CV in a Nutshell (I)

Yi Lihttp://users.cecs.anu.edu.au/~yili/

CVinNutshell.htm

Outline

• Introduction• Image Formation• Early vision• Cognition in psychology• Face recognition (I)

Paper discussion (1)

• Recognition by Components:– Segmentation: blocks, cylinders, wedges, cones– Curvature, collinearity, symmetry, parallel– Contour, surface, texture– Occlusion– Top-down or bottom-up?– Relation: pairwise?

http://euron.upc.es/dbtm/show_image.php?id=36

Paper discussion (2)

• Face Recognition– extremely low-resolution images (Yang and Ma)– Occlusion (sparse)– Component vs hollistic– Context! – Facial expression (Cohn)– Illumination (Basri and Jacobs)– Specialized (Martinez)

Image Formation

• Geometry– image plane– projection

• Physics of light– Brightness / Illumination– Light source– Lambertian

• scattered such that the apparent brightness of the surface to an observer is the same regardless of the observer's angle of view (wiki)

nikonweb.com

Lighting

http://www.cs.umd.edu/~djacobs/CMSC828/Lighting.pdf

Early Vision

• Early year of computer vision– David Marr (Psychologist, MIT)– Azriel Rosenfeld (Mathematician, Maryland)– Takeo Kanade (Engineer, CMU)

• Visual path– How early?– Recognition?– Saliency / gist

scienceblogs.com

http://i.neoseeker.com/mgv/436139-Triforce%20of%20Wisdom/139/15/lizard_display.jpg

Illusion

• Aperture problem• http://www.cfar.umd.edu/~fer/optical/move

ment2.html• http://www.michaelbach.de/ot/

Skeletonization

http://www.inf.u-szeged.hu/~palagyi/skel/skel.html

Template Matching

• Find transformation to align two images• cost function• Example: Chamfer Matching

• Example 2: Hough transform• Example 3: Probabilistic voting

http://www.gavrila.net/Research/Chamfer_System/chamfer_system.html

Deformable

• Shape matching– Shape Context

• Snake– Active Contour, Active Appearance

• Articulated objects– Scissor– Human body

Face Recognition

• Linear subspaces– PCA and LDA– Eigenfaces vs Fisherfaces

http://www.cs.umd.edu/~djacobs/CMSC828/LinearSubspacesGeometry.pdf

Q/A

• Introduction• Image Formation• Early vision• Cognition in psychology• Face recognition (I)