JP2021173545A - Optical measurement device and optical measurement method - Google Patents

Abstract

To provide an optical measurement device capable of appropriately determining propriety of a measurement condition of a speckle contrast or a sparkle contrast.SOLUTION: An optical measurement device 1 includes: an image sensor 4 for capturing an image of emission light from a measured surface 2 of a speckle contrast or a sparkle contrast; and a determination section 5 for determining propriety of a measurement condition of a speckle contrast or a sparkle contrast based on a standard deviation of a radiance difference between corresponding pixels of a first image captured in a first pixel area of the image sensor and a second image captured in a second pixel area of the image sensor.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an optical measuring device and an optical measuring method.

For example, as disclosed in Patent Document 1, speckles generated by the coherence of laser light are measured. The speckle contrast measuring device described in Patent Document 1 is configured to image a laser beam diffused by a moving diffuser and projected on a screen, and measure speckle contrast based on the imaging result. .. Further, a device for measuring sparkle contrast in a display equipped with a so-called antiglare layer, which reduces the effect of directly observing the reflected light of external light on the display surface, has been proposed (Unlicensed Document 1).

Japanese Unexamined Patent Publication No. 2014-32371

Japanese Patent Application No. 2019-81243

However, in the speckle contrast measuring device described in Patent Document 1, no effective proposal has been made for appropriately determining the suitability of the speckle contrast measurement conditions.

The present disclosure has been made in consideration of the above points, and an object of the present disclosure is to provide an optical measuring device and an optical measuring method capable of appropriately determining the suitability of speckle contrast or sparkle contrast measuring conditions. do.

The optical measuring device according to the present disclosure is
An image sensor that captures an image of the light emitted from the surface under test with speckle contrast or sparkle contrast,
Based on the standard deviation of the difference in radiance between the corresponding pixels of the first image captured in the first pixel region of the image sensor and the second image captured in the second pixel region of the image sensor, the said A determination unit for determining the suitability of measurement conditions for speckle contrast or sparkle contrast is provided.

In the optical measuring device according to the present disclosure,
The second pixel region may be at least partially different in position from the first pixel region and may have the same number of pixels.

In the optical measuring device according to the present disclosure,
The determination unit may determine the suitability of the measurement conditions based on the ratio of the standard deviation of the difference to the standard deviation of the radiance of the first image.

In the optical measuring device according to the present disclosure,
The determination unit may determine the suitability of the measurement conditions based on the ratio of the standard deviation of the difference to the standard deviation of the radiance of the second image.

In the optical measuring device according to the present disclosure,
The determination unit determines the suitability of the measurement conditions based on the ratio of the standard deviation of the difference to the average value of the standard deviation of the radiance of the first image and the standard deviation of the radiance of the second image. You may.

In the optical measuring device according to the present disclosure,
The difference in radiance between the corresponding pixels of the first image and the second image is corrected so that the average value of the radiance of the first image and the average value of the radiance of the second image are aligned. It may be the difference between the radiance of the corrected first image and the radiance of the corrected second image.

In the optical measuring device according to the present disclosure,
The standard deviation of the difference may be the square root of the sum of squares of the standard deviation of the radiance of the first image and the standard deviation of the radiance of the second image.

In the optical measuring device according to the present disclosure,
The difference in radiance between the corresponding pixels of the first image and the second image is corrected so that the average value of the radiance of the first image and the average value of the radiance of the second image are aligned. It is the difference between the radiance of the corrected first image and the radiance of the corrected second image.
The determination unit obtained the predetermined value when the ratio of the radiance of the corrected first image and the standard deviation of the difference based on the radiance of the corrected second image was a predetermined value. It may be determined that the number of pixels in the first pixel region and the second pixel region at the time is appropriate as the number of pixels used in the measurement of the speckle contrast or the sparkle contrast as the measurement condition.

In the optical measuring device according to the present disclosure,
The predetermined value of the ratio of the standard deviations of the differences may be ^{2 1/2.}

In the optical measuring device according to the present disclosure,
The number of pixels in the first pixel region and the second pixel region is the standard deviation of the difference when the average value of the radiance of the first image and the average value of the radiance of the second image are the same. It is a known number of pixels that makes the ratio a predetermined value,
When the ratio of the standard deviation of the difference is different from the predetermined value, the determination unit determines the average value of the radiance of the first image when the ratio of the standard deviation of the difference different from the predetermined value is obtained and the said. It may be determined that the average value of the radiance of the second image is not appropriate as the average value of the radiance of the image used for measuring the speckle contrast or the sparkle contrast as the measurement condition.

In the optical measuring device according to the present disclosure,
The corresponding pixels of the first pixel region and the second pixel region may be separated by at least three times or more the average size of the speckle pattern or the sparkle pattern.

In the optical measuring device according to the present disclosure,
The surface to be measured may be an exit surface of the antiglare layer in a display device having an antiglare layer.

In the optical measuring device according to the present disclosure,
The surface to be measured may be a pixel matrix surface of a display device.

In the optical measuring device according to the present disclosure,
The surface to be measured may be an exit surface of the backlight device.

In the optical measuring device according to the present disclosure,
The surface to be measured may be an exit surface of a screen that projects light emitted from the projector.

In the optical measuring device according to the present disclosure,
A measuring unit for measuring speckle contrast or sparkle contrast according to measurement conditions determined to be appropriate may be provided.

但し、Ｃ_Ｓ−Ｅは、測定されたスペックルコントラストまたはスパークルコントラストの値であり、Ｃ_Ｓ−Ｃは、前記対応関係において数式（１）の値を０（％）にする既知のスペックルコントラストまたはスパークルコントラストである。 In the optical measuring device according to the present disclosure,
An optical system that forms an image of the light emitted from the surface under test with speckle contrast or sparkle contrast,
An image sensor in which the emitted light is imaged and an image of the emitted light is captured.
A determination unit for determining the suitability of the speckle contrast or sparkle contrast measurement conditions is provided.
In the determination unit, the value of the following formula (1) expressed by speckle contrast or sparkle contrast measured based on the image captured in the predetermined pixel region of the image sensor is the number of pixels in the pixel region and the value of the following formula (1). When the F number of the optical system and the value of the mathematical formula (1) fall within the permissible range shown in the known correspondence, the number of pixels in the pixel region and the optical It may be determined that the F number of the system is appropriate as the measurement condition of the speckle contrast or the sparkle contrast.

However, C _S-E is the measured value of the speckle contrast or sparkle contrast, C _S-C is known speckle contrast value to 0 (%) of Equation (1) in the correspondence relation Or sparkle contrast.

In the optical measuring device according to the present disclosure,
The correspondence is two curves line-symmetrical with respect to the horizontal axis when the number of pixels in the pixel area is taken on the horizontal axis and the value of the mathematical formula (1) is taken on the vertical axis. Within the permissible range surrounded by two curves that converge toward 0 (%) on the vertical axis as the number of pixels increases, a plurality of appropriate values of the mathematical formula (1) that differ depending on the F number and the number of pixels are contained. It may be a relationship.

