TikZ–tikzexternalize to png

Technical Note — 21 Jul 2015

Contents

Latex code — tikz-ext-png.tex

Here we render out two png files: one at 150dpi and a second at 600dpi.

\documentclass[a4paper]{article}
\usepackage[margin=8mm]{geometry}

\usepackage{tikz,pgfplots}
\usetikzlibrary{matrix}
\pgfplotsset{compat=1.12}
\usepgfplotslibrary{external} % creates a tight self-contained pdf figure for each tikzpicture
\tikzexternalize % comment out to debug if latex errors: generates the external pdf
\tikzset{external/force remake} % otherwise will use external pdf if it exists
\tikzset{png export/.style={
	external/system call={
		pdflatex \tikzexternalcheckshellescape
			-halt-on-error -interaction=batchmode -jobname "\image" "\texsource";
		convert -units pixelsperinch -density 150 "\image.pdf" "\image.png";
		convert -units pixelsperinch -density 600 "\image.pdf" "\image-600.png";
}}}
\tikzset{png export}
\tikzsetexternalprefix{figures/} % output the pdf to an existing directory (needs to exist)
\tikzsetnextfilename{myfigure}

\begin{document}

\section*{tikzpicture to be externalized to pdf and converted to png(s)}

\begin{tikzpicture}
	\matrix (m) [matrix of math nodes,row sep=3em,column sep=4em,minimum width=2em]
	{ F_t(x) \pgfmatrixnextcell F(x) \\
		A_t \pgfmatrixnextcell A \\};
	\path[-stealth]
		(m-1-1) edge node [left] {$\mathcal{B}_X$} (m-2-1)
						edge [double] node [below] {$\mathcal{B}_t$} (m-1-2)
		(m-2-1.east|-m-2-2) edge node [below] {$\mathcal{B}_T$}
						node [above] {$\exists$} (m-2-2)
		(m-1-2) edge node [right] {$\mathcal{B}_T$} (m-2-2)
						edge [dashed,-] (m-2-1);
\end{tikzpicture}

\section*{Checking quality and size of converted png(s)}

Check that the native figure size is correct by importing the generated png(s) \emph{without scaling}.

\subsection*{150dpi figure}
\includegraphics{figures/myfigure.png}

\subsection*{600dpi figure}
\includegraphics{figures/myfigure-600.png}

\end{document}

Output png figure — myfigure.png

fig1

Output png figure — myfigure-600.png (600dpi)

fig2

Exporting to png Notes

  • this is always done by first generating the vector graphic pdf and then rasterizing to png
  • png is web friendly and defaults with a transparent background
  • \usepgfplotslibrary{external} needs your latex system to be configured to run shell commands
    • for example in TeXShop, adding --shell-escape such as
      pdflatex --file-line-error --shell-escape --synctex=1
    • enabling this can make your system vulnerable to malicious latex documents
  • make sure you have an existing figures subdirectory if you use the \tikzsetexternalprefix line (as above)
    • this will create files figures/myfigure.pdf and figures/myfigure.png
    • otherwise just comment out this line to have the files myfigure.pdf and myfigure.png (in the same directory)
  • png generation uses the convert command from Imagemagick®
    • Imagemagick® needs to be installed and can be a bit horendous to set up
    • Imagemagick® is usually, but not always, installed at /opt/local/bin
  • alternative png generation using: sips — scriptable image processing system
    • use: sips -s format png --out "\image.png" "\image.pdf";
    • good: sips is pre-installed on OSX
    • bad: it won’t let you rasterize the pdf at other than a fixed 150dpi.

Debugging Latex code — tikz-ext-png-debug.tex

Use the modified latex:

\documentclass[a4paper]{article}
\usepackage[margin=8mm]{geometry}

\usepackage{tikz,pgfplots}
\usetikzlibrary{matrix}
\pgfplotsset{compat=1.12}
\usepgfplotslibrary{external} % creates a tight self-contained pdf figure for each tikzpicture
\tikzexternalize % comment out to debug if latex errors: generates the external pdf
\tikzset{external/force remake} % otherwise will use external pdf if it exists
\tikzset{png export/.style={
	external/system call={
		% print some info to console
			echo "\\n---- Checking Imagemagick/convert available ----\\n\\nPATH:" $PATH "\\n";
			which convert; echo; convert -version;
		pdflatex \tikzexternalcheckshellescape
			-halt-on-error -interaction=batchmode -jobname "\image" "\texsource";
		% convert from pdf to png
		convert -units pixelsperinch -density 150 "\image.pdf" "\image.png";
		convert -units pixelsperinch -density 600 "\image.pdf" "\image-600.png";
}}}
\tikzset{png export}
\tikzsetexternalprefix{figures/} % output the pdf to an existing directory (needs to exist)
\tikzsetnextfilename{myfigure}

\begin{document}

\section*{tikzpicture to be externalized to pdf and converted to png(s)}

\begin{tikzpicture}
	\matrix (m) [matrix of math nodes,row sep=3em,column sep=4em,minimum width=2em]
	{ F_t(x) \pgfmatrixnextcell F(x) \\
		A_t \pgfmatrixnextcell A \\};
	\path[-stealth]
		(m-1-1) edge node [left] {$\mathcal{B}_X$} (m-2-1)
						edge [double] node [below] {$\mathcal{B}_t$} (m-1-2)
		(m-2-1.east|-m-2-2) edge node [below] {$\mathcal{B}_T$}
						node [above] {$\exists$} (m-2-2)
		(m-1-2) edge node [right] {$\mathcal{B}_T$} (m-2-2)
						edge [dashed,-] (m-2-1);
\end{tikzpicture}

\section*{Checking quality and size of converted png(s)}

Check that the native figure size is correct by importing the generated png(s) \emph{without scaling}.

\subsection*{150dpi figure}
\includegraphics{figures/myfigure.png}

\subsection*{600dpi figure}
\includegraphics{figures/myfigure-600.png}

\end{document}

If convert is succesfully found should induce this portion of the console message:

---- Checking Imagemagick/convert available ----

PATH: /usr/bin:/bin:/usr/sbin:/sbin:/usr/texbin:/usr/local/bin:/opt/local/bin

/opt/local/bin/convert

Version: ImageMagick 6.9.0-0 Q16 x86_64 2015-07-29 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2014 ImageMagick Studio LLC
Features: DPC Modules
Delegates (built-in): bzlib djvu fftw fontconfig freetype gslib jbig jng jp2 jpeg lcms ltdl lzma openexr png ps tiff webp x xml zlib

If convert cannot be found or your PATH can’t point to it then hardwire the path such as follows:
/opt/local/bin/convert -units pixelsperinch -density 150 "\image.pdf" "\image.png";

If silent weird things are happening then comment out the externalization like this %\tikzexternalize. This will let latex stop and display errors.

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