In the name of Allah the compassionate, the merciful Digital Image - PowerPoint PPT Presentation

In the name of Allah the compassionate, the merciful

Digital Image Processing S. Kasaei Kasaei S. Room CE307, SUT E-Mail: skasaei@sharif.ed Home Page: http://ce.sharif.edu http://ipl.ce.sharif.edu http://sharif.edu/~skasaei Kasaei 3

Chapter 11 Image Data Compression Kasaei 4

Introduction (cntd) Kasaei 5

Introduction (cntd) Kasaei 6

Introduction (cntd) Different types of redundancy to be � removed/decreased in the compression algorithm include: Interpixel redundancy, 1. Psychovisual redundancy, 2. Coding redundancy, 3. Temporal redundancy, & 4. Spectral redundancy. 5. Kasaei 7

Introduction (cntd) Model Components of a coding system. Kasaei 8

Introduction (cntd) A general compression system model (the codec). Kasaei 9

Introduction (cntd) An encoder system (compressor). Kasaei 10

Introduction (cntd) A decoder system (decompressor). Kasaei 11

Introduction (cntd) General Image Coder Structure. Kasaei 12

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Introduction (cntd) A compression system model (the codec). Kasaei 19

Introduction (cntd) A source encoder and decoder system. Kasaei 20

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Pixel Coding Kasaei 34

Pixel Coding (cntd) Kasaei 35

Pixel Coding (cntd) Kasaei 36

Pixel Coding (cntd) � Types of entropy coding schemes: � FLC to VLC: � Huffman Coding, [1952]; used in JPEG98, WSQ. � Golomb-Rice coding. � VLC to FLC: � Run-Length Coding (RLC) for b/w, [1977]; used in JPEG98, WSQ. � Bitplane-RLC for gray. � Lempel-Ziv-Welch (LZW), [1977], requires no a priori knowledge of the probability of occurrence of symbols; used in GIF, TIFF, UNIX gzip. � VLC to VLC: � Arithmetic Coding, [1975]. � Adaptive arithmetic coding; used in JPEG2000, MPEG-4, H264. Fixed-Length Coding: FLC Variable-Length Coding: VLV Kasaei 37

Pixel Coding (cntd) Kasaei 38

Huffman Coding � Idea: more frequent symbols � shorter codewords. � Algorithm: • Huffman coding generates prefix code. ☺ • Can be applied to one symbol at a time (scalar coding), or a group of symbols (vector coding), or one symbol conditioned on previous symbols (conditional coding). Kasaei 39

Pixel Coding (cntd) Kasaei 40

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Arithmetic Coding � Basic idea: � Represent a sequence of symbols by an interval with length equal to its probability. � The interval is specified by its lower boundary ( l ), upper boundary ( u ), & length d (=probability). � The codeword for the sequence is the common bits in binary representations of l & u. � The interval is calculated sequentially starting from the first symbol: � The initial interval is determined by the first symbol. � The next interval is a subinterval of the previous one, determined by the next symbol. Kasaei 47

Pixel Coding (cntd) Kasaei 48

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Encoding: 3/8 - 1/4 = 1/8 1/8 / 2 = 1/16 1/4 + 1/16 = 5/16 Binary Representation: /2 Decoding:

Huffman vs. Arithmetic Coding � Huffman coding: � Converts a fixed number of symbols into a variable length codeword. � Efficiency: � To approach entropy rate, must code a large number of symbols together. � Used in all image and video coding standards. � Arithmetic coding: � Converts a variable number of symbols into a variable length codeword. � Efficiency: � Can approach the entropy rate by processing one symbol at a time. � Easy to adapt to changes in source statistics. � Integer implementation is available. � Used as advanced options in image and video coding standards. Kasaei 51

Pixel Coding (cntd) Kasaei 52

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Predictive Techniques A lossy feed-forward prediction coding model. Kasaei 55

Predictive Techniques (cntd) A lossy feed-backward prediction coding model. Kasaei 56

