COLOR VISION Stephen E Palmer 2002 COLOR VISION

COLOR VISION © Stephen E. Palmer, 2002

COLOR VISION “The Color Story” is a prototype for Cognitive Science Contributions from: Physics (Newton) Philosophy (Locke) Art (Munsell) Psychophysics (Maxwell) Physiology (De Valois) Cognitive Psychology (Rosch) Neurology (Zeki) Linguistics (Lakoff) Cognitive Anthropology (Berlin & Kay) Computer Science (Zadeh) © Stephen E. Palmer, 2002

COLOR VISION “The Color Story” is a prototype for Cognitive Science Contributions from: * Berkeley faculty Physics (Newton) Philosophy (Locke) Art (Munsell) Psychophysics (Maxwell) Physiology (De Valois) Cognitive Psychology (Rosch) Neurology (Zeki) Linguistics (Lakoff) Cognitive Anthropology (Berlin & Kay) Computer Science (Zadeh) © Stephen E. Palmer, 2002

The Physics of Light: Electromagnetic energy whose wavelength is between 400 nm and 700 nm. (1 nm = 10 -6 meter) © Stephen E. Palmer, 2002

The Physics of Light Some examples of the spectra of light sources © Stephen E. Palmer, 2002

The Physics of Light % Photons Reflected Some examples of the reflectance spectra of surfaces Red 400 Yellow 700 400 Blue 700 400 Wavelength (nm) Purple 700 400 700 © Stephen E. Palmer, 2002

The Psychophysical Correspondence There is no simple functional description for the perceived color of all lights under all viewing conditions, but …. . . A helpful constraint: Consider only physical spectra with normal distributions mean area variance © Stephen E. Palmer, 2002

The Psychophysical Correspondence Hue # Photons Mean Wavelength © Stephen E. Palmer, 2002

The Psychophysical Correspondence Saturation # Photons Variance Wavelength © Stephen E. Palmer, 2002

The Psychophysical Correspondence Brightness # Photons Area Wavelength © Stephen E. Palmer, 2002

Physiology of Color Vision Two types of light-sensitive receptors Cones cone-shaped less sensitive operate in high light color vision Rods rod-shaped highly sensitive operate at night gray-scale vision © Stephen E. Palmer, 2002

The Microscopic View

Rods and Cones in the Retina http: //www. iit. edu/~npr/Dr. Jennifer/visual/retina. html

What Rods and Cones Detect Notice how they aren’t distributed evenly, and the rod is more sensitive to shorter wavelengths

• Center / Surround Strong activation in center, inhibition on surround • The effect you get using these center / surround cells is enhanced edges top: the stimuli itself middle: brightness of the stimuli bottom: response of the retina • You’ll see this idea get used in http: //www-psych. stanford. edu/~lera/psych 115 s/notes/lecture 3/figures 1. html Regier’s model

How They Fire • No stimuli: – both fire at base rate • Stimuli in center: – ON-center-OFF-surround fires rapidly – OFF-center-ON-surround doesn’t fire • Stimuli in surround: – OFF-center-ON-surround fires rapidly – ON-center-OFF-surround doesn’t fire • Stimuli in both regions: – both fire slowly

Theories of Color Vision Two main algorithmic theories of color vision: Trichromatic Theory (Palmer/Young/Helmholtz) Hermann von Helmholtz Opponent Process Theory (Hering) Ewald Hering © Stephen E. Palmer, 2002

Physiology of Color Vision Three kinds of cones: Absorption spectra Opponent Processes: R/G = L-M G/R = M-L B/Y = S-(M+L) Y/B = (M+L)-S Implementation of Trichromatic theory © Stephen E. Palmer, 2002

Physiology of Color Vision Opponent-Process Cells in LGN (De Valois) Implementation of opponent process theory (Similar color behavior in retinal ganglion cells) © Stephen E. Palmer, 2002

Physiology of Color Vision Double Opponent Cells in V 1 G + R- Y+ B- R+ G - B+ Y- G + R- Y+ B- Red/Green Blue/Yellow © Stephen E. Palmer, 2002

Color Blindness Not everybody perceives colors in the same way! What numbers do you see in these displays? © Stephen E. Palmer, 2002

Color Blindness There are several forms of inherited variations of color vision. Trichromatic (“normal”) color vision Dichromatic color vision 2 forms of red-green color blindness 1 form of yellow-blue color blindness Monochromatic color vision 4 forms Various forms of “color weakness” © Stephen E. Palmer, 2002

Color Blindness What does the world look like to a color blind person? Normal Trichromat Protanope Deuteranope Tritanope © Stephen E. Palmer, 2002

