[Rd] minor oddity in pdf() help page

[Prof Brian Ripley]

No, it means what it actually says.

If you include R's PDF in another application, the latter will usually 
compress *if you asked the application for compressed PDF*.

On Thu, 2 Mar 2006, Hin-Tak Leung wrote:

> Roger D. Peng wrote:
>> The following paragraph from ?pdf struck me as a bit odd:
>>
>>       'pdf' writes uncompressed PDF.  It is primarily intended for
>>       producing PDF graphics for inclusion in other documents, and
>>       PDF-includers such as 'pdftex' are usually able to handle
>>       compression.
>>
>> Should that be "...and PDF-includers such as 'pdftex' are usually _un_able to
>> handle compression" ?
>
> Hmm, I think the documentation is correct but incomplete - pdftex *can*
> handle compression, but compression is not implemented in R's pdf
> output device. So it should say:
>
> "... PDF-includers such as 'pdftex' are usually able to handle
> compression, but R's pdf device does not utilise that feature of pdf."
>
> (I have checked a pdf generated by R, and it doesn't compress, and I was
> using pdflatex this morning to include a compressed pdf, so both
> parts are correct).
>
> There is a caveat: the PDF specs (and the postscript language standard)
> actually defines a few stream compression schemes - LZW and deflate
> are two I know of from the top of my head, I think there are more.
> But LZW used to be tangled up with the Unisys patent until recently
> when the patent expired, so most open-source softwares won't do
> it. deflate is implemented in zlib and ghostscript-written pdf
> usually have stream compression on. i.e. For some purposes such
> as getting smaller pdf's, it may be better to output from R
> postscript and use ghostscript to do ps2pdf rather than doing
> it directly from R, and to be pedantic, pdftex can only handle
> deflate encoded compression, AFAIK, for the reason I outlined above,
> but it is sufficient for most purposes, since most tools cannot
> generate LZW-compressed pdf's.
>
> HTL
>
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>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595