[NTG-pdftex] Creating identical PDF files with different pdfTeX runs

Reinhard Kotucha reinhard.kotucha at web.de
Thu Mar 16 00:02:58 CET 2006

>>>>> "Frank" == Frank Küster <frank at debian.org> writes:

  > Is it possible to achieve identical pdf files directly, by adding
  > the proper commands, or would it be possible to add this feature?

This would be useful for package authors who want to compare the
output of different versions of their macro packages using the same
version of pdftex.

If you want to compare different versions of pdftex, your tests will
hopefully always fail and it is sufficient to compare file sizes.

For some time Hartmut is trying to convince pdftex to produce
significantly smaller pdf files, especially if font expansion is used.
The current version includes the same font with a modified FontMatrix
for each expasion factor, while the next version will embed each font
only once.

There are a few other things which will not provide such a large
improvement and hence might be postponed for future versions.

As an example, the width of glyphs can be specified by setting a
variable or by providing an array.  pdftex always provides arrays but
for monospaced fonts it is sufficient to set the variable and omit the

Comparing bitmaps, as some people already suggested, is a good thing.

It shouldn't be too difficult to write a script which produces a
bitmap file for each page (using ghostscript) and then creates a file
which consists of lines like

<pagenumber> <md5sum of the bitmap file>

The bitmap files can be removed by the script when it is finished and
standard UNIX tools can be used to examine the output files.

Particularly, diff(1) can be used efficiently.  It will tell you the
numbers of the pages which are different.

However, it would be nice if the pdftex version number could be
retrieved more easily.  At the moment the options "-v" and "--version"
are both quite verbose and provide copyright stuff.

Maybe one of these options should provide the pdftex version
("1.30.7-beta" for example) only and nothing else.  A script might
want to insert the pdftex version number into its output filename, but
at the moment it can only be done using something like sed|awk|perl.

And maybe the output of pdftex {-v,--version} will change in the
future, which will break such scripts.

Reinhard Kotucha			              Phone: +49-511-4592165
Marschnerstr. 25
D-30167 Hannover	                      mailto:reinhard.kotucha at web.de
Microsoft isn't the answer. Microsoft is the question, and the answer is NO.

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