Computational%20Vision

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Computational Vision

• Jitendra Malik
• University of California, Berkeley

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What is in an image?
The input is just an array of brightness values
humans perceive structure in it.
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From Pixels to Perception
outdoor wildlife
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If visual processing was purely feedforward(it
isnt)
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Boundaries of image regions defined by a number
of attributes

• Brightness/color
• Texture
• Motion
• Binocular disparity
• Familiar configuration

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Grouping is hierarchical
Perceptual organization forms a tree
Image
BG
L-bird
R-bird
bush
far
grass
beak
body
beak
body
head
eye
eye
head
Two segmentations are consistent when they can
be explained by the same segmentation tree

• A,C are refinements of B
• A,C are mutual refinements
• A,B,C represent the same percept

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Humans assign a depth ordering to surfaces across
a contour

• R1 appears in front of R2
• R2 appears in front of R3

This can be done for images of natural scenes
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Figure-Ground Labeling

• - red is near blue is far

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Figure/Ground Organization

• A contour belongs to one of the two (but not
  both) abutting regions.

Important for the perception of shape
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Some other aspects of perceptual organization
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What do we see here?
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And here?
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Some Pictorial Cues
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Support, Size
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Cast Shadows
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Shading
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Measuring Surface Orientation
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Binocular Stereopsis
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Optical flow for a pilot
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Object Category Recognition
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Shape variation within a category

• DArcy Thompson On Growth and Form, 1917
• studied transformations between shapes of
  organisms

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Attneaves Cat (1954)Line drawings convey most
of the information
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Objects are in Scenes
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Human stick figure from single image
Input image
Stick figure
Support masks
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This is hard

• Variety of poses
• Clothing
• Missing parts
• Small support for parts
• Background clutter

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Taxonomy and Partonomy

• Taxonomy E.g. Cats are in the order Felidae
  which in turn is in the class Mammalia
• Recognition can be at multiple levels of
  categorization, or be identification at the level
  of specific individuals , as in faces.
• Partonomy Objects have parts, they have
  subparts and so on. The human body contains the
  head, which in turn contains the eyes.
• These notions apply equally well to scenes and to
  activities.
• Psychologists have argued that there is a
  basic-level at which categorization is fastest
  (Eleanor Rosch et al).
• In a partonomy each level contributes useful
  information for recognition.

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Visual Control of Action

• Locomotion
• Navigation/Way-finding
• Obstacle Avoidance
• Manipulation
• Grasping
• Pick and Place
• Tool use

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Camera Obscura(Reinerus Gemma-Frisius, 1544)
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Camera Obscura(Angelo Sala, 1576-1637)
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