I'm trying to run a supervised classification on a Landsat8 multi-band raster in ArcMap. Every time I run the classification it returns Error 010108 and Error 010067. The 010108 error says "The number of bands in the signature file is less than the number of bands in the raster", so I tried using the Composite Bands tool to compress my raster to a single band, but it still returns a raster with the same number of bands as the original. Is compressing my multi-band raster to a one band raster the right solution? If so, how do I do so without extracting bands individually? I can't find any other suggested tool than Composite Bands and it's still just producing an identical multi-band raster.