Optical sensor for simultaneous displacement sensing and multi / hyperspectral imaging

Abstract

The invention relates to optical sensors for displacement / 2D profile sensing and multispectral and / or hyperspectral imaging. The invention also includes methods for using such sensors and for simultaneously measuring the displacement of a measurement object relative to the sensor, reconstructing the 2D profile or 3D shape of the measurement object, and / or multi / hyperspectral imaging of the measurement objection. The optical sensor is configured to project polychromatic measurement light including at least one marker into a measurement region, to focus measurement light reflected from the measurement region onto the surface of a first diffractive or non-specular reflective component using a first lens component with longitudinal chromatic dispersion and to image measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component onto an active surface of a photodetector. The at least one marker is used to determine the displacement or profile of a measurement object positioned within the measurement region, and is used as an offset for determining the wavelength of light incident at each position on the photodetector.

Description

[0001] OPTICAL SENSOR FOR SIMULTANEOUS DISPLACEMENT SENSING AND

[0002] MULTI / HYPERSPECTRAL IMAGING

[0003] Technical Field

[0004] The invention relates to optical sensors for displacement / 2D profile sensing and multispectral and / or hyperspectral imaging. The invention also includes methods for using such sensors and for simultaneously measuring the displacement of a measurement object relative to the sensor, reconstructing the 2D profile or 3D shape of the measurement object, and / or multi / hyperspectral imaging of the measurement object.

[0005] Background

[0006] The combination of displacement information, 2D profile information or 3D shape information with spectral reflectance information is typically needed for full quality inspection in industrial manufacturing processes.

[0007] Traditional displacement, 2D and / or 3D sensors cannot provide simultaneous spectral reflectance measurement of the surface of an object being measured and multi- or hyperspectral imaging systems cannot obtain displacement, 2D profile, or 3D shape information. Furthermore, accurate multi- or hyperspectral imaging systems generally require a separate and application specific illumination arrangement, which further complicates the measurement system.

[0008] Summary of the Invention

[0009] According to a first aspect of the invention, an optical sensor for multispectral and / or hyperspectral imaging of the surface of a measurement object and for determining a displacement or a two-dimensional profile of the measurement object is provided. The optical sensor configured to:

[0010] • project polychromatic measurement light into a measurement region, wherein the polychromatic measurement light includes a plurality of spectral bands for multispectral and / or hyperspectral imaging and at least one marker, and wherein the at least one marker is an identifiable feature in the spectral profile of the measurement light and wherein the at least one marker has a known wavelength or spectral band;

[0011] • focus measurement light reflected from the measurement region onto the surface of a first diffractive or non-specular reflective component using a first lens component with longitudinal chromatic dispersion such that measurement light of a given wavelength reflected from the measurement region is in focus at a given position on the surface of the first diffractive or non-specular reflective component depending on i) the displacement of the surface of the measurement object relative to the optical sensor, and ii) the given wavelength of the reflected measurement light;

[0012] • image measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component onto an active surface of a photodetector, wherein the photodetector is configured to sense the intensity of light incident at different positions on the active surface of the photodetector.

[0013] The optical sensor may be configured to project the polychromatic measurement light into the measurement region along a projection axis and wherein the projection axis is aligned with the optical axis of the first lens component.

[0014] The optical sensor may be configured to project the polychromatic measurement light in a plurality of points spread along first direction that extends perpendicular to the projection axis, as a line spread across the first direction that extends perpendicular to the projection axis, or as a combination of points and lines spread across the first direction that extends perpendicular to the projection axis.

[0015] The measurement region is defined as the area or volume of space that extends along the projection axis and the first direction perpendicular to the projection axis in which the polychromatic measurement light is projected and from which reflected measurement light is focused onto the first diffractive or non-specular reflective component by the first lens component and sensed by the photodetector.

[0016] The measurement region and the surface of the first diffractive of non-specular reflective component may be parallel and aligned along the optical axis of the first lens component. The dimension of the measurement region measured perpendicular to the projection axis and the first direction may be less than 50 pm, less than 40 pm, less than 30pm, less than 20pm or less than 10pm.

[0017] The optical sensor may comprise a laser line generator or one or more LEDs in combination with a thin slit for generating the polychromatic measurement light and / or at least one marker.

[0018] The wavelength or spectral band of the at least one marker may fall within one or more of the plurality of spectral bands for multispectral and / or hyperspectral imaging.

[0019] One or more markers of the at least one marker may be separated from the plurality of spectral bands for multispectral and / or hyperspectral imaging in the frequency domain.

[0020] The intensity of measurement light within the wavelength or spectral band of the at least one marker may be at least 5 % higher or lower than measurement light of wavelengths falling outside of the wavelength of narrow spectral band of the marker.

[0021] The at least one marker may be identifiable based on the first or second derivative of the spectrum sensed by the optical sensor.

[0022] The optical sensor may be configured to focus measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component or grating onto the active surface of the photodetector using a sensor lens component, and the optical axis of the sensor lens component may be normal or within 5 degrees, 10 degrees, 15 degrees, 30 degrees, or 45 degrees of normal to the active surface of the photodetector.

[0023] The optical sensor may be further configured to:

[0024] • focus measurement light reflected from the measurement region onto the surface of a second diffractive or non-specular reflective component using the first lens component such that measurement light of a given wavelength reflected from the measurement region is in focus at a given position on the surface of the second diffractive or non- specular reflective component depending on i) the displacement of the surface of the measurement object relative to the optical sensor, and ii) the given wavelength of the reflected measurement light; and image measurement light diffracted or reflected from the surface of the second diffractive or non-specular reflective component or grating onto the active surface of the photodetector.

[0025] The first region of the active surface of the photodetector and the second region of the active surface of the photodetector may be non-overlapping and the optical sensor may be further configured to:

[0026] • image measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component onto a first region of the active surface of the photodetector; and

[0027] • image measurement light diffracted or reflected from the surface of the second diffractive or diffusely reflective component onto a second region of the active surface of the photodetector.

[0028] The optical sensor may be configured to focus measurement light reflected from the measurement region onto the surface of the first diffractive or non-specular reflective component and the second diffractive or non-specular reflective component using a first specular reflective surface and a second specular reflective surface. The first specular reflective surface may be configured to reflect light received from a first side of the measurement region onto the surface of the first diffractive or non-specular reflective component. A second specular reflective surface of the at least two specular reflective surfaces may be configured to reflect light received from a second side of the measurement region. The first specular reflector may be oriented at a 45-degree angle extending in a first direction relative to the optical axis of the first lens component, and the second specular reflector may be oriented at a 45-degree angle extending in a second direction, opposite to the first direction, relative to the optical axis of the first lens component.

