Imaging system and method regarding three-dimensional imaging based on light triangulation

Abstract

To provide a method for supporting reduction of distortions in an imaging system for three-dimensional imaging based on light triangulation.SOLUTION: An imaging system 500 comprises a camera 530 and a light source 510 configured to provide an illumination of an object 520 including structured light 511. The structured light 511 intersects a virtual volume 524 including the object 520, the virtual volume 524 corresponding to a volume where the object 520 that the imaging system is configured to image is present during the imaging. At least during the imaging by the camera 530, stray light from the light source 510 is prevented from reaching the virtual volume 524 within a field of view 532 of the camera 530. In the imaging system 500, this is accomplished by light shields 550a, 550b arranged outside the structured light 511 between the light source 510 and the virtual volume 524.SELECTED DRAWING: Figure 5A

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments herein relate to an imaging system for three-dimensional imaging based on optical triangulation. [Background technology]

[0002] Industrial vision cameras and systems for factory and logistic automation may be based on three-dimensional (3D) machine vision, where 3D images of scenes and / or objects are acquired. By 3D images is meant images that do not, or at least do not, comprise information about pixels only in two dimensions (2D), such as intensity and / or color, as in conventional images, but also comprise "height" or "depth" information. That is, each pixel of the image may comprise information that is associated with the pixel's position and maps to the position of what is imaged, e.g. the object. Processing may then be applied to extract information about the object's properties, i.e. the object's 3D properties, from the 3D image and convert it, for example, into various 3D image formats. Such height information may be referred to as range data, which may thus correspond to data from a height measurement of the object being imaged, or in other words from a range or distance measurement of the object. Alternatively or additionally, the pixels may comprise information about material properties, such as, for example, light scattering or reflection of certain light wavelengths in the imaged area.

[0003] Thus, the pixel value may for example relate to the intensity and / or to range data and / or to material properties of the pixel.

[0004] Line-scan image data arises when image data of an image is scanned or provided one line at a time, for example by a camera with a sensor configured to sense and provide image data one line pixel at a time. A special case of line-scan image is image data provided by optical triangulation using a "sheet of light" that illuminates the object being scanned with light. The sheet of light intersecting the object results in a line of light that is projected on the object and reflected. Typically, a laser is used, resulting in a laser line that is reflected on the object and thereby towards the camera. Although lasers are often preferred, and therefore optical triangulation is sometimes referred to as laser triangulation, other light sources capable of providing a "sheet of light", i.e. a plane of light, or other structured light can also be used. That is, light sources capable of providing light that remains focused and does not diverge too much, or in other words light that is "structured", e.g. light provided by a laser or a light emitting diode (LED). In general, optical triangulation as described above is therefore based on using structured light for illumination.

[0005] Structured light corresponds to a defined, typically predefined, pattern of light for illumination of an object as part of optical triangulation. Often, as shown above, structured light is in the form of a light plane that, when illuminated on the object surface, leads to a line of light projected on the object surface and reflected and imaged by the camera. Other examples of structured light include light edges of illumination provided over a larger area, which can be considered to correspond to a thick line of light illuminating the object, and the light edges projected on the object correspond to the light lines in the case of a light plane and may be used accordingly. Other structured light may also be used for illumination of an object in optical triangulation, leading to lines, dots, grids, bars, etc., that are projected on the object surface and reflected.

[0006] In either case, the structure of the structured light makes it possible to identify real-world locations where reflections on object surfaces occur, e.g., at a light plane if the structured light corresponds to a light plane, and to map these locations to an image sensor and to an image where light, e.g., reflected light lines, are acquired. As should be appreciated, this is the underlying principle of optical triangulation-based 3D imaging.

[0007] 3D machine vision systems are often based on optical triangulation as described above. In such systems, an object has a light source that shines structured light, such as a plane of light that results in a line of light on the object, along which the 3D properties of the object can be obtained, corresponding to the object's profile. By scanning the object with such a line, a line scan of the object can be performed, corresponding to multiple profiles, and the 3D properties of the entire object can be obtained, if the line and / or object are moved.

[0008] Typically, to generate a 3D image based on optical triangulation, reflected light from an object to be imaged is acquired by an image sensor of a camera, leading to the imaging of a line of light projected on the object, for example. Intensity peaks are then detected in the resulting image data. The peaks occur at positions, in sensor coordinates, that correspond to the places on the object that reflected the structured light acquired by the image sensor. Due to a mapping, typically known from a calibration procedure during the setup of the imaging system, between the real world coordinates to which the structured light is provided and the image sensor coordinates where the reflected structured light is acquired, the image data contains said height information for the object where the reflection occurred. Typically, but not necessarily, the imaging system is set up such that intensity peaks for the reflected light should occur and be expected for each row of sensors, with the positions within the row mapping to height.

[0009] From the above, it is observed that intensity peaks in the image data other than those resulting from the optical triangulation itself can cause problems and, if they occur, should not be detected and / or used at least as intensity peaks belonging to the optical triangulation itself. Also, too strong intensity peaks that saturate the image sensor pixels can cause problems and make it difficult to detect the peaks with the desired resolution. Results from unwanted intensity peaks such as those mentioned above can result in artifacts in the resulting profile images and also in the resulting full 3D image formed from the multiple profile images, for example artifacts in the form of "spikes" in the 3D image.

[0010] Unwanted intensity peaks, which may be caused for example by secondary reflections due to structured light and / or very strong specular reflections, are typically mitigated in the prior art by solutions "post-image sensing", i.e. by processing the resulting image data, for example before or as part of an intensity peak detection algorithm. The challenge is to find and / or identify only "necessary" intensity peaks for optical triangulation, resulting from specular reflections on the object surface due to structured light, and / or to not use or avoid using unnecessary intensity peaks for optical triangulation, such as intensity peaks caused by secondary reflections due to structured light. It is recognized that if the unnecessary intensity peaks are used as necessary, i.e. "as if they were necessary for optical triangulation", it is not possible to arrive at a correct 3D imaging of the object.

[0011] Since structured light itself is required and used by optical triangulation, it is natural to focus on "post-image sensing" strategies to identify the required intensity peaks. Spurious reflections often cause the above-mentioned types of distortions in the form of "spikes", i.e. very narrow peaks in the 3D image, and therefore median filtering or the like is often used in the prior art to mitigate problems with spikes "post-image sensing".

[0012] Another "pre-image sensing" prior art solution is directed to mitigating problems from specular reflection of structured light by using polarized light. For example, while this reduces specular reflection, it can still provide diffuse reflection that can be used for light triangulation. A drawback with this is that polarizing filters to achieve polarization cause the removal of a large amount of the generated light, making it less energy efficient.

[0013] Despite these existing solutions directed at mitigating the negative effects from specular reflection during optical triangulation-based 3D imaging, there are still problems with distortions, such as the "spikes" mentioned above, especially when the object being imaged has a highly reflective surface. Summary of the Invention [Problem to be solved by the invention]

[0014] In view of the above, it is an object to provide one or more improvements or alternatives to the prior art, such as facilitating the elimination and / or reduction of distortions, such as "spikes," in 3D images from 3D imaging systems based on optical triangulation. [Means for solving the problem]

[0015] According to a first aspect of an embodiment herein, the object is achieved by an imaging system for three-dimensional imaging of an object based on optical triangulation. The system comprises a camera and a light source configured to provide illumination of the object with structured light. The camera is positioned with respect to the provided structured light such that the camera can capture in an image the structured light (511) reflected from the object as part of said optical triangulation, whereby according to the optical triangulation, the position of the reflected structured light captured in the image maps to a real-world position where the structured light is reflected by the object. The structured light intersects with a virtual volume containing the object, the virtual volume corresponding to a volume in which one or more objects are present during imaging, including said object, which the imaging system is configured to image. The imaging system further comprises a light blocker positioned outside the structured light between the light source and said virtual volume, the light blocker being positioned such that the light blocker blocks stray light from the light source and thereby prevents it from reaching the virtual volume within the field of view of the camera.

