JP6225519B2 - Measuring apparatus and measuring method - Google Patents

Description

  The present invention relates to a measurement apparatus and a measurement method suitable for measuring a spectroscopic spectrum, and more particularly to a measurement apparatus and a measurement method based on the configuration of a plenoptic camera.

Conventionally, a color luminance meter is already known as a device for measuring the luminance and chromaticity of light emitted from an object.
For example, it is a so-called XYZ camera using an optical bandpass filter corresponding to a color matching function defined in the XYZ color system by the International Commission on Illumination (CIE).
Human retina cells have sensory tissues corresponding to R (red), G (green), and B (blue) for reflected light from an object, and transmit signals corresponding to the strength to the brain. The color of the object is perceived by the ratio of each signal.
The sensitivity of the sensory tissue corresponding to R, G, and B has a characteristic as shown in FIG. 15, and this characteristic is called a color matching function.

The integral values X, Y, and Z of the spectral distribution of light reflected from the object and entering the human eye multiplied by the color matching function are called tristimulus values. A color is felt by this amount of stimulation.
The object color is perceived as red when the X stimulus amount is large, as green when the Y stimulus amount is large, and as blue when the Z stimulus amount is large.

In this type of apparatus for measuring luminance and chromaticity, a phenomenon occurs in which the amount of light in the peripheral area of the image sensor becomes smaller than the center due to a decrease in the amount of light around the camera lens.
For this reason, there was a problem that high-precision measurement could not be performed in the entire measurement region.
In order to solve this problem, Patent Document 1 discloses that a scanning optical unit having a scanning lens and a rotating mirror scans a measurement region to be measured by dividing it into a plurality of regions, and takes in from each position of the measurement target. A color luminance measuring device that makes the amount of light uniform is disclosed.
Since the solid angle captured by the scanning lens of the scanning optical unit is substantially constant regardless of the scanning position of the measurement object, the unevenness in the amount of light can be made uniform.

However, in the configuration described in Patent Document 1, since the scanning timing in the divided areas changes with time, it is not possible to simultaneously measure the spectral data of the two-dimensional surface.
Since measurement environment conditions such as the intensity of light from the light source change every moment, simultaneous measurement is desirable to obtain highly accurate measurement data.
Further, when the measurement object moves, accurate measurement data cannot be obtained by the above-described divided scanning method.
Furthermore, since the movable part (rotating mirror) is indispensable in the above-described divided scanning method, there is a concern that the scanning accuracy may be lowered due to deterioration of the movable part over time.
The above problem also applies to the measurement of the spectrum.

  The present invention was devised in view of such a current situation, and provides a measuring apparatus capable of simultaneously and accurately measuring spectral data (spectral spectrum) of a two-dimensional surface with a configuration having no movable part. Its main purpose.

In order to achieve the above object, the present invention provides an optical system, light receiving means for converting optical information collected by the optical system into an electrical signal, and a spectral transmittance that is disposed near the stop of the optical system. A plurality of optical bandpass filters, a lens array disposed between the optical system and the light receiving means, and a plurality of lenses arranged substantially parallel to a two-dimensional plane direction of the light receiving means, and the electric signal and a correcting means for correcting each light receiving position of the light receiving means, said optical bandpass filter, Ri color filter der corresponding to spectrum, it said correction means criteria become values obtained from the color sample When, characterized that you corrected by multiple regression analysis using the value calculated from an output value of the measuring device.

The present invention also provides an optical system, light receiving means for converting optical information collected by the optical system into an electrical signal, and a plurality of optical bands having different spectral transmittances disposed near the stop of the optical system. A color filter corresponding to a spectral spectrum, a lens array disposed between the optical system and the light receiving means, and a plurality of lenses arranged substantially parallel to a two-dimensional plane direction of the light receiving means; A measurement method using an apparatus comprising: a step of acquiring imaging data by the light receiving means; a reference value acquired from a color sample; and a value calculated from an output value of the apparatus. And a step of correcting the imaging data for each light receiving position of the light receiving means by multiple regression analysis .

