This disclosure describes methods, non-transitory computer readable storage media, and systems that utilize color density estimation in a blended boundary region of a digital image to generate an image mask. For example, the disclosed system extracts a foreground region, a background region, and a blended boundary region from a digital image. The disclosed system determines a color histogram—within a color space selected utilizing the foreground region and the background region—for a portion of the background region along an edge of the blended boundary region. Additionally, the disclosed system generates a color density map for the blended boundary region by comparing colors in the blended boundary region to colors in the color histogram of the background band. The disclosed system then generates a final mask for the digital image based on the color density map.