System and method for measuring the color of an area of ​​a sample

Abstract

A system and method for measuring the color of an area of ​​a sample. The system includes: a light source; a first optical arrangement for scanning the area of ​​the sample portion by portion; a second optical arrangement including a second optical device and optical elements for collecting light scattered from the sample; a spectrometer for receiving the collected scattered light and measuring the light spectrum of each of the portions; and a computing device. The system is configured to synchronize the scanning of the area with the recording of the light spectra for multiple portions of the area. The second optical device is configured to change and dynamically orient the propagation direction of the redirected scattered light in synchronization with the first optical device. The computing device determines color coordinates, calculates and analyzes the overall light spectrum, and calculates XYZ tristimulus values.

Description

[Technical Field]

[0001] The present invention is directed generally to measuring color, and more particularly to a system and method for measuring the color of an area of ​​a sample.

[0002] Some of the most demanding color measurement use cases require systems and methods that can provide accurate color measurements at high speed and low cost. Some of the more demanding use cases further require measuring the color of an object from a remote location, along with the ability to do so in conjunction with other parallel processes, such as processes occurring on a factory production line. Most of the prior art available in the field of color measurement fails to meet some of these requirements because it involves systems and methods that require complex and expensive equipment or special conditions, such as little or no ambient lighting and / or placing the sample in or in contact with a special case and / or touching the sample with a color measurement device, to achieve accurate and rapid measurements, which are incompatible with the circumstances under which the color measurements must be performed. Similarly, accurately determining the color of a sample often requires performing accurate multi-angle measurements on the sample, which are difficult to do from a remote location and in situations where the sample is subject to strong environmental illumination.

[0003] Patent Document 1 describes a multi-angle colorimeter including a light projecting / receiving optical system, a spectral block, a control unit, and a case, and also describes that the color of a sample can be measured, the observed color of which changes depending on the colorimetric observation direction at each of a plurality of light receiving angles. However, Patent Document 1 also describes that a pressing portion of the case is pressed against the sample when measuring the color.

[0004] Patent document 2 similarly describes a multi-angle colorimeter for measuring an object, the colorimeter including an illumination system, a torus-shaped mirror, a light detection system, a controller / calculator, and a housing having a measurement opening, the measurement opening facing the surface of the object and having an outer periphery for defining a predetermined measurement area on the surface of the object.

[0005] From the foregoing, it can be seen that there is a need for a method and system capable of simultaneously providing multiple angle measurements for accurately measuring the color of a sample from a distance. Furthermore, there is a need for a method and system that ensures or aims to achieve such accurate color measurements, particularly during such multiple angle measurements, without the need to reposition the illumination source and / or spectrometer during measurements or without the need to use multiple illumination sources and / or spectrometers. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 0180480 [Patent Document 2] U.S. Patent Application Publication No. 2006 / 0109474 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a system and method for measuring color, where color is measured remotely, in-line, at-line, or offline, in real time, and the measurement is not affected by ambient lighting. The system and method are non-invasive, and the sample under study remains undamaged and unchanged after analysis (e.g., there is no need to cut out a piece of the sample to measure its color). The present invention is particularly suitable for measuring the color of a variety of materials, such as textiles, polymers, organic materials, plastics, glass, metals, wood, ceramics, and pigments (natural or synthetic) for painting or staining. The present invention enables advanced color measurement in or near existing production lines or other complex setups. The present invention provides a system that is easily scalable and robust, and can have a compact form factor for versatility and portability. The present invention does not require the use of extremely expensive equipment. The present invention enables measurement of areas of various sizes and shapes. The present invention enables color mapping with high resolution. Most importantly, the present invention allows for multi-angle color measurements to be made without the need to reposition the illumination source and / or spectrometer during the measurement, and without the need to use multiple illumination sources and / or spectrometers. [Means for solving the problem]

[0008] To this end, an embodiment of the present invention discloses a system for measuring the color of an area of ​​a sample, the system comprising: a light source configured to emit light for illuminating a sample; a first optical arrangement configured to receive the light and output and direct a collimated beam of the light toward a surface of the sample located at a given distance, the first optical arrangement comprising a first optical device configured to scan an area of ​​the sample portion-by-portion by changing the direction of the collimated beam and dynamically orienting it relative to the sample; a second optical arrangement configured to collect light scattered from the sample as the sample is illuminated with the collimated beam; a spectrometer configured to receive the collected scattered light (i.e., the scattered light collected by the second optical arrangement) and record an optical spectrum of the collected scattered light portion-by-portion; and a computing device operatively connected to the spectrometer. "Part-by-part" may be line-by-line, point-by-point, or spot-by-spot. Preferably, the area is scanned by illuminating a plurality of lines across the area, i.e. the area is scanned line by line. The scattered light received by the spectrometer may be or may include backscattered light, i.e. light that is backscattered from the sample when the collimated beam illuminates the sample.

[0009] The second optical apparatus includes a second optical device and an optical element, the second optical device configured to receive light scattered by the sample at an observation angle α relative to a direction of a specular reflection component reflected from the sample when the collimated beam is incident on the surface of the sample, and the second optical device further configured to redirect the received scattered light toward the optical element.

[0010] Furthermore, the second optical device is configured to synchronize with the first optical device to dynamically orient and change the propagation direction of the redirected scattered light so that the propagation direction of the redirected scattered light remains constant (i.e., the same) relative to the optical element while scanning the area of ​​the sample.

[0011] In the system proposed herein, the light emitted by the light source comprises a spectrum of simultaneously emitted wavelengths, the spectrum continuously covering a band of wavelengths in the visible range from at least a first wavelength to a second wavelength. Furthermore, the light emitted by the light source is spatially coherent for all wavelengths in the band from at least the first wavelength to the second wavelength. The spectrum is most preferably broad, e.g., a spectrum wider than 10 nm, 50 nm, or 100 nm.

[0012] The system is further configured to synchronize the scanning of the area with the recording of the optical spectrum for the portions of the area by the spectrometer as the first optical device scans the area, and similarly, the system is configured such that the recording of the optical spectrum for each portion lasts for an optical spectrum integration time equal to the duration of the scanning of the portion by the first optical device.

[0013] The first optical device for outputting the collimated beam is configured to maintain the spatially coherent light collimated if or when the spatially coherent light is collimated, and / or the optical device further comprises a collimator for performing collimation of the spatially coherent light, preferably located at a certain distance from an end of the light source.

[0014] Thus, the spatially coherent light emitted by the light source may or may not be collimated upon exiting the light source. Similarly, the light may or may not be collimated before being received by the first optical device. The first optical device can maintain the collimation of the light by including optical elements that do not destroy the collimation. Similarly, the first optical device may include a collimator, as described above, to cause or improve the collimation of the light. Similarly, the system may optionally include a collimator between the light source and the first optical device to collimate the light from the light source toward the first optical device.

[0015] Therefore, an option is conceivable in which the first optical device comprises a collimator, e.g. a collimating lens or a collimating mirror, located at a distance (corresponding to the focal length of the collimator) from the end of the light source in order to convert the spatially coherent light into a collimated beam.

[0016] The computing device is configured to calculate an overall light spectrum from a statistical calculation over all or a portion of the light spectrum corresponding to all or a portion of the scanned portion of the area, and to determine color coordinates of the area of ​​the sample in a given color space by analyzing the overall light spectrum, wherein the analysis includes calculating XYZ tristimulus values ​​corresponding to the overall light spectrum. It will be clearly understood that calculating the overall light spectrum involves performing the statistical calculation, i.e., calculating the overall light spectrum includes or is performed by performing the statistical calculation.

[0017] The overall light spectrum may optionally be a statistical mean, median or mode, among other statistical figures of merit, of all or some of the light spectra corresponding to all or some of the scanned portions of the area. Preferably, the overall light spectrum is an average light spectrum calculated over all of the light spectra corresponding to all of the scanned portions of the area.

[0018] In a preferred embodiment, the propagation direction of the redirected scattered light is parallel to the main optical axis of the optical element, and preferably the optical element is an off-axis parabolic mirror, so that the system advantageously benefits from an optical design that is simple to implement yet performs well.

[0019] In a preferred embodiment, the observation angle α is about 45°, and the first optical device is further configured to dynamically change and orient the direction of the collimated beam about a central direction perpendicular to the surface of the sample while scanning the area of ​​the sample portion by portion. Thus, the system can optionally provide CIE 0 / 45 (i.e., 0° / 45°) color measurement, which is required for standardization purposes in many industrial applications.

