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

Abstract

The present disclosure at least relates to imaging systems and methods relating to three-dimensional imaging based on light triangulation. An imaging system (500; 500 ') for three-dimensional imaging based on light triangulation. 700); 800) and a method for supporting distortion reduction in three-dimensional imaging based on light triangulation. The imaging system comprises a camera (530) and a light source (510) configured to provide illumination of an object (520), the illumination comprising structured light (511). The structured light (511) intersects with a virtual volume (524) comprising the object (520), the virtual volume corresponding to a volume in which one or more objects that the imaging system is configured to image during imaging are located, the one or more objects comprising the object (520). At least during said imaging by the camera (530), stray light from the light source is prevented from reaching a virtual volume within the field of view of the camera. In an imaging system, this is achieved by a light shield arranged outside the structured light between the light source and the virtual volume.

Description

Technical Field

[0001] Embodiments herein relate to imaging systems for three-dimensional imaging based on optical triangulation. Background Art

[0002] Industrial vision cameras and systems for factory and logistics automation can be based on three-dimensional (3D) machine vision, in which 3D images of scenes and / or objects are captured. A 3D image refers to an image that also includes "height" or "depth" information rather than only or at least not only information about only two-dimensional (2D) pixels as in a conventional image (such as intensity and / or color). That is, each pixel of the image can contain information associated with the position of the pixel and mapped to the position of, for example, an object that has been imaged. Processing can then be applied to extract information about the characteristics of the object (i.e., the 3D characteristics of the object) from the 3D image and, for example, convert it into various 3D image formats. This information about height can be referred to as range data, where the range data can therefore correspond to data from a height measurement of the object being imaged, or in other words, to data from a range or distance measurement of the object. Alternatively or additionally, a pixel can include information about, for example, material properties, such as information related to the scattering of light in the imaging area or the reflection of light of a specific wavelength.

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

[0004] Line scanned image data is generated when image data for an image is scanned or provided one line at a time, for example by a camera having a sensor configured to sense and provide image data one line at a time. A special case of line scanned images is the image data provided by light triangulation using a "sheet of light" to illuminate an object being scanned by light. The sheet of light that intersects the object produces light that is projected on the object and reflected by the object. Lasers are typically used, whereby laser lines are produced on the object and reflected by the object to the camera. Lasers are typically preferred, and light triangulation is sometimes referred to as laser triangulation, but other light sources that can provide a "sheet of light" (i.e., a plane of light or other structured light) can also be used. That is, a light source that can provide light that remains focused and does not spread out too much, or in other words, "structured" light (such as light provided by a laser or light emitting diode (LED)). Therefore, in general, light triangulation as mentioned above is based on illumination using structured light.

[0005] Structured light corresponds to a defined (usually predefined) light pattern used to illuminate an object as part of light triangulation. Generally, as indicated above, structured light in the form of a light plane when it illuminates an object surface produces light that is projected on and reflected from the object surface and imaged by a camera. Other examples of structured light include light edges of illumination provided over a larger area, which can be considered to correspond to coarse light rays illuminating an object, where the light edges projected on the object correspond to and can be used correspondingly as the light rays in the case of the light plane. Other structured light can also be used to illuminate objects in light triangulation, such as producing lines, dots, grids, strips, etc. that are projected on and reflected from the object surface.

[0006] In any case, the structure of the structured light makes it possible to identify the real-world locations where reflections occur on the surface of an object in the light plane (e.g., if the structured light corresponds to the light plane) and map those locations onto the image sensor and into the image of the captured light (e.g., the reflected light). As should be appreciated, this is the basic principle of 3D imaging based on light triangulation.

[0007] 3D machine vision systems are usually based on light triangulation as described above. In such a system, there is a light source that illuminates the object with structured light, such as a light plane that produces light on the object and along which the 3D characteristics of the object corresponding to the contours of the object can be captured. By scanning the object with such lines and performing line scans on the object (involving movement of the lines and / or the object), the 3D characteristics of the entire object corresponding to multiple contours can be captured.

[0008] Typically, to generate a 3D image based on light triangulation, reflected light from an object to be imaged is captured by an image sensor of a camera, e.g., generating an image of the light projected on the object. Intensity peaks are then detected in the resulting image data. The peaks occur at locations in sensor coordinates corresponding to locations on the object where the structured light captured by the image sensor was reflected. By providing a mapping between the real-world coordinates of the structured light and the image sensor coordinates where the reflected structured light was captured (typically known from a calibration process when the imaging system was set up), the image data contains said height information about the object where the reflection occurred. Typically, but not necessarily, the imaging system is set up so that the intensity peaks associated with the reflected light should appear and be expected in each column of the sensor, and the positions within the columns are mapped to heights.

[0009] It is appreciated from the above that such intensity peaks in the image data other than those produced by light triangulation may cause problems and, if they occur, should at least not be detected and / or used as such intensity peaks belonging to light triangulation. Moreover, excessively strong intensity peaks that saturate the image sensor pixels may cause problems and make it difficult to detect the peaks with the desired resolution. As described above, the result of unwanted intensity peaks may be artifacts in the resulting contour image and in the resulting complete 3D image formed from multiple contour images, for example artifacts in the form of "spikes" in the 3D image.

[0010] Unwanted intensity peaks may be caused, for example, by secondary reflections of structured light and / or very strong specular reflections, and in the prior art they are typically mitigated by "post-image sensing" solutions, i.e., by processing the resulting image data, e.g., before or as part of an intensity peak detection algorithm. The challenge is to find and / or identify "wanted" intensity peaks for light triangulation caused by direct reflections of structured light on the surface of the object, and / or to remove or avoid using unwanted intensity peaks for light triangulation, such as intensity peaks caused by secondary reflections of structured light. It has been recognized that if an unwanted intensity peak is used as a wanted intensity peak, i.e., "as if it were a wanted intensity peak for light triangulation", then correct 3D imaging of the object cannot be produced.

[0011] Since such structured light is desired and used by light triangulation, it is natural to focus on "post-image sensing" solutions to identify the desired intensity peaks. False reflections usually cause the type of distortion in the form of "spikes", i.e., very narrow peaks in the 3D image, so the prior art often uses median filtering or similar techniques to reduce the problem using "post-image sensing" of spikes.

[0012] Another "pre-image sensing" prior art solution involves reducing the specular reflection problem of structured light by using polarized light. This reduces specular reflections while still providing usable diffuse reflections for light triangulation, see for example. The downside of this is that implementing a polarizing filter for polarized light results in a significant amount of generated light being removed and reduces energy efficiency.

[0013] While existing solutions as described above deal with mitigating the negative effects of specular reflections during light triangulation based 3D imaging, there are still distortion issues such as the described "spikes", especially when the imaged object has a highly reflective surface. Summary of 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 removal and / or reduction of distortions, such as "spikes", in 3D images from 3D imaging systems based on optical triangulation.

[0015] According to a first aspect of an embodiment of the present invention, the object is achieved by an imaging system for three-dimensional imaging of an object based on light triangulation. The system includes a camera and a light source configured to provide illumination of the object, the illumination including structured light. The camera is arranged relative to the provided structured light so that as part of the light triangulation, the camera can capture reflected structured light (511) from the object in an image, so that according to the light triangulation, the position of the captured reflected structured light in the image is mapped to the real-world position of the object reflecting the structured light. The structured light intersects a virtual volume, which includes the object and corresponds to a volume in which one or more objects including the object are located that the imaging system is configured to image during imaging. The imaging system also includes a light shield, which is arranged outside the structured light between the light source and the virtual volume, so that the light shield shields stray light from the light source, thereby preventing the stray light from reaching the virtual volume within the camera field of view.