[0016] In some embodiments, the light blocking body has one or more major light blocking surfaces that have an extension in one or more directions perpendicular to the direction of illumination of the structured light.

[0017] In some embodiments, the occluder extends outside the structured light between the light source and the virtual volume, with the distance to the structured light decreasing in the direction of the virtual volume.

[0018] In some embodiments, the light blocking body is positioned outside the structured light at a distance to the structured light, thereby avoiding the light blocking body blocking light of illumination closer to the structured light than where the illumination has dropped to 5% of its maximum intensity.

[0019] In some embodiments, the light blocking body is positioned outside the structured light at a distance from the structured light, but close enough that the light blocking body at least blocks light from the illumination where the illumination has dropped to 1% of its maximum intensity.

[0020] In some embodiments, the light blocking body comprises: a first light blocking portion arranged on a first side of the structured light in the direction of the camera; and / or A second light blocking portion is provided disposed on a second side of the structured light, facing away from the camera.

[0021] In some embodiments, the first blocker portion is positioned outside at least a portion of the field of view of the camera covering the structured light in the virtual volume.

[0022] In some embodiments, the occluder is closest to the structured light where the occluder is closest to the virtual volume and / or where the occluder is closest to where the illumination has a focus.

[0023] According to a second aspect of an embodiment herein, the object is achieved by a method for supporting reduction of distortion in three-dimensional imaging based on optical triangulation, said three-dimensional imaging being performed by an imaging system. The imaging system comprises a camera and a light source for providing illumination of an object to be imaged. Said illumination comprises structured light used for optical triangulation. The camera is positioned with respect to the provided structured light such that the imaging camera acquires in an image the structured light reflected from the object as part of said optical triangulation, whereby according to the optical triangulation, the position of the reflected structured light acquired in the image maps to a real-world position where the structured light was reflected by the object. The structured light intersects with a virtual volume including the object, the virtual volume corresponding to a volume in which one or more objects are present during imaging, including said object, which the imaging system is configured to image. The method comprises a step of preventing stray light from the light source from reaching the virtual volume within the field of view of the camera, at least during said imaging by the camera.

[0024] In some embodiments, the prevention of stray light is achieved by blocking stray light with a light blocker disposed outside the structured light between a light source and the virtual volume. The light blocker may be as described above. Effect of the Invention

[0025] The embodiments herein are based on the finding that reflections due to stray light are very weak and seemingly and typically negligible with respect to the structured light used for optical triangulation, but can nevertheless be problematic if they cause specular reflections in the virtual volume to the camera's field of view, for example reflections on the object being imaged but outside the structured light or on adjacent objects in the virtual volume, such as objects that will be imaged next or were imaged immediately before the object being imaged. Even if the stray light itself is very weak with respect to the structured light reflected from the object towards the camera, it has been found that said specular reflections, mainly specular but sometimes also secondary specular reflections, of stray light towards the camera cause unwanted intensity peaks caused by said structured light that are difficult to distinguish from the required intensity peaks according to optical triangulation. Post-imaging methods for optical triangulation, i.e. for finding the required intensity peaks corresponding to the specular reflections from the object, typically focus on eliminating unwanted intensity peaks other than from specular stray light reflections, such as those caused by secondary reflections of said structured light or other phenomena. Preventing stray light from entering the field of view in the virtual volume, for example by blocking the stray light, as in the embodiments herein, will reduce the risk of problematic specular stray reflections that would otherwise lead to distortions, such as "spikes", in the 3D image. Thus, the embodiments herein also enable or at least support this reduction and thereby improved 3D imaging.

[0026] Example embodiments herein will now be described in more detail with reference to the accompanying schematic drawings which are briefly described below. [Brief description of the drawings]

[0027] [Figure 1] 1 illustrates generally an example of a prior art imaging system for optical triangulation-based 3D imaging on which embodiments herein may be based. [Figure 2A] 2 illustrates diagrammatically the situation and some of the relationships that exist for a prior art imaging system such as in FIG. [Figure 2B] 2 illustrates diagrammatically the situation and some of the relationships that exist for a prior art imaging system such as in FIG. [Figure 3A] 1A-1C are schematic illustrations of examples and situations for prior art imaging systems that can lead to problems with stray light; [Figure 3B] 1A-1C are schematic illustrations of examples and situations for prior art imaging systems that can lead to problems with stray light; [Figure 3C] 1A-1C are schematic illustrations of examples and situations for prior art imaging systems that can lead to problems with stray light; [Figure 3D] 1A-1C are schematic illustrations of examples and situations for prior art imaging systems that can lead to problems with stray light; [Figure 4A] 1 illustrates diagrammatically how illumination including structured light used in optical triangulation also includes stray light and how it may be related to the structured light. [Figure 4B] 1 illustrates diagrammatically how illumination including structured light used in optical triangulation also includes stray light and how it may be related to the structured light. [Figure 4C] 1 illustrates diagrammatically how illumination including structured light used in optical triangulation also includes stray light and how it may relate to the structured light. [Figure 5A] 1A and 1B are schematic illustrations of an imaging system according to embodiments herein with a first example light blocking member; [Figure 5B] 1A and 1B are schematic illustrations of an imaging system according to embodiments herein with a first example light blocking member; [Figure 5C] 1A and 1B are schematic illustrations of an imaging system according to embodiments herein with a first example light blocking member; [Figure 6A] 1 is an image illustrating the results from 3D imaging of a highly specular metal foil based on optical triangulation using a prior art imaging system. [Figure 6B] 1 is an image illustrating results from optical triangulation-based 3D imaging of a highly specular metal foil using an imaging system according to embodiments herein. [Figure 7] 13A and 13B are schematic diagrams illustrating an imaging system according to embodiments herein in a second example of a light blocking device; [Figure 8] 13A and 13B illustrate a third example of an imaging system according to embodiments herein in which a light blocking member is provided; [Figure 9] 1 is a flow chart for generally illustrating an embodiment of a method according to embodiments herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The embodiments herein are illustrative embodiments. It should be noted that these embodiments are not necessarily mutually exclusive. Although elements from one embodiment may be implicitly assumed to be present in another embodiment, it will be clear to one skilled in the art how those elements may be used in other illustrative embodiments.

[0029] As part of the development towards the embodiments herein, the circumstances mentioned in the background will first be explained and described in further detail.

[0030] Even if most of the light from the light source is the structured light used in and by the light triangulation, in practice it is typically not possible to completely avoid that the illumination by the light source also leads to some stray light outside the structured light. Total stray light is, and often is, by definition in principle very small compared to the structured light and negligible in comparison. Stray light does not usually cause a problem in the case of object surfaces that only provide diffuse reflection.

[0031] Stray light is traditionally ignored in the context of optical triangulation because the amount of stray light is very small and seemingly insignificant compared to the structured light used in optical triangulation. As noted in the background, problems with specular reflection are attributed to and arise from structured light, and various solutions exist for this.

[0032] In addition to the fact that stray light appears seemingly insignificant to structured light, and is often so, the following may explain why problems with stray light in optical triangulation have not been recognized, or at least not adequately, in the prior art, even though 3D imaging by optical triangulation has existed for a long time. Such "post-image sensing" measures acting on image data, mentioned in the background, also solve at least some of the problems with unwanted intensity peaks caused by stray light. Any stray light induced intensity peaks will typically be mixed with other unwanted intensity peaks, such as those caused by secondary structured light reflections. Stray light reflections are in principle only problematic when one or more objects being 3D imaged based on optical triangulation have highly reflective surfaces, in which case the unwanted intensity peaks caused by secondary and higher order reflections of structured light are also multiplied.