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Transform Coding A transform coding system. Kasaei 64

Transform Coding (cntd) Kasaei 65

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Transform Coding (cntd) A wavelet transform coding system. Kasaei 70

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Transform Coding (cntd) A basic DPCM/DCT encoder for motion compensated video coding. Kasaei 74

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The JPEG Standard entropy table Q-table AC compressed Zigzag scan VLC image data image DCT Q differential VLC Offset DC (128) entropy table Kasaei 76

JPEG Example 139 144 149 153 155 155 155 155 1260 -1 -12 -5 2 -2 -3 1 • • 144 151 153 156 159 156 156 156 -23 -17 -6 -3 -3 0 0 -1 • • 150 155 160 163 158 156 156 156 -11 -9 -2 2 0 -1 -1 0 • • 159 161 162 160 160 159 159 159 -7 -2 0 1 1 0 0 0 • • 159 160 161 162 162 155 155 155 -1 -1 1 2 0 -1 1 1 • • 161 161 161 161 160 157 157 157 2 0 2 0 -1 1 1 -1 • • 162 162 161 163 162 157 157 157 -1 0 0 -1 0 2 1 -1 • • 162 162 161 161 163 158 158 158 -3 2 -4 -2 2 1 -1 0 • • 16 11 10 16 24 40 51 61 79 0 -1 0 0 0 0 0 12 12 14 19 26 58 60 55 -2 -1 0 0 0 0 0 0 14 13 16 24 40 57 69 56 -1 -1 0 0 0 0 0 0 14 17 22 29 51 87 80 62 -1 0 0 0 0 0 0 0 18 22 37 56 68 109 103 77 0 0 0 0 0 0 0 0 24 35 55 64 81 104 113 92 0 0 0 0 0 0 0 0 49 64 78 87 103 121 120 101 0 0 0 0 0 0 0 0 72 92 95 98 112 100 103 99 0 0 0 0 0 0 0 0 Kasaei 77

JPEG Example 79 0 -1 0 0 0 0 0 -2 -1 0 0 0 0 0 0 -1 -1 0 0 0 0 0 0 -1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 79 0 -2 -1 -1 -1 0 0 -1 EOB Kasaei 78

JPEG (Com.) كﻮﻠﺑ ﻚﻳ 8×8 كﻮﻠﺑ ﻚﻳ 8×8 ﺮهراﺪﻘﻣ ار ﻞﺴﻜﻴﭘ زا 128 ﻢآ يدورو ﺮﻳﻮﺼﺗ ﻢﻴﻨآ ﻲﻣ يﺎﻬآﻮﻠﺑ زا يا ﻪﺘﺷر 8× 8 ﻲﻠﺴﻜﻴﭘ كﻮﻠﺑ 8×8 لﺎﻤﻋا ياﺮﺑ ﻩدﺎﻣﺁ DCT DCT ﻞﻳﺪﺒﺗرﺰﻳﺎﺘﻧاﻮآ Compressed data Kasaei 79

JPEG (Decom.) كﻮﻠﺑ 8×8 ياﺮﺑ ﻩدﺎﻣﺁ لﺎﻤﻋا رﺰﻳﺎﺘﻧاﻮآ يد IDCT ﻞﻳﺪﺒﺗ Compressed data IDCT ﺮهراﺪﻘﻣ ﻪﺑ ﻞﺴﻜﻴﭘ 128 ﻲﻣ ﻪﻓﺎﺿا ﻢﻴﻨآ ﻩﺪﺷ يزﺎﺳزﺎﺑ ﺮﻳﻮﺼﺗ ﻩﺪﺷ يزﺎﺳزﺎﺑ يﺎه كﻮﻠﺑ زا يا ﻪﺘﺷر Kasaei 80

JPEG VS JPEG 2000 JPEG at 0.125 bpp JPEG2000 at 0.125 bpp (192:1) (192:1) Kasaei 81

Lossy Techniques (WT-Based) Original Image Reconstructed; 56:1, PSNR: 23.98 Kasaei 82

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