Scientific Visualization: Color Properties
Science: Earth and Environmental Science
NC Scientific and Technical Visualization Objectives:
Level I: 4.03C Identify color properties
G Identify and apply guidelines for the effective use of visual properties
to code visualization variables.
Level II: 2.01B Advanced color usage
2.01C4b Isoline graphs
3.01C Identify and apply color lookup table techniques.
3.02 Apply advanced area rendering techniques
NC Earth and Environmental Science Goals and Objectives (objectives from 1994 revision):
Goal 6: The learner will have an understanding of
location and mapping.
6.1.1 Through activities,
recognize the types of information provided by different kinds of
maps and the methods used in their construction.
Scion ImageTeacher Instructions
NIH Image
CorelDraw
Color is a valuable tool in creating a scientific visualization. Beyond making a visualization more attractive, color can be used to encode data, elucidate patterns, and draw the viewers attention to important details. In order to choose the color scheme for a visualization the perceptual properties of colors and the anticipated output medium must be considered. In this exercise students will work with different color schemes to explore their perceptual properties. They will participate in discussion, create isolines and color coding for given maps, and answer discussion questions. Suggestions for a final project which may also be assigned are included. Students should be encouraged to use the correct technical terms which are outlined in the key vocabulary section below in discussion. The teacher may choose to include a more technical discussion of the electromagnetic spectrum and the wavelength of light. This could be related to objectives in Physics and Physical Science.
DISCUSSION OUTLINE
This activity requires the use of isolines which students may be more
familiar with as contour lines if they have ever worked with a topographic
map. If they are not familiar with topographic maps they should see
one, preferably of their home area. They can also visit http://mapping.usgs.gov/mac/isb/pubs/booklets/topo/topo.html
which is an excellent discussion from the USGS (United States Geological
Survey) on topographic maps.
Begin a class discussion of color coding in maps by viewing a selection of maps from various sources - newspaper weather maps, census maps, historical maps etc. are a good place to start work but if possible have students find internet examples of different types of color coding. Discuss the use of color to code for data. What color schemes are familiar? ( For example, the use of darker colors to represent more and the use of reds to represent warmer temperatures.) What issues do we have to be careful of when using color coding? (Colors that are too close for people to perceive the difference, distracting people from the information, needs related to the output medium.) What types of data are best coded by hue shifts? lightness and saturation shifts? (Hue often indicates qualitative data such as vegetation type, lightness and saturation signal quantitative shifts.)
Below are some internet examples from February 1999. Of course these should be checked before the lesson as internet material is subject to change. Most of these maps use combinations of all three perceptual properties of color. After discussing some of the maps as a class ask students to work independently or in small groups to analyze and discuss the use of color in a selection of other maps.
Maps where hue is used:
http://edcintl.cr.usgs.gov/adds/c1/doc/demd/c1demd.gif
This map of Africa uses mostly hue but also saturation for elevation.
Elevation, which is quantitative variable, could also be shown
effectively with lightness and saturation but color is more vivid
and indicates the qualitative differences in the ecology of these regions
at the same time.
Maps where lightness is used:
satellite weather image from Feb. 12, 1999
or check for today's image at http://iwin.nws.noaa.gov/iwin/nc/nc.html
These images use gray scale which can be thought of as completely desaturated
with no hue. Changes in lightness are also referred to as changes in value
or brightness. Gray scale must be used when there is a possibility
of a black and white output medium (most printers in schools). Gray
scale in combination with one color (red) in density slicing where areas
with a particular value can be highlighted.
Maps where both are used:
http://www.botanik.uni-bonn.de/biodiv/phytodiv.htm This map uses an effective combination of hue and saturation. The saturation shift shows the quantitatively greater number of species in the highly saturated areas which are also for the most part small in area so that the high saturation emphasizes these areas without being overwhelming. The hue shift helps the viewer perceive the differences.
http://www.wcmc.org.uk/forest/data/wfm.htm This map uses hue and saturation ineffectively. The colors used for tropical dry and for mangrove are difficult to distinguish from other colors and the saturation shift is being used inappropriately for a qualitative variable.
North Carolina Temperature Anomaly Map
- used with permission from the State
Climate office of North Carolina This map shows
how temperature patterns in North Carolina differed from normal in 1997.