[0020] In a preferred embodiment, the first optical device and the second optical device each comprise a galvanometer (galvanometric, galvo) mirror. The use of galvanometer mirrors, particularly those that are commercially available, advantageously simplifies the optical design of the overall system. Optionally and preferably, the second optical device further comprises an optical fiber optically coupled to the spectrometer. The use of an optical fiber to optically couple (i.e., connect) the spectrometer to the second optical device advantageously contributes to minimizing the form factor of the system and / or making the system portable. Furthermore, in a preferred embodiment, the optical element is configured to receive the scattered light redirected by the optical element and further redirect the scattered light towards the input of any of the optical fibers.

[0021] In a preferred embodiment, the optical element of the system is an off-axis parabolic mirror having a through hole, and the system further includes a laser configured to emit laser light through the hole toward the second optical device. The second optical device can then further redirect the laser light toward the surface of the sample. The position of the laser light and the position of the collimated beam illuminating the sample can be used to perform optical alignment of the first optical device and the second optical device before performing the color measurement. The optical alignment can function to coincide the laser light and the collimated beam on the surface of the sample to ensure that the second optical device properly redirects the scattered light parallel to the optical axis of the off-axis parabolic mirror. This advantageously optimizes the collection of scattered light by the second optical device.

[0022] Optionally and preferably, the spatially coherent light source is or comprises a supercontinuum light source. The light source, e.g., the optional supercontinuum light source, optionally comprises a nonlinear optical fiber or an optical fiber configured to be excited by light and emit a supercontinuum. Advantageously, this option further makes it possible to obtain a compact, robust and portable system.

[0023] In one embodiment, the first wavelength is in the range of 370 nm to 460 nm, and the second wavelength is in the range of 620 nm to 780 nm. In one particular embodiment, the first wavelength is 430 nm. In another particular embodiment, the second wavelength is 750 nm. In another particular embodiment, the first wavelength is 400 nm. In another particular embodiment, the second wavelength is 780 nm. In yet another particular embodiment, the first wavelength is 380 nm, and the second wavelength is 750 nm. Optionally, controlling the first wavelength and the second wavelength can improve measurement accuracy and / or allow the system to adapt depending on the expected color of the sample.

[0024] In some embodiments, the collimated beam has a maximum full-angle divergence of 0.46° or less for all wavelengths from the first wavelength to the second wavelength. Optionally, but preferably, the maximum full-angle divergence is between 0.01° and 0.20° for all wavelengths from the first wavelength to the second wavelength. This option can allow control over beam directionality and diameter, and can contribute to accurate measurements of samples at various distances from the system.

[0025] In one embodiment, the first optical device comprises a collimator, preferably a collimating lens, and at a distance from the collimator (which distance corresponds to the focal length of the collimator), the diameter of the cross section of the collimated beam is equal to or smaller than 5 mm, in particular smaller than 2.15 mm, for all wavelengths from the first wavelength to the second wavelength, and the diameter is equal to or smaller than 1 / e 2 This option can contribute to achieving a high spatial resolution and a good signal-to-noise ratio during the measurement.

[0026] In some embodiments, the diameter of the cross section of the collimated beam is 10 mm or less at any distance within 1 m from a point on the first optical device for all wavelengths from the first wavelength to the second wavelength, and / or the diameter is 100 mm or less at any distance within 10 m from the point on the first optical device, and the diameter is 1 / e 2 The point is considered in width. When the first optical device comprises the collimator, the point is preferably at the position of the collimator. Optionally, the point is also at the position of an optical exit from the first optical device, the optical exit being an optical port, aperture, material, or void from which the light beam exits the first optical device.

[0027] Similarly, optionally, the point is at the location of the first optical device configured to change the direction of light for dynamic orientation. These options can contribute to improved measurement of the sample with good resolution and at various distances when the sample is receiving a lot of other light from the environment.

[0028] In one embodiment, the beam quality factor M of the collimated beam is 2 is in the range of 1.0 to 2.0 for all wavelengths from the first wavelength to the second wavelength. 2 is less than 1.4. This option can help control and optimize the illumination of the sample by the system.

[0029] In one embodiment, the intensity of the collimated beam, which is comprised of all wavelengths from the first wavelength to the second wavelength, is 1 mW / cm at any distance of 1 m or less from a point on the first optical device. 2 and optionally or additionally, the luminance is 0.01 mW / cm at any distance within 10 m of the point on the first optical device. 2 or more, wherein the point is preferably at the position of the collimator when the first optical device includes the collimator. In a specific embodiment, the luminance is 136 mW / cm at a distance of 1 m from the collimating lens. 2 and 2.8 mW / cm at a distance of 10 m from the collimating lens. 2 These options can contribute to optimizing the accuracy of the measurement.

[0030] An embodiment of the present invention also discloses a method for measuring the color of an area of ​​a sample, the method comprising the steps of: emitting light using a light source to illuminate a sample located at a given distance, the light comprising a spectrum of simultaneously emitted wavelengths, the spectrum continuously covering a band of wavelengths in the visible range from at least a first wavelength to a second wavelength, the light being spatially coherent at least at all wavelengths from the first wavelength to the second wavelength; receiving the spatially coherent light at a first optical device located at a distance from an end of the light source; maintaining the collimated spatially coherent light in the first optical device if the spatially coherent light is collimated and / or collimating the spatially coherent light using a collimator; and transmitting the collimated beam of spatially coherent light from the first optical device to a desired location. the step of outputting and directing the collimated beam towards the surface of the sample located at a given distance; the step of scanning an area of ​​the sample portion by portion; the step of dynamically orienting the collimated beam by changing the direction of the directed collimated beam by a first optical device of the first optical arrangement; the step of collecting light scattered from the sample by a second optical arrangement, the second optical arrangement comprising a second optical device and an optical element; the step of recording, by a spectrometer, an optical spectrum of the scattered light collected from the sample by the second optical arrangement for each (scanned) portion; the step of synchronizing the scanning of the area with the recording of the optical spectrum for a plurality of the portions of the area by the spectrometer, the recording of the optical spectrum for each of the portions lasting an optical spectrum integration time equal to the duration of the scanning of the portion by the optical device;and calculating, by a computing device operatively connected to the spectrometer, an overall light spectrum from statistical calculations over all or a portion of the light spectrum corresponding to all or a portion of the scanned portion of the area, and measuring color coordinates of the area of ​​the sample in a given color space by analyzing the overall light spectrum, wherein the analysis includes calculating XYZ tristimulus values ​​corresponding to the overall light spectrum. In the method according to the present invention, collecting scattered light with the second optical device includes receiving, with the second optical device, light scattered by the sample at an observation angle relative to a direction of a specular component reflected from the sample when the collimated beam is incident on (i.e., incident on) the surface of the sample; redirecting, with the second optical device, the received scattered light towards the optical element; and dynamically orienting, with the second optical device, in synchronization with the first optical device, the propagation direction of the redirected scattered light during the scanning of the area of ​​the sample, so that the propagation direction of the redirected scattered light is constant relative to the optical element;

[0031] In the method, optionally and preferably, the given distance of the location of the sample from the first optical device is 0.5 m or more. Optionally, the method includes providing the sample at the given distance.

[0032] In one embodiment, the synchronizing step is performed using a time-dependent voltage signal, preferably a squared voltage signal.

[0033] In some embodiments, the sample further receives other light from the environment while being illuminated with the collimated beam.

[0034] In one embodiment, the optical spectrum integration time is determined by the steps of: continuously scanning a portion of an area of ​​the white reference by the first optical device; simultaneously with the step of scanning the portion, recording optical spectra with different optical spectrum integration times that increase stepwise and discretely with a certain time difference by the spectrometer; and selecting a maximum optical spectrum integration time at which the recorded optical spectrum is not saturated at any wavelength. Optionally and preferably, the portion is the periphery of the area of ​​the white reference.

[0035] In one embodiment, calculating the XYZ tristimulus values ​​includes calculating a reflectance curve (preferably "overall" means "average") using the overall light spectrum of the area of ​​the sample, the overall light spectrum of a white reference, and a background spectrum; and multiplying the calculated reflectance curve by a CIE standard illuminant spectral curve, a CIE standard observer spectral curve, and a normalization constant. Note that the CIE standard observer is described by three different spectral curves (functions), i.e., three CIE standard observer spectral curves (functions), each of which is used separately to calculate X, Y, and Z [References 4, 5].

