IMUNSHARPEN(r;t;a;s) applies an unsharp mask to the RGB image in matrix
r: this first applies a Gaussian blur with standard deviation
s; it then finds the difference between pixels in the blurred image and in the original and, if this is greater than
t in each channel, it adds the amount specified by scalar
a multiplied by the difference from the original value.
Updated on December 4, 2017