chroma.js

chroma.js is a tiny JavaScript library (12kB) for dealing with colors!

Quick-start

Here are a couple of things chroma.js can do for you:

read colors from a wide range of formats
analyze and manipulate colors
convert colors into wide range of formats
linear and bezier interpolation in different color spaces

Here's an example for a simple read / manipulate / output chain:

chroma('pink').darken().saturate(2).hex()

Aside from that, chroma.js can also help you generate nice colors using various methods, for instance to be used in color palette for maps or data visualizations.

chroma.scale(['white','green','blue']).colors(5)

chroma.js has a lot more to offer, but that's the basic gist of it.

API

chroma

The first step is to get your color into chroma.js. That's what the generic constructor chroma() does. The function is trying to guess the color format for you. For instances, it will recognized any named color from the W3CX11 specification:

chroma('hotpink')

If there's no matching named color chroma.js checks for a hexadecimal string. It ignores case, the # sign is optional, and the shorter three letter format is recognized as well. So any of these are valid hexadecimal representations: #ff3399, FF3399, #f39, etc.

chroma('#ff3399'); 
chroma('F39');

In addition to hex strings, hexadecimal numbers (in fact, just any number between 0 and 16777215), will be recognized, too.

chroma(0xff3399)

If you pass the RGB channels individually, too. Each parameter must be within 0..255. You can pass the numbers as individual arguments or as array.

chroma(0xff, 0x33, 0x99);
chroma(255, 51, 153);
chroma([255, 51, 153]);

You can construct colors from different color spaces by passing the name of color space as the last argument. Here we define the same color in HSL by passing the h*ue angle (0-360) and percentages for saturation and lightness:

chroma(330, 1, 0.6, 'hsl')

chroma.hsl

Alternatively, every color space has its own constructor function under the chroma namespace. For a list of all supported color spaces, check the appendix.

chroma.hsl(330, 1, 0.6)

chroma.hsv

chroma.lab

chroma.lch

L: Lightness, c: chroma (0-1), h: hue (0-1).

chroma.lch(80, 40, 130);
chroma(80, 40, 130, 'lch');

chroma.hcl

You can use hcl instead of Lch, too. It is all the same, except that lightness and hue channels are switched to be more consistent with HSL.

chroma.hcl(130, 40, 80);
chroma(130, 40, 80, 'hcl');

chroma.cmyk

cyan, magenta, yellow, black, each between 0 and 1.

chroma.cmyk(0.2, 0.8, 0, 0);
chroma(0.2, 0.8, 0, 0, 'cmyk');

chroma.gl

GL is a variant of RGB(A), with the only difference that the components are normalized to the range of 0..1.

chroma.gl(0.6, 0, 0.8);
chroma.gl(0.6, 0, 0.8, 0.5);
chroma(0.6, 0, 0.8, 'gl');

chroma.temperature

light 2000K, bright sunlight 6000K. Based on Neil Bartlett's implementation.

chroma.temperature(2000); // candle light
chroma.temperature(3500); // sunset
chroma.temperature(6000); // bright sunlight

The effective temperature range goes from 0 to about 20000 Kelvin:

f = function(i) {
    return chroma.temperature(i * 20000)
}

chroma.mix

Simplest way. Mix two colors can be achieved in multiple ways. Change the mix ratio by passing a value between 0 and 1 as third parameter. In the following example, red will be mixed with blue.

chroma.mix('red', 'blue');
chroma.mix('red', 'blue', 0.25);

The color mixing produces different results based on what color space the colors are interpolated in. The default color space is rgb but in the following example we interpolate in Lab instead.

chroma.mix('red', 'blue', 0.5, 'rgb');
chroma.mix('red', 'blue', 0.5, 'hsl');
chroma.mix('red', 'blue', 0.5, 'lab');
chroma.mix('red', 'blue', 0.5, 'lch');

chroma.average

Similar to chroma.mix(color1, color2, 'rgb'), but works with more than two colors. Simple averaging of R,G,B components and the alpha channel.

