IL283055B - System and method for detecting inclusions in a gemstone - Google Patents

Description

- 1 – SYSTEM AND METHOD FOR DETECTING INCLUSIONS IN A GEMSTONE TECHNOLOGICAL FIELD The invention relates to the field of detecting inclusions in gemstones, particularly, in cut diamonds for the purpose of their clarity grading.

BACKGROUND Attempts to develop systems and methods for detecting inclusions in diamonds have been made in the past though until now they do not seem to have led to commercially available results, that would provide a high degree of repeatability and could be used in automatic clarity grading of gemstones, particularly cut diamonds.Examples of publications relating to detection of inclusions in cut diamonds for their clarity grading are US 20100086179, US 20100088348, US 20140107986 and US 6,980,283.

GENERAL DESCRIPTION According to one aspect of the presently disclosed subject matter there is provided a system for detecting inclusions in a gemstone, comprising(a) illumination system configured to selectively illuminate each of a plurality of spaced apart light entrance areas of the gemstone from corresponding illumination directions, and to provide a number of illumination patterns each defined by a unique combination of such light entrance areas illuminated simultaneously;(b) a controller configured to control said illumination system to successively produce illumination patterns each selected so as to simultaneously provide an internal uniform illumination of one or more predetermined light exit regions of the gemstone;(c) an image acquisition device for capturing images of the gemstone when illuminated by the illumination system as defined in item (b); and(d) an image processing system for processing said images and identifying inclusions based on non-uniformities in the internal illumination detected in said images. 0279844210-01 - 2 – The system can further comprise a transparent table configured for mounting the gemstone thereon so that, if the gemstone is a cut gemstone, its table facet faces the image acquisition device.The illumination system can comprise a first hemispherical illumination surface, which, for example, can be in the form of a first diffusively reflecting surface. In this case, the illumination system can further comprise a first light source configured to selectively illuminate a plurality of zones on the first hemispherical illumination surface, the first reflecting surface and the first light source being disposed on two sides of the gemstone.In addition or alternatively, the illumination system can comprise a second hemispherical illumination surface, which, for example, can be in the form of a second diffusively reflecting surface. In this case, the illumination system can further comprise a second light source configured to selectively illuminate a plurality of zones on the second hemispherical illumination surface, the second reflecting surface and the second light source being disposed on the same side of the transparent table.The system can have an optical axis passing through a center of the first hemispherical illumination surface, and the latter surface can comprise an opening surrounding said axis. In this case, the illumination system can also comprise a third light source configured to illuminate the gemstone through said opening. In addition or alternatively, the image acquisition device can be configured to capture images of the gemstone through said opening.At least one of the light exit regions can be, or can have an area of, at least one facet disposed in the field of view of the image acquisition device.The illumination patterns for each gemstone to be detected can be calculated in a number of ways. One way includes using a ray tracing model, e.g. obtained based on 3D modeling of the gemstone. Such 3D modelling, the corresponding ray tracing and simulation of illumination patterns can all be performed by an external simulation system outside the detection system according to the presently disclosed subject matter. In this case, the controller of system of the presently disclosed subject matter can be configured to receive a sequence of instructions from said external simulation system, each defining the illumination pattern. Alternatively, the 3D modeling of the gemstone to be detected and the corresponding ray tracing can be performed externally by a ray tracing system, 0279844210-01 - 3 – configured to output correlations between different light exit regions in the gemstone to be detected and their corresponding combinations of light entrance regions and directions of the incident and imaging beams. In this case, the system of the presently disclosed subject matter, can be configured to receive the information outputted from the above ray tracing system, and make a decision on the illumination patterns.The illumination patterns calculated as described above can constitute initial illumination patterns, which the controller of the detection system of the presently disclosed subject matter can be configured to use in an initial, pre-detection operation of the system, said pre-detection operation being configured to result in the controller's calculation of adjustments, if any, to be performed in the initial illumination patterns for their use as final illumination patterns in the detection operation of the system.Alternatively, the initial illumination patterns can be manually input by the operator or can be pre-stored in the controller's memory so as to allow the operator to select those he considers to be appropriate to the particular gemstone to be detected or to input in the system information regarding such gemstone, based on which the controller can select the initial illumination patterns.The image acquisition device of the above detection system can further be configured for capturing the images of the gemstone at a plurality of imaging depths in the gemstone.The image processing can be configured to identify said non-uniformities in said images using at least one of the following: i) comparing images of said predetermined light exit regions with their simulated images calculated as if these regions were illuminated uniformly; or ii) comparing illumination intensity of said regions in said images relative to a predetermined intensity; iii) comparing illumination intensities at pixels indicative of illumination intensities of said regions, relative to that of their surrounding pixels.The image processing system can be configured to exclude false-positive detections when identifying inclusions.The system can further comprise a dark-field illumination device. Such device can comprise a combination of reflecting