Instructor Side
JCE Classroom Activity: #7
How Many Colors in Your Computer? Discovering the Rules for Making Colors by the Journal’s Editorial Staff
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Background Most people in our society use computer technology every day, and depend upon it (for government and tax records, banking, medical records, etc.), even if they never touch a computer themselves. However, very few people have a good understanding of how the technology works. This lesson demonstrates some very simple science behind a complex device, the color computer monitor. The activity was inspired by the Viewpoints article “The Computer as a Materials Science Benchmarks” (1). In the description of how advances in materials chemistry have led to our ability to visualize information through the computer, there is a note describing how to see the red, blue, and green contributions to each pixel using a magnifying glass.
About The Activity Part 1. The color contributions to each pixel are easier to see when the screen is set to the lowest number of colors and the smallest resolution, but they should be visible as dots or lines with a typical magnifying glass at all resolutions. Combinations of red, blue, and green are the only colors present in the pixels, no matter what the color depth or what color is displayed on the screen. These three colors are mixed with various intensities to make all of the other colors. Examining colored areas on the screen, students should be able to discover this. Part 2. In this activity, students will mix colors of light found on the computer screen. They should discover that red and green light combine to make yellow, red and blue combine to make magenta, blue and green combine to make cyan, and red, blue, and green combine to make white light. (Students may identify magenta as purple or violet or pink and cyan as aqua or blue-green.) An inexpensive source of colored plastic sheets for use in this activity is colored report covers. These are usually available in red, blue, green, and many other colors at stores that sell school or office supplies. If the intensity of the plastic colors is not consistent, you can double or triple layers of plastic. The covers can easily be cut into pieces for use by several students or groups of students. The activity works best if all the light sources are of equal, relatively high intensity. This part can easily be used as a classroom demonstration by using three overhead projectors as light sources. If three projectors are not available, you can use mirrors to reflect light of one or two colors onto the third. An interesting discussion question that students can experiment with is why the result is different from mixing projected color light and projecting light through two colored filters. This will lead into the third part of the activity. Part 3. In this part students will mix colors of paint or crayon to produce other colors. This should be a far more familiar activity than mixing colored light for most students. They 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.
Integrating the Activity into Your Curriculum This activity can be used in discussions of Solid State Chemistry when LEDs, phosphors, or liquid crystals are discussed. It may also be appropriate when introducing spectroscopy because it deals with absorption and emission of colored light. It would be an excellent introduction to a unit on practical applications of chemistry discussing the chemistry behind computers. Such a lesson could be designed based on the Viewpoints article (1).
Reference 1. Campbell, D. J.; Lorenz, J. K.; Ellis, A. B.; Kuech, T. F.; Lisensky, G. C.; Whittingham, M. S. The Computer as a Materials Science Benchmark. J. Chem. Educ. 1998, 75, 297–312.
Additional Related Activities 1. Ellis, A. B.; Geselbracht, M. J.; Johnson, B. J.; Lisensky, G. C.; Robinson, W. R. Teaching General Chemistry: A Materials Science Companion; ACS Books: Washington, DC, 1993. 2. Lisensky G. C; Ellis, A. B. Solid State Resources [CD-ROM]; J. Chem. Educ. Software, 1996, Special Issue 12. 3. http://www.exploratorium.edu/publications/ (accessed January 1998). 4. http://www.iit.edu/~smile/ph9709.html (accessed January 1998) and Silverstein, T.P. Polarity, Miscibility, and Surface Tension of Liquids. J. Chem. Educ. 1993, 70, 253.
This Activity Sheet may be reproduced for use in the subscriber’s classroom. JChemEd.chem.wisc.edu • Vol. 75 No. 3 March 1998 • Journal of Chemical Education
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JCE Classroom Activity: #7
Student Side
How Many Colors in Your Computer? Discovering the Rules for Making Colors by the Journal’s Editorial Staff
Introduction Innovations in solid state chemistry have made many of the rapid advancements in computer technology possible. Most modern computer monitors can display at least 256 different colors–many can display millions of colors. The discovery of materials from which LEDs (light emitting diodes), phosphors, and liquid crystals are made makes these colors possible. The smallest unit on the computer screen is called a pixel. Each pixel can display only one color at a time. How many colored sources are required per pixel to display all of the colors possible?
Try This Paint) or any application capable of displaying large areas of a single color is recommended. Record your observations for each step. 1. Start the computer and load a graphics (or other) application. Display a large white area on the screen. 2. Examine the white area with your magnifying glass. Can you see the pixels? How many colors can you see for each pixel? 3. Repeat step 2 with large areas of other colors, such as red, orange, yellow, green, blue, violet. How many colors can you see for each pixel? 4. If your computer can display different color depths (16, 256, thousands, millions) or different resolutions (640 ↔ 480, 800 ↔ 600, etc.) repeat the steps above with different settings.
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Part 1. You will need a computer with a color monitor and a magnifying glass. A simple graphics program (Draw/
Part 2. You will need red, blue, and green plastic sheets, tape, three light sources (flashlights, lamps, overhead
projectors), a white wall or screen, and a darkened room. You will probably need a partner to complete this exercise. 1. Tape a colored plastic sheet over each flashlight or lamp, or place one sheet on each overhead projector. (Be sure light sources do not get hot enough to melt the plastic!) 2. In a darkened room, turn on each light source and project the light onto the white wall. Note the color of each. 3. Using two of the colors, project the light onto the same spot on the wall. What color do you see? Try all possible combinations of two colors. 4. Project all three colors onto the same spot on the wall. Now what color is the light? Part 3. Artists combine a few basic colors to create all the colors they need. For artists (like computer monitors!) there
Questions __1. Color computer graphics are usually described as RGB or CMYK where the letters represent the colors used. What do these letters stand for? What is the relationship between RGB and CMYK? __2. How did the results in Parts 2 and 3 differ? Are the fundamental colors used by the computer the same as those used by artists? Explain. __3. How would you make black and white with three colors of light? Three colors of paint?
Related Information from the World Wide Web 1. http://brianjones.ctss.colostate.edu/Spots.html 2. http://mc2.cchem.berkeley.edu/Java/ 3. http://www.ppsa.com/ppsa/science/coloradd.htm 4. http://www.ppsa.com/ppsa/science/colorsub.htm 5. http://www.contrib.andrew.cmu.edu/usr/dw4e/color/basics.html#mixing 6. http://www.tomruley.com/Photoshop_pages/Color.html 7. http://www.yorku.ca/eye/color.htm All Web sites accessed January 1998.
This Activity Sheet may be reproduced for use in the subscriber’s classroom. 312B
Journal of Chemical Education • Vol. 75 No. 3 March 1998 • JChemEd.chem.wisc.edu
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are three fundamental colors. You will need a set (8 colors) of water color paints or crayons and white paper. 1. Mix colors of paint or crayon two at a time on the white paper until you find three colors that you can use to create all of the others. 2. What color do you get if you mix equal amounts of the three fundamental colors you identified? 3. What color do you get if you combine red, green, and blue? How is this different from step 4 in Part 2?