  According to the present invention, the correction is performed using the reference value and the value calculated from the output value from the measuring apparatus, so that the spectral spectrum of the two-dimensional surface of the object can be accurately measured.

It is a figure which shows the structure of the color filter of the measuring apparatus which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows the spectral transmittance of a color filter. It is a schematic block diagram which shows an example of a measuring device, (a) is a front view, (b) is a side view. It is a schematic block diagram which shows an example of a measurement system, (a) is a front view, (b) is a side view. It is a schematic diagram for demonstrating the principle of the measuring apparatus which concerns on the 1st Embodiment of this invention. It is a characteristic view which shows the spectral transmittance of each color filter in case the incident angle of the light ray in a color measurement Example is 0 degree | times. It is a figure which shows the geometrical design example of the color filter in a color measurement Example. It is a characteristic view which shows the incident angle dependence of the spectral transmittance of the color filter in a color measurement Example. It is the figure which looked at the lens array from the optical axis direction. It is a top view of the image image | photographed with the structure of FIG. FIG. 10 is an enlarged view of macro pixels constituting the image of FIG. 9. It is a figure which shows the example of the color checker as a color sample. It is a plot figure to xy chromaticity diagram of 24 colors of a color checker. It is a flowchart which shows the processing flow of correction | amendment calculation. FIG. 5 is a characteristic diagram of color matching functions of an XYZ color system defined by CIE.

Embodiments of the present invention will be described below with reference to the drawings.
First, before describing the embodiment of the present invention, an example in which a color is a measurement object will be described.
FIG. 5 is a diagram for explaining the principle of the measuring apparatus according to the present embodiment, and also serves as a diagram for explaining the principle of the measuring apparatus according to the embodiment of the present invention.
Here, for easy understanding, the main lens 24 as an optical system is shown as a single lens, and the aperture position S of the main lens 24 is the center of the single lens.

A color filter 26 as an optical bandpass filter is disposed at the center of the main lens 24.
The color filter 26 is a filter corresponding to a tristimulus value of a color having a spectral transmittance based on the color matching function of the XYZ color system.
That is, the color filter 26 includes a plurality (three in this case) of color filters 26a, 26b, and 26c having different spectral transmittances based on the color matching functions of the XYZ color system.

  “A plurality of optical bandpass filters having different spectral transmittances” is a concept for both a case where a plurality of filters having different spectral transmittances are combined and a case where different spectral transmittances are provided for each region on one filter. including.

Actually, the color filter is not located in the lens.
The color filter 26 is disposed near the stop of the main lens 24. “Near the aperture” means a portion including the aperture position through which light rays with various angles of view can pass.
In other words, it means a design allowable range of the color filter 26 with respect to the main lens 24.

FIG. 6 shows the spectral transmittance of each color filter when the incident angle of the light beam is 0 degree.
The solid line, the broken line, and the dotted line in FIG. 6 are the spectral transmittances T _X (λ) and T _{Y of} the color filters 26 a (F _X ), 26 b (F _Y ), and 26 c (F _Z ) based on the following color matching functions, respectively. (Λ), T _Z (λ).

An example of the geometric design of the color filter is shown in FIG.
In FIG. 7, the color filter 26 is roughly divided into three in a fan shape, but it is of course not limited to this, and the whole may not be circular or may be divided into rectangles.
Also, the area ratio of each filter need not be equally divided.
As is apparent from FIGS. 6 and 15, the area surrounded by the color matching function line for Z is smaller than the others. The size of this area correlates with the magnitude of the signal to noise ratio (S / N ratio).
From the viewpoint of increasing the S / N ratio, the area of the color filter 26c corresponding to Z may be made larger than the others.

