1994.09.16 17:47 "Re: TIFF ReferenceBlackWhite Field Versus Leffler's TIFF Software", by Sam Leffler
the spec explicitly says that the ReferenceBlackWhite tag is to be used with RGB and YCbCr images only. So if you find this tag in a file, SamplesPerPixel ought to be 3.
Is it so, then, that there can be no extra samples if the ReferenceBlackWhite tag is used? I am skeptical.
The colorimetry tags are not applied to extra samples.