[0033] The embodiments herein are based on the discovery and recognition that stray light, even if its total amount appears insignificant relative to the structured light, can still cause problematic unwanted intensity peaks in the image data, some of which may be particularly difficult to remove by the above-mentioned "post-image sensing" methods that operate on the image data to find the intensity peaks required for optical triangulation. Therefore, the embodiments herein are further based on the recognition that 3D imaging based on optical triangulation can be improved if stray light can be prevented from causing reflections that lead to unwanted intensity peaks in the first place. In this way, there will be fewer unwanted intensity peaks in the image data that would be dealt with, for example, by conventional or other "post-image sensing" methods.

[0034] Before describing and explaining the embodiments herein in more detail, some basics about prior art 3D imaging systems based on optical triangulation, and such systems in general, as well as detailed examples of situations in which stray light can cause problems, as discussed above, will be described in order to facilitate understanding of the embodiments herein and their differences compared to prior art and conventional 3D imaging systems based on optical triangulation.

[0035] FIG. 1 illustrates in a schematic way an example of a prior art imaging system 100 for 3D imaging based on optical triangulation on which embodiments herein may be based. The imaging system 100 may alternatively be named imaging system for 3D machine vision based on optical triangulation, for example for obtaining information on 3D properties of a target object. The imaging system 100 is illustrated in the figure in a normal operating situation, i.e. typically after a calibration has been performed and thus the system is calibrated. The imaging system 100 is configured to perform optical triangulation, here in the form of light sheet triangulation, i.e. optical triangulation in which structured light, a light plane, is used. The imaging system 100 further comprises a light source 110, such as a laser, for illumination of the object to be imaged with structured light, typically a specific light pattern. There is structured light 111 in the form of a light plane in the example and in the figure. The light may be laser light, but this is not necessarily the case, it may alternatively be light from, for example, one or more light emitting diodes (LEDs). Another example of structured light that is similar, but not traditional, to a light plane of similar effect, is a light edge, i.e. the edge of an area of ​​illumination. The generated light and illumination is typically provided through one or more lenses, for example to focus the light. Moreover, the camera is typically configured and provided such that it has a focal plane that is co-located, in other words aligned, with the structured light 111, typically the light plane, based on the so-called Scheimpflug principle. In this way, the object reflection occurring at the light plane will be focused at the image sensor. In the illustrated example, the object to be imaged is illustrated by a first object 120 in the form of a car and a second object 121 in the form of a gear structure. The object to be imaged may be referred to as a measurement object. When the structured light 111 is incident on the object, this corresponds to a projection of the structured light 111 on the object, and the structured light 111 may be observed to intersect with the object. For example, in the illustrated example, the structured light 111 in the form of a light plane leads to a light line 112 on the first measurement object 120.The structured light 111 is reflected by the object, more specifically by a portion of the object, at the intersection, i.e. in the illustrated example at light line 112. The imaging system 100 further comprises a camera 130 with an image sensor (not shown in FIG. 1). The camera and image sensor are arranged with respect to the light source 110 and the object to be imaged such that the structured light 111, when reflected by the object, becomes incident on the image sensor. The image sensor is a device, typically implemented as a chip, for converting incident light into image data. The portion of the object causes the incident light to the image sensor by reflection, which may be captured by the camera 130 and the image sensor, and corresponding image data may be generated and provided for further use. For example, in the illustrated example, the structured light 111 will be reflected in light line 112 on a portion of the car roof of the first object 120 towards the camera 130 and the image sensor, thereby generating and providing image data with information about the portion of the car roof. According to the principles of optical triangulation, with knowledge of the geometry of the imaging system 100, e.g., how image sensor coordinates relate to world coordinates, such as coordinates of a coordinate system 123, such as Cartesian coordinates, associated with the object being imaged, the image data can be converted into information about 3D characteristics, e.g., in the form of a 3D shape or profile, of the object being imaged in a suitable format. The information about the 3D characteristics may include data describing the 3D characteristics in any suitable format.

[0036] By moving the light source 110 and / or the object to be imaged, such as the first object 120 or the second object 121, such that multiple portions of the object are illuminated causing reflected light to be sensed in the image by the image sensor, in effect typically scanning the object with structured light 111, image data may be generated that corresponds to multiple successive profiles of each object depicting a more complete 3D shape of each object, such as, for example, the illustrated profile images 140-1 to 140-N of the first object 120. Each profile image shows the outline of the first object 120 from which the structured light 111 was reflected when the image sensor of the camera unit 130 sensed the light that led to the profile image. As shown in the figure, a movable object support structure 122, such as a conveyor belt or the like, may be used to move and thereby scan the object through the structured light 111 while the light source 110 and camera unit 130 are typically kept stationary. Alternatively, structured light 111 may be moved across the object such that all parts of the object, or at least all parts facing the light source 110, are illuminated and the camera receives light reflected from all parts of the object that it is desired to image.

[0037] As can be seen, during imaging of, for example, the first object 120, each image or image frame provided by the camera 130 and its image sensor may correspond to or be used to provide one of the profile images 140-1-140-N. Each location of the contour of the first object shown in any of the profile images 140-1-140-N is typically determined based on identifying intensity peaks in the image data acquired by the image sensor and finding the locations of these intensity peaks. The imaging system 100 and conventional peak finding algorithms are typically configured to look for intensity peaks by pixel column in each image frame. If the sensor coordinates are u,v, and for example u corresponds to a pixel location along a row in the image sensor and v corresponds to a pixel location along a column as shown in the figure, then for each position u of the image frame searched, there is a peak location along v, and the peaks identified in the image frame may lead to one "clean" profile image as shown in the figure, and a 3D image of the first object 120 can be created using the total number of image frames and profile images.

[0038] 2A-2B illustrate diagrammatically the situation and some relationships existing for a prior art imaging system as in FIG. 1, with FIG. 2A being a 3D view and FIG. 2B being a 2D side view of that shown in FIG. 2A. The illustrated system may correspond to the imaging system 100, but is shown in a more schematic and simple view to draw attention to and explain some details associated with such a system. The details shown in the figures are for facilitating understanding of the embodiments herein presented further below and for later comparison with those embodiments. The illustrated imaging system 200 can be considered to correspond to a basic configuration, and comprises a first light source 210 for illuminating an object 220 with structured light 211 as part of light triangulation for 3D imaging of the object 220. The structured light 211 is also provided here in the form of a light plane and may correspond to the structured light 111. A camera 230 having an image sensor 231 arranged to sense the first light reflected from the object 220 as part of the above-mentioned optical triangulation for 3D imaging, i.e., configured and arranged relative to each other for optical triangulation. This typically requires that the first light source 210 and the camera 230 are arranged in a predetermined fixed position and in a known relationship to each other for optical triangulation. The camera 230 has a field of view 232 that covers at least part of the light plane, particularly the part of it where the object 220 and other objects that the system is configured to image may intersect with the light plane.

[0039] In a system such as in the figure, and also in prior art imaging systems generally for 3D imaging based on optical triangulation as illustrated in FIG. 1, there is a virtual volume, illustrated diagrammatically in FIGS. 2A-2B and explicitly indicated by a dashed-dotted line in the figures as virtual volume 224. As used herein, a virtual volume, such as virtual volume 224, corresponds to a volume in which one or more objects that the imaging system 200 is configured to image, such as objects 220a-b shown in the figures, exist during imaging. The virtual volume includes where the structured light exists for illumination of the objects and thus intersects with it during imaging. Furthermore, the virtual volume extends on either side of the structured light, both towards and away from the camera. Structured light 211 is thus provided such that it intersects with the virtual volume, as shown in the figures. In the figure, structured light 211 is shown as it intersects virtual volume 224 and object 220a, resulting in light lines 212 being projected onto object 220a and onto object support structure 222 at the "bottom" of virtual volume 224, which corresponds, for example, to the surface of the conveyor belt in the example of Figure 1. The maximum object height supported by the imaging system typically determines the height of the virtual volume and therefore where the structured light first reaches the virtual volume.

