code: function toColourspace (colourspace) {
    if (!is.string(colourspace)) {
      throw new Error('Invalid output colourspace ' + colourspace);
    }
    this.options.colourspace = colourspace;
    return this;
  }
docs: Set the output colourspace.
  By default output image will be web-friendly sRGB, with additional channels interpreted as alpha channels.
  @param {String} [colourspace] - output colourspace e.g. `srgb`, `rgb`, `cmyk`, `lab`, `b-w` [...](https://github.com/libvips/libvips/blob/master/libvips/iofuncs/enumtypes.c#L568)
  @returns {Sharp}
  @throws {Error} Invalid parameters