Poor quality of resulting formula images

[chlarsen]

Dear Andreas,
Thank you a million times for all the terrific work on DokuWiki, this plugin included.
I seem to have a pesky issue with the quality of the resulting formula display on screen (and then, of course also in any exported .pdf or .odt format. Here is a simple example:

<m 11>\ \ \ \ Out-of-Pocket spending as percentage of total health expenditure</m>

<m 13>\= { {Out-of-pocket spending} / {Total health expenditure}} * 100</m>

I get the attached formula (as image).

I have deliberately added some trailing heading for you to see the difference in sharpness.
I am running PHP 7.3 on FreeBSD 11.3 in a jail, and have the required dependencies instaled, or so I hope:

===>>> freetype2-2.10.2
===>>> libgd-2.3.0,1
===>>> php73-gd-7.3.18
===>>> php73-tokenizer-7.3.18
===>>> php73-zlib-7.3.18
===>>> png-1.6.37

Anything I may have missed?
Thank you so much!
Chris