chroma.average(['white', 'yellow', 'red', 'teal']);
chroma.average(['red', 'rgba(0,0,0,0.5)']).alpha();

chroma.blend

Blends two colors using RGB channel-wise blend functions. Valid blend modes are multiply, darken, lighten, screen, overlay, burn, and dogde.

chroma.blend('4CBBFC', 'EEEE22', 'multiply');
chroma.blend('4CBBFC', 'EEEE22', 'darken');
chroma.blend('4CBBFC', 'EEEE22', 'lighten');

chroma.random

Returns a random color.

chroma.random();
chroma.random();
chroma.random();

chroma.contrast

Computes the WCAG contrast ratio between two colors. A minimum contrast of 4.5:1 is recommended to ensure that text is still readable against a background color.

// contrast smaller than 4.5 = too low
chroma.contrast('pink', 'hotpink');
// contrast greater than 4.5 = high enough
chroma.contrast('pink', 'purple');

chroma.brewer

chroma.brewer is an map of ColorBrewer scales that are included in chroma.js for convenience. chroma.scale uses the colors to construct.

chroma.brewer.OrRd

chroma.limits

chroma.limits(data, mode, n) is a little helper function that computes class breaks for you, based on data. It supports the modes equidistant (e), quantile (q), logarithmic (l), and k-means (k). Let's take a few numbers as sample data.

var data = [2.0,3.5,3.6,3.8,3.8,4.1,4.3,4.4,
            4.6,4.9,5.2,5.3,5.4,5.7,5.8,5.9,
            6.2,6.5,6.8,7.2,8];

equidistant breaks are computed by dividing the total range of the data into n groups of equal size.

chroma.limits(data, 'e', 4);

In the quantile mode, the input domain is divided by quantile ranges.

chroma.limits(data, 'q', 4);

logarithmic breaks are equidistant breaks but on a logarithmic scale.

chroma.limits(data, 'l', 4);

k-means break is using the 1-dimensional k-means clustering algorithm to find (roughly) n groups of "similar" values. Note that this k-means implementation does not guarantee to find exactly n groups.

chroma.limits(data, 'k', 4);

color

color.alpha

Get and set the color opacity using color.alpha.

chroma('red').alpha(0.5);
chroma('rgba(255,0,0,0.35)').alpha();

color.darken / brighten

Once loaded, chroma.js can change colors. One way we already saw above, you can change the lightness.

chroma('hotpink').darken();
chroma('hotpink').darken(2);
chroma('hotpink').brighten();

color.saturate

You can also saturate colors. chroma.js will use the Lch color space to saturate/desaturate the colors.

chroma('slategray').saturate(); 
chroma('slategray').saturate(2);

color.desaturate

chroma('hotpink').desaturate();
chroma('hotpink').desaturate(2);
chroma('hotpink').desaturate(3);

color.set

Set a channel of a color space.

// change hue to 0 deg (=red)
chroma('skyblue').set('hsl.h', 0);
// set chromacity to 30
chroma('hotpink').set('lch.c', 30);

Relative changes work, too:

// half Lab lightness
chroma('orangered').set('lab.l', '*0.5');
// double Lch saturation
chroma('darkseagreen').set('lch.c', '*2');

color.get

chroma('orangered').get('lab.l');
chroma('orangered').get('hsl.l');
chroma('orangered').get('rgb.g');

color.luminance

Returns the relative brightness of any point in a colorspace, normalized to 0 for darkest black and 1 for lightest white according to the WCAG definition.

chroma('white').luminance();
chroma('aquamarine').luminance();
chroma('hotpink').luminance();
chroma('darkslateblue').luminance();
chroma('black').luminance();

chroma.js also allows you to adjust the luminance of a color. The source color will be interpolated with black or white until the correct luminance is found.

