Methods having corresponding apparatus and tangible computer-readable media comprise: capturing a first image of ambient light upon a surface; generating a first grayscale image based on a selected color channel of the first image; projecting a primary color of light upon the surface; capturing a second image of the primary color of light projected upon the surface; generating a second grayscale image based on the selected color channel of the second image; generating a difference image, comprising subtracting the first grayscale image from the second grayscale image; and generating a projector mask, comprising detecting edges of a shape in the difference image, and reproducing the shape based upon the edges of the shape.