[poppler] XYZ white point correction patch

[Albert Astals Cid]

A Dilluns, 18 de maig de 2009, Hal V. Engel va escriure:
> On Sunday 17 May 2009 12:44:51 pm Albert Astals Cid wrote:
> > A Diumenge, 17 de maig de 2009, Hal V. Engel va escriure:
> > > Here is a patch that will apply the white point correction after a call
> > > to getXYZ().  This patch can be applied to current git.
> > >
> > > Hal
> >
> > Do you have a pdf that shows what this fixes?
> >
> > Albert
>
> #35 on the altona test pdf shows this for the Lab to XYZ conversion. 
> Without the white point correction the difference between the upper right
> ECI-RGB ICCBased image and the lower left CIELAB image is apparent although
> it was not a huge difference.  With this fix the difference goes away.  
> This was testing with color management enabled.  This test is NOT valid
> with color management disabled.
>
> I don't have test PDFs for the calRGB or calGray cases.  The altona test
> PDF does not have any CalRGB or CalGray objects.   The CIE to XYZ
> conversions do need a white point correction other than CalRGB.  At least
> that is what is shown in the PDF specification for these conversions.
>
> After looking closer just now at the CalRGB to XYZ documentation I see that
> the CalRGB to XYZ conversion does not use the white point values in the
> conversion unlike CalGray to XYZ and Lab to XYZ.    But the original code
> was doing a white point correction but it was dividing by the white point
> so this was clearly incorrect because the conversion should not do a
> separate white point correction since this is handled by the matrix.  I
> made a mistake when I saw the incorrect WP conversion in the CalRGB code
> and assumed that it should be the same as the CalGray and Lab code when in
> fact it should have been removed.
>
> Also it might be common for these objects to use the default white point of
> X = Y= Z = 1.0 in which case this will not make any difference.  But I am
> not sure how common this is and the PDF documentation implies that D65 is
> the recommended WhitePoint ([ 0.9505 1.0000 1.0890 ]) for CalRGB and
> CalGray.
>
> I have attached a new version of the patch that removes all white point
> corrections from the code for CalRGB.

With #35 you mean the circled 35 in altona_visual_1v2a_x3.pdf ? If so pdftoppm 
generates exactly the same files with your patch and without your patch here, 
so i guess it's not "fixing" anything for me.

Albert

>
> Hal