Additive vs' Subtractive

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Color Mixing

• Additive vs. Subtractive

There are two different ways to mix colors.
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Color Mixing

• Additive vs. Subtractive

What do you get if you use a prism to combine all
wavelengths of light?
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Color Mixing

• Additive vs. Subtractive

What do you get if you use a prism to combine all
wavelengths of light?
White
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Color Mixing

• Additive vs. Subtractive

What do you get if you mix a bunch of paint?
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Color Mixing

• Additive vs. Subtractive

What do you get if you mix a bunch of paint?
Black
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Color Mixing

• Additive vs. Subtractive

WHY?
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Color Mixing

• Additive mixing is most intuitive

ADD wavelengths redgreen yellow redblue
magenta bluegreen cyan redgreenbluewhite
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Exploring Additive Mixing

• use color sliders to adjust R,G,B values

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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?

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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!
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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

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Color Mixing

• Example blue yellow green

Technically its called cyan
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Color Mixing

• The result of a mixture depends on what
  wavelengths dont get absorbed by the two pigments

Amount of filtering
green
yellow
red
blue
wavelength
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Color Mixing

• Both yellow and blue pigments reflect a bit of
  green

Amount of filtering
green
yellow
red
blue
wavelength
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Color Mixing

• Subtractive mixing is commonly used in color
  printers

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Exploring Subtractive Mixing

• use color sliders to adjust C, M, Y values

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Color is an illusion

• Everything youve learned so far is wrong.

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Color is an illusion

• Everything youve learned so far is wrong.
• Well, not really wrong, just far from complete.

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L A N D
Everthing you thought you knew about color is
wrong...
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L A N D
Everthing you thought you knew about color is
wrong...
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What is color for?

• What is color vision used for?

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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

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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

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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?
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What Newton Found (and everyone believed)

• White light can be split into all wavelengths by
  a prism

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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
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What twist did Land do to this paradigm that
confounds the conventional understanding of color
mixing?
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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
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How did Land project the appropriate ratio of
wavelengths?
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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
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What is Lands interpretation? How do we
perceive color?
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Lands interpretation

• perception of color is a weighing of the ratio of
  shorter and longer wavelengths

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Lands interpretation

• perception of color is a weighing of the ratio of
  shorter and longer wavelengths

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Why would the visual system have this design?
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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

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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

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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

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Color Constancy

• Tricky question
• why does a window look blue from the outside when
  theres a TV going inside?

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Color Constancy

• Tricky question
• why does a window look blue from the outside when
  theres a TV going inside?
• The wavelengths emitted by a TV are mostly in the
  blue end of the spectrum

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Color Constancy

• Really Tricky question
• why doesnt 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.

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Next Time

• ATTENTION!