Next, the design of T _X (λ), T _Y (λ), and T _Z (λ) will be described.
Each spectral transmittance in FIG. 6 is obtained from the color matching function defined in the CIE-1931 color system, the spectral transmittance T _L (λ) of the optical system excluding the lens filter, and the spectral sensitivity S (λ) of the light receiving element. Designed.
That is, it can be written as:

In the formulas (1), (2), and (3), the sensor itself has spectral sensitivity, and is divided by S (λ) to eliminate the non-uniformity.
In Expressions (1), (2), and (3), T _X (λ), T _Y (λ), and T _Z (λ) are obtained by standardizing each maximum value as the transmittance of 100%.
By standardizing, the SN ratio can be improved particularly for color filters corresponding to x (λ) and y (λ).
When a color filter designed in this way is used, when a light beam that has passed through the color filter is detected by a light receiving element, the normalization based on the maximum value is simply calculated backward, and the output value is directly converted to X, Y, Z (three (Stimulus value).

Although T _X (λ), T _Y (λ), and T _Z (λ) are complex waveforms, they can be produced with values close to design values.
As a manufacturing method, a dielectric multilayer film can be used. The multilayer film functions as a bandpass filter by optical interference.
Since the spectral transmittance of the color filter realizes a bandpass function by interference action, it has a dependency on the incident angle of light in principle.
FIG. 8 shows an example of the incident angle dependency in the color filter 26a (F _X ).
A solid line, a broken line, and a dotted line are spectral transmittances of incident angles of 0 degrees, 20 degrees, and 30 degrees, respectively. It can be seen that the transmission band shifts to the short wavelength side as the incident angle increases.

As shown in FIG. 5, an MLA 3 as a lens array composed of a plurality of microlenses (small lenses) is disposed near the condensing position of the main lens 24.
On the image surface 6, a light receiving element array is disposed as a light receiving means for converting light information collected by the main lens 24 into electronic information (electrical signal).
The light receiving element array includes a plurality of light receiving elements (sensors). In the following, reference numeral 6 is expressed as a light receiving element array.
The diameter of the micro lens of the MLA 3 and each light receiving element constituting the light receiving element array 6 are in a relation of approximately 30: 1 to 2: 1.

FIG. 9 shows the MLA 3 viewed from the optical axis direction.
In FIG. 9, white circles indicate portions of the respective lenses, and black portions indicate light shielding portions (light shielding means).
That is, light is shielded by the light shielding means except for the lens portion constituting the lens array. The light shielding means in the present embodiment is a vapor deposition of chromium oxide.
The light shielding portion is a flat portion having no curvature or a region where the curvature does not satisfy the design value specification in terms of manufacturing.
Since the light from these regions may cause a light beam not intended in the design to reach the light receiving element, the electrical signal assumed from the design can be obtained by shielding the light. This is important for obtaining accurate measurements.

The light receiving element array 6 is a monochrome sensor in which a color filter for each pixel is not mounted. Hereinafter, the light receiving element array is also referred to as a “monochrome sensor”.
Of the light emitted from the object 1, the light beam that enters the aperture of the main lens 24 and passes through the stop is the object of measurement.
The light beam incident on the main lens is a collection of innumerable light beams, and each light beam passes through different positions of the stop of the main lens.
In this embodiment, since the three color filters 26a, 26b, and 26c are arranged at the aperture position of the main lens, each light beam passes through three filters having different spectral transmittances.
At this time, the angle of the light ray incident on the filter surface varies depending on the object height. This can also be seen from the fact that the principal rays of the light beams emitted from the points on the object represented by P and Q in FIG. 5 pass through the diaphragm surface of the main lens at different angles.

The light rays that have passed through the color filter 26 once form an image in the vicinity of the MLA 3, and then reach different positions of the sensor by the MLA 3.
That is, since the position of the sensor surface (light receiving position) corresponds to the filter surface through which the light beam has passed, the value obtained by decomposing light emitted from a certain point of the object into tristimulus values X, Y, and Z in terms of wavelength is measured. Can do.
However, as described with reference to FIG. 8, the spectral transmittance of the color filter has an incident angle dependency. Therefore, if the output of the light receiving element is simply used, two-dimensional including the off-axis is sufficient even if it is on the optical axis. It is not possible to measure the exact tristimulus values X, Y, Z of the surface.