The optical measurement method according to the present disclosure is
An image of the light emitted from the surface to be measured with speckle contrast or sparkle contrast is captured by an image sensor.
_{To the standard deviation (σ sub} ) of the difference in radiance between the corresponding pixels of the first image captured in the first pixel region of the image sensor and the second image captured in the second pixel region of the image sensor. Based on this, the suitability of the measurement conditions for the speckle contrast or the sparkle contrast is determined.

According to the present disclosure, it is possible to appropriately determine the suitability of the measurement conditions for speckle contrast or sparkle contrast.

FIG. 1 is a diagram showing an optical measuring device according to the first embodiment. FIG. 2 is a diagram showing an example of a surface to be measured in the optical measuring device according to the first embodiment. FIG. 3 is a diagram showing another example of the surface to be measured in the optical measuring device according to the first embodiment. FIG. 4 is a diagram showing another example of the surface to be measured in the optical measuring device according to the first embodiment. FIG. 5 is a flowchart showing an operation example of the optical measuring device according to the first embodiment. FIG. 6 is a diagram showing a process of acquiring a first image and a second image in an operation example of the optical measuring device according to the first embodiment. FIG. 7 is a diagram showing a speckle contrast measurement system using diffused light of coherent light as an experimental example of the optical measuring device according to the first embodiment. FIG. 8 is a diagram showing the ratio of the difference standard deviation to the standard deviation of the speckle contrast and the radiance of the first image measured by the measurement system of FIG. 7 when the effective F number of the lens is 2.1. FIG. 9 is a diagram showing the ratio of the difference standard deviation to the standard deviation of the speckle contrast and the radiance of the first image measured by the measurement system of FIG. 7 when the effective F number of the lens is 8.7. FIG. 10 is a diagram showing the ratio of the difference standard deviation to the standard deviation of the speckle contrast and the radiance of the first image measured by the measurement system of FIG. 7 when the effective F number of the lens is 17.4. FIG. 11 is a diagram showing the ratio of the difference standard deviation to the standard deviation of the speckle contrast and the radiance of the first image measured by the measurement system of FIG. 7 when the effective F number of the lens is 33.3. FIG. 12 is a flowchart showing an operation example of the optical measuring device according to the second embodiment. FIG. 13 shows, as an experimental example of the optical measuring device according to the second embodiment, the speckle contrast measured by the measuring system of FIG. 7 and the radiance of the first image when the F number of the optical system is 17.4. It is a figure which shows the ratio of the difference standard deviation with respect to the standard deviation. FIG. 14 is a flowchart showing an operation example of the optical measuring device according to the third embodiment. FIG. 15 is a diagram showing the correspondence between the number of pixels in the pixel region and the F number of the optical system and the mathematical formula (1) as an experimental example of the optical measuring device according to the third embodiment. FIG. 16 is a diagram showing an example of a method for correcting radiance.

Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the drawings attached to the present specification, the scale, aspect ratio, etc. are appropriately changed from those of the actual product and exaggerated for the convenience of illustration and comprehension.

In addition, the terms such as "equivalent" and "same" and the values of length and angle used in the present specification to specify the shape and geometric conditions and their degrees are bound to a strict meaning. The interpretation shall be made to include the range in which similar functions can be expected. In the following description of each embodiment, the same reference numerals are used for parts having the same or similar basic configurations, and duplicate description will be omitted.

(First Embodiment)
FIG. 1 is a diagram showing an example of the optical measuring device 1 according to the first embodiment. The optical measuring device 1 shown in FIG. 1 can be used for measuring speckle contrast or sparkle contrast contained in an optical image formed on a surface to be measured 2 of a light emitting electronic display or a light emitting surface. ..

In general, speckle refers to an irregular spatially modulated image resulting from the interference of coherent light on the sensor surface of the observer's visual system. A speckle is a statistically irregular radiance distribution of light. Typically, the radiance distribution of light is the luminance distribution. Speckle contrast is a typical evaluation index of speckles used to estimate how strongly speckles are observed. Speckle contrast is defined by the following equation.

数式（２）において、σは、センサ面上の光の放射輝度分布の標準偏差であり、典型的には輝度分布の標準偏差である。数式（２）において、

は、放射輝度の平均値すなわち平均放射輝度であり、観察者を人間と想定した場合には、典型的には平均輝度である。

In equation (2), σ is the standard deviation of the radiance distribution of light on the sensor surface, typically the standard deviation of the brightness distribution. In formula (2)

Is the average value of radiance, that is, the average radiance, which is typically the average brightness when the observer is assumed to be a human being.

Sparkle is an irregular spatial modulation that occurs as a result of imaging on the sensor surface of the observer's visual system by a combination of a pixel matrix of a direct-view display and a diffusion layer arranged near the surface of the display. Refers to an image. The sparkle contrast is a typical evaluation index of sparkle, and can be defined as the ratio of the standard deviation to the average radiance as in the equation (2).

The surface to be measured 2 for which such speckle contrast or sparkle contrast should be measured may take various forms depending on the type of the electronic display or the light emitting surface.

For example, as shown in FIG. 2, the surface to be measured 2 may be the surface of an antiglare layer 9, that is, a diffusion layer, which is laminated on a display device 8 having a pixel matrix 81 and a black matrix 82. In the example shown in FIG. 2, the optical measuring device 1 can measure the sparkle contrast of the surface to be measured 2. The display device 8 is typically a liquid crystal display device including a liquid crystal panel having a pixel matrix 81 and a black matrix 82, and a backlight device (not shown) installed on the back surface of the liquid crystal panel. The backlight device may be an edge light system in which the light emitted from the light source arranged on the side of the light guide plate is internally reflected in the light guide plate and guided to the liquid crystal panel side, or directly under the liquid crystal panel. A direct type system in which a plurality of light sources are evenly arranged may be used. As the edge light type light source, for example, a cold cathode tube or a light emitting diode (LED) that emits incoherent light can be used. As the direct type light source, for example, a light emitting diode can be used. However, the display device is not limited to the liquid crystal display device, and may be, for example, an organic EL display or a quantum dot (QD) display.

Further, as shown in FIG. 3, the surface to be measured 2 may be an exit surface of the backlight device 14. In the example shown in FIG. 3, the backlight device 14 includes a light source 141, a light guide plate 142 that guides light emitted from the light source 141, a reflector 143 laminated on the back surface of the light guide plate 142, and a light guide plate. It is composed of a diffuser plate 144 laminated on the front surface of 142. The surface to be measured 2 is the surface of the diffuser plate 144. In the example shown in FIG. 14, the backlight device is of the edge light type, but the optical measuring device 1 may measure the speckle contrast or the sparkle contrast of the direct type backlight device.

Further, as shown in FIG. 4, the surface to be measured 2 may be an exit surface of the screen 15. In the example shown in FIG. 4, the screen 15 is a device that transmits and displays the coherent light projected from the projector 16 as an image. When measuring such projection light, speckle is generated but sparkle is not generated. The object of measuring the sparkle contrast is limited to a direct-view type display having an antiglare layer as described above.

