[pdftex] How to impose pdf page groups?

Martin Schröder martin at oneiros.de
Fri Jun 28 16:39:12 CEST 2002

the pdfTeX team currently has a problem and I hope somebody here
has the needed knowledge to solve it.

PDF 1.4 introduced transparency and with it the concept of page
groups. These are xobjects attached to a page that specify the
interaction between transparent objects on the page and the
page background (sections 7.3.6 and 7.5.5 of the pdf reference
have all the details).

The problem is: What to do with these groups when pages with
these groups are imposed on another pdf (i.e. when including
these pages in another pdf in pdfTeX)?  Simply copying them into
the generated xobject does not work (gs does not like the
resulting pdf). Not copying them works with Acrobat but also fails
with gs and Jaws. Illustrator9 generates new page groups when
imposing pages with groups, but that leads to another problem:
groups specify a color space. What to do when two included pages
have groups   with different color spaces? Convert the objects of
one space to the other color space? That's not something we want
to do in pdfTeX...

Any ideas?

Thanks in advance

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