It is an interesting color coding example because it uses one hue, blue,
to code for negative differences from average and other hues, green
and yellow to code for positive differences. Lightness is used to
code for the amount of the difference in the blues.
http://nic.fb4.noaa.gov/products/analysis_monitoring/enso_advisory/advfig1.gif
These two sea surface temperature maps are good choices for student analysis.
MAP ACTIVITY
Now students should take a map with numerical data and use color to code it. They may start with the linked map below or use another map that allows the same type of exercise. Click here to get a downloadable tiff file which can be opened in Scion Image: North Carolina Temperature Map
Some possible map assignments are listed below. More group assignments can be developed as necessary by mixing different temperature ranges with different color coding schemes. You could assign all students to produce all maps but that is not necessary for the lesson. Each working group of students can produce 2 or 3 maps and then all of the maps should be posted or projected for discussion. Each group should produce at least one map where lightness alone is used to code and should produce maps with two different widths of temperature ranges. Students will follow directions on the student assignment sheet to create a custom LUT (color lookup table).
Group 1:
map 1:
2º temp ranges, uses hue changes only,
keep lightness and saturation constant.
48-49
50-51
52-53
54-55
56-57
58-59
60-61:
map 2: 5º degree temperature ranges, red map: use lightness
changes only.
45-49
50-54
55-59
60-64
Group 2:
map 1: 2º temp ranges, blue map: change lightness and saturation.
48-49
50-51
52-53
54-55
56-57
58-59
60-61
map 2: 5º temp ranges, yellow map: use lightness
changes only.
45-49
50-54
55-59
60-64
Students should begin by finding and drawing lines around regions that are in the same temperature range. They need to be sure each region is completely enclosed, otherwise the paint bucket tool will spill the color into the next region. Then they use the paint bucket to fill each region with a different color according to their assignment. Finally they will develop a legend and present their map to the class - either printed on a color printer or on screen. After viewing and discussing all of the maps students should answer the discussion questions.
Here is an example of the type of map students should be producing:
This map uses only lightness - hue (Blue = 160) and saturation (full =
240) remain the same. The temperature range width is five degrees
so only four color codes are needed.
A possible extension is to ask students to produce a color coded map of their choice and write a brief reflection on why the color coding scheme they chose is appropriate for their data. Students can scan in or find on the internet the base map they use for their project but the color coding scheme should be their own.
Possible ideas for student maps:
North Carolina Rainfall: data is not neatly summarized anywhere. http://iwin.nws.noaa.gov/iwin/nc/nc.html is a site with links to a lot of North Carolina weather information. An hourly summary of temperature etc is available at: http://iwin.nws.noaa.gov/iwin/nc/hourly.html while .http://iwin.nws.noaa.gov/iwin/nc/climate.html has daily summaries and a variety of other info (sunrise and set times, record for the day, mean monthly temps etc). A site with links to http://www.nc-climate.ncsu.edu/
Range and population estimates for different species of animal (e.g. mountain lions, grizzly bears). Students could produce a map showing where various species are found, investigate the habitat of the various species, do population density maps etc. Data, particularly for the endangered and charismatic megafauna (like wolves, bears, and whales) is available at many sites. This is also good web search project. For example bear data can be found at: http://www.bearden.org/species.html
Census Topics - this can combine social studies and science: data available at: http://www.census.gov/
Epidemiology of various diseases: http://www.epibiostat.ucsf.edu/epidem/epidem.html
A color coded map of your school.
Human Anatomy: data available at: http://www.nlm.nih.gov/research/visible/
Key Vocabulary: Students will explore the meanings of these key terms during the lesson. Definitions should not be given out as notes, however they should be used correctly in the discussion of the maps as a part of the conclusion of the lesson.
color: The quality of a surface which results from a response to lightness, hue, and value. Hue is often confused with color since the names of the hues are used as the primary classification term for color. (e.g. red, purple, blue, etc.)
color lookup table (LUT) A database which allows colors to be mapped to specific data values. A color table can be associated with a single image or used as a standard table in a library.
hue: the controlling spectral wavelength of the perceived color. Hue and color are often confused because the name given the hue is often synonymous with the color.
saturation: A perceptual color quality indicating the ratio of the primary spectral wavelength (hue) to all the wavelengths in the color. A high saturation color appears vivid whereas a low saturation color appears grayish.
value (lightness, brightness) A quality of color indicating the total quantity of light energy. On a gray scale the lightest color, pure white, has the highest quantity of light.
isolines: often called contour lines, are used in mapping quantitative data such as temperature or altitude. All of the values along an isoline are equal.
