Colortable mystery: black isn't black

Ronald Wiemer ronald at
Fri May 7 09:14:03 EDT 1993

I had about the same problem when converting an Xwindowdump to pnm.
Instead of black not being real black, white appeared to be not really white.
I tried to figure out what xwdtopnm does, and it appeared that the program
thought the maximum (X) value of RGB should be 65535. In our case, the maximum
value was 65280!!!. When I changed the 65535 to 65280 at the appropriate places in the program, everything worked fine. I can imagine that this can also 
cause your blacks not being real blacks. BTW, we also have a program, called
xpr, wich can make (B&W)postscript out of an X-windowdump.

Ronald Wiemer,

ARCHIS-centre of expertise,
Amersfoort, The Netherlands.

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