Theories of Color Vision Opponent Process theory (Hering): All colors are combinations of responses in three underlying bipolar systems (Red/Green, Blue/Yellow, Black/White). © Stephen E. Palmer, 2002

Theories of Color Vision Dual Process Theory (Hurvich & Jameson): The color vision system contains two stages: an initial trichromatic stage and a later opponent-process stage. Trichromatic stage Opponent. Process stage Dual Process Theory © Stephen E. Palmer, 2002

Theories of Color Vision A Dual Process Wiring Diagram Trichromatic Stage Opponent Process Stage © Stephen E. Palmer, 2002

COLOR VISION: Part 4 1. Color Constancy: Surface-based processing 2. Color Naming: Category-based processing © Stephen E. Palmer, 2002

Color Constancy: the ability to perceive the invariant color of a surface despite ecological Variations in the conditions of observation. Another inverse problem: Physics of light emission and surface reflection underdetermine perception of surface color © Stephen E. Palmer, 2002

Color Constancy Iw Lw Rw © Stephen E. Palmer, 2002

Color Constancy © Stephen E. Palmer, 2002

Color Constancy Two approaches to lightness constancy Unconscious Inference (Helmholtz) Luminance = Intensity * Reflectance If you know L and I, you can solve for R! Invariant Relations (Hering) Luminance ratios are invariant with illumination © Stephen E. Palmer, 2002

Color Constancy Luminance ratio is invariant over illumination: Luminance Ratio = 9: 1 © Stephen E. Palmer, 2002

Color Constancy The anchoring problem: What about absolute lightness? How do we know what is white? (How big is the anchor? ? ? ) © Stephen E. Palmer, 2002

Anchoring heuristic: The lightest region is taken as white

Color Naming Basic Color Terms (Berlin & Kay) Criteria: 1. Single words -- not “light-blue” or “blue-green” 2. Frequently used -- not “mauve” or “cyan” 3. Refer primarily to colors -- not “lime” or “gold” 4. Apply to any object -- not “roan” or “blond” © Stephen E. Palmer, 2002

Color Naming BCTs in English Red Green Blue Yellow Black White Gray Brown Purple Orange* Pink © Stephen E. Palmer, 2002

Color Naming Five more BCTs in a study of 98 languages Light-Blue Warm Cool Light-Warm Dark-Cool © Stephen E. Palmer, 2002

The WCS Color Chips • Basic color terms: – – Single word (not blue-green) Frequently used (not mauve) Refers primarily to colors (not lime) Applies to any object (not blonde) FYI: English has 11 basic color terms

Results of Kay’s Color Study Stage I II IIIa / IIIb IV V VI VII W or R or Y W W W Bk or G or Bu R or Y R R Bk or G or Bu Y Y Bk G or Bu G G G Bk Bu Bu Bu Bk Bk Bk Y+Bk (Brown) W R Y R+W (Pink) Bk or G or Bu R + Bu (Purple) R+Y (Orange) B+W (Grey) If you group languages into the number of basic color terms they have, as the number of color terms increases, additional terms specify focal colors

Color Naming Typical “developmental” sequence of BCTs © Stephen E. Palmer, 2002

Color Naming (Berlin & Kay) Studied color categories in two ways Boundaries Best examples © Stephen E. Palmer, 2002

Color Naming (Rosch) MEMORY : Focal colors are remembered better than nonfocal colors. LEARNING: New color categories centered on focal colors are learned faster. Categorization: Focal colors are categorized more quickly than nonfocal colors. © Stephen E. Palmer, 2002

Color Naming A fuzzy logical model of color naming (Kay & Mc Daniel) Fuzzy set theory (Zadeh) Degree of Membership © Stephen E. Palmer, 2002

Color Naming “Primary” color categories © Stephen E. Palmer, 2002

Color Naming “Primary” color categories Red Green Blue Yellow Black White © Stephen E. Palmer, 2002

Color Naming “Derived” color categories Fuzzy logical “ANDf” © Stephen E. Palmer, 2002

Color Naming “Derived” color categories Orange = Red ANDf Yellow Purple = Red ANDf Blue Gray = Black ANDf White Pink = Red ANDf White Brown = Yellow ANDf Black (Goluboi = Blue ANDf White) © Stephen E. Palmer, 2002

Color Naming “Composite” color categories Fuzzy logical “ORf” Warm = Red Orf Yellow Cool = Blue Orf Green Light-warm = White Orf Warm Dark-cool = Black Orf Cool © Stephen E. Palmer, 2002

Color Naming © Stephen E. Palmer, 2002