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Chapter 9. Visual SNHC Tools > View-Dependent Scalability

9.5. View-Dependent Scalability

Scalability is one of the major functionalities in MPEG-4, as it can provide solutions to harmonize platforms with different capabilities, for example, in terms of bandwidth or computational power. In a 3D game scene, the user terminal might be burdened if it has to download the scene graph and all of its entities, especially when the user terminal is a mobile device. However, the virtual world, which the user can experience with MPEG-4, is bounded by the viewing position and field of view, just as human beings are bounded by eye positions and capabilities in the real world. View-dependent scalability is a tool for sending first to the decoding terminal only the visually needed data. If the user's viewing position or angle is changed, the server can update the visual data based on the new position and angle, but no useless data is sent (e.g., corresponding to angles where the user has never been).

The view-dependent scalability tool is useful when there is a back channel from the user to the server (see Figure 9.33). Hence, the major target applications for view-dependent scalability are network games and virtual reality applications in which terminals may vary in performance (e.g., computing power, memory size, and available bandwidth).


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