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Download PDF: 2011-05-22_Changing_PoP1_Images.pdf (975kB)
Download ODT: 2011-05-22_Changing_PoP1_Images.odt (673kB)
It was released on May 22nd, 2011. Credits are inside the file.
Note: the home directory (which contains the .gimp-n.n/palettes/*.gpl files) differs per OS.
Wikipedia has more information about home directories.
Too difficult? An alternative is to use SDLPoP, which has all images in its data/ directory.
This allows you to edit images without having to use PR or gpl2jascpal.