Finalized version with multiple sizes packs : See packs downloads below Set of 4 Ubuntu wallpapers with scripts to install as animated background for Gnome 2.28.1 at least. Read the readme file included to know how to use as animated BG.
Of course, each jpeg file in the packs can be used as an independent wallpaper.
I've worked a lot on the gradient banding, added a light pattern and some light noise. The resulting png was 4Mb large so I've uploaded jpg file ( ~950Kb each ). Thanks Notmiown for feedbacks! The previous archive can be found here: [link]