school of maths and physical sciences · 2017-01-23 · rainbow colour scales are popular....
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© University of Reading 2008 www.reading.ac.uk
School of Maths and Physical Sciences
Using colour
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Data assimilation and visualization in environmental sciences, 17 September 2014
Rainbow colour scales are popular. They’re pretty.
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Data assimilation and visualization in environmental sciences, 17 September 2014
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Data assimilation and visualization in environmental sciences, 17 September 2014
Can you put these circles in order?
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Data assimilation and visualization in environmental sciences, 17 September 2014
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Data assimilation and visualization in environmental sciences, 17 September 2014
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Data assimilation and visualization in environmental sciences, 17 September 2014
Let’s look at the colour scale from the map again. By looking at just luminance values, we can see the problem.
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Data assimilation and visualization in environmental sciences, 17 September 2014
This is the luminance plot for ‘jet’.
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Data assimilation and visualization in environmental sciences, 17 September 2014
Here are some examples of rainbow vs grayscale
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Data assimilation and visualization in environmental sciences, 17 September 2014
It’s not just me.
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“What kind of insane colormap has the property that values spanning the extreme ends of the scale stand out less, and can’t be distinguished as easily as values in the noisy middle? Why, it’s MATLAB’s default colormap, of course!”
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Data assimilation and visualization in environmental sciences, 17 September 2014
Choosing the right colour scale depends on the type of data you are plotting. Some well-behaved palettes:
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Data assimilation and visualization in environmental sciences, 17 September 2014
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Data assimilation and visualization in environmental sciences, 17 September 2014
An example. Which model performs better?
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Model 1 performs better
Model 2 performs better
RMS error for model 2 - RMS error for model 1
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Data assimilation and visualization in environmental sciences, 17 September 2014
How about now?
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Model 1 performs better
Model 3 performs better
RMS error for model 3 - RMS error for model 1
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Data assimilation and visualization in environmental sciences, 17 September 2014
Same data. Different colour scale. Same answer?
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Data assimilation and visualization in environmental sciences, 17 September 2014 26
Model 1 performs better
Model 3 performs better
RMS error for model 3 - RMS error for model 1
Model 1 performs better
Model 2 performs better
RMS error for model 2 - RMS error for model 1
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Data assimilation and visualization in environmental sciences, 17 September 2014
Another example: Let me introduce you to my friend Nick.
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Data assimilation and visualization in environmental sciences, 17 September 2014
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Data assimilation and visualization in environmental sciences, 17 September 2014
Let’s assume I’m showing him this recent article in nature.
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Data assimilation and visualization in environmental sciences, 17 September 2014
He sees the plot like this.
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Data assimilation and visualization in environmental sciences, 17 September 2014
Do you need colour at all?
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Data assimilation and visualization in environmental sciences, 17 September 2014
To recap. Some guidance…
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Data assimilation and visualization in environmental sciences, 17 September 2014
• Don’t just use default settings – choose your colour scale
with care.
– Be especially of rainbow/multi-hue colour scales!
• Check whether changing your colour scale changes your
interpretation of the data.
• Be aware of colourblindness.
• Consider using greyscale!
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Data assimilation and visualization in environmental sciences, 17 September 2014
There are resources to help you!
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Data assimilation and visualization in environmental sciences, 17 September 2014
Resources • ColorBrewer – lots of lovely colour scales that can be loaded into your favourite
plotting program
• CubeHelix – an interesting way of constructing a perceptual colour scale
• Colour blindness test: – http://aspnetresources.com/tools/colorBlindness
[there are lots more online] – Firefox add-on:
https://addons.mozilla.org/en-us/firefox/addon/colorblind-simulator/
• Blog posts and articles: – http://cresspahl.blogspot.co.uk/2012/03/expanded-control-of-octaves-colormap.html – http://abandonmatlab.wordpress.com/2011/05/07/lets-talk-colormaps/ – http://eagereyes.org/basics/rainbow-color-map – http://www.research.ibm.com/people/l/lloydt/color/color.HTM – http://www.perceptualedge.com/articles/visual_business_intelligence/rules_for_using_color
• Borland and Taylor paper in IEEE Computer Graphics and Applications
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"We as a visualization community must do better, making the rainbow color map as rare in visualization as the goto statement is in programming.”
Borland and Taylor, IEEE Computer Graphics and Applications, 2007
xkcd.com