[0016] In some embodiments, the light shield has one or more light shielding major surfaces extending in one or more directions orthogonal to the illumination direction of the structured light.

[0017] In some embodiments, the light shield extends outside of the structured light between the light source and the virtual volume, and the distance from the structured light decreases along the direction of the virtual volume.

[0018] In some embodiments, the light shield is disposed outside of the structured light at a distance from the structured light such that the light shield thereby avoids shielding light of the illumination closer to the structured light than where the illumination drops to 5% of its maximum intensity.

[0019] In some embodiments, the light shield is disposed outside the structured light, at a distance from the structured light but close enough so that the light shield shields light from at least the illumination where the illumination drops to 1% of its maximum intensity.

[0020] In some embodiments, the light shield comprises:

[0021] A first light shield member is arranged on a first side of the structured light in the direction of the camera; and / or

[0022] The second light shield member is arranged on a second side of the structured light in an opposite direction of the camera.

[0023] In some embodiments, the first light shield component is disposed outside of at least a portion of the structured light in the coverage virtual volume of the camera field of view.

[0024] In some embodiments, the sunshade is closest to the structured light where the sunshade is closest to the virtual volume and / or where the sunshade is closest to a location where the illumination has a focus.

[0025] According to a second aspect of an embodiment of the present invention, the object is achieved by a method for supporting the reduction of distortion in three-dimensional imaging based on light triangulation, wherein the three-dimensional imaging is performed by an imaging system. The imaging system includes a camera and a light source for providing illumination of an object to be imaged. The illumination includes structured light for light triangulation. The camera is arranged relative to the provided structured light so that the camera captures reflected structured light from the object in the image during imaging as part of the light triangulation, so that according to the light triangulation, the position of the captured reflected structured light in the image is mapped to the real-world position of the object reflecting the structured light. The structured light intersects a virtual volume, which includes the object and corresponds to a volume in which one or more objects including the object are located that the imaging system is configured to image during imaging. The method includes preventing stray light from the light source from reaching the virtual volume within the camera field of view at least during the imaging performed by the camera.

[0026] In some embodiments, the stray light prevention is achieved by shielding the stray light by a light shield arranged outside the structured light between the light source and the virtual volume. The light shield may be as described above.

[0027] Embodiments herein are based on the discovery that, while the reflection of stray light is very weak and appears to be generally negligible relative to the structured light used in light triangulation, the reflection of stray light can still be problematic when it causes specular reflections in the camera's field of view within the virtual volume, such as reflections on the imaged object but outside the structured light or reflections on adjacent objects in the virtual volume (such as the next object to be imaged or the object imaged just before the imaged object). Even so, the stray light is very weak relative to the structured light reflected from the object toward the camera, but it has been found that specular reflections of the stray light (primarily direct reflections, but sometimes also secondary specular reflections) toward the camera can result in unwanted intensity peaks that are difficult to distinguish from the wanted intensity peaks caused by the structured light based on light triangulation. Post-imaging methods for finding the wanted intensity peaks for light triangulation (i.e., corresponding to the direct reflections from the object) typically focus on excluding other unwanted intensity peaks other than those from specular stray light reflections, such as those from secondary reflections of the structured light or caused by other phenomena. As described in the embodiments herein, by preventing stray light from entering the field of view within the virtual volume (e.g., by shielding the stray light), the risk of problematic specular stray light reflections occurring, which would otherwise cause, for example, distortions (such as "spikes") in the 3D image, is reduced. Therefore, the embodiments herein enable or at least support reducing this, thereby also improving 3D imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Examples of embodiments herein are described in more detail with reference to the accompanying schematic drawings which are briefly described below.

[0029] Figure 1 An example of a prior art imaging system for 3D imaging based on light triangulation, upon which embodiments herein may be based, is schematically illustrated.

[0030] Figure 2A -B schematically illustrates the Figure 1 The situations and some relationships presented by the prior art imaging system.

[0031] Figure 3A -D schematically illustrates examples and situations of prior art imaging systems that may cause problems due to stray light.

[0032] Figure 4A -C schematically illustrates how the illumination including structured light used in light triangulation also includes stray light and how it is related to the structured light.

[0033] Figure 5A -C schematically illustrates an imaging system with a first example of a light shield according to an embodiment of the present invention.

[0034] Fig. 6A -B is an image illustrating the results of 3D imaging of a highly specular metal foil based on light triangulation using a prior art imaging system and using an imaging system according to embodiments herein.

[0035] Figure 7 An imaging system with a second example of a light shield according to embodiments herein is schematically illustrated.

[0036] Figure 8 An imaging system with a third example of a light shield according to embodiments herein is schematically illustrated.

[0037] Fig. 9 is a flow chart schematically illustrating an embodiment of a method according to embodiments herein. DETAILED DESCRIPTION

[0038] The embodiments herein are exemplary embodiments. It should be noted that these embodiments are not necessarily mutually exclusive. It can be assumed by default that components from one embodiment exist in another embodiment, and it is obvious to those skilled in the art how those components can be used in other exemplary embodiments.

[0039] As part of the development of the embodiments herein, the situation discussed in the background technology will first be further elaborated and discussed.

[0040] Even if most of the light from the light source is structured light in and used by the light triangulation, in practice it is usually not possible to completely avoid that the illumination of the light source will also result in some stray light in addition to the structured light. In principle, by definition, all stray light is very small compared to the structured light and usually seems to be negligible in comparison. In the case where the surface of the object only provides diffuse reflection, stray light usually does not cause problems.

[0041] Since the total amount of stray light is very small compared to the structured light used in light triangulation and appears to be insignificant on the surface, stray light is conventionally ignored in the context of light triangulation. As discussed in the background, the problem of specular reflection has been attributed to and caused by structured light, and different solutions exist for this problem.

[0042] Besides the fact that stray light seems to be generally insignificant relative to structured light, the following situation may explain why the problem of stray light in optical triangulation has not been recognized, or at least not well recognized, in the prior art, despite the long history of 3D imaging by optical triangulation: Such “post-image sensing” solutions mentioned in the background, operating on image data, solve at least some of the problems of unwanted intensity peaks caused by stray light. Any intensity peak caused by stray light will usually be mixed with other unwanted intensity peaks, such as those caused by secondary structured light reflections. In principle, stray light reflections only become a problem if one or more objects being imaged in 3D based on optical triangulation have highly reflective surfaces, in which case unwanted intensity peaks caused by secondary and higher-order reflections of structured light will also add up.

[0043] Embodiments herein are based on the discovery and recognition that stray light, even if its total amount seems insignificant relative to structured light, can still cause problematic unwanted intensity peaks in the image data, some of which can be particularly difficult to eliminate by "post-image sensing" methods that operate on the image data to find the intensity peaks wanted by light triangulation. Therefore, embodiments herein are further based on the recognition that 3D imaging based on light triangulation can be improved if stray light can be prevented from causing reflections that produce unwanted intensity peaks in the first place. In this way, there will be fewer unwanted intensity peaks in the image data to deal with, for example, by conventional or other "post-image sensing" methods.

