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An in-depth exploration of various theories related to visual perception, focusing on color perception. Topics include Trichromatic Theory, its limitations, and the Opponent Process Theory proposed by Hering. Additionally, the document discusses Color Constancy, a phenomenon where surfaces appear to have consistent color despite varying illumination conditions.
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Slide 1 ICS 280: Visual Perception
^ Complementary after imagesComplementary after images Red and green complementsRed and green complements (^) Blue and yellow complementsBlue and yellow complements
Simultaneous Color ContrastSimultaneous Color Contrast
Visualizing colorsVisualizing colors
Slide 3 ICS 280: Visual Perception
^ Patterns onPatterns on rightright
^ GanzfeldGanzfeld (^) Experiment withExperiment with ping pong ballping pong ball
Slide 7 ICS 280: Visual Perception
Prolonged exposure to redProlonged exposure to red ^ RR^ ++^ GG^ - -^ cells fire less stronglycells fire less strongly GG ++^ RR - -^ cells fire more stronglycells fire more strongly
^ Red looks less saturatedRed looks less saturated
^ Green looks more saturatedGreen looks more saturated
^ Other colors seem to have a greenish tintOther colors seem to have a greenish tint
Slide 9 ICS 280: Visual Perception
^ Prolonged exposure to greenProlonged exposure to green GG ++^ RR - -^ is fatiguedis fatigued
When try to view whiteWhen try to view white (^) RR ++^ GG - -^ cells fire more and hence red afterimagecells fire more and hence red afterimage
Similar for blue/yellowSimilar for blue/yellow
Still Cannot explain simultaneous contrastStill Cannot explain simultaneous contrast
Double opponentDouble opponent cells in visualcells in visual cortexcortex
^ Similar logic asSimilar logic as lateral inhibitionlateral inhibition
Slide 13 ICS 280: Visual Perception
^ Multiplication ofMultiplication of Illumination spectrumIllumination spectrum (^) Reflectance spectrumReflectance spectrum
Together give the spectrum that we seeTogether give the spectrum that we see
No inherent difference in theirNo inherent difference in their representationrepresentation
How can we separate what is due toHow can we separate what is due to illumination and what is due to reflectance?illumination and what is due to reflectance?
^ Same surface have different spectrum ofSame surface have different spectrum of reflected light depending on thereflected light depending on the illumination spectrumillumination spectrum A white paper appears white in sunlightA white paper appears white in sunlight and also under a reading lightand also under a reading light
^ Called color constancyCalled color constancy (^) Lightness constancyLightness constancy ^ Chromatic constancyChromatic constancy
Slide 15 ICS 280: Visual Perception
An achromatic surface appears to have sameAn achromatic surface appears to have same lightness irrespective of different illuminationlightness irrespective of different illumination conditionsconditions ^ Indoor illumination: 100 photonsIndoor illumination: 100 photons Black: 10 photonsBlack: 10 photons (^) White: 90 photonsWhite: 90 photons Outdoor Illumination: 10,000 photonsOutdoor Illumination: 10,000 photons Black: 1000 photonsBlack: 1000 photons ^ WhiieWhiie: 9000 photons: 9000 photons Black in outdoor is almost 900 times more thanBlack in outdoor is almost 900 times more than white in indoorwhite in indoor ^ Still it is perceived as blackStill it is perceived as black
Visual system adaptsVisual system adapts ^ More sensitive to dim lightMore sensitive to dim light Less sensitive to bright lightLess sensitive to bright light
^ Illumination is thus factored out by aIllumination is thus factored out by a average adaptation of the eyeaverage adaptation of the eye
Slide 19 ICS 280: Visual Perception
^ Cannot be determined directly from theCannot be determined directly from the imageimage
(^) FindingFindingR(R(λλ) is just a division)is just a division
Left out all detailsLeft out all details
Proposed by HelmholtzProposed byHelmholtz
^ Can be directly determined from the imageCan be directly determined from the image Due to surface reflectanceDue to surface reflectance (^) Absolute amount of light from neighboring regionsAbsolute amount of light from neighboring regions changechangedrasticallydrastically But, relative amount of light from neighboringBut, relative amount of light from neighboring regions remain the sameregions remain the same Perceived lightness depends on the relativePerceived lightness depends on the relative contrastcontrast Wallach propsesWallachpropses that luminance ratios arethat luminance ratios are importantimportant Two pair of projector experiment confirms thisTwo pair of projector experiment confirms this
Slide 21 ICS 280: Visual Perception
^ How to calculate suchHow to calculate such luminance ratios?luminance ratios? (^) Local luminance ratiosLocal luminance ratios atatedges matteredgesmatter
How does these ratios at edges getsHow does these ratios at edges gets integrated over the image?integrated over the image?
Assumes illumination does not show anyAssumes illumination does not show any discontinuitydiscontinuity Multiplication of the contrast ratios at theMultiplication of the contrast ratios at the edgesedges
Slide 25 ICS 280: Visual Perception
^ However, this theory fails if there is anHowever, this theory fails if there is an illumination edgeillumination edge (^) Basis of the theory is edge is reflectance edgeBasis of the theory is edge is reflectance edge
Identifying edges as illumination orIdentifying edges as illumination or reflectance edge is importantreflectance edge is important ^ Experiments with same edge created by bothExperiments with same edge created by both shadow and reflectance and its effect on theshadow and reflectance and its effect on the perceived luminance of an objectperceived luminance of an object
The solutionThe solution ^ Illumination MapIllumination Map Reflectance MapReflectance Map
^ They are multiplied to get the imageThey are multiplied to get the image
^ Somehow we need to find these two mapsSomehow we need to find these two maps
Slide 27 ICS 280: Visual Perception
^ FuzzinessFuzziness Illumination edges are often not sharpIllumination edges are often not sharp Only point light sources create sharp edgesOnly point light sources create sharp edges (^) But real lights are extended and hence penumbraBut real lights are extended and hence penumbra Reflectance edge is usually sharpReflectance edge is usually sharp PlanarityPlanarity ^ Depth information separates out non coplanar regionDepth information separates out non coplanar region Perceived as illumination edgePerceived as illumination edge More information than just present in an imageMore information than just present in an image
^ Magnitude ratiosMagnitude ratios (^) Reflectance edge can be at most 10:1Reflectance edge can be at most 10: However, illumination edge can be as large asHowever, illumination edge can be as large as 1000:11000: ^ Color produces additional informationColor produces additional information ^ Reflectance edge produces edge in both hueReflectance edge produces edge in both hue and saturationand saturation Illumination edge produces edge only inIllumination edge produces edge only in luminanceluminance
Slide 31 ICS 280: Visual Perception
^ Similar experience with colorSimilar experience with color Red does not cease to be red in differentRed does not cease to be red in different lighting conditionslighting conditions
^ More constraints due to colorMore constraints due to color Restricted ReflectanceRestricted Reflectance
Models proposed based on theseModels proposed based on these retrictionsretrictions