[0029] The optical sensor may be further configured to:

[0030] • focus measurement light reflected from the measurement region onto the surface of a second diffractive or non-specular reflective component using the first lens component such that measurement light of a given wavelength reflected from the measurement region is in focus at a given position on the surface of the second diffractive or non- specular reflective component depending on i) the displacement of the surface of the measurement object relative to the optical sensor, and ii) the given wavelength of the reflected measurement light; and

[0031] • focus measurement light diffracted or reflected from the surface of the second diffractive or non-specular reflective component onto an active surface of a second photodetector.

[0032] The optical sensor may be further configured to:

[0033] • determine the two-dimensional profile of the measurement object based on the locations at which the at least one marker is in focus on the active surface of the photodetector of the optical sensor; and

[0034] • determine multispectral and / or hyperspectral imaging data of the surface of the measurement object based on the intensity of light received at locations surrounding the at least one marker on the active surface of the photodetector.

[0035] The optical sensor may be configured to determine the locations at which the at least one marker is in focus by:

[0036] • receiving light intensity data from the optical sensor, the light intensity data including a plurality of data points, each data point defining a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position, wherein the two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, and a second coordinate, which corresponds to a second direction perpendicular to the first coordinate;

[0037] • grouping the received light intensity data into a plurality of groups according to the second coordinates of the light intensity data, and each group corresponding to a single second coordinate or a range of adjacent second coordinates; and

[0038] • identifying the first coordinate of the at least one marker within each group (e.g. identifying the coordinate at which the at least one marker is in focus).

[0039] The optical sensor may be configured to determine the two-dimensional profile of the measurement object by compiling the determined locations at which the at least one marker is in focus and, optionally, interpolating the determined locations to generate a continuous two-dimensional profile. The optical sensor may be configured to carry out multispectral and / or hyperspectral imaging of the surface of a measurement object by determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker.

[0040] The optical sensor may be further configured to repeatedly determine the two-dimensional profile of the measurement object at different positions on the measurement object and generating output data comprising the determined two-dimensional profiles and the displacements between the determined two-dimensional profiles.

[0041] The optical sensor may be further configured to process the determined two-dimensional profiles of the measurement object and displacements between the determined two- dimensional profiles to generate the three-dimensional model of the measurement object.

[0042] According to a second aspect of the invention, a system comprising the optical sensor as described above and at least one processing unit is provided. The at least one processing unit is configured to:

[0043] • determine the two-dimensional profile of the measurement object based on the locations at which the at least one marker is in focus on the active surface of the photodetector of the optical sensor; and

[0044] • determine multispectral and / or hyperspectral imaging data of the surface of the measurement object based on the intensity of light received at locations surrounding the at least one marker on the active surface of the photodetector.

[0045] The at least one processing unit may be configured to determine the locations at which the at least one marker is in focus by:

[0046] • receiving light intensity data from the optical sensor, the light intensity data including a plurality of data points, each data point defining a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position, wherein the two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, and a second coordinate, which corresponds to a second direction perpendicular to the first coordinate;

[0047] • grouping the received light intensity data into a plurality of groups according to the second coordinates of the light intensity data, and each group corresponding to a single second coordinate or a range of adjacent second coordinates; and

[0048] • identifying the first coordinate of the at least one marker within each group (e.g. identifying the coordinate at which the at least one marker is in focus).

[0049] The at least one processing unit may be configured to determine the two-dimensional profile of the measurement object by compiling the determined locations at which the at least one marker is in focus and, optionally, interpolating the determined locations to generate a continuous two-dimensional profile.

[0050] The at least one processing unit may be configured to carry out multispectral and / or hyperspectral imaging of the surface of a measurement object by determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker.

[0051] The at least one processing unit may be further configured to repeatedly determine the two- dimensional profile of the measurement object at different positions on the measurement object and generating output data comprising the determined two-dimensional profiles and the displacements between the determined two-dimensional profiles.

[0052] The at least one processing unit may be further configured to process the determined two- dimensional profiles of the measurement object and displacements between the determined two-dimensional profiles to generate the three-dimensional model of the measurement object.

[0053] According to a third aspect of the invention, a method for multispectral and / or hyperspectral imaging of the surface of a measurement object and for determining a two-dimensional profile of the measurement object using the optical sensor of described above is provided. The method comprises:

[0054] • determining the two-dimensional profile of the measurement object based on the locations at which the at least one marker is in focus on the active surface of the photodetector of the optical sensor; and determining multispectral and / or hyperspectral imaging data of the surface of the measurement object based on the intensity of light received at locations surrounding the at least one marker on the active surface of the photodetector.

[0055] The method may comprise determining the locations at which the at least one marker is in focus by:

[0056] • receiving light intensity data from the optical sensor, the light intensity data including a plurality of data points, each data point defining a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position, wherein the two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, and a second coordinate, which corresponds to a second direction perpendicular to the first coordinate;

[0057] • grouping the received light intensity data into a plurality of groups according to the second coordinates of the light intensity data, and each group corresponding to a single second coordinate or a range of adjacent second coordinates; and

[0058] • identifying the first coordinate of the at least one marker within each group (e.g. identifying the coordinate at which the at least one marker is in focus).

[0059] Determining the two-dimensional profile of the measurement object may comprise compiling the determined locations at which the at least one marker is in focus and, optionally, interpolating the determined locations to generate a continuous two-dimensional profile.

[0060] Multispectral and / or hyperspectral imaging of the surface of a measurement object may comprise determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker.

[0061] The method may further comprise repeatedly determining the two-dimensional profile of the measurement object at different positions on the measurement object and generating output data comprising the determined two-dimensional profiles and the displacements between the determined two-dimensional profiles. The method may further comprise processing the determined two-dimensional profiles of the measurement object and displacements between the determined two-dimensional profiles to generate the three-dimensional model of the measurement object.

[0062] Brief Description of the Drawings

[0063] Figure 1 depicts a first optical sensor for displacement / 2D profile sensing and multispectral and / or hyperspectral imaging.

[0064] Figures 2Aand 2B show exemplary spectral power density plots for polychromatic measurement light.

[0065] Figure 3A is a perspective drawing demonstrating projection of polychromatic measurement light onto a measurement object.

[0066] Figures 3B and 3C illustrate possible configurations of a light source.