surfaces and can be configured to be mounted so as 0279844210-01 - 4 – to receive light from the first light source mentioned above and re-directing it onto the gemstone while preventing direct entry of light beams from this source into the image acquisition device.The gemstone can be a cut gemstone, in which case the plurality of images can be captured from a view point facing the table facet of the gemstone.The system can further be configured to provide a mapped illustration of detected inclusions within the gemstone.The system can further be configured for grading the clarity of the gemstone based on detected inclusions.According to another aspect of the present presently disclosed subject matter there is provided a method for detecting inclusions in a gemstone, comprising: (a) controlling an illumination system configured to selectively illuminate each of a plurality of spaced apart light entrance areas of the gemstone from corresponding illumination directions, and to provide a number of illumination patterns each defined by a unique combination of such light entrance areas illuminated simultaneously, to successively produce illumination patterns each selected so as to simultaneously provide an internal uniform illumination of one or more predetermined light exit regions of the gemstone; (b) capturing a plurality of images the gemstone when illuminated as defined in step (a), optionally at different imaging depths; and (c) processing the images and identifying inclusions in said images based on non­uniformities in the internal illumination detected in said images.The above method can further comprise any of steps/operations described above with respect to the system according to the first aspect of the presently disclosed subject matter.In accordance with a still further aspect of the presently disclosed subject matter there is provided an add-on dark-field illumination device for use in a system comprising a table having a central axis for placing a gemstone thereon and a light source spaced from the table along the axis so as to face the gemstone. The device comprises an annular flat wall with a horizontal reflecting surface, having a central circular hole and configured to be placed on the table so that the hole is coaxial with the central axis and surrounds an 0279844210-01 - 5 – area on the table where the gemstone is to be placed and so that the reflecting surface faces the light source. The device further comprises a frusto-conical wall with an inclined reflecting surface spaced from the horizontal reflecting surface along the central axis, the arrangement being such that, when the device is placed on the table, light beams from the light source emitted towards the horizontal reflecting surface are reflected thereby towards the inclined reflecting surface, which then reflects the beams towards the central circular hole.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which: Fig. 1is a schematic illustration of a general optical set-up of a system according to one example of the presently disclosed subject matter; Fig. 2Ais an isometric view of a system having a set-up similar to that shown in Fig. 1, according to an embodiment of the presently disclosed subject matter, the view showing a detection chamber of the system as being partially open; Fig. 2Bis an isometric view of the system of Fig. 1, with a 90 deg. cutout extending along a central axis of the system; Fig. 3is a cross-sectional front view of the system shown in Figs. 1 and 2, taken along a plane containing its central axis; Fig. 4Ashows a 3D model of a cut diamond with a trajectory of one light beam therein, of the kind that can be used in a method according to an embodiment of the presently disclosed subject matter; Fig. 4Bis a top view of the 3D model shown in Fig. 4A, without the light beam, in which an exit region is marked, whose uniform internal illumination can be achieved by a combination of internal light beam including the light beam of Fig. 4A; Fig. 5Aand 5Deach illustrates a top view of a cut diamond with a schematic indication of a spot to be internally illuminated; 0279844210-01 - 6 – Figs. 5Band 5Care respective side and plan views of a lower hemisphere and table of the system shown in Figs. 2A to 3, with a cut diamond disposed on the table and a schematic indication of an area on the lower hemisphere, from which a light beam has to be reflected towards the cut diamond to have such a trajectory within the cut diamond as to provide internal illumination of the spot thereon shown in Fig. 5A; Figs. 5Eand 5Fare respective side and plan views of the upper hemisphere and the table with a cut diamond disposed on the table and a schematic indication of an area on the upper hemisphere, from which a light beam has to be reflected towards the cut diamond, to have such a trajectory within the cut diamond as to provide internal illumination of the spot thereon shown in Fig. 5D; Figs. 6A-6Care plan views of the lower hemisphere with areas thereof illuminated by a projector of the system shown in Figs. 2A to 3, in different illumination patterns; Figs. 7Aand 7Beach is a plan image of a diamond obtained in a system of the kind shown in Figs. 2A to 3, the diamond having two facets illuminated internally with a higher illumination uniformity than other facets of the diamond; Figs 8A-8Ceach is a plan image of a diamond obtained in a system of the kind shown in Figs. 2A to 3, where an inclusion (Figs. 8A and 8B) or reflected image of an inclusion (Fig. 8C) is seen at a facet, which would otherwise be illuminated internally with a higher illumination uniformity than other facets of the diamond; Fig. 9shows an illustrative image of a diamond with inclusions marked therein after they have been detected by a system of the kind shown in Figs. 1 and 2; Fig. 10Ais a perspective view of a dark-field illumination device configured for use in the system shown in Figs. 1 to 3; Fig. 10Bis a front view of the system shown in Figs. 2A to 3, with the dark-field illumination device shown in Fig. 10A, mounted therein; Fig. 10Cis an enlarged view of the system shown in Fig. 10B, with a schematic illustration of the trajectory of light beams emitted by the projector of the system and reflected by the dark illumination device, to obtain a desired illumination pattern on a diamond; 0279844210-01 - 7 – Fig. 11Ais a block-diagram scheme exemplifying a preparatory phase of a method for detecting inclusions in a gemstone, in which illumination intensities are adjusted; and Fig. 11Bis a block-diagram scheme exemplifying a method for detecting inclusions in a gemstone in accordance with an embodiment of the presently disclosed subject matter.

