1. A computer-implemented method comprising: receiving, by a computing device, an input representing a selection of a plurality of pixels in a digital source image, each of the plurality of pixels having a color associated therewith; generating, by the computing device: a standard pixel mask having a first plurality of opacity values corresponding to the selected pixels, an extended pixel mask having a second plurality of opacity values corresponding to pixels other than the selected pixels, and a minimal output pixel mask having a third plurality of opacity values corresponding to the selected pixels, the third plurality of opacity values based on the first and second opacity values and on the colors of the pixels under the standard and extended pixel masks; and applying, by the computing device, a blemish removal operation to the selected pixels based on the third plurality of opacity values in the output pixel mask.