Therefore, in the present embodiment, correction is made for each light receiving position using a reference value and a value calculated from an output value from the measuring apparatus so as to obtain an accurate tristimulus value on a two-dimensional surface. This is a technique generally called multiple regression analysis.
In the multiple regression analysis, explanatory variables and objective variables are prepared in advance, and a correction operation is performed using a regression matrix obtained from them.
The procedure is specifically described below.
First, the procedure for calculating the output value from the measuring apparatus will be described. This corresponds to an explanatory variable in the multiple regression analysis.

The image photographed with the configuration of FIG. 5 is an array of small circles as shown in FIG.
The reason for forming a circle is that the aperture shape of the single lens (main lens) is a circle. Here, each small circle is called a “macro pixel”.
Each macro pixel is formed directly under each small lens constituting the lens array. The internal structure of the macro pixel corresponds to the structure of the color filter shown in FIG.
An enlarged view of the macro pixel is shown in FIG.
Compared to FIG. 7, the top, bottom, left, and right are inverted because they have passed through the optical system. However, since this correspondence depends on the optical system, it is not limited to this example.

The internal structures M _X , M _Y , and M _Z of the macro pixels are the results of arrival of light that has passed through the color filters F _X , F _Y , and F _Z , respectively.
_Assume that the output values of the light receiving elements M _X , M _Y , and M _Z are v = [v _X , v _Y , v _Z ] ^t . t means transposition of the matrix.
How to take the output _value, M _X, may take the average value of _{M Y, M Z, M X} , M Y, then select one light receiving element from the _{M Z} be adopted output value as a representative value Good.

Next, a method for obtaining a reference value will be described. This corresponds to the objective variable in the multiple regression analysis.
A color sample covering a wide range in the color space is measured by a device such as a spectroscope that measures X, Y, and Z values, and these are used as reference values.
As the color swatch, for example, a widely used 24-color rectangular color swatch called a “color checker” can be used.
An example of a color checker is shown in FIG.
FIG. 13 shows the results of plotting the measured values of 24 colors included in the color checker on the xy chromaticity diagram.

The color sample is not limited to the color checker, and if the object to be measured is known, a better correction result can be obtained by using a value close to that color as a reference value.
A reference value of X, Y, Z (tristimulus values) for a color sample is assumed to be r = [r _X , r _Y , r _Z ] ^t .

Next, the flow of correction calculation will be described.
First, a color sample is measured with a measuring instrument to obtain a reference value. When a 24 color checker is used for the color swatch, a number is given for convenience, and a reference value for the _first color is r ₁ = [r _1X r _1Y r _1Z ] ^t .
That is, values from r _{1 to} r ₂₄ are obtained. Let R = [r ₁ ,..., R ₂₄ ]. R is a 3 × 24 matrix. This R is an objective variable.

Next, a color sample is photographed with the measuring apparatus shown in FIG. 5 to obtain imaging data.
At this time, it is arranged so that one color sample appears in the entire image. Get v from each macro pixel.
Similarly to the reference value, V = [v1,..., V24] is obtained. This V becomes an explanatory variable.
A matrix G is obtained from R and V obtained so far.
G = RV ^t (VV ^t ) ⁻¹ (4)

This G is called a regression matrix and is used for correction calculation.
Since V has a different value for each macro pixel, G is also calculated for each macro pixel.
The above is preparation for correction calculation.

The flow of actual measurement will be described.
An object to be measured is imaged with this measuring apparatus. An output value is calculated for each macro pixel included in the captured image.
This is defined as v _C = [v _CX , v _CY , v _CZ ] ^t . Next, a tristimulus value r _C corrected by the following equation is obtained.
r _C = Gv _C (5)
By obtaining r _C for each macro pixel, an accurate tristimulus value of the two-dimensional surface can be obtained.

In the above flow, V or v _C using the output value as it is is used, but it can be extended as follows.
_{v = [v X, v Y} , v Z 1 v X 2 v Y 2 v Z 2 ···] t (6)
... refers to the higher-order terms, such as _v X _{v Y} and _v ^{X 3.}
By performing such expansion, the accuracy of correction may be increased and a more accurate value may be obtained. When the regression matrix G is obtained with the expanded V, the expanded v _C must be used even in the measurement using the equation (5).

