Understanding Compression: Data Compression for Modern Developers

241 Pages·2016·11.003 MB·English

by  Colt McAnlis, Aleks Haecky

Understanding
Compression
DATA COMPRESSION FOR MODERN DEVELOPERS
Colt McAnlis & Aleks Haecky

Understanding Compression
Data Compression for Modern Developers
Colt McAnlis and Aleks Haecky
BBeeiijjiinngg BBoossttoonn FFaarrnnhhaamm SSeebbaassttooppooll TTookkyyoo
Understanding Compression
by Colt McAnlis and Aleks Haecky
Copyright © 2016 Colton McAnlis and Aleks Haecky. All rights reserved.
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978-1-491-96153-7
[LSI]
From CLM
To JAM and MLM: I swear to Zuul, that if you don’t eat your broccoli right now, I’m
going to write a book. And in the dedication of that book, I’m going to call you out as
being afraid of a piece of foliage that humans have been eating for thousands of genera‐
tions. Then, 20 years from now, when you have kids of your own, I’m going to pull that
book out, and show you what I wrote, and laugh in your face, because you’ll know how
crazy you’re making me right now. #parenting
To KMKM: How about another decade, just for good measure?
From AH
To AHS and GHS: I hoped you’d learn to cook. Instead, you proved that humankind can
survive on fresh apples and stale supermarket sushi.

Table of Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
Chapter Synopsis 18
1. Let’s Not Be Boring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
The Five Buckets of Compression Algorithms 1
Claude Shannon Is Infuriating! 2
The Only Thing You Need to Know about Data Compression 3
A World Built on Data Compression 4
2. Do Not Skip This Chapter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Understanding Binary 9
Base 10 System 9
Binary Number System 10
Information Theory 13
An Excursion into Binary Search 14
Entropy: The Minimum Bits Needed to Represent a Number 16
Standard Number Lengths 17
3. Breaking Entropy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Understanding Entropy 19
What This Entropy Stuff Is Good For 21
Understanding Probability 22
Breaking Entropy 23
Example 1: Delta Coding 24
Example 2: Symbol Grouping 25
Example 3: Permutations 26
v
Information Theory Versus Data Compression 31
4. Variable-Length Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Morse Code 33
Probability, Entropy, and Codeword Size 36
Variable-Length Codes 38
Using VLCs 38
Creating VLCs 42
A Handful of Example VLCs 44
Finding the Right Code for Your Data Set 51
5. Statistical Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Statistically Compressing to Entropy 53
Huffman Coding 55
Building a Huffman Tree 55
Generating Codewords 57
Encoding and Decoding 58
Practical Implementations 58
Arithmetic Coding 60
Finding the Right Number 61
Encoding 62
Picking the Right Output Value 64
Decoding 64
Practical Implementations 69
Asymmetric Numeral Systems 69
Encoding and Decoding Using a Transform Table 70
Creating the Reference Table 71
Using ANS for Compression 74
Decoding Example 75
So Where Does the Compression Come From? 76
Practical Compression: Which Statistical Algorithm Do I Choose? 77
6. Adaptive Statistical Encoding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Locality Matters for Entropy 79
Adaptive VLC Encoding 81
Dynamically Building a VLC Table 81
Literals 84
Resets 87
Knowing When to Reset 88
Using This in Practice 89
Adaptive Arithmetic Coding 89
Adaptive Huffman Coding 90
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The Modern Choice 91
7. Dictionary Transforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
A Basic Dictionary Transform 94
Finding the Right “Words” 95
The Lempel-Ziv Algorithm 98
How LZ Works 99
Encoding 104
Decoding 105
Compressing LZ output 106
LZ Variants 107
Collect Them All! 110
8. Contextual Data Transforms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
Run-Length Encoding 112
Dealing with Short Runs 112
Compressing 114
Delta Coding 115
XOR Delta Coding 118
Frame of Reference Delta Coding 119
Patched Frame of Reference Delta Coding 120
Compressing Delta-Encoded Data 123
Does It Work on Text? 123
Move-to-Front Coding 123
Avoiding Rogue Symbols 125
Compressing MTF 126
Burrows–Wheeler Transform 126
Ordering Is Important! 128
How BWT Works 128
Inverse BWT 130
Practical Implementations 132
Compressing BWT 132
9. Data Modeling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
The Chains of Markov 136
Markov and Compression 139
Practical Implementations 145
Prediction by Partial Matching 145
The Search Trie 147
Compressing a Symbol 149
Choosing a Sensible N Value 150
Dealing with Unknown Symbols 150
Table of Contents | vii
Context Mixing 150
Types of Models 151
Types of Mixing 153
The Next Big Thing? 154
10. Switching Gears. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Media-Specific Compression 155
General-Purpose Compression 156
Compression in Practice 157
11. Evaluating Compression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Compression Usage Scenarios 159
Compressed Offline, Decompressed On-Client 159
Compressed On-Client, Decompressed In-Cloud 160
Compressed In-Cloud, Decompressed On-Client 160
Compressed On-Client, Decompressed On-Client 161
Compression Need 161
Compression Ratio 162
Compression Performance 163
Decompression Performance 164
Ability to Decode-Stream 164
Comparing Compressors 165
12. Compressing Image Data Types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
Understanding Quality Versus File Size 167
What Reduces Image Quality? 169
Measuring Image Quality 171
Making This Work 173
Image Dimensions Are Important 173
Choosing the Correct Image Format 175
PNG 175
JPG 176
GIF 177
WebP 177
And Now for Choosing... 177
GPU Texture Formats 179
Vector Formats 180
Eyes on the Prize 182
13. Serialized Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Understanding Common Use Cases 184
Dynamically Server-Built Data 184
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