As a specific configuration for measuring the speckle contrast or sparkle contrast of the various measured surfaces 2 as described above, as shown in FIGS. 1 to 4, the optical measuring device 1 includes the optical system 3 and specifications. It includes a two-dimensional sensor array 4, which is an example of an image sensor that captures an image of light L emitted from a surface 2 to be measured having contrast or sparkle contrast, a determination unit 5, and a measurement unit 6. Hereinafter, the constituent parts of these optical measuring devices 1 will be described in detail.

(Optical system 3)
The optical system 3 has a lens 31 and an aperture 32 provided with an aperture 321.

The optical system 3 refracts the light L emitted from the surface 2 to be measured with speckle contrast or sparkle contrast to form an image on the two-dimensional sensor array surface 41 of the two-dimensional sensor array 4.

In the example shown in FIG. 1, the optical system 3 has one lens 31, but the optical system 3 may have a plurality of lenses. In this case, the plurality of lenses may have a combination of powers suitable for reducing the aberration of the emitted light L. Further, the optical system 3 may include an optical filter 33. Specifically, it is a Y filter, an XYZ filter, an RGB filter, a linear polarizing filter, a circular polarizing filter, an ND filter, or the like. For example, FIG. 1 shows an example in which the optical filter 33 is arranged between the aperture 32 and the lens 31, but the number and positions of the optical filters 33 are not limited to the example in FIG. The aperture 32 may be configured such that the size of the aperture 321 can be changed by an actuator or the like so that the F number of the optical system 3, that is, the lens 31 can be adjusted.

(Two-dimensional sensor array 4)
The two-dimensional sensor array 4 has a two-dimensional sensor array surface 41 on which the emitted light L from the surface to be measured 2 is imaged, and captures an image of the emitted light L.

The two-dimensional sensor array 4 has a plurality of pixels 42 adjacent to each other, and the surface of the pixels 42 constitutes the two-dimensional sensor array surface 41. The emitted light L received by the pixel 42 is converted into an electric signal by photoelectric conversion, and the converted electric signal is used for calculating speckle contrast or sparkle contrast.

The two-dimensional sensor array 4 is an image sensor having a solid-state image sensor, and may be, for example, a CCD (Charge Coupled Device) sensor or a CMOS sensor.

(Judgment unit 5)
As shown in equation (2), speckle contrast and sparkle contrast are expressed as the ratio of the standard deviation of radiance to average radiance. In the measurement of speckle contrast or sparkle contrast, in order to define the region where the speckle contrast or sparkle contrast is to be measured, a part of the pixel area, that is, a part of the pixel group of the total pixels 42 of the two-dimensional sensor array 4 is used. The speckle contrast or sparkle contrast may be calculated using the measurement result of the radiation brightness of. The pixel area used for measuring such speckle contrast or sparkle contrast can also be called a measurement field.

However, if the number of pixels in the pixel region used for measuring speckle contrast or sparkle contrast, that is, the number of samples, is insufficient, even if the average brightness in the measurement field is uniform, the statistical number of samples is insufficient. There may be some variation in the standard deviation itself. Further, the average radiance of the image in this pixel region may be different from the average radiance of the image in other pixel regions. That is, there is a local fluctuation in the average radiance in the image of the emitted light L captured by the two-dimensional sensor array 4.

When such local fluctuations in average radiant brightness occur, if the positions of the pixel areas used for measuring speckle contrast or sparkle contrast are different, the effect of fluctuations in average radiated brightness is affected by the standard deviation in equation (2). In addition, the local average emission brightness is also different, and as a result, the measurement results of speckle contrast or sparkle contrast are also different. As described above, as the measurement condition of the speckle contrast or the sparkle contrast, when the number of pixels in the pixel area used for the measurement is insufficient or when the local average radiation brightness fluctuates, the speckle contrast or the sparkle contrast is measured. Measurement errors can occur.

Since the measurement results of speckle contrast and sparkle contrast including such measurement errors are inaccurate, it is effective to set or correct the measurement conditions so that the measurement errors do not occur in order to obtain accurate measurement results. Is. For that purpose, it is effective to appropriately evaluate whether or not the current measurement conditions do not cause measurement error.

Therefore, based on the viewpoint of whether or not a measurement error is caused, the determination unit 5 determines the suitability of the measurement conditions for speckle contrast or sparkle contrast using the image captured by the two-dimensional sensor array 4.

Specifically, the determination unit 5 has a pixel corresponding to the first image captured in the first pixel region of the two-dimensional sensor array 4 and the second image captured in the second pixel region of the two-dimensional sensor array 4. Based on the standard deviation of the difference between the radiances of each other, the suitability of the measurement conditions of speckle contrast or sparkle contrast is determined. Corresponding pixels are, for example, positionally corresponding pixels, that is, pixels arranged at the same relative positions in the first pixel region and the second pixel region. The position of the second pixel region is at least partially different from that of the first pixel region, and the number of pixels is the same. Hereinafter, the standard deviation of the difference in radiance between the corresponding pixels of the first image and the second image is also referred to as a difference standard deviation.

The difference standard deviation is a value indicating the variation in the difference in radiation brightness between the corresponding pixels of the first image and the second image, but in calculating the difference standard deviation, each of the first image and the second image is used. If the radiation brightness data of the pixels can be regarded as completely independent as a set, the difference standard does not go through the process of individually calculating the difference in radiation brightness between the corresponding pixels of the first image and the second image. The deviation can be calculated easily.

数式（３）において、σ_ｓｕｂは、差分標準偏差であり、σ_１は、第１画像の放射輝度の標準偏差であり、σ_２は、第２画像の放射輝度の標準偏差である。 Specifically, the difference standard deviation can be calculated as the square root of the sum of squares of the standard deviation of the radiance of the first image and the standard deviation of the radiance of the second image, as shown in the following equation.

In equation (3), σ _sub is the difference standard deviation, σ ₁ is the standard deviation of the radiance of the first image, and σ ₂ is the standard deviation of the radiance of the second image.

In particular, the average radiance is the same between the first image and the second image, σ ₁ and σ ₂ are the same, the number of pixels in the first pixel region and the second pixel region is sufficiently large, and there is a statistical error. If it does not occur, the difference standard deviation can be expressed by the following equation.

However, the mathematical formula (4) is established when the speckle patterns or sparkle patterns of the first image and the second image are statistically random and independent. In order for the speckle patterns or sparkle patterns of the first and second images to be statistically random and independent, the corresponding pixels in the first pixel region and the second pixel region are at least in the following equation. 3 times the average size R of the indicated speckle or sparkle: 3R apart.

数式（５）において、Ｒは、スペックルまたはスパークルの平均サイズであり、Ｆ＃_{ｉｍａｇｅ}は、光学系３の像側の実効Ｆナンバーであり、λは、出射光Ｌの波長である。

In formula (5), R is the average size of speckle or sparkle, F # _image is the effective F number on the image side of the optical system 3, and λ is the wavelength of the emitted light L.

