
Reference numeral 12 is a cap, and 13 is a light emission control unit. Note that FIG.
In FIG. 3, the same parts as those shown in FIG. 1 are designated by the same reference numerals.

The cap 12 protects the image pickup lens 1, and is put in or removed from the image pickup lens 1 by the user of the image pickup device 14.

The light-emission control unit 13 adjusts the brightness of the light source 6 stepwise including non-light-emission, and is responsible for the processing performed by the computer 9 and the brightness adjustment unit 8 in FIG.

In this embodiment, after the black level of the image pickup device 2 is acquired by the same procedure as that of the first embodiment, the image pickup lens 1
With the cap 12 removed, the focus is on the display of the subject 5. Next, with the cap 12 fitted in the imaging lens 1, the light emission control unit 13 causes the light source 6 to emit light with a required brightness to perform imaging.

Then, the cap 12 is removed from the image pickup lens 1, the subject 5 is imaged, and the black level of the image pickup element 2 and the sensitivity unevenness of the image pickup lens 1 and the image pickup element 2 are removed by the same method as in the first embodiment. Then, the display unevenness of the subject 5 is inspected.

When the image pickup device 14 images various subjects 5, the image pickup data obtained by picking up the image of each subject 5 is stored together with the image pickup condition of the image pickup lens 1, and the image pickup device 14 is stored. When the user of 14 finishes the imaging of each subject 5 and the cap 12 is fitted in the imaging lens 1 as a trigger, the sensitivity unevenness in the state of focusing on each subject 5 is acquired, and You may make it remove from imaging data.

<Third Embodiment> FIG. 4 is a schematic diagram of a sensitivity unevenness removing apparatus according to a third embodiment of the present invention. In FIG. 4, reference numeral 15 is a transmissive white diffuser plate. 4, the same parts as those in FIG. 1 and the like are designated by the same reference numerals.

Like the cap 12 shown in FIG. 3, the white diffuser plate 15 is attachable to and detachable from the image pickup lens 1 and diffuses the light from the display which is the subject 5. For example, acrylic or glass is used as the material, and the transmittance is 80% ~
It is about 95%.

After the black level is obtained by the same procedure as in the first embodiment, the entire surface of the display, which is the subject 5, emits white light with the same brightness without the white diffuser plate 15 being fitted in the imaging lens 1. Then, the image sensor 2 is focused on the subject 5. Next, imaging is performed with the white diffusion plate 15 attached to the imaging lens 1.

At this time, the light from the subject 5 is diffused by the white diffuser plate 15 and enters the image pickup device 2. The image pickup device 2 is based on the image pickup data obtained by this image pickup.
The sensitivity unevenness of is measured.

Then, the white diffuser plate 15 is removed from the image pickup lens 1, the subject 5 is imaged, and the black level and the sensitivity unevenness of the image pickup device 2 are removed by the same method as in the first embodiment.
The display unevenness of the subject 5 is inspected.

[0066]

As described above, according to the present invention,
Since it is possible to easily remove the sensitivity unevenness of the imaging device without preparing a special light source, it is possible to easily and accurately inspect the display unevenness of the display device, for example.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a sensitivity unevenness removing apparatus according to a first embodiment of the present invention.

FIG. 2 is another schematic configuration diagram of the sensitivity unevenness device according to the first embodiment of the present invention.

FIG. 3 is a schematic configuration diagram of an image pickup apparatus according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a sensitivity unevenness removing apparatus according to a third embodiment of the present invention.

FIG. 5 is a diagram showing sensitivity unevenness of a conventional image pickup device and display device.

[Explanation of symbols]

1 Imaging lens 2 image sensor 3 Black level memory 4 Sensitivity unevenness storage section 5 subject 6 light source 7 Light source transport section 8 Brightness adjustment section 9 computers 10 Operation part 11 Subject calculation section 12 caps 13 Light emission control unit 14 Imaging device 15 Diffuser

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) // H04N 9/04 H04N 9/04 B 5C065 (72) Inventor Toshiyuki Kanda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masa Tada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yukio Hiraki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. Inner F term (reference) 2G051 AA90 BB07 CA04 EA14 FA10 2G086 EE01 EE10 5C022 AB15 AB37 AC42 5C024 CX27 CX35 CY44 DX01 5C061 EE11 EE21 5C065 BB06 BB22 BB41 BB48

Claims (9)

[Claims] 1. A sensitivity unevenness removing device for removing sensitivity unevenness of the imaging device from imaged data of a subject imaged by the imaging device, wherein the sensitivity unevenness removing device is arranged at an interval different from an interval between the imaging device and the object. A light source having a light emitting surface and the sensitivity unevenness of the image pickup device is calculated based on image pickup data of the light source obtained by picking up light from the light emitting surface of the light source under a condition in which the subject is focused. A sensitivity unevenness removing device, comprising: a calculation unit that removes the sensitivity unevenness from image data of a subject. 2. A sensitivity unevenness removing device for removing sensitivity unevenness of the image pickup device from image pickup data of the object picked up by the image pickup device, wherein the subject is arranged between the image pickup device and the subject. And a diffuser for diffusing the light of the subject, and the unevenness of sensitivity of the imaging device is calculated based on the imaging data obtained by imaging the light diffused by the diffuser under a condition in which the subject is focused. A sensitivity unevenness removing device, comprising: a calculation unit that removes the sensitivity unevenness from imaged data. 3. In a state in which the subject is focused in advance, the image pickup device and the light source or the diffuser are conveyed such that the distance between them is different from the distance between the image pickup device and the subject. Item 1. The uneven sensitivity removing device according to item 1 or 2. 4. The sensitivity unevenness of the image pickup device is unevenness in sensitivity between an image pickup device that picks up light from the subject and an optical system that collects the light on the image pickup device. A sensitivity unevenness removing device according to the item. 5. The sensitivity nonuniformity removal according to claim 4, wherein the black level of the image pickup device is acquired by performing image pickup in a state where no light is incident on the image pickup device, and the black level is removed from the image pickup data. apparatus. 6. An image pickup device having pixels arranged two-dimensionally, an optical system for collecting light from a subject to the image pickup device, and a light emitting surface capable of being conveyed between the optical system and the subject. The sensitivity unevenness of the image pickup device and the optical system is calculated based on the image pickup data of the light source obtained by performing the image pickup of the light from the light emitting surface of the light source under the condition where the subject is focused by the light source and the optical system. And an arithmetic unit that removes the unevenness in sensitivity from the imaged data of the subject. 7. An image pickup device having pixels arranged two-dimensionally, an optical system for collecting light from a subject to the image pickup device, and a diffuser capable of being conveyed between the optical system and the subject. Calculating the sensitivity unevenness of the image pickup device and the optical system based on the image pickup data of the subject obtained by picking up the light diffused by the diffuser under the condition that the subject is focused by the optical system, An image pickup apparatus comprising: a calculation unit that removes the sensitivity unevenness from image pickup data of a subject. 8. The image pickup apparatus according to claim 6, wherein the light source or the diffuser is provided in a cap attached to an image pickup lens. 9. An image pickup device for picking up light from a display device, a light source that can be conveyed on a line connecting the display device and the image pickup device, and a light emitting surface of the light source under a condition in which the display device is focused. An arithmetic unit for calculating the sensitivity unevenness of the image pickup device based on the image pickup data of the light source obtained by picking up the light from the object and removing the sensitivity unevenness of the image pickup device from the image pickup data of the subject, and the arithmetic unit An inspection system for a display device, comprising: a determination device that determines whether or not the image pickup data of the display device from which the sensitivity unevenness is removed falls within a predetermined threshold value.