Transcript Depth Perception - School of Cognitive Sciences

Depth Perception & 3D Vision
Reza Rajimehr
3-D Perception: Inferential leap
from image to environment
Inverse Problem: depth ambiguity
No inverse problem with 3-D retina
Reducing the problem
Perceiving distance
Depth
Perceiving 3-D objects
Surface orientation:
Slant and Tilt
Surface layout: recovering orientation at a distance
Visible surfaces
Theoretical Frameworks
For solving the inverse problem
Ecological optics
Active exploration of the environment
(ecology)
Information theory and computer vision
Information available in the optic flow is
sufficient for the perception (direct perception),
no need for internal representations
J.J. Gibson
Adding temporal dimension to the 2-D optic
array (dynamic optic array) could solve the
inverse problem
Texture gradient
But it is insufficient to solve
the problem uniquely!
Heuristic assumptions
Veridical perception vs. Perceptual illusions
Helmholtz
Probabilistic view of perception
Leading to unique interpretation
Solving the inverse problem
Computational approaches to
ecological optics
Marr’s 2.5-D sketch
David Marr
X Modules
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
Sources of depth information Depth cues
Ocular information
Stereoscopic information
Dynamic information
Pictorial information
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
Convergence
Ocular/Binocular/Static/Absolute/
Quantitative
Useful for close distances
Convergence and accommodation
are not independent
Stereoscopic information
Optical/Binocular/Static/Relative/Q
uantitative
Finger Experiment
Binocular disparity
Direction of disparity:
Crossed disparity: close
Uncrossed disparity: far
Magnitude of disparity:
How much closer or farther
Effective within 30 meters
Stereoscopic information
The Horopter
Also fixation point has zero disparity.
Stereoscopic information
Diplopia (doubleness)
Repeat finger experiment
Stereoblindness in Strabismus,
also in children with cataract in one eye
Panum’s fusional area
Stereograms
Crossed convergence method
Seeing stereograms with Stereoscope
Uncrossed convergence method
The correspondence problem
Random Dot Stereograms
Bela Julesz
However, there may well be some primitive shape analysis before stereopsis.
How to construct RDS?
Computational Algorithms for solving
the correspondence problem
e.g. Marr-Poggio, 1977
taking heuristic constraints into account (e.g. surface opacity and surface continuity)
Autostereograms
Christopher Tyler
Autostereograms
Autostereograms
Vertical Disparity
Da Vinci Stereopsis
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
Disparity selectivity in area MT
fMRI of Stereopsis
Binocular Rivalry
Red/Green filter glasses
Convergence method
Mirror devices
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.
Dynamic Information
Optic flow (optic expansion)
Dynamic Information
Kinetic depth effect
(KDE)
Rigidity heuristic
Pictorial Information
Linear perspective
Pictorial Information
Horizon
Pictorial Information
Relative size
Familiar size:
absolute depth cue
Pictorial Information
Texture gradients
systematic changes in the shape
and size of texture elements
Notice to the background of slides!
Pictorial Information
Partial occlusion or interposition
Junctions
Pictorial Information
Shading
Pictorial Information
Cast shadows
Perceiving the height of objects
Pictorial Information
Non-homogeneous textures, 2004
Integration/Interaction of different
depth cues
Pseudoscope
Cue conflict between disparity and monocular depth cues
Main Reference:
Vision Science Palmer (Chap 5)