When the difference standard deviation satisfies the equation (4), the determination unit 5 determines that the number of pixels in the first pixel region and the second pixel region is speckle contrast or sparkle contrast as a measurement condition of speckle contrast or sparkle contrast. It is determined that the number of pixels used for the measurement of is appropriate.

Here, even if the average radiance differs between the first image and the second image at the beginning of imaging, the determination unit 5 corrects the radiance for each pixel of the first image and the second image. , The average radiance of the first image and the second image can be adjusted ex post facto. This is based on the premise that the ratio of the local standard deviation to the average value of the radiance is constant in the speckle pattern or the sparkle pattern. That is, when the average brightness fluctuates locally, the standard deviation also fluctuates locally at the same rate, but the uniform standard deviation and average brightness distribution that should be originally can be obtained by correction. ..

Therefore, in equation (4), σ ₁ is the standard deviation of the corrected radiance of the first image corrected so that the average radiance of the first image and the average radiance of the second image are aligned. σ ₂ may be the standard deviation of the corrected radiance of the second image corrected so that the average radiance of the first image and the average radiance of the second image are aligned. That is, in the formula (4), σ _sub is the standard deviation of the difference between the corresponding pixels of the radiance of each pixel of the corrected first image and the radiance of each pixel of the corrected second image. There may be.

When the radiance of the corrected first image and the radiance of the corrected second image are used, if the number of pixels in the first pixel region and the second pixel region, that is, the number of samples is sufficient, the mathematical formula (4) Is established.

As a specific example of determining the measurement conditions of speckle contrast or sparkle contrast based on the difference standard deviation of the equation (4), the determination unit 5 determines the ratio of the difference standard deviation σ _{sub to the standard deviation σ 1 of the radiation brightness of the first image.} The suitability of the measurement conditions may be determined based on σ _sub / σ _1. In this case, when the ratio σ _sub / σ ₁ ^{is 2 1/2} , which is an example of a predetermined value, the determination unit 3 determines that the first pixel region and the second pixel region when ^{2 1/2 is obtained.} It is determined that the number of pixels is appropriate as the number of pixels used for measuring speckle contrast or sparkle contrast as a measurement condition. The fact that the ratio σ _sub / σ ₁ is 2 ^1/2 is equivalent to the difference standard deviation σ _sub satisfying the equation (4). However, in order to determine that the number of pixels is appropriate, the ratio σ _sub / σ ₁ does not necessarily exactly match ^{2 1/2} , and has a slight margin of error with respect to ^{2 1/2.} May be. That is, the determination unit 3 may determine that the number of pixels is appropriate when it is determined that _{the ratio σ sub} / σ _{1 is} approximately 2 ^1/2.

_{In addition to σ sub} / σ ₁ , the determination unit 5 determines the suitability of the measurement conditions based on the ratio σ _sub / σ ₂ of the difference standard deviation σ _{sub to the standard deviation σ 2} of the radiance of the second image. You may. Alternatively, the determination unit 3 sets the ratio of the difference standard deviation σ _sub to the average value σ _{ave of the standard deviation σ 1} of the radiation brightness of the first image _{and the standard deviation σ 2} of the radiation brightness of the second image _{σ sub} / σ _ave . The suitability of the measurement conditions may be determined based on the above. Even in these cases, the determination unit 3 determines the first pixel region and the second pixel region when 2 ^1/2 _{is obtained when the ratios σ sub} / σ ₂ and σ _sub / σ _ave are 2 ^1/2. It can be determined that the number of pixels in the pixel region is appropriate as the number of pixels used for measuring speckle contrast or sparkle contrast.

The determination unit 5 outputs the determination result of the measurement conditions of the speckle contrast or the sparkle contrast to the measurement unit 6. The determination unit 5 may display the determination result on the display. The determination unit 5 is composed of hardware such as a CPU and memory, that is, a computer. A part of the determination unit 5 may be configured by software.

The determination unit 5 may perform calibration before the start of measurement of speckle contrast or sparkle contrast, that is, adjustment of measurement conditions, based on the determination result. In this case, when the determination result is negative, the determination unit 5 corrects the measurement conditions according to a predetermined correction amount until a positive determination result is obtained, and determines the suitability of the corrected measurement conditions. do it. Specifically, when the determination unit 5 determines that the number of pixels is not appropriate, the determination unit 5 increases the number of pixels in the first pixel region and the second pixel region by a predetermined increase amount until the number of pixels becomes appropriate, and pixels. The suitability of the number of pixels may be re-determined using the difference standard deviation based on the first and second images captured in the first and second pixel regions after the number is increased.

(Measuring unit 6)
The measuring unit 6 measures the speckle contrast or the sparkle contrast according to the measurement conditions determined to be appropriate by the determination unit 5. Specifically, the measuring unit 6 calculates the average radiance of the image captured in the pixel region of the number of pixels determined by the determination unit 5 and the standard deviation of the radiance, and the calculated average radiance is calculated. The speckle contrast or sparkle contrast is calculated by substituting the standard deviation of the radiance and the radiance into the equation (2). The measuring unit 6 outputs the calculated speckle contrast or sparkle contrast. The measuring unit 6 outputs the calculated speckle contrast or sparkle contrast. The output destination of the calculated speckle contrast or sparkle contrast may be a memory for storing the calculation result or a display for displaying the calculation result. The calculation unit 6 is composed of hardware such as a CPU and memory, that is, a computer. A part of the calculation unit 6 may be configured by software.

(Operation example)
Next, an operation example of the optical measuring device 1 according to the first embodiment will be described. FIG. 5 is a flowchart showing an operation example of the optical measuring device 1 according to the first embodiment.

First, as shown in FIG. 5, the two-dimensional sensor array 4 images the measured surface 2 by forming an image of the light L emitted from the measured surface 2 on the two-dimensional sensor array surface 41 via the optical system 3. (Step S1).

FIG. 6 is a diagram showing a process of acquiring a first image and a second image in an operation example of the optical measuring device 1 according to the first embodiment. After imaging the surface to be measured 2, the determination unit 5 selects a first pixel region and a second pixel region having a preset number of pixels from the two-dimensional sensor array surface 41, and images are taken in the first pixel region. The first image and the second image captured in the second pixel region are acquired (step S2). For example, as shown in FIG. 6, the first pixel region PA1 and the second pixel region PA2 are rectangular regions having a predetermined number of pixels in the X direction and a predetermined number of pixels in the Y direction. The corresponding pixels in the first pixel area and the second pixel area are displaced by three times or more the average size R of the speckle or sparkle shown in the mathematical formula (5). For example, as shown in FIG. 6, one pixel P1 (x1, y1) in the first pixel region PA1 and one in the second pixel region PA2 positionally corresponding to the pixel P1 (x1, y1). Pixel P2 (x1 + Δx, y1 + Δy) is displaced by 3 times or more the average size R of speckle or sparkle. As a result, the speckle pattern or the sparkle pattern is statistically random and independent of the first image captured in the first pixel region and the second image captured in the second pixel region. It should be noted that the positions of the corresponding pixels of the first pixel area and the second pixel area need be more than three times as large as the average size R of speckle or sparkle, and the entire first pixel area and second pixel area are present. May partially overlap. Further, the first pixel area and the second pixel area may be set according to the input of the user, or may be automatically set according to the program.

