June 10, 2004

Contents

Sharpen

This is a convolution operation, sometimes called 'unsharp masking'. It amounts to subtracting a blurred (low pass or mean-filtered) image from the original, and then enhancing the contrast back to full range.

  Convolution kernel for a 3x3 mean filter smoothing. Each pixel is replaced with the sum (or average) of itself and its 8 neighbors.
 1 1 1
1 1 1
1 1 1
Convolution which does nothing but reproduce the original (at 9x original pixel values).
 0 0 0
0  9 0
0 0 0
Convolution kernel for the 3x3 sharpen. The first kernel on the left is subtracted from the second.
 -1 -1 -1
-1 12 -1
-1 -1 -1
Kernel file in Sample Images / Kernels for getting equivalent results with Process / Convolve Process / Filters / Convolve  Mean( 3x3).txt  ---  SHRP3X3-12.TXT

The crystals appear much 'crisper' than in the original. The boundaries may appear sharper, but are actually not - the original version should be used for processing, not this sharpened version.

 

This degree of sharpening is often too severe.