Chapter 27 Color
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Transcript of Chapter 27 Color
Apr 22, 2023 Physics 1 (Garcia) SJSU
Chapter 27Color
Apr 22, 2023 Physics 1 (Garcia) SJSU
Spectrum of Visible Light
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Wavelengths & Photons
Red Photon
Blue Photon
Green Photon
Yellow Photon
PrismSpectrum
Particles of light, called photons, each have a wavelength.
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Newton’s Color WheelPrism spectrum is a straight line, so why did Isaac Newton describe color using a circular wheel?
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Additive Color Wheel
SpectralColors
Not in the spectrum. How do we see these?
R
Y
B G
M
C
RedYellowGreenCyanBlueMagenta
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Adding Colored Lights
Stream ofred & green photons looks same as yellow photons(metamerism)
Theatrical lighting
or
YELLOW
Eye toBrain
Notice overlap of red, green, & blue is seen as whitewhite light
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Demo: Seeing YellowSodium lamps emit yellow photons
Color monitor can only emit red, green, and blue (RGB); creates other colors by selectively turning RGB pixels on or off.
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Trichromatic Theorists
Thomas Young (1773-1829) English physicist
Hermann von Helmholtz (1821-1894)German physicist
James Clerk Maxwell(1831-1879)Scottish physicist
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Simple Trichromatic TheoryYellow &
Redphotons
excite me
Yellow, Green &
Cyanphotons
excite me
Cyan &Blue
photons excite me
Inside your eye there are three receptors
MOECURLY
LARRY
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Trichromatic: Seeing YellowYellow &
Redphotons
excite me. I’M
EXCITED
Yellow, Green &Cyan photons
excite me.I’M EXCITED
Cyan & Bluephotons excite
me.Yawn.
Yellow seen when Curly and Larry excited, either by yellow photons or red & green photons.
MOE
CURLYCURLY
LARRY
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Trichromatic: Seeing MagentaYellow &
Redphotons
excite me. I’M
EXCITED
Yellow, Green &Cyan photons
excite me.Yawn.
Cyan & Bluephotons excite me.
I’M EXCITED
Magenta is seen by eye when Moe and Larry excited, which no single type of photon can achieve.
MOE
CURLYCURLY
LARRY
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Demo: Maxwell Color DiskDisk painted half red, half blue looks
magenta when rapidly spinning.
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Mixing Blue & Red Paint
Mixing paint or ink is different from adding colors together by light.
Mix of blue and red paint produces a blackish brown
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Trichromatic: Seeing WhiteWhiteYellow &
Redphotons
excite me. I’M
EXCITED
Yellow, Green &Cyan photons
excite me.I’M EXCITED
Cyan & Bluephotons excite me.
I’M EXCITED
White seen when all three very excitedGray seen when all three less excited
MOE
CURLYCURLY
LARRY
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Trichromatic: Color BlindnessRed , Yellow,
Green &Cyan photons
excite me.I’M EXCITED
Cyan & Bluephotons excite me.
Yawn.
MOE
CURLYCURLY
LARRY
Color blindness occurs if the eye is missing one of the three receptors. Other receptors try to compensate but cannot distinguish some colors.
Do I see red or green?
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Color Blindness
ClassificationIncidence (%)
Males FemalesAnomalous
Trichromacy 6.3 0.37
Protanomaly(Red-cone weak) 1.3 0.02
Deuteranomaly(Green-cone weak) 5.0 0.35
Tritanomaly(Blue-cone weak) 0.0001 0.0001
Dichromacy 2.4 0.03 Protanopia
(Red-cone absent) 1.3 0.02
Deuteranopia(Green-cone absent) 1.2 0.01
Tritanopia(Blue-cone absent) 0.001 0.03
Rod Monochromacy(no cones) 0.00001 0.00001
29 or 70? 21 or 74?
Weakness or absence of one of the three types of cones is the cause of color blindness, leading to a reduced ability to distinguish colors.
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Trichromatic: After-Image
First stare at RED
I’M EXCITED!Yawn.
Yawn.
MOECURLYCURLY LARRY
Me too, but tired.
ME TOO!
I’M EXCITED!
MOECURLYCURLY LARRY
Then stare at WHITE
Moe and Curly are excited so what color is seen?CYAN (light blue-green)
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Negative After-image
Stare, unfocused, at the red cross for 10 seconds then look at white wall
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Negative After-image
Cyan
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Negative After-image
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Negative After-image
Cyan Magenta Yellow
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Simple Additive Color WheelLARRY
MOE CURLY
Newton’s color wheel is a simple formulation of trichromatic theory.White
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Color Vision in the Eye
Three types of cones (color)One type of rod (B/W only)
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CIE Hue-Saturation Diagram
Eye is not a perfectoptical instrument.
Color “wheel” isactually distortedcone shape.
Rim is full saturation,center is white
LARRY %
CU
RLY
%
50% Larry50% Curly0% Moe
33% Larry33% Curly33% Moe
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Spectral Reflectance Curves
When white light shines on an object, some photons absorbed, others reflected by the object’s surface.
White Red
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Name That Color
White Red Dark Brown(Burnt Sienna)
BLUE GREEN RED
0%
100% BLUE GREEN RED BLUE GREEN RED
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Name That Color
Bluish Green Bright Yellow Blue(Cobalt)
BLUE GREEN RED
0%
100% BLUE GREEN RED BLUE GREEN RED
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Subtractive Color
Absorbing filters or absorbing pigments remove colors from white light.
Check Yourself:Yellow = Red + GreenCyan = Blue + GreenYellow & Cyan filters (or pigments)combine to give … Overlapping color filters
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Check Yourself
A soap film absorbs red, green, or blue light, depending on the film’s thickness.
What colors do we see where red is removed?
Where green is removed?
Where blue is removed?
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Four Color Printing
Magenta Yellow Cyan Black
Magenta+ Yellow+ Cyan
All Four
Green balloon printed with mix of yellow and cyan inks
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Check Yourself
Magenta Yellow Cyan Black
Which inks are mixed for the bright red balloon and dark red dress?