image-js/src/image/transform/mask/mask.js

Image processing and manipulation in JavaScript

import { getThreshold as convertThreshold } from '../../../util/converter';
import Image from '../../Image';
import getThreshold from '../../utility/getThreshold';

const THRESHOLD = 'threshold';

/**
 * Creation of binary mask is based on the determination of a threshold
 * You may either choose among the provided algorithm or just specify a threshold value
 * @memberof Image
 * @instance
 * @param {object} [options]
 * @param {ThresholdAlgorithm|'threshold'} [options.algorithm='threshold']
 * @param {number} [options.threshold=0.5] - If the algorithm is 'threshold' specify here the value (0 to 1).
 * @param {boolean} [options.useAlpha=true] - Apply the alpha channel to determine the intensity of the pixel.
 * @param {boolean} [options.invert=false] - Invert the resulting image
 * @return {Image} - Binary image containing the mask
 */
export default function mask(options = {}) {
  let {
    algorithm = THRESHOLD,
    threshold = 0.5,
    useAlpha = true,
    invert = false,
  } = options;

  this.checkProcessable('mask', {
    components: 1,
    bitDepth: [8, 16],
  });

  if (algorithm === THRESHOLD) {
    threshold = convertThreshold(threshold, this.maxValue);
  } else {
    threshold = getThreshold.call(this, options);
  }

  let newImage = new Image(this.width, this.height, {
    kind: 'BINARY',
    parent: this,
  });

  let ptr = 0;
  if (this.alpha && useAlpha) {
    for (let i = 0; i < this.data.length; i += this.channels) {
      let value =
        this.data[i] +
        ((this.maxValue - this.data[i]) * (this.maxValue - this.data[i + 1])) /
          this.maxValue;
      if ((invert && value <= threshold) || (!invert && value >= threshold)) {
        newImage.setBit(ptr);
      }
      ptr++;
    }
  } else {
    for (let i = 0; i < this.data.length; i += this.channels) {
      if (
        (invert && this.data[i] <= threshold) ||
        (!invert && this.data[i] >= threshold)
      ) {
        newImage.setBit(ptr);
      }
      ptr++;
    }
  }

  return newImage;
}