Texture_ Contours and Regions Cu by fjwuxn

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									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
Craik-O’Brien-Cornsweet
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
Transparency
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
Accomodation
Depth of field of human eye
Convergence
Convergence angle vs. distance
Binocular Stereopsis
Optical flow for a pilot
Some Pictorial Cues
Shading
Cast Shadows
Geometry of cast shadows

								
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