After acquiring the first image and the second image, as shown in FIG. 5, the determination unit 5 determines the radiance of the first image so that the average radiance of the first image and the average radiance of the second image are aligned. And the radiance of the second image are corrected (step S3). The radiance correction is performed according to, for example, the international standard IEC62906-5-4.

を乗じる。ただし、

は、規定の放射輝度平均値であり、Ｉ_ＸＹは、要素（Ｘ，Ｙ）内の局所的な平均輝度である。全ての要素マトリクス毎に上記パラメータを適用することで、全マトリクスの平均放射輝度を

に揃えることができ、かつ各マトリクス内における平均放射輝度と標準偏差との関係をオリジナルのデータと同じに保つことができる。 Specifically, in the correction of radiance, as shown in FIG. 16, the measurement field is divided into a matrix. Then, the following parameters are added to the radiance data of all the pixels in the element (X, Y).

Multiply. However,

Is the specified radiance average value, and _IXY is the local average brightness within the element (X, Y). By applying the above parameters to all element matrices, the average radiance of all matrices can be obtained.

And the relationship between the average radiance and the standard deviation in each matrix can be kept the same as the original data.

After correcting the radiance of the first image and the radiance of the second image, as shown in FIG. 5, the determination unit 5 determines the radiance of the corrected first image and the radiance of the corrected second image. Based on this, the ratio σ _sub / σ ₁ of the difference standard deviation σ _{sub to the standard deviation σ 1} of the radiance of the first image is calculated (step S4).

After calculating the ratio sigma _sub / sigma ₁ difference standard deviation sigma _sub to the standard deviation sigma ₁ radiance of the first image, the determining unit 5, the calculated ratio sigma _sub / sigma ₁ is approximately ^{2 1/2,} For example, it is determined whether or not it is 1.40 or more and 1.43 or less (step S5).

When the ratio σ _sub / σ _{1 is} approximately 2 ^1/2 (step S5: Yes), the determination unit 5 determines that the number of pixels is appropriate (step S6). In this case, the measuring unit 6 sets the number of pixels determined to be appropriate as a measurement condition, and uses the pixel region of the set number of pixels for measuring the speckle contrast or the sparkle contrast.

On the other hand, when the ratio σ _sub / σ ₁ is not approximately 2 ^1/2 (step S5: No), the determination unit 5 determines that the number of pixels is inappropriate (step S6). In this case, the determination unit 5 may change the number of pixels in the first pixel region and the second pixel region, and repeat the determination using the first pixel region and the second pixel region of the changed number of pixels.

The number of pixels in which the ratio σ _sub / σ ₁ becomes approximately 2 ^1/2 is not limited to a specific number of pixels, and may have a certain extent. For example, when the number of pixels is X × Y: 100 × 100 pixels or 150 × 150 pixels, the ratio σ _sub / σ ₁ converges to about 2 ^1/2 for the first time, and thereafter, the ratio σ _{sub as the number of pixels increases.} The state in which / σ ₁ has converged to approximately 2 ^{1/2 may continue.} In this case, when the number of pixels is 100 × 100 pixels or 150 × 150 pixels, even if the ratio σ _sub / σ ₁ becomes approximately 2 ^1/2 _{, the ratio σ sub} / σ corresponds to a slight decrease in the number of pixels. ₁ is an unstable state that can greatly deviate from ^{2 1/2.} _{Therefore, even if the ratio σ sub} / σ ₁ becomes approximately 2 ^1/2 when the number of pixels is 100 × 100 pixels or 150 × 150 pixels, it can be considered that the number of pixels is still insufficient, that is, inappropriate. .. Therefore, when it is desired to obtain a highly reliable determination result that the number of pixels is appropriate, the determination unit 5 sequentially increases the number of pixels in the first pixel region and the second pixel region by a predetermined increase amount. Each time, the determination of whether or not _{σ sub} / σ ₁ acquired based on the images of the first pixel region and the second pixel region where the number of pixels is increased becomes approximately 2 ^{1/2 is repeated.} When a positive determination result is continuously obtained a predetermined number of times, the number of pixels at that time may be determined to be an appropriate number of pixels. In other words, even if the determination unit 5 determines that the maximum number of pixels in a predetermined number of pixels is the appropriate number of pixels when the state in which _{σ sub} / σ ₁ becomes approximately 2 ^{1/2 is continuous for a predetermined number of pixels.} good. _{As an example, in the determination unit 5, even if the ratio σ sub} / σ ₁ becomes approximately 2 ^1/2 when the number of pixels is 100 × 100 pixels or 150 × 150 pixels, the number of pixels is appropriate at that time. However, it may be determined that ^{200 × 200 pixels are appropriate when the state of approximately 2 1/2} is continuous until the time of 200 × 200 pixels.

(Experimental example)
Next, as an experimental example of the optical measuring device 1 of FIG. 1, a measurement example of the speckle contrast using diffused coherent light and the ratio of the difference standard deviation to the standard deviation of the radiance of the first image will be described. FIG. 7 is a diagram showing a measurement system using coherent light whose diffusion state is changed with time.

The measurement system of FIG. 7 includes an SHG (Second Harmonic Generation) laser 17 that emits a laser beam having a wavelength of 533 nm as coherent light, a rotating diffuser 18, a screen 20, and an imaging camera 10.

The rotary diffuser 18 diffuses the laser light emitted from the SHG laser 17 to reduce coherence. The laser light diffused by the rotating diffuser 18 as spot light having a diameter of about 1 cm is emitted onto the screen 20 1.2 m away from the rotating diffuser 18. The screen 20 diffuses and reflects the diffused light emitted from the rotating diffuser 18 toward the image pickup camera 10. The diffused light that is diffusely reflected is received by the image pickup camera 10 and the speckle contrast is measured. As the screen 20, a diffuse reflection target manufactured by Lovesphere Co., Ltd .: SRT-99-050 was used. The imaging camera 10 has a focal length of 50 mm when an object is taken at infinity, a lens with an effective F number on the image side variable from 2.1 to 33.3, and a cooled CCD with a pixel pitch of 9 μm. An imaging camera equipped with and was used. Further, as shown in FIG. 7, the screen 20 is arranged so that the incident angle of the laser beam is 30 °. The distance from the screen 20 to the imaging camera 10 was fixed at 0.62 m.

In such a measurement system, 2.1, 8.7, 17.4, and 33.3 are sequentially set as the effective F-number F # _image of the lens, and under each effective F-number, the first pixel region and the first pixel region and the third are set. The speckle contrast and the change in the ratio σ _sub / σ ₁ with respect to the change in the number of pixels in the two-pixel region were measured.

