Pattern Recognition Vidya Manian Dept. of Electrical and Computer Engineering University of Puerto Rico INEL 5046, Spring 2007

Human Perception Humans have developed highly sophisticated skills for sensing their environment and taking actions according to what they observe, e.g., –Recognizing a face –Understanding spoken words –Reading handwriting –Distinguishing fresh food from its smell We would like to give similar capabilities to machines

What is a Pattern? “A pattern is the opposite of a chaos; it is an entity vaguely defined, that could be given a name.” (Watanabe)

What is Pattern Recognition? A pattern is an entity, vaguely defined, that could be given a name, e.g., > Fingerprint image>speech signal > handwritten word>DNA sequence >human face>… Pattern recognition is the study of how machines can –Observe the environment –Learn to distinguish patterns of interest –Make sound and reasonable decisions about the categories of the patterns

Recognition Identification of a pattern as a member of a category we already know, or we are familiar with –Classification (known categories) –Clustering (creation of new categories) Category “A” Category “B” Classification Clustering

Pattern Recognition Given an input pattern, make a decision about the “category” or “class” of the pattern Pattern recognition is a very broad subject with many applications In this course we will study a variety of techniques to solve P.R. problems and discuss their relative strengths and weaknesses

Pattern Class A collection of “ similar ” (not necessarily identical) objects A class is defined by class samples (paradigms, exemplars, prototypes) Inter-class variability Intra-class variability

Pattern Class Model Different descriptions, which are typically mathematical in form for each class/population Given a pattern, choose the best-fitting model for it and then assign it to class associated with the model

Intra-class and Inter-class Variability The letter “T” in different typefaces Same face under different expression, pose….

Identical twins Characters that look similar Inter-class Similarity

Pattern Recognition Having been shown a few positive examples (and perhaps a few negative examples) of a pattern class, the system “learns” to tell whether or not a new object belongs in this class (Watanabe) COGNITION= Formation of new classes RECOGNITION= known classes

Pattern Recognition Applications Speech recognition Detection and diagnosis of disease Remote sensing (terrain classification, tanks detection) Character recognition Identification and counting of cells Fingerprint identification Web search Inspection (PC boards, IC masks, textiles)

Fish Classification Preprocessing will involve image enhancement, separating touching/occluding fishes and finding the boundary of the fish

Length Feature Training (design or learning) Samples

Lightness Feature Overlap in the histograms is small compared to length feature

Two-dimensional Feature Space (Representation) Two features together are better than individual features Cost of misclassification?

Complex Decision Boundary Issue of generalization

Boundary With Good Generalization Simplify the decision boundary!

Models for Pattern Recognition Template matching Statistical (geometric) Syntactic (structural) Artificial neural network (biologically motivated?) Hybrid approach

Statistical Pattern Recognition Preprocessing Feature extraction Classification Learning Feature selection Recognition Training pattern Patterns + Class labels Preprocessing

Each pattern is represented as a point in the d-dimensional feature space Features are domain-specific and be invariant to translation, rotation and scale Good representation  small intraclass variation, large interclass separation, simple decision rule No redundant features, too many features and less samples- curse of dimensionality (Huges phenomena) Pattern Representation using features x1x1 x2x2 x1x1 x2x2

Artificial Neural Networks Massive parallelism is essential for complex pattern recognition tasks (e.g., speech and image recognition) –Human take only a few hundred ms for most cognitive tasks; suggests parallel computation Biological networks attempt to achieve good performance via dense interconnection of simple computational elements (neurons) –Number of neurons  – –Number of interconnections/neuron  10 3 – 10 4 –Total number of interconnections  10 14

Artificial Neural Networks Nodes in neural networks are nonlinear, typically analog where is internal threshold or offset x1x1 x2x2 xdxd Y (output) w1w1 wdwd

Feed-forward nets with one or more layers (hidden) between the input and output nodes A three-layer net can generate arbitrary complex decision regions These nets can be trained by back-propagation training algorithm Multilayer Perceptron d inputs First hidden layer NH 1 input units Second hidden layer NH 2 input units c outputs

Statistical Pattern Recognition Patterns represented in a feature space Statistical model for pattern generation in feature space Given training patterns from each class, goal is to partition the feature space.

Image Analysis and Segmentation (classification) using texture features Aerial photograph of Anasco,PR Classified using Logical operators

Classification of color images using texture features Texture mosaic of 3 colored tiles and canvas texture. Classified image

Classification in Remote Sensing

Sensor

Classification of Landsat image of San Juan area, PR using Gabor texture features Landsat image 7 bands (R, G, B, IR and Thermal) Classified image using R,G,B