These are all the possible values for the IG_ISIS_TAG_FILETYPE tag.

Values:

IG_ISIS_FILETYPE_TIFF	TIFF.
IG_ISIS_FILETYPE_PDA	PDA.
IG_ISIS_FILETYPE_PCX	PCX.
IG_ISIS_FILETYPE_PICT	PICT.
IG_ISIS_FILETYPE_DCX	DCX.
IG_ISIS_FILETYPE_GIF	GIF.
IG_ISIS_FILETYPE_BMP	BMP.
IG_ISIS_FILETYPE_FILENET	IMG.
IG_ISIS_FILETYPE_JPEG	JPEG.
IG_ISIS_FILETYPE_JP2	JPEG 2000.
IG_ISIS_FILETYPE_CALS	CALS.
IG_ISIS_FILETYPE_DISCORP	CMP.
IG_ISIS_FILETYPE_MODCA	MDA, IBM's MO:DCA.
IG_ISIS_FILETYPE_TG4	TG4, Tiled G4.
IG_ISIS_FILETYPE_PDF	PDF, portable document format.
IG_ISIS_FILETYPE_PLEXUSTIFF	Plexus TIFF format.
IG_ISIS_FILETYPE_JBIG	JBG, JBIG data stream.
IG_ISIS_FILETYPE_PNG	PNG.