The first pixel region and the second pixel region are set so that the corresponding pixels are separated from each other by 30 pixels, that is, 270 μm on the sensor surface. As shown in FIG. 6, under some conditions, the first pixel region and the second pixel region are set to partially overlap. By setting the first pixel region and the second pixel region to such an extent that they partially overlap in this way, it is possible to make it easier to make the average brightness of the first image and the second image uniform. Further, according to the international standard IEC62906-5-4, the brightness distribution of the low spatial frequency of the first image and the second image was corrected so that the average brightness of the first image and the second image would be the same. The number of pixels in the first pixel region and the second pixel region was changed from 10 × 10 pixels to 200 × 200 pixels.

The measurement results of the above measurement system are shown in FIGS. 8 to 11. FIG. 8 is a diagram showing _{speckle contrast and ratio σ sub} / σ ₁ measured by the measurement system of FIG. 7 when the effective F number of the lens is 2.1. FIG. 9 is a diagram showing _{speckle contrast and ratio σ sub} / σ ₁ measured by the measurement system of FIG. 7 when the effective F number of the lens is 8.7. FIG. 10 is a diagram showing _{speckle contrast and ratio σ sub} / σ ₁ measured by the measurement system of FIG. 7 when the effective F number of the lens is 17.4. FIG. 11 is a diagram showing _{speckle contrast and ratio σ sub} / σ ₁ measured by the measurement system of FIG. 7 when the effective F number of the lens is 33.3.

As shown in FIGS. 8 to 11, in any effective F number, the ratio σ _sub / σ ₁ ^{is 2 1/2 as the} number of pixels increases when the number of pixels exceeds approximately 100 × 100 pixels. Convergence started toward, and it was confirmed that it was stable at ^{about 2 1/2 at 200 × 200 pixels.} According to this result, it can be considered that 200 × 200 pixels is appropriate as the number of pixels used for the measurement of speckle contrast. In other words, it can be considered that the speckle contrast Cs measured at the time of 200 × 200 pixels is an appropriate measurement result.

As described above, according to the first embodiment, it is possible to appropriately determine the suitability of the measurement conditions for speckle contrast or sparkle contrast based on _{the difference standard deviation σ sub.} Also, based on whether the ratio sigma _{sub /} sigma ₁ difference standard deviation sigma _sub to the standard deviation sigma ₁ radiance of the first image is ^21/2, conveniently the appropriateness of the number of pixels as a measurement condition And it can be judged appropriately. Further, the radiance of the first image and the second image is corrected so that the average radiance of the first image and the average radiance of the second image are aligned, and the radiance of the corrected first image and the corrected first image are corrected. By using the difference standard deviation acquired based on the radiance of the two images, the suitability of the number of pixels can be determined more appropriately.

(Second Embodiment)
So far, the radiance of the first image and the second image has been corrected so that the average radiance of the first image and the average radiance of the second image are the same, and the radiance of the corrected first image and the second image has been corrected. An example of determining the suitability of the number of pixels as a measurement condition using the difference standard deviation acquired based on the brightness has been described. On the other hand, in the second embodiment, the determination unit 5 does not assume the correction of the radiation brightness of the first image and the second image, but is based on the radiation brightness of the first image and the second image at the time of imaging. Based on the acquired difference standard deviation, the suitability of the in-plane distribution of the local average radiation brightness as a measurement condition of speckle contrast or sparkle contrast is determined. However, in the second embodiment, the number of pixels in the first pixel region and the second pixel region is the radiation of the first image when the average radiance of the first image and the average radiance of the second image are the same. It is a known number of pixels such that the ratio of the difference standard deviation σ _sub to the standard deviation σ _{1 of the radiance σ sub} / σ ₁ ^{is 2 1/2} as a predetermined value.

_{That is, in the second embodiment, the number of pixels such that the ratio σ sub} / σ ₁ becomes 2 ^1/2 when there is no fluctuation in the average radiance is acquired in advance, and the image is taken with that number of pixels. The presence or absence of fluctuations in radiance at low spatial frequencies is determined based on whether or not _{the ratio σ sub} / σ ₁ calculated based on the image is actually 2 ^1/2.

Specifically, when the ratio σ _sub / σ ₁ of the difference standard deviation σ _{sub to the standard deviation σ 1} of the radiance of the first image is different from 2 ^1/2 , the determination unit 5 sets the ^{2 1/2} . The average radiance of the first image and the average radiance of the second image when different ratios σ _sub / σ ₁ are obtained are used as the average radiance of the image used to measure the speckle contrast or sparkle contrast as the measurement conditions. Judge as inappropriate.

The determination unit 5, the difference standard deviation to the standard deviation sigma ₂ radiance of the second image in place of the ratio sigma _{sub /} sigma ₁ difference standard deviation sigma _sub to the standard deviation sigma ₁ radiance of the first image sigma _sub ratio sigma _sub / sigma ₂ or the ratio of the difference standard deviation sigma _sub to the average value sigma _ave of the standard deviation sigma ₁ and standard deviation sigma ₂ radiance of the second image of the radiance of the first image sigma _sub / sigma The suitability of the average radiation brightness may be determined based on the _ave.

(Operation example)
Next, an operation example of the optical measuring device 1 according to the second embodiment will be described. FIG. 12 is a flowchart showing an operation example of the optical measuring device 1 according to the second embodiment.

First, as shown in FIG. 12, the two-dimensional sensor array 4 images the measured surface 2 by forming an image of the light L emitted from the measured surface 2 on the two-dimensional sensor array surface 41 via the optical system 3. (Step S11).

_{After imaging the surface to be measured 2, the determination unit 5 reduces the} ratio σ sub / σ ₁ to approximately 2 ^1/2 when the average radiation brightness of the first image and the second image is the same from the two-dimensional sensor array surface 41. A first pixel region and a second pixel region having a known number of pixels are selected, and a first image captured in the first pixel region and a second image captured in the second pixel region are acquired. (Step S12). As in the first embodiment, the corresponding pixels in the first pixel region and the second pixel region are separated from each other by three times or more the average size R of speckle or sparkle.

After acquiring the first image and the second image, the determining unit 5, based on the radiance of the radiation intensity and the second image of the first image, the difference standard deviation sigma for standard deviation sigma ₁ radiance of the first image _{The sub} ratio σ _sub / σ ₁ is calculated (step S13).

After calculating the ratio sigma _sub / sigma ₁ difference standard deviation sigma _sub to the standard deviation sigma ₁ radiance of the first image, the determining unit 5, the calculated ratio sigma _sub / sigma ₁ is approximately ^{2 1/2,} For example, it is determined whether or not it is 1.40 or more and 1.43 or less (step S14).

When the ratio σ _sub / σ _{1 is} approximately 2 ^1/2 (step S14: Yes), the determination unit 5 determines that the average radiance is appropriate (step S15). In this case, the measuring unit 6 measures the speckle contrast or the sparkle contrast using the first image or the second image determined to have an appropriate average radiance.

