1. Chapter 27 Color
29-Apr-18
Physics 1 (Garcia) SJSU

2. Spectrum of Visible Light
29-Apr-18
Physics 1 (Garcia) SJSU

3. Wavelengths & Photons
Particles of light, called photons, each have a wavelength.
Red Photon
Yellow Photon
Green Photon
Blue Photon
Prism
Spectrum
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Physics 1 (Garcia) SJSU

4. Newton’s Color Wheel
Prism spectrum is a straight line, so why did Isaac Newton describe color using a circular wheel?
29-Apr-18
Physics 1 (Garcia) SJSU

5. Not in the spectrum. How do we see these?
Additive Color Wheel
Not in the spectrum. How do we see these?
Spectral
Colors R M Y
Red
Yellow
Green
Cyan
Blue
Magenta B G C
29-Apr-18
Physics 1 (Garcia) SJSU

6. Adding Colored Lights Stream of red & green photons looks same as
yellow photons
(metamerism)
YELLOW
Eye to
Brain or
Notice overlap of red, green, & blue is seen as white light
Theatrical lighting
29-Apr-18
Physics 1 (Garcia) SJSU

7. Demo: Seeing Yellow Sodium 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.
29-Apr-18
Physics 1 (Garcia) SJSU

8. Trichromatic Theorists
Thomas Young
( )
English physicist
Hermann von Helmholtz
( )
German physicist
James Clerk Maxwell
( )
Scottish physicist
29-Apr-18
Physics 1 (Garcia) SJSU

9. Simple Trichromatic Theory
Yellow, Green &
Cyan
photons excite me
Yellow &
Red
photons excite me
Cyan &
Blue
photons excite me
MOE
LARRY
CURLY
Inside your eye there are three receptors
29-Apr-18
Physics 1 (Garcia) SJSU

10. Trichromatic: Seeing Yellow
Yellow, Green &
Cyan photons excite me.
I’M EXCITED
Yellow &
Red
photons excite me. I’M EXCITED
Cyan & Blue
photons excite me.
Yawn.
CURLY
MOE
LARRY
Yellow seen when Curly and Larry excited, either by yellow photons or red & green photons.
29-Apr-18
Physics 1 (Garcia) SJSU

11. Trichromatic: Seeing Magenta
Yellow &
Red
photons excite me. I’M EXCITED
Cyan & Blue
photons excite me.
I’M EXCITED
Yellow, Green &
Cyan photons excite me.
Yawn.
CURLY
MOE
LARRY
Magenta is seen by eye when Moe and Larry excited, which no single type of photon can achieve.
29-Apr-18
Physics 1 (Garcia) SJSU

12. Demo: Maxwell Color Disk
Disk painted half red, half blue looks magenta when rapidly spinning.
29-Apr-18
Physics 1 (Garcia) SJSU

13. 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
29-Apr-18
Physics 1 (Garcia) SJSU

14. Trichromatic: Seeing White
Yellow &
Red
photons excite me. I’M EXCITED
Cyan & Blue
photons excite me.
I’M EXCITED
Yellow, Green &
Cyan photons excite me.
I’M EXCITED
CURLY
MOE
LARRY
White seen when all three very excited
Gray seen when all three less excited
29-Apr-18
Physics 1 (Garcia) SJSU

15. Trichromatic: Color Blindness
Red , Yellow, Green &
Cyan photons excite me.
I’M EXCITED
Cyan & Blue
photons excite me.
Yawn.
Color blindness occurs if the eye is missing one of the three receptors. Other receptors try to compensate but cannot distinguish some colors.
CURLY
MOE
LARRY
Do I see red or green?
29-Apr-18
Physics 1 (Garcia) SJSU

16. Color Blindness
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.
Classification
Incidence (%)
Males
Females
Anomalous 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
Dichromacy
2.4
0.03
Protanopia (Red-cone absent)
Deuteranopia (Green-cone absent)
1.2
0.01
Tritanopia (Blue-cone absent)
0.001
Rod Monochromacy (no cones)
29 or 70?
21 or 74?
29-Apr-18
Physics 1 (Garcia) SJSU

17. Trichromatic: After-Image
First stare at RED
I’M EXCITED!
Yawn.
MOE
CURLY
LARRY
Me too, but tired.
ME TOO!
I’M EXCITED!
MOE
CURLY
LARRY
Then stare at WHITE
Moe and Curly are excited so what color is seen?
CYAN (light blue-green)
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Physics 1 (Garcia) SJSU

18. Negative After-image
Stare, unfocused, at the red cross for 10 seconds then look at white wall
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Physics 1 (Garcia) SJSU

19. Negative After-image
Cyan
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Physics 1 (Garcia) SJSU

20. Negative After-image
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Physics 1 (Garcia) SJSU

21. Negative After-image Cyan Magenta Yellow 29-Apr-18
Physics 1 (Garcia) SJSU

22. Simple Additive Color Wheel
LARRY
Newton’s color wheel is a simple formulation of trichromatic theory.
White
CURLY
MOE
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Physics 1 (Garcia) SJSU

23. Color Vision in the Eye Three types of cones (color)
One type of rod (B/W only)
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Physics 1 (Garcia) SJSU

24. CIE Hue-Saturation Diagram
Eye is not a perfect
optical instrument.
Color “wheel” is
actually distorted
cone shape.
Rim is full saturation,
center is white
CURLY %
50% Larry
50% Curly
0% Moe
33% Larry
33% Curly
33% Moe
29-Apr-18
Physics 1 (Garcia) SJSU
LARRY %

25. Spectral Reflectance Curves
White
Red
                                                      
When white light shines on an object, some photons absorbed, others reflected by the object’s surface.
29-Apr-18
Physics 1 (Garcia) SJSU

26. Name That Color Dark Brown White Red (Burnt Sienna) 100% 0% 29-Apr-18
BLUE GREEN RED 0%
100%
BLUE GREEN RED
BLUE GREEN RED
Dark Brown
(Burnt Sienna)
White
Red
29-Apr-18
Physics 1 (Garcia) SJSU

27. Name That Color Bluish Green Bright Yellow Blue (Cobalt) 100% 0%
BLUE GREEN RED 0%
100%
BLUE GREEN RED
BLUE GREEN RED
Bluish Green
Bright Yellow
Blue
(Cobalt)
29-Apr-18
Physics 1 (Garcia) SJSU

28. Subtractive Color
Absorbing filters or absorbing pigments remove colors from white light.
Check Yourself:
Yellow = Red + Green
Cyan = Blue + Green
Yellow & Cyan filters (or pigments)
combine to give …
Overlapping color filters
29-Apr-18
Physics 1 (Garcia) SJSU

29. 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?
29-Apr-18
Physics 1 (Garcia) SJSU

30. Four Color Printing Magenta Yellow Cyan Black Magenta + Yellow + Cyan
Green balloon printed with mix of yellow and cyan inks
Magenta
+ Yellow
+ Cyan
All Four
29-Apr-18
Physics 1 (Garcia) SJSU

31. Check Yourself
Which inks are mixed for the bright red balloon and dark red dress?
Magenta
Yellow
Cyan
Black
29-Apr-18
Physics 1 (Garcia) SJSU