PSB stands for Photoshop Big: it's for Photoshop files larger than the arbitrary size of 30000x30000 pixels or 3 GB, whichever is smaller. PSB files can be up t

PSB stands for Photoshop Big: it's for Photoshop files larger than the arbitrary size of 30000x30000 pixels or 3 GB, whichever is smaller. PSB files can be up to 300,000 pixels wide. More information than you ever wanted about Adobe file formats: http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/ http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/