I think it's because .gif is good with solid blocks of colour
and .jpg is good for photos (which anything detailed is closer to)
(
Jessie © needs pirate name suggestions,
Mon 6 Oct 2008, 18:14,
archived)
The science only confuses the poor dears*
*I never bothered to remember it, just a simplification to help me choose when optimising
(
Jessie © needs pirate name suggestions,
Mon 6 Oct 2008, 18:21,
archived)