1. Straightness, structure, and shadows. VSS 2001 Edward Adelson David Somers MIT

2. Illusions can inform us about the operation of the lightness system. Same gray

3. To see cool lightness demos (& paper): go to http://www-bcs.mit.edu/gaz or www.tedadelson.org

4. 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?

5. Example 1: folding the plaid adds junctions, 3D cues. Illusion is enhanced Illusion is slightly reduced + + + Alternately look at +

6. Example 2: blur the bars to give penumbra Illusion is enhanced Illusion is slightly reduced + + +

7. 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 + + +

8. Amplitude of wiggles Big wiggles: Big effect. Small wiggles: Smaller effect but still there. + + ++

9. Rough texture works + +

10. Combine cues to build strong illusions. Articulation, biased statistics Smooth gradients Straightness of contour

11. Ripple strip

12. Snake cylinder

13. 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 see www.tedadelson.org

14. 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.) + +

15. Effect of texture

16. Misalignment: do psi junctions matter?

17. Pinstripes

18. Wiggle styles

19. Lightness illusions For papers and demos see www-bcs.mit.edu/people/adelson

20. 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

21. 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?)

22. The basic intuition for using the plaid discounting decreases illusion discounting increases illusion If horizontal strip is transparentIf vertical strip is transparent

23. The basic intuition for using the plaid discounting decreases illusion discounting increases illusion If horizontal strip is transparentIf vertical strip is transparent

25. Frequency of wiggles 1 w/cycle 16 w/cycle It works for a wide range of frequencies.