[0036] Other embodiments of the invention disclosed herein also include software programs for performing the steps and operations of the method embodiments outlined above and described in detail below. More particularly, one embodiment is a computer program product having a computer-readable medium including computer program instructions encoded thereon that, when executed by at least one processor of a computer system, cause the processor to perform the operations set forth herein as embodiments of the invention.

[0037] These and other advantages and features will be more fully understood from the following detailed description, which is to be understood as illustrative and non-limiting, and which refers to the accompanying drawings. [Brief explanation of the drawings]

[0038] [Figure 1] FIG. 1 is a schematic diagram of a system for measuring the color of an area of ​​a sample, according to one embodiment of the present invention. [Figure 2A] FIG. 2A shows a graphical illustration of the spatial and temporal procedure of synchronization between scanning the sample and recording the optical spectrum. [Figure 2B] FIG. 2B shows an oscilloscope trace of an example voltage signal for synchronization between the galvanometric scanner and the spectrometer. [Figure 3A] FIG. 3A is a photograph illustrating the steps of illumination of a sample as in some embodiments of the method according to the invention. [Figure 3B] FIG. 3B is a photograph illustrating the steps of illuminating a sample as in some embodiments of the method according to the invention. [Figure 3C] FIG. 3C is a photograph showing a step of illumination of a sample similar to some embodiments of the method according to the invention. [Figure 4] FIG. 4 is a photograph illustrating the steps of illumination of a sample as in some embodiments of the method according to the invention. [Figure 5] Figure 5 illustrates how color perception depends on the relative orientation between the illumination source, the sample, and the observer, and also shows the angle of reflection θ of the specular component and the angle of observation α relative to the direction of the specular component. [Figure 6A] FIG. 6A is a schematic diagram of an embodiment of a system according to the present invention. [Figure 6B] FIG. 6B is a schematic diagram of an embodiment of a system according to the present invention. [Figure 7A] FIG. 7A is a schematic diagram of an embodiment of a system according to the present invention. [Figure 7B]FIG. 7B is a schematic diagram of an embodiment of a system according to the present invention. [Figure 8] Figure 8 shows the reflectance spectrum of a coated aluminum sample measured using an embodiment of the system and method of the present invention. Figure 8 also shows the theoretical reflectance spectrum provided by the sample manufacturer. DETAILED DESCRIPTION OF THE INVENTION

[0039] 1 illustrates one embodiment of a system proposed herein for measuring the color of an area of ​​a sample 300, some non-limiting examples of which include textiles, polymers, organic materials, plastics, glass, metals, wood, ceramics, pigments (natural or synthetic), etc. In the embodiment of FIG. 1, the system includes a light source 100; a first optical device 200; a second optical device 500; a spectrometer 400; and a computing device (not shown) having one or more processors and at least one memory operably connected to the spectrometer 400.

[0040] The light emitted by light source 100 includes a spectrum of simultaneously emitted wavelengths, which for the embodiment of Figure 1 continuously covers a band of wavelengths within the visible range from at least a first wavelength (370-460 nm) to a second wavelength (620-780 nm).

[0041] The light emitted by the light source 100 is spatially coherent for at least all wavelengths from the first wavelength to the second wavelength. Preferably, the spatially coherent light propagates in the form of a collimated beam for at least all wavelengths from the first wavelength to the second wavelength, as described above. "Spatially coherent light" is understood, according to known definitions, as light having a beam profile in which the electric fields at different positions across the beam profile have a fixed phase relationship and are therefore correlated. The spatial coherence of the light can enhance the directionality of the light used, thereby facilitating the minimization of any optical losses in the system and enabling robust color measurements and color mapping of samples with the highest possible resolution, even when the sample is far from the system or receives a large amount of ambient light.

[0042] The spatially coherent light may preferably have a high degree of spatial coherence, e.g., the absolute value of the complex mutual coherence |γ 12 (Δz≡0)| [Reference 1] and can be measured, for example, by fiber optic interferometry or by Young's double slit method, as in [Reference 1, Reference 2]. For the spatially coherent light of the system, the absolute value of the complex mutual coherence factor can be, for example, in the range of 0.5 to 1.0, preferably 0.8 to 1.0, for all wavelengths, preferably at least from the first wavelength (370 to 460 nm) to the second wavelength (620 to 780 nm).

[0043] 1, the light source 100 is a fiber optic supercontinuum light source, and supercontinuum light is generated in an optical fiber and delivered through the optical fiber 101, or through another optical fiber 101, to the end of the light source. In such an embodiment, the end of the light source is the end of the fiber 101 used to deliver the light of the supercontinuum light source. In the above-mentioned preferred embodiment, the light is emitted into free space (e.g., air) from the end, which is an interface between the optical fiber and free space (e.g., air), which can be in the form of a transversely polished interface (e.g., particularly an ultra-physical contact (UPC) connector) or an angled polished interface (e.g., an angled polished contact (APC) connector).

[0044] In the preferred embodiment described above, the spectrum of the supercontinuum light continuously covers a wavelength band from at least a first wavelength (370 to 460 nm) to a second wavelength (620 to 780 nm). In the preferred embodiment described above, all of these wavelengths are propagated only in the fundamental transverse mode of the optical fiber used to deliver the supercontinuum light to the end of the light source. As a result, the light emitted by the light source of this embodiment is spatially coherent for at least all wavelengths from the first wavelength (370 to 460 nm) to the second wavelength (620 to 780 nm). All of these wavelengths can be simultaneously emitted into free space from the end of the light source.

[0045] Other non-limiting examples of light sources that can be used in the systems proposed herein are, among others: - in particular for example titanium-sapphire mode-locked lasers, or Yb 3+ Mode-locked laser, or Er 3+A light source comprising a mode-locked laser, such as a mode-locked laser, and also comprising a nonlinear crystal or a nonlinear optical fiber used to double or triple the infrared radiation frequency of the optical radiation emitted by the mode-locked laser, wherein the light emitted by the nonlinear crystal or the nonlinear optical fiber may be spatially coherent light. - Light sources including spatially coherent superluminescent light emitting diodes, known as SLDs or SLEDs. a light source comprising a broadband light source, in particular an incandescent lamp, a halogen lamp or a white LED, said broadband light source being adapted to emit spatially incoherent light, said light source also comprising a pinhole for spatially filtering said spatially incoherent light and converting it into spatially coherent light. a light source comprising a broadband light source, in particular an incandescent lamp, a halogen lamp or a white LED, said broadband light source being adapted to emit spatially incoherent light, said light source also comprising a single-mode optical fiber for converting said spatially incoherent light into spatially coherent light, said broadband light source being coupled to said single-mode optical fiber. - A light source including a nonlinear crystal for generating supercontinuum light.

[0046] All of the above light sources may be spatially coherent over a wide band of wavelengths in the visible range and may simultaneously emit these wavelengths. The light emitted by these light sources may propagate naturally in the form of a collimated beam or may be converted into a collimated beam by a collimator, such as a collimating mirror or a collimating lens or a collimating lens set. The light source may optionally be equipped with a collimator.

[0047] Optionally, if the light source does not naturally emit light in the form of a collimated beam, as in the embodiment of Figure 1, the first optical device 200 comprises a collimator 205 adapted to convert the spatially coherent light into a collimated beam. In an embodiment, the first optical device comprises a collimator, the collimator being positioned at a distance from the end of the light source, the distance corresponding to the focal length of the collimator. In a preferred embodiment where the light source is a fiber optic supercontinuum light source, such a collimator is positioned at a distance from the end of the light source corresponding to the focal length of the collimator, the distance being measured in the direction of the propagation axis of the optical fiber that delivers the supercontinuum light to the end of the light source.

