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PDF generation, do not compress already compressed images?

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  PDF generation, do not compress already compressed images? mathog <dmathog@gmail.com> - 2014-10-08 13:51 -0700
    Re: PDF generation, do not compress already compressed images? jdaw1 <jdawiseman@gmail.com> - 2014-10-09 01:31 -0700
      Re: PDF generation, do not compress already compressed images? mathog <dmathog@gmail.com> - 2014-10-09 10:21 -0700
        Re: PDF generation, do not compress already compressed images? Helge Blischke <h.blischke@acm.org> - 2014-10-11 21:29 +0200

#2067 — PDF generation, do not compress already compressed images?

This may be a bit off topic...

A website I maintain has PDFs generated on Macs from keynote 
presentations.  (I don't generate them, just put them on the web site.) 
  When image compression is turned on some of the images are fuzzy and 
look bad and others look OK.  If no image compression is turned on they 
all look about the same.  I suspect that what is happening is that the 
original keynote presentation has some compressed images and some raw 
images.   Compressing a compressed image doesn't usually work very well, 
which is why some of the images in the PDF turn out poorly.  The ones 
which were not initially compressed, on the other hand, compress well.

So, is there any switch in the OS X PDF generator, or in keynote, that 
will cause already compressed images to go into the PDF without further 
modification, but will still allow compression of raw images?  We can 
already get a sharp PDF by disabling compression, but would like to make
the PDFs for the web smaller, if possible.

Thanks,

David Mathog

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#2068

This is a PostScript forum, and your question is about PDFs. The question is fine, but should be re-posted elsewhere.

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#2069

jdaw1 wrote:
> This is a PostScript forum, and your question is about PDFs. The question is fine, but should be re-posted elsewhere.
>

Well, yes, but this is also the forum for ghostscript questions, and 
ghostscript is one tool that might be used to take a PDF containing
a mix of compressed and raw images and selectively apply compression
to the raw ones.  Ghostscript is also the program underneath some of the 
free PDF printer drivers, like PDFcreator, so if ghostscript
does have this capability, it might be reflected somewhere in the
option for that driver.

Regards,

David Mathog

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#2070

mathog wrote:

> jdaw1 wrote:
>> This is a PostScript forum, and your question is about PDFs. The question
>> is fine, but should be re-posted elsewhere.
>>
> 
> Well, yes, but this is also the forum for ghostscript questions, and
> ghostscript is one tool that might be used to take a PDF containing
> a mix of compressed and raw images and selectively apply compression
> to the raw ones.  Ghostscript is also the program underneath some of the
> free PDF printer drivers, like PDFcreator, so if ghostscript
> does have this capability, it might be reflected somewhere in the
> option for that driver.
> 
> Regards,
> 
> David Mathog

I suspect it is due to the quality and format of the original images. The 
PDF export of Keynote only offers three quality levels for embedded
images without detailed information what it does then.

Helge

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