io.imsave() problems with passing arguments to plugin "freeimage"

Hallo! To read uncompressed TIFF files I use the freeimage plugin. The reading works great but since last week I need to save a summed Image. I used the io.imsave() with the freeimage plugin but by default it writs a compressed TIFF file. The freeimage documentation provides Flags to use for different compressions or for a non compressed type (TIFF_NONE). Can someone tell me how to pass theses Flags to the plugin? I saw that Christophs 'tifffile' plugin does the job but still I would like to know how to use the freeimage plug-n for it. Thanks! Siggi