The creator of the format is documented as having confirmed the pronunciation is "jif", but I don't care. Once he created it and put it into the world, he relinquished his control.
I honestly believe he was just trolling when he said that and he probably giggles to himself everytime someone says (shudder) 'jif'. It's a hard G from graphics so I don't know how else is could be reasonably pronounced.
This is a jem of a response, but by jeneralizing pronunciations of acronyms only by the way they are spelt, you are opening a jigantic can of worms on etymology and linguistics.
The jist of it is that English is a weird language, jenerally descriptive, and there can be many correct answers to the same pronunciation problem.
Debunked? Its a counterpoint to the fact that it's pronounced that way because it's spelled with a g. If that poor argument wasn't used, the giraffe one wouldn't have to come up. It's not evidence of anything other than that letters can be pronounced in more than one way.
For the graphical thing, imagine pronouncing NASA wrong because of the way aeronautical is pronounce. Or underwater in scuba. World in WHO? The I in AIDS isn't pronounced anything like immunodeficiency.