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; for each pixel from among pixels bounding a first rectangular sub-region of a predetermined size within the digital image, averaging, by a hardware processor, an associated hue coordinate pair value to obtain a chroma value of the bounding pixel; determining, by the hardware processor, whether one or more of the bounding pixels of the first rectangular sub-region satisfy a specified criterion, where the specified criterion comprises whether a chroma value of the bounding pixel meets or exceeds a threshold value; if a predetermined percentage of the bounding pixels satisfy the specified criterion, assuming that all pixels within the first rectangular sub-region also satisfy the specified criterion; and selectively performing, by the hardware processor, an image analysis algorithm on the digital image using the assumption that all pixels within the rectangular sub-region also satisfy the specified criterion.