Transcript Document

It’s A Colorful Life
Dr. Larry Woolf
[email protected]
www.sci-ed-ga.org
General Atomics
Presented 10/21/06 at the
California Science Teachers Association Meeting
San Francisco, CA
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Resources
• This workshop and other related ones
– www.sci-ed-ga.org (click on presentations)
• It’s a Colorful Life educational module
– www.sci-ed-ga.org (click on education modules)
• Color materials
– www.sci-ed-ga.org (click on educational materials)
– There is also an order form here
– These materials are also all sold by Flinn Scientific;
some are sold by Arbor Scientific
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What do you or your students
know about color?
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Let’s see what are the primary colors
according to expert sources
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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.)”
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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.”
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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.”
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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.”
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Not much agreement or
consistency in the meaning of
primary colors!
Even the “experts” are confused!
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What is meant by “primary colors?”
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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
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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?
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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
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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
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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?
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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…
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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?
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Color math
W
W
C
W
W–R=C
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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?
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Color math
M
W
W–G=M
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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?
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Color math
Y
W
W–B=Y
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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?
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Color math
W
W–R–G–B =0
W=R+G+B
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Alternate model
W–R–G–B =0
Each colored
film subtracts a
primary color of
light: hence
C,M,Y are
called the
subtractive
primaries
W=R+G+B
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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?
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Color math
B
(R +G +B) – R – G = B
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Now use an alternate pictorial model
to show what happens:
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Alternate pictorial model
(R +G +B)
-R
= G +B
(G +B)
-G
=B
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What color results from each pair of colored film?
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What color results from these pair of colored film?
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What is the one big idea that
determines color?
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What is the one big idea that
determines color?
• Color is determined by light absorption
• More generally, students will learn in subsequent
physics classes the following big idea:
When light interacts with matter, it can be
reflected, absorbed, or transmitted
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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
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Color Wheel Model for
Subtractive Colors
Y
M
C
What colors are between each of the subtractive primaries?
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Color Wheel Model for Subtractive
Colors
Y
Now let’s deconstruct the
model in terms of cyan,
magenta, and yellow
components
R
G
M
C
B
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Deconstruct the model in terms of cyan, magenta,
and yellow components
Y
R
G
M
C
Now, how could you
make this “real?”
B
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Put them together and see what happensDo you make a color wheel?
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Color Wheel Model for Subtractive Colors
Y
What are the limitations
of this model?
Does it show all the
possible colors?
Does this model explain
how our eyes see color?
R
G
M
C
B
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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?
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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
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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 = ?
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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
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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 = ?
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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
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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 = ?
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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
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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 48
Color Wheel Model for Additive Colors
R
G
What colors lie
between them?
B
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Color Wheel Model for Additive Colors
Y
R
The same as the
color wheel for
subtractive
colors!
The color cube
is also the same
– just different
primaries!
G
M
C
B
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Relationship of additive and subtractive colors
Red from a subtractive color point of
view (Start with white light and subtract
green (with magenta film) and blue (with
yellow film) light components)
W-G-B=R
Red from an additive color point of view
(Start with no light and add red light)
R
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Dark red
Light red
Light red
spectrum
700nm
600nm
500nm
400nm
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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
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