r - Combining vector and bitmap graphics in a pdf

Question

When plotting images or heatmaps to pdfs as in the example below they are saved as vector objects where every pixel in the image or cell in the heatmap is represented by a square. Even at modest resolutions this results in unnecessarily large files that also renders uglily on some devices. Is there a way to make R save only the image area as a png or jpg embedded in the pdf but keep text, axes, anotations etc as vector graphics?

I'm asking since I am often printing R graphics, sometimes on large posters, and would like to combine the best of the two worlds. Of course I could save the entire figure as a high resolution png but that would not be as elegant, or combine it manually e.g. in Inkscape but it is quite tedious.

my.func <- function(x, y) x %*% t(y)
pdf(file="myPlot.pdf")
image(my.func(seq(-10,10,,500), seq(-5,15,,500)), col=heat.colors(100))
dev.off()

Thanks for your time, ideas and hopefully solutions!

Answer 1

Use ?rasterImage, or more conveniently in recent versions image with option useRaster = TRUE.

That will dramatically reduce the size of the file.

my.func <- function(x, y) x %*% t(y)
pdf(file="image.pdf")
image(my.func(seq(-10,10,,500), seq(-5,15,,500)), col=heat.colors(100))
dev.off()

pdf(file="rasterImage.pdf")
image(my.func(seq(-10,10,,500), seq(-5,15,,500)), col=heat.colors(100), useRaster = TRUE)
dev.off()

file.info("image.pdf")$size

file.info("rasterImage.pdf")$size

image.pdf: 813229 bytes

rasterImage.pdf 16511 bytes

See more details about the new features here:

http://developer.r-project.org/Raster/raster-RFC.html

http://journal.r-project.org/archive/2011-1/RJournal_2011-1_Murrell.pdf