1. A method performed by a software process executing on a computer system, the method comprising: accessing a digital image comprising a plurality of pixels encoded in a color space that defines hue as a pair of Cartesian coordinates; calculating a chroma value for a specified pixel by determining a distance between a point corresponding to a hue coordinate pair value for the specified pixel in the digital image and a Cartesian origin point; comparing the calculated chroma value to a predetermined threshold; and performing an image processing operation on the digital image based on a result of the comparison.