DETAILED DESCRIPTION OF EMBODIMENTS Fig. 1 illustrates schematically a system 1according to one example of presently disclosed subject matter, has a central axis Xand comprises an illumination system including a lower illumination sub-system 3aand an upper illumination sub-system 3b , a table 2 therebetween configured for the placement of a diamond D thereon in alignment with the central axis Xso as to expose the diamond to illumination produced by each of the sub-systems; and an image acquisition device 24coaxial with the central axis and configured to capture images of the diamond when mounted on the table and illuminated by the illumination sub-systems. The table can constitute a bottom of a container configured for carrying an immersion medium, if desired. Such medium can be of the kind having a refraction index higher than that of the air and being transparent at the room temperature. The amount of the immersion medium can such as to allow it either to surround the entire diamond or only its part, e.g. its table facet, to reduce the amount of direct reflections therefrom . In addition, conditions can be provided in the system suitable for using the.In the described example, the diamond Dis placed on the table so that its table facet faces in the direction of the lower illumination sub-system 3a , and the table 2is transparent to illumination, by which this sub-system is configured to illuminate the diamond so that light beams originated from the lower illumination sub-system pass through the table prior to their impinging the diamond.In the described example, the lower illumination sub-system 3acomprises a lower illumination surface 4aand the upper illumination sub-system 3bcomprises an upper illumination surface 4b , each formed with an opening 5aand 5b , respectively. The image acquisition device 24is disposed at a distance from the opening 5aand is configured to 0279844210-01 - 8 – view through this opening the table 2at least at its central area where the diamond is to be disposed.The lower illumination surface is configured to receive, via the table 2 , light from a first light source 8mounted within or in the vicinity of the opening 5bin the upper illumination surface 4band to diffusively reflect it so that at least a part of the reflected light can reach the diamond, again through the table 2 . The first light source 8in the described example is in the form of a projector that can create any desired illumination pattern and thus illuminate a plurality of selected zones of desired geometry on the lower illumination surface 4a . The manner, in which these zones are selected will be described in more detail further in the present specification, though already at this stage it can be indicated that the selection is such as to illuminate the diamond at pre-determined areas/facets thereof with the light beams reflected from the above zones in pre-determined directions.The lower illumination sub-system 3afurther includes a beam splitter 14 disposed on the central axis Xbetween the image acquisition device 24and the opening 5a , and a second light source 12spaced from the central axis Xand disposed with respect to the beam splitter so as to direct light, by means of the beam splitter, to the table 2along the axis X , to enable illuminating the table facet of the diamond through the table 2 . The beam splitter is further configured to allow imaging light beams exiting the diamond in the direction of the opening 5ato pass through the beam splitter towards the image acquisition device 24 .The upper illumination sub-system 3bcomprises an upper illumination surface 4b configured to receive light from a third light source 10and to diffusively reflect it so that at least a part of the reflected light can illuminate the diamond from above. The third light source 10in the described example has an annular configuration and it is disposed at the periphery of the table 2or at least closer to the table than to at least a majority of the upper illumination surface 4b . The third light source 10can be configured so as to create any desired illumination pattern on the upper illumination surface 4b . For example, the third illumination source can be in the form of a plurality of LEDs that can be individually controlled.It is to be noted that each light source of the illumination sub-system can be configured to provide visible and/or UV and/or IR illumination, and they can all provide 0279844210-01 - 9 – the same or different kinds of illumination depending on the purpose for which it is used. Thus, for example, UV illumination can be used when it is desired to exclude false­positive detections caused by dust or other foreign particles on the outer surface of the diamond, as described in more detail below.The lower and upper illumination surfaces 4aand 4bin the present example are each in the form of a continuous diffusively reflecting surface of a hemispheric shape, though any or each of them can be in the form of a plurality of discrete small reflectors, which can be stationary or moveable to change their orientation relative to the central axis of the system.Moreover, the structure of the lower and upper illumination sub-systems does not necessarily need to be as described above, in order to illuminate pre-determined areas on the diamond as desired. For example, any or each of the lower and upper illumination surfaces can be in the form of a plurality of individually controllable light emitters, in which case the system does not need to include the first light source 8and/or the third light source 10 , respectively. In case the lower illumination surface 4ais designed in this manner, the table 2would need to be transparent only at its area configured to contact