For the photographic darkroom unsharp masking (an image sharpening technique often available in digital image processing software), a large-format glass plate negative is contact-copied onto a low-contrast film or plate to create a positive image; which is made with the copy material in contact with the back of the original, rather than emulsion-to-emulsion, so it is blurred.
For the photographic darkroom process, a large-format glass plate negative is contact-copied onto a low-contrast film or plate to create a positive image. However, the positive copy is made with the copy material in contact with the back of the original, rather than emulsion-to-emulsion, so it is blurred. The same differencing principle is used in the unsharp-masking tool in many digital-imaging software packages, such as Adobe Photoshop and GIMP. Digital unsharp masking is a flexible and powerful way to increase sharpness, especially in scanned images. 
