Performs the non-linear response compression portion of the iCAM tone mapping
algorithm described in this paper:
G.M. Johnson and M.D. Fairchild.
Rendering HDR Images. IS&T/SID 11th Color Imaging Conference. 36-41 (2003)
The input image should be normalized, and the whitepoint image should be
at the same scale factor as the input image. The output image should be
normalized before viewing.