[0044] Before further discussing and explaining the embodiments of the present invention in detail, some basics about prior art 3D imaging systems based on optical triangulation and the general situation of such systems will be discussed, as well as detailed examples of situations where stray light may cause problems such as those mentioned above. This is done to facilitate understanding of the embodiments of the present invention and the differences compared to the prior art and conventional 3D imaging systems based on optical triangulation.

[0045] Figure 1An example of a prior art imaging system 100 for 3D imaging based on light triangulation is schematically illustrated, on which embodiments of the present invention may be based. The imaging system 100 may alternatively be, for example, an imaging system for 3D machine vision based on light triangulation, for capturing information about 3D characteristics of a target object. The imaging system 100 shown in the figure is in a normal operating situation, i.e., typically after calibration is performed, and the system is therefore calibrated. The imaging system 100 is configured to perform light triangulation, here in the form of light sheet triangulation, i.e., light triangulation using structured light as a light plane. The imaging system 100 also includes a light source 110, such as a laser, for illuminating an object to be imaged with structured light (usually a specific light pattern). In the examples and figures, there is structured light 111 in the form of a light plane. The light may be (but need not be) a laser, or may alternatively be, for example, light from one or more light emitting diodes (LEDs). Another example of structured light that is similar but not a conventional light plane (but has a similar effect) is a light edge, i.e., an edge of an area with illumination. The generated light and illumination are usually provided by one or more lenses, for example, in order to focus the light. In addition, the camera is usually configured and positioned so that based on the so-called Scheimpflug law, its focal plane is co-located with the structured light 111 (usually the light plane), in other words, aligned with the structured light 111. In this way, the object reflection occurring in the light plane will be focused in the image sensor. In the example shown, the object to be imaged is exemplified 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 can be referred to as a measurement object. When the structured light 111 is incident on the object, this corresponds to the projection of the structured light 111 on the object, which can be observed when the structured light 111 intersects with the object. For example, in the example shown, the structured light 111 in the form of the light plane generates a light 112 on the first measurement object 120. The structured light 111 is reflected by the object, more specifically, it is partially reflected by the object at the intersection (i.e., at the light 112 in the example shown). The imaging system 100 also includes a camera 130, which includes an image sensor ( Figure 1). The camera and the image sensor are arranged relative to the light source 110 and the object to be imaged so that the structured light 111 becomes incident light on the image sensor when reflected by the object. The image sensor is an arrangement, usually implemented as a chip, for converting the incident light into image data. The portion of the object that causes the incident light on the image sensor by reflection can thereby be captured by the camera 130 and the image sensor, and corresponding image data can be generated and provided for further use. For example, in the example shown, the structured light 111 will be reflected to the camera 130 and the image sensor at the light 112 on a portion of the roof of the first object 120, so that image data with information about the portion of the roof can be generated and provided. According to the principle of light triangulation, by understanding the geometry of the imaging system 100, such as how the image sensor coordinates are related to the world coordinates (such as the coordinates of the coordinate system 123 (such as Cartesian coordinates) associated with the imaged object), the image data can be converted into information about the 3D characteristics (e.g., the form of a 3D shape or contour) of the object being imaged in an appropriate format. The information about the 3D characteristics may include data describing the 3D characteristics in any suitable format.

[0046] By moving the light source 110 and / or the object to be imaged, such as the first object 120 or the second object 121, so that multiple portions of the object are illuminated and the image sensor senses the reflected light in the image, in effect, by scanning the object with the structured light 111, image data describing a more complete 3D shape of the corresponding object can be generated, for example, corresponding to a plurality of continuous contours of the corresponding object, such as the contour images 140-1 to 140-N of the first object 120 shown. Each contour image shows the shape of the first object 120 where the structured light 111 is reflected when the image sensor of the camera unit 130 senses the light that generates the contour image. As indicated in the figure, a movable object support structure 122 such as a conveyor belt or the like can be used to move the object through the structured light 111 and thereby scan the object, wherein the light source 110 and the camera unit 130 are generally fixed. Alternatively, the structured light 111 can be moved over the object so that all portions of the object, or at least all portions facing the light source 110, are illuminated and the camera receives light reflected from all portions of the object desired to be imaged.

[0047] As can be understood from the above, for example, during imaging of the first object 120, the corresponding images or image frames provided by the camera 130 and its image sensor can correspond to any one of the contour images 140-1 to 140-N, or be used to provide any one of the contour images 140-1 to 140-N. Each position of the outline of the first object shown in any one of the contour images 140-1 to 140-N is generally determined based on identifying intensity peaks in the image data captured by the image sensor and finding the positions of these intensity peaks. The imaging system 100 and the conventional peak finding algorithm are generally configured to search for intensity peaks for each pixel column in each image frame. If the sensor coordinates are u, v, and for example, u corresponds to a pixel position along a row in the image sensor as indicated in the figure, and v corresponds to a pixel position along a column, then for each position u of the image frame, the peak position along v is searched, and the peaks identified in the image frame can produce such a "clean" contour image as shown in the figure, and the sum of the image frame and the contour image can be used to create a 3D image of the first object 120.

[0048] Figure 2A -B schematically illustrates the Figure 1 The prior art imaging system presents the situation and some relationships in which Figure 2A is a 3D view, and Figure 2B yes Figure 2A 2D side view of what is shown in . The system shown may correspond to the imaging system 100, but is shown in a more schematic and simplified view to focus on and explain some details associated with such a system. The details shown in the figure are to facilitate understanding of the embodiments of the present invention further presented below and for subsequent comparison with the embodiments of the present invention. The imaging system 200 shown can be considered to correspond to a basic configuration and includes: 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 can correspond to the structured light 111. A camera 230 with an image sensor 231 is arranged to sense a first reflected light from the object 220 as part of the light triangulation for 3D imaging, i.e., configured and positioned relative to each other for light triangulation. This typically involves arranging the first light source 210 and the camera 230 at predetermined fixed positions and in a known relationship with each other for light triangulation. Camera 220 has a field of view 232 that at least partially covers the light plane, and in particular covers portions of the light plane where object 220 and other objects that the system is configured to image may intersect the light plane.

[0049] In the system shown in the figure, and in prior art imaging systems commonly used for 3D imaging based on light triangulation, such as Figure 1 As shown in , there is a virtual volume, Figure 2A -B, and explicitly indicated in dashed lines in the figure as a virtual volume 224. As used herein, a virtual volume (such as virtual volume 224) corresponds to a volume in which one or more objects (e.g., objects 220a-b shown in the figure, which the imaging system 200 is configured to image) are present during imaging. The virtual volume includes locations where structured light is presented to illuminate the objects during imaging and thereby intersects the objects. In addition, the virtual volume extends on both sides of the structured light, both toward and away from the camera. The structured light 111 thus provided intersects the virtual volume, as shown in the figure. The structured light 111 is shown in the figure in a situation where it intersects the virtual volume 224 and the object 220a, so that the light ray 212 is projected onto the object 220a and the object support structure 222 at the "bottom" of the virtual volume 224 (e.g., intersecting the camera). Figure 1 The maximum object height supported by the imaging system typically determines the height of the virtual volume and, therefore, determines where the structured light first reaches the virtual volume.

[0050] An example real-world Cartesian coordinate system xyz and xy is also shown for reference.

