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BeWise Colorful Life 3-24-07

VIEWS: 7 PAGES: 69

									It’s A Colorful Life
        Dr. Larry Woolf
     Larry.Woolf@ga.com
      www.sci-ed-ga.org
       General Atomics
      Presented 3/24/07 to
       BEWiSE students



                             1
             Why study color?
• Color is multidisciplinary and interdisciplinary –
  involving physics, chemistry, biology, technology,
  engineering, mathematics
• Color mixing is the basis for much color display
  technology
• A wide variety of models and methods are used, so
  it provides an interesting educational experience
• Color is colorful!
• Most books are inconsistent/incorrect – don’t trust
  everything you read! Provides interesting lesson in
  “truth.”
                                                    2
     Addition and Subtraction
• Suppose you are limited to numbers from 0
  to 100.
• Starting at 0, how do you get to 70?
• Starting at 100, how do you get to 70?




                                              3
         Bar chart addition

100
              Suppose you start with 3 bar charts that
              are empty (all at 0)

 0
      R G B

100
              By addition, how could you end up
              with this result?

 0
      R G B                                              4
        Bar chart subtraction

100
              Suppose you start with 3 bar charts that
              are full (all at 100)

 0
      R G B

100
              By subtraction, how could you end up
              with this result?

 0
      R G B                                              5
What do you know about color?




                                6
What is meant by “primary colors?”




                                     7
What is meant by “primary colors?”

• You can make “all” other colors
  – (not really true but OK to say – 3 primary
    colors can actually produce about 50% of the
    colors that can be seen)
• You can’t make a primary color by mixing




                                                   8
Using your colored films, let’s do the experiment:
    Are the primary colors red, yellow, blue?
 • What colors can you make by mixing red, yellow
   and blue?
 • What colors can you make by mixing cyan,
   magenta, and yellow?
 • Which set of 3 produces the largest range of
   colors?
 • Can you make any of these “primary colors” by
   mixing?
 • What are likely candidates for the 3 primary
   colors? What cannot be the primary colors?

                                                    9
Using your colored films, let’s do the experiment:
    Are the primary colors red, yellow, blue?
 • What colors can you make by mixing red, yellow and blue films?
   – Mixing red and blue makes black
   – Mixing red and yellow makes red
   – Mixing yellow and blue makes black
 • What colors can you make by mixing cyan, magenta, and yellow films?
   – Red, green, and blue
 • Which set of 3 produces the largest range of colors?
     – Cyan, magenta, and yellow
 • Can you make any of these “primary colors” by mixing?
     – Yes, you can make red by mixing magenta and yellow
     – Yes, you can make blue by mixing magenta and cyan
 • What are likely candidates for the 3 primary colors?
     – Cyan, magenta, and yellow
 • What cannot be the primary colors?
     – Red, yellow, and blue because you can make red and blue by mixing 2 other
       colors and because you can’t generate a wide range of colors using red,
       yellow, and blue
                                                                            10
        Let’s learn more about
          how we see color

Basic simplifying assumptions:
1. The color we see results from light of that color
entering our eye.
2. This room is illuminated by uncolored (white)
light




                                                   11
  Absorption of light by colored films

• Place C film over color wheel on white paper
  – C film absorbs what color of light?
• Place M film over color wheel on white paper
  – M film absorbs what color of light?
• Place Y film over color wheel on white paper
  – Y film absorbs what color of light?
• Place C, M, Y films on top of each other over
  color wheel on white paper
  – What happens? What does this mean?
                                              12
 Absorption of light by colored films
• Place C film over color wheel on W paper
    – C film absorbs R light
• Place M film over color wheel on W paper
    – M film absorbs G light
• Place Y film over color wheel on W paper
    – Y film absorbs B light
• Place C, M, Y films on top of each other
    – All light (white light) is completely absorbed by the R
      light absorber,G light absorber, and B light absorber

How can these observations be written mathematically?
(R is red light, G is green light, and B is blue light and
W is white light) See next page for guidance…                   13
   Consider the cyan film on white paper

• When cyan film is placed on white paper…
  –   What color light do you start with?
  –   What color of light is subtracted?
  –   What color light remains after the subtraction?
  –   How can you write this mathematically?




                                                        14
    Color math
         W               C
W   W




                 W–R=C



                             15
      Consider the magenta film on white paper

• When magenta film is placed on white paper…
  –   What color light do you start with?
  –   What color of light is subtracted?
  –   What color light remains after the subtraction?
  –   How can you write this mathematically?




                                                        16
    Color math

W           M




    W–G=M



                 17
   Consider the yellow film on white paper

• When yellow film is placed on white paper…
  –   What color light do you start with?
  –   What color of light is subtracted?
  –   What color light remains after the subtraction?
  –   How can you write this mathematically?




