CS 559: Computer VisionLecture 1Prof. Sinisa [email protected]•Gestalt laws for grouping2Perceptual Grouping -- Gestalt Laws•Similarity•Proximity•Closure•Good continuation•Common fate•Figure-ground•Symmetry•PeriodicityGestalt laws are summaries of image properties imposed by the constraints of real world3Gestalt Laws -- Similarity•We tend to group objects with similar properties (color, shape, texture)•Because objects of the same kind are made of the same matter, and same matter often yields same image propertiesSource: N. Ahuja4Gestalt Laws -- Proximity•We tend to group nearby objects•Because matter is cohesive resulting in meaningful configurations of nearby objectsSource: N. Ahuja5Gestalt Laws -- Closure•We tend to ignore gaps and hallucinate complete, closed contours•Because objects occupy finite 3D volumes, and thus have closed surfaces, and so their image projections occupy regions with closed boundariesSource: N. Ahuja6Gestalt Laws -- Good Continuation•We prefer to see configurations forming smooth contours•Because objects have locally smooth surfaces, and a smooth surface projects in image as a smooth boundary contourSource: N. Ahuja7Gestalt Laws -- Common Fate•We tend to see distinct objects with same motion as a unit •Because a moving object may consist of parts whose motions depend on the objectʼs motion, and thus project in image coherentlySource: N. Ahuja8Gestalt Laws -- Figure-Ground•We tend to see certain image areas as foreground or figure and the remaining areas as background or ground •Because our knowledge is in terms of distinct objectsSource: N. Ahuja9Gestalt Laws -- Symmetry•We tend to see symmetric objects as figure against asymmetric background •Because many man-made and natural objects are symmetric due to functionality/growth/reproduction processes, and image formation usually preserves symmetrySource: N. Ahuja10Gestalt Laws -- Periodicity•We prefer to see objects that periodically repeat •Because many man-made and natural objects are spatially periodic due to functionality/growth/reproduction processes, and image formation usually preserves periodicitySource: N. Ahuja11Gestalt Laws -- Periodicity•We prefer to see objects that periodically repeat •Because many man-made and natural objects are spatially periodic due to functionality/growth/reproduction processes, and image formation usually preserves periodicitySource: N. AhujaM. sinense bacteria12Which Gestalt Laws Do We Use Here?What Gestalt law should we apply first?Different orderings of the Gestalt laws 󲰛 Different groupings13From Low-Level Immediately to High-Level ReasoningT-junctions 󲰛 Occlusion14From Low-Level Immediately to High-Level ReasoningT-junctions 󲰛 Occlusion14From Low-Level Immediately to High-Level ReasoningT-junctions 󲰛 Occlusion15From Low-Level Immediately to High-Level ReasoningT-junctions 󲰛 Occlusion15From Low-Level Immediately to High-Level ReasoningT-junctions 󲰛 Occlusion15Top-down Interpretation from Context•Context and feedback from higher levels resolve low-level ambiguities•Because of the context we may not be even aware of alternativesSource: N. Ahuja16Top-down Interpretation from Context•Context and feedback from higher levels resolve low-level ambiguities•Because of the context we may not be even aware of alternativesSource: N. Ahuja16Top-down Interpretation from Context•Context and feedback from higher levels resolve low-level ambiguities•Because of the context we may not be even aware of alternativesSource: N. Ahuja16Top-down Interpretation from Context•Context and feedback from higher levels resolve low-level ambiguities•Because of the context we may not be even aware of alternativesSource: N. Ahuja16Top-down Interpretation from Context•Context and feedback from higher levels resolve low-level ambiguities•Because of the context we may not be even aware of alternativesSource: N.