Apparatus and method for fluorescence grading of gemstones

A method comprising:

• obtaining at least a first image and a second image of a sample gemstone from an image capture system, the first image captured under non-UV light and the second image captured under UV light;
• generating a fluorescence mask for the second image based on an outline mask determined using the first image and/or a determined fluorescence area of the sample gemstone, wherein the outline mask excludes a portion of the first image outside of determined boundary lines of the sample gemstone in the first image;
• converting values for color components in each pixel of at least the second image that are within the fluorescence mask to parameters representing a color characteristic of each pixel;
• calculating a first fluorescence score of the sample gemstone based on an average value of parameters of pixels in a defined area in the second and third color pixelated images within the corresponding fluorescence mask;
• calculating a second fluorescence score based on pixels within the outline mask;
• and
• assessing a fluorescence characteristic of the sample gemstone based on a comparison of the first fluorescence score and/or the second fluorescence score with fluorescent scores of one or more control gemstones.