[0040] For reference, an illustrative real world Cartesian coordinate system xyz and xy is also shown in the figure.

[0041] 3A-3D illustrate generally examples and situations for prior art imaging systems that have been identified that lead to problems with stray light. The illustrated imaging system 300 may correspond to any one of the imaging systems 100, 200, except that the object to be imaged for has a specular, mirror-like, spherical surface, which is a type of object that is very difficult to image in 3D using optical triangulation. The objects are illustrated generally in the figures as a first object 320-1 and a second object 320-2. The figures and examples in the following are intended to explain and illustrate how stray light, although weak, can also cause problems in these and similar situations.

[0042] As mentioned, imaging system 300 may correspond to any one of imaging systems 100, 200, and so there is correspondingly a camera 130, 230, a camera 330 with a field of view 332, which may correspond to field of view 132, 232 and light source 110, 210, and a light source 310. Light source 310 provides illumination in the form of a light plane and including structured light 311, which may correspond to structured light 111, 211. There is also an object support structure 322, which may correspond to object support structure 122 or 222. A virtual volume 324 is also shown and may correspond to virtual volume 224.

[0043] 3A illustrates a first illustrative situation where the first object 320-1 is outside the structured light 311, e.g., so that no light has yet reached the object. According to optical triangulation, this should not lead to any object-related intensity peaks at all in the image taken in the illustrated situation. If there is an intensity peak, it would simply be from diffuse reflection at the object support structure 322. However, stray light 315a from illumination by the light source 310, and therefore outside the structured light 311 itself used for optical triangulation purposes, albeit very weak relative to the structured light 311, can reach the surface of the first object 320-1 and cause a specular reflection, as shown diagrammatically in the figure, whereby stray light 316a reflected towards the camera 330 can be imaged. This would appear in the image as an intensity peak as if there had been a diffuse reflection by the structured light 311 on the object at the point 322a shown in the figure. Therefore, there will be unwanted intensity peaks in the image that may not be as strong as they could be if caused by second or higher order reflections by structured light 311, but may still be comparable to or stronger than the intensity peaks from the wanted diffuse reflection of structured light 311. As a result, it is difficult to distinguish the unwanted intensity peaks in this case from the wanted intensity peaks, for example by using conventional post-imaging processing to find the wanted intensity peaks.

[0044] FIG. 3B illustrates a second illustrative situation in which a first object 320-1 is illuminated by structured light 311. The first object 320-1 may have moved to this position from the position in the situation illustrated in FIG. 3A as part of the object scanning. According to optical triangulation, this should lead to a required intensity peak caused by the reflection of the structured light on the surface of the first object 320-1. However, stray light 315b from the illumination by the light source 310 and therefore outside the structured light 311 itself used for optical triangulation purposes may also reach the surface of the first object 320-1 and cause a specular reflection, as illustrated diagrammatically in the figure, whereby the reflected stray light 316b towards the camera 330 is imaged. This would appear in the image as an intensity peak as if there was a diffuse reflection by the structured light 311 on the object surface at point 322b shown in the figure. Therefore, there would be an unwanted intensity peak in the image, which may be comparable or stronger than the required diffuse reflection of the structured light 311 on the object. As a result, for example, if the first object 320-1 diffusely reflects the structured light 311 towards the camera, only a single, desired one would be expected, and there would be at least two intensity peaks that would be difficult to distinguish from one another, for example by conventional post-imaging processing to find the desired intensity peak.

[0045] 3C illustrates a third illustrative situation where the first object 320-1 is illuminated by the structured light 311 and the first object may have moved further to the left after the situation illustrated in FIG. 3B. According to optical triangulation, there should be the required intensity peak again caused by the reflection of the structured light on the surface of the first object 320-1. However, stray light 315c from the illumination by the light source 310 and therefore outside the structured light 311 may reach the surface of the first object 320-1 outside the structured light 311 and cause a specular reflection, as illustrated diagrammatically in the figure. If this part of the first object is highly reflective, such as a mirror, as is assumed in the example, it may cause a specular reflection in the form of a first reflected stray light 316c towards the second object 320-2, as illustrated in the figure. If the second object 320-2 is also highly reflective, at least where the first reflected stray light 316c is reflected by the second object, there may be a secondary reflected stray light 317c imaged by it towards the camera 330, as shown in the figure. This will appear in the image as an intensity peak as if there was a diffuse reflection by the structured light 311 on the object surface at point 322c shown in the figure. Therefore, there will be an unwanted intensity peak in the image that may be as strong or stronger than the wanted diffuse reflection of the structured light 311. As a result, if for example the first object 320-1 diffusely reflects the structured light 311 towards the camera, there will be at least two intensity peaks that are difficult to distinguish from each other, e.g., by conventional post-imaging processing to find the wanted intensity peak, whereas only the wanted one is expected.

[0046] 3D is to explicitly show, by means of a thick dashed-dotted line, a portion or sub-volume 326 of the virtual volume 324 where specular reflections occur, including the stray light problem discussed above. Sub-volume 326 corresponds to a field of view 332 within the virtual volume 324. This is therefore where it is particularly desirable to avoid or reduce the introduction of stray light.

[0047] In general, for imaging systems based on optical triangulation, particularly if the object to be imaged has or is in close proximity to a highly reflective surface, it has been found to be advantageous to avoid or reduce the intrusion of stray light resulting from illumination including structured light into the camera's field of view within a virtual volume, which corresponds to a volume in which one or more objects that the imaging system is configured to image are present during imaging.

[0048] The embodiments herein, as illustrated and described in some detail below, are based on the above discovery and insight that reduction of stray light into the field of view within a virtual volume is preferably achieved by blocking stray light, thereby preventing it from entering the field of view within the virtual volume.

[0049] 4A-4C illustrate generally how the illumination including structured light used in optical triangulation also includes stray light, and are used below to describe stray light and structured light in relation to each other.

[0050] FIG. 4A illustrates diagrammatically a portion of a structured light 411, for example corresponding to the structured light 311 in FIGS. 3A-3D, i.e. what is illustrated may correspond to a thickness of a cross section of a light plane. The figure is also intended to illustrate that the light intensity is not distributed equally, but of course is a portion of the structured light 411, here decreasing away from the maximum intensity of illumination at the center of the structured light 411. The structured light 411 is illustrated as having a thickness 412. However, as will be appreciated, there is in fact no abrupt stop where there is no light at all where the dash-dotted line is in FIG. 4A, but instead there is a continuous decrease of light as one moves away from the center according to a certain light distribution applied, typically Gaussian. The thickness 412 may correspond to a certain measure used to indicate how thick or thin the light plane (or the resulting line corresponding to the projection of the light plane on an orthogonal surface) is and / or to identify properties related to illumination and light sources. This is the so-called full width at half maximum (FWHM), a measure sometimes used to indicate that this is the full width of the eight distributions when the maximum intensity has fallen by half, corresponding to the peak. For the purposes of this example, it may be assumed that the thickness shown in FIG. 4A corresponds to the FWHM, although other measures for thickness may also be used.

[0051] FIG. 4B illustrates diagrammatically how a light distribution as described above in connection with FIG. 4A may look, here light distribution 440. The FWHM thickness 412 is indicated in the figure. The maximum intensity 441 of the light distribution 440 is also indicated, with line 442 indicating where the maximum intensity starts to drop off on the left side of the light distribution 440. Additionally, the location by line 444 where the light intensity of the light distribution 440 has dropped to 5% of the maximum value is indicated, indicated in the figure by "5% of maximum light intensity" line 445. The reason for 5% will be discussed and explained below. As can be seen in the figure, line 444 indicates the distance 446 between lines 442 and 444.

