[R] Transparency and trellis device

[pomchip at free.fr]

Dear R-users,

I am trying to produce trellis (png, or jpeg) graphs with transparent background, but I cannot manage to make that happen. I tried to play around with themes but to no avail. Any advise on the following example will be greatly appreciated:

Thank you

Sebastien

####
library(lattice)

df <- data.frame(a=rep(1:4,4), b=rep(1:4,4), c=rep(1:4,each=4))

settings <- standard.theme()
settings <- modifyList(settings,
                       list(background=list(alpha=1,
                                            col="transparent")))
str(settings)

trellis.device(png,
               file="test.png",
               theme=settings)

myplot<-xyplot(b~a|c, data=df)

print(myplot)

dev.off()

####