async getImage(index = 0) {
    const ifd = await this.requestIFD(index);
    return new GeoTIFFImage(
      ifd.fileDirectory, ifd.geoKeyDirectory,
      this.dataView, this.littleEndian, this.cache, this.source,
    );
  }
Get the n-th internal subfile of an image. By default, the first is returned.

@param {number} [index=0] the index of the image to return.
@returns {Promise<GeoTIFFImage>} the image at the given index