1. Color Mixing Additive vs. Subtractive
There are two different ways to mix colors.

2. Color Mixing Additive vs. Subtractive
What do you get if you use a prism to combine all wavelengths of light?

3. Color Mixing White Additive vs. Subtractive
What do you get if you use a prism to combine all wavelengths of light?
White

4. Color Mixing Additive vs. Subtractive
What do you get if you mix a bunch of paint?

5. Color Mixing Black Additive vs. Subtractive
What do you get if you mix a bunch of paint?
Black

6. Color Mixing
Additive vs. Subtractive
WHY?

7. red+green+blue=white
Color Mixing
Additive mixing is most intuitive:
ADD wavelengths:
red+green = yellow
red+blue = magenta
blue+green = cyan
red+green+blue=white

8. Exploring Additive Mixing
use color sliders to adjust R,G,B values

9. Color Mixing
What color can only exist as a metamer (an additive mixture of wavelengths)? In other words, what color cannot be made with a single wavelength?

10. Color Mixing
What color can only exist as a metamer (an additive mixture of wavelengths)? In other words, what color cannot be made with a single wavelength?
Magenta
Think about why!

11. Color Mixing
Subtractive mixing is much less intuitive (but much more common)
Subtractive mixing happens when we mix pigments (paint) together
Different pigments subtract different wavelengths:
red subtracts all but red, blue all but blue, green subtracts blue and red, etc…

12. Color Mixing Example: blue + yellow = green
Technically it’s called “cyan”

13. Color Mixing
The result of a mixture depends on what wavelengths don’t get absorbed by the two pigments
Amount of filtering
green
yellow
red
blue
wavelength

14. Color Mixing Both yellow and blue pigments reflect a bit of green
Amount of filtering
green
yellow
red
blue
wavelength

15. Color Mixing
Subtractive mixing is commonly used in color printers

16. Exploring Subtractive Mixing
use color sliders to adjust C, M, Y values

17. Color is an illusion
Everything you’ve learned so far is wrong.

18. Color is an illusion Everything you’ve learned so far is wrong.
Well, not really wrong, just far from complete.

19. Everthing you thought you knew
L A N D
Everthing you thought you knew
about color is wrong...

20. Everthing you thought you knew
L A N D
Everthing you thought you knew
about color is wrong...

21. What is color for?
What is color vision used for?

22. What is color for? What is color vision used for?
Identification - what is this thing?
Discrimination - what other things is this like?
Communication - indicates this thing to others

23. What is color for?
What is color vision used for?
Identification - what is this thing?
Discrimination - what other things is this like?
Communication - indicates this thing to others
But in each case color refers not to the illuminating light, but to the surface of the object itself

24. What is color for?
What is color vision used for?
Identification - what is this thing?
Discrimination - what other things is this like?
Communication - indicates this thing to others
But in each case color refers not to the illuminating light, but to the surface of the object itself
Does the color of an object remain constant under different lighting conditions?

25. What Newton Found (and everyone believed)
White light can be split into all wavelengths by a prism

26. What Newton Found (and everyone believed)
White light can be split into all wavelengths by a prism
According to previous theories: two wavelengths combine to yield intermediate color and no others
Red Light
Green Light
Red + Green = YELLOW

27. What twist did Land do to this paradigm that confounds the conventional understanding of color mixing?

28. What Land found:
Two bands (colors) of the spectrum recombine to produce all the possible colors
provided the appropriate relative amount of each wavelength is projected
Red Light
Green Light
transparency slides

29. How did Land project the “appropriate” ratio of wavelengths?

30. Short- and Long- “record”
Camera
Capture two grey-scale images of the scene using filters that allow only the wavelengths you will project
“Long” filter
Object
“short” filter
film
Projector
Image
“Long” filter
“short” filter

31. What is Land’s interpretation? How do we perceive color?

32. Land’s interpretation:
perception of color is a weighing of the ratio of shorter and longer wavelengths

33. Land’s interpretation:
perception of color is a weighing of the ratio of shorter and longer wavelengths

34. Why would the visual system have this design?

35. Why would the visual system have this design?
Hint: “Within broad limits, the actual values of the wavelengths make no difference, nor does the over-all available brightness of each”

36. Color Constancy
The “color” of objects is independent of the ambient light
yellow bananas and green leaves look yellow and green regardless of whether they are viewed in direct sunlight or by the light of a fire

37. Color Constancy Land Mondrian:
demonstration of color constancy: all the wavelengths of the colored squares are shifted by the same amount into the blue end of the spectrum - your brain ignores the shift

38. Color Constancy Tricky question:
why does a window look blue from the outside when there’s a TV going inside?

39. Color Constancy Tricky question:
why does a window look blue from the outside when there’s a TV going inside?
The wavelengths emitted by a TV are mostly in the blue end of the spectrum

40. Color Constancy Really Tricky question: why doesn’t a TV look blue?
Color Constancy causes you to perceive the areas of the screen with the greatest proportion of long wavelengths as “red”, the greatest proportion of short wavelengths as “blue” and everything else in between.

41. Next Time
ATTENTION!