PSB

From GDWiki

PSB is a variation of Photoshop's PSD file format, the difference being that PSB supports extra large image files. If a Photoshop image is larger than 30,000 x 30,000 pixels, the PSB format needs to be used, which has a maximum dimension limit of 300,000 x 300,000 pixels. This format is quite irrelevant for independent game developers.