How does an unsharp mask work?

Question

I\'ve been playing around with image processing lately, and I\'d like to know how the unsharp mask algorithm works. I\'m looking at the source code for Gimp and it\'s implement

Answer 1

Consider the code below, which takens in an input image, IMG.

IMGblur = blur(IMG) // get all the low frequency pixels 
temp = IMG - IMGblur // all the low frequency pixels will be 0 
IMGsharp = IMG + k(temp) // k is in [0.3,0.7]
// in this final result , all low frequency pixels of IMGsharp is same as IMG, 
// but all high frequency signals of IMGsharp is (1+k)times higher than IMG 

Hope this helps!

Soon Chee Loong,

University of Toronto