[GRASSLIST:1404] Re: r.patch geotiff-mosaic wrong color problem

[Frank Warmerdam]

Juergen Ambrosy wrote:
> Hello,
> 
> I'm very new to Grass GIS and have just compiled 5.0.2 and installed it 
> succesfully on Suse Linux 8.1.
> Now I'm trying to merge several Geotiff 8-bit images into one mosaic, but I 
> have problems with r.patch. The output shows only one image - first one - 
> with correct colors - the others are totally scrambled. Just overlaying one 
> by another it shows that the import with r.in.gdal was ok.
> I found that Mr. Neteler had some problems with r.patch, too. But if I use his 
> script i.image.mosaic (which uses r.mapcalc to patch the images) I get no 
> color output - although I set the map region big enough.
> 
> I'm kind of desperate now - anybody got an idea how to create a mosaic of 
> several geotiff images?

Juergen,

I imagine these 8bit images are using colormaps, and that they are different
colormaps.  So you won't be able to directly merge them.  What you need to
do is expend them to 24bit images (inside GRASS or outside) and then patch
those together.  I don't know the details of how to accomplish that though.

Good luck,
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