On Sun, Aug 23, 2009 at 1:33 PM, <dar...@chaosreigns.com> wrote: > I'm looking for a mathematical definition of this scale. > > http://docs.gimp.org/en/gimp-tool-levels.html says 0 is black and 255 is > white. What's in between? Is 7 double the brightness of 6?
Have you not experimented with it? 7 is nowhere near being double the brightness of 6. > > What is the luminance / brightness of each of the levels? luminance (n) = n (or n/255. if you want luminance on a 0..1 scale) > > Is it a logarithmic scale? no. It's a nominally linear scale, which is then modified by gamma parameter (if gamma == 1.0, that's no change). 0..255 simply correspond to sRGB pixel intensity values directly. So if you want a truly linear measurement of intensity, you need to apply the inverse of the sRGB curve. scipy used to provide an implementation of that -- see http://mail.scipy.org/pipermail/scipy-svn/2007-February/000703.html (rgbp2rgb function) _______________________________________________ Gimp-user mailing list Gimp-user@lists.XCF.Berkeley.EDU https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user
