1 It’s A Colorful Life Dr. Larry Woolf General Atomics Presented 10/21/06 at the California Science Teachers Association Meeting San Francisco, CA

2 Resources This workshop and other related ones – (click on presentations) It’s a Colorful Life educational module – (click on education modules) Color materials – (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

3 What do you or your students know about color?

4 Let’s see what are the primary colors according to expert sources

5 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.)”

6 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.”

7 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.”

8 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.”

9 Not much agreement or consistency in the meaning of primary colors! Even the “experts” are confused!

10 What is meant by “primary colors?”

11 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 What is meant by “primary colors?”

12 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?

13 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

14 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

15 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?

16 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…

17 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?

18 Color math WW W C W – R = C

19 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?

20 Color math W M W – G = M

21 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?

22 Color math W Y W – B = Y

23 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?

24 Color math W W – R – G – B = 0 W = R + G + B

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

26 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?

27 Color math (R +G +B) – R – G = B B

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

29 Alternate pictorial model (R +G +B)-R= G +B -G(G +B)= B

30 What color results from each pair of colored film?

31 What color results from these pair of colored film?

32 What is the one big idea that determines color?

33 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 What is the one big idea that determines color?

34 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

35 Color Wheel Model for Subtractive Colors Y MC What colors are between each of the subtractive primaries?

36 Color Wheel Model for Subtractive Colors R Y M B G C Now let’s deconstruct the model in terms of cyan, magenta, and yellow components

37 R Y M B G C Deconstruct the model in terms of cyan, magenta, and yellow components Now, how could you make this “real?”

38 Put them together and see what happens- Do you make a color wheel?

39 Color Wheel Model for Subtractive Colors R Y M B G C What are the limitations of this model? Does it show all the possible colors? Does this model explain how our eyes see color?

40 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?

41 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

42 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 = ?

43 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

44 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 = ?

45 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

46 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 = ?

47 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

48 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

49 Color Wheel Model for Additive Colors R B G What colors lie between them?

50 Color Wheel Model for Additive Colors R B G M Y C The same as the color wheel for subtractive colors! The color cube is also the same – just different primaries!

51 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 Relationship of additive and subtractive colors Red from an additive color point of view (Start with no light and add red light) R

52 Dark red Light red Light red spectrum 700nm600nm500nm400nm

53 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