image-js/lib/image/utility/getChannel.js

Image processing and manipulation in JavaScript

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = getChannel;
var _channel = require("../../util/channel");
var _Image = _interopRequireDefault(require("../Image"));
var _model = require("../model/model");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
/**
 * Create a grey image based on the selected channel
 * @memberof Image
 * @instance
 * @param {number|string} channel
 * @param {object} [options]
 * @param {boolean} [options.keepAlpha]
 * @param {boolean} [options.mergeAlpha]
 * @return {Image} A grey image with the extracted channel
 */
function getChannel(channel, options = {}) {
  let {
    keepAlpha = false,
    mergeAlpha = false
  } = options;
  keepAlpha &= this.alpha;
  mergeAlpha &= this.alpha;
  this.checkProcessable('getChannel', {
    bitDepth: [8, 16]
  });
  channel = (0, _channel.validateChannel)(this, channel);
  let newImage = _Image.default.createFrom(this, {
    components: 1,
    alpha: keepAlpha,
    colorModel: _model.GREY
  });
  let ptr = 0;
  for (let j = 0; j < this.data.length; j += this.channels) {
    if (mergeAlpha) {
      newImage.data[ptr++] = this.data[j + channel] * this.data[j + this.components] / this.maxValue;
    } else {
      newImage.data[ptr++] = this.data[j + channel];
      if (keepAlpha) {
        newImage.data[ptr++] = this.data[j + this.components];
      }
    }
  }
  return newImage;
}