System and method for grading clarity of gemstones

A method for grading a gemstone, the method comprising:

• supporting the gemstone onto a holder, with the holder positioned along a line of sight of an image capturing device and a table facet of the gemstone is perpendicular to the line of sight;
• selectively controlling one or more illumination arrangements to generate a plurality of illumination patterns for the gemstone;
• selectively configuring the image capturing device to capture an image of each of the generated plurality of illumination patterns;
• selectively tilting the holder at different angles with respect to the line of sight to obtain different orientations of the gemstone;
• selectively configuring the image capturing device to capture images at different depths of focus of the gemstone at each of the obtained different orientations thereof;
• and
• processing the captured images to grade the gemstone;
• the method further comprising determining autofocusing and registering gemstone 3D position, by:
• a) calculating a gemstone two-dimensional image size in pixels, using a 3D model of the gemstone and system known parameters;
• b) locating the gemstone in the image using the image size in pixels and system known parameters;
• c) cropping the image to a calculated region of interest;
• d) calculating an initial table focus height using the 3D model of the gemstone and the system parameters;
• e) moving the image capturing device to the calculated initial table focus height;
• f) determining table focus height by capturing an image at the initial table focus height;
• g) determining the culet height position for the image capturing device using the table focus height and the 3D model;
• h) capturing a culet height image from the culet height position;
• i) determining the girdle height position for the image capturing device using the table focus height and the 3D model;
• j) capturing a girdle height image from the girdle height position;
• and
• k) calculating and registering the 3D position of the gemstone by processing the images captured in the steps (f), (h) and (j).