[0067] Figures 4Aand 4B depict the image of the measurement light that is focused on the diffractive or non-specular reflective surface and on the photodetector.

[0068] Figure 5 depicts a second optical sensor for displacement / 2D profile sensing and multispectral and / or hyperspectral imaging.

[0069] Figure 6 is a flow chart depicting a method for multispectral and / or hyperspectral imaging of the surface of a measurement object and for determining a two-dimensional profile of the measurement object using an optical sensor.

[0070] Detailed Description of the Invention

[0071] The present invention relates to optical sensors for displacement / 2D profile sensing and multispectral and / or hyperspectral imaging. In particular, the invention enables simultaneous displacement / 2D profile sensing and multi- or hyperspectral imaging by projecting polychromatic measurement light that includes a plurality of spectral bands for multispectral and / or hyperspectral imaging and at least one marker onto a measurement object. The polychromatic measurement light includes at least one marker. A marker is a feature of the spectral profile of the measurement light that can be clearly identified in the spectrum of measurement light reflected from the surface of the measurement object. A marker corresponds to a known wavelength or frequency of light. The features that may be used as a marker are discussed in more detail below with respect to Figures 2A and 2B.

[0072] Measurement light reflected from the surface of the measurement object is focused by a first lens component, which may be a singlet lens or a compound lens made up of lenses and optionally other optical components, onto the surface of a diffractive or non-specular reflective component, e.g. a diffraction grating or a surface from which a ray of incident light is scattered at many angles. The first lens component exhibits longitudinal chromatic dispersion, i.e. it focuses light at different distances from the lens depending on the wavelength of the light. In this way, the spectrum of measurement light reflected from the surface of the measurement object is spread across the surface of diffractive or non-specular reflective component.

[0073] Measurement light diffracted or reflected (i.e. scattered) from the surface of the diffractive or non-specular reflective component is imaged by a photodetector, i.e. a light sensor capable of sensing the intensity of light incident at different positions on the active surface of the photodetector. In other words, measurement light diffracted or reflected from each point on the surface of the diffractive or non-specular reflective component is focused onto a corresponding point on the active surface of the photodetector. In this way, the spatial intensity distribution of the measurement light diffracted or reflected from the diffractive or non-specular reflective component is captured by a photodetector,.

[0074] The displacement or 2D profile of the measurement object can be determined from the output of the photodetector by identifying the position at which reflected measurement light of the at least one marker is incident on the photodetector.

[0075] Multi- or hyperspectral reflectance data, i.e. the reflectance of the measurement object at a given wavelength or spectral band, can be determined from the intensity of light sensed at different positions on the photodetector by using on the position of the at least one marker on the photodetector as an offset, as will be explained in more detail below. The three-dimensional shape of the measurement object and full multi- or hyperspectral imaging can be synthesised from the 2D profile and multi- or hyperspectral reflectance data respectively by scanning the measurement light and measuring the reflected measurement light, as described above, across the surface of the measurement object.

[0076] It will also be appreciated that the present invention may function as a displacement sensor when only a single point of light is projected onto the measurement object. In this arrangement with a single point of light, spectral reflectance data may also be obtained and may be used to generate multi- or hyperspectral imaging data by scanning the point across both X and Y directions.

[0077] Figure 1 depicts an optical sensor 100 for displacement / 2D profile sensing and multispectral and / or hyperspectral imaging according to a first embodiment of the present invention.

[0078] The sensor 100 includes a light source 101 configured to generate polychromatic measurement light, which is projected onto the surface of a measurement object 103 to determine the displacement of the measurement object 103 relative to sensor and / or to determine a 2D profile of the measurement object 103, and to determine multi- or hyperspectral reflectance measurements of the surface of the measurement object 103. Figures 2Aand 2B, described below, provide more information about the spectral properties of the polychromatic measurement light. In general, while the term “light” is used, it should not be interpreted to be restricted to visible light, but also to possibly include other regions of the electromagnetic spectrum such as infrared and ultraviolet light.

[0079] The light source 101 is configured to project polychromatic measurement light onto the measurement object 103 along a projection axis 102. The Z-axis as shown in Figure 1 is defined as parallel to the optical axis 106 of the first lens component 105. Measurement light may be projected onto the measurement object 103 as a single point, for measuring the displacement of the surface of the measurement object 103 relative to the sensor 100, or across a line which extends into and out of the plane of the drawing of Figure 1 , i.e. parallel to the X-axis shown in Figure 1 . This is shown in more detail in Figure 3A, described below. It will be appreciated that it is not practically possible to project measurement line in an ideal zero-dimensional point or ideal one-dimensional line. Thus, where the terms “point” is used in the present context, it should be understood to encompass two-dimensional shapes with similar width and length, e.g. having a ratio of length to width less than 2:1. Where the term “line” is used in the present context, it should be understood to mean a two-dimensional shape with a large ratio of length to width, e.g. greater than 2:1 .

[0080] Where measurement light is projected across a line, rather than as a point, it may take the form of a continuous line, a series of discrete points spread across the line parallel to the X- axis, or a combination of discrete lines and points spread across the line parallel to the X- axis. The light source 101 preferably includes or consists of a laser generator or one or more LEDs combined with an aperture, e.g. a pinhole or slit. Where a continuous or broken line of measurement light is projected onto the surface of the measurement object 103, it may extend over a distance of, for example, 15mm parallel to the X-axis, and have a thickness, measured parallel to the Y-axis of less than 50 pm, and preferably less than 30 pm. The thickness of the projected measurement light in the Y-axis is inversely related to the sharpness of the image of the reflected measurement light on the photodetector. The sharper the image, the lower the uncertainty in the measurement.

[0081] Measurement light is projected along the projection axis 102 into a measurement region 104. The measurement region 104 is defined as the volume of space that extends along the projection axis, the first direction perpendicular to the projection axis in which the polychromatic measurement light is projected (i.e. parallel to the X-axis) and the second direction perpendicular to the projection axis and the first axis (i.e. parallel to the Y-axis) and from which reflected measurement light is focused onto the diffractive or non-specular reflective component by the first lens component and sensed by the photodetector, as explained in more detail below.

[0082] The measurement light could also be projected along the line 102 through the lens 105 or through a hole in the lens 105. In these cases, the light source 101 is no longer positioned between the lens 105 and object 103.