  FIG. 14 shows the flow of processing. With this measurement method, the color of the two-dimensional surface can be simultaneously and accurately measured with a simple apparatus.

A first embodiment of the present invention will be described with reference to FIGS.
In the present embodiment, the output of the measuring device is a spectral spectrum. Spectral spectra can also be converted into color quantitative values.
In the above example, the measurement target is a color, but in this embodiment, a spectral spectrum that can be said to be the true color is taken as the measurement target.
The difference in configuration from the above embodiment is the configuration of the color filter 26. An example of the color filter 26 of this embodiment is shown in FIG.
The color filter 26 includes six types of optical bandpass filters. An example of the spectral sensitivity of each filter is shown in FIG.

The color filter 26 has transmittance in six different wavelength regions. Similar to the color filter 26 of the above example, the bandpass filter of this embodiment also has an incident angle dependency. Therefore, correction for each position of the light receiving element is necessary.
The correction procedure is the same as in the above embodiment. However, since the output of the present embodiment is not a tristimulus value of X, Y, and Z but a spectral spectrum, a color sample or the like is measured by a measuring instrument that can measure the spectral value of the reference value.

For example, the standard value for a color sample can be written as:
r = [r400 r410... r690 r700] (7)
r400 is a value of a spectral spectrum for light having a wavelength of 400 nm.
The value corresponding to the explanatory variable in the above embodiment is
v = [v _{# 1} v _{# 2} v _{# 3} v _{# 4} v _{# 5} v _{# 6} ] (8)
It becomes.

Similar to the above embodiment, the regression matrix G is obtained from R and V for each macro pixel, and correction calculation is performed using the regression matrix G, thereby making it possible to accurately measure the spectral spectrum of the two-dimensional surface.
The accuracy can be improved by using higher-order terms for V and v _C as in the above embodiment.
In the present embodiment, the number of bands is set to 6, but of course not limited to this.
In general, it is said that various waveforms can be measured with high accuracy by using six or more appropriate bands.
The number of bands may be increased to increase the accuracy, and the color to be measured is limited. When the frequency of the waveform is low, an accurate waveform can be measured with a smaller number of bands.

  The shape of the filter is not limited to a fan shape. Further, the overall shape of the filter may not be circular, and may be divided into rectangles. The proportion need not be equally divided.

FIG. 3 shows a specific configuration of the measuring apparatus of the present embodiment.
The measurement apparatus 10 includes an imaging unit 12 that acquires spectral information from an object, and an FPGA (Field-Programmable Gate) as a spectral image generation unit that generates a plurality of types of spectral images based on the spectral information acquired by the imaging unit 12. Array) 14.
The FPGA 14 also functions as a correction unit that performs the above correction calculation for measuring the color.
The imaging unit 12 includes a lens module 18 and a camera unit 20, and the FPGA 14 is built in the camera unit 20.
The lens module 18 includes a lens barrel 22, a main lens 24 provided in the lens barrel 22, a color filter 26, and a lens 28.

The camera unit 20 includes an MLA 3, a monochrome sensor 6, and an FPGA 14 therein.
The MLA 3 has a configuration in which a plurality of microlenses are arranged in a direction orthogonal to the optical axis of the main lens 24.
In other words, the MLA 3 is disposed substantially parallel to the two-dimensional plane direction of the light receiving element array 6.

A plurality of LEDs 30 as light sources are provided at the distal end portion of the lens barrel 22 in an embedded state at equal intervals in the circumferential direction. By using the LED 30 as a light source, stable spectral information can be acquired regardless of the shooting environment conditions.
As the correcting means, an ASIC (Application Specific Integrated Circuit) may be used instead of the FPGA 14.
A part or all of the correction means may be separated from the measurement apparatus main body and electrically connected as necessary.

FIG. 4 shows the measurement system.
The measurement system 32 includes the measurement apparatus 10 and a PC (personal computer) 34 as a determination unit that performs determination based on data obtained by the measurement apparatus 10.
The PC 34 includes a central processing unit (CPU), a storage device, and the like (not shown), and performs the above correction calculation processing by software executed by the CPU.
That is, the PC 34 also serves as the correction means.
For example, the PC 34 determines whether or not the color to be measured is the same as the comparison color, and displays the result on the display.

