2003.09.02 05:43 "[Tiff] Reading and writing to memory.", by Väinö Järvelä
Can't you just read in one tile or strip at a time, manipulate it and write it out to the new file.
The TIFFReadTile, TIFFReadRawTile (uncompressed data is returned) should do it?
Actually this is how i'm doing it right now. But writing it to memory would be faster as i'm going to run the image through multiple functions that use the whole image.