[0083] Measurement light reflected from the surface of the measurement object 103, i.e. from the intersection of the surface of the measurement objection 103 and the measurement region 104, is received at a first lens component 105. The first lens component 105 may be a singlet lens or a compound lens made up of multiple single lenses, or a compound optical component made up of one or more singlet lenses and other optical components. In the embodiment of Figure 1 , the first lens exhibits longitudinal chromatic dispersion, i.e. axial chromatic aberration, which means that light is focused at different distances from the lens, measured parallel to the optical axis of the lens, depending on the wavelength of the light. This is depicted in Figure 1 by a set of dashed lines indicating the path of rays of light of a first wavelength Ai and a set of dotted lines indicating the path of rays of a second wavelength 2.

[0084] In Figure 1 , the optical axis 106 of the first lens component 105 is aligned with and parallel to the projection axis 102, i.e. the optical axis 106 lies within the measurement region 104 and is parallel to the idealised line (in the case of a single point of measurement light being reflected) or plane (in the case where measurement light extends over a line) in which measurement light is projected. Alternatively, the optical axis 106 of the first lens component and the projection axis 102 may not be parallel. The projection axis may be arranged at another angle in the X-Z plane, where the angle between the optical axis of the first lens component and the projection axis is less than 90 degrees. This arrangement may lead to shadowing of high aspect ratio features on the surface of the measurement object, but allows for the light source and any necessary optics for the projection of measurement light onto the measurement object to be kept out of the path of measurement light reflected from the surface of the measurement object towards the first lens component 102.

[0085] The region of focus in which measurement light reflected from the measurement region is focused by the first lens component 105 is also aligned with and parallel to the optical axis 106. Furthermore, chromatic dispersion caused by the first lens component 105 leads to different wavelengths of measurement light being focused at different positions within the same region of focus. As a result, measurement light reflected from the intersection of the surface of the measurement object 103 and the measurement region 104 is dispersed across the region of focus according to wavelength, and the spectrally dispersed measurement light is offset within the region of focus according to the distance from the first lens component 105 to the intersection of the surface of the measurement object 103 and the measurement region 104.

[0086] The region of focus in which the reflected measurement light is offset and spectrally dispersed is coincident with the surface of a diffractive or non-specular reflective element 107. In other words, the measurement light reflected from the intersection of the surface of the measurement object 103 and the measurement region 104 is focused on and spectrally dispersed across the surface of the diffractive or non-specular reflective element 107 by the first lens component 105. The diffractive or non-specular reflective element 107 may be, for example, a diffraction grating or an object with a surface that scatters incident light rays across a range of directions.

[0087] The diffractive or non-specular reflective element 107 is imaged by the photodetector 110 via the second lens component 108 in order to measure the intensity of light in focus at different positions on the diffractive or non-specular reflective element 107. In other words, measurement light diffracted or reflected from each point on the surface of the diffractive or non-specular reflective component is focused onto a corresponding point on the active surface of the photodetector. In this way, the spatial intensity distribution of the measurement light diffracted or reflected from the diffractive or non-specular reflective component is captured by a photodetector.

[0088] The function of the diffractive or non-specular reflective element 107 is to allow the focused and spectrally dispersed measurement light to be imaged by the photodetector 110 at or close to a zero angle, i.e. such that the optical axis 109 of the second lens component 108, which is used to focus an image of the focused and spectrally dispersed measurement light onto the photodetector, is normal or within 5 degrees, 10 degrees or 15 degrees of normal to the active surface of the photodetector. In general, the sensitivity of photodetectors decreases as the angle of incidence of light on the photodetector increases. Thus, imaging at a low or zero angle, as described above, increases the sensitivity of the photodetector and allows for a more sensitive measurement of the intensity of light given the same output power of the light source 101. Greater angles may also be used, although the performance will not be as high as when the photodetector is positioned at a low or zero angle. The main point is that the diffractive or non-specular reflective component 107 should produce at least scattered or diffracted light that could be sensed by the photodetector.

[0089] Preferably, the diffractive or non-specular reflective element 107 is a diffraction grating. A diffraction grating, in particular a blazed diffraction grating, results in a larger proportion of the light incident on the diffractive or non-specular reflective element 107 being redirected within the angle of acceptance of the second lens component 108 compared to a non-specular reflective component. In Figure 1 a reflective diffractive or non-specular reflective element 107 is depicted, but a transmissive diffractive element may alternatively be used. Figures 2Aand 2B show exemplary spectral power density plots for polychromatic measurement light. While the invention it not limited to spectral power densities depicted in either Figure 2A or 2B, they can be used to illustrate certain aspects of the invention.

[0090] Figure 2A depicts a first example of polychromatic measurement light, which may be output by a supercontinuum white laser source. In the example of Figure 2 the spectrum extends from approximately 400nm to 2300nm, i.e. from ultraviolet to infrared light. The spectral range of a light source used in the present invention extends at least across the range of wavelengths of light for which multi- or hyperspectral imaging is to be carried out. As is typical for a supercontinuum spectrum, the wavelength of the source light is visible as a clear peak 201 in the spectrum. This source peak may be used as a marker, as described above. Alternatively, or additionally, one or more markers may be produced by one or more separate light sources and combined with the measurement light using a beam combiner, for example. Such a marker, produced by a separate light source, may have a wavelength within the spectrum used for multi- and / or hyperspectral imaging, as shown in Figure 2A, or may have a wavelength outside the spectrum used for multi- and / or hyperspectral imaging, as shown by peak 202 in Figure 2B.

[0091] In general, a marker is a feature of the spectral profile of the measurement light that corresponds to a known wavelength or spectral band, i.e. range of wavelengths, and can be clearly identified in the spectrum of measurement light reflected from the surface of the measurement object. Practically, any feature of the spectral profile of the measurement light that can be reliably identified in the reflected measurement light can be used as a marker. As such, the specific features of a given spectral profile that may be used as a marker depend on the reflectance properties of the measurement object. Both solid and liquid surfaces, which the sensor of the present invention may be used to measure the profile or displacement of, have relatively smooth reflectance spectra, i.e. the reflection of the measurement light generally does not cause any sharp spectral intensity peaks in the reflected measurement light. Therefore, if a marker (or markers) with a relatively sharp intensity peak is inserted or is present in the polychromatic measurement light, this will generally be the only sharp intensity peak in the reflected measurement light. A marker may also be defined by its use, i.e. a feature of the spectral profile of the projected and reflected measurement light that is used to determine the relative position from which the measurement light was reflected, i.e. to determine the displacement and / or profile of the measurement object, and / or used as an offset to determine the wavelength of measurement light incident and sensed at each point on the surface of the photodetector.

