047-tikz-png.Rnw

\documentclass{article}
% you do not really need this, since png has higher priority to pdf by default
\DeclareGraphicsExtensions{.png,.pdf,.jpeg,.jpg}

\begin{document}

This is an example showing you how to convert PDF figures generated by tikz to PNG via ImageMagick:

<<setup, include=FALSE>>=
library(knitr)
opts_chunk$set(cache=TRUE)
options(width = 60)
knit_hooks$set(tikz2png = function(before, options, envir) {
  # use this hook only for dev='tikz' and externalized tikz graphics
  if (before || options$dev != 'tikz' || !options$external || options$fig.num == 0) return()
  figs = knitr:::all_figs(options, ext = 'pdf')  # all figure names
  # note the tikz2png option is the extra parameters passed to 'convert'
  for (fig in figs) {
    system(sprintf('convert %s %s %s', options$tikz2png, fig, sub('\\.pdf$', '.png', fig)))
  }
})
@

The plot in this chunk is converted to PNG:

<<test-a, dev='tikz', fig.width=4.4, fig.height=3.3, tikz2png='-density 300'>>=
(x=rnorm(20))
par(mar = c(4.5, 4, .1, .1))
hist(x, main='', xlab='$x$ (how the fonts look like here?)',
  ylab='$\\hat{f}(x) = \\frac{1}{nh}\\sum_{i=1}^n \\cdots$')
@

This chunk uses the PDF device, and it is not converted:

<<test-b, dev='pdf', fig.height=3>>=
par(mar = c(4.5, 4, .1, .1))
plot(x, pch = 19)
@

\end{document}