Re: [Lcms-user] What does cmsFLAGS_NOOPTIMIZE actually do?

[Elle S. <l.e...@gm...>]

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 <bo...@va...> 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
>


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