[0048] The collimated beam has a total angular divergence angle of 0.46° or less for all wavelengths from the first wavelength to the second wavelength. In certain embodiments, the total angular divergence angle is 0.01 to 0.20° for all wavelengths from 430 to 780 nm. Similarly, optionally, the cross-sectional diameter of the collimated beam may be 5 mm or less at a distance from collimator 205 corresponding to the focal length of collimator 205 for all wavelengths from the first wavelength to the second wavelength, and the diameter is 1 / e of the beam. 2 Width, i.e., from the central maximum light intensity point of the beam cross section, the light intensity is 1 / e of the maximum light intensity as described above. 2 The diameter is considered as the distance between points on the sides of the cross section of the beam, where the diameter is the distance from the collimator 205 that corresponds to the focal length of the collimator 205. In a specific embodiment, the diameter is between 2.1 mm and 2.15 mm for all wavelengths between 430 and 780 nm.

[0049] Additionally or alternatively, for all wavelengths from the first wavelength to the second wavelength, the diameter of the cross section of the collimated beam may be 10 mm or less at any distance of 1 m or less from a point on the first optical device 200, and / or 100 mm or less at any distance of 10 m or less from the point on the first optical device 200, the point on the first optical device 200 preferably being at the collimator 205 if / when the first optical device 200 comprises a collimator 205, and the diameter is 1 / e 2 Width, i.e., from the central maximum light intensity point of the beam cross section, the light intensity is 1 / e of the maximum light intensity as described above. 2 In a particular embodiment in which the first optical device comprises a collimator 205, the diameter is between 2.1 mm and 5.3 mm at a distance of 1 m from the collimator for all wavelengths between 430 and 780 nm, and the diameter is between 5 mm and 37 mm at a distance of 10 m from the collimator for all wavelengths between 430 and 780 nm.

[0050] Thus, in certain embodiments where the system includes a collimator, 1 / e of the cross section of the light beam incident on a sample located at a distance of 1 m or less from the collimator 2 The diameter in width is 10 mm or less for all wavelengths from the first wavelength to the second wavelength, and is 1 / e of the diameter of the light beam incident on a sample located 10 m or less away from the collimator. 2The diameter in width is 100 mm or less for all wavelengths from the first wavelength to the second wavelength. In certain embodiments where the system includes a collimator, the diameter is preferably 2.1 mm to 5.3 mm at a distance of 1 m from the collimator 205 for all wavelengths from 430 to 780 nm, and the diameter is preferably 5 mm to 37 mm at a distance of 10 m from the collimator 205 for all wavelengths from 430 to 780 nm. For illustrative purposes, FIG. 4 shows a photograph of light scattered by a textile sample when illuminated by a collimated beam of a supercontinuum light source as in certain embodiments of the present invention. In the example associated with the photograph of FIG. 4, the (1 / e) cross-section of the beam incident on the sample is plotted. 2 The diameter values ​​(at) are 2.1 to 5.3 mm for all wavelengths from 430 to 780 nm, and the sample distance from the collimating lens is 0.95 to 1 m for all positions of the beam at all samples.

[0051] The spatial resolution of the system (the spatial resolution is understood as the smallest area of ​​a sample for which the system can provide color coordinates and distinguish them from color coordinates of adjacent areas of the same size) is 1 / e 2 The spatial resolution can be assumed to be the area of ​​the light beam incident on the sample, which corresponds to the beam diameter in width. Therefore, the spatial resolution is 78.6 mm for any sample located at a distance of 1 m or less from the first optical device or a point within the first optical device. 2 or less, or 78.6 mm for any sample located at a distance of 10 m or less from the first optical device or a point within the first optical device. 2 In a particular embodiment in which the first optical device comprises a collimator, the spatial resolution may be 22.1 mm or less at a distance of 1 m from the collimator. 2 , 10.7cm at a distance of 10m from the collimator 2 is.

[0052] The total angular divergence angle and diameter of a collimated beam may have different values ​​when measured in different directions in the plane of the beam's cross section. This may be the case, for example, for a beam with an elliptical cross section. Thus, in the present invention, the total angular divergence angle of a beam is preferably the largest total angular divergence angle measured in any direction in the plane of the beam's cross section. Similarly, in the present invention, the diameter of a beam is preferably the largest diameter measured in any direction in the plane of the beam's cross section. Optionally, in the preferred case where the beam has a circular cross section, the divergence angle and the diameter of the beam are equal in any direction in the plane of the beam's cross section.

[0053] Optionally, the beam quality factor M of the collimated beam 2 is in the range of 1.0 to 2.0 for all wavelengths from the first wavelength to the second wavelength, where 1.0 is the M of a diffraction-limited Gaussian beam. 2 The value of M 2 is the physically possible minimum value [Reference 3]. Preferably, the quality factor M 2 is less than 1.4 for all wavelengths from the first wavelength to the second wavelength. Optionally and preferably, the intensity of a collimated beam made up of all wavelengths from the first wavelength to the second wavelength is less than 1 mW / cm at any distance of 1 m or less from a point on the first optical device. 2 and / or 0.01 mW / cm at any distance of 10 m or less from said point on said first optical device 2 and the point is preferably at the collimator when the first optical device comprises the collimator. In a particular embodiment in which the first optical device comprises a collimator, the luminance is 136 mW / cm at a distance of 1 m from the collimating lens. 2 , 2.8mW / cm at a distance of 10m from the collimating lens 2 is.

[0054] At the same time that the sample 300 is illuminated by the collimated beam, the sample 300 may be illuminated by ambient light or may not be illuminated at all. Unlike conventional systems configured to measure the color of an area using a spectroscope (spectrophotometer), which must avoid ambient light to obtain an adequate measurement of color, in the system of the present invention, the color measurement is not affected by simultaneous illumination by ambient light (and therefore measurements can be performed in an ambiently lit space). This is due in part to the arbitrarily high brightness of the beam incident on the sample, which is typically much higher than the brightness of the ambient light incident on the sample.

[0055] 1 , the first optical apparatus 200 also includes a first optical device 203, such as an XY galvanometer mirror, configured to perform portion-by-portion scanning of an area of ​​the sample 300 by changing the direction of a collimated beam and dynamically orienting it relative to the sample 300.

[0056] As mentioned above, an area of ​​the sample 300 is preferably scanned line by line. A more complete description of this line by line scanning process in one embodiment follows: As shown in FIG. 2A (right side of the figure), a collimated beam is dynamically directed by optical device 203 to sequentially impinge on different points on the sample. In FIG. 2A (right side of the figure), the locations of these points on the sample are represented by their corresponding coordinates (x, y). The beam is scanned from position (x0, y0) to position (x0+L x , y0) in order. This is the length L x The beam then moves from position (x0, y1) to position (x0+L x , y1) and a second line scan is performed. Continuing this procedure, the sample is scanned along a line with side lengths L x and L y Scan the sample area at position (x0, y1) on other lines (each one of an arbitrary number n) until the sample area is completely scanned. n ) to position (x0+Lx ,y n ) is scanned.

[0057] Optionally, the scanning of an area may be performed with only a single line. In practice, since the size of the beam cross section or spot is finite, scanning of a line may be performed by illuminating a single point or spot on the sample. Therefore, the smallest area that can be scanned may be the area of ​​the cross section of the beam incident on the sample, which corresponds to the spatial resolution of the system as described above.

[0058] 1 , the second optical apparatus 500 is configured to collect light scattered from a sample when the sample is illuminated with a collimated beam. To collect the scattered light, the second optical apparatus 500 includes a second optical device 503 and an optical element 504 configured as follows: the second optical device 503 is configured to receive light scattered by the sample at an observation angle relative to the direction of a specular component reflected from the sample when the collimated beam is incident on the surface of the sample. The second optical device 503 is further configured to redirect the received scattered light towards the optical element 504. The second optical device 503 is also configured to dynamically orient the redirected scattered light by changing its propagation direction in synchronization with the first optical device 203, thereby maintaining the propagation direction of the redirected scattered light constant relative to the optical element 504 during the scanning of the area of ​​the sample 300. In the preferred embodiment of FIG. 1, the optical element 504 is an off-axis parabolic mirror and the second optical device 503 comprises a galvanometer mirror.

[0059] Spectrometer 400 is configured to measure the optical spectrum of the collected scattered light, i.e. the scattered light collected by second optical arrangement 500, for each scanned portion of said area. To this end, in the preferred embodiment of Figure 1, optical element 504 is configured to receive said scattered light redirected by first optical device 503 and to further redirect said scattered light towards the input of spectrometer 400.

