lec16 Face Recognition-II

lec16 Face Recognition-II - Results of Hand Recognition...

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1 CSE190a Fal 06 Face Recognition: Fisherfaces and lighting Biometrics CSE 190-a Lecture 16 CSE190a Fal 06 Results of Hand Recognition!! 64% Alex 42% Warren (Nearest Neighbor) 32% Warren (Bayesian) 60% Taurin (Nearest Neighbor) 64% Taurin (Statistical) 86% Tom Nearest Neighbor 82% Tom Bayesian 92% Vikram (CS2) Nearest Neighbor 42% Vikram (CS1) Why is Face Recognition Hard? CS252A, Winter 2005 Computer Vision I Image as a Feature Vector • Consider an n-pixel image to be a point in an n-dimensional space, x R n . • Each pixel value is a coordinate of x . x 1 x 2 x 3 CS252A, Winter 2005 Computer Vision I Nearest Neighbor Classifier { { R j } } are set of training images. x 1 x 2 x 3 R 1 R 2 I ) , ( min arg I R dist ID j j = CS252A, Winter 2005 Computer Vision I Comments • Sometimes called “Template Matching” • Variations on distance function (e.g. L 1 , robust distances) • Multiple templates per class- perhaps many training images per class. • Expensive to compute k distances, especially when each image is big (N dimensional). • May not generalize well to unseen examples of class. • Some solutions: – Bayesian classification – Dimensionality reduction
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2 CS252A, Winter 2005 Computer Vision I Appearance-based (View-based) • Face Space: – A set of face images construct a face space in R n – Appearance-based methods analyze the distributions of individual faces in face space CS252A, Winter 2005 Computer Vision I Eigenfaces: linear projection •An n -pixel image x R n can be projected to a low-dimensional feature space y R m by y = W x where W is an n by m matrix. • Recognition is performed using nearest neighbor in R m . • How do we choose a good W ? CS252A, Winter 2005 Computer Vision I Eigenfaces: Principal Component Analysis (PCA) Some details: Use Singular value decomposition, “trick” described in text to compute basis when n<<d CS252A, Winter 2005 Computer Vision I How do you construct Eigenspace? [ ] [ ] [ x
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lec16 Face Recognition-II - Results of Hand Recognition...

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