Re: Ghostscript/GhostPDL 9.22 Release Candidate 1

[Ken Sharp]

At 15:44 19/09/2017 +0200, David Kastrup wrote:


> Are there any example documents with thousands of pages and ten
> thousands of PDF inclusions one could look at?

I would suggest that the fact you want to 'include' tens of thousands of 
PDF files to be the problem, really.

I appreciate you are trying to deal with an existing problem, but using 
Ghostscript to do something it wasn't intended for isn't really the best 
idea for solving the problem.

As I've said elsewhere there is a genuine bug which can be exposed doing 
what you want with Ghostscript and it would not surprise me if in the long 
run it causes you another problem.

It would be possible to write a tool which could reliably detect identical 
fonts in a PDF file, remove the duplicates and alter the references so that 
the PDF continued to work. In all honesty, if the problem is as important 
as you say, this is probably a better solution. A tailored program, 
specifically designed to solve a specific problem is much more likely to 
work reliably than trying to use a general purpose program, designed for a 
different problem.

That said, it would be quite a big job, and I'm not actually offering to 
take it on.

My suggestion, which may not be feasible, is to keep everything in an 
editable format until the last second

This is extracted from an email I decided earlier not to send:
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While I can tell you a lot about PostScript and PDF I can't help you at all 
with TeX. In general, however, my experience of working with large 
documents is that the content should be maintained in the layout 
application native format until the last moment. Broadly speaking this is 
similar to keeping bitmap data in something like TIFF and only converting 
to JPEG at the last moment, and for similar reasons.

When you create a PDF you are discarding all the 'metadata' that describes 
the layout to the typesetting or layout application. Its all but impossible 
to recover that information once its been lost.

Your problem with multiple fonts pretty much exhibits that; once you've got 
the PDF file, a layout engine can't tell that all the fonts are the same. 
Ghostscript can't either, which is why it now doesn't strip the duplicates 
out. While I appreciate this is a problem for your particular use case, it 
is actually a considerable improvement for users in general.

Assuming that you are using TeX throughout for your documentation, then it 
seems to me that you should be creating your final document by appending 
the various TeX documents together and then producing a final PDF, instead 
of appending multiple PDF files.

Presumably you want to show some parts of Lilypond as well, so I would 
create EPS figures for those. It will of course increase the number of font 
inclusions again, but in the case of Lilypond I don't think that you can be 
merging the fonts anyway, because Lilypond always uses glyphshow, and 
pdfwrite will create a uniquely named font for each usage. So you aren't 
gaining any benefit from exploiting the Ghostscript bug with the Lilypond 
output.

So by maintaining the text and layout in TeX, inserting EPS figures as 
required, and only producing PDF as the last step in the process you would 
create a file which (as I understand it) would only contain a single 
instance of each font.

in short I'm not really suggesting that you change anything except your 
working practices, and maintain your files as TeX files rather than as PDF. 
Because I don't have any knowledge of your workflow (or TeX) I cannot say 
if this is reasonable, it may well not be.


                Ken