The eyes have three different kinds of color receptors; One kind is most sensitive to short wavelengths, one to middle wavelengths, and one to long wavelengths

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Vision The Eye

• The eyes have three different kinds of color
  receptors One kind is most sensitive to short
  wavelengths, one to middle wavelengths, and one
  to long wavelengths

2
Color Mixing
There are two ways to control how much red,
green, and blue light reaches the eye
Additive Mixing Starting with black, the
right amount of red, green, and blue light are
added to an image. Subtractive Mixing
Starting with white, the right amount of red,
green, and blue light are subtracted from an
image.
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Additive Color Mixing
By exciting the red, green, and blue sensitive
cones, any color can be produced by adding
together the three additive primaries (R,G,B).

• Mixing the three color sources is known as
  additive mixing to distinguish it from mixing
  paints or dyes (subtractive mixing).

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Additive Color Mixing
For example, when blue and green lights overlap,
the blue and green cones are illuminated, and we
perceive cyan
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Additive Color Mixing
green blue cyan

• red blue magenta

red green blue white
red green yellow
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Additive Color Mixing
red green/2 orange
red green yellow
red/2 green lime
red green blue white
red green blue gray
red green blue gray
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Additive Color Reproduction

• Color video projectors use additive color mixing
• Projected red, green, and blue images contribute
  RGB components to create color images

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Spatial Mixing (Video Monitor)

• Because the visual system has limited spatial
  resolution, small areas of different colors are
  mixed perceptually.

Spatial addressability of typical monitors goes
from (640 x 480) to (1600 x 1280) pixels.
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Temporal Mixing (Digital Cinema)

• Because the visual system has limited temporal
  resolution, rapidly changing colors are mixed
  perceptually.

time
time
time
10
Subtractive Color Mixing

• Color hardcopy devices cant use additive mixing
  because they arent sources of light they cant
  add Red, Green, or Blue components.

Instead, they use subtractive mixing. Starting
with white light reflected by the substrate, they
subtract the unwanted red, green, and blue
components using cyan, magenta, and yellow
colorants.
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Subtractive Color Mixing

• The goal is the same to control the amount of
  Red, Green, and Blue light getting to the eyes
  three cone types
• Each colorant absorbs 1/3 and transmits 2/3 of
  white light

white substrate
cyan colorantminus red
magenta colorantminus green
yellow colorantminus blue
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Subtractive Color Mixing

• Other colors are made by varying the amount of
  colorant in each layer.

yellow magenta red
yellow magenta
yellow magenta/2 orange
cyan black
13
Subtractive Color Reproduction

• Color printing uses subtractive color mixing.
• Adding black allows more accurate grays, and
  conserves the more expensive CMY colorants.