[Tex/LaTex] Compile a LaTeX document into a PNG image that’s as short as possible

conversionformattinggraphicsscaling

I need to convert my LaTeX documents into PNG. The problem is, I also need the resulting image to be as short as possible (height-wise). I've tried latex followed by dvipng, but the result is always the size of a page. For instance, take a .tex file containing:

\documentclass{article}  
\begin{document}  
Hello. This is a test.
\begin{equation}
  L = 2                                                                     
\end{equation}  
\end{document}

If I compile it with latex, and then run dvipng, I get a PNG file that's the size of a full page. What I need is for the PNG file to be only as tall as needed for everything to fit. So the image would end immediately after the equation. The image still needs to have full width (because of the equation numbering).

Is there a way to achieve that?

Best Answer

You can use the standalone class for this. It loads the preview package automatically to crop the resulting PDF to the content. This makes the usage of pdfcrop unnecessary.

Simply exchange the article class with standalone. (It uses article internally but another class can be specified using the class option.) Note that since v1.0 the default option has been changed from preview to crop. The latter is better for pictures etc. but doesn't support line breaks. Either select preview manually or use the varwidth option.

\documentclass[preview]{standalone}
\begin{document}
Hello. This is a test.
\begin{equation}
L = 2
\end{equation}
\end{document}

There is a border class option which sets the border around the content (the default is 0.5bp). This option excepts either one (border for all sides), two (left/right, top/bottom) or four values (left, bottom, right, top).

To convert it to a PNG I recommend to use the convert command of Image Magick:

pdflatex file
convert -density 300 file.pdf -quality 90 file.png

Here the density is 300 DPI which can be adapted to your needs. The quality setting selects the compression level and other things and 90 is AFAIK the optimum.

You can also select the DPI resolution for X and Y separately and also resize the resulting image, e.g.:

convert -density 600x600 file.pdf -quality 90 -resize 1080x800 file.png

Update 2011/12/21:

The new version 1.0 standalone now has the ability to call the above command line (and others) automatically, e.g.:

\documentclass[convert={density=300,size=1080x800,outext=.png}]{standalone}

or simply (using default setting 300dpi, no resizing, PNG):

\documentclass[convert]{standalone}

This needs the -shell-escape compiler option to allow the execution of the conversion program from within the LaTeX document.

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