// set lumincance to 50% for all colors
chroma('white').luminance(0.5);
chroma('aquamarine').luminance(0.5);
chroma('hotpink').luminance(0.5);
chroma('darkslateblue').luminance(0.5);

By default, this interpolation is done in RGB, but you can interpolate in different color spaces by passing them as second argument:

chroma('aquamarine').luminance(0.5); // rgb
chroma('aquamarine').luminance(0.5, 'lab');
chroma('aquamarine').luminance(0.5, 'hsl');

color.hex

Finally, chroma.js allows you to output colors in various color spaces and formats.

Most often you will want to output the color as hexadecimal string.

chroma('orange').hex()

color.name

Returns the named color. Falls back to hexadecimal RGB string, if the color isn't present.

chroma('#ffa500').name();
chroma('#ffa505').name();

color.css

Returns a RGB() or HSL() string representation that can be used as CSS-color definition.

chroma('teal').css();
chroma('teal').alpha(0.5).css();
chroma('teal').css('hsl');

color.rgb

Returns an array with the red, green, and blue component, each as number within the range 0..255.

chroma('orange').rgb()

color.hsl

Returns an array with the hue, saturation, and lightness component. Hue is the color angle in degree (0..360), saturation and lightness are within 0..1. Note that for hue-less colors (black, white, and grays), the hue component will be NaN.

chroma('orange').hsl();
chroma('white').hsl();

color.hsv

Returns an array with the hue, saturation, and value components. Hue is the color angle in degree (0..360), saturation and value are within 0..1. Note that for hue-less colors (black, white, and grays), the hue component will be NaN.

chroma('orange').hsv();
chroma('white').hsv();

color.hsi

Returns an array with the hue, saturation, and intensity components, each as number between 0 and 255. Note that for hue-less colors (black, white, and grays), the hue component will be NaN.

chroma('orange').hsi();
chroma('white').hsi();

color.lab

Returns an array with the L, a, and b components.

chroma('orange').lab()

color.lch

Returns an array with the Lightness, chroma, and hue components.

chroma('skyblue').lch()

color.hcl

Essentially an alias of lch, but with the components in reverse order.

chroma('skyblue').hcl()

color.temperature

Estimate the temperature in Kelvin of any given color, though this makes the only sense for colors from the temperature gradient above.

chroma('#ff3300').temperature();
chroma('#ff8a13').temperature();
chroma('#ffe3cd').temperature();
chroma('#cbdbff').temperature();
chroma('#b3ccff').temperature();

color.gl

chroma('33cc00').gl();

For a complete list of supported output formats, read the API docs.

color scales

chroma.scale

A color scale, created with chroma.scale, is a function that maps numeric values to a color palette. The default scale has the domain 0..1 and goes from white to black.

f = chroma.scale();
f(0.25);
f(0.5);
f(0.75);

You can pass an array of colors to chroma.scale. Any color that can be read by chroma() will work here, too. If you pass more than two colors, they will be evenly distributed along the gradient.

chroma.scale(['yellow', '008ae5']);
chroma.scale(['yellow', 'red', 'black']);

scale.domain

You can change the input domain to match your specific use case.

// default domain is [0,1]
chroma.scale(['yellow', '008ae5']);
// set domain to [0,100]
chroma.scale(['yellow', '008ae5']).domain([0,100]);

You can use the domain to set the exact positions of each color.

// default domain is [0,1]
chroma.scale(['yellow', 'lightgreen', '008ae5'])
    .domain([0,0.25,1]);

scale.mode

As with chroma.mix, the result of the color interpolation will depend on the color mode in which the channels are interpolated. The default mode is RGB:

chroma.scale(['yellow', '008ae5']);

This is often fine, but sometimes, two-color RGB gradients goes through kind of grayish colors, and Lab interpolation produces better results:

chroma.scale(['yellow', 'navy']);
chroma.scale(['yellow', 'navy']).mode('lab');

Other useful interpolation modes could be HSL or Lch, though both tend to produce too saturated / glowing gradients.

chroma.scale(['yellow', 'navy']).mode('lab');
chroma.scale(['yellow', 'navy']).mode('hsl');
chroma.scale(['yellow', 'navy']).mode('lch');

chroma.brewer

chroma.js includes the definitions from ColorBrewer2.org. Read more about these colors in the corresponding paper by Mark Harrower and Cynthia A. Brewer.

