code: function boolean (operand, operator, options) {
    this.options.boolean = this._createInputDescriptor(operand, options);
    if (is.string(operator) && is.inArray(operator, ['and', 'or', 'eor'])) {
      this.options.booleanOp = operator;
    } else {
      throw new Error('Invalid boolean operator ' + operator);
    }
    return this;
  }
docs: Perform a bitwise boolean operation with operand image.
  
  This operation creates an output image where each pixel is the result of
  the selected bitwise boolean `operation` between the corresponding pixels of the input images.
  
  @param {Buffer|String} operand - Buffer containing image data or String containing the path to an image file.
  @param {String} operator - one of `and`, `or` or `eor` to perform that bitwise operation, like the C logic operators `&`, `|` and `^` respectively.
  @param {Object} [options]
  @param {Object} [options.raw] - describes operand when using raw pixel data.
  @param {Number} [options.raw.width]
  @param {Number} [options.raw.height]
  @param {Number} [options.raw.channels]
  @returns {Sharp}
  @throws {Error} Invalid parameters