I am fairly certain that changing the DPI setting in render to disk does not effect the amount of information stored in the image. It is merely a calcuation to derive the correct print size. The factor determining the resolution of an image is the number of pixcels. Rendering a 1024x768 image on screen has exactly the same amount of information as a 1024x768 image rendered to disk, regardless of the DPI set. If a 1024x768 image is to be printed however, it may only be printed at 3.41 x 2.56 inches (assuming a minimum desired print quality of 300dpi). Printing that image at that size will result in a 300dpi resolution even if printed on a printer with more than 300 dpi quality. Bitmap is definately the best format to choose as it does not have any compression.