                                                        18
    Color math
W            Y




     W–B=Y



                 19
Place cyan, magenta, and yellow films on top
               of each other

• What happens and why?
• How do you describe this mathematically and
  pictorially?
• What does white light consist of?




                                                20
 Color math
W




W–R–G–B =0
W=R+G+B

              21
Alternate model

                  Each colored
                  film subtracts a
                  primary color of
                  light: hence
                  C,M,Y are
                  called the
                  subtractive
W–R–G–B =0        primaries

W=R+G+B

                                22
   Place a cyan film over a magenta film


What color of light do you start with?
What colors of light are subtracted?
What color of light remains?
How can you describe this mathematically?
How can you describe this pictorially?

                                            23
 Color math
                        B




(R +G +B) – R – G = B


                            24
Now use an alternate pictorial model
     to show what happens:




                                   25
      Alternate pictorial model




(R +G +B)   -R   = G +B
                  (G +B)   -G   =B

                                     26
What color results from each pair of colored film?




                                                     27
What color results from these pair of colored film?




                                                      28
What is the one big idea that
    determines color?




                                29
      What is the one big idea that
          determines color?
• Color is determined by light absorption
• More generally, you will learn in subsequent
  physics classes the following big idea:

   When light interacts with matter, it can be
    reflected, absorbed, or transmitted




                                                 30
               Color mixing
• We found that mixing cyan and magenta
  films made a blue film
• Mixing cyan film and yellow film makes a
  green film
• Mixing yellow and magenta films makes a
  red film
  Now let’s make a model that describes
  these results

                                             31
         Color Wheel Model for
           Subtractive Colors
                            Y




              M                          C


What colors are between each of the subtractive primaries?
                                                        32
     Color Wheel Model for Subtractive
                 Colors
                                Y
                            R            G
Now let’s deconstruct the
model in terms of cyan,
magenta, and yellow
components                  M            C


                                B
                                             33
Deconstruct the model in terms of cyan, magenta,
            and yellow components


                      Y
               R                G



               M                 C

Now, how could you
make this “real?”      B                     34
Put them together and see what happens-
      Do you make a color wheel?




                                          35
  Color Wheel Model for Subtractive Colors

                               Y
                           R         G
What are the limitations
of this model?
Does it show all the
possible colors?           M          C
Does this model explain
how our eyes see color?

                               B
                                         36
               So What?
• Let’s see what subtractive color mixing is
  good for:
• Look at the color gradient strips and overlay
  the C, M, Y, and K (K is the letter used to
  represent black) strips to make different
  colors. Can you make more colors than the
  original films?
• Take a look at the colored magazines using
  the handheld microscope.
• How are colored pictures made?
                                             37
          Other color models
• Color Cube
• HSV (Hue/Saturation/Value) model
  – Color strips
     • Each has same Hue
     • Each square on a strip differs in color
       Saturation
  – Placing a K square under any color changes the
    Value
                                                 38
     Let’s look at a cyan film from a
           different perspective




  (R +G +B)      -R     = G +B
We see this color as cyan, so cyan light is entering our eye
 So C = ?
                                                       39
     Let’s look at a cyan film from a
           different perspective




  (R +G +B)      -R     = G +B
We see this color as cyan, so cyan light is entering our eye
 So C = G + B
                                                       40
  Let’s look at a magenta film from a
          different perspective




  (R +G +B)      -G     = R +B
We see this color as magenta, so magenta light is entering
our eye
              So M = ?                                41
    Let’s look at a single colored film
      from a different perspective




  (R +G +B)      -G     = R +B
We see this color as magenta, so magenta light is entering
our eye
              So M = R + B                            42
    Let’s look at a yellow film from a
           different perspective




  (R +G +B)      -B     = R +G
We see this color as yellow, so yellow light is entering our
eye
               So Y = ?                                 43
    Let’s look at a single colored film
      from a different perspective




  (R +G +B)      -B     = R +G
We see this color as yellow, so yellow light is entering our
eye
              So Y = R + G                              44
    We just developed the rules for
    mixing colors of light (additive
            color mixing)!
•   W=R+G+B
•   C=G+B
•   M=R+B
•   Y=R+G
•   R, G, B light sources used to generate wide
    range of colors for color displays
Now let’s make a model that describes these results 45
Let’s now confirm these rules for
  additive color mixing using 2
 light sources (slide projectors)




                                46
 Color Wheel Model for Additive Colors



                  R         G


What colors lie
between them?



