image-js/lib/image/utility/combineChannels.js

Image processing and manipulation in JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = combineChannels;
var _Image = _interopRequireDefault(require("../Image"));
var _model = require("../model/model");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * Create a new grey Image by combining the channels of the current image.
 * @memberof Image
 * @instance
 * @param {function} method
 * @param {object} [options]
 * @param {boolean} [options.mergeAlpha=false]
 * @param {boolean} [options.keepAlpha=false]
 * @return {Image}
 */
function combineChannels(method = defaultCombineMethod, options = {}) {
  let {
    mergeAlpha = false,
    keepAlpha = false
  } = options;
  mergeAlpha &= this.alpha;
  keepAlpha &= this.alpha;
  this.checkProcessable('combineChannels', {
    bitDepth: [8, 16]
  });
  let newImage = _Image.default.createFrom(this, {
    components: 1,
    alpha: keepAlpha,
    colorModel: _model.GREY
  });
  let ptr = 0;
  for (let i = 0; i < this.size; i++) {
    // TODO quite slow because we create a new pixel each time
    let value = method(this.getPixel(i));
    if (mergeAlpha) {
      newImage.data[ptr++] = value * this.data[i * this.channels + this.components] / this.maxValue;
    } else {
      newImage.data[ptr++] = value;
      if (keepAlpha) {
        newImage.data[ptr++] = this.data[i * this.channels + this.components];
      }
    }
  }
  return newImage;
}
function defaultCombineMethod(pixel) {
  return (pixel[0] + pixel[1] + pixel[2]) / 3;
}