[0051] Figure 3A -D schematically illustrates examples and situations of prior art imaging systems that have been identified as causing problems due to stray light. Thus, the imaging system 300 shown may therefore correspond to any of the imaging systems 100, 200, but the objects to be imaged have mirrored, mirror-like, spherical surfaces, which are the types of objects that are very difficult to image in 3D using optical triangulation. These objects are schematically illustrated in the figure as a first object 320-1 and a second object 320-2. The following figures and examples are used to explain and show how stray light, although weak, can cause problems in these and similar situations.

[0052] As described above, since imaging system 300 may correspond to any of imaging systems 100, 200, there is correspondingly a camera 330 having a field of view 332 and a light source 310, which may correspond to cameras 130, 230, fields of view 132, 232, and light sources 110, 310. Light source 210 provides illumination including structured light 311 in the form of a light plane, 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 indicated, which may correspond to virtual volume 224.

[0053] Figure 3AA first exemplary case is shown, in which the first object 320-1 is located outside the structured light 311, for example because the structured light 311 has not yet reached the first object 320-1. According to light triangulation, this should not lead to any object-related intensity peaks in the image captured in the shown case. If there are any, then the intensity peaks should only come from diffuse reflections in the object support structure 322. However, although very weak relative to the structured light 311, stray light 315a from the illumination of the light source 310 (thus located outside the structured light 311 so used for the purpose of light triangulation) may reach and cause specular reflections at the surface of the first object 320-1 as schematically shown in the figure, and the reflected stray light 316a is directed towards the camera 330 and imaged by the camera 330. This will appear as an intensity peak in the image, as if the structured light 311 had been diffusely reflected on the object at the point 322a indicated in the figure. As a result, there will be an unwanted intensity peak in the image, which may not be as intense if caused by secondary or higher order reflections of structured light 311, but may still be as intense or stronger than the intensity peak from the desired diffuse reflection of structured light 311. Therefore, it is difficult to distinguish the unwanted intensity peak from the desired intensity peak in this case, for example by using conventional post-imaging processing to find the desired intensity peak.

[0054] Figure 3B A second exemplary situation is shown, in which a first object 320-1 is illuminated by structured light 311. The first object 320-1 may have been illuminated by structured light 311. Figure 3A 320-1 as part of the object scan. According to light triangulation, this should result in a desired intensity peak caused by reflection of the structured light in the surface of the first object 320-1. However, stray light 315b from the illumination of the light source 310 (thus located outside the structured light 311 used for the purpose of light triangulation) may also arrive and cause specular reflection in the surface of the first object 320-1 as schematically shown in the figure, with reflected stray light 316b heading towards and imaged by the camera 330. This will appear as an intensity peak in the image, just as if the structured light 311 had been diffusely reflected in the surface of the object at the point 322b indicated in the figure. As a result, there will be an unwanted intensity peak in the image, which may be as strong or stronger than the desired diffuse reflection of the structured light 311 on the object. Thus, for example, if first object 320-1 diffusely reflects structured light 311 toward the camera, at least two intensity peaks will exist where only a single, desired intensity peak is expected and will be difficult to distinguish from one another, for example, by conventional post-imaging processing for finding the desired intensity peak.

[0055] Figure 3C A third exemplary situation is shown, in which a first object 320-1 is illuminated by structured light 311, wherein the first object is Figure 3B 311). According to the light triangulation, there should also be the desired intensity peak caused by the reflection of the structured light in the surface of the first object 320-1. However, stray light 315c of the illumination from the light source 310 (and therefore outside the structured light 311) may arrive as schematically shown in the figure and cause specular reflection in the surface of the first object 320-1 outside the structured light 311. If this part of the second object (as assumed in the example) is highly reflective, such as mirror-like, then it may cause specular reflection towards the second object 320-2 in the form of first reflected stray light 316c as shown in the figure. If the second object 320-2 is also highly reflective, at least at the location where the first reflected stray light 316c is reflected by the second object, then there may be secondary reflected stray light 317c towards the camera 330 and imaged by the camera 330 as shown in the figure. This will appear as an intensity peak in the image, as if the structured light 311 had been diffusely reflected in the surface of the object in the point 322c indicated in the figure. As a result, there will be an unwanted intensity peak in the image that may be as strong or stronger corresponding to the desired diffuse reflection of structured light 311. Thus, for example, if first object 320-1 diffusely reflects structured light 311 toward the camera, at least two intensity peaks will be present where only one desired intensity peak is expected and will be difficult to distinguish from one another, for example, by conventional post-imaging processing for finding the desired intensity peak.

[0056] Figure 3D A portion or sub-volume 326 of the virtual volume 324 where problematic specular reflections of stray light as discussed above occur is explicitly indicated with a thick dashed line. The sub-volume 326 corresponds to the field of view 332 within the virtual volume 324. Therefore, this is a location where it is particularly desirable to avoid or reduce the entry of stray light.

[0057] In general, for imaging systems based on optical triangulation, in particular if the object to be imaged has a highly reflective surface or is located near a highly reflective surface, it has been found to be advantageous to avoid or reduce stray light originating from illumination including structured light from entering the field of view of the camera within a virtual volume, where the virtual volume corresponds to the volume in which one or more objects are located that the imaging system is configured to image during imaging.

[0058] Embodiments herein, as illustrated and described in some detail below, are based on the above findings and insights, wherein reducing stray light entering a field of view within a virtual volume is preferably accomplished by shielding the stray light, thereby preventing it from entering the field of view within the virtual volume.

[0059] Figure 4A-C schematically illustrates how the illumination including structured light used in light triangulation also includes stray light, and is used hereinafter to discuss stray light and structured light in relation to each other.

[0060] Figure 4A A portion of structured light 411 is schematically shown, for example, Figure 3A -D corresponds to the structured light 311, i.e., what is shown may correspond to the thickness of the cross section of the light plane. The figure also attempts to illustrate that the light intensity is not uniformly distributed, but decreases in the direction away from the maximum intensity of the illumination, which is of course part of the structured light 411 and is located here at the center of the structured light 411. The structured light 411 is shown as having a thickness 412. However, as realized, in reality, Figure 4A The location at the middle dashed line does not suddenly stop with a complete absence of light, but rather the light continues to decrease as you move away from the center, according to some applicable light distribution (usually a Gaussian distribution). Thickness 412 can correspond to some measurement that is used to indicate how thick or thin the light plane is (or the resulting line corresponding to the projection of the light plane on a vertical surface) and / or specifies characteristics about the illumination and light source. A measurement that is sometimes used to indicate this is the so-called full width at half maximum (FWHM), which is the full width of the light distribution when the maximum intensity corresponding to the peak intensity is reduced to half. Other thickness measurements can also be used, but for this example, it can be assumed that Figure 4A The thickness indicated in corresponds to the FWHM.

[0061] Figure 4B Schematically illustrates the Figure 4A What the associated above light distribution (here light distribution 440) might look like. The FWHM thickness 412 is indicated in the figure. The maximum intensity 441 of light distribution 440 is also shown in the figure, and line 442 indicates where the maximum intensity on the left side of light distribution 440 begins to decrease. In addition, line 444 shows where the light intensity of light distribution 440 has decreased to 5% of the maximum value, indicated in the figure by the "5% of maximum light intensity" line 445. The reason for 5% is discussed below. As can be seen in the figure, line 444 indicates the distance 446 between lines 442 and 444.

