hi christian, great to hear! thanks to ulrich for fixing this. i think this classifies as a bugfix that would totally go into a minor revision, it's not very intrusive for the other code paths.
as to your question: we don't do any gamut mapping in the internal colour management code path. in fact we just keep the values outside [0,1] as they are and only in the very last step they might be clamped depending on the output format. if you exported a 16-bit tiff that would be the time (not sure about floating point tiffs, i think floating point pfm might keep everything unclamped). certainly no perceptual rendering intent-like stretching of colours takes place. cheers, jo On Wed, Jan 16, 2019 at 9:53 PM Christian Stromberg <christian.stromb...@gmx.net> wrote: > > I've compiled the updated PR1996 and ran some tests. First using the > Rec2020 as output profile, but distinct posterization was visible in > comparison to e.g. sRGB. > > Then, I installed eciRGBv2 in Darktable, which is one of the profiles > suited well to scans with the intention to print them and my default > "scan-to" profile. I exported a non-compressed TIF in Darktable with > eciRGBv2 using its internal CMS, which probably uses a perceptive > rendering (?), and opened this exported TIF in Photoshop. At the same > time I opened the original LAB scan in Photoshop and performed a > conversation into the eciRGBv2 profile using perceptive rendering > without blackpoint compensation. Both images now look like twins, > totally identical, with identical histrograms! Photoshop's histogram > statistics report the same average and deviation down to the last digit. > > I think we can say: mission accomplished! Astonishing speed of > implementation. > > Will the feature be publicly available with a v2.6.1 release or is it > restricted to v2.7 developement? > > Thanks a lot for all the work, > > Christian > > Am 15.01.19 um 18:37 schrieb Ulrich Pegelow: > > > Am 15.01.19 um 15:33 schrieb Christian Stromberg: > >> Hi, > >> > >> thanks for the hints! It took me some time to fill up all missing > >> dependencies. Because it's the first time I am compiling a whole > >> program, I wasn't familiar with the specific library names for Linux > >> Mint. Looking them up and installing them while continuously running > >> the built script to see if a missing component was successfully > >> installed took the largest part of the time. > >> > >> I've got the new version running and from my point of view, I can > >> happily report that the display of the files is absolutely identical > >> (see attachments). Thank you very much for your efforts! > > > > Nice to hear! > > > >> > >> Is sRGB know just used for displaying or is the export output also > >> restricted to sRGB? > > > > Export is not restricted, you may chose the output gamut from some > > pre-defined profiles and you may also use third party profiles. > > However, right now PR1996 would be limited to sRGB on the *input* side > > when it comes to CIELAB or ICCLAB Tiff files. Color dynamics outside > > of sRGB is lost for these files. > > > >> > >> The color profiles of the scanners I sent you have been created using > >> IT8 targets. So the range of colors included in these profiles is not > >> theoretical but a practical measurement using real slide films > >> showing IT8 color tables and correcting the scanners colors by using > >> lab measurements that are provided alongside the IT8 slide film > >> targets. This is also the reason why, using the same Fuji Provia 100F > >> IT8 target, the range of colors within the ICC profile of the Tango > >> is much larger than that of the Nexscan: the Tango is a drum scanner > >> while the Nexscan is a CCD based flatbed scanner. > >> > > > > I've checked your profiles and they are significantly larger than sRGB > > or even AdobeRGB. In order to cope with these colors we would need to > > internally convert to a wide gamut profile. Rec2020 and ProPhoto come > > into mind. As darktable has already Rec2020 defined, this would be my > > profile of choice in this case. > > > > I'v just enhanced PR1996 accordingly. > > > > Ulrich > > > >> But if export is not restricted to sRGB and it is just the displaying > >> part that uses sRGB, I would think that most users can live with that > >> just fine. > >> > >> Best wishes, > >> > >> Christian > >> > >> > > ____________________________________________________________________________ > > > > darktable user mailing list > > to unsubscribe send a mail to > > darktable-user+unsubscr...@lists.darktable.org > > > > > ____________________________________________________________________________ > darktable user mailing list > to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org > ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org