chroma.scale('YlGnBu');
chroma.scale('Spectral');

To reverse the colors you could simply reverse the domain:

chroma.scale('Spectral').domain([1,0]);

You can access the colors directly using chroma.brewer.

chroma.brewer.OrRd

scale.correctLightness

Sometimes

chroma.scale(['yellow', '008ae5']).mode('lch');

chroma.scale(['yellow', '008ae5'])
	.mode('lch')
	.correctLightness();

chroma.bezier

chroma.bezier returns a function that performs a bezier interpolate. The input range of the function is [0..1]. Bezier interpolation is always done in Lab space.

// linear interpolation
chroma.scale(['yellow', 'red', 'black']);
// bezier interpolation
chroma.bezier(['yellow', 'red', 'black']);
// convert bezier interpolator into chroma.scale
chroma.bezier(['yellow', 'red', 'black'])
    .scale().colors(5);

Bezier interpolation

chroma.cubehelix

Dave Green's cubehelix color scheme!!

Parameters (description copied from Dave Green):

start color for hue rotation, default=300
rotations: number of rotations (e.g. 1=360°, 1.5=`540°``), default=-1.5
hue: controls how saturated the colour of all hues are. either single value or range, default=1
gamma factor: can be used to emphasise low or high intensity values, default=1
lightness range: default: [0,1] (black -> white)

// use the default helix...
chroma.cubehelix();
// or customize it
chroma.cubehelix()
    .start(200)
    .rotations(-0.5)
    .gamma(0.8)
    .lightness([0.3, 0.8]);

You can call cubehelix.scale() to use the cube-helix through the chroma.scale() interface.

chroma.cubehelix()
    .start(200)
    .rotations(-0.35)
    .gamma(0.7)
    .lightness([0.3, 0.8])
  .scale() // convert to chroma.scale
    .correctLightness()
    .colors(5);

scale.padding

Reduces the color range by cutting of a fraction of the gradient on both sides. If you pass a single number, the same padding will be applied to both ends.

chroma.scale('RdYlBu');
chroma.scale('RdYlBu').padding(0.15);

Alternatively you can specify the padding for each sides individually by passing an array of two numbers.

chroma.scale('OrRd');
chroma.scale('OrRd').padding([0.2, 0]);

scale.colors

You can call scale.colors(n) to quickly grab n equi-distant colors from a color scale. If called with no arguments, scale.colors returns the original array of colors used to create the scale.

chroma.scale('OrRd').colors(5);
chroma.scale(['white', 'black']).colors(12);

scale.classes

If you want the scale function to return a distinct set of colors instead of a continuous gradient, you can set custom class breaks:

chroma.scale('OrRd').classes(5);
chroma.scale('OrRd').classes(8);

You can also define custom class breaks by passing them as array:

chroma.scale('OrRd').classes([0,0.3,0.55,0.85,1]);

Note that this works with any color scale:

chroma.cubehelix()
    .rotations(-0.35)
    .lightness([0.1, 0.8])
    .scale()
    .classes(breaks)

Files

index.md

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index.md

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chroma.js

Quick-start

API

chroma

chroma.hsl

chroma.hsv

chroma.lab

chroma.lch

chroma.hcl

chroma.cmyk

chroma.gl

chroma.temperature

chroma.mix

chroma.average

chroma.blend

chroma.random

chroma.contrast

chroma.brewer

chroma.limits

color

color.alpha

color.darken / brighten

color.saturate

color.desaturate

color.set

color.get

color.luminance

color.hex

color.name

color.css

color.rgb

color.hsl

color.hsv

color.hsi

color.lab

color.lch

color.hcl

color.temperature

color.gl

color scales

chroma.scale

scale.domain

scale.mode

chroma.brewer

scale.correctLightness

chroma.bezier

chroma.cubehelix

scale.padding

scale.colors

scale.classes