CT20A6100 MACHINE VISION AND DIGITAL IMAGE ANALYSIS MPEG Pauli Jutila Cristina Petre.
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Transcript of CT20A6100 MACHINE VISION AND DIGITAL IMAGE ANALYSIS MPEG Pauli Jutila Cristina Petre.
CT20A6100MACHINE VISION AND DIGITAL
IMAGE ANALYSIS
MPEG
Pauli Jutila
Cristina Petre
Contents
1. Introduction to MPEG 2. MPEG Family3. Intra Frame Coding Techniques4. Non-Intra Frame Coding Techniques5.Summary
Why do we need video compression?
Example video compression- 1920x1080 pixels 30 frames/sec 8 bits/color => 1.5Gb/sec
- 6MHz channel bandwidth => 19.2Mb/sec
=> compression 83:1
The MPEG Family
MPEG-1
● Basic form using motion compensated block-based transform coding techniques
● Optimized to work for 352x240 at 30frames/sec
or 352x288 at 25frames/sec ,possible to go up
to 4095x4095
● Defined for progressive frames only
● No direct provision for interlaced video applications
MPEG-2
● Designed for digital television broadcasting
● Potentially high quality video (4-9Mb/sec)
● Profiles and levels :
profile - bitstream scalability, colorspace resolution
level - image resolution, maximum bit-rate/profile
● MP@ML : 720x480 at 30 frames/sec
● MP@HL : 1920x1080 at 30 frame/sec
MPEG-4
● Interactive content
● Object-oriented composite files
● Image blocks are arbitrary shaped
● Multiplexes and synchronizes data
● Divided into a number of parts-compatibility issue
Coding Techniques
Intra Frame Coding
Video Filter DCT Quantizer Run-Lenght VLC
Bit-StreamBuffer
Bit-Rate Control
Video Filter
• The human eye is less sensitive to chrominance than luminance.
• RGB YCbCr• Choice of sub-sampling ratios:
• 4:4:4 (Professional, Post-Production)• 4:2:2 (same as above)• 4:1:1 (DV Camcorder) • 4:2:0 (Web, DVD)
Discrete Cosine Transform
• Nearly optimal in energy consentration and decorrelating
• The human eye is less sensitive to changes in higher frequencies
• Calculated in blocks, usually 8x8
DCT Coefficient Quantization
• 12-bit coefficient is divided by a corresponding value from intra quantization matrix
• Each value in the resultant matrix is pre-scaled by multiplying by a single value, known as the quantizer scale code (1-112)
• The goal is to force as many of the DCT coefficients to zero or near zero
Variable Length Coding
• Zigzag-scanning long runs of consecutive zeros
• Alternate pattern in MPEG-2 (for interlaced video)• Huffman coding
Coding Techniques
I,P,B Frames
I-pictures: intra-coded no motion-compensated prediction used as reference picture
P-picture: inter-coded forward predicted (from I or P frame)
B-picture: inter-coded bi-directional prediction high coding efficiency
I,P,B Frames
Motion Estimation
Matching
Prediction Error Compensation
Non-Intra Decoding
Summary
● Video compression is needed!
● MPEG enables a wide range of applications
● Different standards but same principles
● Spatial and temporal processing
References
● Barry G. Haskell, Atul Puri, Arun N. Netravali, Digital Video: An Introduction to MPEG-2, Chapman and Hall, 1997.
● Joan L. Mitchell, William B. Pennebaker, Chad E. Fogg, Didier J. LeGall, MPEG Video Compression Standard, Chapman and Hall, 1997.
● John Wiseman, An Introduction to MPEG Video Compression, 1998
● Marius Preda, Les standards MPEG dans l'espace multimedia, 2005
● E. G. Richardson, Video Codec Design, Wiley, 2002● Wikipedia