PNG screenshots were showing up with odd coloration due to incorrect
or malformed color management settings (ICC profiles). In an earlier
commit, thes PNG files were transformed to JPEGs, and this did cause
the coloration problems to go away, but a new problem took its place;
during docbook PDF generation, warnings like the following started
showing up:
An ICC profile is present but it is invalid (Invalid ICC Profile
Data). The color profile will be ignored. (.../quotes-aggregator.jpg)
The solution was to download Seashore (http://seashore.sourceforge.net,
Mac-only) which has an embedded ICC profile editor. Each of the three
offending JPEG images were loaded and re-saved to JPEG format, but
targeting 'web' output which eliminates all ICC profile metadata.
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