[0052] The structured light used for optical triangulation includes at least the maximum intensity of the light distribution and most of the illumination, including light that is down to some extent below the maximum intensity. For example, the structured light typically includes light at least up to the FWHM or according to some similar measure. However, a more practical approach is to define the structured light as light that is effectively used by and useful for optical triangulation, not just light within, for example, the FWHM. The light distribution typically varies depending on the light source, how the light source is configured to provide illumination, etc. What exact part of the light distribution is used as the structured light for optical triangulation may vary from application to application (although of course it is always the part that includes the maximum intensity value). Therefore, exactly where the structured light ends up is not always the same. However, in practice, the limit for the structured light for a system setup for a given optical triangulation application can be found by simple experimentation. The shading element may be moved towards the structured light, for example, perpendicular to the illumination direction, as in the embodiments herein and as described below, and when negative effects on the results from and results of the optical triangulation begin to appear and / or when visual impairment of the light, such as visual impairment and / or interference of the light projected onto the object or object supporting surface, begins to appear, the portion of the shading element closest to the structured light indicates where the structured light begins to be used and useful for optical triangulation.

[0053] Stray light, in the context of optical triangulation and as used herein, is defined as light that is not useful for optical triangulation per se, and so may be light that is part of the illumination but outside of what is considered and used as structured light for optical triangulation, or in other words, stray light is light that is not used to and by optical triangulation per se.

[0054] If the structured light and its light distribution have a center, for example in the case of a light plane whose thickness encompasses the structured light, as in the case of structured light 411, defined for example according to FWHM, then stray light refers to light at least outside this thickness, for example outside thickness 412, or at a certain distance outside this thickness.

[0055] Stray light may be defined or predefined with respect to the light distribution, e.g., should be defined such that, should there be a certain drop in intensity from the maximum intensity, the structured light used for the light triangulation is at least not included. For example, a certain distance from the maximum intensity of the light distribution may be defined for the light to be considered as stray light. Preferably, such distance is defined for where the light distribution has dropped to a certain degree relative to its maximum and / or center position, such that it has dropped to at least x% of the maximum intensity value. In general, or as a rule of thumb, it has been found through experiments such as those described above that the structured light used for and useful for the light triangulation associated with the embodiments herein is no longer present once the light distribution has dropped to at least 5% of its maximum value, and therefore the stray light is typically no closer to the maximum intensity than this. This is the reason for the line 444 and the "5% of maximum light intensity" line 445 in FIG. 4B.

[0056] FIG. 4C is an alternative schematic diagram illustrating structured light and stray light simultaneously. Besides the structured light 411, the figure shows line 444, which corresponds to distance 446 from line 442 showing where the maximum intensity starts to decrease, i.e. stray light 415, considered starting from where the light intensity has decreased to 5% of its maximum intensity. As illustrated in the figure, according to the light distribution 440, the closer to the structured light 412 there is more light, and therefore more stray light, than further away. It can be seen from the figure that the light distribution is not the same at different places along the illumination, such as at different heights. It should be noted that the thickness 412 including the structured light 411 is not illustrated in the figure, but in reality the thickness also varies along the illumination.

[0057] 5A-5C illustrate generally an imaging system 500 according to an embodiment herein including a first example of a light blocking body for blocking stray light, namely a first light blocking body 550. As shown in FIG.

[0058] 5A illustrates a schematic of an imaging system 500 in a similar side view as in the above example for ease of comparison. The side view corresponds to a cross-section of a light blocking body 550.

[0059] FIG. 5B illustrates the imaging system 500 generally from a top view to provide an improved understanding of what it also looks like in the lateral dimension.

[0060] The imaging system 500 may correspond to any one of the imaging systems 100, 200, 300 and is therefore also an imaging system for 3D imaging based on optical triangulation, but in addition it also comprises a light blocking body 550. The imaging system 500 therefore comprises a camera 530 with a field of view 532 which may correspond to any one of the cameras 130, 230, 330 with a field of view 132, 232, 332. There is also a light source 510 providing illumination comprising structured light 511 in the form of a light plane which may correspond to any one of the light sources 110, 210, 310 and which may correspond to any one of the structured light 111, 211, 311. There is also an object support structure 522 which may correspond to any one of the object support structures 122, 222, 322. A virtual volume 524 is also shown, which may correspond to the virtual volume 324 or 224 and a sub-volume 526 which may correspond to the sub-volume 326. Sub-volume 526 corresponds to a field of view 532 in virtual volume 524. As an example, an object 520 to be imaged into virtual volume 524 is also shown diagrammatically. Object 520 may correspond to any of the objects to be imaged as shown and described in the examples and figures above, and may have one or several surfaces or surface portions that are highly reflective, e.g. mirror-like, which may give rise to problems of the kind related to stray light mentioned above.

[0061] The light blocker 550 extends between the light source 510 and the virtual volume 524 and comprises a first light blocker portion 550a disposed on a first side of the structured light 511 toward the camera 530 and a second light blocker portion 550b disposed on a second side of the structured light 511 in the opposite direction from the camera 530. It is advantageous to provide the light blocker with at least two portions oriented to block light on each side of the structured light as this allows for blocking more stray light.

[0062] As can be seen, the shade 550 has a funnel shape due to the first and second shade portions 550a,b of the shade 550 extending between the light source 510 and the virtual volume 524 with the distance to the structured light 511 decreasing in the direction of the virtual volume 524. The funnel shape allows for efficient and practical stray light blocking with a relatively small total shader. While a relatively small shade surface can cover and block most of the stray light, it can still have a minimum distance to the structured light in a single location located where it is often most efficient, such as along the structured light or near the virtual volume.

[0063] It can be seen from the figure that the light blocking body 550 has the effect of blocking stray light from the light source 510, ie at least a portion of the stray light, or in other words the illumination provided, that would otherwise reach the sub-volume 526.

[0064] As used herein, a light blocker generally refers to a structure or arrangement, such as light blocker 550, that prevents at least some light incident on the blocker from passing through the blocker to reach an area or volume, such as subvolume 526, that would otherwise be reached by the blocked light without the blocker. Typically, to achieve illumination with structured light, such as structured light 511, for use in 3D imaging by optical triangulation as in the embodiments herein, all or a majority of the light incident on the blocker, or at least all light within a certain wavelength, e.g., all wavelengths of light provided by a light source, such as light source 510, should be prevented from passing through.

[0065] As can be seen in Fig. 5A, the shading body is disposed in the field of view 532, but such that it does not obstruct the part of the field of view that covers the structured light 511 in the virtual volume 524, i.e., such that it does not adversely affect the imaging of the structured light 511 in the virtual volume 524, since this is where objects occur during imaging and reflect the structured light 511 towards the camera 530. In general, the shading body in the embodiments herein may block part of the field of view and the imaging of the structured light in the virtual volume, but this is usually undesirable, since this is at the cost of a reduced effective field of view. Typically the field of view is provided such that its upper limit in Fig. 5A just covers the maximum object height supported, i.e., it is aligned with the height of the virtual volume such that it covers the structured light in the virtual volume, but no or very little structured light outside this, since objects to be imaged should not occur there, and the result is therefore a reduced utilization of the camera's image sensor for object imaging. However, in the case of a field of view that also covers some structured light outside the virtual volume, as in the example field of view 532 in the figure, it is recognized that there is no further penalty to object imaging if the occluder 550 is in the field of view 532 as shown in the figure, but outside the portion of the field of view 532 that covers the structured light 511 in the virtual volume 524. In other words, in such a case, the occluder 550 should be outside an imaginary line 533 that extends from where the structured light 511 intersects the virtual volume 524 to where the field of view begins from the camera 530, as shown in Figure 5A. The imaginary line 533 in such a case is the limit and represents the effective field of view 532' for object imaging, which is reduced compared to the real field of view 532.

