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VI. Video Compression
Coding efficiency/Compression ratio:
6.1 Basci concepts and Tech. of Video Coding-Introduction
The loss of information or distortion measure:
6.1 Basci concepts and Tech.s of Video Coding-Introduction
The functional elements of the generalized model:
Spatial operator Quantizer Variable length coding
The elements required in the feedback loop: Inverse operators Delayed frame memory Motion estimation Motion compensation
6.1 Basci concepts and Tech. of Video Coding-Introduction
A fundamental issue facing the design of video compression systems: the tradeoff between bitrate and quality or distortion
Factors in design and selection of a video compression system:
Video characteristic Transmission requirement Compression system characteristics and
performance Rate-distortion requirement Standards requirement
6.1 Basci concepts and Tech. of Video Coding-Application Requirements
6.1 Basci concepts and Tech.s of Video Coding-Application Requirements
Sampling of Analog Video Signals Two-dimensional spatial sampling and one-
dimensional temporal sampling Nyquist sampling theorem: defines the
conditions under which sampled analog signals can be perfectly reconstructed.
6.1 Basci concepts and Tech. of Video Coding-Digital Video Signals and Formats
Digital Video Formats
6.1 Basci concepts and Tech.s of Video Coding-Digital Video Signals and Formats
Entropy and Predictive Coding Discrete memoryless source (DMS) – VLC
coding: Huffman and arithmetic coding Markov source – predictive coding: differential pulse code modulation coding
(DPCM)
6.1 Basci concepts and Tech.s of Video Coding-Video Compression Tech.s
Block Transform Coding: The Discrete Cosine Transform
Has fast implementations using real calculations
Does not produce any significant discontinuities at the block edges when reconstruction
6.1 Basci concepts and Tech.s of Video Coding-Video Compression Tech.s
Block Transform Coding: The Discrete Cosine Transform
Has fast implementations using real calculations
Does not produce any significant discontinuities at the block edges when reconstruction
6.1 Basci concepts and Tech.s of Video Coding-Video Compression Tech.s
Quantization Uniform scalar quantizer Non-uniform quantization Vector quantizers
6.1 Basci concepts and Tech.s of Video Coding-Video Compression Tech.s
Motion Compensation and Estimation Motion estimation and compensation are
common techniques used to encode the temporal aspect of a video signal.
Three stages of motion compensated video coding:
1. motion estimation 2. motion compensation 3. encode the prediction error
6.1 Basci concepts and Tech.s of Video Coding-Video Compression Tech.s
Motion Compensation and Estimation Motion estimation is an interframe prediction
process falling in two general categories: 1. pel-recursive algorithms 2. block-matching algorithms: measure and
search
6.1 Basci concepts and Tech.s of Video Coding-Video Compression Tech.s
The H.261 recommendation is targeted at the videophone and videoconferencing application market running on connection-based ISDN at p x 64 kbps, p = 1, . . . ,30.
It explicitly defines the encoded bit stream syntax and decoder, while leaving the encoder design to be compatible with the decoder specification.
The video encoder is required to carry a delay of less than 150 ms so that it can operate in real-time bidirectional videoconferencing applications.
6.1 Basci concepts and Tech.s of Video Coding-H.261 Standards
The H.261 is part of a group of related ITU recommendations that define visual telephony systems.
This group includes the following:
6.1 Basci concepts and Tech.s of Video Coding-H.261 Standards
6.1 Basci concepts and Tech.s of Video Coding-H.261 Standards
6.1 Basci concepts and Tech.s of Video Coding-H.261 Standards
6.1 Basci concepts and Tech.s of Video Coding-H.261 Standards
Motion Compensation Transformation and Quantization Scalabilities --one scalable coded file that offers
increasingly greater spatial resolution, higher frame rates, or a better signal-to-noise ratio.
6.2 Spatiotemporal Wavelet Video Compression-Video Compression Basics
Hybrid Wavelet Coder temporal differential PCM (DPCM)+wavelet
based coders in the spatial dimension
Spatiotemporal Wavelet Coder Without motion compensation With motion compensation
Zero Coding and Embedding
6.2 Spatiotemporal Wavelet Video Compression-Wavelet Compression
Segmenting objects Temporal linking of objects Encoding objects “Inter” mode—encoding objects by the
motion parameters (I objects) “Intra” mode—encoding those that can
not be predicted (P objects)
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
Joint Motion Estimation and Segmentation
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
The likelihood functional that describes how well the observed images match the motion field data:
Joint Motion Estimation and Segmentation
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
A priori density of motion and enforces prior constraints on the motion field:
Joint Motion Estimation and Segmentation
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
A priori expectations for the object label field itself:
Maximation ApproachMAP solutionTwo-step iterative hierarchical
procedure: motion estimation & segmentation
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
Coding of Video Objects I mode: motion compensated predictive
(MCP) coding in hybrid object-based (OB)-MCP
P mode: spatial wavelet coding
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
Object Motion/Segmentation Coding Object-based 3-D wavelet coding (OB-
3DSBC) coder
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
6.2 Spatiotemporal Wavelet Video Compression-Object-Based Wavelet Compression
Represent visual data in terms of regions, defined by their contour and texture, possibly corresponding to objects or to parts of objects.
emphasize visually sensitive data while neglecting visually insignificant information
Second-generation concept is now widely accepted and has become the basic philosophy of the new MPEG-4 standard
Is called dynamic coding
6.3 Object-Based Video Coding-Introduction
6.3 Object-Based Video Coding-Second-Generation Coding
6.3 Object-Based Video Coding-Object-Based Video Coding
Intramode(I)—an object is coded independently
Intermode(P)—a video object is coded taking into account information available on its past
6.3 Object-Based Video Coding-Object-Based Video Coding
Object Shape and Geometry Coding A progressive contour coding based on a
polygonal approximation of the shape boundary is used to code the outline of object.
Suitable for sketch-based retrieval that is based on video object shapes
A geometrical shape boundary description can be integrated into an object-based mesh coding scheme
6.3 Object-Based Video Coding-Object-Based Video Coding
6.3 Object-Based Video Coding-Object-Based Video Coding
6.3 Object-Based Video Coding-Object-Based Video Coding Lossless shape representation-- altered
boundary triangles
6.3 Object-Based Video Coding-Object-Based Video Coding
Object Motion Estimation, Compensation, and Coding
Texture Representation
6.3 Object-Based Video Coding-Object-Based Video Coding