MPEG Graphics Compression Model
MPEG doc#: N9892
Date: May 2008
Author: Marius Preda (Institut TELECOM
1. What is P25?
The goal of ISO/IEC 14496-25 (P25)  is to specify an architectural model able to accommodate
- third-party XML based description of scene graph and graphics primitives with
- (potential) binarization tools and with
- MPEG-4 3D Graphics Compression tools
The advantages of such approach are on one side the use of powerful compression tools for graphics and one other side the generality of graphics primitives representation. Hence, compression tools developed in ISO/IEC 14496-2, ISO/IEC 14496-11 and ISO/IEC 14496-16 would not be applied only to the scene graph defined by ISO/IEC 14496-11 but to any scene graph definition. The bitstreams obtained when using the model are MP4 formatted and contains XML (or binarized XML) for the scene graph and binary elementary streams for graphics compression (geometry, texture and animation).
The architecture model is composed by three layers: textual data representation, binarization and compression.
The current model can accommodate any scene graph and graphics primitives’ representation formalism. The only requirement on this representation is that it should be expressed in XML. Any XML Schema (specified by MPEG or by external bodies) may be used. Currently three XML Schemas are supported: XMT, COLLADA and X3D.
The binarization layer is ensured by using gzip. The compression layer refers to MPEG-4 tools for 3D graphics (geometry, texture and animation) defined in ISO/IEC 14496-2, ISO/IEC 14496-11 and ISO/IEC 14496-16.
2. Why use P25 tools in 3D applications?
P25 is a transparent layer allowing to reduce the data size and exposing a bitsream syntax that is streaming friendly. P25 can be plugged to authoring tools for 3D graphics as final module before storage or transmission as well as to rendering engines or visualization tools as initial module.
 ISO/IEC 14496‑16: MPEG‑4 Part 25, 3D Graphics Compression Model.