[0066] FIG. 5C illustrates a schematic close-up of the cross-sectional view of the light blocking body 550 in FIG. 5A. The view shows a minimum distance 552, corresponding to a gap, for the structured light 511 to pass through. In the corresponding implementation of the "funnel" design light blocking body as illustrated in FIG. 5A-5C used in testing and experimentation, the distance corresponding to the minimum distance 552 was 0.9 mm. In either case, each blocking body portion on each side of the structured light 511 may be positioned at a minimum distance to the structured light based on the above discussion in conjunction with FIG. 4A-4C so as not to block the structured light used for light triangulation. This means that for an embodiment with two blocking bodies, as in FIG. 5A-5C, in addition to the first minimum distance 552a between the first blocking body portion 550a and the structured light 511, the second minimum distance 552b between the second blocking body portion 550b should be sufficient to not block the structured light as well. How this can be achieved in practice is determined, for example, by the same type of experiments as disclosed above in connection with Figures 4A-4C. That is, if the shading body is so close to the structured light that it has a visual effect on the structured light, such as interference with the projection of the structured light, e.g. a light plane, on the object or object support surface, then the shading body is too close to the structured light and blocks and / or affects the structured light to an undesirable extent. For most conventional light sources used in light triangulation and structured light, such as light planes, this means that the shading body is preferably placed at a distance to the structured light that is not as close as when the structured light has dropped to at least 5% of its maximum value. Or in other words, at a distance when the illumination including the structured light has dropped to at least 5% of its maximum value. That is, the shading body should typically not be placed closer to the structured light than at least according to this. The shading body may therefore only block stray light at this distance or further away from the maximum intensity of the structured light. For example, this means that the respective minimum distances 552a, 552b in some embodiments are no closer to the maximum intensity of the structured light 511 than if the intensity of the light distribution of the illumination had dropped to 5% of the maximum intensity.However, in some cases, for the reasons given above, it may still be preferable to position the light blocking portion such that the minimum distance is greater, i.e. further away from the structured light, e.g. no closer than when the intensity of the light distribution has dropped to 4%, 3%, 2% or 1% of the maximum intensity.

[0067] In applications and cases of very narrow light distribution, for example provided by a narrow laser, very small changes, such as by accident or by accidental movement of the light blocking body during operation, can adversely affect the structured light by blocking it if it is too close. In such situations, it may be preferable to arrange the light blocking body with some larger margin to the structured light.

[0068] In general, however, it may be preferable for the light blocking body to be as close as possible to the structured light used for optical triangulation, but without adversely affecting the structured light and thereby the optical triangulation itself, i.e., without thereby adversely affecting the imaging of the object by optical triangulation.

[0069] Furthermore, it may be preferable for the minimum distance to the structured light to be as close as possible to the virtual volume without affecting the structured light used for optical triangulation and without blocking and / or impeding object imaging, which may make it easier to achieve an efficient stray light blocking effect since it is closer to the virtual volume.

[0070] For the placement of the shading body and especially where the minimum distance to the structured light may be placed, it should be taken into account that the light source typically has a lens through which the structured light is provided. To ensure that the light distribution is not too narrow in the virtual volume (as it is desirable to exploit some sufficient "width" of the structured light so that the peak position can be identified with sub-pixel resolution), the focal point of the lens is often outside the virtual volume, i.e. "in front or behind". If the focal point is "in front" of the virtual volume, it may be beneficial to use a shading body with a minimum distance to the structured light at or near the focal point, since it is possible to be closer without adversely affecting the structured light.

[0071] For example, as above, by ensuring that the shading body blocks at least some of the stray light that would otherwise reach the "junction" between the camera's field of view and the virtual volume, i.e., the field of view within the virtual volume, it is ensured that the shading body will have the effect of not only blocking stray light that is too far away. However, as mentioned above, while the shading body should not be too close to affect the structured light, a small or at least not too large gap between the shading body and the structured light may be beneficial, since not too much stray light close to the structured light will escape. Therefore, the shading body is preferably placed at a distance from the maximum intensity (peak value) such that it is at least at the point where the light distribution has dropped to 1% of its maximum value. This is to prevent too much stray light close to the structured light from escaping the shading body, thereby reducing the effect from the embodiments herein.

[0072] In summary, taking the above into consideration, it is found that the light shield is preferably arranged at a distance from the maximum intensity (peak value) of the light distribution not so close as when the structured light has dropped to at least 5% of its maximum value, and at the same time it may be preferred that the light shield is present where the light distribution has dropped to 1% of its maximum value, e.g. it is present and covers at least a part of the area extending between 5% and 1%. In many applications this corresponds to the light shield being present around the structured light, e.g. the light plane, and / or at a gap that is very little from its maximum intensity, or about one or half a millimeter or a few millimeters to about one centimeter. The light shield, e.g. the light shield part thereof, may extend away from the structured light such that the light shield extends perpendicular to the illumination direction and covers at least a few centimeters above the virtual volume, longer or shorter as appropriate depending on the application.

[0073] Furthermore, as will be appreciated by those skilled in the art, the light blocking body as in the embodiments herein and as described above, as well as any part thereof involved in blocking, may be made of any one or more of a wide variety of materials. The exact material is not important as long as it has light blocking properties. However, it may be preferred to use some opaque plastic materials and / or coatings or covers with surface materials on the substrate or core material to achieve or improve light blocking properties. For example, making the light blocking body more light absorbing and / or non-reflective. Matte and preferably dark surfaces may be preferred to avoid or minimize reflections from the light blocking body itself. Finally, in some embodiments, it may be preferred to ensure that one or more surfaces facing the virtual volume, such as surfaces 554a-1, 554b-1, are non-reflective, such as by making them specifically light absorbing, and / or that these surfaces are matte and / or dark, because such surfaces, being reflective, may cause secondary reflections of the reflected light coming from the virtual volume and reflect it back into the virtual volume, thereby causing unwanted intensity peaks in the image. It may not be of great importance if one or more of the shading surfaces, such as surfaces 554a-2, 554b-2 facing the light source, e.g. light source 510, cause some reflection, since there is still a blocking effect and light reflected on that side is unlikely to end up in subvolume 526 and cause problems. However, there is of course typically no sense in having such surfaces be highly reflective, and in fact it may be simplest to have all shading surfaces made from the same material and / or have the same coating, e.g. matte and preferably dark, low reflectivity and light absorption.

[0074] 6A-6B are images illustrating the results from 3D imaging of a highly specular metal foil based on optical triangulation using a prior art imaging system and using the same system as in the embodiment herein but with a light shield against stray light. More specifically, the images shown result from an imaging system 500 as in FIGS. 5A-5C without and with a light shield as light shield 500. The object being imaged is one and the same in the two images and corresponds to a type of object that is usually very difficult to 3D image based on optical triangulation, a highly reflective metal foil given a random height profile with many height differences. In the implementation example, the illumination with structured light, corresponding to structured light 511, was provided by a laser as a light source, corresponding to light source 510, where the structured light corresponds to the laser plane. The distance corresponding to the minimum distance 552 between the light shield parts was 0.9 mm and the light shield was placed such that it was not closer to the structured light than 5% of the maximum intensity of the illumination by the laser at this place of the light shield. The structured light, and therefore here the laser plane, was centered in the gap formed by a distance of 0.9 mm. The two shield parts, corresponding to the shield parts 550a,b, therefore had a respective minimum distance, corresponding to the respective distances 552a,b, between the respective shield parts and the structured light, which was less than half the distance of 0.9 mm, i.e. less than 0.45 mm. Although the shields were not fine-tuned in any way for the application, one can clearly see the improvement of the 3D image based imaging due to the presence of the shield, since the implementation and testing were more than a "proof of concept". With the shields present, not many "spikes" in the image, corresponding to distortions, occur. As shown in the introduction above, this kind of "spikes" are typically caused by unwanted intensity peaks, for example those caused by specular reflection of stray light, as in this case. Their presence in 3D images such as the one in the figure is often due to the fact that "post-image sensing" processing has problems distinguishing between wanted and unwanted intensity peaks, and therefore sometimes selects the unwanted ones instead of the actually wanted intensity peaks, which are intensity peaks caused by specular reflection on the object by structured light.

