Unsharp masking

Unsharp masking (also: " Selective Focus " ) referred to in the image processing, a filter method, in which the sharpness of a photo with a blurred copy of the photo is increased.

Principle

Sharpened images appear more detailed, because the human perception is optimized for the detection of edges and lines out (see also Mach stripes). The information content is not increased as in all subsequently made image operations.

See main article: Sharpening

The principle of unsharp masking illustrates the picture: To increase the sharpness of the photos above left, first a blurred copy is created, the bottom left. In analog technology, they used a Transparent copy to, together with the negative of the original to expose photos. In digital technology subtracting the blurred image from the original image and receives as a result of the middle photo. In the enlarged detail of the eye on the right, the contrast enhancement of the brightness transitions through the filtering can be clearly seen. The diagram below right shows the brightness distribution of a horizontal line dar. level of eye Subtracting the green curve of the blurred image of the black line of the output image, obtained by adjusting the overall contrast, as a result of the red line. The arrows point to some areas that have a higher fluctuation after the image operation and are interpreted by the eye as the increase in sharpness.

In addition to the degree of blur of the difference image and the brightness of the difference image, the digital technology allows to introduce additional parameters to control the sharpening.