[poppler] XYZ white point correction patch
Albert Astals Cid
aacid at kde.org
Mon Jul 13 14:51:30 PDT 2009
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
> Anyone else?
> > Hal
> poppler mailing list
> poppler at lists.freedesktop.org
More information about the poppler