the table facet of the diamond. Furthermore, the table 2can be in the form of a holder configured to hold the diamond at its girdle so as to directly expose it to the illumination from the lower and upper illumination sub-systems.The illumination system 3can comprise add-on components configured to be used with one or more of the light sources 8 , 10and 12 , to provide illumination different from that provided by the lower and upper illumination sub-systems. One example of such add-on component is a dark-field illumination device configured to be used with the light source 8and mounted above the table 2so as to prevent any light from the light source 8 from directly reaching the table 2and so as to receive light from the light source 8in a pre-determined pattern for directing it as side illumination to the diamond for imaging inclusions that cannot be detected as desired using the illumination sub-systems 3aand 3b.One specific example of such dark-field component is shown in Fig. 10A.In case the image acquisition device has a relatively short depth of focus, the system can further comprise an actuator (not shown in Fig. 1) for manipulating the image acquisition device 14so as to move the focal plane thereof along the central axis Xand thereby enable it to scan the diamond, slice by slice, along the central axis X . 0279844210-01 - 10 – Alternatively or in addition, the image acquisition device can have a variable depth of focus to suit different sizes of diamonds.The system 1further comprises a controller 6configured to control its operation and, particularly, the operation of its illumination sub-systems 3aand 3bso as to selectively simultaneously illuminate in a pre-determined manner pre-determined entrance areas on the diamond.More particularly, the controller 6can operate the illumination sub-systems to provide such pattern of illumination beams simultaneously entering the diamond, that corresponding imaging beams simultaneously exiting the diamond, usually the entering areas are different from the exiting regions, and forming its image at the image acquisition device are distributed at predetermined exit regions more uniformly than in other regions of the diamond, for using images of the pre-determined exit regions for detecting inclusions in the diamond as described in more detail below. In other words, prior to exiting the diamond at the pre-determined exit regions, the light beams which entered the diamond in the corresponding pre-determined entrance areas from corresponding pre­determined directions, undergo predicted internal reflections and create an internal illumination of the corresponding exit regions, with a higher uniformity compared with the remainder of the diamond. The exit regions that can be simultaneously internally illuminated in the 'more uniform' manner as described above, can be one or more facets of the diamond that are seen in the top view thereof. For example, they can be two adjacent crown facets, full table or a part thereof or even the entire diamond. The number of the illumination patterns, which the illumination system will need to create will thus be defined by the number of combinations of the exit regions that are to be simultaneously uniformly internally illuminated.The controller can also control the acquisition device such that it synchronizes the image capturing sessions with the production of the illumination patterns by the illumination system.For the determination of the exit regions and the corresponding entrance areas, the diamond can first be scanned to obtain its 3D model, and its ray tracing and illumination simulation can be performed using the 3D model and the optical set-up of the system. Having said that, it is possible to perform the above determination without modeling the diamond. For example, generic, pre-stored illumination patterns can be 0279844210-01 - 11 – applied to the diamond in the system and based on achieved internal illumination intensities at the light exit regions, entrance areas, corresponding illumination patterns and/or illumination intensities at the entrance areas can be adjusted by trial and error, to achieve the desired uniformity of internal illumination of the exit regions.The system 1may also comprise a user interface 9 . The user interface 9may present a live view of the acquisition device 14and the system may be operated therefrom.Fig. 4A illustrates how the ray tracing is used to determine an entrance area and entrance direction for one incident illumination beam, given its desired exit region and exit direction. Thus, Fig. 4 shows a 3D model of an example of a diamond, one incident illumination light beam LILL , and its trajectory between a predetermined entrance area A, at which the incident light beam LILLimpinges the diamond from a predetermined direction defining with the diamond table an entrance angle α , and a predetermined exit region R , at which a corresponding imaging light beam LIMAGexits this region in a predetermined direction defining with the diamond table an exit angle β , , which is the direction of the image acquisition device 24 . The light beam thus undergoes a number of interactions with the diamond's facets, resulting in its being split into an internal beam LINT , which after having entered the diamond at the entrance area A , continues travelling within the diamond by reflection from its facets, and one or more refracted beams LEXT, which exit the diamond at regions other than the predetermined exit region R .A combination of a sufficient number of the internal light beams LINTcreated by the simultaneous operation of the illumination system, whose trajectory has been calculated so as to exit the region Rin the same direction as the beam LIMAG , allows this region to be internally illuminated with a uniformity of such internal illumination being higher to a desired extent than that of other regions of the diamonds. Fig. 4B illustrates such exit region R. The system also includes an image processor 7configured to process images captured by the image acquisition device and identify inclusions within the diamond based on deviation of uniformity of the internally illuminated exit regions Rfrom the corresponding uniformity which should have been provided by the internal light beams LINTcorresponding to the imaging light beams LIMAG , which were expected to participate in the imaging of the exit regions R.The processor can further be provided with a suitable software to determine clarity grade of the diamond based on the detected inclusions. 