[0060] The computing device executes / implements one or more algorithms that determine the color coordinates of the area of ​​the sample 300 in a given color space by calculating an overall light spectrum, which is preferably an average light spectrum. To do this, it preferably averages all the light spectra corresponding to all scanned portions and calculates the XYZ tristimulus values ​​corresponding to the average light spectrum. Optionally, the system may determine color coordinates from a single scanned or illuminated portion of the sample.

[0061] The system proposed herein therefore uses a collimated, spatially coherent illumination source, allowing localized illumination over long distances, and measures color by directing (or orienting) the illumination light using the above-mentioned first optical device 203, which in one particular embodiment consists of a pair of x,y movable galvanometer mirrors, but which may alternatively be a rotating polygon mirror, an acousto-optical deflector, or an electro-optical deflector based on the propagation of light in a nonlinear crystal, among others. Thus, the first optical device 203 can be used to rapidly scan large areas of the sample 300. In the system proposed herein, such areas may be, for example, 22 mm 2 ~2.25m 2 (e.g., a square area of ​​1.5 m x 1.5 m). The total scan time for such an area may range, for example, from 0.1 ms to 1000 s.

[0062] To measure the color of a given area of ​​the sample 300, the scanning of the area is synchronized with the recording of the optical spectrum of multiple portions of the area by the spectrometer 400, with the recording of the optical spectrum of each portion lasting an optical spectrum integration time equal to the duration of the scan of the portion by the first optical device 203. As described above, the area is scanned portion by portion. For each portion, the spectrometer 400 records one spectrum corresponding to the collected scattered light for the time it takes the first optical device 203 to scan the portion (i.e., the spectrometer integration time to record one spectrum matches the scan time of one portion). Preferably, the spectrometer 400 remains passive for the time it takes the first optical device 203 to move to the first point of the next portion to be scanned (called the time of flight). When the next portion is scanned, the spectrometer 400 records a new spectrum, and this continues until the spectrometer 400 has recorded spectra corresponding to all portions of the scanned area.

[0063] 2A shows a graphical illustration of a non-limiting example of a synchronization procedure between scanning a sample and recording an optical spectrum in an embodiment where an area is scanned line by line, said example being as follows: A squared voltage signal (represented as a function of time on the left (top) of FIG. 2A) is used to synchronize the scanning and spectrum recording times. This voltage signal is fed simultaneously to the synchronization input ports of the first optical device 203 and the spectrometer 400. When the signal is coupled to a low-state voltage V L to high-state voltage V H (rising trigger event), the movement of the first optical device 203 to scan the line and the recording of the spectrum are simultaneously started. This rising trigger event occurs at time t n occurs while the signal is in a high state (integration time T H ), the first optical device 203 maps a line on the sample to a point (x0, y n ) to the point (x0+L x ,y n), and the spectrometer 400 scans for an integration time T H The spectrometer 400 records spectrum n by integrating the photodetector signal generated by all scattered light collected by the second optical device 500 during the period n. When the signal changes from a high state voltage to a low state voltage (a drop trigger event), the first optical device 203 starts moving to translate the collimated beam to the first point of the next line, and the spectrometer 400 stops recording the spectrum. While the signal is in the low state (time of flight T L ), first optical device 203 translates the collimated beam to the first point of the next line, while spectrometer 400 remains passive. This procedure is repeated sequentially until all lines from n=0 to n=N of the area have been scanned and a spectrum n for each line n has been recorded. A computing device operatively connected to the spectrometer performs statistical calculations whereby all or a portion of the spectra corresponding to all the lines are used to calculate an overall spectrum, and preferably the computing device calculates an average spectrum by averaging all of the spectra corresponding to all the lines.

[0064] FIG. 2B shows an oscilloscope trace of an example voltage signal for synchronization between a galvanometer scanner and a spectrometer, where the integration time is T H is 11.93 ms, and the time of flight T L is 571.3 milliseconds.

[0065] In one embodiment, in order to calculate the color of sample 300, the following are measured: the spectrum of scattered light from sample 300 and the spectrum of scattered light from a white reference. Thus, in one embodiment, the procedure described above is performed to obtain an average spectrum of scattered light from an area of ​​sample 300, and also to obtain an average spectrum of scattered light from the white reference. Most preferably, the white reference is positioned the same distance from the system as sample 300. Likewise, most preferably, the scanned area of ​​the white reference is the same size as the scanned area of ​​the sample. Preferably, the white reference is measured prior to measuring the sample.

[0066] Advantageously, the highest accuracy in color determination is obtained when the entire dynamic range of the spectrometer 400 is preferably utilized when recording the spectra of the white reference and the sample 300. Such a full dynamic range can be obtained when the integration time of the spectrometer for recording the optical spectrum is set to be equal to the maximum optical spectrum integration time at which the response of the spectrometer, and therefore the recorded optical spectrum, is not saturated at any wavelength. In one embodiment of the method proposed herein, the maximum optical spectrum integration time, prior to saturation, is determined as follows: the first optical device 203 is configured / programmed to continuously scan a portion, preferably the periphery, of an area of ​​the white reference, similar to that shown in FIG. 3A. Simultaneously, the spectrometer 400 is configured / programmed to record spectra at different integration times that are discretely increased with a fixed time difference. The maximum of these integration times at which the corresponding recorded spectra are not saturated at any wavelength is set as the integration time for recording the reference and sample spectra, and the corresponding time of the high state voltage of the synchronization signal between the scanner and the spectrometer (integration time T ) mentioned above and shown in FIG. 2A is set. H )

[0067] This determination of integration time is made using a white reference because the white reference scatters a higher percentage of the intensity than the sample 300, and so the spectrometer 400 will not be saturated by light scattered from the sample 300 if it is not saturated by light scattered from the white reference, provided that the integration time is the same in either case.

[0068] The required integration time T determined above H can be reduced by the brightness of the collimated beam. H may be inversely proportional to the brightness of the collimated beam. As an example, if the brightness of the collimated beam (composed of all wavelengths from 430 to 780 nm and measured at a distance of 1 m from the collimator 205) is 1 mW / cm 2 If the integral time TH In an embodiment where λ is 1622.48 ms, the luminance value is 136 mW / cm 2 If the integral time T H is 11.93 milliseconds.

[0069] In one embodiment, the XYZ tristimulus values ​​are calculated by performing the following steps:

[0070] - Step 1. Measuring the spectrum: Measurement of the spectrum of an area with a white reference, obtained using the synchronization procedure described above. The integration time T determined above H 2. Measurement of the background spectrum recorded during the measurement. Background is noise recorded by the spectrometer generated by detected ambient light and / or by the inherent electrical noise of the spectrometer. The background spectrum is recorded by turning off or blocking (e.g., using an electromechanical shutter optionally included in the system) the illuminating collimated beam at the light source, or at a point between the light source and the sample, or between the first optical device 203 and the light source. Measurement of the spectrum of an area of ​​the sample 300, obtained by the synchronization procedure described above. The area of ​​the sample and the area of ​​the white reference are equal and are located at the same distance from the edge of the illumination source.

[0071] Step 2. Calculation of the reflectance curve of said area of ​​sample 300: Here, the reflectance curve R(λ) is considered to be a spectrum representing the amount of light reflected by the area of ​​sample 300 in percentage (%) at each wavelength λ, said reflected light comprising scattered light from said area of ​​sample and specular reflection components, if / when present, reflected from said area of ​​sample. The reflectance curve of said area of ​​sample 300 is calculated by said computing device as follows:

[0072]

number

[0073] where W(λ) is the spectrum of the area of ​​the white reference, I(λ) is the spectrum of the area of ​​the sample, and B(λ) is the spectrum of the background measured as described above, all expressed in the same units (e.g., spectrometer counts, optical power, or spectral power density, among others).

[0074] Step 3. Calculation of the tristimulus values ​​X, Y, Z: From the reflectance curve of the area of ​​sample 300, the tristimulus values ​​X, Y, and Z of the area of ​​sample 300 are calculated by a calculation device using the following standard formulas established by the CIE (International Commission on Illumination) [References 4, 5]:

[0075]

number

[0076]

number

[0077] where S(λ) is the normalized spectrum of a CIE standard illuminant (i.e., the theoretical spectrum of a light source of a type established as a standard by the CIE). Examples of CIE standard illuminants are, among others, A: incandescent lamp, D65: daylight, and F2: fluorescent lamp.

