rpolitsr wrote:
It does exactly the opposed to what it’s name suggest: It SHARPENS your images. In my opinion it is the best filter yet to sharpen your photos whit a minimum of adverse side effects.
The name comes from a well known process in a real darkroom were the photographer used an unsharpened copy of the negative in the process of sharpening the print.
As I did nothing but basic darkroom work, I leave the explanation of the film technique to a better trained photographer (Terry?)
The origional Purpose of unsharp mask was to neutralise the fuzzy edges caused by poor focus.
On a picture of a black object on a white ground. those edges taper from black through grey to white.
To neutralize them, the negative was contact printed with a piece of clear film between the negative and the copy film, to give space for light to diffuse and make soft edges on the copy film. this was exposed and processed to give a mask that maintained those soft edges, but now of course it would be a posative.
When the origional neg and the copy posative were taped together in register and printed the new edges neutralized the negatives edges and made the print seem sharper.
Unlike unsharp mask in photoshop it only had an effect on edges, fine detail was not changed,( if there was any)
It was mainly done in process houses when the final output was to be used in printing books or advertisements, as it was a slow and expensive process.
Photoshop cs2 now has a super unsharp mask called smart sharpen, which is even better. than unsharp mask.