On the other hand, when the ratio σ _sub / σ ₁ is not approximately 2 ^1/2 (step S14: No), the determination unit 5 determines that the average radiance is inappropriate (step S16). In this case, the determination unit 5 corrects the radiance of the first image and the second image so that the average radiance of the first image and the second image are the same, and the corrected radiance of the first image and the second image. The determination may be repeated using _{the ratio σ sub} / σ ₁ acquired based on the brightness.

(Experimental example)
Next, as an experimental example of the optical measuring device 1 according to the second embodiment, a measurement example of the speckle contrast and the ratio of the difference standard deviation to the standard deviation of the radiance of the first image using the same measurement system as in FIG. Will be described.

This measurement example differs from the measurement example of FIG. 7 in that the brightness of the first image and the brightness of the second image are not corrected so that the average brightness of the first image and the average brightness of the second image are the same. .. Other measurement conditions are the same as those in the measurement example of FIG.

The measurement result of this measurement example is shown in FIG. FIG. 13 is a diagram showing the measurement results of _{the speckle contrast and the ratio σ sub} / σ ₁ when the effective F number of the lens is 17.4.

In the example shown in FIG. 13, when the average brightness of the first image and the average brightness of the second image are the same, the known number of pixels such that the _{ratio σ sub} / σ ₁ is approximately 2 ^{1/2 is obtained.} It is assumed that the number of pixels is 200 × 200. However, in the 200 × 200 pixels shown in FIG. 13, the ratio σ _sub / σ ₁ is significantly different from ^{2 1/2.} From this, if the brightness of the first image and the brightness of the second image are not corrected so that the average brightness of the first image and the average brightness of the second image are the same, even if the number of pixels is sufficient. It was confirmed that the ratio σ _sub / σ ₁ did ^{not become 2 1/2.}

As described above, also in the second embodiment, the suitability of the speckle contrast or sparkle contrast measurement conditions can be appropriately determined based on _{the difference standard deviation σ sub.} Also, based on whether the ratio sigma _{sub /} sigma ₁ difference standard deviation sigma _sub to the standard deviation sigma ₁ radiance of the first image is ^21/2, local average radiance as measurement conditions It is possible to easily and appropriately determine the suitability of the distribution of.

(Third Embodiment)
So far, an example in which the suitability of the measurement conditions of speckle contrast or sparkle contrast is determined in advance based on the difference standard deviation σ _{sub has been described.} On the other hand, in the third embodiment, the determination unit 5 subsequently determines the suitability of the speckle contrast or sparkle contrast measurement conditions based on the speckle contrast or sparkle contrast measurement results.

数式（１）において、Ｃ_Ｓ−Ｅは、測定されたスペックルコントラストまたはスパークルコントラストの値である。Ｃ_Ｓ−Ｃは、画素領域の画素数および光学系のＦナンバーと数式（１）の値との既知の対応関係において数式（１）の値を０（％）にする既知のスペックルコントラストまたはスパークルコントラストである。 Specifically, the determination unit 5 has the value of the following mathematical formula (1) expressed by speckle contrast or sparkle contrast measured based on an image captured in a predetermined pixel region of the two-dimensional sensor array 4. , The pixel area when the speckle contrast or sparkle contrast is measured when the number of pixels in the pixel area and the F number of the optical system are within the permissible range shown in the known correspondence between the value of the equation (1). It is determined that the number of pixels and the F number of the optical system 3 are appropriate as measurement conditions for speckle contrast or sparkle contrast.

In formula (1), _CSE is the measured speckle contrast or sparkle contrast value. C _S-C is known speckle contrast to formula 0 (%) values of (1) in a known relationship between the F-number and the value of Equation (1) of the number of pixels and the optical system of the pixel area or Sparkle contrast.

The known correspondence between the number of pixels and the F number of the optical system and the value of the formula (1) is that the horizontal axis is the number of pixels in the pixel area and the value of the formula (1) is on the vertical axis. The F number and the number of pixels are within the permissible range surrounded by the two curves that are line-symmetrical with respect to It may be a relationship in which a plurality of appropriate values of different mathematical formulas (1) are accommodated accordingly. By setting the area surrounded by two curves and having a specific number of pixels or more as appropriate, it is possible to narrow down the data to have less statistical error. Further, the determination unit 5 may store such a correspondence relationship in advance for determination.

(Operation example)
Next, an operation example of the optical measuring device 1 according to the third embodiment will be described. FIG. 14 is a flowchart showing an operation example of the optical measuring device 1 according to the third embodiment.

First, as shown in FIG. 14, the two-dimensional sensor array 4 images the measured surface 2 by forming an image of the light L emitted from the measured surface 2 on the two-dimensional sensor array surface 41 via the optical system 3. (Step S21).

After imaging the surface to be measured 2, the determination unit 5 selects a pixel region having a predetermined number of pixels from the two-dimensional sensor array surface 41, and acquires an image captured in the selected pixel region (step S22).

After the image has been acquired, the measurement unit 6 calculates the speckle contrast C _S-E based on the radiance of the acquired image (step S23).

After speckle contrast C _S-E has been calculated, the determination unit 5 calculates the value of Equation (1) based on the calculated speckle contrast C _S-E and the known C _S-C (step S24).

After calculating the value of the formula (1), the determination unit 5 determines that the calculated value of the formula (1) is a known correspondence between the number of pixels in the pixel area and the F number of the optical system and the value of the formula (1). It is determined whether or not it falls within the permissible range shown in the relationship (step S25).

When the calculated value of the mathematical formula (1) is within the permissible range (step S25: Yes), the determination unit 5 determines the number of pixels in the pixel region and the optical system 3 when the _{speckle contrast CSE is measured.} It is determined that the F number is appropriate as a measurement condition for speckle contrast (step S26).

On the other hand, when the calculated value of the mathematical formula (1) does not fall within the permissible range (step S25: No), the determination unit 5 determines the number of pixels in the pixel region and the optics when the _{speckle contrast CSE is measured.} It is determined that the F number of the system 3 is inappropriate as a measurement condition for speckle contrast (step S27).

(Experimental example)
Next, as an experimental example of the optical measuring device 1 according to the third embodiment, measurement of the number of pixels in the pixel region and the correspondence between the F number of the optical system and the mathematical formula (1) using the same measuring system as in FIG. An example will be described.

In the present measurement example, the speckle contrast C _S-E based on the luminance of the first image and the speckle contrast C _S-E based on the luminance of the second image, with different conditions of number of pixels and the F-number calculated plurality of ways, based on the respective speckle contrast C _S-E of plural kinds which are calculated, to calculate a plurality as a value of equation (1).

The calculation result of the value of the mathematical formula (1) in this measurement example is shown in FIG. Figure 15, plots the values of the calculated equation (1) based on the speckle contrast C _S-E is the number of pixels on the horizontal axis, and the vertical axis is the dot on the value and the coordinate system of the formula (1) Has been done. In the footnote of FIG. 15, the F number and the type of image corresponding to the plotted dots are described. For example, the dots with "# 2.1-1" indicate the value of the mathematical formula (1) based on the first image when the effective F number is 2.1. The dots with "# 3.0-2" indicate the value of the mathematical formula (1) based on the second image when the effective F number is 3.0.

