To make halftone printing dots smaller. Using negative separations, sharpening is accomplished with dot etching. Over exposure will also sharpen the negative films. When positive working plates are made using positive transparencies, sharpening happens automatically and the size of the printing dots are reduced by 5%. This sharpening is called negative dot gain.
To decrease in strength, as when halftone dots become smaller; opposite of "thicken" or "dot spread."
To decrease in color strength, as when halftone dots become smaller; opposite of dot spread or dot gain.