Whats about "Photometric Interpretation"

[Crashdown]

Hello,
at first thanx for your nice software. I like it really.

Now my Question/Problem.
i have to change 1 bit tiff from 600x600dpi to 720x720dpi
that works fine with nconvert and xnconvert.
now the photometric interpretation set in the original file to
white=0
after the convertation the falue is
black=1
If i look with xnview, the file looks normal but the 600dpi file are printed normal and the new 720dpi file the black is inverted.
Now maybe i have found a workaround. If i add the values in xnconvert and say iptc/XMP and uncheck the option "keep and add new value" the value in photometric interpretation is like from the original file. I have no printing machine here and have to test it tomorrow but it looks not bad so far.
My question is, how can i modify the value in xnconvert?
Can you help me out with this?

Thanx a lot
cheers
Sven