[R] write a png inside a pdf for large graphics?

[baptiste auguie]

Hi,

On 24 April 2012 05:00, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:
> On 23/04/2012 10:49 AM, Adam Wilson wrote:
>>
>> I routinely write graphics into multi-page PDFs, but some graphics (i.e.
>> plots of large spatial datasets using levelplot()) can result in enormous
>> files.  I'm curious if there is a better way.  For example:
>>
>> #First, make some data:
>> library(lattice)
>> d=expand.grid(x=1:1000,y=1:1000)
>> d$z=rnorm(nrow(d))
>>
>> #Now, the PDF.  The following produces a PDF that's ~50MB.
>> pdf(width=11,height=8.5,file="test1.pdf")
>> levelplot(z~x*y,data=d)
>> dev.off()
>>
>> #If you write the same graphic to a png with reasonable resolution, the
>> file size is ~500k:
>> png(width=1024,height=768,file="test1.png")
>> levelplot(z~x*y,data=d)
>> dev.off()
>>
>> #  I would prefer to embed a png (or other raster format) inside a PDF
>> directly from R.
>> #  Is this possible?  I'm looking for some way to achieve something like
>> the following (of course this doesn't work):
>> pdf(width=11,height=8.5,file="test1.pdf")
>>      png(width=1024,height=768,file="current device")
>>              levelplot(z~x*y,data=d)
>>      dev.off()
>> dev.off()
>>
>>
>> Of course the PDF preserves vector scalability, but there are times it's
>> not worth the extra file size.  And you can write out the png's as
>> separate
>> files and then merge them with imagemagick or ghostscript.  I currently
>> get
>> around this by writing the graphics to a potentially very large (>>100MB)
>> PDF, then use ghostscript to convert *only* the large pages of the pdf to
>> png and put it back together as a PDF (a function I wrote for this is
>> described here:
>> http://planetflux.adamwilson.us/2010/06/shrinking-rs-pdf-output.html).
>>
>> I'm curious if there is a way to do it directly by instructing R to write
>> a
>> png and embed it within the already open PDF device.  Any ideas?
>
>
> I haven't tried this, but rasterImage() can plot to PDF.  So you just need
> to get your PNG display into a raster image.

There's a corresponding panel.levelplot.raster function in lattice. It
usually results in smaller files than using rectangular tiles, and
it's also faster.

HTH,

baptiste

>
> Duncan Murdoch
>
>
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