0279844210-01 - 12 – More particularly, with given parameters of illumination provided by the system in each image capturing session, it is expected that the exit regions Rselected for this section will be internally illuminated with a pre-determined illumination uniformity. If in an image of this region, the illumination uniformity differs from the pre-determined one for these exit regions R , it is suspected to be caused by an inclusion that changed the anticipated trajectory of the corresponding internal light beams LINT . .The image processor thus processes the plurality of images captured by the acquisition device in all the image capturing sessions and identify inclusions based on the non-uniformities in the internal illumination detected in these images at the exit regions that were expected to be uniformly internally illuminated. The detection of such non­uniformities can be performed by any appropriate manner. For example, the detection can be performed by at least one of the following: (i) comparing images of the predetermined light exit regions with their ray-tracing simulated images calculated under the assumption that these regions were internally illuminated uniformly; and/or (ii) comparing brightness/intensity of the light exit regions in their images with a pre-calculated expected brightness/intensity.In each of the above options (i) and (ii), the comparison can be facilitated by using simulation of the gemstone to recognize edges of the diamond that can lead to false­positive detection results and to exclude them from being considered as potentially detected inclusions.Other false-positive detection can occur due to dust or other foreign particles that can adhere to the outer surface of the diamond. Identification of such false-positive detections for their further exclusion from the detection results can be carried out, for example, by illuminating the outer surface of the diamond with UV light and acquiring images of the illuminated outer surface to detect light emitted by the particles, if any, under the influence of the UV light. This option is based on a known phenomenon that a fluorescent substance emits light of a distinct color in the visible region of the spectrum when the radiation absorbed thereby is in the UV region of the spectrum, and thus invisible to the human eye and/or various detectors such as color CCD cameras.Figs. 2A, 2B and 3 illustrate one specific manner in which the system 1 described above can be implemented. 0279844210-01 - 13 – Thus, a system 100shown in Figs. 2A, 2B and 3, has components similar to those of the system 1 described above with reference to Fig. 1. In particular, as best seen in Fig. 3, the system 100has a central axis Xand comprises a transparent round table 102having a diamond supporting surface 101and positioned in the middle of a sphere 104for mounting a diamond thereon with its table facet contacting the supporting surface 101of the table 102 . The table 102can have the capability of movement by a centering device 106that can move the table in a plane perpendicular to the central axis X , and/or rotate the table around this axis. The movement of the transparent table 102can facilitate aligning the diamond with the central axis, if necessary.The sphere 104constitutes a part of an illumination system 103and it comprises lower and upper halves having lower and upper hemispheric diffusively reflecting surfaces 104aand 104b , respectively, formed with a bottom opening 105aand a top opening 105blocated at the bottom and the top of the lower and upper hemispheres, respectively, such that the central axis Xpasses through the centers of the openings.The illumination system 103further comprises the following light sources:- a top light source 108 , which in this example is in the form of a projector configured to illuminate the lower hemispheric diffusively reflecting surface 104avia the opening 105band to be controlled to provide a variety of illumination configurations on the diffusively reflecting surface 104asuch that each illuminated spot on this surface may be illuminated in a different intensity;- a central light source 110configured to illuminate the hemispheric upper surface 104b; in the present example, the central light source is in the form of an array of LEDs disposed annularly around the table 102closer to the table than at least a majority of the upper hemisphere 104b ; the LEDs can illuminate portions of the diffusively reflecting surface 104bso as to provide the desired illumination pattern; and- a lateral bottom light source 112spaced from the axis Xand associated with a beam splitter 114disposed on the central axis X , both located at the exterior of the lower surface 104band configured to provide illumination of a central area of the table, which is to be contacted by the table facet of the diamond when positioned on the table, by light beams passing via the opening 0279844210-01 - 14 –

