1. A method comprising: receiving an indication of a desired access to a JPM file; accessing a binary codestream and a JPEG 2000 codestream from the JPM file; using index values in shared data entry boxes to identify parts of the JPEG 2000 codestream that are contained in the shared data entry boxes; and extracting a portion of the JPEG 2000 codestream from the shared data entry boxes based on the desired access and the index values.