Suppose you take a photo of a beautiful scene of mountains and a lake. The representation devotes half of the scale between black and white to the bright surface of the lake, and the other half to the subtle shadings of the mountains. Is it possible to change the mapping so that only ¼ of the scale is devoted to the lake's colors, and ¾ to the mountains shades? If so, how would you do it?

  • $\begingroup$ I did my best explaining it in words. $\endgroup$ – user65652 Nov 28 '15 at 17:54
  • $\begingroup$ do you still need more clarification ? $\endgroup$ – user65652 Nov 28 '15 at 19:06

Yes, using a non-linear mapping function on the intensity. Let us for the moment suppose you have a grayscale image (because of the words "black and white", "shadings"), with luminance $0\leq p_{i,j} <1$.

The piecewise linear mapping: $f( p_{i,j}) = \frac{p_{i,j}}{2}$ if $p_{i,j}<\frac{1}{2}$, and $f( p_{i,j}) = \frac{3}{2} (p_{i,j}-\frac{1}{2})+\frac{1}{4}$ if $p_{i,j}\geq\frac{1}{2}$ can do the job.

This is a simple example of "Non-linear Contrast Enhancement". If that works for you, you can try with smoother functions.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.