Bertoline, G.R., Wiebe, E.N., Miller, C., & Mohler,J.L. (1997)
Technical Graphics Communications. (2nd Edition). Burr Ridge; IL:WCB/McGraw
Hill color: p995-998, contour plots, isolines: 948-950, choosing colors:
958-961, perceptual accuracy p. 963-964.
Purpose: To create and compare maps with a variety of color coding schemes.
1. Open the North Carolina Temperature map in Scion Image (or another image processing software).
2. Save a copy of your map with a different name.
3. Draw isolines for the regions assigned.
4. Magnify your map to be sure that each region is completely closed. Add lines to close the regions where needed.
5. Choose colors according to your assignment. In order to manipulate the hue lightness and saturation separately you will have to custom create a LUT. In Scion Image choosing the eight grays LUT and changing some of the grays to custom colors is a good way to start. You can do this in Scion Image by first going into color tables on the options menu and selecting 8 grays, then select the color picker tool (that's the one that looks like an eye dropper) and then double click on the LUT region that you want to choose a new color for. The color palette dialog box will pop up and allow you to experiment with changing the hue, saturation and light separately either by moving the cursor within the color box or by separately adjusting the numerical value for each of these color factors.. You can't pick all eight colors at once - you must click on the color picker and then double click on a new region of the LUT and go back to the palette dialog each time you want to add a color to the LUT.
6. Once you have a LUT that fills the requirements of your assignment use the paint bucket to fill the different temperature regions. If the paint spills out of the desired area you have a hole in the lines enclosing a region. To fix the problem you must use undo (under the edit menu) before doing anything else or else revert to saved. Then magnify your image, find the hole and draw a line to close it.
7. Set up a temperature color legend.
8. Produce other assigned maps according to the same steps.
9. After looking at and discussing all of the maps answer the worksheet questions.
10. Choose a topic which will illustrate the use of color coding in mapping, define a purpose for and produce a final map. Your map should illustrate excellent use of color coding. Keep in mind that the choice of color scheme depends on the output medium assigned.
11. Write a brief reflection on why the color scheme you chose
is most appropriate for this map.
Questions:
1. From your observations of the maps produced by the class which hue has the greatest perceived lightness range? The smallest?
2. The U.S. temperature forecast map in most newspapers gives a different color code for each 10 degree change in temperature.
a) Would this be appropriate to show the temperatures on the North Carolina map in this exercise? Why or why not?
b) What advantages and disadvantages does the 10 degree range have for the US temperature map?
(Eric you suggested "Is this color increment appropriate for the US map -since it is widely used I would assume and so will the students that the answer is yes - what I want to draw out is that a 10 degree increment on a small scale map leaves out a lot of local detail (like elevation related changes in the Rockies) but gives a clear overall picture.)
3. Discuss the advantages and disadvantages of using a narrower
range of temperature for each color code. What does using a
narrow range and a lightness shift imply to the viewer - perception compared
to a larger range and a hue shift. What width of temperature range
do you think is most appropriate for the map used in this exercise?
4. A meteorologist decides to make it easier for people
to see the boundaries between regions by alternating light and dark
in her temperature scale. The scale looked like this:
90-100 very dark red
80 - 90 light red
70 - 80 dark red
60 - 70 medium red
50 - 60 white
What is wrong with a scale like this for a temperature map?
5. What is a color lookup table?
6. In what situations is it better to use a gray scale?
7. Precipitation maps often use lightness or saturation for coding while vegetation maps usually use hue or a combination of hue and lightness or saturation.
a. Why is this?
b. What would be best for coding population density?
c. What would be best for coding a world map showing the language spoken by the majority population in each region or country?
d. What would be best for coding region's mineral resources (keep in mind that some regions may have several minerals while others have none)?
8. When you plan a project you need to know what type of output medium you will be using. Write how planning will be affected by each of the following output devices:
color laser printer
color bubble jet printer
laser printer
web page
web page to be projected in a classroom using a LCD projector
web page to be broadcast on TV
Success will be measured by the following criteria:
Produces assigned maps:
5 draws isolines
5 shades regions
10 demonstrates ability to keep hue and saturation
constant while changing lightness
5 saves map
5 prints or presents map
35 Answers questions
Final project map
10 Produces student map
10 good use of color for chosen data
15 paragraph on why color choice is appropriate
