Files with the extension .FPX are multi-resolution bitmap image files. The .FPX file format utilises Microsoft's 'structured storage' format which allows for the storage of hierarchical data in a single file.

.FPX files are in themselves large in size for a graphics file, however due to the hierarchical nature of the file and the way they interact with web-browsers, when a request is made for download only the resolution required is sent via the internet resulting in shorter download times and bandwidth usage.