How we perceive the reflectance of a visual object depends on the assumptions our visual system makes about the illumination of the object (as indicated e.g. by shadows falling onto the object) and on the actual luminance of the object (the amount of light emitted by the object).
(define observed-luminance 3.0)
(define samples
(mh-query
1000 10
(define reflectance (gaussian 1 1))
(define illumination (gaussian 3 0.5))
(define luminance (* reflectance illumination))
reflectance
(= luminance (gaussian observed-luminance 0.1))))
(multiviz "Mean reflectance: " (mean samples)
(hist samples "Reflectance"))
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