setChannel.js

import { validateChannel } from '../../util/channel';

/**
 * @memberof Image
 * @instance
 * @param {*} channel
 * @param {Image} image
 *
 * @return {this}
 */
export default function setChannel(channel, image) {
  this.checkProcessable('setChannel', {
    bitDepth: [8, 16],
  });

  image.checkProcessable('setChannel (image parameter check)', {
    bitDepth: [this.bitDepth],
    alpha: [0],
    components: [1],
  });

  if (image.width !== this.width || image.height !== this.height) {
    throw new Error('Images must have exactly the same width and height');
  }

  channel = validateChannel(this, channel);

  let ptr = channel;
  for (let i = 0; i < image.data.length; i++) {
    this.data[ptr] = image.data[i];
    ptr += this.channels;
  }

  return this;
}