Texture_ Contours and Regions Cu by fjwuxn


									Human vision

 Jitendra Malik
 U.C. Berkeley
Cerebral Cortex
Monocular Visual Field: 160 deg (w) X 175 deg (h)
Binocular Visual Field: 200 deg (w) X 135 deg (h)
Cones and Rods
Receptor density vs eccentricity
Processing in the retina
ON and OFF cells in retinal ganglia
Visual Processing Areas
    The visual system performs
• Measurement of light and spatial relations
• Perceptual Organization
• Active interaction with environment
Measurement of light and spatial relations

• Measuring light
  – Sensitivity over high dynamic range
  – Gain control results in ―Weber Machine‖
  – Sensitivity to contrast rather than absolute
    luminance level—discounting the illuminant
• Measuring Spatial relations
  – Contrast sensitivity function
  – Vernier Acuity
Threshold vs. Intensity
        Weber Contrast Cw = ΔL/L
Michelson Contrast CM = (Lmax – Lmin)/2 Lmean
Why contrast is the right variable..
Simultaneous Contrast
Mach Band
A Mach Band in 1D profile
Contrast Sensitivity Function at different luminances
Receptor density vs eccentricity
CSF as function of eccentricity
Cortical Magnification Factor
Mapping from Retina to V1
Physiological Optics 1840-1894
The Empiricist-Nativist debate
              The debate..
      (and sometimes both were right !)
• Helmholtz argued that perception is
  unconscious inference. Associations are
  earned through experience.
• Hering proposed physiological
  mechanisms—opponent color channels,
  contrast mechanisms, conjunctive and
  sisjunctive eye movements..
      The Twentieth Century..
• The Gestalt movement emphasized
  perceptual organization.
  – Grouping
  – Figure/ground
  – Configuration effects on perception of
    brightness and lightness
Grouping factors
Grouping Factors
The Figure-Ground Problem
Wallach’s Brightness ratios
Gibson’s ecological optics (1950)
• Emphasized richness of information about
  shape and surface layout available to a
  moving observer
  – Optical flow
  – Texture Gradients
  – ( and the classical cues such as stereopsis etc)
Measuring Surface Orientation
Depth of field of human eye
Convergence angle vs. distance
Binocular Stereopsis
Optical flow for a pilot
Some Pictorial Cues
Cast Shadows
Geometry of cast shadows

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