image-js/lib/image/compute/colorHistogram.js

Image processing and manipulation in JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = getColorHistogram;
var _newArray = _interopRequireDefault(require("new-array"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * @memberof Image
 * @instance
 * @param {object} [options]
 * @param {boolean} [options.useAlpha=true]
 * @param {number} [options.nbSlots=512]
 * @return {number[]}
 */
function getColorHistogram(options = {}) {
  let {
    useAlpha = true,
    nbSlots = 512
  } = options;
  this.checkProcessable('getColorHistogram', {
    bitDepth: [8, 16],
    components: [3]
  });
  let nbSlotsCheck = Math.log(nbSlots) / Math.log(8);
  if (nbSlotsCheck !== Math.floor(nbSlotsCheck)) {
    throw new RangeError('nbSlots must be a power of 8. Usually 8, 64, 512 or 4096');
  }
  let bitShift = this.bitDepth - nbSlotsCheck;
  let data = this.data;
  let result = (0, _newArray.default)(Math.pow(8, nbSlotsCheck), 0);
  let factor2 = Math.pow(2, nbSlotsCheck * 2);
  let factor1 = Math.pow(2, nbSlotsCheck);
  for (let i = 0; i < data.length; i += this.channels) {
    let slot = (data[i] >> bitShift) * factor2 + (data[i + 1] >> bitShift) * factor1 + (data[i + 2] >> bitShift);
    if (useAlpha && this.alpha) {
      result[slot] += data[i + this.channels - 1] / this.maxValue;
    } else {
      result[slot]++;
    }
  }
  return result;
}