CODING SYNTHETIC VISUAL SCENES	•
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							Core
					Scalable still
					texture			Animated 2D
								Mesh
Facial Animation		Simple Face	Simple FBA		Binary Shape		Basic
							Animated
Parameters
							Texture
				2D dynamic mesh
		Body Animation		(uniform topology)			2D dynamic mesh
							(Delaunay
		Parameters
							topology)

Figure 5.74 Tools and objects for animation

5.7.2 The Core Studio Profile

The Core Studio object is intended for distribution of studio-quality video (for example between production studios) and adds support for Sprites and P-VOPs to the Simple Studio tools. Sprite coding is modified by adding extra sprite control parameters that closely mimic the properties of ‘real’ video cameras, such as lens distortion. Motion compensation and motion vector coding in P-VOPs is modified for compatibility with the MPEG-2 syntax, for example, motion vectors are predictively coded using the MPEG-2 method rather than the usual MPEG-4 median prediction method.

5.8 CODING SYNTHETIC VISUAL SCENES

For the first time in an international standard, MPEG4 introduced the concept of ‘hybrid’ synthetic and natural video objects for visual communication. According to this concept, some applications may benefit from using a combination of tools from the video coding community (designed for coding of ‘real world’ or ‘natural’ video material) and tools from the 2D/3D animation community (designed for rendering ‘synthetic’ or computer-generated visual scenes).

MPEG4 Visual includes several tools and objects that can make use of a combination of animation and natural video processing (Figure 5.74). The Basic Animated Texture and Animated 2D Mesh object types support the coding of 2D meshes that represent shape and motion, together with still texture that may be mapped onto a mesh. A tool for representing and coding 3D Mesh models is included in MPEG-4 Visual Version 2 but is not yet part of any profile. The Face and Body Animation tools enable a human face and/or body to be modelled and coded [8].

It has been shown that animation-based tools have potential applications to very low bit rate video coding [9]. However, in practice, the main application of these tools to date has been in coding synthetic (computer-generated) material. As the focus of this book is natural video coding, these tools will not be covered in detail.

5.8.1 Animated 2D and 3D Mesh Coding

A 2D mesh is made up of triangular patches and covers the 2D plane of an image or VO. Deformation or motion between VOPs can be modelled by warping the triangular patches. A 3D