Colour blindness and grayscale previews in QGIS 2.4

Since QGIS 2.4 is nearing feature freeze it seems like a good time to start exploring some of the great new features in this release. So, let’s get started with my most recent addition to QGIS’ print composer… preview modes!

As every first year cartography text book will tell you, it’s important to know your target media and audience when creating a usable map. Some important considerations are whether or not your map will be photocopied or printed in black and white, and whether you need to consider colour blind map readers in your audience. In the past, designing maps with these considerations has been a time consuming, tedious process. You’d have to export your map, open it in another graphics editing program, apply some colour transform, work out what issues there are, flip back to QGIS, make your changes and repeat. If you’re working with a tight deadline it can be difficult to justify the time this all takes.

QGIS 2.4 will help to make this whole process a lot simpler. In the print composer there’s now an option to enable a number of different live “preview modes“. These include grayscale, monochrome, and two colour blindness simulations (Protanope and Deuteranope).

Composer preview modes in QGIS 2.4

Composer preview modes in QGIS 2.4

These preview modes are live, so you can continue to edit and tweak the colours in your composition while a preview mode is active! For a quick demonstration, let’s start with this creatively coloured thematic map:

bad_colored_map

While it might not be the most aesthetically pleasing map, at least the thematic colours can be easily matched to their corresponding values in the legend. Let’s see what would happen if we photocopied this map. This is as easy as activating the “Simulate photocopy (grayscale)” preview mode:

greyscalepreview

Hmm… not so usable now. The five thematic colours have been reduced to just three discernible colours. Oh well, at least we haven’t had to export our map to find this out, and it’s nice and easy to adjust the colours and composition to work for photocopies without having to leave QGIS to test the results!

Let’s see how this map would look to someone with colour blindness, by activating the “Simulate colour blindness (Protanope)” mode:

color_blindness

In this case, our map isn’t too bad. The different classes are still discernible and the map can be interpreted by someone with protanopia.

So there we have it – now it’s easy to determine how our map outputs will look under different circumstances and adjust them to suit! Composer preview modes will be a part of the upcoming 2.4 release of QGIS, which is due out at the end of June 2014.

Update:

This feature has also been added to the main map canvas.

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6 thoughts on “Colour blindness and grayscale previews in QGIS 2.4

  1. Excellent, will save time when preparing maps for publications!

  2. […] a quick follow-up to my last post on colour preview modes for the print composer in QGIS 2.4, this feature has also been added to the main map canvas […]

  3. John Duncan says:

    It’s amazing how quickly your work on Composer has turned it from something that can do basic map layout (followed by hours of tweaking in Illustrator/Inkscape) into an unparalleled tool for making beautiful and functional maps. Thank you! :)

    Would it be possible to build upon these new preview modes to not just simulate different visual effects but also display a warning if the colours used are likely to cause problems? And/or add a simulated CMYK plotter mode?

    • Nyall Dawson says:

      I’d love to add a CMYK preview mode. The difficulty is in finding a reliable algorithm for realistic conversion between RGB/CMYK. I think we’d need to hook into an external color management library to do this… Something to look into for future releases!

  4. […] latest release of QGIS (version 2.4) offers color blind and grayscale simulators so users can make sure their maps are […]

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