[0062] The structured light used in light triangulation includes at least the maximum intensity of the light distribution and the main part of the illumination, and also includes light that drops to some level below the maximum intensity. For example, structured light typically includes light at least to FWHM or according to some similar measurement. However, a more pragmatic approach is to define structured light as light that is effectively used and useful for light triangulation, which may not be just light within, for example, FWHM. The light distribution typically differs depending on the light source, how the light source is configured to provide illumination, etc. The exact part of the light distribution that is structured light used for light triangulation can also vary from application to application (although it will of course always include a portion of the maximum intensity value). Therefore, the exact end position of the structured light is not always the same. However, in practice, for a system setup for a certain light triangulation application, the limitations of the structured light can be found from simple experiments: for example, as in the embodiments herein and as described below, the shading element can be moved toward the structured light perpendicular to the illumination direction, and when a negative impact on the results of the light triangulation and its results begins to occur, and / or when visual interference with the light begins to occur, for example, visual interference and / or interference with the light projected onto the object or the object supporting surface, the part of the shading element closest to the structured light indicates the starting position of the structured light used for and useful for light triangulation.

[0063] In the context of light triangulation and as used herein, stray light can be defined as light that is not useful for such light triangulation and is therefore light that is part of the illumination but is outside of the light that is considered and used as structured light in the light triangulation, or in other words, stray light is light that is not used in such light triangulation and is not used by the light triangulation itself.

[0064] If the structured light and its light distribution have a center, for example in the case of a light plane with a thickness that encompasses the structured light, such as in the case of structured light 412, for example according to the FWHM definition, then stray light refers to at least light outside this thickness, for example outside thickness 412, or at a certain distance outside this thickness.

[0065] Stray light can be defined or predefined relative to the light distribution, for example, there should be a certain intensity reduction from the maximum intensity and should be defined so that it at least does not include structured light used for light triangulation. For example, it can be defined that light at a certain distance from the maximum intensity of the light distribution is considered to be stray light. Preferably, such a distance is defined relative to the position where the light distribution is reduced to a certain extent (such as reduced to at least x% of the maximum intensity value) relative to its maximum and / or center position. Through such experiments as described above, it is found that, in general, or based on experience, when the light distribution is reduced to at least 5% of its maximum value, the structured light used and useful in the light triangulation related to the embodiments of the present invention no longer exists, so the stray light will usually not be closer to the maximum intensity than this. This is Figure 5B The reason for the center line 444 and the "5% of maximum light intensity" line 445.

[0066] Figure 4C 4 is an alternative schematic diagram for illustrating structured light and stray light at the same time. The figure indicates structured light 412 and stray light 415, where it is considered that stray light 415 starts at line 444, that is, the position where the light intensity has decreased to 5% of its maximum intensity, which corresponds to the distance 446 to the line 442 indicating that the maximum intensity begins to decrease. As shown in the figure, according to the light distribution 440, the light at the position closer to the structured light 412 is more than the light at the farther position, and therefore the stray light is also more. It can be understood from the figure that the light distribution is not the same at different positions along the illumination (such as at different heights). Note that although not shown in the figure, in fact, the thickness 412 including the structured light 411 also varies in thickness along the illumination.

[0067] Figure 5A FIG. 5C schematically illustrates an imaging system 500 according to an embodiment of the present invention, which includes a first example of a light shield, ie, a first light shield 550 , for shielding stray light.

[0068] Figure 5A Similar to the above examples, imaging system 500 is schematically shown in a side view to facilitate comparison. The side view corresponds to a cross-section of light shield 550.

[0069] Figure 5B The imaging system 500 is schematically shown from a top view to better understand what it looks like in the lateral dimension.

[0070] The imaging system 500 may correspond to any of the imaging systems 100, 200, 300 and is therefore also an imaging system for 3D imaging based on light triangulation, but in addition comprises a light shield 550. Thus, the imaging system 500 comprises a camera 530 having a field of view 532, and the camera 530 may correspond to any of the cameras 130, 230, 330 having a field of view 132, 232, 332. There is also a light source 510, which may correspond to any of the light sources 110, 210, 310 and provides illumination comprising structured light 511 in the form of a light plane, which may correspond to any of the structured light 111, 211, 311. There is also an object support structure 522, which may correspond to any of the object support structures 122, 222, 322. A virtual volume 524 is also indicated, which may correspond to the virtual volume 324 or 224, wherein a subvolume 526 is indicated, which may correspond to the subvolume 326. The subvolume 526 corresponds to the field of view 532 within the virtual volume 524. As an example, an object 520 to be imaged in the virtual volume 524 is also schematically shown. The object 520 may correspond to any object to be imaged as shown and discussed in the above examples and figures, and may, for example, have one or several surfaces or surface portions that are highly reflective, such as mirror-like, which may cause problems of the stray light type discussed above.

[0071] The light shield 550 extends between the light source 510 and the virtual volume 524 and includes a first light shield part 550a arranged on a first side in the direction of the camera 530 of the structured light 511 and a second light shield part 550b arranged on a second side in the opposite direction of the camera 530 of the structured light 511. Providing the light shield in an orientation to shield at least two portions of light on either side of the structured light is advantageous because it enables more stray light to be shielded.

[0072] As can be seen, the light shield 550 has a funnel shape because the first light shield component 550a and the second light shield component 550b of the light shield 500 extend between the light source 511 and the virtual volume 524, and the distance to the structured light 511 decreases in the direction of the virtual volume 524. The funnel shape enables efficient and practical stray light shielding with a relatively small total light shield. The relatively small shielding surface can cover and shield most of the stray light, while it can still have a minimum distance to the structured light at a single location along the structured light (and usually most efficiently, such as near the virtual volume).

[0073] It can be appreciated from the figure that the light shield 550 has the effect of shielding stray light, ie shielding at least some stray light from the light source 510 , or in other words, shielding stray light of the provided illumination, which would otherwise reach the sub-volume 526 .

[0074] As used herein, a light shield generally refers to a structure or arrangement, such as light shield 550, that prevents at least some light incident on the light shield from passing through the light shield and reaching an area or volume, such as subvolume 526, that would otherwise reach the area or volume if the light shield were not present. Typically, all or a substantial portion of the light incident on the light shield should be prevented from passing through, or at least all light within a particular wavelength (e.g., all wavelengths of light provided by a light source, such as light source 511) should be prevented from passing through, to enable illumination using structured light, such as structured light 511, for 3D imaging by optical triangulation, as described in the embodiments herein.

[0075] like Figure 5A , the light shield is positioned in the field of view 532 but does not interfere with the portion of the field of view that covers the structured light 511 in the virtual volume 524, i.e., does not negatively impact the imaging of the structured light 511 in the virtual volume 524, since this is where objects appear during imaging and reflect the structured light 511 toward the camera 530. In general, the light shield in the embodiments herein will block a portion of the field of view and the imaging of the structured light in the virtual volume, but this is generally undesirable since this is at the expense of reducing the effective field of view. Typically, the field of view is provided such that it is within Figure 5A The upper limit in just covers the maximum supported object height, i.e., is aligned with the height of the virtual volume so that it covers structured light in the virtual volume, but covers no or little structured light outside the virtual volume, since the object to be imaged should not appear there, so the result is a reduced utilization of the camera's image sensor for object imaging. However, in the case of a field of view such as the example field of view 532 in the figure (which also covers some structured light outside the virtual volume), it is recognized that if the light shield 532 (as shown) is in the field of view 532, but outside the portion of the field of view 532 covering the structured light 511 in the virtual volume 524, then there is no further impairment of object imaging. In other words, in such a case, as Figure 5A As shown in , the light shield 532 should be located outside the virtual line 533, which extends from the location where the structured light 511 intersects the virtual volume 524 to the location where the field of view at the camera 530 begins. In this case, the virtual line 533 is the limit of the effective field of view 532' where the object is imaged, and marks the effective field of view 532', and is reduced compared to the actual field of view 532.