Next, a second embodiment will be described.
The present embodiment is characterized in that the correction calculation is corrected using a device model (design model).
The output of the measuring device is a value obtained by quantifying the color.
First, a flow in which light emitted from a measurement object passes through an optical system and becomes an output value of a macro pixel is formulated. The above flow can be written as follows.

In the present embodiment, m = 6. l is the sampling number (for example, 30) in the wavelength direction of the spectral spectrum to be obtained.
If H = St, Equation (9) can be summarized in the form of a linear system as shown below.
g = Hr + n (10)
H is called a system matrix.
The spectral spectrum r of the object is obtained from the band output value g. When m <l as in the present embodiment, there are an infinite number of solutions that satisfy Equation (10), and they are not uniquely determined.
Such a problem is generally called a defect setting problem. One of the solutions that is often selected for the defect setting problem is the minimum norm solution. When noise can be ignored in Equation (10), the minimum norm solution is expressed by the following equation.

The minimum norm solution obtained by Expression (11) is the continuous spectral reflectance.
The fact that the system matrix differs for each macro pixel is apparent from the difference in the incident angle dependency of the filter.
Therefore, H is calculated for each macro pixel. At that time, the incident angle of the light beam corresponding to the macro pixel is calculated, and the spectral transmittance of the filter at the incident angle is used.
By doing so, it is possible to accurately perform the estimation by the equation (11).
However, the difference in the system matrix for each macro pixel does not depend only on the incident angle dependence of the spectral transmittance of the color filter. In fact, the manufacturing error of the small lenses that make up the lens array and the amount of light around the main lens A decline is also included.
For this reason, the multiple regression analysis method of the first embodiment can be expected to have a higher correction effect.

3 MLA as a lens array
6 Light receiving element array as light receiving means 14 FPGA as correcting means
24 Main lens as optical system 26 Color filter as optical bandpass filter 34 PC as correction means and discrimination means

JP 2010-271246 A

Claims (7)

Optical system,
A light receiving means for converting optical information collected by the optical system into an electrical signal;
A plurality of optical bandpass filters disposed near the stop of the optical system and having different spectral transmittances;
A lens array arranged between the optical system and the light receiving means, and a plurality of lenses arranged substantially parallel to a two-dimensional plane direction of the light receiving means;
Correction means for correcting the electrical signal for each light receiving position of the light receiving means;
With
The optical bandpass filter, Ri color filter der corresponding to spectrum,
Wherein the correction means includes a value that is a acquired reference from a swatch, the Measurement device you and correcting by multiple regression analysis using the value calculated from the output value of the device. The measuring apparatus according to claim 1,
The number of said optical band pass filters is six or more, The measuring apparatus characterized by the above-mentioned. The measuring apparatus according to claim 1 or 2,
The optical bandpass filter, measuring device characterized that you have formed a dielectric multilayer film. In the measuring device according to any one of claims 1 to 3 ,
The measuring apparatus is characterized in that light is shielded by light shielding means except for the lens portion of the lens array . The measuring apparatus according to claim 4, wherein
The measuring device characterized in that the light shielding means is a vapor-deposited chromium oxide . In the measuring apparatus as described in any one of Claims 1-5,
A measuring apparatus, wherein a part or all of the correcting means is separated from a measuring apparatus main body . Optical system,
A light receiving means for converting optical information collected by the optical system into an electrical signal;
A plurality of optical bandpass filters disposed near the aperture of the optical system and having different spectral transmittances, a color filter corresponding to a spectral spectrum;
A lens array arranged between the optical system and the light receiving means, and a plurality of lenses arranged substantially parallel to a two-dimensional plane direction of the light receiving means;
A measuring method using an apparatus comprising:
Acquiring imaging data by the light receiving means;
Correcting the imaging data for each light receiving position of the light receiving means by multiple regression analysis using a reference value acquired from a color sample and a value calculated from the output value of the device;
Measuring method .

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