clldomps@cs.ruu.nl (Louis van Dompselaar) (04/08/91)
I'm looking for a reference to an article about how to enhance the contrast of computer pictures. I'm using a low-budget scanner which gives a kind of blurry image. The contrast could be enhanced by just changing the colours (gray-shades (32)) of the pixels, but this doesn't improve the resolution, and loses a lot of details. If the solution is (relatively) simple, could you please mail it directly, because I'm not sure if I can get my hands on any old articles (although our CS library seems to have a lot of them). Louis clldomps@praxis.cs.ruu.nl
rick@hanauma.stanford.edu (Richard Ottolini) (04/08/91)
In article <1991Apr08.100539.13053@cs.ruu.nl> clldomps@cs.ruu.nl (Louis van Dompselaar) writes: >I'm looking for a reference to an article about how to >enhance the contrast of computer pictures. Some techniques: (1) gamma correction: raise each sample to a signed power. .5 or square root is useful. If you do this many times, then use table lookup for speed. (2) Histogram equalization: sort the image samples into amplitude bins, then redistribute them to fill the color space. (3) Edge detector and derivative operators: 2-D FFT the image and weight the higher frequencies. A weight porportional to freuqency is the the first derivative, but this may enchance contrast too strongly, so try something less. A derivative operation can sometimes be implemented more cheaply by convolving the image with small grid operater, e.g. {{1 -1} {-1 1}}.