colour-extractor

Extract colour palettes from photos using Node.js.

Installation

Is as simple as with any other Node.js module:

$ npm install colour-extractor

NOTE: colour-extractor depends on gm module, which in turn depends on GraphicsMagick.

Sample

Usage

colour-extractor exports two functions:

ce = require('colour-extractor')
ce.topColours('Photos/Cats/01.jpg', true, function (colours) {
  console.log(colours);
});

topColours function takes three arguments:

• path to your photo,
• true if you'd like the resulting array to be sorted by frequency, false if you'd like to get colours sorted as they appear in the photo (top-to-bottom),
• a callback function.

Callback function will be passed an Array with RGB triplet of each colour and its frequency:

[
  [1,   [46, 70, 118]],
  [0.3, [0,   0,   2]],
  [0.2, [12,  44,  11]]
]

The second function, colourKey, returns an array with nine colours, where each one can be mapped to a 3x3 box, ie. super-pixelised representation of the photo.

ce.colourKey('Photos/Cats/999999.jpg', function (colours) {
  database.store('colour-keys', photoId, colours);
  res.send(colours);
  // render colours to user while they wait for the photo to load.
  // (or something equally brilliant)
});

Utilities

colour-extractor exports two more utility functions:

> ce.rgb2hex(100, 10, 12);
'#640a0c'
> ce.rgb2hex([44, 44, 44]);
'#2c2c2c'
> ce.hex2rgb('#ffffff');
[255, 255, 255]
> ce.hex2rgb('45c092')
[69, 192, 146]

How does it work?

That's what I'd like to know as well! Anyhow, colour-extractor parses GraphicMagick's histogram, tries to detect similar colours and remove ones which appear less frequently than others.

If you happen to know an actual algorithm that deals with this sort of stuff, don't hesitate to contact me!

License

colour-extractor is published under MMIT license, please see the LICENSE file for full details.

Photos used in the sample can be downloaded from Flickr:

• Title?
• nel profondo del blu
• Reykjavík revisited