The process of subtracting a low-pass filtered or blurred image from an original.
It is a technique used to emphasize edges in images.
Subtracting a low-pass filtered (or unsharp) image is equivalent
to adding a high-pass filtered image.
Hence the unsharp masking operation can be expressed mathematically as
where v(m,n) is the resulting image, u(m,n) is the original image, and g(m,n) is a high-pass filtered image of the original
such as
The factor lambda will determine how much high frequency boost is desired.
The Laplacian mask [0 -0.25 0; -0.25 1 -0.25; 0 -0.25 0] represents the high pass filter used in this applet.
The steps taken are: