Re: [Lcms-user] First experiments with LCMS2

[Maurice L. <mau...@gm...>]

Hi Marti,

Thank you very much for the quick response and the fix.

With kind regards,
Maurice

Op do 3 okt. 2019 om 11:03 schreef <Mar...@li...>:

>
>
> > When looking at the resulting input profile in ICC Profile Inspector I
> see
> > that the resulting profile is a version-2.4 profile (as requested) with
> > linear (out = in) input and output channels (consisting of 2 points
> each, 0
> > and 65535), which is fine.
> >
> > But the value of the first CLUT entry (for CMYK = (0, 0, 0, 0)) is equal
> to
> > (65535, 32896, 32896), which is the version-4 encoding for Lab (100, 0,
> 0).
> >
> > It should have been (65280, 32768, 32768) which is the version-2 encoding
> > for Lab = (100, 0, 0).
>
>
> Hi, thanks for reporting. This is actually a bug, which I have already
> fixed in github. If you want to modify your sources directly, in
> cmsvirt.c, you need to add this:
>
>   if ((xform ->ExitColorSpace) == cmsSigLabData && (Version < 4.0)) {
>
>          dwFlags |= cmsFLAGS_NOWHITEONWHITEFIXUP;
>          if (!cmsPipelineInsertStage(LUT, cmsAT_END,
> _cmsStageAllocLabV4ToV2(ContextID)))
>              goto Error;
>
> Which fixes this special case.
>
> Regarding the other case you report, media white, the code has no idea
> on which is the media white point when you are building input profiles
> by chaining. Actually it takes it from the first profile, which seems
> reasonable in many cases.
> On the other hand, many V2 devicelink profiles does not use any media
> white at all, so if you use a devicelink as the first profile you
> probably will end in D50 as media white.
> In V4 workflows, this is not so terrible at all, since media white is
> not used anymore, even V4 absolute colorimetric is assuming fully
> adapted observers.
>
> Best regards
> Marti
>
>