[R] Print density of 600 dpi for a plot

[Barry Rowlingson]

On Fri, Mar 12, 2010 at 9:52 PM, Bob Green <bgreen at dyson.brisnet.org.au> wrote:
>
> I have to create a plot with a print density of 600 dpi . Within R, is there
> a way to determine the print density of a plot?
>
> Any assistance is much appreciated,

 A PostScript, embedded PostScript, or PDF file has essentially
infinite dpi, since it is a vector representation.

 If you create a raster representation, such as with the png graphics
device, then the dpi is going to depend on the final size of the plot
in inches and the pixel size of the image. This png device call will
create a png image that is 1800x1800 pixels:

 png(width=3,height=3,units="in",res=600)

 If you expand that to a 6x6inch final image on paper, it'll be 300
dpi. Print it on a full page of A0 and the dpi will be small enough
for you to see the individual pixels as blocks. The printer may still
be doing 600 dots per inch though.

 So I think the solution, when someone says "We need these figures at
600dpi", is to ask them how big in inches they want them, then use the
png() device. I've sometimes had people insist on 600dpi resolution
images, but then not have a clue what final size the image is going to
be.

Barry