[pdftex] bug with included transparent graphics

Victor Ivrii vivrii at gmail.com
Mon Dec 31 13:42:28 CET 2007

On Dec 31, 2007 6:53 AM, Martin Schröder <martin at oneiros.de> wrote:
> 2007/12/30, James Quirk <jjq at hmx.galcit.caltech.edu>:
> > After looking inside the PDF I generate at my end (I'm using pdftex
> > 1.40.3-2.2) it looks like the /SMask for the png image is affecting the
> > whole page. For instance, one can comment out "/Im1 Do" from the page
> > stream, to suppress the png image, and the color for page 2 is still
> > affected. On the other hand, if the /SMask is commented out of
> > the png's /XObject then the png is drawn without transparency (the cutout
> > appears as a red square) and the color for page 2 is correct.
> > I havn't yet fully digested the PDF Reference to know whether
> > AR is at fault or pdftex is generating erroneous PDF.
> > Martin do you have a feel for which it is?
> No. But I wouldn't be surprised if AR needs the same kind of magic as
> with page groups (i.e. an image with a /Group key works only on a Page
> with a /Group key), i.e. an image with /SMask needs some magic in the
> Page object to work correctly. Or it's simply a bug in AR8 at Linux.
> Can anybody please confirm the behaviour on Windows or MacOS?

On Mac OSX 10.4.11, pdftex-1.40.3 neither AR 8.1.1 nor AR 7.0.9 nor 3
other pdf viewers show any difference between colors on the first and
second pages (I run few tests uncommenting corresponding lines). At
least for me. I am not sure how to measure accurately and objectively
colors (I cannot rely upon much on my eyes comparing two close

However it is a well-known effect that the visual perception of the
same color changes if the surrounding objects change their colors; I
suspect that the degree of this illusion could be individual.

> Best
>    Martin
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Victor Ivrii, Professor, Department of Mathematics, University of Toronto

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