When I georeference a map of vegetation types (about 20 colours, each representing a certain vegetation) the quality of the georeferenced map is really bad and some colours have changed (e.g. black becomes white), which makes it almost impossible to recognise certain types.
I did the "usual" procedure: transformation type: linear, method: nearest neighbor. For source I tried jpeg & tiff, same bad result.
Any suggestions how to improve the quality of the map and the originality of the map?