ImageMagick recipes I should stuff into config files or scripts, but
haven't yet.
* Configuration
** Allow conversion from/to PDF
- Open ImageMagick's =policy.xml= configuration file.
- Locate the =<policy>= tag with a =pattern= including "PDF".
- Comment it out.
* Comparing images
~magick compare~ is a thing; ~magick convert~ can also do [[https://stackoverflow.com/a/33673440][neat stuff]]:
#+begin_src sh
convert '(' a.png -flatten -grayscale Rec709Luminance ')' \
        '(' b.png -flatten -grayscale Rec709Luminance ')' \
        '(' -clone 0-1 -compose darken -composite ')' \
        -channel RGB -combine diff.png
#+end_src