cubehelix

A JavaScript library implementing Dave Green's `cubehelix' algorithm to generate a family of mapping functions. I.e., a family of functions that map values in the [0, 1] domain to points in the RGB colorspace employing a wide variety of color and ensuring that the perceived brightness monotonically increases.

For a description of the algorithm see:

• http://astron-soc.in/bulletin/11June/289392011.pdf
• http://www.mrao.cam.ac.uk/~dag/CUBEHELIX/

A demo of the wide variety of colormap functions that this algorithm can generate is available here. The demo can also help users in choosing configuration parameters different than the default.

how to use

import {cubehelix, defaultHelixConfig} from 'cubehelix';

/*
 * Generate a mapping function with the default
 * helix configuration. I.e. default start, rotations,
 * hue and gamma are assumed
 */
var mappingFunction = cubehelix();

/*
 * Get the RGB values (scaled in the [0, 1] range) for a
 * value with intensity 0.5 (0 being the lowest, 1 the highest)
 */        
var rgb = mappingFunction(0.5);

/*
 * Generate a different mapping function by providing
 * a full helix configuration different than the default
 */
mappingFunction = cubehelix({start: 0.75, r:-0.5, hue:0.8, gamma:2.0});

/*
 * Alternatively, you may choose to provide only some of the configuration
 * parameters while keeping default values for the rest
 */
mappingFunction = cubehelix({r:-0.5, gamma: 2.0});

/*
 * NB: for many non-default helix configuration values the mapping
 * function may generate RGB components outside of the [0, 1] range
 * The client programmer is responsible for clipping to [0, 1].
 * The more clipping occurs, the more the monotonicity of perceived luminosity 
 * may suffer.
 */

/*
 * Print the default helix configuration
 */
console.log(JSON.stringify(defaultHelixConfig));