[R] Resolution of plots

Thomas Lumley tlumley at u.washington.edu
Thu Jun 17 17:00:53 CEST 2004

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.

The default is good for screen display, and irrelevant if you are
including the file in a document, but photo editing software will show the
true resolution, and publishers may care.

One way to change the resoluton of PNG files is to use SNG
(sng.sourceforge.net) to translate the PNG to a text format, edit the pHYs
chunk and translate it back.


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