Abstract
This chapter is dedicated to professionals of 3D graphics industry, solution providers for on-line systems involving 3D content (games, persistent universes, virtual spaces with graphical representation), students and professors in digital sciences. The first section aims at presenting the background of the compression for multimedia signals. The second section presents the latest developments in MPEG-4 with respect to the compression and streaming of 3D graphics objects and scenes. The MPEG-4 tools, categorized into geometry, appearance and animation, are introduced. While MPEG standards specify only the bit-stream syntax and the architecture of the decoder, scheme for encoders’ implementation are presented in this section. In the third section we describe a recently adopted MPEG model for 3D graphics consisting in opening the representation of graphics primitives to any XML-based format and completing it with binarization and compression layers. This shift in the manner of using MPEG-4 for 3D graphics is concretized in Part 25 of MPEG-4 (Preda, Jovanova, Arsov& Prêteux, 2007).
TopBackground
A generic compression schema aims at eliminating redundancy in the data representation. Additionally when dealing with lossy compression, it makes also possible to identify the attributes for which a less precise reconstruction results in an acceptable signal distortion for human observers. As example, image and video encoders exploits the way that humans perceive the colors. In general, a compression schema is based on prediction, frequency transform, quantization, and entropy encoder as illustrated in Figure 1.
Figure 1. Generic signal compression schema
Key Terms in this Chapter
3DGC: “3D Graphics Compression” – an MPEG working group dealing with specifications of 3D Graphics tools and integration of synthetic and natural media in hybrid scenes.
XMT: “eXtensible MPEG 4 Textual Format” – a XML formalism defined by MPEG in the standard ISO/IEC 14496-11 for representing the scene graph.
MPEG: “Motion Picture Expert Group”, marketing name of the “ISOIEC SC29 WG11” standardization committee, affiliated to ISO (International Standardization Office) and creator of the multimedia standards: MPEG-1, MPEG-2, MPEG-4, MPEG-7 and MPEG-21.
COLLADA: An XML based formalism standardized by the Khronos consortium for representing 3D graphics assets.
3DMC: “3D Mesh Compression” – a part of MPEG-4 specifications dealing with the specification of the bit-stream syntax for compressed meshes.
WSS: “Wavelet Subdivision Surfaces” – a part of MPEG-4 specifications dealing with the specification of the bit-stream syntax for compressed meshes described in a hierarchical manner.
FAMC: “Frame-based Animation Compression” – a part of MPEG-4 specifications dealing with the specification of the bit-stream syntax for a set of meshes with consistent connectivity and temporal updates of vertex attributes.