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node-potrace

A NodeJS-compatible fork of Potrace in JavaScript with some additions, which is in turn a port of the original Potrace — a tool for tracing bitmaps.

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Example and demo

Original imagePotrace outputPosterized output

(Example image inherited from online demo of the browser version)

Usage

Install

npm install potrace

Basic usage

var potrace = require('potrace'),
    fs = require('fs');

potrace.trace('./path/to/image.png', function(err, svg) {
  if (err) throw err;
  fs.writeFileSync('./output.svg', svg);
});

You can also provide a configuration object as a second argument.

var params = {
  background: '#49ffd2',
  color: 'blue',
  threshold: 120
};

potrace.trace('./path/to/image.png', params, function(err, svg) {
  /*...*/
});

If you want to run Potrace algorithm multiple times on the same image with different threshold setting and merge results together in a single file - posterize method does exactly that.

potrace.posterize('./path/to/image.png', { threshold: 180, steps: 4 }, function(err, svg) {
  /*...*/
});

// or if you know exactly where you want to break it on different levels

potrace.posterize('./path/to/image.png', { steps: [40, 85, 135, 180] }, function(err, svg) {
  /*...*/
});

Advanced usage and configuration

Both trace and posterize methods return instances of Potrace and Posterizer classes respectively to a callback function as third argument.

You can also instantiate these classes directly:

var potrace = require('potrace');

// Tracing

var trace = new potrace.Potrace();

// You can also pass configuration object to the constructor
trace.setParameters({
  threshold: 128,
  color: '#880000'
});

trace.loadImage('path/to/image.png', function(err) {
  if (err) throw err;

  trace.getSVG(); // returns SVG document contents
  trace.getPathTag(); // will return just <path> tag
  trace.getSymbol('traced-image'); // will return <symbol> tag with given ID
});

// Posterization

var posterizer = new potrace.Posterize();

posterizer.loadImage('path/to/image.png', function(err) {
  if (err) throw err;
  
  posterizer.setParameter({
    color: '#ccc',
    background: '#222',
    steps: 3,
    threshold: 200,
    fillStrategy: potrace.Posterize.FILL_MEAN
  });
  
  posterizer.getSVG();
  // or
  posterizer.getSymbol('posterized-image');
});

Callback function provided to loadImage methods will be executed in context of the Potrace/Posterizer instance, so if it doesn't go against your code style - you can just do

new potrace.Potrace()
  .loadImage('path/to/image.bmp', function() {
    if (err) throw err;
    this.getSymbol('foo');
  });

Jimp module is used on the back end, so first argument accepted by loadImage method could be anything Jimp can read: a Buffer, local path or a url string. Supported formats are: PNG, JPEG or BMP. It also could be a Jimp instance (provided bitmap is not modified)

Parameters

Potrace class expects following parameters:

Posterizer class has same methods as Potrace, in exception of .getPathTag(). Configuration object is extended with following properties:

Notes:

Thanks to

License

The GNU General Public License version 2 (GPLv2). Please see License File for more information.