Claims (8)

1./- 20 - CLAIMS: 1. An illumination system for illuminating a gemstone in a system for detecting inclusions in the gemstone, the latter system having a central axis and comprising in addition to the illumination system a transparent table configured for mounting the gemstone thereon so that the central axis passes therethrough and an image acquisition device coaxial with the central axis and configured to capture images of the gemstone when illuminated by the illumination system, the illumination system being controllable to successively produce illumination patterns on the gemstone each selected so as to simultaneously provide an internal uniform illumination of one or more predetermined light exit regions of the gemstone; the illumination system comprising: - a first hemispherical diffusively reflecting surface having a first opening in its center and configured to be mounted on one side of the transparent table so that the central axis passes through said opening and so as to allow the image acquisition device to capture images of the gemstone through said opening; - a first light source configured for being mounted on a side of the transparent table opposite to that of the first hemispherical diffusively reflecting surface so as to selectively illuminate a first plurality of zones on the first hemispherical illumination surface through the transparent table; - a second hemispherical diffusively reflecting surface and a second light source configured for being mounted on the same side of the transparent table so as to allow the second light source to selectively illuminate a second plurality of zones on the second hemispherical illumination surface; whereby said illumination system is configured to selectively illuminate each of a plurality of spaced apart light entrance areas of the gemstone from illumination directions corresponding to the first and second plurality of zones on the respective first and second hemispherical diffusively reflecting surfaces, and to provide said illumination patterns each defined by a unique combination of such light entrance areas illuminated simultaneously.

2. The system of claim 1, wherein the second light source is in the form of an array of LEDs configured to be disposed annularly around said table.

3. The system of claim 1 or 2, further comprising a third light source and a beam splitter, said third light source being configured to illuminate the gemstone through said 283055/- 21 - first opening via the beam splitter, while allowing imaging light beams exiting via said opening to pass through the beam splitter towards the image acquisition device.

4. The system of claim 3, wherein the third light source is configured to illuminate a central area of the table.

5. The system of any one of claims 1 to 4, wherein the second hemispherical diffusively reflecting surface has a second opening at its center via which the central axis passes, and the first light source is configured to be mounted at, or illuminate the first hemispherical diffusively reflecting surface through, said second opening.

6. The system of claim 5 when dependent on claim 3 or 4, further comprising an additional light source surrounding the second opening and configured to illuminate the gemstone directly from directions other than those provided by the first, second and third light sources.

7. The system of any one of the preceding claims, further comprising a dark-field illumination device.

8. The system of claim 7, wherein said dark-field device comprises a combination of reflecting surfaces and is configured to be mounted so as to receive light from the first light source while preventing direct entry of light beams from this source into the image acquisition device.