[GRASS-user] Is mosaicing 24 bit images possible in Grass 6.2?

[Hamish]

Nagesh wrote:
> I intend to mosaic two 24 bit images in LAT LON location.
> I imported a 24 bit coloured PNG image in Grass using
> r.in.gdal in an x-y location.
> GRASS treated it as a combination of three 8 bit images,
> one for red, one for green, and one for blue and imported
> them as three separate maps.
> 
> After going through the archives, I tried to use r.patch to
> combine all the three components.

I think you mean to use r.composite there, not r.patch.

> The output of which wasn't a 24bit image but was only
> one of the components. (Not coloured)

the first map was "patched" over top of the other two.
 
> d.rgb module does display a coloured 24 bit image after
> inputing the three components to it.

Correct.
 
> I geocoded them to get non-coloured 8 bit geocoded images
> in the target location.
> 
> I did the same for the second 24 bit image.
> Mosaicing works fine(i.image.mosaic), but i need to use 8
> bit images(24 bit images converted to 8 bit images prior to
> importing, using xv; resolution weak)
> or any one of the 8 bit components of a 24 bit image.
> 
> Is there a way to mosaic 24 bit images and to output it as
> a single 24 bit image?

# expand region to cover both image regions
g.region rast=map1.red,map2.red

# merge bands together
for COLOR in red green blue ; do
  r.patch in=map1.${COLOR},map2.${COLOR} out=map.${COLOR}
end

# display mosaicked image
d.rgb r=map.red g=map.green b=map.blue

You will lose information if you use r.composite, best to keep bands separate unless you absolutely must combine them. (e.g. for NVIZ color drape)


Hamish