node-retricon

create indenticon-like image hashes styled like Github and Gravatar (retro) avatars WITHOUT USING NODE-CANVAS AND CAUSING YOUR INSTALL TO FAIL DUE TO MISSING libCairo-dev

Example

var retricon = require('retricon');
var fmt = require('util').format;

console.log(fmt("<img alt='kibo' src='%s' />", retricon('kibo', {pixelSize: 16}).toDataURL()));

Output

<img alt='kibo' src='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAFAAAABQCAYAAACOEfKtAAAABmJLR0QA/wD/AP+gvaeTAAAA7UlEQVR4nO3asQ3CQBAAwX9kiVqogP5DV0AtRFDEBCfDTm6/vbrodfv5un/WoPPx3vL89PffJg//BQVEBUQFRAVEBUQFRAVEBUQFRAVEBUQFRAVEBUR7+j7t6ppAVEBUQFRAVEBUQFRAVEBUQFRAVEBUQFRAVEBUQES7eWv5ft70fqCe3wSiAqICogKiAqICogKiAqICogKiAqICogKiAqICouPf9wP1/5tAVEBUQFRAVEBUQFRAVEBUQFRAVEBUQFRAVEBUQHToC66+39d94LACogKiAqICogKiAqICogKiAqICogKiAqICogKiL2SGHPJ+jTmVAAAAAElFTkSuQmCC' />

API

retricon(str, pixelSize, border)

• str: string - username, email, or other string to hash
• opts: object
  • pixelSize: int (default: 10) - width and height in pixels to render each tile
  • bgColor: mixed (default: null) - color to fill background
    • null for transparent
    • 0 or 1 for first (brighter) or second (darker) random color
    • CSS hex colorspec (e.g. '#F0F0F0')
  • pixelPadding: int (default: 0) - background pixels within the border of each rendered tile. Use negative values for overlap, as in Github- style identicons
  • imagePadding: int (default: 0) - padding around outside of image
  • tiles: int (default: 5) - number of tiles wide and high to render
  • minFill: float (default: 0.3) - proportion of tiles which must be filled. Hash chaining is used to satisfy fill criteria.
  • maxFill: float (default: 0.9) - maximum proportion of tiles which may be filled.
  • pixelColor: mixed (default: 0) - color to fill foreground tiles. All bgColor values are valid for pixelColor.

Returns a Canvas object containing the rendered image.

Styles

All style options can be changed, but retricon comes with several prerolled styles:

default

Coloured tiles against a transparent background.

mini

Tiny 3x3 identicons with padded tiles.

gravatar

Not a perfect replica of Gravatar's "retro" style, but close.

mono

Black tiles on a grey background.

mosaic

Padded tiles, for a mosaic effect.

window

Transparent, padded tiles against coloured background.

github

Faithful replica of Github's identicon style.

custom example

Absurd settings, such as: { pixelSize: 8, pixelPadding: -2, tiles: 30, pixelColor: 0, bgColor: 1 } can still yield quite serviceable results.

Algorithm

The input string is converted to a buffer of UTF-8 bytes. A one-byte iterator is appended to this, initialized at zero, for hash chaining. The buffer is passed through SHA-512, and the output buffer is iteratively XORed to produce a final buffer of only the number of required bytes (currently eighteen). The first six bytes are taken as RGB values for the colours. The remaining bytes are quantized to boolean values at a threshold of 127. If a minimum proportion of the booleans are true, but not more than the maximum proportion, the hash is accepted. Otherwise, the iterator is incremented, and the process repeated.

The array of booleans is taken to be a row-major array covering the left half of the final image. It is reflected about the central vertical axis (or column, for odd-order arrays) which is then rendered as the final visual hash.

Known Limitations

• 30x30 tile images are the maximum which can be generated from SHA-512.