1Ch. 9 - Color• Spectral and non-spectral colors• Intensity distribution curve• Intensity, hue, saturation• Additive primaries: R, G. B.• Subtractive primaries: C, M, Y• Hair, skin, and eye color• CIE diagram• Lighting, painting and printingWe are here2PaintPaints: consist of pigment particles in a liquid vehicle.The vehicle may dry to a glossy or matte finish.The vehicle may be clear or it may contain dye.Dye is colored at the molecular level, no solid particles. Pigment flakes may be partially transparent and work by selective absorption or they may be opaque and work by selective reflection. The size of the particle makes a difference, with smaller particles transmitting more and absorbing less.Paints appear different (often brighter) when wet because a wet surface is glossy.More about paints and dyes• Pigments (usually solid mineral particles)– earths (red ochre)– chemical (cadmium yellow)• Dyes (usually in a liquid solvent, no solid particles)– Vegetable: indigo (a plant) “Levi’s”– Animal: cochineal (boiled insects), Tyrian purple (snails)• Synthetic organics• “Lakes,” dyed translucent particles used as pigments• Oil (a vehiclefor pigment, often linseed oil)• Tempera (a vehicle for pigment)– Egg yolk is used with pigment mixed in. – Advantage: stickiness! Water-based.• Watercolors: finely ground pigment in water and gum Arabic binder• Fresco: watercolor on fresh plaster34Surfaces, glossy and mattePhotographs can have a glossy or matte finish and so can house paint. Paint can also be semi-gloss (looks “frosted”).Glossy surfaces are smooth and part of the light is reflected specularly(like from a mirror) and part is reflected diffusely. Glossy surfaces look brighter. Wet surfaces tend to be glossy, so all paints are glossy when they go on and may become matte as they dry.5Blue sky and red sunsetblue is scattered in every directionlooks blue from herelooksred fromhereShort wavelength light is scattered more by atoms. 6Blue sky and red sunsetair air airNoon sunSetting sunWhen the sun is setting, you are looking through the most air and have lostthe most blue.Chapter 10: Color perceptionLec. 19,Tuesday, March 16• Trichromacy• Metamers• Psychological primaries• Channels • Color deficiency• Animal vision• Temporal processing7We are hereTrichromacy• You have 3 kinds of color receptors (cones)• Wavelengths: Short Intermediate Long8Fig. 10.3 in textbook. We know this because we can find the wavelengths absorbed by the cones.Metamers (again)• Yellow (600) looks like red (650) + green (550)• No mixturewill look like blue or red. 9Why blue+yellow looks white10S+I+L stimulated is the same stimulation as from white lightHow colors are perceived• Blue excites S receptors• Cyan excites S + I• Green excites I mostly• Yellow excites I + L• Orange excites I + L• Red excites L11Sensitivity of cones12http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=rgcbChapter 10: Color perception• Trichromacy• Metamers• Psychological primaries• Channels • Color deficiency• Animal vision• Temporal processing13We are herePsychological primariesWhat is the minimum number of colors you need to describe any color verbally?Answer:Blue Green Yellow Red Yellow cannot be described as reddish green. 14Psychological opponentsThey are:red – green yellow – blue We cannot imagine these being added. There is no bluish yellow or reddish green. 15ChannelsReceptors are wired into three channels. 1. Yellow minus blue (y-b)2. Red minus green (r-g)3. White minus black (w-bk)16Channel wiring details17Example: red and green both turn up the yellow – blue channelChannels and the CIE diagramVisual color channel are “top minus bottom” and “left minus right.”18Color constancyYour visual perception system corrects for changes in lighting (red sunset, for example) so that colors remain relatively constant. If the light is red, the visual system adds green. If the light is yellow, it adds blue. 1920The blue tile is gray. The yellow tile is gray.21Are these colors the same?Lateral inhibition works for color channels.Signal processingSimultaneous color contrast Lateral inhibition applied to r-g or y-b channels.Example:22Simultaneous color contrast (again)23Lateral inhibition (again)24What color is the wide line?Lateral inhibition (again)25Compare to simultaneous lightness contrast26Chapter 10: Color perception• Trichromacy• Metamers• Psychological primaries• Channels • Color deficiency• Animal vision• Temporal processing27We are hereColor deficiency(not color blindness)Several kinds of color vision problems:• Wavelength of one kind of cone is shifted• One type of cone missing (S, I or L)• Channel wiring is incorrect (r-g, y-b)28Some texts say S,M,L not S,I,L.Color vision anomalies29XX5%1%1%1%http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=rgcb&rendertype=figure&id=rgcb.F2Names for color deficiencies• Trichromats ("three colors"): persons with one of the color channels shifted slightly from the usual band of wavelengths. • Dichromats("two colors"): persons missing one type of cone or one of the two color channels (r-g or y-b). • Deuteranomalous:A kind of trichromat. About 5% of males. I channel is incorrect in wavelength nearer to red. Missing cone types: • Protanope:a person lacking an "L" (red) type cone. About 1% of males.• Deuteranope:a person lacking an "I" (green) type cone. About 1% of males.• Tritanope: a person lacking “S” (blue) cones30Color deficiency test (may not reproduce here with the correct colors)31Ishihara’s printed test is “official”32Color deficiency test (may not reproduce here with the correct colors)33Color deficiency test (may not reproduce here with the correct colors)Colblindor.com has the Farnsworth test, which is nicer in many ways.Why are males more likely to be color deficient?• 8% of males and 0.5% of females have deficiency. • Women have twox chromosomes, men one. • In women, vision is ok if either oneis good. • In men, if the x is bad, that’s bad.34Chapter 10: Color perception• Trichromacy• Metamers• Psychological primaries• Channels • Color deficiency• Animal vision• Temporal processing35We are hereAnimal visionDetermined by survival needs predator/prey relation, predators: eyes in front (hawks, lions)prey: eyes on the side (cows, frogs)mate finding