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White Fuzzy Color Oblong Texture Shape

Most problems in vision are underconstrained White Color Most problems in vision are underconstrained

The goal of computational vision: To identify and formalize the strategies and assumptions the visual system uses to overcome under-constrainedness.

The goal of computational vision: To identify and formalize the strategies and assumptions the visual system uses to overcome under-constrainedness. David Marr

Processing Framework Proposed by Marr Recognition 3D structure; motion characteristics; surface properties Shape From stereo Motion flow Shape From motion Color estimation Shape From contour Shape From shading Shape From texture Edge extraction Emphasis on ‘Bottom-up’ processing Image

My research interests Image Recognition Edge extraction TANGENT ALERT! Mechanisms of recognition ‘Top-down’ Influences on perception Shape From stereo Motion flow Shape From motion Color estimation Shape From contour Shape From shading Shape From texture Edge extraction Image

The importance of edges Depth discontinuity (Object border) Orientation change (Object shape) Reflectance change (Object property)

What is an edge? - a point at which image luminance (I) changes steeply - a point at which the first derivative of I has a peak

Detecting edges Grid of numbers Denoting edge Strength at each Point in image Edge map Thresholding Convolution (dot-products all over the image) Edge operator 1 Image Network implementation of convolution

What is an edge? - a point at which image luminance (I) changes steeply - a point at which the first derivative of I has a peak - a point at which the second derivative of I has a zero crossing

Second order differential operators Image A B C D First differences (A-B) (B-C) (C-D) Second differences (A-2B+C) (B-2C+D) Why would we want to use second order Operators rather than first order ones?

Second order differential operators Image A B C D First differences (A-B) (B-C) (C-D) Second differences (A-2B+C) (B-2C+D) Zero crossings can Be detected with Circularly symmetric Filters! (orientation Independence)

The link between models of edge detection and physiology

Detecting edges at different scales

The scale integration problem

The scale integration problem Witkin, 1983

Detecting illusory contours Where do conventional edge-detectors fail? Detecting illusory contours No luminance difference across long sections of the perceived contours