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Straightness, structure, and shadows.
VSS 2001
Edward Adelson
David Somers
MIT
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Illusions can inform us about the operation of the lightness system.
Same gray Same gray
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To see cool lightness demos (& paper):go to http://www-bcs.mit.edu/gaz
or
www.tedadelson.org
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The snake illusion
Diamonds are same gray.Illusion is enhanced
Same diamonds, same backgrounds
Illusion is slightly reduced
Same diamonds, same backgrounds
What about this reduction? Do wiggles interfere with discounting?
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Example 1: folding the plaid adds junctions, 3D cues.
Illusion is enhanced
Illusion is slightly reduced
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Example 2: blur the bars to give penumbra
Illusion is enhanced
Illusion is slightly reduced
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Crooked strips enhance or reduce illusion
Proposal: crooked vs. straight is a cue for the discounting process in lightness perception, just like penumbra or junctions.
Enhanced
Reduced
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Amplitude of wiggles
Big wiggles:Big effect.
Small wiggles:Smaller effectbut still there.
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Rough texture works
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Combine cues to build strong illusions.
• Articulation, biased statistics
• Smooth gradients
• Straightness of contour
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Ripple strip
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Snake cylinder
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Summary
• Straightness & structure influence lightness illusions.
• Visual system may take structure as a cue to distinguish reflectance from illumination (atmosphere).
• I.e., visual system may “believe” that shadows are soft and straight, paint is crisp and crooked.
• There’s life left in plaids.
For related paper and demos seewww.tedadelson.org
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Checkerboard works, too.
(Note that the checkerboard strips can be seen as transparent, but the illusion behaves as if the plain strips, not the checkerboards, were transparent.)
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Effect of texture
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Misalignment: do psi junctions matter?
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Pinstripes
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Wiggle styles
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Lightness illusions
For papers and demos see
www-bcs.mit.edu/people/adelson
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More to try• Dark vs light articulation
• Artic in dark areas vs light areas
• Scission connection
• Add overall backgrnd texture
• Amplitude of sine
• Combine blur & straight, measure tradeoff
• Color
• Stereo
• Motion
• Figure ground
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Observations and inferences
Experimental observation: Straightness of contour effects strength of illusions. Big effects.
Possible interpretation: The lightness system “assumes” that shadows/transparency/atmospheres tend to be straight, whereas reflectance/paint tends to be crooked.
(Another observation: the illusion strength effects are not always predicted by subjective transparency & scission).
(Another question: how to rephrase in terms of groups and frameworks?)
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The basic intuition for using the plaid
discounting decreases illusion
discounting increases illusion
If horizontal strip is transparent If vertical strip is transparent
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The basic intuition for using the plaid
discounting decreases illusion
discounting increases illusion
If horizontal strip is transparent If vertical strip is transparent
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Frequency of wiggles
1 w/cycle
16 w/cycle
It works for a wide range of frequencies.