Re: Ghostscript/GhostPDL 9.22 Release Candidate 1

[David Kastrup]

Ken Sharp <address@hidden> writes:

> At 13:42 19/09/2017 +0200, David Kastrup wrote:
>
>>So the mechanisms mostly out of our own control are Ghostscript in its
>>ps2pdf facility, various TeX engines when including lots of
>>ps2pdf-generated PDF files into a main document.
>
> To me this is where the problem lies, PDF is good as a terminal
> document format, and that was its original aim. Its not good as an
> intermediate format, or for inclusion in more complex documents.
>
> I feel the correct answer to this is not to use PDF as an intermediate
> format, it seem to me you should stick with a typesetting format
> because that allows you to determine that fonts which are named the
> same, are in fact the same, and you don't need to include them
> multiple times. In fact for a layout format, you wouldn't normally
> include the actual fonts at all, of course.

PDF is at least a format.

PostScript is not even a format but a programming language, and one
using global resources to boot.  That makes inclusion tricky.  EPS is a
black-boxed actual inclusion format but with rather little dependable
information.  Now in our case, the PostScript is generated entirely
under our control, but the inclusion into other documents (and
possibility distillation into PDF) isn't, so we are dealing with
inclusion mechanisms catering to more general use cases.

As a programmer, I am sympathetic to your feelings about the correct
answer for intermediate formats, but "in the real world," "this ship has
sailed."

PDF is extensively used as a format for graphics inclusion.  When you
submit papers with figures to basically any journal, they want the
figures to be submitted as PDF.

So I don't see that Ghostscript can reasonably avoid dealing with the
fallout of PDF being used as intermediate format basically everywhere,
whether or not you consider it suitable for that.

>>For this use case, we want a process that avoids excessive font
>>duplication.  The process so far involved an additional Ghostscript
>>run removing most of the duplicates from the TeX-generated PDF
>>(someone please correct me if I got this wrong).
>
> This only works because all the PDF files you are using (so far) embed
> the whole font, don't use subsets, and use the same Encoding (or use
> different names so that they are clearly different fonts). Were you to
> start using PDF files (from whatever source) where that is not the
> case, and I quoted OpenOffice as an example, then you might run into
> the problem with the bug you are exploiting.

For the technical details of either PostScript or PDF, I am not
competent (I've done some basic graphics stuff in either).  I was only
trying to paint the big picture we are more or less dealing with because
Masamichi-san was not really able to communicate it well.

But he definitely still is the go-to guy for discussing the detailed
problems occuring with each approach and basically did much of the
testing required to figure out the individual shortcomings of each in
practice.

-- 
David Kastrup