Observers measured the Color Constancy

of 3 papers

matched in 27 different spectral illuminants

3 Papers                               27 Illuminants

This experiment used 27 different spectral illuminants.

  • Mixtures of 625, 530, 455 nm narrowband LEDs

  • 3 colored papers on a white background

  • Observers matched to Munsell Book

  • Plot matches in L*a*b* Color Space

RESULTS

Discount Illumination                   Edge Ratios          

Predictions                            Predictions  

Compare Color Constnacy mechanisms:

  • Chromatic Adaptation - Discount Illumination

      • Predicts cloud of 27 different matches (left)

  • Build scene from Reflectance Edge Ratios (right)  

       • Predicts line of matches for chromatic papers

       • Predicts spot of matches for achromatic papers

Matches support Edge Ratio mechanism:

Predicted Edges Ratios fit Matches

Obsever Matches in L*a*b* space of 3 papers in 27 spectral illuminants

Video of predicted Matches in L*a*b* based on

edge ratios of cone responses

Predictions respond to Crosstalk between L, M, S cone quanta catches

Orange and violet predictions form linear shapes,

and grays form a small spot

Achromatic papers have constant preictions

Do Humans “Discount the Illuminant”?

J. J. McCann, Proc. SPIE Vol. 5666, 9-16, 2005.

Proc. SPIE Vol. 5666

Mechanism of Color Constancy

J. J. McCann,  Proc. IS&T Color Imaging Conference, Scottsdale, Arizona, 12, 29-36, 2004 2004c CIC12.pdf

The shape of 3-D plots of observed color matches is the signatue of Color Constancy's mechanism

   •  27 illuminants forms clouds of matches in L*a*b* space

       •  Chromatic Adaption predictions maintain the chromatl shifts caused by illumination (I)

             • All three paper reflectances (R) behave the same - All papers form a 3-D grid

           •  Shifted by changes in illuminations

      •  Edge Ratio predictions use ratios of spectral integrated cone responses [R * I]

              •  Achromatic reflectance predictions are a single spot ( Cone Crosstalks cancel )

              •  Chromatic reflectance predictions forms lines in  L*a*b*

            •  L*a*b* Signature of Color Constancy Matches predicted by Cone Crosstalk

      •  Edge Ratio predictions fit Observer matches

Video of predicted Matches in L*a*b* based on CIECAM incomplete adaptation

Predictions respond to shifts in illumination

Orange, violet, gray predictions form identical 3-D cloud shapes

All paper's respond solely to shifts in illumination

Observe matched orange and violet papers to form linear shapes,

and grays form a small spot

Cone Crosstalk, not the spectra of illumination,

models the small departures from percect Color Constancy

with changes in illumination spectra