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I compile small latex math snippets using the standalone document class. I rasterize the resulting PDF to a PNG image using ImageMagick and finally include these images in some HTML document. However, for technical reasons of this procedure, I want to ensure a specific height of the document above + below the baseline, let's say the letter "Q" should always fit vertically, even if the document only contains one single "a".

I thought about including a phantom letter, but this also introduces additional whitespace in the horizontal dimension. Is there an easy way to tell standalone (or a special environment) to at least include a specific height above + below the baseline of the text? Is there some phantom-similar thing which enlarges the bounding box but doesn't occupy space by itself? I also thought abut a tikz image which doesn't draw anything but specify a bounding box. However, including the tikz package for this reason only will make compilation very slow since I have to compile dozens of latex snippets.

I use lualatex (but only because of the easy integration of true type fonts) and currently I compile the latex snippets using the following document template (the ... is replaced with the latex snipped to be rendered):


(If this is not possible, I'll just use a phantom text to specify my minimum vertical bounding box + auto-crop the rasterized image horizontally.)

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There is \vphantom that only uses the vertical dimensions. – egreg Nov 27 '12 at 21:09
Nice! This solves the problem. Thank you, @egreg – leemes Nov 27 '12 at 21:16
up vote 8 down vote accepted

There are many ways to do it; the simplest is perhaps to use \vphantom{Q} instead of \phantom{Q}, that uses only the vertical dimensions of "Q".

Another method is to use a strut:

\strut a

The command \strut produces an invisible object such that its height and depth sum up to the baseline skip. Here are three examples: the first is with


the second with


and the third is with the strut. I've added the frames to better see the result.

enter image description here

share|improve this answer
Thank you very much, especially for the second solution, which is exactly what I had in mind. – leemes Nov 27 '12 at 21:40
I'm still struggling: I want exactly 2\baselineskip above and below the baseline of the text (so I can exactly measure where the baseline is in the rasterized image plus measure the line spacing). The "Q" only was a start to solve the problem. Like with the "Q", the strut will not allow me to measure the baseline exactly. Can you please help me again? I hope you understand the problem. ;) Thanks! – leemes Nov 28 '12 at 21:55
@leemes Try \vrule width 0pt height 2\baselineskip depth 2\baselineskip in place of \strut – egreg Nov 28 '12 at 21:57
Ok this was fast. And it works like a charm, like expected ;) Thank you so much! – leemes Nov 28 '12 at 21:58

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