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xvi Contents

Force-Based Thinning 228
Definitions 229
Use of a Force Field 230
Subpixel Skeletons 234
Source Code for Zhang-Suen/Stentiford/Holt Combined
Algorithm 235
Website Files 246
References 247

Chapter 7 Image Restoration 251
Image Degradations — The Real World 251
The Frequency Domain 253
The Fourier Transform 254
The Fast Fourier Transform 256
The Inverse Fourier Transform 260
Two-Dimensional Fourier Transforms 260
Fourier Transforms in OpenCV 262
Creating Artificial Blur 264
The Inverse Filter 270
The Wiener Filter 271
Structured Noise 273
Motion Blur — A Special Case 276
The Homomorphic Filter — Illumination 277
Frequency Filters in General 278
Isolating Illumination Effects 280
Website Files 281
References 283
Chapter 8 Classification 285
Objects, Patterns, and Statistics 285
Features and Regions 288
Training and Testing 292
Variation: In-Class and Out-Class 295
Minimum Distance Classifiers 299
Distance Metrics 300
Distances Between Features 302
Cross Validation 304
Support Vector Machines 306
Multiple Classifiers — Ensembles 309
Merging Multiple Methods 309
Merging Type 1 Responses 310
Evaluation 311
Converting Between Response Types 312