slide 1 john redman, ti physicist, imaging and color expert: color only exists in our minds, i.e.,...
TRANSCRIPT
Slide 1
John Redman, TI physicist, imaging and color expert:
Color only exists in our minds, i.e., it is strictly a perceptual attribute.
Newton stated that color depends on “imagination and fantasy and invention.”
Response per intensity unit
Vector nature of color:
“Spectral” (rainbow) colors are those perceived from light of narrow band of w, . l
Color is determined by the relative stimuli to three cone cells. [Sr, Sg, Sb].
Orange “color”: [Sr, Sg, Sb] =
Your eye perceives this color for narrow-band 600 nm light.
Vector nature of color:
Infinite number of other spectra give the “orange” stimulus ratios. Which approx combination of 550 nm and 650 nm light intensities will give the same as 600 nm pure light? 550 to 650 ______
a) 1:1 b) 1:2 c) 2: 1 d) 1:6 e) 6: 1
Vector nature of color:
Explain why brown e.g. [4, 2, 1] can’t be in the rainbow
Can you come up with a stimulus ratio [Sr, Sg, Sb] that isn’t a color (no
combination of light can make this ratio in our eyes)? e.g [0, 1, 0].
Slide 6
COLOR SYSTEMS
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B G R C M Y
Additive: dashed linesSubtractive: solid lines
Additive coloring :
(light emission, screens, projection)Can create any color by superimposing three primary colors with varying intensities.
Requirements for primary spectral colors?
The human eye can distinguish between about 10 million colors.
How many colors are there in this color model?
What is white in this RGB model?
gray?
black?
2563=224 =108
One color system (HSV)Hue: basic “color”: from differences in R, G, BValue (brightness) based on contextSaturation: degree differences stand out above “white”
Hue: YellowYellow, fully saturated: (R,G,B) = Yellow, less saturated (pastel): (R,G,B) = Yellow, less bright: (R,G,B) =
Play online
Rayleigh scattering occurs when particle size << l(air molecules)This scattering is most efficient at ________ frequencies or _________ wavelengths!
4_ 4
1dipole radiationI
Blue sky
Scattering of E/M waves by a polarizable sphere vs freq
Rayleigh scattering
Mie scattering
Resonant Mie scattering
d = d = 10
Mie scattering:Why do so many things look white?
Salt
When any non absorbing material (glass, water, salt) is broken into pieces of size >l they scatter all wavelengths equally,
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/colviscon.html#c1
Subtractive coloring
uses dyes, inks, and pigments to absorb some wavelengths of light and not others.
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C M Y
Subtractive coloring
paint: white-scattering spheres (TiO2) mixed with absorbing pigments
colored paper, and fabric: white-scattering fibers coated with absorbing dyes.
“Reflection” vs transmission, scattering:
You write with red ink on white paper, and now the paper looks red. This is because the red ink itself is good at a) scattering red lightb) transmitting red lightc) reflecting red light
For a physicist, “reflection” is “specular” at a smooth interface between two materials. “Scattering” is what puts rays out at random angles from small objects.
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“Reflection” vs transmission, scattering:
From , and where n and k vary most, at what colors do we expect the surface of a smooth pool of red ink to reflect well?
a) colors transmitted by red inkb) colors absorbed by red ink
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A yellow piece of paper “scatters” yellow light. The yellow ink transmits yellow light (absorbing reds and blues), and the white paper base scatters white light. The paper does not “reflect” yellow light.
From an optics point of view, what’s the biggest difference between what’s inside the two red plastics?
Irridenscence in nature
http://www.webexhibits.org/causesofcolor/15A.html
Interference/diffraction (“structural”) colors in nature: iridescence
http://www.webexhibits.org/causesofcolor/15A.html
Nocturnal animalshave layer of cells behind retina with multilayer mirrors that reflect unabsorbed light back through it!
Cameleonhttp://www.youtube.com/watch?v=7Yxq_G05cHU
Change colors for camouflage,
mood1. Outer layer: cells that can concentrate red or yellow pigment in center (cells almost clear), or spread them over cell (colored)
2. Middle layer: sacks of photonic crystal plates, reflecting blue
3. Inner layer: cells that can concentrate melanin (black) in center (cells almost clear), or spread them over cell (black)
Only 1 and 3 controlled by nerves?