[0078]

number

[0079]

number

[0080] The X, Y, and Z values ​​related to the reflectance of the above area of ​​the white reference are X n , Y n , Z n , which are also calculated by the above formulas using the same CIE standard illuminant and the same CIE observer, or can be considered as given or predetermined properties of the white reference.

[0081] - Step 4: Calculation of the color coordinates in a color space such as CIEXYZ, CIE L*a*b*, CIE L*Ch or HUNTER Lab, among others. By way of example, in the case of the CIE L*a*b* space, the coordinates L*, a* and b* of said area of ​​the sample are calculated by a calculation device using the following formulas:

[0082]

number

[0083] Some details of an example of the above-described procedure for obtaining color coordinates of an area of ​​a textile sample are as follows: the example relates to an embodiment in which the first optical device comprises a collimator, a galvanometer mirror, and an electromechanical shutter. In the example, the sample is illuminated by a collimated beam of a fiber optic supercontinuum light source simultaneously emitting a band of wavelengths from 430 to 780 nm in the visible range. In the example, the light spectrum is recorded with a commercially available spectrometer, model OCEAN-HDX-VIS-NIR, manufactured by OceanInsight. In the example, the following parameters are considered: area of ​​the sample: 10 × 10 cm 2Distance of the sample from the collimating lens: in the range of 0.95 to 1 m for all positions of the beam within the above area of ​​the sample; Visible spectral range: 430 to 780 nm; Intensity of the collimated beam (composed of all wavelengths from 430 to 780 nm) at a distance of 1 m from the collimating lens: 136 mW / cm 2 ;Spectral integration time T H : 11.93 ms; time of flight T L time to scan the entire area: 0.62 seconds. In the same example, the computing device is configured to determine the color coordinates of the area of ​​the sample for CIE Standard Illuminants A, B, D50, D65, F2; CIE Standard Observers 2° and 10°; standard color coordinate spaces CIEXYZ, CIEL*ab, CIEL*Ch, HUNTERLab; and to determine the whiteness and yellowness indices of ASTM E313.

[0084] In the above example, first, the spectral integration time T H To determine T, the perimeter of the area of ​​the fabric white reference is illuminated similarly to that shown in Figure 3A, resulting in T H = 11.93 ms. Next, in the same example, the area of ​​the white reference is scanned line by line, similar to that shown in FIG. 3B, where 7 of the 50 total lines are shown. The time it takes to perform a complete scan of each line is 11.93 ms integration time T H corresponds to the flight time T L The time it takes for the scanning galvanometer mirror to translate the collimated beam from the last point of one line to the first point of the next line is 0.57 milliseconds. Simultaneously, in the same example, the spectrometer records a spectrum for each line being scanned. Then, in this example, an electromechanical shutter positioned between the collimator and the galvanometer mirror blocks the illumination beam, and a background spectrum is recorded. The area of ​​the textile sample for which color coordinates are to be obtained is then scanned line by line, similar to the example shown in FIG. 3C.

[0085] In this example, the integration time T H , flight time T L The conditions of the number of lines, the area of ​​the sample, and the position of the sample relative to the end of the collimator and the galvanometer mirror are the same as those of the previous scanning procedure of the white reference. At the same time, in this example, a spectrometer records a spectrum for each line during the scan. Next, in this example, a computing device calculates an average spectrum of the 50 lines of the white reference and an average spectrum of the 50 lines of the textile sample. Finally, in this example, the computing device calculates a reflectance curve according to the above-mentioned Equations 1 to 4a, 4b, and 4c, and calculates the color coordinates of the area of ​​the sample from the reflectance curve.

[0086] To further evaluate the usefulness of the present invention for determining the color coordinates of an area of ​​a sample made of any material, the color coordinates of a sample of aluminum sheet coated with a paint pigment, for example produced by coil coating techniques, were calculated according to the procedure described above. As an example, an aluminum sheet coated with a green paint pigment was studied using the same measurement procedure as described further above for the textile sample. In the above example for the aluminum sample, the following parameters exist: Area of ​​the sample: 13 x 13 cm 2 Distance of the sample from the collimating lens: in the range of 0.95 to 1 m for all positions of the beam within the above area of ​​the sample; Visible spectral range: 420 to 750 nm; Spectral integration time T H : 1.55 ms; time of flight T LTime to scan the entire area: 0.07 milliseconds; number of lines: 6; time to scan the entire area: 9.72 seconds. In this example, the first and second optical devices of the present embodiment are galvanometer mirrors. The first galvanometer mirror (first optical device) scans the area of ​​the sample by dynamically changing and orienting a collimated beam (incidence angle = approximately 0°) around a central direction perpendicular to the surface of the sample. The second galvanometer mirror (second optical device) receives scattered light from the surface at an observation angle α of approximately 45°, redirects the received scattered light in synchronization with the first galvanometer mirror, and dynamically changes and orients the propagation direction of the redirected scattered light so that the propagation direction is constant and parallel to the flat surface of the sample while scanning the area of ​​the sample. An off-axis parabolic mirror receives the redirected light and focuses it into a multimode fiber, which directs it to the input of a spectrometer (similar to that shown in Figures 7A and 7B). Figure 8 shows the reflectance spectrum (curve A) obtained from the above procedure used to measure the coated aluminum sample for an incident angle θ = 0° and an observation angle α = 45° (a standard geometry for measuring color, known in the art as 0 / 45), as well as the theoretical reflectance spectrum (curve B) provided by the sample manufacturer. In Figure 8, reflectance R (%) is shown as a function of wavelength λ (nm). As shown in Figure 8, by following the above experimental procedure, accurate measurement of the predicted reflectance spectrum of the sample in the 0 / 45 geometry is achieved. From the reflectance spectrum obtained, the color coordinates of the area of ​​the aluminum sample under study in the CIE L*a*b* color space for illuminant D50 and observer 2° are calculated as follows: L*=37.88, a*=-53.39, b*=20.71.

[0087] In some embodiments, the reference spectrum may be a reference overall optical spectrum, which is preferably calculated in a similar manner to the calculation of the overall optical spectrum of the sample. Thus, in some embodiments, the method applied to the calculation of the overall optical spectrum of the area of ​​the sample is applied to a reference sample, for example a white reference sample, to calculate the reference overall optical spectrum.

[0088] The utility of the invention described herein for measuring the color of an area of ​​a sample can be applied for a variety of purposes, including quality control in manufacturing processes, development of coating materials, and material inspection for industrial sorting, recycling, or classification, among others. In one non-limiting example, the invention is used to distinguish between multiple samples based on their color differences. In this example, the color coordinates of two samples can be calculated in CIE L*a*b*, CIE L*Ch, and HUNTER Lab. The ASTM E313 yellowness parameter can also be calculated for both samples.

[0089] In particular, these color coordinates calculated in CIE L*ab space can be located within a graphical representation of CIE L*ab space (L*, a, b axes). In this example, the color difference between both samples can be expressed as ΔL, Δa, Δb, and ΔE, where:

[0090]

number

[0091] It should be clarified that the notation of the parameters L*, a*, b*, and ΔE* in the text can also be written as L, a, b, and ΔE (without the symbol *), respectively.

[0092] FIG. 4 is a photograph of light scattered by a textile sample when illuminated by a collimated beam of a supercontinuum light source, as in one embodiment of the present invention, in which the first optical device comprises a collimator and the beam cross-sectional diameter (1 / e 2) is between 2.1 and 5.3 mm for all wavelengths between 430 and 780 nm. In the same embodiment, the distance of the sample from the collimating lens is between 0.95 and 1 m for all positions of the beam within the sample.

[0093] Figure 4 shows, from left to right: 1) static incidence of the beam on a white reference textile sample; 2) time of 11.93 ms (integration time T H ) dynamic incidence of the beam on the same white reference fabric sample, scanning a line of 10 cm length during the time; 3) static incidence of the beam on the fabric sample under test (to obtain color coordinates); 4) a time of 11.93 ms (integration time T H ) is shown, scanning a 10 cm long line between the beam incident on the same fabric sample.