[0075] FIG. 7 illustrates a schematic representation of an imaging system 700 according to an embodiment herein in which the shading body is a second example, namely shading body 750. Apart from the different shading body, the rest of the imaging system 700 is the same as the imaging system 500 in FIGS. 5A-5C. This is for ease of comparison. However, as will be appreciated by those skilled in the art, shading bodies as in the embodiments herein are of course compatible with and can be used in 3D imaging systems based on optical triangulation in general, and not just used strictly as illustrated in the examples herein. In the following, the focus is therefore on the shading body 750 in the imaging system 700 and the differences compared to the shading body 550 in the imaging system 500. What is not mentioned may be assumed to be the same or similar as described above in connection with FIGS. 5A-5C.

[0076] Imaging system 700 is illustrated in a side view similar to that in Figure 5A. The side view corresponds to a cross-section of occluder 750. Although a corresponding top view is not shown as in Figure 5B, occluder 750 can be assumed to extend similarly across the lateral extent of virtual volume 524, i.e., in the y-direction in the example coordinate system used herein. It should be noted that an occluder as in the embodiments herein need not extend across the entire lateral extent of the virtual volume, although this is typically preferred, and may in some embodiments only extend partially across the lateral extent of the virtual volume.

[0077] Additionally, light blocking body 750 extends between light source 510 and virtual volume 524 and comprises a first light blocking body portion 750a disposed on a first side of structured light 511 toward camera 530 and a second light blocking body portion 750b disposed on a second side of structured light 511 away from camera 530. It should be noted that it is not necessary for all embodiments to have a light blocking body portion on both sides of the structured light, although this is typically preferred.

[0078] The first blocker portion 750 a , and therefore also the blocker 750 , now extends between the light source 510 and the virtual volume 524 with the distance to the structured light 511 decreasing in the direction of the virtual volume 524 .

[0079] The light blocking body in the embodiments herein may therefore have a virtual volume, e.g., a tapered or funnel-like extension towards the virtual volume, and the minimum distance to the structured light may be towards the virtual volume and may be the portion of the light blocking body closest to the virtual volume.

[0080] It can also be seen that the light blocker 750 has the effect of blocking at least some of the stray light from the light source 510 that would otherwise reach the sub-volume 526 .

[0081] As can be seen in the illustrated example, both shading portions 750a,b may be positioned very close to the virtual volume and along its upper edge, except where this is not possible in order to not block the field of view 532 that covers the structured light 511 in the virtual volume 524, for which reason the first shading portion 750a is aligned along the imaginary line 533 in the figure.

[0082] 7 is a blocker that is instead positioned much closer to the light source, e.g., corresponding to second block portion 750b being translated upwards in the figure to a line shown at the same level as light source 510. In such an embodiment, there may be a first blocker portion similar to the second block portion, but on the other side of structured light 511 and therefore not tilted as first block portion 750a, e.g., at the same level and parallel as the second block portion, extending from outside structured light 511 towards where imaginary line 533 in camera 530 meets the upper limit of field of view 532.

[0083] 8 illustrates a schematic of an imaging system 800 according to an embodiment herein in which the shade is a third example, namely shade 850. Apart from the different shade, the remainder of the imaging system 800 is the same as the imaging system 500 in FIGS. 5A-5C or the imaging system 700 in FIG. 7. This is for ease of comparison. In the following the focus is therefore on what is different about shade 850 in imaging system 800 compared to shades 550, 750. What is not stated may be assumed, where possible, to be the same or similar as described above for imaging systems 500, 700 and shades 550, 750.

[0084] Imaging system 800 is illustrated in a side view similar to that in Figures 5A and 7. The side view corresponds to a transverse cross-section of shading body 850. Although a corresponding top view is not shown as in Figure 5B, shading body 850 can be assumed to extend similarly across the lateral extent of virtual volume 524, i.e., in the y-direction in the example coordinate system used herein.

[0085] Also, light blocking body 850 lies extending between light source 510 and virtual volume 524 and comprises a first light blocking body portion 850a arranged on a first side of structured light 511 in the direction of camera 530 and a second light blocking body portion 850b arranged on a second side of structured light 511 in the opposite direction to camera 530. It can also be seen from the figure that light blocking body 850 has the effect of blocking stray light from light source 510, i.e. at least a portion of stray light, that would otherwise reach sub-volume 526.

[0086] Shading body 850 is an example of an alternative shading body that, although functional, is expected to be less effective and / or less advantageous than shading body 550, 750 due to shading body 550, 750 having a shading major surface that extends perpendicular to the illumination direction of structured light 511. This is not the case for shading body 850, since its major shading surface extends exclusively vertically, i.e., parallel to the illumination direction of structured light 511. Shading major surfaces that extend perpendicular to the illumination direction of structured light 511 are beneficial for efficient shading and coverage of the virtual volume, while allowing the shading body to be placed at a distance from the light source and close to the virtual volume while still providing good shading of the virtual volume. This also facilitates that the shading body can be placed at a distance from the light source and still be efficient.

[0087] Above, it is not shown or described how the light blocking bodies in the embodiments herein may be supported and / or mounted in and / or to the imaging system and other units. Each light blocking body may be attached and / or mounted to a light source, an object support structure, or some other suitable stable part in or near the imaging system. A frame or similar structure may be used to hold, etc., the light blocking body in a desired, preferably fixed position during the imaging and scanning of the object. With respect to an imaging system set up for a specific application of 3D scanning of an object, the light blocking body may be adapted to the set up to achieve blocking of stray light as described herein, and the light blocking body may thereafter remain as it is, e.g., in one and the same fixed position, in the imaging system as long as there are no changes that affect the light blocking body. However, as can be seen from this, and from the above explanations etc. regarding the distance and positioning of the light blocking body and the light blocking body parts relative to the structured light, the location and positioning of the light blocking body and its parts may need to be (re)adapted for each specific application and significant changes to the rest of the imaging system.

[0088] In view of the above, it may be preferable to set up and / or adjust the shading relative to the imaging system during setup of the imaging system, for example after the shading has been set up for the optical triangulation itself, so that it is as close to the light plane as possible without risking visual interference with the structured light or visual interference during operation, or to use a fixed shading configured for the light source being used and associated with a certain optical triangulation usage.

[0089] Further, it may therefore be advantageous to have an adjustable shade, e.g. a shade device with adjustment means operating on its shade parts, e.g. the shade itself. This allows and / or facilitates using one and the same shade device for differently set up imaging systems to achieve a shade that is adapted for the specific imaging system set up and application. The set up of the imaging system itself may be conventional.

[0090] Therefore, it may be beneficial for the shield to be adjustable, and in the case of two shield parts, they may be independently adjustable. The adjustment may be performed manually and / or mechanically and / or by some electrically controlled adjustment means or device during the setup of the imaging system. The adjustment is preferably at least in a direction orthogonal to the structured light so that said distance to / from the structured light can be adjusted. Moreover, it may be advantageous if the shield and / or the respective shield part is adjustable in the direction to / from the virtual volume, e.g. up / down between the virtual volume and the light source. The extension of the shield and / or shield part, which influences how the shield can cover the virtual volume and block stray light, may likewise be advantageous if it can be adjusted, e.g. to be able to cover the virtual volume in a desired manner, adaptively. Furthermore, in the case of a tilted shield or shield part, the tilt angle is preferably also adjustable, e.g. to achieve a decreasing distance to the structured light towards the virtual volume. This may be particularly advantageous for the first shield part facing the camera, since then it can be adjusted taking into account the virtual volume and the field of view of the camera.

