[R] saving graphics in jpeg format

[Marc Schwartz]

On Tue, 2006-11-21 at 18:46 -0600, Marc Schwartz wrote:
> On Tue, 2006-11-21 at 22:29 -0200, Paulo Barata wrote:
> > Dear R users,
> > 
> > I need to save a graph in jpeg format. After plotting the graph,
> > when the graphics window is active, in the File menu, the
> > Save as / Jpeg / 100% quality correctly saves the graph in jpeg format.
> > But I would like to know, how could I control the resolution (in dpi)
> > of the saved jpeg file? I need to produce a jpeg at 1200 dpi.
> > 
> > I have tried also the jpeg function in the package grDevices.
> > A simple command like this works correctly:
> > 
> > jpeg(filename="test01.jpg", width = 800, height = 600, quality = 100,
> >     pointsize = 250)
> > barplot(1:5,col=1:5)
> > dev.off()
> > 
> > But I can't figure out the relation between pointsize, pixels, points
> > and dpi. For example, to be specific, to save a graph measuring
> > width = 6 inches, height = 4 inches, at 1200 dpi, which parameters
> > should I use in the jpeg function?
> > 
> > I have consulted the R documentation and the R list archive, but
> > haven't found any proper (to me) information on this matter.
> > 
> > I am using R 2.4.0 running under Windows XP.
> > 
> > Thank you very much.
> > 
> > Regards,
> > 
> > Paulo Barata
> > 
>  
> 
> See ?bitmap, for which you will need Ghostscript installed:
> 
>  bitmap("test.jpg", res = 1200, height = 4, width = 6, type = "jpeg")
>  barplot(1:5,col=1:5)
>  dev.off()

The one key point I forgot to include here, is that given the bitmapped
image, the size of the resultant image when viewed, will be entirely
dependent upon the dpi of the device upon which the image is displayed.

Keep that in mind.

Marc