Depth Perception

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Depth Perception 3D Vision

• Reza Rajimehr

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3-D Perception Inferential leap from image to
environment
Inverse Problem depth ambiguity
No inverse problem with 3-D retina
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Reducing the problem
Perceiving distance

• Depth
• Surface orientation Slant and Tilt

Perceiving 3-D objects
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Surface layout recovering orientation at a
distance
Visible surfaces
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Theoretical Frameworks

• For solving the inverse problem

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Ecological optics

• Active exploration of the environment (ecology)
• Information available in the optic flow is
  sufficient for the perception (direct
  perception) no need for internal representations
• Adding temporal dimension to the 2-D optic array
  (dynamic optic array) could solve the inverse
  problem

Information theory and computer vision
J.J. Gibson
Texture gradient
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But it is insufficient to solve the problem
uniquely!
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Heuristic assumptions
Veridical perception vs. Perceptual illusions
Helmholtz
Probabilistic view of perception
Leading to unique interpretation
Solving the inverse problem
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Computational approaches to ecological optics
Marrs 2.5-D sketch
David Marr
X Modules
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Sources of depth information -Depth cues

• Ocular information / Optical information
• Binocular information / Monocular information
• Static information / Dynamic information
• Absolute information / Relative information
• Quantitative information / Qualitative information

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Sources of depth information -Depth cues

• Ocular information
• Stereoscopic information
• Dynamic information
• Pictorial information

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Accommodation

• Ocular/Monocular/Static/Absolute/Quantitative
• Visual system should have access to the
  information about the tension of the muscles
• Useful for close distances
• Accommodation is derived by image blur so that
  the output of high spatial frequency channels is
  maximized
• The best depth cue in the African chameleon

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Convergence

• Ocular/Binocular/Static/Absolute/Quantitative
• Useful for close distances
• Convergence and accommodation are not independent

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Stereoscopic information
Finger Experiment

• Optical/Binocular/Static/Relative/Quantitative
• Binocular disparity

Direction of disparity Crossed disparity
close Uncrossed disparity far Magnitude of
disparity How much closer or farther
Effective within 30 meters
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Stereoscopic informationThe Horopter
Also fixation point has zero disparity.
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Stereoscopic information
Diplopia (doubleness)
Repeat finger experiment
Stereoblindness in Strabismus also in children
with cataract in one eye
Panums fusional area
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Stereograms
Crossed convergence method Uncrossed convergence
method
Seeing stereograms with Stereoscope
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The correspondence problem
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Random Dot Stereograms
Bela Julesz
However there may well be some primitive shape
analysis before stereopsis.
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How to construct RDS
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Computational Algorithms for solving the
correspondence problem
e.g. Marr-Poggio 1977
taking heuristic constraints into account (e.g.
surface opacity and surface continuity)
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Autostereograms
Christopher Tyler
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Autostereograms
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Autostereograms
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Vertical Disparity
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Da Vinci Stereopsis
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Physiological mechanisms of binocular disparity
Recording from V2

• V1 Responds to zero or near-zero disparity
• V2 Responds to large disparities
• (Hubel Wiesel Barlow Blakemore)
• Recently V3A V4 and MT

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Disparity selectivity in area MT
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fMRI of Stereopsis
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Binocular Rivalry
Red/Green filter glasses
Convergence method
Mirror devices
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Dynamic Information
Old depth cues in evolution

• Motion Parallax

Objects closer to you travel at faster speeds and
in the opposite direction further objects travel
slower and in the same direction.
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Dynamic Information

• Optic flow (optic expansion)

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Dynamic Information

• Kinetic depth effect (KDE)

Rigidity heuristic
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Pictorial Information

• Linear perspective

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Pictorial Information

• Horizon

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Pictorial Information

• Relative size

• Familiar size
• absolute depth cue

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Pictorial Information

• Texture gradients
• systematic changes in the shape and size of
  texture elements

Notice to the background ofs!
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Pictorial Information

• Partial occlusion or interposition

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Junctions
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Pictorial Information

• Shading

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Pictorial Information

• Cast shadows

Perceiving the height of objects
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Pictorial Information
Non-homogeneous textures 2004
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Integration/Interaction of different depth cues
Pseudoscope
Cue conflict between disparity and monocular
depth cues
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• Main Reference
• Vision Science Palmer (Chap 5)