code: function trim (threshold) {
    if (!is.defined(threshold)) {
      this.options.trimThreshold = 10;
    } else if (is.number(threshold) && threshold > 0) {
      this.options.trimThreshold = threshold;
    } else {
      throw is.invalidParameterError('threshold', 'number greater than zero', threshold);
    }
    return this;
  }
docs: Trim "boring" pixels from all edges that contain values similar to the top-left pixel.
  The `info` response Object will contain `trimOffsetLeft` and `trimOffsetTop` properties.
  @param {Number} [threshold=10] the allowed difference from the top-left pixel, a number greater than zero.
  @returns {Sharp}
  @throws {Error} Invalid parameters