[0076] Figure 5C Schematically shows Figure 5A 550 in FIG. 5. The figure shows the minimum distance 552 that the structured light 511 passes through, which corresponds to the gap. Figure 5A In the embodiment of the light shield with a corresponding "funnel" design shown in -C, the distance corresponding to the minimum distance 552 is 0.9 mm. Figure 4A -C, the corresponding light shield components on the corresponding sides of the structured light 511 can be arranged to have a minimum distance from the structured light so as not to shield the structured light used in the light triangulation. This means that for example Figure 5A In the embodiment with two light shield components shown in FIG. 5-C, the first minimum distance 552a between the first light shield component 5501 and the structured light 511 and the second minimum distance 552b between the second light shield component 550b should be sufficient to not shield the structured light. How to achieve this in practice has been described above in conjunction with Figure 4A -C is disclosed and can be determined, for example, by the same type of experiment. That is, if the light shield is so close to the structured light that it has a visual impact on the structured light, such as a visual impact such as interference in the projection of the structured light (e.g., the light plane) on the object or the object support surface, then the light shield is too close to the structured light and will also shield and / or affect the structured light to an undesirable extent. For most conventional light sources and structured light (e.g., the light plane) used for light triangulation, this means that the light shield is preferably arranged at a distance from the structured light that is not less than a position where the structured light has been reduced to at least 5% of its maximum value. Or in other words, it is located at a position where the illumination including the structured light has been reduced to at least 5% of its maximum value. That is, the light shield should generally at least not be arranged at a position closer to the structured light than according to this distance. Therefore, the light shield can only shield stray light at or farther than this distance from the maximum intensity of the structured light. For example, this means that in some embodiments, the corresponding minimum distances 552a, 552b are no closer to the maximum intensity of the structured light 511 than the position where the intensity of the light distribution of the illumination has decreased to 5% of the maximum intensity. However, in some cases, for the reasons mentioned above, it may still be preferred to use a larger minimum distance, i.e., to arrange the light shield component farther away from the structured light, for example, to make it no closer than the position where the intensity of the light distribution has decreased to 4%, 3%, 2% or 1% of the maximum intensity.

[0077] In applications and situations where the light distribution is very narrow (e.g., provided by a narrow laser), if it is too close, then slight changes in the light shield (such as accidental or accidental movement of the light shield during operation) can block it and negatively affect the structured light. In such cases, the light shield may preferably be in a position with a larger margin to the structured light.

[0078] However, in general, it may be preferred to place the light shield as close as possible to the structured light used in light triangulation without negatively affecting the structured light and thus the light triangulation itself, i.e., the object being imaged by light triangulation.

[0079] In addition, the minimum distance to the structured light is preferably as close to the virtual volume as possible without affecting the structured light used in light triangulation and without blocking and / or interfering with object imaging. Since it is close to the virtual volume, it may be easier to achieve an effective stray light shielding effect.

[0080] For the placement of the light shield, especially to the position with the minimum distance to the structured light, it should be taken into account that the light source usually has a lens through which the structured light is provided. The focal point of the lens is often outside the virtual volume, that is, "in front of or behind" the virtual volume, in order to ensure that the light distribution in the virtual volume is not too narrow (since it is desirable to utilize some sufficient "width" of the structured light so that the peak position can be identified with sub-pixel resolution). If the focal point is "in front of" the virtual volume, then using a light shield with the minimum distance to the structured light at or near the focal position can be beneficial, because it can be closer to the structured light without negatively affecting it.

[0081] For example, as described above, by ensuring that the light shield shields at least some stray light (which would otherwise reach the "intersection" between the camera's field of view and the virtual volume, i.e., the field of view within the virtual volume), it can be ensured that the light shield has an effect, rather than just shielding stray light that is too far away. However, while the light shield should not be too close to the structured light to affect the structured light, as discussed above, it is beneficial for the gap between the light shield and the structured light to be small or at least not too large, so that not too much stray light close to the structured light can escape. Therefore, the light shield is preferably arranged to maintain a certain distance from the maximum intensity (peak) so that it exists at least at the position where the light distribution is reduced to 1% of its maximum value. This is to prevent too much stray light close to the structured light from escaping the light shield, thereby reducing the effect of the embodiments herein.

[0082] In summary, taking into account the above, it has been found that the light shield is preferably arranged at a distance from the maximum intensity (peak) of the light distribution that is not less than the position where the structured light has decreased to at least 5% of its maximum value, and at the same time, the light shield is preferably located at a position where the light distribution has decreased to 1% of its maximum value, for example, the light shield is present in and covers at least a portion of the area extending between 5% and 1%. In many applications, this corresponds to the light shield having a gap around the structured light (e.g., the light plane) and / or to its maximum intensity that is only a fraction of a millimeter, or about 1 millimeter or half a millimeter, or a few millimeters to about one centimeter. The light shield (e.g., a light shield part thereof) can extend away from the structured light from there, so that the light shield stretches perpendicular to the illumination direction and covers at least a few centimeters above the virtual volume, but longer or even shorter light shields may be suitable depending on the application.

[0083] In addition, as will be appreciated by those skilled in the art, the sunshade and any part thereof involved in the sunshade as discussed in the embodiments herein and above can be made of any one or more of a variety of different materials. It is not important which material(s) is used specifically, as long as it has sunshade properties. However, it may be preferred to use some opaque plastic materials and / or to coat or cover the substrate or core material with a surface material to achieve or enhance the sunshade properties. For example, in order to make the sunshade more absorbing and / or non-reflective, it may be preferred to use a matte and preferably dark surface to avoid or minimize the reflection from the sunshade 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 particularly absorbing light and / or ensuring that these surfaces are matte and / or dark, because such reflective surfaces may, in the worst case, result in secondary reflection of the reflected light from the virtual volume and reflect it back to the virtual volume, where unwanted intensity peaks may appear in the image. If one or more light shielding surfaces (such as surfaces 554a-2, 554b-2) facing a light source (e.g., light source 510) cause some reflection, then it may not be so important because there is still a shielding effect and any light reflected on that side is unlikely to end up entering subvolume 526 and cause problems. However, of course, this does not generally mean that such surfaces are highly reflective, and in practice, the simplest approach is to have all light shielding surfaces made of the same material and / or have the same coating, such as low reflection and light absorption, such as a matte and preferably dark color.

