A process by which the printing size of halftone dots is reduced and is often performed to reduce the effects of dot gain. On color separation negatives, sharpening is accomplished by means of dot etching or overexposure of the negative. On positive working plates (printing plates prepared from film positives), the sharpening effect tends to happen automatically, often referred to as negative dot gain.
Sharpen is also descriptive of an unwanted tendency for halftone dots to print smaller than those on the original, due to any of a wide variety of causes.
The term sharpen also means to increase and enhance the contrast around the edges of an image. (See Sharpness.)