[0094] Figure 5 illustrates the principle of operation of many color measurement systems. As is well known, the color of a sample perceived by an observer can depend on the relative orientation between the illumination source, the sample, and the observer. The same sample illuminated by the same light source and observed by the same observer may be perceived as a different color if the angle of incidence and / or observation angle from normal to the sample changes from observation to observation. This effect can be particularly relevant in the case of partially reflective samples, where the specular component of the light reflected by the sample can obscure the "real" color of the sample. Figure 5 illustrates this effect, where θ is the angle of incidence of the light (i.e., the angle formed between the direction of propagation of the illuminating light and the direction normal to the plane of the sample). The specular component has an angle of reflection equal to θ, while scattered light from the sample propagates in all directions. Information about the "real" color of the sample is provided by the scattered light. Therefore, to perceive the "real" color of the sample, the observer must preferably move away from the θ direction by an angle α (the observation angle relative to the direction of the specular component). The larger α, the lower the intensity of the specular reflection component received by the observer.

[0095] In previously known standard systems for measuring color, the illumination source and observer are positioned at θ = 0° and α = 45°, respectively (0 / 45 configuration), to minimize the influence of specular reflection components. However, these previously known systems miss out on valuable information about perceived color values ​​at other observation angles, which is highly valued in various industrial fields, such as automotive. Systems that can measure color at multiple different observation angles are called "multiangle." Known multiangle systems for measuring color have a discrete and limited number of observation angles, requiring multiple illumination sources positioned at different locations and multiple light receiving devices positioned at different locations. Furthermore, the illumination area of ​​known systems is limited to a few centimeters. 2 is.

[0096] FIG. 6A shows an embodiment of the present invention useful for illustrative purposes. In FIG. 6A, the first optical device 203 and the second optical device 503 are galvanometer mirrors (galvanometers) whose rotation axes are parallel to each other. Therefore, the propagation direction of the collimated beam and the propagation direction of the scattered light received by the optical element 504 are coplanar. In the embodiment of FIG. 6A, the surface of the sample 300 is flat and parallel to a line between the rotation axes of the galvanometer mirrors. Also referring to FIG. 6A, the propagation direction of the redirected scattered light received by the optical element 504 from the second galvanometer mirror 503 is parallel to the surface of the sample (sample plane). The present invention allows this direction to be kept constant while the first galvanometer 203 scans the sample. Therefore, while the first galvanometer rotates to scan the sample, the second galvanometer can be rotated to keep the direction constant. The relative angular geometry between the mirrors to maintain the direction constant and parallel to the surface of the sample is shown in FIG. 6A. As also shown in FIG. 5, θ is the angle of incidence of light, determined by the rotation angle of the first galvanometer mirror. The reflection angle of the specular reflection component is equal to θ, and α is the observation angle relative to the direction of the specular reflection component. A change in θ causes a change in the point of illumination on the sample. Therefore, α, determined by the fixed position of the second mirror, changes correspondingly. Referring to FIG. 6A, if γ is the rotation angle of the second galvanometer relative to a line between the rotation axes of the galvanometer mirrors, then θ, α, and γ must be maintained in the following angular relationship to maintain the propagation direction of the redirected scattered light received by the optical element parallel to the surface: θ + α + 2γ = 90°. In the embodiment of FIG. 6A, the second galvanometer mirror is synchronized with the first galvanometer mirror to maintain this angular relationship during a scan to measure the color coordinates of the area of ​​the sample.

[0097] Figure 6B shows an embodiment similar to that of Figure 6A. In Figure 6B, the angle of incidence θ of the light is 0° and the observation angle α relative to the direction of the specular component is 45°. The embodiment of Figure 6B is preferred because it calculates the color coordinates of the area of ​​the sample for a geometry known as 0 / 45, a standard geometry that is widely accepted by the industry and users of color measurement equipment.

[0098] 6A and 6B, compared to state-of-the-art instruments for measuring the color of an area of ​​a sample, the present invention offers the advantage that the observer (spectroscope) can be kept in a fixed position relative to the position of the optical elements and the position of the light source output while the illumination angle θ and observation angle α are varied over time. This fixed position ensures that the observer (spectroscope) always receives scattered light from the sample at the same receiving angle. Therefore, the scattered light received by the observer / spectroscope to determine the color of the sample is always received by the observer / spectroscope at the same receiving direction.

[0099] As a result, the system of the present invention for measuring the color of an area of ​​a sample can provide multiple illumination and observation angles, which preferably vary continuously, and more preferably are provided using a single illumination source located at a fixed, single location and a single light receiving device (preferably a spectrometer) located at a fixed, single location.

[0100] FIG. 7A shows another preferred embodiment similar to that of FIG. 6A. In the embodiment of FIG. 7A, optical element 504 is an off-axis parabolic mirror, and the propagation direction of the scattered light redirected by the second galvanometer mirror is parallel to the main optical axis of the off-axis parabolic mirror. Furthermore, the scattered light received by the off-axis parabolic mirror is focused by the off-axis parabolic mirror onto the input end of optical fiber 600, which may preferably be a multimode optical fiber. In the embodiment of FIG. 7A, the fiber 600 is fixed at a specific position that does not need to change when the illumination angle θ and the observation angle α change. The optical fiber 600 delivers the focused light to the input of the spectrometer 400. In one non-limiting example, the system is similar to that shown in FIG. 7A, and some details of this example are as follows: the optical element is a 90° off-axis parabolic mirror MPD149-M01 manufactured by Thorlabs GmbH, with a diameter of 25.4 mm and a reflected focal length of 101.6 mm; the optical fiber is a multimode fiber QP600-2-VIS-NIR manufactured by Ocean Optics Inc., with a core diameter of 600 um; the spectrometer is an OCEAN-HDX-VIS-NIR spectrometer manufactured by Ocean Optics Inc.; and the galvanometer mirror is a copyright SCANLAB 7mm Scan Kit AIO manufactured by SCANLAB GmbH, with a scan range of ±0.42 rad.

[0101] FIG. 7B illustrates a variation of the configuration of the embodiment of FIG. 7A. In the embodiment of FIG. 7B, the off-axis parabolic mirror has a through hole coaxial with the main optical axis of the parabolic mirror, and the through hole contains a laser pointer 700. In the embodiment of FIG. 7B, the beam of the laser pointer 700 propagates through the coaxial hole in a direction opposite to the propagation direction of the scattered light redirected by the second galvanometer. In the embodiment of FIG. 7B, the function of the laser pointer is to control the rotation angle γ of the second galvanometer mirror so that a certain condition is achieved: the scattered light redirected by the second galvanometer is always parallel to the main optical axis of the off-axis parabolic mirror. As shown in FIG. 7B, because the laser pointer beam propagates along the same optical path as the redirected scattered light in the opposite direction, this condition is achieved when the laser pointer beam strikes the point of incidence of the collimated light source beam on the sample. In one non-limiting example, the off-axis parabolic mirror is a 90° off-axis parabolic mirror MPD249H-M01 manufactured by Thorlabs GmbH, with a diameter of 50.8 mm and a reflected focal length of 101.6 mm.

[0102] While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.

[0103] For example, other aspects may be implemented in hardware, or software, or a combination of hardware and software.

[0104] Additionally, the software programs included as part of the present invention may be embodied as a computer usable medium, such as a readable memory device, such as a hard drive device, flash memory device, CD-ROM, DVD-ROM, or computer diskette, having computer readable program code segments stored thereon.

[0105] The computer readable medium may also include optical, wired or wireless communications links over which program code segments are transmitted as digital or analog signals.

[0106] The scope of the present invention is defined in the following set of claims.

