I also notice, upon correcting this, that the BlackIs1 parameter is
actually being set to the opposite of what it "should" be. "Should" in
the sense of producing a pdf that displays as expected in the usual pdf
readers. I can't quite figure out why, though: after reading the TIFF
and PDF specs, it seems that the current implementation is correct; but
the results are incorrect according to the interpretation of all the pdf
readers I have access to.