See the Forest Through the Trees

I’ll wager that the vast majority of you cannot make sense of this graphic.


Yes, this image does include a bunch of dots of varying size and shades of green all assembled to make a circle; I’ll buy that. You might also conclude that it’s not a very attractive image;  I would agree with that too. However, there is much more here than meets the eye……..

If you still can’t draw any deeper meaning in this melange have no fear. I’ve played a didactic trick on you using ColorOracle – a colorblindness simulator.

Color Vision Impairment

In fact, this image is an Ishihara plate that I’ve adjusted  to mimic what someone with deuteranopia (a subtype of red-green color deficiency) would see. The original image looks like this:dotmatrixMost of you can now plainly see that the number 74 is encoded in the image using green dots that are distinguished from the background matrix of red dots. That is assuming that you don’t have a red-green vision impairment (i.e., color blindness). Approximately, 8% of all men have this color deficiency – of which deuteranopia is the most common form. Red-green vision impairment is much rarer among women (<1%). This owes to the fact that the greater proportion of red-green vision impairments are inherited as sex-linked traits.

Red-Green color impairment is more nuanced than most of us are aware. For example, those affected may also have difficulty distinguishing gray, purple, and blue-green colors. Two other forms of red-green impairment are also recognized, protanopia, and tritanopia. The latter results in an inability to distinguish colors in the green-yellow portion of the spectrum and the former impacts color differentiation in the green-yellow-red spectrum. Of the three, protanopia is the rarest.

Color Friendly Graphics

When using graphics to communicate an idea(s) or concept(s), educators should elect designs that promote learner comprehension.  Those affected by a red-green color impairment process information more slowly and are generally less successful in search tasks where color is an encoding element – these impacts are heightened under low illumination levels (cole, 2004). How then should we design or encode  graphics to be clear to those with red-green vision impairment or, for that matter, those who are completely colorblind (a condition called monochromacy)? Here are a few tips that might be helpful in this regard:

  • Encode symbols using variations in color brightness/saturation
  • Use overlay hatching on symbols or patch maps
  • Select color combination’s that avoid red-green comparisons or yellow and green in the same display
  • Pick alternative symbols  for different variables
  • Manipulate line width where appropriate
  • Annotate data directly
  • Avoid rainbow color ramps for raster data

There are also a number of digital applications and website to help us optimize graphics for the color impaired. I already mentioned ColorOracle which is a free, downloadable, cross-platform, colorblindess simulator (deuteranopia, protanopia and tritanopia). In use, it applies a full screen color filter, in real time, so that an observer can interpret how any on-screen information appears to someone with red-green color deficiencies. Other simulators include SimDaltonism which is designed for use on Mac OSX operating system and Vischeck which can be used online or as a Photoshop plugin. Other design aids promote apriori choices for color and contrast. For example, ColorBrewer can be used to select appropriate color combinations for choropleth maps.

Want to Learn More?

To learn more about instructional graphics and color vision impairment, I suggest you start with an article called “Color Design for the Color Vision Impaired” by Jennie and Kelso (2007) as well as  “Controversial Color Use on Maps” by Brewer (2007).  The “We are Colorblind” website has some useful information including the use/problems of selected data charts and other information graphics. You might also wish to register for NITLE’s  Visual Literacy Wordshop-to-Go which focuses on effective teaching and learning with images and much, much more.

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Posted on November 10, 2009 at 7:24 am by Sean Connin · Permalink
In: Liberal Education, Pedagogy, Science, Technology · Tagged with: , , ,

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