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       rgb3toppm - combine three portable graymaps into one portable pixmap
       rgb3toppm redpgmfile greenpgmfile bluepgmfile
       Reads three portable graymaps as input.  Combines them and produces one
       portable pixmap as output.
       ppmtorgb3(1), pgmtoppm(1), ppmtopgm(1), ppm(5), pgm(5)
       Copyright (C) 1991 by Jef Poskanzer.
                               15 February 1990                   rgb3toppm(1)