[R] Resolution of plots

Prof Brian Ripley ripley at stats.ox.ac.uk
Thu Jun 17 23:15:11 CEST 2004

On Fri, 18 Jun 2004, Patrick Connolly wrote:

> On Thu, 17-Jun-2004 at 08:00AM -0700, Thomas Lumley wrote:
> |> On Wed, 16 Jun 2004, Prof Brian Ripley wrote:
> |> 
> |> > You will have to tell us more.  Exporting how: to what format using what
> |> > device and what exact command on what operating system?
> |> >
> |> > The only device I know of that even knows about dpi is bitmap() and that
> |> > has no such limit unless imposed by your implementation of ghostscript.
> |> 
> |> There is an issue with PNG. libpng provides png_set_pHYs to set resolution
> |> (in pixels/metre) but provides a default if it is not set.  We don't set
> |> it, and so get the default resolution.
> I don't follow.  Is that in relation to the function bitmap() or to
> png()?

png().  That records a nominal 72dpi in the info, although it isn't much
used even by PhotoShop/GIMP etc.  (Almost all digital cameras record JPEGs
set to 72dpi, for example. If you want to use such a program to resize to
a physical size it is very easy to edit their idea of the dpi.)  

The original question was about a 96dpi limit and I still await
elucidation of what that was about.

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

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