As a default, Poserframes calculates the aspect ratio of your image and matches that to the closest of the standard formats 2x3, 6x4.5 (645), 6x7, 4x5 or square. The shapes are drawn in those aspect ratios and the borders will look best if you keep your images close to those. However, Poserframes will stretch the shapes to accommodate whatever aspect ratio your image has. You can take advantage of this by bypassing the default format assignment (by adding the optional setting force_format, set to 35, 645, 45, 67 or square) and make Poserframes use the format you define. In this way, it’s possible to use a 6x7 scanner mask and negative style with a 645 image, for instance.