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Friday
Aug162013

Five things about colour

The fact that colour is a slippery subject is powerfully illustrated by my favourite optical illusion. Look at this:

Squares A and B are the same shade of grey. It's so hard to believe that you might need to see the proof to be convinced. 

Chromostereopsis is a similarly disarming effect that you may have noticed on maps with bright spectrum colour bars. Most people perceive blue and red on different depth planes, so the pseudo-3D effect can work in your favour and make the map 'pop' (This is not a good reason to use a spectrum colour bar, however... more on this next time). I notice that at least one set designer knows about the effect, making William Shatner pop on the TV show Have I Got News For You:

Color is a fun way to test your colour intuition. The game starts easy, but is very hard by the end as you simulatneously match colour tetrads. The first time I played I managed 9.8, which I am not-very-secretly quite pleased about. But I haven't been able to repeat the performance.

X-Rite's Online Color Challenge is also tough. You have to sort the very subtle colours into order. It takes a while to play but is definitely worth it. If your job depends on spotting subtle effects in images (like seismic data, for example) then stand by to learn something about your detection system. 

Color blindness will change how these games work, of course, and should change how we make maps, figures, and slides. Since up to about 5% of a large audience might be colour blind, you might want to think about how your presentations look to them. You can easily check with Vischeck and correct images for colourblind people with the Daltonizer. They can still be beautiful, but you can avoid certain colour combinations and reach a wider audience.

I have lots more links about colour to share in the next post, including some required reading from Rob Simmon and Matteo Niccoli, among others. In the meantime, have you come across any handy colour tools, or has colour ever caught you out? Let us know in the comments.

The image of William Shatner is copyright and courtesy of Hat Trick Productions Ltd, London, UK, and used with permission.

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Reader Comments (4)

Nice post Matt and couple of great examples.

Another level of variation comes from 3D rendering. As soon as we start to do things like map attributes over horizons in order to get a 3D feel of things or bump map 2D displays which is also popular, we spent some of our available luminance & colour on getting that 3D effect.

So on top of the visual challenges or perceiving similar colours, in rendering with lighting we have changed how a particular colour/shade maps onto our amplitude or attribute, in a non linear (and non obvious) way.

August 16, 2013 | Unregistered CommenterSteve Purves

@Steve: Good point — topographic (shape) data can be communicated via luminance. I often slap a discontinuity attribute onto the luminance channel too, but it can get confusing. I've often wished for a web app to play with mapping data onto surfaces and volumes. How many datasets can we visualize simultaneously and still make sense of it? What's the best way to co-render data to glean geological insights? I don't think we have experimented enough with it as a community.

For example, most software maps a single attribute onto hue and opacity, then lets the user arbitrarily 'sculpt' an opacity function of the same data. But I'd like to map a different attribute to opacity — some uncertainty parameter, say, like goodness of fit, or data quality. This would be a sort of 2D colour map, which is a whole area I've only seen a couple of people explore (some of Guo & Marfurt's papers, if memory serves).

And don't even get me started on colour in logs. Look at all this wonderful stuff.

August 16, 2013 | Registered CommenterMatt Hall

Matt,
As someone who is colorblind (red-green), I think about this often. They way people perceive colors can be very different, and I find it helpful when doing interpretation on seismic sections to change the colors from typical grey scale to brown to blue.

August 16, 2013 | Unregistered CommenterThomas Martin

@Thomas: I worked a little with Henry Posamentier in Calgary in the early noughties, mostly trying to help him use Landmark's EarthCube product, which he (quite rightly) didn't like much. He too is color blind and would spend a lot of time fiddling with colour bars. Indeed, he'd often avoid colour completely, and stick to greyscale.

I'm curious: what sort of colour bars do you use for maps and other non-seismic data?

August 16, 2013 | Registered CommenterMatt Hall

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