[0092] A marker may be, for example, a single wavelength of narrow spectral band that has a clearly higher or lower intensity than other wavelengths of measurement light in both the measurement light projected onto the measurement object and reflected from the surface of the measurement object, as shown in the example of Figure 2A. In general, a feature may be suitable for use as a marker if it has an intensity that is 5%, 10%, 15%, 30%, or 50% higher or lower than any other wavelength within a region of the polychromatic measurement light that is projected onto the measurement object within the measurement region. The necessary sharpness of the peak depends on the reflectance characteristics of the measurement object 103 to be measured. A measurement object with a smooth reflectance spectrum does not require as sharp an intensity peak for the marker (or markers) as a measurement object with a less smooth reflectance spectrum. In principle, if the width of the marker is wide and comparable to the (existing) spectral reflectance peaks of the object 103, the exact position of the maximum of the reference peak is affected by the composition of the object 103, which makes the distance measurement inaccurate.

[0093] Alternatively, or additionally, a marker may be a particularly sharp peak, trough, or step in the spectral profile, which may be identified according to a sufficiently large (magnitude) value of the first or second derivative of the spectral profile. The size of the increase or decrease per wavelength in the illumination light spectrum should be greater than any local change in the real reflectance spectrum of the surface. These peaks, troughs or steps may be “natural” features of the polychromatic measurement light, i.e. arising normally in the course of generating the polychromatic measurement light (e.g. Figure 2A), or “artificial” features, i.e. features separately introduced into the polychromatic measurement light by, e.g. combining light from multiple light sources (e.g. Figure 2B). The advantage of using artificial features is that they may be generated with sufficiently distinct sharpness, intensity, or other distinguishing property, from the rest of the polychromatic measurement light, and may therefore allow the sensor to use the same features of the measurement light for more different types of measurement object with different reflectance properties. The ability to distinguish markers within the measurement light may also be enhanced by including multiple markers within the polychromatic measurement light, or by designating multiple smaller intensity peaks already present in the polychromatic measurement light as markers. Since the wavelength separation of the markers is known, the distance between the markers in the image formed on the photodetector can also be used to identify the markers.

[0094] Figure 3A is a perspective drawing demonstrating projection of polychromatic measurement light onto a measurement object 103. Figure 3A shows a single feature on the surface of the measurement object, but it will be appreciated that the optical sensor of the present invention is capable of measuring the 2D profile of many different shapes of measurement objects. Measurement light is projected along the projection axis 102, which is parallel to the Z-axis shown in the drawings. Figure 3A shows an example in which measurement light is projected across a line which extends parallel to the X-axis. Measurement light is reflected from the surface of the measurement object 103 at the points where the surface of the measurement object intersects the incoming line of light. In the case of Figure 3A, this is shown by lines 301 . It will be readily apparent to the skilled person, in view of the rest of the disclosure of this document, how different patterns of light, e.g. a series of points or points and lines as discussed above, can be projected onto the measurement object in a similar manner.

[0095] Measurement light reflected from the surface of the measurement object 103 at line 301 is scattered from the surface of the measurement object 103. Some of the reflected (scattered) measurement light is incident on the first lens component 105 as depicted in Figure 1. When the intersection of the surface of the measurement object 103 and the projected measurement light falls within the measurement region 104, i.e. when the surface of the measurement object 103 intersects the measurement region 104, measurement light reflected from the intersection 301 is focused by the first lens component 105 onto the diffractive or non-specular reflective element 107, as described above.

[0096] As mentioned above, the thickness of the projected measurement light parallel to the Y-axis is preferably as small as possible. On the other hand, the width of the projected measurement light parallel to the X-axis could be large, since it does not affect the sharpness of the image projected onto the photodetector 110. When using a laser source as the light source 101 , the spread or divergence of measurement light parallel to the Y-axis can be made small which gives a sharp image line at all positions on the photodetector 110. With other light sources, such as LEDs, the radiance of the light source is small and in order to get enough light power to the measurement region the numerical aperture, i.e. divergence, of the illumination optics must be increased. This is illustrated in Figures 3B and 3C, which illustrate possible configurations of light source 101 of Figure 1 and 501 of Figure 5, described below. The increase in numerical aperture parallel to the X-axis does not affect the image resolution. The increased numerical aperture parallel to the Y-axis increases the thickness of the measurement region when the distance of the surface is not exactly at the focus point of the illumination optics. As a result, a reasonably thin measurement volume in Y- direction at all Z-positions within the measurement region could be achieved also with an LED light source and narrow line slit 311 , 313 when the numerical aperture of the illumination optics is small parallel to the Y-axis but maximal parallel to the X-axis. If the designed wavelength dispersion range 314, i.e. the useable or used range over which light is dispered, is 5 mm and the cone angle of the lens 105 in Y-direction is 20 degrees, the Y-axis thickness 315 of the measurement region of 20 pm gives an Z-position uncertainty of around 55 pm, which is 1 ,1 % of the wavelength range. When this cone angle is larger the uncertainty is smaller. Imaging optics 105 should be implemented so that very low cone angles (e.g lower than +- 5 ... 10 degrees) are not used, e.g. by using a central baffle, and the maximum cone angle is made as large as possible. Furthermore, in many applications a lower wavelength resolution than 1 .2 % is very often useful, thus a Y-axis thickness of 50 pm or less is feasible for lower resolution application.

[0097] Figures 4Aand 4B depict the image of the measurement light that is focused on the diffractive or non-specular reflective surface 107 and on the photodetector 110. The photodetector may be formed of an array of pixel sensors in a linear grid arranged across the X and Z axes depicted in Figure 4A. The pixel sensors may be grouped according to their X-coordinate, i.e. into columns. In Figure 4A, 25 columns are depicted. However, in practice, a much higher number of pixel sensors will be used, for example a 4 megapixel sensor, with pixel sensors arranged in a 2048x2048 grid may be used. A grouping of pixel sensors may be a single column of pixel sensors or a group of neighbouring columns. The number of pixel sensors used is a balance between sensitivity and resolution. Larger pixel sensors are more sensitive and may therefore provide better accuracy and noise performance, but smaller pixel sensors allow for more pixel sensors in a given area, thereby increasing resolution. The photodetector may be a CMOS sensor, for example. While the above description refers primarily to photodetectors with pixel sensors, it will be appreciated that any type of photodetector may be used provided it is possible to logically group intensity readings according to the X-axis position from which they were reflected. Furthermore, if the photodetector is not arranged at a zero angle with respect to the diffractive of non-specular reflective element 107, the groups, e.g. columns of pixel sensors, referred to above may not be aligned parallel to the Z-axis, but may be tilted. However, the invention still functions as long as the light incident on each group corresponds to the same X-axis position within the measurement region 104 from which measurement light is reflect from the surface of the measurement object 103.

