phash-imagemagick/lib/compare.js

get and compare perceptual hashes (as computed by imagemagick)

// see http://www.fmwconcepts.com/misc_tests/perceptual_hash_test_results_510/index.html
exports.THRESHOLD_COLOR = 21;
exports.THRESHOLD_GRAY = 1.2;

function toArray(x) {
  return x.match(/[\-0-9]{4}/g).map(function(x) {
    return parseInt(x, 10) / 100;
  });
}

exports.compare = function(obj1, obj2) {
  var x = toArray(obj1.pHash),
    y = toArray(obj2.pHash),
    sse = 0;

  for (var i = 0; i < x.length; i++) {
    sse += Math.pow(x[i] - y[i], 2);
  }

  return sse;
};

exports.eq = function() {
  for (var i = 0; i < arguments.length; i++) {
    for (var j = i + 1; j < arguments.length; j++) {
      var sse = exports.compare(arguments[i], arguments[j]);
      var threshold;
      if (arguments[i].colorType === arguments[j].colorType) {
        //`identify -list Type` for the list of Type
        threshold = /^Gray/.test(arguments[i].colorType)
          ? exports.THRESHOLD_GRAY
          : exports.THRESHOLD_COLOR;
      } else {
        threshold = exports.THRESHOLD_COLOR;
      }
      if (sse > threshold) {
        return false;
      }
    }
  }

  return true;
};