[GRASS-user] RE: r.mapcalc on RGB composite

Jarle Pedersen mybigb at gmail.com
Wed May 9 11:37:07 EDT 2007

Regarding the earlier questions posed, I figured out the correct syntax  
for r.mapcalc. However, if anyone care to, I'd still like to know why this  
shift in coloration happens.

------- Videresendt melding -------
Fra: "Jarle Pedersen" <mybigb at gmail.com>
Til: grassuser at grass.itc.it
Emne: r.mapcalc on RGB composite
Dato: Wed, 09 May 2007 16:19:55 +0200

Hi again folks. Next noobie question:

I'm trying to use r.mapcalc to set the sea of some landsat imagery to
null-values in order for me to view my much nicer background. My workflow
was as follows:

1. r.composite -d -c red="b1" green="b4" blue="b7" levels=32 output="RGB"
2. r.mapcalc "RGB_water=if(dem=0,null(),RGB)"

This does not fill the water with null, rather keeps the original values
and distorts the colors to yellow/greenish output.

What am I missing?

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