[gs-bugs] [Bug 690258] can't read pdf because of unbalanced >>

[bugs.ghostscript.com-bugzilla-daemon at ghostscript.com]

http://bugs.ghostscript.com/show_bug.cgi?id=690258





------- Additional Comments From ken.sharp at artifex.com  2009-01-29 03:26 -------
In general Ghostscript will continue to process PDF files after errors, when
this is possible. Note that you have quoted two faults, the first is an
unbalanced dictionary mark (>>) the second is an incorrect object count in an
object stream. These may occur in the same place, or may not. 

Object streams are a method for compressing additional types of objects in a PDF
file for greater overall compression and smaller file size.

An object stream starts with an index of objects and their byte offset within
the stream. Unlike 'normal' PDF objects, these are not preceded by their object
definition (eg 2 0 obj), but are simply the contents of the objects, run
together. It can be difficult to know where one object stops and another starts. 

We can tell that something is wrong, but not necessarily whether it is the
content or the index which is incorrect. We can't scan the content looking for
'<index> <generation> obj...endobj' constructions to rebuild the index, which
can be done for damaged xref tables, because the content of an object stream
doesn't contain these markers.

Now, as to where the error is, if you run GS with '-dPDFDEBUG' on the command
line you should be able to see from the GS window which object it is processing
when the error occurs. Since the object stream is compressed, it would be hard
to fix it, and in order to 'see' the problem you will have to decompress the
content of the object stream.

That's about all that can be said without looking at the actual PDF file. If
you'd like someone to look at it, you'll need to attach it to this bug report.
If you want you can mark it as private immediately after you attach it, which
will prevent anyone except Artifex employees and contractors from accessing it.





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