[0098] Figure 4B shows a plot of intensity of light received at the photodetector 110 against the Z- position at which the light is received. As discussed above, if the photodetector is not aligned with the Z-axis, the Z-position referred to here refers more generally to a position within the grouped intensity readings derived from the same X-axis point or region from which measurement light is reflected from the surface of the measurement object. Two intensity profiles 401 , 402 are depicted in Figure 4B corresponding to two of the columns 401 , 402 depicted in Figure 4A. In the example depicted in Figure 4B, the marker within each column is clearly discernible as an intensity peak. As discussed above, the marker may be discernible in other ways. The Z-position of the marker in column 401 is labelled Zi and the Z-position of the marker in column 402 is labelled Z2. Positions Z1 and Z2 correspond to the distance between the sensor and of the surface of the measurement object 103 from which measurement light is reflected at the X-coordinate corresponding to each column 401 , 402 respectively. Furthermore, positions Z1 and Z2 can be used to determine the offset of the dispersed spectrum received around the marker. In other words, the distance from the sensor to the surface of the measurement object 103 is determined based on the Z-position of the marker on the photodetector 110 and the reflectance spectrum of the surface is measured around the known wavelength of the marker. The lateral magnification of the lens 105 typically varies based on the distance of the surface point to the lens 105. This affects the mutual distance of different wavelengths on the surface of the diffractive / scattering element 107. However, this effect can be corrected by calibrating the system to different distances of the object 103.

[0099] Figure 5 depicts an optical sensor 500 according to a second embodiment of the invention. Reference numerals 501-510 refer to features which perform the same or a corresponding function as features 101-110 of the optical sensor 100 of the first embodiment. Light source 501 , projection aixs 502, measurement object 503, measurement region 504, first lens component 505 and optical axis 506 of the first lens component 505 are arranged and function as described above with respect to the equivalent components of optical sensor 100 of Figure 1 .

[0100] Optical sensor 500 differs from optical sensor 100 in that one or more specular reflectors 511 are positioned between the first lens element 505 and two diffractive or non-specular reflective elements 507a, 507b. In Figure 5, a single reflector 511 with two specular reflective surfaces is depicted, but it will be appreciated that other equivalent arrangements are possible, for example each specular reflective surface may be provided by a separate component. Compared to the optical sensor 100, reflector 511 enables light received at the first lens component on both sides of the measurement region 504 to be directed towards a diffractive or non-specular reflective elements 507a, 507b, which can both be imaged by a photodetector to sense the displacement or 2D profile of the measurement object 503 and the spectral reflectance of the surface of the measurement object 503. This essentially doubles the amount of measurement light entering the sensor, providing a higher-accuracy sensor with a higher signal-to-noise ratio for a given intensity of measurement light emitted by the light source 501. It also provides more redundancy to the spectral and distance measurement and increases the usable angle range to the surface 503. This all increases the overall accuracy of the system.

[0101] In the example depicted in Figure 5, both diffractive or non-specular reflective elements 507a, 507b are imaged by a single photodetector 510 via beam combiner 508c and second lens components 508a, 508b and 508d, which focus light diffracted or reflected from the diffractive or non-specular reflective elements 507a, 507b onto the photodetector, preferably at a zero angle as described above. Alternatively, diffractive or non-specular reflective elements 507a, 507b may be imaged by separate photodetectors.

[0102] In the example shown in Figure 5, the specular reflectors 511 are angled at 45 degrees to the optical axis of the first lens component 505 such that the surface of the diffractive or non- specular reflective elements 507a, 507b are parallel and can both be imaged by the same photodetector 510 at a zero angle, as discussed above. In the example of Figure 5 where diffractive or non-specular reflective elements 507a, 507b are both imaged by the same photodetector 510, the image of each diffractive or non- specular reflective elements 507a, 507b is incident on a different non-overlapping section of the photodetector, e.g. on different halves of the photodetector. The photodetector can be logically split into two, with each logical photodetector corresponding one of the nonoverlapping sections on which the images of diffractive or non-specular reflective elements 507a, 507b are incident. The process for determining the displacement / 2D profile and spectral reflectance data is carried out for each logical photodetector as described above in the context of optical sensor 100. Where the diffractive or non-specular reflective elements 507a, 507b are imaged by different photodetectors, the specular reflectors 511 need not be angled at 45 degrees relative to the optical axis of the first lens component 505 as described above.

[0103] Figure 6 is a flow chart depicting a method for multispectral and / or hyperspectral imaging of the surface of a measurement object and for determining a two-dimensional profile of the measurement object using an optical sensor according to the present invention.

[0104] At step 601 , the locations on the active surface of the photodetector 110, 510 at which the at least one marker is in focus are determined. Where the photodetector 110, 510 is a pixelbased sensor, this step may include receiving light intensity data which includes data points that define a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position. The two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, i.e. the Z-axis as shown in the drawings, and more generally, a direction corresponding to the projection axis 102, 502. The second coordinate corresponds to a second direction perpendicular to the first coordinate, i.e. the X-axis as shown in the drawings or, more generally, a direction corresponding to a line perpendicular to the projection axis 102 over which measurement light is projected. The received light intensity data is divided into a plurality of groups according to the second coordinates of the light intensity data. Each group corresponding to a single second coordinate or a range of adjacent second coordinates, e.g. columns based on the X-axis coordinates as described above. Within each group, the first coordinate of the at least one marker is identified. This may be a single pixel with the highest intensity, where the group is a single column of pixels within each group and the marker has the highest intensity of any wavelength in the projected measurement light.

[0105] At step 602, a two-dimensional profile of the measurement object is determined by compiling the locations at which the at least one marker is in focus determined in step 601 . As can be seen in Figure 4A, for example, the Z-position of the markers (indicated by a black square in each column) corresponds to the profile of the measurement object. Determining the two- dimensional profile may also include interpolating the determined locations to generate a continuous two-dimensional profile from the sampled profile determined by compiling the marker locations from each group.

[0106] At step 603, multispectral and / or hyperspectral imaging of the surface of a measurement object is performed by determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker. The changing height (i.e. position along the projection axis) of the measurement object across its profile causes the dispersed reflectance spectrum to be offset on the active surface of the photodetector 110, 510 by the height. Therefore, the height within each group, i.e. the marker location determined at step 601 , can be used to correct the offset within each group. Calibration of the sensor or selection of a first lens component 103, 503 with known dispersive properties enables the absolute wavelength at each position relative to the marker position to be identified. A multi- or hyperspectral image can be therefore be obtained based on the measured light intensity at different positions relative to the marker.

