Survey of Dirac: A Wavelet Based Video Codec for Multiparty Video Conferencing and Broadcasting - Intelligent Video Event Analysis and Understanding - page 239

such that the base layer is coded to provide the basic video quality and the
enhancement layer(s) when added back to the base layer reconstruct a higher
quality reproduction of the input video. Since the enhancement layer is said to
enhance the signal-to-noise ratio of the base layer, this type of scalability is called
SNR scalability. This scalability is a tool intended for use in many video
applications, for example, telecommunications and multiple quality video services
with standard TV and High-Definition TV; Multi quality video on-demand
services.
Fig. 28 SNR Scalability
7.1.2 Spatial Scalability
Spatial scalability involves generating two or more layers of the same
spatiotemporal resolution but different video sizes from a single video source such
that the base layer is coded to provide the basic video size and the enhancement
layer(s) when added back to the base layer reconstruct a higher size reproduction
of the input video. Since the enhancement layer is said to enhance the base layer
for getting bigger size picture, this type of scalability is called Spatial scalability.
In Wavelet Based Video Codecs, Spatial scalability allows you to reconstruct
video of smaller size using fewer numbers of bands without compromising the
video quality. It provides a tradeoff between the number of bands and video size.