color-temperature

color-temperature

Converts color temperature in Kelvin to a color in RGB color space -- and vice versa.

The conversion is designed to be fast and usable for image processing. More details on color temperature and the algorithm can be found here.

Installation

$ npm install --save color-temperture

Usage

var ct = require('color-temperature');

//convert kelvin to RGB
// eg convert typical candlelight (1850K ) to RGB
var rgb = ct.colorTemperature2rgb(1850);

var red = rgb.red;
var green = rgb.green;
var blue = rgb.blue;

RGB color is represented in JSON format: An RGB of [0, 128, 255] would be represented as

{
  red : 0,
  green : 128,
  blue : 255
}

Examples

Often, the convertor is deployed as part of an image processing loop. The following example uses streams to generate a PNG similar to that at the top of this README file.

var fs = require('fs');
var png_encoder = require('png-stream');
var ct = require('color-temperature');
var width = 500;
var height = 100;
var kelvinStart = 10;
var kelvinEnd = 40000;

var pixels = new Buffer(width * height * 3);
for (var w = 0; w < width; w += 1) {
  for (var h = 0; h < height; h += 1) {
      var i = ((h*width)+w)*3;

      kelvin = ((kelvinEnd-kelvinStart)/width)* w + kelvinStart;
      var rgb = ct.colorTemperature2rgb(kelvin);

      pixels[i] = rgb.red;
      pixels[i + 1] = rgb.green;
      pixels[i + 2] = rgb.blue;
  }
}

var enc = new png_encoder.Encoder(width, height);
enc.pipe(fs.createWriteStream('color-temperature-'+kelvinStart+'-'+kelvinEnd+'.png'));
enc.end(pixels);

There are examples in the examples directory.

API

NOTE The conversions use approximations and are suitable for photo-mainpulation and other non-critical uses.

Accuracy is best between 1000K and 40000K.

require('color-temperature').colorTemperature2rgb(kelvin);

Convert a color temperature in Kelvin to RGB. This method uses an approximation based on a curve fit of data from a sparse RGB to Kelvin mapping.

require('color-temperature').colorTemperature2rgbUsingTH(kelvin);

A JavaScript port of the original algorithm from Tanner Helland. This method is mainly here for comparison purposes. Generally, colorTemperature2rgb provides more accurate results.

require('color-temperature').rgb2colorTemperature(rgb);

Convert a color in RGB format to a color temperature in Kelvin.

License

The code is released under an MIT license.

Release History

• 0.1.0 Initial release