since nobody else has any ideas, i'll give it a whirl...
what you can do:
Use a RasterCellCoercer to convert your rastercells to polygons and then a dissolver to dissolve them by value.
This might become slow and memoryintense though ..
you can get some ideas about raster2vector operations in fme here:
and more general info about raster hacking here:
also see this from Perdue..looks helpful... let us know if this helps..
Hi Min Oo, you can explain more you process to raster to vector ? what softwares you use ?