TIFF FX is from ITU T.37 and IETF RFCs 2301-2305.

S: minimal black-and-white mode, using binary MH compression [T.4]
F: extended black-and-white mode, using binary MH, MR and MMR compression [T.4, T.6]
J: lossless JBIG black-and-white mode, with JBIG compression [T.85, T.82]
C: lossy color and grayscale mode, using JPEG compression [T.42, T.81]
L: lossless color and grayscale mode, using JBIG compression [T.43, T.82]
M: mixed raster content mode [T.44], using a combination of existing compression methods.

Regards,
Technical Support Team