yan karklin. cns lunch - 02/16/05

Specular Reflections and the Perception of Shape

Roland W. Fleming, Antonio Torralba, Edward H. Adelson

Journal of Vision (2004)

yan karklin. cns lunch - 02/16/05

observation: we are able to recover some depth using only specular reflections

problem:how is this accomplished?

no “traditional” cues available

- motion

- disparity

- texture

- lambertian shading

yan karklin. cns lunch - 02/16/05

can we really recover depth from specularities?

-3 objects

- patch w/spec reflections

- subjects try to guess original object in 3 expts:

Savarese, Li, Perona (2004): No, they’re “only a very weak cue.”

yan karklin. cns lunch - 02/16/05

can we really recover depth from specularities?

- stimuli: irregular, smooth, w/boundaries

- subjects adjust randomly initialized normals to perceived orientation

Fleming, et al (2003, 2004): Yes, and “reliably and quite acccurately.”

yan karklin. cns lunch - 02/16/05

what information is available?

yan karklin. cns lunch - 02/16/05

what information is available?

...and we don’t rely on boundaries

yan karklin. cns lunch - 02/16/05

what information is available?

a relationship between curvature and reflection compression

yan karklin. cns lunch - 02/16/05

we have to make some assumptions

• about the object

• about the surroundings

texture compression can be computed quickly (though roughly) with filters

• using steerable pyramid

• 24 filter orientations at each location

• 1 scale – very local

yan karklin. cns lunch - 02/16/05

texture compression can be computed quickly (though roughly) with filters

• using steerable pyramid

• 24 filter orientations at each location

• 1 scale – very local

yan karklin. cns lunch - 02/16/05

stable across different scenes

yan karklin. cns lunch - 02/16/05

stable across different scenes

yan karklin. cns lunch - 02/16/05

correspondence between truth and guesswork

yan karklin. cns lunch - 02/16/05

how realistic are the stimuli?

- smoothness

- limited world scenes

- specularity only

yan karklin. cns lunch - 02/16/05

orientation fields for shaded/specular objects can be consistent

yan karklin. cns lunch - 02/16/05

...or very inconsistent

yan karklin. cns lunch - 02/16/05

so how do we disambiguate the two?

yan karklin. cns lunch - 02/16/05

discussion

• claims

• simple, quick computations can give some information about depth

• evaluation

• subjects can perceive shape from specularity alone

• orientation field and its anisotropy correlate with curvature

• this is stable across scenes and varies shape-to-shape

• reflection-induced orientation fields are [consistent/inconsistent] with texture and shading

• implication

• fast, biologically relevant computation

• real world settings require parallel processing of shading/reflection

• what’s missing

• priors on objects, world, inference, separation of reflection