Apparatus for generating data for determining a property of a gemstone

An apparatus configured to generate image data for use in determining a visual property of a gemstone, the apparatus comprising:

• a support structure configured to support the gemstone placed at an observation position, the support structure being configured to support the gemstone having an axis of symmetry such that the axis of symmetry is parallel to an X axis passing through the observation position;
• a light source configured to illuminate the gemstone with a spatially varied light pattern;
• a rotator, configured to rotate the gemstone relative to the light pattern substantially about the X axis;
• a camera arranged to capture electronic images of light of the gemstone and to output the images as image data;
• and
• a controller configured to control the rotator and the camera such that the camera is configured to capture an electronic image of the gemstone at each of a plurality of rotational positions of the support structure relative to the light pattern, the images being captured generally along the X axis;
• wherein the light source comprises a reflector having a concave surface arranged to reflect light generally towards the gemstone,
• wherein the concave surface has at least one relatively reflective region and at least one relatively unreflective region, whereby said light pattern is generated,
• wherein the length of a boundary between the relatively reflective and relatively unreflective regions is greater than the radial distance between the center and the edge of the concave surface.