[0091] FIG. 9 is a flow chart for illustrating in a schematic manner an embodiment of a method according to embodiments herein. The method is for supporting the reduction of distortions, such as the above-mentioned "spikes", in three-dimensional imaging based on optical triangulation, especially when one or more objects to be imaged comprise one or more highly reflective surfaces, such as mirror-like, causing specular reflection. The above-mentioned three-dimensional imaging is performed by an imaging system, such as any one of the imaging systems 500, 700, 800. The method may also be performed by the imaging system. Thus, the imaging system comprises a camera, such as the camera 530, and a light source, such as the light source 510, for providing illumination of the object to be imaged, such as the object 520. The illumination comprises structured light, such as the structured light 511, used for optical triangulation. The camera is positioned with respect to the provided structured light such that the imaging camera captures the structured light reflected from the object in an image as part of the above-mentioned optical triangulation, whereby according to the optical triangulation, the position of the reflected structured light captured in the image maps to a real-world position where the structured light was reflected by the object. The structured light intersects with a virtual volume, e.g., virtual volume 524, that corresponds to a volume in which one or more objects are present during imaging, including the objects and that the imaging system is configured to image.

[0092] The method includes the following acts.

[0093] operation 901 Stray light, such as stray light 415, of illumination from a light source is prevented from reaching the virtual volume within the field of view of the camera, for example virtual volume 524 within field of view 532, at least during the imaging by the camera.

[0094] Prevention is preferably achieved by blocking stray light, which may be achieved by a light shield, such as any one of the light shields 550, 750, 850, as described above.

[0095] It should be noted that any enumerated terminology, such as first device, second device, first surface, second surface, etc., should itself be considered open-ended, and the terminology itself does not imply any particular hierarchical relationship. In the absence of explicit information to the contrary, designation by enumeration should simply be considered a means of providing different names.

[0096] As used herein, the expression "configured to" may mean that a processing circuit is configured or adapted, using software or hardware configurations, to perform one or more of the operations described herein.

[0097] As used herein, the term "number" or "value" may refer to any kind of number, such as a binary number, a real number, an imaginary number, or a rational number. Moreover, a "number" or "value" may be one or more symbols, such as a character or a string of characters. Also, a "number" or "value" may be represented by a string of bits.

[0098] As used herein, the phrases "may" and "in some embodiments" are typically used to indicate that the described features can be combined with any of the other embodiments disclosed herein.

[0099] In the drawings, features that may be present in only some embodiments are typically, but not necessarily, depicted using dotted or dashed lines.

[0100] When the word "comprises" or "comprising" is used, it is to be taken as meaning open-ended, i.e. "consisting at least of".

[0101] The embodiments herein are not limited to the above-described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the present disclosure, which is defined by the appended claims. [Explanation of symbols]

[0102] 411 Structured Light 412 Thickness 415 Stray Light 440 Light distribution 441 Maximum strength 442 line 444 line 445 "5% of maximum light intensity" line 446 distance 500 Imaging System 510 Light source 511 Structured Light 520 Object 522 Object support structure 524 Virtual Volumes 526 Subvolumes 530 Camera 532 Field of view 532' Effective Field of View 533 Virtual Line 550 Shading body 550a First light shielding body part 550b Second light shielding body part 552 minimum distance 552a First Minimum Distance 552b Second Minimum Distance 554a-1, 554a-2, 554b-1, 554b-2 surface 700 Imaging System 750 Shading body 750a First light shielding body part 750b second light shielding part 800 Imaging System 850 Shading body 850a First light shielding body part 850b Second light shielding part

Claims

1. An imaging system (500; 700; 800) for three-dimensional imaging of an object (520) based on optical triangulation, comprising a camera (530) and a light source (510) configured to provide illumination of said object (520) with structured light (511), said camera (530) being positioned with respect to said provided structured light (511) such that said camera (530) can capture an image of the structured light (511) reflected from said object (520) as part of said optical triangulation. whereby, according to the optical triangulation, the positions of the reflected structured light captured in the image are mapped to real-world positions where the structured light (511) was reflected by the object (520), and the structured light (511) intersects with a virtual volume (524) including the object (520), the virtual volume (524) corresponding to a volume in which one or more objects are present during the imaging, including the object (520) that the imaging system is configured to image; The imaging system (500; 700; 800) further comprises a light shield (550; 750; 850) positioned outside the structured light (511) between the light source (510) and the virtual volume (524), the light shield (550; 750; 850) positioned to block stray light (415) from the light source (510), thereby preventing it from reaching the virtual volume (524) within the field of view (532) of the camera (530).

2. The imaging system of claim 1 , wherein the light blocking body (550; 750; 850) has one or more light blocking major surfaces having an extension in one or more directions perpendicular to the irradiation direction of the structured light (511).

3. 3. The imaging system of claim 1 or 2, wherein the light blocking body (550; 750; 850) extends outside the structured light (511) between the light source (510) and the virtual volume (524) with the distance to the structured light (511) decreasing in the direction of the virtual volume (524: 724; 824).

4. 4. The imaging system of claim 1, wherein the light blocking body (550; 750; 850) is positioned outside the structured light (511) at a distance from the structured light (511) thereby avoiding the light blocking body (550; 750; 850) blocking light of the illumination closer to the structured light (511) than the point where the illumination has dropped to 5% of its maximum intensity.

5. 5. The imaging system of claim 1, wherein the light blocking body (550; 750; 850) is positioned outside the structured light (511) at a distance from the structured light (511) but close enough that the light blocking body (550; 750; 850) at least blocks light of the illumination where the illumination has dropped to 1% of its maximum intensity.

6. The light blocking body is a first light blocking body part (550a; 750a; 850a) arranged on a first side of the structured light (511) in the direction of the camera (530); and / or 6. The imaging system of claim 1 , further comprising a second light blocking portion (550b; 750b; 850b) arranged on a second side of the structured light (511) in a direction opposite the camera (530).

7. 7. The imaging system of claim 6, wherein the first light blocking portion (550a; 750a; 850a) is positioned outside at least a portion (532'; 732'; 832') of the field of view (532; 732; 832) of the camera (530) that covers the structured light (511) in the virtual volume (524).

8. 8. The imaging system of claim 1 , wherein the light blocking body (550; 750; 850) is closest to the structured light where the light blocking body (550; 750; 850) is closest to the virtual volume (524) and / or where the light blocking body (550; 750; 850) is closest to where the illumination has a focus.

9. A method for supporting distortion reduction in three-dimensional imaging based on optical triangulation, said three-dimensional imaging being performed by an imaging system (500; 700; 800) comprising a camera (530) and a light source (510) for providing illumination of an object (520) to be imaged, said illumination comprising structured light (511) used for said optical triangulation, said camera (530) being adapted to capture an image of the structured light (511) reflected from said object (520) as part of said optical triangulation during imaging. a virtual volume (524) including the object (520) that the imaging system is configured to image, the virtual volume (524) corresponding to a volume in which one or more objects are present during the imaging, the virtual volume (524) including the object (520) that the imaging system is configured to image, the virtual volume (524) being positioned relative to the provided structured light (511) such that, according to the optical triangulation, a position of the reflected structured light captured in the image maps to a real-world position where the structured light (511) is reflected by the object (520); The method includes preventing stray light (415) from the light source (510) from reaching the virtual volume (524) within a field of view (532) of the camera (530) at least during the imaging by the camera (530).

10. 10. The method of claim 9, wherein the step of preventing stray light is achieved by blocking the stray light with a light shield (550; 750; 850) positioned outside the structured light (511) between the light source (510) and the virtual volume (524).

Images