A photographic technique used for processing images to reveal fine detail. A positive contact copy of a glass photographic plate is made on low-contrast film. The copy is blurred because of the glass between the film and the image on the plate. This blurred image contains the large-scale structure of the image and constitutes the unsharp mask. When replaced in contact with the back of the original plate, it effectively cancels out the large-scale structure, leaving fine detail to be seen much more easily.