increase png resolution when using saveHTML() {animation} in R

Question

I am in need of a way to increase the resolution of the png files created by saveHTML().

Here is a dummy script of what I am trying to do where in reality plot() is a number of nested loops:

x<-y<-rep(1,10)
saveHTML( for (i in 1:10){
plot.new()
plot.window(xlim=c(0,10),ylim=c(0,10))
plot(x[i],y[i])
}
,ani.dev="png",img.name="test",htmlfile="test")

A few things I have tried: 1) increase the animation size using ani.options(ani.height,ani.width) but I only get a larger grainy image. 2) call png() device inside the saveHTML expression and set the resolution there, but ultimately I dont get any figures. 3) call a new windows() device for plotting and setting the window size, but again this does not increase the resolution.

The most straight forward work-around that I came across is to create hi-res pngs and animate using ffmpeg. But I am not ready to re-work my script just yet.

Has anyone found a way to increase png resolution inside the saveHTML() function?

Answer 1

Instead of passing ani.dev="png", you can pass ani.dev = function(...){png(res=75*grain,...)}, where grain is some number > 1. If you specify the options ani.height and/or ani.width and multiply these values by the same factor grain, then you effectively increase the pixel resolution of the output by this factor.

N.B.: the default resolution 75 above might be machine dependent, I did not see it documented.