[0107] In the foregoing description and the context of the present invention, the terms “multispectral imaging” and “hyperspectral imaging” refer to the collection and processing of electromagnetic radiation across a broader spectrum at a plurality of spectral bands broader than or greater in number than conventional three-colour imaging, e.g. RGB image sensors. In the art, the boundary between the definition of multispectral and hyperspectral imaging is poorly defined. “Multi-spectral imaging” may refer to this type of collection and processing of electromagnetic radiation in a relatively small number of spectral bands, e.g. 4 to 15 bands, which may be discrete bands separated by a range of wavelengths that are not imaged. “Hyperspectral imaging” may refer to the collection and processing of a relatively large number of bands, e.g. 15 or more spectral bands, which may be contiguous spectral bands. The term “lens” should generally be understood to refer to an optical device that focuses or disperses light by means of refraction, and may be a singlet lens, a compound lens, or a combination of singlet and / or compound lenses with other optical components.

[0108] The term “measurement light” refers to light emitted from a light source for the purpose of measuring the displacement / 2D profile or multi-Zhyperspectral reflectance of a measurement object. The term “polychromatic” means electromagnetic radiation made up of many different wavelengths of radiation, and includes electromagnetic radiation with continuous ranges of wavelengths of radiation as well as multiple discrete, i.e. separate, ranges of wavelengths.

Claims

1. Claims1 . An optical sensor for multispectral and / or hyperspectral imaging of the surface of a measurement object and for determining a displacement or a two-dimensional profile of the measurement object, the optical sensor configured to: project polychromatic measurement light into a measurement region, wherein the polychromatic measurement light includes a plurality of spectral bands for multispectral and / or hyperspectral imaging and at least one marker, and wherein the at least one marker is an identifiable feature in the spectral profile of the measurement light and wherein the at least one marker has a known wavelength or spectral band; focus measurement light reflected from the measurement region onto the surface of a first diffractive or non-specular reflective component using a first lens component with longitudinal chromatic dispersion such that measurement light of a given wavelength reflected from the measurement region is in focus at a given position on the surface of the first diffractive or non-specular reflective component depending on i) the displacement of the surface of the measurement object relative to the optical sensor, and ii) the given wavelength of the reflected measurement light; image measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component onto an active surface of a photodetector, wherein the photodetector is configured to sense the intensity of light incident at different positions on the active surface of the photodetector.

2. The optical sensor of claim 1 , wherein the optical sensor is configured to project the polychromatic measurement light into the measurement region along a projection axis and wherein the projection axis is aligned with the optical axis of the first lens component.

3. The optical sensor of claim 2, wherein the optical sensor is configured to project the polychromatic measurement light in a plurality of points spread along first direction that extends perpendicular to the projection axis, as a line spread across the first direction that extends perpendicular to the projection axis, or as a combination of points and lines spread across the first direction that extends perpendicular to the projection axis.

4. The optical sensor of claim 3, wherein the measurement region is defined as the area or volume of space that extends along the projection axis and the first direction perpendicular to the projection axis in which the polychromatic measurement light is projected and from which reflected measurement light is focused onto the first diffractive or non-specular reflective component by the first lens component and sensed by the photodetector.

5. The optical sensor of claim 4, wherein the measurement region and the surface of the first diffractive of non-specular reflective component are parallel and aligned along the optical axis of the first lens component.

6. The optical sensor of any of claims 3 to 5, wherein the dimension of the measurement region measured perpendicular to the projection axis and the first direction is less than 50 pm, less than 40 pm, less than 30pm, less than 20pm or less than 10pm.

7. The optical sensor of any of claims 3 to 6, wherein the optical sensor comprises a laser line generator or one or more LEDs in combination with a thin slit for generating the polychromatic measurement light and / or at least one marker.

8. The optical sensor of any preceding claim, wherein the wavelength or spectral band of the at least one marker falls within one or more of the plurality of spectral bands for multispectral and / or hyperspectral imaging.

9. The optical sensor of any preceding claim, wherein one or more markers of the at least one marker are separated from the plurality of spectral bands for multispectral and / or hyperspectral imaging in the frequency domain.

10. The optical sensor of claim 8 or 9, wherein the intensity of measurement light within the wavelength or spectral band of the at least one marker is at least 5 % higher or lower than measurement light of wavelengths falling outside of the wavelength of narrow spectral band of the marker.11 . The optical sensor of any of claims 8 to 10, wherein the at least one marker is identifiable based on the first or second derivative of the spectrum sensed by the optical sensor.

12. The optical sensor of any preceding claim, wherein the optical sensor is configured to focus measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component or grating onto the active surface of the photodetector using a sensor lens component, wherein the optical axis of the sensor lens component is normal or within 5 degrees, 10 degrees, 15 degrees, 30 degrees, or 45 degrees of normal to the active surface of the photodetector.

13. The optical sensor of any preceding claim, wherein the optical sensor is further configured to: focus measurement light reflected from the measurement region onto the surface of a second diffractive or non-specular reflective component using the first lens component such that measurement light of a given wavelength reflected from the measurement region is in focus at a given position on the surface of the second diffractive or non-specular reflective component depending on i) the displacement of the surface of the measurement object relative to the optical sensor, and ii) the given wavelength of the reflected measurement light; and image measurement light diffracted or reflected from the surface of the second diffractive or non-specular reflective component or grating onto the active surface of the photodetector.

14. The optical sensor of claim 13, wherein the optical sensor is configured to: image measurement light diffracted or reflected from the surface of the first diffractive or non-specular reflective component onto a first region of the active surface of the photodetector; and image measurement light diffracted or reflected from the surface of the second diffractive or diffusely reflective component onto a second region of the active surface of the photodetector; wherein the first region of the active surface of the photodetector and the second region of the active surface of the photodetector are non-overlapping.

15. The optical sensor of claim 14, wherein: the optical sensor is configured to focus measurement light reflected from the measurement region onto the surface of the first diffractive or non-specular reflective component and the second diffractive or non-specular reflective component using a first specular reflective surface and a second specular reflective surface; the first specular reflective surface is configured to reflect light received from a first side of the measurement region onto the surface of the first diffractive or non- specular reflective component; and a second specular reflective surface of the at least two specular reflective surfaces being configured to reflect light received from a second side of the measurement region; the first specular reflector is oriented at a 45-degree angle extending in a first direction relative to the optical axis of the first lens component; and the second specular reflector is oriented at a 45-degree angle extending in a second direction, opposite to the first direction, relative to the optical axis of the first lens component.