[0107] Non-patent references [Reference 1] CK Hitzenberger, M. Danner, W. Drexler and AF Fercher, “Measurement of the spatial coherence of superluminescent diodes,” Journal of Modern Optics, 46:12, 1763-1774 (1999). [Reference 2] K. Saastamoinen, J. Tervo, J. Turunen, P. Vahimaa, and AT Friberg, “Spatial coherence measurement of polychromatic light with modified Young's interferometer,” Optics Express, 21:4, 4061-4071 (2013). [Reference 3] ISO Standard 11146, “Lasers and laser-related equipment - Test methods for laser beam widths, divergence angles and beam propagation ratios” (2005) [Reference 4] COLORIMETRY -PART 3: CIE TRISTIMULUS VALUES, ISO / CIE 11664-3:2019(E) http: / / cie.co.at / publications / colorimetry-part-3-cie-tristimulus-values-2 [Reference 5] CIE 1931 color space, article in Wikipedia, https: / / en.wikipedia.org / wiki / CIE_1931_color_space

Claims

1. A system for measuring the color of a certain area of ​​a sample, A light source (100) configured to emit light for illuminating a sample (300); A first optical device (200) configured to receive the light and to output and orient a collimated beam of the light toward the surface of the sample (300) located at a given distance, wherein the first optical device (200) comprises a first optical device (203) configured to scan a portion of an area of ​​the sample (300) by changing the direction of the collimated beam and dynamically aligning it with the sample (300); A second optical device (500) is configured to collect light scattered from a sample when the sample is illuminated by the collimating beam, the second optical device (500) comprises a second optical device (503) and an optical element (504), the second optical device (503) is configured to receive light scattered by the sample at an observation angle (α) with respect to the direction of the specular reflection component reflected from the sample when the collimating beam is incident on the surface of the sample, and the second optical The second optical device (503) is further configured to reorient the received scattered light toward the optical element (504), and the second optical device (503) is further configured to dynamically adjust the propagation direction of the reoriented scattered light in synchronization with the first optical device (203) so that the propagation direction of the reoriented scattered light remains constant with respect to the optical element (504) while scanning the area of ​​the sample (300); A spectrometer (400) configured to receive the scattered light collected by the second optical device (500) and to record the optical spectrum of the collected scattered light in parts; and, The spectrometer (400) is equipped with a computing device that is operably connected to it. The light emitted by the light source (100) includes a spectrum of multiple wavelengths emitted simultaneously, the spectrum continuously covers a band of wavelengths within the visible range, at least from a first wavelength to a second wavelength; The light emitted by the light source (100) is spatially coherent with respect to all wavelengths in the band from at least the first wavelength to the second wavelength; The first optical device (200) for outputting the collimated beam is configured to maintain the collimated spatially coherent light when the spatially coherent light is collimated, and / or the optical device (200) further comprises a collimator (205) for performing the collimation of the spatially coherent light; The system is configured such that when the first optical device (203) scans the area, the scan of the area is synchronized with the recording of the optical spectrum of a plurality of portions of the area by the spectrometer (400), and the recording of the optical spectrum of each portion is configured to last for an optical spectral integration time equal to the duration of the scan of the portion by the first optical device (203); The computing device is configured to determine the color coordinates of the area of ​​the sample (300) in a given color space by calculating an overall light spectrum from statistical calculations over all or part of the light spectrum corresponding to all or part of the scanned portion of the area, and by analyzing the overall light spectrum, the analysis including calculating the XYZ tristimulus values ​​corresponding to the overall light spectrum; The system wherein the first wavelength is in the range of 370 nm to 460 nm, and the second wavelength is in the range of 620 nm to 780 nm.

2. The system according to claim 1, wherein the propagation direction of the reoriented scattered light is parallel to the principal optical axis of the optical element (504).

3. The observation angle (α) is 45°, and the first optical device (203) is further configured to dynamically adjust the orientation of the collimating beam by changing its direction around a central direction perpendicular to the surface of the sample while scanning the area of ​​the sample in sections.

4. The first optical device (203) and the second optical device (503) each include a galvanometer mirror; The second optical apparatus further comprises an optical fiber optically connected to the spectrometer (400); The system according to claim 1, wherein the optical element (504) is configured to receive the scattered light reoriented by the second optical device (503) and to further reoriented the scattered light toward the input of the optical fiber.

5. The system according to claim 1, wherein the optical element (504) is an off-axis parabolic mirror having a through hole, and the system further comprises a laser configured to emit laser light through the hole toward the second optical device (503).

6. The system according to claim 1, wherein the light source is a supercontinuum light source.

7. The diameter of the cross-section of the collimated beam is 10 mm or less at any distance within 1 m from a point on the first optical device (200) or 100 mm or less at any distance within 10 m from a point on the first optical device (200) for all wavelengths from the first wavelength to the second wavelength, and the diameter is 1 / e ２ The system according to claim 1, which is considered in terms of width.

8. The luminance of the collimated beam, which is composed of all wavelengths from the first wavelength to the second wavelength, is 1 mW / cm² at any distance of 1 m or less from a point on the first optical device (200). ２ The above is true, or 0.01 mW / cm² at any distance within 10 m from the point on the first optical device (200). ２ The system described in claim 1 is as described above.

9. A method for measuring the color of a certain area of ​​a sample, The step of emitting light using a light source in order to illuminate a sample located at a given distance, wherein the light comprises a spectrum of multiple wavelengths emitted simultaneously, the spectrum continuously covers a band of wavelengths in the visible range from at least a first wavelength to a second wavelength, the light is spatially coherent at least all wavelengths from the first wavelength to the second wavelength, the first wavelength is in the range of 370 nm to 460 nm, and the second wavelength is in the range of 620 nm to 780 nm; A step of receiving the spatially coherent light in a first optical device located at a certain distance from the end of the light source; In the first optical device, if the spatially coherent light is collimated, the steps include maintaining the collimated spatially coherent light or collimating the spatially coherent light using a collimator; The first optical device outputs and directs the spatially coherent collimated beam of light toward the surface of the sample located at a given distance from the first optical device; A step of scanning a portion of the sample; A step of dynamically aligning the orientation of the oriented collimated beam by changing its direction using the first optical device of the first optical apparatus; A step of collecting light scattered from the sample using a second optical device, wherein the second optical device comprises a second optical device and an optical element, the second optical device receiving the light scattered by the sample at an observed angle with respect to the direction of the specular reflection component reflected from the sample when the collimated beam is incident on the surface of the sample, the second optical device reorienting the received scattered light toward the optical element, and the second optical device, in synchronization with the first optical device, dynamically adjusting the propagation direction of the reoriented scattered light while scanning the area of ​​the sample, so that the propagation direction of the reoriented scattered light remains constant with respect to the optical element; A step of recording the optical spectrum of the scattered light collected from the sample in parts using a spectrometer; A step of synchronizing the scan of the area with the recording of the optical spectrum of a plurality of parts of the area by the spectrometer, wherein the recording of the optical spectrum of each part lasts for an optical spectral integration time equal to the duration of the scan of the part by the first optical device; and, The step of measuring the color coordinates of the area of ​​the sample in a given color space by calculating an overall light spectrum from statistical calculations over all or part of the light spectrum corresponding to all or part of the scanned portion of the area using a computing device operably connected to the spectrometer, and analyzing the overall light spectrum, wherein the analysis includes calculating the XYZ tristimulus values ​​corresponding to the overall light spectrum. The method, including the method described above.

10. The method according to claim 9, wherein a time-dependent voltage signal is used to carry out the synchronization step.

11. The method according to claim 9 or 10, wherein the sample further receives other light from the environment while being illuminated by the collimated beam.

12. The collimated beam has a maximum total angle divergence of 0.46° or less for all wavelengths from the first wavelength to the second wavelength; or The diameter of the cross-section of the collimated beam is 10 mm or less at any distance within 1 m from a point on the first optical device, or 100 mm or less at any distance within 10 m from a point on the first optical device, for all wavelengths from the first wavelength to the second wavelength, and the diameter is 1 / e ２ Considered in terms of width; or The beam quality factor M of the collimated beam ２ For all wavelengths from the first wavelength to the second wavelength, the value is in the range of 1.0 to 2.0; or The luminance of the collimated beam, which is composed of all wavelengths from the first wavelength to the second wavelength, is 1 mW / cm² at any distance of 1 m or less from a point in the first optical device. ２ The above is true, or the reading is 0.01 mW / cm² at any distance within 10 m from the point on the first optical device (200). ２ That's all; The method according to claim 9, wherein when the first optical device includes the collimator, the point on the first optical device is at the position of the collimator.

13. The aforementioned optical spectral integration time is calculated in the following steps: - The first optical device continuously scans a portion of the white reference area; - Simultaneously with the step of scanning the portion, the spectrometer records a plurality of different optical spectral integral times that increase stepwise and discretely with a certain time difference; and, - A step of selecting the maximum optical spectral integration time at which the recorded optical spectrum does not saturate at any wavelength. The method according to claim 9, which is determined by carrying out the procedure.

14. The aforementioned XYZ tristimulus values ​​are: - A step of calculating a reflectance curve using the overall light spectrum of the area of ​​the sample, the reference overall light spectrum of the white reference, and the background spectrum; - A step of multiplying the calculated reflectance curve by the CIE standard emitter spectral curve, the CIE standard observer spectral curve, and a normalization constant. The method according to claim 9, calculated by...

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