[0084] Fig. 6A -B is an image illustrating the results of 3D imaging of a highly specular metal foil based on light triangulation using a prior art imaging system versus the results of 3D imaging using the same system but with a light shield for stray light as in the embodiments herein. More specifically, the images shown are from Figure 5A -C is produced without a light shield and with a light shield (such as light shield 500). The object imaged in both images is the same and corresponds to a class of objects that are generally difficult to image in 3D based on light triangulation, which is a highly reflective metal foil with a random height profile and large height differences. In an embodiment, the illumination including structured light (corresponding to structured light 511) is provided by a laser as a light source, which corresponds to the light source 510 with structured light (corresponding to the laser plane). The distance corresponding to the minimum distance 552 between the light shield parts is 0.9 mm and is arranged so that the distance between the light shield and the structured light is not less than 5% of the maximum intensity of the laser illumination at the location of the light shield. Therefore, the structured light, here the laser plane, is located in the center of the gap formed by the 0.9 mm distance. The two light shield parts corresponding to the light shield parts 550a, b have a corresponding minimum distance, which corresponds to the corresponding distance 552a, b between the corresponding light shield parts and the structured light, and thus the distance is less than half of the 0.9 mm distance, i.e., less than 0.45 mm. Although the light shield was not fine-tuned for the application in any way, because the implementation and testing were more of a "proof of concept", the improvement of the 3D image based on the imaging in the presence of the light shield can be clearly seen. When the light shield is present, many of the "spikes" in the image (corresponding to distortion) do not occur. As indicated in the introduction above, such "spikes" are usually caused by unwanted intensity peaks, such as the intensity peaks caused by specular reflections of stray light in this example. Their presence in the 3D image (as shown in the figure) is often due to the "post-image sensing" processing having problems in distinguishing wanted intensity peaks from unwanted intensity peaks, and thus sometimes selecting unwanted intensity peaks instead of the actual wanted intensity peaks, where the wanted intensity peaks are the intensity peaks caused by the direct reflection of the structured light on the object.

[0085] Figure 7 The imaging system 700 according to an embodiment of the present invention is schematically illustrated, which has a second example of a light shield, namely, a light shield 750. Except for the light shield, the rest of the imaging system 700 is the same as Figure 5A -C. This is to facilitate comparison. However, as will be appreciated by those skilled in the art, the light shield in the embodiments herein is of course compatible with and can be used in general light triangulation-based 3D imaging systems, not just 3D imaging systems such as those schematically illustrated in the examples herein. Therefore, the following will focus on the light shield 750 in imaging system 700 and the differences compared to the light shield 550 in imaging system 500. Anything not discussed can be assumed to be related to the above. Figure 5A -C The content discussed is the same or similar.

[0086] The imaging system 700 is Figure 5A The side view corresponds to the cross section of the light shield 750. Although not shown as Figure 5B , but it can be assumed that the light shield 750 extends in a similar manner across the lateral extension of the virtual volume 524, i.e., in the y direction in the example coordinates used herein. Note that the light shield in the embodiments herein need not extend to the entire lateral extent of the virtual volume, but this is generally preferred, and in some embodiments may only extend partially to the lateral extent of the virtual volume.

[0087] Furthermore, the light shield 750 extends and exists between the light source 510 and the virtual volume 524, and includes a first light shield component 750a disposed on a first side of the structured light 511 in the direction of the camera 530 and a second light shield component 750b disposed on a second side of the structured light 511 in the opposite direction of the camera 530. Note that it is not necessary to have light shield components on both sides of the structured light in all embodiments, but this is generally preferred.

[0088] Here too, the first light shield element 750 a (and therefore also the light shield 750 ) extends between the light source 511 and the virtual volume 524 , with its distance from the structured light 511 decreasing in the direction of the virtual volume 524 .

[0089] Therefore, the sunshade in the embodiments herein may have a tapered or funnel-shaped extension towards the virtual volume, for example, in the virtual volume, the smallest distance to the structured light may be towards and may be the part of the sunshade closest to the virtual volume.

[0090] It can be seen from the figure that the light shield 750 also has the effect of shielding stray light, that is, shielding at least some stray light from the light source 510 that would otherwise reach the sub-volume 526 .

[0091] As can be seen in the example shown, both sunshade components 750a, b are arranged very close to the virtual volume and can be along its upper boundary, unless this cannot be done in order not to block the field of view 533 covering the structured light 511 in the virtual volume 524, which is why the first sunshade component 750a is along the virtual line 533 in the figure.

[0092] Figure 7An alternative light shield to the middle light shield 750 is a light shield that is arranged very close to the light source, but, for example, corresponds to the second light shield component 750b being translated upward in the figure to a line that is at the same level as the light source 510. In such an embodiment, there can be a first light shield component that is similar to the second light shield component, but is located on the other side of the structured light 511 and is therefore not tilted like the first light shield component 750a, for example, at the same level and parallel to the second light shield component, extending from the outside of the structured light 511 toward the location where the virtual line 533 at the camera 530 merges with the upper limit of the field of view 532.

[0093] Figure 8 The imaging system 800 according to an embodiment of the present invention is schematically illustrated, which has a third example of a light shield, namely, a light shield 850. Except for the light shield, the rest of the imaging system 800 is the same as that of the present invention. Figure 5A - Imaging system in C 500 or Figure 7 700 in the same manner. This facilitates comparison. Therefore, the following will focus on the light shield 850 in the imaging system 800 and the differences compared to the light shields 550, 750. Contents not discussed can be assumed to be the same or similar to those discussed above for the imaging systems 500, 700 and light shields 550, 750, where possible.

[0094] Imaging system 800 with Figure 5A and Figure 7 The side view corresponds to the cross section of the light shield 850. Although not shown as Figure 5B , but it may be assumed that the light shield 850 extends in a similar manner across the lateral extension of the virtual volume 524, i.e., in the y-direction in the example coordinates used herein.

[0095] Moreover, the light shield 850 extends and exists between the light source 510 and the virtual volume 524, and includes a first light shield part 850a arranged on a first side of the structured light 511 in the direction of the camera 530 and a second light shield part 850b arranged on a second side of the structured light 511 in the opposite direction of the camera 530. It can be appreciated from the figure that the light shield 850 also has the effect of shielding stray light, that is, shielding at least some stray light from the light source 510 that would otherwise reach the sub-volume 526.

[0096] Light shield 850 is an example of an alternative light shield that is feasible but is not expected to be as effective and / or advantageous as light shields 550, 750 because the latter have a light shielding primary surface extending perpendicular to the illumination direction of structured light 511. This is not the case for light shield 850 because its primary light shielding surface only extends perpendicularly, i.e., parallel to the illumination direction of structured light 511. Light shielding primary surfaces extending perpendicular to the illumination direction of structured light 511 facilitate efficient light shielding and coverage of the virtual volume, and at the same time enable the light shield to be arranged away from the light source and close to the virtual volume while still providing good shielding of the virtual volume. This also facilitates that the light shield can be arranged away from the light source and still be efficient.

[0097] It is not shown or discussed above how the light shield in the embodiments of the present invention is supported and / or mounted in and / or about its imaging system and other units thereof. The corresponding light shield may be attached and / or mounted to a light source, an object support structure, or some other suitable stable component in or near the imaging system. During the imaging and scanning of the object, the light shield may be arranged (such as maintained) in a desired and preferably fixed position using a frame or similar structure. For an imaging system that has been set up for a specific application of 3D scanning of an object, the light shield may be adapted to the setting to achieve shielding of stray light as described herein, and thereafter the light shield may remain in this state, such as in the same fixed position in the imaging system, as long as any factors affecting the light shield are not changed. However, as will be appreciated from this point and from the above discussion of the distance and placement of the light shield and light shield components relative to structured light, etc., the position and placement of the light shield and its components may need to be (re) adapted to significant changes in each specific application and the rest of the imaging system.

