The comparisons are at: http://ninedegreesbelow.com/temp/icc-profile-conversion-bugs.html http://ninedegreesbelow.com/temp/profile-conversion-errors.html
The same problem also happens when converting from linear prophoto to regular prophoto. On 7/27/12, Boudewijn Rempt <b...@valdyas.org> wrote: > Hi! > > I've had a long discussion with Elle Stone who did a huge comparison of the > results image applications have when converting between 16 bits linear rgb > and srgb. It turned out that Krita gave different results from tifficc, so I > dug in a bit and found that the reason was that I didn't use the > cmsFLAGS_NOOPTIMIZE flag when creating transforms, while tifficc does. Code > like this: > > > quint16 src[4]; > src[0] = 257; > src[1] = 257; > src[2] = 257; > src[3] = 65535; > > quint16 dst[4]; > > cmsHPROFILE sRgbProfile = cmsCreate_sRGBProfile(); > QByteArray rawData = linearRgb->profile()->rawData(); // from krita... > it's a linear scRGB profile, as attached. > cmsHPROFILE linearRgbProfile = > cmsOpenProfileFromMem((void*)rawData.constData(), rawData.size()); > > cmsHTRANSFORM tf = cmsCreateTransform(linearRgbProfile, > TYPE_BGRA_16, > sRgbProfile, > TYPE_BGRA_16, > INTENT_RELATIVE_COLORIMETRIC, > cmsFLAGS_NOOPTIMIZE | > cmsFLAGS_BLACKPOINTCOMPENSATION); > > cmsDoTransform(tf, (quint8*)&src, (quint8*)&dst, 1); > > qDebug() << dst[0] << dst[1] << dst[2]; > > > returns 3266,3266,3266, while > > > cmsHTRANSFORM tf = cmsCreateTransform(linearRgbProfile, > TYPE_BGRA_16, > sRgbProfile, > TYPE_BGRA_16, > INTENT_RELATIVE_COLORIMETRIC, > cmsFLAGS_BLACKPOINTCOMPENSATION); > > returns 1595,1595,1595 > > Which surprises me, since I would have thought optimization wouldn't have > any influence on the actual results obtained. Is this a bug, or should I > always use cmsFLAGS_NOOPTIMIZE to get accurate results? > > -- > Boudewijn Rempt > http://www.valdyas.org, http://www.krita.org, http://www.boudewijnrempt.nl > -- http://ninedegreesbelow.com Articles and tutorials on open source digital imaging and photography ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
