Looks like rescaling in Preview breaks things badly, so individually it is.
Turns out the images must be 16-bit, not 8-bit or they break.
Removed everything modified by the GIMP as it turned out to be useless.
Trying a program called Pixelmator.
The Pixelmator file.
Pixelmator file and corresponding PNG export (instead of save copy).
It looks like exporting works, but save as does not.
Merge pull request #15 from Hasimir/master

Image file updates