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8/9/2019 Session 08 2
1/31
Special Module on Media Processingand Communication
Dayalbagh Educational Institute(DEI)
Dayalbagh Agra
Indian Institute of Technology Delhi(IITD)
New Delhi
8/9/2019 Session 08 2
2/31
SlideSlide 22Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Recap
Lecture 1
Overview
Digital Representation
Audio
Image
Video
Geometry
Need of Compression
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SlideSlide 33Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionCompression Ratio
Cr = no/nc
no = Number of carrying units (bits) in the originaldata (image)
nr = Number of carrying units (bits) in the compresseddata (image)
Also,Rd = 1 1/ Cr
Rd = Relative data redundancy
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SlideSlide 44Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionFidelity Criteria
Measure of loss or degradation
Mean Square Error (MSE)
Signal to Noise Ratio (SNR) Subjective Voting
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SlideSlide 55Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
CompressionCompression Techniques
Loss-less CompressionInformation can be compressed andrestored without any loss of information
Lossy CompressionLarge compression, perfect recovery isnot possible
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SlideSlide 66Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
CompressionCompression Techniques
Symmetric Same time for compression (coding) and
decompression (decoding)
Used for dialog (interactive) mode applicationsAsymmetric
Compression is done once so can take longer Decompression is done frequently so should be fast Used for retrieval model applications
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SlideSlide 77Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionData Redundancy
CodingVariable length coding with shorter codesfor frequent symbols
InterpixelNeighboring pixels are similar
PsychovisualHuman visual perception - limited
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SlideSlide 88Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionCoding Redundancy
variable length codingAvg length=2.7 bits
fixed length codingAvg length=3 bits
Example: (from Digital Image Processing by Gonzalez and Woods)
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SlideSlide 99Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionInterpixel Redundancy
Image
Histogram
Example: (from Digital Image Processing by Gonzalez and Woods)
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SlideSlide 1010Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionInterpixel Redundancy
Image
Histogram
High interpixel correlation
Example: (from Digital Image Processing by Gonzalez and Woods)
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SlideSlide 1111Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionPsychovisual Redundancy
Original 256 levels 16 level quantization IGS quantization
Example: (from Digital Image Processing by Gonzalez and Woods)
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SlideSlide 1212Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionLoss-less Techniques
Coding redundancyVariable length coding
Interpixel redundancyRun length codingPredictive coding
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SlideSlide 1313Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionVariable Length Coding (Huffman Coding)
Sequence of symbols (a1, a2, a3, a4, a5) with associatedprobabilities (p1, p2, p3, p4, p5)
Start with two symbols of the least probabilitya1:p1a2:p2
Combine (a1 or a2) with probability (p1+p2)
Do it recursively (sort and combine) A binary tree construction
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SlideSlide 1414Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image Compression
a2 (0.4)
a1(0.2)
a3(0.2)
a4(0.1)
a5(0.1)
Sort inprobability
Variable Length Coding (Huffman Coding)
Symbols and their probabilities of occurrencea1 (0.2), a2 (0.4), a3 (0.2), a4 (0.1), a5 (0.1)
Example:
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SlideSlide 1515Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image Compression
a2 (0.4)
a1(0.2)
a3(0.2)
a4(0.1)
a5(0.1)
Sort
Variable Length Coding (Huffman Coding)
Example:
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SlideSlide 1616Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image Compression
a2 (0.4)
a1(0.2)
a3(0.2)
a4(0.1)
a5(0.1)
Sort
0.2
combine
Variable Length Coding (Huffman Coding)
Example:
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SlideSlide 1717Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image Compression
a2 (0.4)
a1(0.2)
a3(0.2)
a4(0.1)
a5(0.1)
Sort
0.2
combine
Variable Length Coding (Huffman Coding)
Example: Sort
0.4
0.2
0.2
0.2
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SlideSlide 1818Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image Compression
a2 (0.4)
a1(0.2)
a3(0.2)
a4(0.1)
a5(0.1)
Sort
0.2
combine Sort
0.4
0.2
0.2
0.2
0.4
combine Sort
0.4
0.2
0.4
0.6
combine
0.6
0.4
Sort
1
combine
Variable Length Coding (Huffman Coding)
Example:
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SlideSlide 1919Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image Compression
a2 (0.4)
a1(0.2)
a3(0.2)
a4(0.1)
a5(0.1)
Sort
0.2
combine Sort
0.4
0.2
0.2
0.2
0.4
combine Sort
0.4
0.2
0.4
0.6
combine
0.6
0.4
Sort
1
combine
Assign code
0
1
1
00
01
1
000
001
01
1
000
01
0010
0011
1
000
01
0010
0011
Variable Length Coding (Huffman Coding)
Example:
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SlideSlide 2020Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionDecoding
Example:
00111010001
?
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SlideSlide 2121Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionRun Length Coding
Run: a string of the same symbol
Example
input: AAABBCCCCCCCCCAAoutput: A3B2C9A2
compression ratio = 16/8 = 2
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SlideSlide 2323Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionPredictive Coding
Compression
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SlideSlide 2424Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionPredictive Coding
Decompression
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SlideSlide 2626Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionLossy
Psychovisual redundancy Keep more important information Trade off between loss (degradation) and compression
Original Compression Ratio: 7.7 Compression Ratio: 12.3 Compression Ratio: 33.9
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SlideSlide 2727Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image CompressionLossy
Recall QuantizationDiscrete value to represent range of valuesIrreversible operation
Information loss !
Predictive Coding Transform Coding
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SlideSlide 2828Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
AudioDigital RepresentationAudio (Sound): continuous signal (wave form) in time
1D function f(x)
Continuous
Discrete
Slide 7 Lecture 1
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SlideSlide 2929Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Image
x
y
2D function f(x,y)
Sampling: Discretization in x and y QuantizationSlide 16 Lecture 1
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SlideSlide 3030Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
VideoVideo is a sequence of images in time
Time
Image
(Frame)
Slide 23 Lecture 1
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SlideSlide 3131Special Module on Media Processing and Communication http://www.it.iitd.ac.in/sil864.html
Graphics
Geometry Data: Meshes Points
Connectivity
Slide 26 Lecture 1
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