[gembud] Understanding LUTS tbls

Greetings..
Is there a tute I'm not finding to understanding the luts structure??
explaination:
I modified this.
http://mailman.unidata.ucar.edu/software/gempak/examples/image_to_grid/sat_landmask/
to produce this:
http://gempak.michiganwxsystem.com/satmaps/nat/ceir/latest.png
I figured because the command
GFUNC = sgt(irsat,112)
was only using items brighter then 112, that would equate to line 112
of the ir_upc3.tbl ...
wrong !! as there is not that many lines in the table
sow how on earth do you figure out what is what??
what I want to do is make my regular IR look the same
ramp from gray to bright white

--
-Jeff Lake
MichiganWxSystem.com
WeatherMichigan.net
TheWeatherCenter.net