PostScript to PDF conversion/slow print issue [GhostScript]

Question

I have several large PDF reports (>500 pages) with grid lines and background shading overlay that I converted from postscript using GhostScript's ps2pdf in a batch process. The PDFs that get created look perfect in the Adobe Reader.

However, when I go to print the PDF from Adobe Reader I get about 4-5 ppm from our Dell laser printer with long, 10+ second pauses between each page. The same report PDF generated from another proprietary process (not GhostScript) yeilds a fast 25+ ppm on the same printer.

The PDF file sizes on both are nearly the same at around 1.5 MB each, but when I print both versions of the PDF to file (i.e. postscript), the GhostScript generated PDF postscript output is about 5 times larger than that of the other (2.7 mil lines vs 675K) or 48 MB vs 9 MB. Looking at the GhostScript output, I see that the background pattern for the grid lines/shading (referenced by "/PatternType1" tag) is defined many thousands of times throughout the file, where it is only defined once in the other PDF output. I believe this constant re-defining of the background pattern is what is bogging down the printer.

Is there a switch/setting to force GhostScript to only define a pattern/image only once? I've tried using the -r and -dPdfsettings=/print switches with no relief.

Answer 1

Patterns (and indeed images) and many other constructs should only be emitted once, you don't need to do anything to have this happen.

Forms, however, do not get reused, and its possible that this is the source of your actual problem. As Kurt Pfiefle says above its not possible to tell without seeing a file which causes the problem.

You could raise a bug report at http://bubgs.ghostscript.com which will give you the opportunity to attach a file. If you do this please do NOT attach a > 500 page file, it would be appreciated if you would try to find the time to create a smaller file which shows the same kind of size inflation.

Without seeing the PostScript file I can't make any suggestions at all.

Answer 2

I've looked at the source PostScript now, and as suspected the problem is indeed the use of a form. This is a comparatively unusual area of PostScript, and its even more unusual to see it actually being used properly.

Because its rare usage, we haven't any impetus to implement the feature to preserve forms in the output PDF, and this is what results in the large PDF. The way the pattern is defined inside the form doesn't help either. You could try defining the pattern separately, at least that way pdfwrite might be able to detect the multiple pattern usage and only emit it once (the pattern contains an imagemask so this may be worthwhile).

This construction:

GS C20 setpattern 384 151 32 1024 RF GR
GS C20 setpattern 384 1175 32 1024 RF GR

is inefficient, you keep re-instantiating the pattern, which is expensive, this:

GS C20 setpattern 
384 151 32 1024 RF
384 1175 32 1024 RF 
GR

is more efficient

In any event, there's nothing you can do with pdfwrite to really reduce this problem.

Answer 3

'[...] when I print both versions of the PDF to file (i.e. postscript), the GhostScript generated PDF postscript output is about 5 times larger than that of the other (2.7 mil lines vs 675K) or 48 MB vs 9 MB.'

• Which version of Ghostscript do you use? (Try gs -v or gswin32c.exe -v or gswin64c.exe -v to find out.)

• How exactly do you 'print to file' the PDFs? (Which OS platform, which application, which kind of settings?)

Also, ps2pdf may not be your best option for the batch process. It's a small shell/batch script anyway, which internally calls a Ghostscript command.

Using Ghostscript directly will give you much more control over the result (though its commandline 'usability' is rather inconvenient and awkward -- that's why tools like ps2pdf are so popular...).

Lastly, without direct access to one of your PS input samples for testing (as well as the PDF generated by the proprietary converter) it will not be easy to come up with good suggestions.