                      B
                                     47
   Color Wheel Model for Additive Colors
                            Y

                    R                G

The same as the
color wheel for
subtractive
colors!            M                  C
The color cube
is also the same
– just different                B
primaries!
                                         48
Why was this slide used at the beginning
        of this presentation?
              Bar chart addition
100
                 Suppose you start with 3 bar charts that
                 are empty (all at 0)

 0
      R G B

100
                 By addition, how could you end up
                 with this result?

 0
      R G B                                             49
Why was this slide used at the beginning
        of this presentation?
              Bar chart subtraction
100
                  Suppose you start with 3 bar charts that
                  are full (all at 100)

 0
      R G B

100
                  By subtraction, how could you end up
                  with this result?

 0
      R G B                                              50
            How do colors of hot objects change
            with increasing temperature?
Increasing
temperature of                                     Blue
star or object
                                            Cyan

                                    White

                           Yellow

                      e

               Blac                         Increasing energy



                  Red Green Blue
Infra-red             Visible                 Ultra-violet
                                                                51
            Application of additive color mixing

Increasing
temperature of                                         Blue
star or object
                                                Cyan

                                       White

                              Yellow

                        Red

                Black                          Increasing energy



                   Red Green Blue
Infra-red                Visible                 Ultra-violet
                                                                   52
   Now let’s look and see how
    colors are produced on a
  computer monitor for another
example of additive color mixing



                               53
                Blue sky
• The Sun is a source of white light.
• The sky scatters blue light a lot more than
  red or green light.
• Draw a diagram and explain the color of the
  Sun and sky



                                            54
How are other colors made, such as lights and darks?

             Dark red


             Light red


                                      Light red
                                      spectrum

 700nm     600nm     500nm    400nm
                                                  55
   Other Simple Color Models
• Color cube
  – Sold as a model for C, M, Y – subtractive color
    mixing
  – Also a model for R, G, B – additive color
    mixing
  – Note that color cube is a more complete model
    than the color wheel
  – Distance between color coordinates quantifies
    color differences
                                                  56
  Distance between color coordinates
      quantifies color differences
• Use color wheel as an example
• Use color cube as an example
So both color and color differences can be
  quantified mathematically.
This is critical for making colored products
  and for determining color consistency, e.g.
  what color differences during production
  are acceptable.
                                                57
 Theory of Color Vision and Implications
• Red (R), Green (G), and Blue (B) cones
   – R(L-long wavelength), G(M-mid wavelength), B(S-short wavelength)
• 3 cone responses are processed to become 3 color receptive
  responses
   – R+G yields brightness and perception of yellow
   – R-G yields red or green response
   – (R+G)-B = Y-B yields yellow or blue response




                                                                  58
Diagram of Human Color Vision
  R                           G                    B




               +
      Sensation of
      yellow and
      sensation of
      lightness




               -                           -
  Sensation of red or green       Sensation of
                                  yellow or blue




                                                       59
Theory of Color Vision and Implications

• We see 4 distinct colors: R, G, Y, B - basis for
  L*a*b* color space
• We do not see reddish greens or yellowish blues
• The blue cone does not contribute to brightness so
  images that only differ in brightness of blue are
  difficult to see. This is why blue is hard to see at
  night and why blue on black is a terrible choice for
  web pages. See example of colors printed at
  different lightnesses.
                                                    60
           A slice of the L* a* b* color system




M-250(3)
                                                  61
4-17-01
           L*a*b* COLOR SPACE




M-250(4)
                                62
4-19-01
Let’s see what are the primary colors
     according to expert sources




                                        63
       Authoritative approach
Webster’s New World Dictionary:
 “color: the primary colors of paints,
 pigments, etc. are red, yellow, and blue,
 which, when mixed in various ways,
 produce the secondary colors (green,
 orange, purple, etc.)”


                                             64
       The gray scale approach
         (neither black or white)
Art Fundamentals Theory and Practice:
 “There are three colors, however, which cannot be
  created from mixtures; these are the hues, red,
  yellow, and blue. They are called the primary
  colors.
  A mixture of the three primaries should
  theoretically result in white; actually this mixture
  produces a neutral grey which may be considered
  a darkened form of white.”
                                                         65
 The 2 correct answers approach
The Journal of Chemical Education:
 “… students should identify the three colors
 needed to produce all the others as red, blue, and
 yellow. Most artists call these the fundamental
 colors, The correct subtractive colors, used by
 printers, for example, are cyan, magenta, and
 yellow.”


                                                      66
 The loosely speaking approach
Hewitt’s Conceptual Physics
 “For this reason, cyan, magenta, and yellow are
 called the subtractive primary colors. In painting
 or printing, the primaries are often said to be red,
 yellow, and blue. Here we are loosely speaking of
 magenta, yellow, and cyan.”



                                                    67
    Not much agreement or
 consistency in the meaning of
         primary colors!
Even the “experts” are confused!
 Let’s look at some other books
 and see how they discuss color
              ideas.
                               68
                 Conclusion
• Primary colors of painting are not R, Y, B; the
  primary colors of painting are C, M, Y
• Subtractive color mixing using CMY generates a
  wide variety of printed colors by absorbing light
• Additive color mixing using RGB generates a
  wide variety of colors of light
• Many models to describe additive and subtractive
  colors including color wheel, color cube
• Many ways to investigate additive and subtractive
  color mixing
                                                  69

								
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