Date: 2014jul24 Product: Adobe Photoshop Q. What is a .PSB file? A. Its an Adobe Photoshop image file. Regular Photoshop files have .PSD extension. PSB = Photoshop Big and can support 300,000 x 300,000 pixels. Apparently they load faster too. First released in Photoshop CS 1. There is a preferences setting to enable it. Photoshop will continue to support .PSD.