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An RGB-HC histogram library for same-origin images
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An RGB-HC histogram library for same-origin images

demonstrator gh-page:

Client-side installation: simply grab the library from the release directory on github, or use bower to install: bower install rgbanalyse.

Node package installation: npm install rgbanalyse.


The library sets up an object with the following properties/functions:

  • defaults - a settings object with default values as analysis options.
  • analyse(img,[options]) - performs image analysis on an image element, with optional tweaks.
  • computeHSL(R,G,B) - convert RGB to HSL (note this requires normalised RGB values).
  • computeRGB(H) - convert HSL (no S/L right now) to RGB, H in range [0,6.28].
  • analyse(img,[options]) - convert HSL to rgb (plain {r,g,b}, using range [0,255]).

The defaults object can be set prior to running analyses, and currently supports the following properties:

  • neutrals - 10 - integer from 0 to 255, indicating the how close together {r,g,b} coordinates must be to be considered neutral
  • smoothing - 5 - used to smooth the hue spectrum when determining dominant hues. (value is distance from mean)
  • distance - 10 - minimum distance between recording two hues to end up recorded as major hues (value can range from 0 to 628)

The analyse function returns a two property object. The first is the analysis property, which houses:

  • rgb - A 3 component object with the histographical data for r, g and b.
  • RGB - A 3 component object with the histographical data for R, G,a nd B.
  • hsl - An object with the histographical data for h, and .dominant, a sorted array of {H,strength} major hues.
  • average - the weighted averages for r, g, b, R, G, B, and h.
  • maxima - the absolute maxima for r, g, b, R, G, B, and h.

The second is the visualization property, available only when using the libary in the browser, which houses image source data-uris for:

  • histogram - a 256 x 256 combined rgb histogram
  • spectrum.histogram - a 360 x 200 hues histogram
  • spectrum.spectogram - a 360 x 50 spectrogram


This code is released as Public Domain code. In jurisdictions that do not recognise the public domain, this code is to be considered under an MIT license (

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