Open Type Fonts have different scale in XeLaTeX

Question

I am trying to create a template that allows easy switching of the main font using fontspec. I have noticed that the size of different fonts varies greatly, as the picture below illustrates. If we take the Palatino fonts as the benchmark, Adobe Garamond Pro and Linux Libertine are much smaller and Minion Pro and Adobe Caslon Pro are slightly larger than those, but still smaller than Palatino.

I always thought that open type fonts are somewhat "normalised" so that this does not occur. I could now use trial and error with fontspec's scale option, but maybe there are some guidelines out there that tell me what I am supposed to do to scale fonts to the same size.

This has been generated with the following MWE (except Pazo Math):

\documentclass{scrartcl}
\usepackage{fontspec}
\defaultfontfeatures{Mapping=tex-text}

\begin{document}

\setmainfont{TeX Gyre Pagella}
The quick brown fox jumps over the lazy dog (TeX Gyre Pagella)

\setmainfont{Adobe Garamond Pro}
The quick brown fox jumps over the lazy dog (Adobe Garamond Pro)

\setmainfont{Linux Libertine O}
The quick brown fox jumps over the lazy dog (Linux Libertine)

\setmainfont{Adobe Caslon Pro}
The quick brown fox jumps over the lazy dog (Adobe Caslon Pro)

\setmainfont{Minion Pro}
The quick brown fox jumps over the lazy dog (Minion Pro)

\end{document}

Answer 1

The question appears to boil down to font design x-heights. A x-height is the height of the letter x, that is, without ascender ( like in d ), or descender ( like in g ). Some font designs, like the mentioned Palatino design by Hermann Zapf, have a larger x-height than some other font designs. As a consequence, it needs to be taken into account when designing the page.

I feel it is easy to think about in this way: How high does the majority of the ink reach on a line. Perhaps it would be good to visualize the difference as well. First, a page set “solid” (the font size is the same as the leading). TeX Gyre Pagella 11/11*24 on the left, and 11/15 on the right:

You can see that a font with a larger x-height needs more air to breathe.

Contrast this to a font with a smaller x-height: Minion Pro 11/11*24 on the left, with 11/12 on the right.

Now, ofcourse you almost always want some lead, because as you can see, the page turns rather black when there is no extra space between the lines.