On Tue, Feb 3, 2009 at 9:47 PM, Gerhard Fuernkranz <nospam456@xxxxxx> wrote: > Pascal de Bruijn wrote: >> The gamma doesn't cut it... The shaper is a quite important part of the >> profiles >> in question. > > Yes, I see, obviously the camera applies an S-shaped TRC. > >> I never expected exact results, with regards to my camera (or DPP) >> processing. >> >> I have attached a .ti3 file, which gives completely different shaper >> when executed >> like: >> >> colprof -qu -aS >> >> Than when it's executed like: >> >> colprof -qh -aS >> colprof -qm -aS >> colprof -ql -aS >> >> In all four cases the matrix seems nearly identical. > > I did take a look at your data now. > > Colprof -qh -aS bails out with "Powell failed" (no profile was > generated). Obviously the optimization did not converge... [You did not > encounter this problem, did you?] > > The options -qm and -qu resulted in shapers which do not differ very > much (see the green and blue curves in the attached diagram). They look > pretty reasonable up to the target's Dmin (about RGB=230...235). > However, the extrapolation beyond Dmin up to RGB=255 (i.e. the very > steep ascent) does not look reasonable at all. I'm also not sure whether > the profile might possibly clip some shadows. I would actually not call > these -qm and -qu shapers bumpy, IMO they are reasonably smooth. > > Option -ql gives indeed a different (less reasonable) shape. I guess the > -ql curve [which have fewer degrees of freedom than the -q m/h/u curves] > is not "flexible" enough to fit the given data, but on the other hand I > find it more bumpy than the -qm -and -qu curves (which is rather a > contradiction). I noticed LCMS has a Gamma Smoothing method called cmsSmoothGamma, to forcibly smooth gamma curves, after normal processing. I'd love to see a similar feature in colprof, where gamma curves can be forcibly smoothed. Regards, Pascal de Bruijn