16. The optical sensor of any of claims 1 to 12, wherein the optical sensor is further configured to: focus measurement light reflected from the measurement region onto the surface of a second diffractive or non-specular reflective component using the first lens component such that measurement light of a given wavelength reflected from the measurement region is in focus at a given position on the surface of the second diffractive or non-specular reflective component depending on i) the displacement of the surface of the measurement object relative to the optical sensor, and ii) the given wavelength of the reflected measurement light; and focus measurement light diffracted or reflected from the surface of the second diffractive or non-specular reflective component onto an active surface of a second photodetector.

17. The optical sensor of any preceding claim, wherein the optical sensor is further configured to:determine the two-dimensional profile of the measurement object based on the locations at which the at least one marker is in focus on the active surface of the photodetector of the optical sensor; and determine multispectral and / or hyperspectral imaging data of the surface of the measurement object based on the intensity of light received at locations surrounding the at least one marker on the active surface of the photodetector.

18. The optical sensor of claim 17, wherein the optical sensor is configured to determine the locations at which the at least one marker is in focus by: receiving light intensity data from the optical sensor, the light intensity data including a plurality of data points, each data point defining a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position, wherein the two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, and a second coordinate, which corresponds to a second direction perpendicular to the first coordinate; grouping the received light intensity data into a plurality of groups according to the second coordinates of the light intensity data, and each group corresponding to a single second coordinate or a range of adjacent second coordinates; and identifying the first coordinate of the at least one marker within each group.

19. The optical sensor of claim 18, wherein the optical sensor is configured to determine the two-dimensional profile of the measurement object by: compiling the determined locations at which the at least one marker is in focus; and, optionally, interpolating the determined locations to generate a continuous two-dimensional profile.

20. The optical sensor of claim 18 or 19, wherein the optical sensor is configured to carry out multispectral and / or hyperspectral imaging of the surface of a measurement object by: determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker.21 . The optical sensor of any of claims 18 to 20, wherein the optical sensor is further configured to: repeatedly determine the two-dimensional profile of the measurement object at different positions on the measurement object and generating output data comprising the determined two-dimensional profiles and the displacements between the determined two-dimensional profiles.

22. The optical sensor of claim 21 , wherein the optical sensor is further configured to: process the determined two-dimensional profiles of the measurement object and displacements between the determined two-dimensional profiles to generate the three- dimensional model of the measurement object.

23. A system comprising the optical sensor of any preceding claim and at least one processing unit, wherein the at least one processing unit is configured to: determine the two-dimensional profile of the measurement object based on the locations at which the at least one marker is in focus on the active surface of the photodetector of the optical sensor; and determine multispectral and / or hyperspectral imaging data of the surface of the measurement object based on the intensity of light received at locations surrounding the at least one marker on the active surface of the photodetector.

24. The system of claim 23, wherein the at least one processing unit is configured to determine the locations at which the at least one marker is in focus by: receiving light intensity data from the optical sensor, the light intensity data including a plurality of data points, each data point defining a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position, wherein the two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, and a second coordinate, which corresponds to a second direction perpendicular to the first coordinate;grouping the received light intensity data into a plurality of groups according to the second coordinates of the light intensity data, and each group corresponding to a single second coordinate or a range of adjacent second coordinates; and identifying the first coordinate of the at least one marker within each group.

25. The system of claim 24, wherein the at least one processing unit is configured to determine the two-dimensional profile of the measurement object by: compiling the determined locations at which the at least one marker is in focus; and, optionally, interpolating the determined locations to generate a continuous two-dimensional profile.

26. The system of claim 24 or 25, wherein the at least one processing unit is configured to carry out multispectral and / or hyperspectral imaging of the surface of a measurement object by: determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker.

27. The system of any of claims 24 to 26, wherein the at least one processing unit is further configured to: repeatedly determine the two-dimensional profile of the measurement object at different positions on the measurement object and generating output data comprising the determined two-dimensional profiles and the displacements between the determined two-dimensional profiles.

28. The system of claim 27, wherein the at least one processing unit is further configured to: process the determined two-dimensional profiles of the measurement object and displacements between the determined two-dimensional profiles to generate the three- dimensional model of the measurement object.

29. A method for multispectral and / or hyperspectral imaging of the surface of a measurement object and for determining a two-dimensional profile of the measurement object using the optical sensor of any preceding claim, the method comprising:determining the two-dimensional profile of the measurement object based on the locations at which the at least one marker is in focus on the active surface of the photodetector of the optical sensor; and determining multispectral and / or hyperspectral imaging data of the surface of the measurement object based on the intensity of light received at locations surrounding the at least one marker on the active surface of the photodetector.

30. The method of claim 29, wherein the method comprises determining the locations at which the at least one marker is in focus by: receiving light intensity data from the optical sensor, the light intensity data including a plurality of data points, each data point defining a two-dimensional position on the active surface of the photodetector of the optical sensor and the intensity of light sensed at the two-dimensional position, wherein the two-dimensional position is defined by a first coordinate, which corresponds to a first direction along which polychromatic measurement light is spectrally dispersed by the first lens component of the optical sensor, and a second coordinate, which corresponds to a second direction perpendicular to the first coordinate; grouping the received light intensity data into a plurality of groups according to the second coordinates of the light intensity data, and each group corresponding to a single second coordinate or a range of adjacent second coordinates; and identifying the first coordinate of the at least one marker within each group.31 . The method of claim 30, wherein determining the two-dimensional profile of the measurement object comprises: compiling the determined locations at which the at least one marker is in focus; and, optionally, interpolating the determined locations to generate a continuous two-dimensional profile.

32. The method of claim 30 or 31 , wherein multispectral and / or hyperspectral imaging of the surface of a measurement object comprises: determining the wavelength of light received at each first coordinate with each group based on the identified first coordinate of the at least one marker and the wavelength of the at least one marker.

33. The method of any of claims 30 to 32, wherein the method further comprises: repeatedly determining the two-dimensional profile of the measurement object at different positions on the measurement object and generating output data comprising the determined two-dimensional profiles and the displacements between the determined two-dimensional profiles.

34. The method of claim 33, wherein the method further comprises: processing the determined two-dimensional profiles of the measurement object and displacements between the determined two-dimensional profiles to generate the three-dimensional model of the measurement object.

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