[poppler] XYZ white point correction patch

[Hal V. Engel]

On Monday 13 July 2009 02:51:30 pm Albert Astals Cid wrote:
> Hal?
>
> Albert

Albert,

If you are asking if I think the last version of the white point correction 
patch that I sent in is good then the answer is yes.  It affects the output 
and with the patch (using a good display profile) the results in the Altona 
test PDF are correct (IE. both parts of the test areas match).  The patch is 
also to the PDF spec. as far as I can tell.  I have also been using it on my 
system for some time now without issues.

Hal

>
> A Dimarts, 23 de juny de 2009, Albert Astals Cid va escriure:
> > A Dissabte, 23 de maig de 2009, Hal V. Engel va escriure:
> > > On Saturday 23 May 2009 02:55:29 am Albert Astals Cid wrote:
> > > > > According to the PDF spec. the Y white point value should always be
> > > > > 1.0. So it might be possible to just do the correction to X and Z
> > > > > since this would make the code slightly more efficient.  Also I now
> > > > > think it would be better to do this in
> > > > > GfxCalGrayColorSpace::getXYZ() and GfxLabColorSpace::setXYZ()
> > > > > instead of in the locations right after calls to these functions.
> > > >
> > > > When i mean no difference i mean "diff" says the files are exactly
> > > > the same, not that i'm not able to see a difference in them.
> > > >
> > > > May it be because i'm not using any color profile?
> > > >
> > > > Albert
> > >
> > > It could be but the current code base defaults to sRGB as the output
> > > profile if one is not specified by the calling app.  So if poppler was
> > > built using USE_CMS then by default it should be using sRGB as the
> > > output color space for CIELab, Cal* and ICC objects.
> > >
> > > To confirm that you are using a profile you might consider modifying
> > > your code so that it explicitly sets the output profile by calling
> > > setOutputProfileName() or setOutputProfile() before opening the
> > > document. For additional testing I am attaching a profile intended for
> > > testing that causes the colors to be transformed in a way that is
> > > unmistakable because it transforms blues into reds and reds into blues.
> > >   Using this profile it should be easy to confirm that your code is
> > > actually using an output profile and also which parts of the rendered
> > > output are using the output profile.
> > >
> > > No matter what output profile is being used there should be at least
> > > some difference in the resulting RGB values of CIELab and CalGray
> > > objects if the white point of the object is NOT X = Y = Z = 1.0.  I
> > > have placed printf() statements in the code to confirm that this is
> > > altering the XYZ values of the CIELab objects in the altona pdf and it
> > > is.  I have also confirmed through testing that this makes a visible
> > > difference in the rendered output at least if the white point is
> > > significantly different from X = Y =Z = 1.0.
> > >
> > > Also I cleaned up the white point code so that the white point
> > > correction is now taking place in the getXYZ() functions which is where
> > > is really belongs. I have attached a patch with this set of changes.
> >
> > Ok, i've tested the patch and yes, i need to load a displayProfile,
> > otherwise it seems to do nothing, the problem is that the differences i
> > see are so minor i can't say if it is correct with the patch or without
> > it.
> >
> > Do you have other PDF that shows a more visible difference?
> >
> > Koji is that inside your area of expertice and can say yay/nay to the
> > patch?
> >
> > Anyone else?
> >
> > Albert
> >
> > > Hal
> >
> > _______________________________________________
> > poppler mailing list
> > poppler at lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/poppler