Question

I’d like to insert a watermark onto a lattice image. In ggplot2, I simply used the the annotate or annotation_custom options to place a logo image and a text below the logo in a corner of the plot. Is there a similar possibility in lattice? Or as an alternative – is it possible to use an image as background of the plot?

Answer 1

This is what Deepayan Sarkar offered on Rhelp a couple of years ago to a similar question:

barchart(variety ~ yield | site, data = barley, groups = year, layout = c(3,1), 
         page = function(n) { 
              grid.text(label = "Privileged and Confidential \nDRAFT", 
              x = unit(0.01, "npc"),
              y = unit(0.95, "npc"), 
              just = c("left", "center")) })

Obviously you would also need to use grid graphics functions to place the logo, (but you haven’t offered one to work with. The first two lines of this next code was found at @baptiste’s blog page cited today on SO.) The second two lines were adapted from Paul Murrell’s article in last years “R Journal” found with Rseek.org:

library(png)
m <- readPNG(system.file("img", "Rlogo.png", package="png"), FALSE)
rimg <- as.raster(m)
grid.raster(rimg, x=.05, y=.9, just="top", width=.1)