index.js

import { isNodePattern, throwError } from '@jimp/utils';

/**
 * Applies a minimum color threshold to a greyscale image.  Converts image to greyscale by default
 * @param {number} options object
 *  max: A number auto limited between 0 - 255
 *  replace: (optional) A number auto limited between 0 - 255 (default 255)
 *  autoGreyscale: (optional) A boolean whether to apply greyscale beforehand (default true)
 * @param {number} cb (optional) a callback for when complete
 * @return {this} this for chaining of methods
 */
export default () => ({
  threshold({ max, replace = 255, autoGreyscale = true }, cb) {
    if (typeof max !== 'number') {
      return throwError.call(this, 'max must be a number', cb);
    }

    if (typeof replace !== 'number') {
      return throwError.call(this, 'replace must be a number', cb);
    }

    if (typeof autoGreyscale !== 'boolean') {
      return throwError.call(this, 'autoGreyscale must be a boolean', cb);
    }

    max = this.constructor.limit255(max);
    replace = this.constructor.limit255(replace);

    if (autoGreyscale) {
      this.greyscale();
    }

    this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, (x, y, idx) => {
      const grey =
        this.bitmap.data[idx] < max ? this.bitmap.data[idx] : replace;

      this.bitmap.data[idx] = grey;
      this.bitmap.data[idx + 1] = grey;
      this.bitmap.data[idx + 2] = grey;
    });

    if (isNodePattern(cb)) {
      cb.call(this, null, this);
    }

    return this;
  }
});