[0098] In view of the above, it may be preferred to set and / or adjust a light shield for the imaging system when setting up the imaging system, after it has been set up for such light triangulation, or to use a fixed light shield that is configured for the light source used and associated with the specific light triangulation application, for example so that the light shield is as close to the light plane as possible without visually interfering with the structured light or risking visually interfering with the structured light during operation.

[0099] Additionally, therefore, the use of an adjustable light shield (e.g., a light shield component thereof, such as a light shield arrangement including adjustment components operating on such a light shield) may be advantageous. This enables and / or facilitates the use of the same light shield arrangement in imaging systems of different settings to achieve a light shield adapted to a particular imaging system setting and application. Thus the imaging system setting may be the same as a conventional setting.

[0100] Therefore, it is beneficial to use an adjustable light shield, and in case there are two light shield parts, they can be independently adjustable. During the setting of the imaging system, the adjustment can be performed manually and / or mechanically and / or by some electrically controlled adjustment means or arrangement. The adjustment is preferably performed at least in a direction perpendicular to the structured light, so that the distance to / from the structured light can be adjusted. Moreover, it can be advantageous if the light shield and / or the corresponding light shield part is adjustable in the direction to / from the virtual volume, for example, up / down adjustment between the virtual volume and the light source. It can also be advantageous if the extension of the light shield and / or the light shield part (which affects how the light shield covers the virtual volume and can shield stray light) can also be adjusted, for example, to be able to adapt and cover the virtual volume in a desired manner. In addition, in the case where the light shield or the light shield part has a tilt, for example in order to achieve a distance to the structured light that decreases in the direction towards the virtual volume, the tilt angle is preferably also adjustable. This can be particularly advantageous for the first light shield part facing the camera, because it can be adjusted according to the virtual volume and the field of view of the camera.

[0101] Fig. 9 is a flowchart schematically illustrating an embodiment of a method according to an embodiment of the present invention. The method is used to support the reduction of distortions in three-dimensional imaging based on optical triangulation, such as the "spike", particularly when one or more objects to be imaged are composed of one or more highly reflective surfaces (such as mirror-like) that cause specular reflections. The three-dimensional imaging is performed by an imaging system (e.g., any one of imaging systems 500, 700, 800). The method can also be performed by this imaging system. Therefore, the imaging system includes a camera (e.g., camera 530) and a light source (e.g., light source 510) for providing illumination for an object to be imaged (e.g., object 520). The illumination includes structured light (e.g., structured light 511) for optical triangulation. The camera is arranged relative to the provided structured light so that the camera captures the reflected structured light from the object in the image during imaging as part of the optical triangulation, whereby, according to the optical triangulation, the position of the captured reflected structured light in the image is mapped to the real-world position where the structured light is reflected by the object. The structured light intersects a virtual volume (eg, virtual volume 524 ) that includes the object and corresponds to a volume in which one or more objects that the imaging system is configured to image (including the object) are present during imaging.

[0102] The method includes the following actions.

[0103] Action 901

[0104] At least during the imaging by the camera, stray light from the illumination of the light source, such as stray light 415 , is prevented from reaching the virtual volume within the camera's field of view, for example, virtual volume 524 within field of view 532 .

[0105] Prevention is preferably performed by shielding against stray light, and the shielding may be performed by a light shield, such as any of light shields 550, 750, 850 as described above.

[0106] It is noted that any enumerated terms (such as first device, second device, first surface, second surface, etc.) should be considered non-restrictive, and these terms themselves do not imply a certain hierarchical relationship. On the contrary, in the absence of any clear information, naming by enumeration should be considered as just a way to implement different names.

[0107] As used herein, the expression "configured to" may mean that the processing circuit is configured to or adapted to perform one or more of the actions described herein by means of software or hardware configuration.

[0108] As used herein, the term "value" or "value" may refer to any kind of number, such as binary, real, imaginary or rational numbers, etc. Moreover, a "value" or "value" may be one or more characters, such as letters or a string of letters. Moreover, a "value" or "value" may be represented by a bit string.

[0109] As used herein, the expressions "may" and "in some embodiments" have generally been used to indicate that the features described can be combined with any other embodiments disclosed herein.

[0110] In the drawings, features that may be present in only some embodiments are generally, but not necessarily, drawn using dotted or dashed lines.

[0111] When the words “comprise” or “comprising” are used, they should be interpreted in a non-limiting sense, ie, meaning “consisting at least of.”

[0112] The embodiments herein are not limited to the above embodiments. Various alternatives, modifications and equivalent forms may be used. Therefore, the above embodiments should not be considered to limit the scope of the present disclosure defined by the appended claims.

Claims

1. An imaging system (500; 700; 800) for three-dimensional imaging of an object (520) based on optical triangulation, the imaging system comprising a camera (530) and a light source (510), the light source being configured to provide illumination of the object (520), the illumination comprising structured light (511), the camera (530) being arranged relative to the provided structured light (511) such that the camera (530) is able to capture reflected structured light (511) from the object (520) in an image as part of the optical triangulation, whereby the position of the captured reflected structured light in the image is mapped to a real-world position where the structured light (511) is reflected by the object (520) according to the optical triangulation, the structured light (511) intersecting a virtual volume (524) comprising the object (520), and the virtual volume corresponding to a volume in which one or more objects are located that the imaging system is configured to image during imaging, the one or more objects comprising the object (520), The imaging system (300; 700; 800) further comprises a light shield (550; 750; 850), which is arranged outside the structured light (511) between the light source (511) and the virtual volume (524), so that the light shield (550; 750; 850) shields stray light (415) from the light source (511), thereby preventing the stray light 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 shield (550; 750; 850) has one or more light shielding main surfaces, and the light shielding main surfaces extend in one or more directions perpendicular to the illumination direction of the structured light (511).

3. An imaging system as described in any one of claims 1 to 2, wherein the light shield (550; 750; 850) extends outside the structured light (511) between the light source (511) and the virtual volume (524), and the distance to the structured light (511) decreases in the direction of the virtual volume (524; 724; 824).

4. An imaging system as described in any one of claims 1 to 3, wherein the light shield (550; 750; 850) is arranged outside the structured light (511) at a certain distance from the structured light (511), so that the light shield (550; 750; 850) avoids shielding light that is closer to the structured light (511) than the point where the illumination is reduced to 5% of its maximum intensity.

5. An imaging system as described in any one of claims 1 to 4, wherein a light shield (550; 750; 850) is arranged outside the structured light (511), at a certain distance from the structured light (511) but sufficiently close to the structured light (511), so that the light shield (550; 750; 850) at least shields the light of the illumination when the illumination is reduced to 1% of its maximum intensity.

6. The imaging system of any one of claims 1 to 5, wherein the light shield comprises: The first light shield component (550a; 750a; 850a), arranged on a first side of the structured light (511) in the direction of the camera (530); and / or A second light shield member (550b; 650b; 750b) is arranged on a second side of the structured light (511) in an opposite direction to the camera (530).

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

8. The imaging system of any one of claims 1-7, wherein the light shield (550; 750; 850) is closest to the structured light where the light shield (550; 750; 850) is closest to the virtual volume (524) and / or where the light shield (550; 750; 850) is closest to a location where the illumination has a focus.

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

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

Images