>temp = pow(abs(x)) >out = copysign(temp, x) Yes, this is reasonable. But it should be placed in the profile by the profile creator, not performed by the CMM. CMM should never "guess" data. If the profile gives a valid math expression for negative numbers, the CMM is free to use it and deal with negative numbers, or to clip to zero as many CMMs does. But this does not work in the inverse way: if the profile does NOT give any clue on what to do on negative numbers, then the CMM has to clip them to zero. This is a sort of critical thing for inter-operability sake.
Regards Marti Maria The LittleCMS project http://www.littlecms.com -----Original Message----- From: Kevin Wheatley [mailto:kevin.j.wheat...@gmail.com] Sent: miércoles, 17 de agosto de 2016 11:05 To: LCMS mailing list <lcms-user@lists.sourceforge.net> Subject: Re: [Lcms-user] Negative channel values are clipped upon floating point conversions to profiles with true gamma TRCs besides the cases already covered with gamut mapping etc, you can also get "negative" values due to uncertainty of where black is. Take for example the case of a digital sensor in a camera, if you capture with the lens cap on, noise will mean you will get a range of values about a mean value, if this is value considered as 0 then there will be some pixels where the value is less than zero, throwing away this by clipping degrades the quality of the images. on the subject of extending/extrapolating trc, one approach is to mirror the function similar to Elle's suggestion using temp = pow(abs(x)) out = copysign(temp, x) this tends to be reasonable as it gives a continuous gradient. Kevin ---------------------------------------------------------------------------- -- _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user ------------------------------------------------------------------------------ _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
