Need for Matching 
viewgraphs.fm—4 
Nevatia - 12 
8/4^95 
• For inference of 3-D from multiple views 
• For registering a model to an image 
• For Object Recognition 
• Problems: 
• To find the right features (descriptions) to match 
• Low level features 
• easier to extract but ambiguous, and not invariant 
• Higher level features 
• more reliable but difficult to compute 
• Suggested by Gestalt Psychologists (~ 1920s) 
Identified grouping properties such as 
• continuation 
• closure 
• symmetry 
but did not provide a computational definition. 
• Requirements for Grouping 
• Properties for Grouping 
• Selection among competing properties 
• Efficiency and generality of the process 
viewgraphs.fm—3 
8/4/95 
Perceptual Grouping