Elm Colormaps

elm-colormaps is a collection of high-quality colormaps intended for data visualization and scientific plotting.

For now it mainly provides a port of the five sequential colormaps (magma, inferno, plasma, viridis, and cividis) that are included in newer versions of matplotlib. These are perceptually uniform, colorblind friendly and can be printed out in grayscale with minimal loss of information.

This library provides these colormaps as functions of type Float -> Color, where the input is expected to be between 0 and 1.

To use, just import Color.Colormaps and use the functions magma, inferno, plasma, viridis, and cividis.

Interop with elm-css

Since elm-css currently has a different Color type than the Base library, colors from Colormap have to be converted. To keep dependencies to a minimum, elm-colormaps does not ship with a conversion function. However, it can easily be written as follows:

colorCoreToCss : Color.Color -> Css.Color
colorCoreToCss c =
    let
        { red, green, blue, alpha } =
            Color.toRgb c
    in
        Css.rgba red green blue alpha

Examples and custom colormaps

The examples directory contains code illustrating all abovementioned functionality. Run the code locally with elm-reactor and open Example.elm. Alternatively, take a look at the results at https://2mol.github.io/elm-colormaps/.

There are also examples included about how to use the various helper functions that can be used to define custom colormaps from lists of RGB tuples.

References

The original exposition on why and how the new Matplotlib colormaps were created. Highly recommended:

https://bids.github.io/colormap/

Some more information on the linearity of several colormaps, as well as some additional ones that might be interesting to port to Elm in the future:

https://matplotlib.org/users/colormaps.html

https://matplotlib.org/gallery/color/colormap_reference.html