As shown in FIG. 15, the correspondence between the number of pixels and the F number of the optical system and the mathematical formula (1) is two curves that converge toward the vertical axis 0 (%) as the number of pixels increases (FIG. 15). It can be seen that the relationship is such that a plurality of appropriate values of the mathematical formula (1), which differ depending on the F number and the number of pixels, fall within the permissible range surrounded by the broken line portion). The determination unit 5 can determine the suitability of the number of pixels and the F number by using such a correspondence relationship.

As described above, according to the third embodiment, it is possible to appropriately determine the suitability of the measurement conditions of the speckle contrast or the sparkle contrast based on the measurement result of the speckle contrast or the sparkle contrast.

It should be noted that the plurality of embodiments described above can be applied in combination thereof as appropriate.

The aspects of the present disclosure are not limited to the individual embodiments described above, but also include various modifications that can be conceived by those skilled in the art, and the effects of the present disclosure are not limited to the contents described above. That is, various additions, changes and partial deletions are possible without departing from the conceptual idea and purpose of the present disclosure derived from the contents defined in the claims and their equivalents.

1 Optical measuring device 7 Measured surface 4 Two-dimensional sensor array 5 Judgment unit

Claims (19)

An image sensor that captures an image of the light emitted from the surface under test with speckle contrast or sparkle contrast,
Based on the standard deviation of the difference in radiance between the corresponding pixels of the first image captured in the first pixel region of the image sensor and the second image captured in the second pixel region of the image sensor, the said An optical measuring device including a determination unit for determining the suitability of measurement conditions for speckle contrast or sparkle contrast. The optical measuring apparatus according to claim 1, wherein the second pixel region is at least partially different in position from the first pixel region and has the same number of pixels. The optical measuring device according to claim 1 or 2, wherein the determination unit determines the suitability of the measurement conditions based on the ratio of the standard deviation of the difference to the standard deviation of the radiance of the first image. The optical measuring device according to claim 1 or 2, wherein the determination unit determines the suitability of the measurement conditions based on the ratio of the standard deviation of the difference to the standard deviation of the radiance of the second image. The determination unit determines the suitability of the measurement conditions based on the ratio of the standard deviation of the difference to the average value of the standard deviation of the radiance of the first image and the standard deviation of the radiance of the second image. , The optical measuring apparatus according to claim 1 or 2. The difference in radiance between the corresponding pixels of the first image and the second image is corrected so that the average value of the radiance of the first image and the average value of the radiance of the second image are aligned. The optical measuring apparatus according to any one of claims 1 to 5, which is the difference between the radiance of the corrected first image and the radiance of the corrected second image. The optical according to any one of claims 1 to 6, wherein the standard deviation of the difference is the square root of the sum of squares of the standard deviation of the radiance of the first image and the standard deviation of the radiance of the second image. measuring device. The difference in radiance between the corresponding pixels of the first image and the second image is corrected so that the average value of the radiance of the first image and the average value of the radiance of the second image are aligned. It is the difference between the radiance of the corrected first image and the radiance of the corrected second image.
The determination unit obtained the predetermined value when the ratio of the standard deviation of the difference based on the radiation brightness of the corrected first image and the radiation brightness of the corrected second image was a predetermined value. According to claims 3 to 5, it is determined that the number of pixels in the first pixel region and the second pixel region is appropriate as the number of pixels used for measuring the speckle contrast or sparkle contrast as the measurement condition. The optical measuring device described. The optical measuring device according to claim 8, wherein the predetermined value of the ratio of the standard deviations of the differences is 2 ^1/2. The number of pixels in the first pixel region and the second pixel region is the standard deviation of the difference when the average value of the radiance of the first image and the average value of the radiance of the second image are the same. It is a known number of pixels that makes the ratio a predetermined value,
When the ratio of the standard deviation of the difference is different from the predetermined value, the determination unit determines the average value of the radiation brightness of the first image when the ratio of the standard deviation of the difference different from the predetermined value is obtained and the said. The optical according to claims 3 to 5, wherein it is determined that the average value of the radiation brightness of the second image is not appropriate as the average value of the radiation brightness of the image used for measuring the speckle contrast or the sparkle contrast as the measurement condition. measuring device. The invention according to any one of claims 1 to 10, wherein the corresponding pixels of the first pixel region and the second pixel region are separated by at least three times or more the average size of the speckle pattern or the sparkle pattern. Optical measuring device. The optical measuring device according to any one of claims 1 to 11, wherein the surface to be measured is an exit surface of the antiglare layer in a display device having an antiglare layer. The optical measuring device according to any one of claims 1 to 11, wherein the surface to be measured is a pixel matrix surface in the display device. The optical measuring device according to any one of claims 1 to 11, wherein the surface to be measured is an exit surface of the backlight device. The optical measuring device according to any one of claims 1 to 11, wherein the surface to be measured is an exit surface of a screen that projects light emitted from a projector. The optical measuring apparatus according to any one of claims 1 to 15, further comprising a measuring unit for measuring speckle contrast or sparkle contrast according to measurement conditions determined to be appropriate. An optical system that forms an image of the light emitted from the surface to be measured with speckle contrast or sparkle contrast,
An image sensor in which the emitted light is imaged and an image of the emitted light is captured.
A determination unit for determining the suitability of the speckle contrast or sparkle contrast measurement conditions is provided.
In the determination unit, the value of the following formula (1) expressed by speckle contrast or sparkle contrast measured based on the image captured in the predetermined pixel region of the image sensor is the number of pixels in the pixel region and the value of the following formula (1). When the F number of the optical system and the value of the mathematical formula (1) fall within the permissible range shown in the known correspondence, the number of pixels in the pixel region and the optical An optical measuring device for determining that the F number of the system is appropriate as a measurement condition for the speckle contrast or the sparkle contrast.

However, C _S-E is the measured value of the speckle contrast or sparkle contrast, C _S-C is known speckle contrast value to 0 (%) of Equation (1) in the correspondence relation Or sparkle contrast. The correspondence is two curves line-symmetrical with respect to the horizontal axis when the number of pixels in the pixel area is taken on the horizontal axis and the value of the mathematical formula (1) is taken on the vertical axis. Within the permissible range surrounded by two curves that converge toward 0 (%) on the vertical axis as the number of pixels increases, a plurality of appropriate values of the mathematical formula (1) that differ depending on the F number and the number of pixels are contained. The optical measuring device according to claim 17, which is related to the above. An image of the light emitted from the surface to be measured with speckle contrast or sparkle contrast is captured by an image sensor.
Based on the standard deviation of the difference in radiant brightness between the corresponding pixels of the first image captured in the first pixel region of the image sensor and the second image captured in the second pixel region of the image sensor, the said An optical measurement method that determines the suitability of speckle contrast or sparkle contrast measurement conditions.

Images