The G is from graphics [ɡɹæfɪks].

Additionally, word-initial single G before short I is always [g] instead of [dʒ] in native English: gift girl give gibbon gimlet gizzard gilded git gimp giddy gig gimbal.

The exceptions are borrowed French words: gin (le gin), ginger (le gingembre), giraffe (la girafe), giblet (OF: gibelet).