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Hi Markus:<br>
Thanks for the quick reply. That indeed was my problem:
misunderstanding the implications of the levels param.<br>
Best,<br>
Micha<br>
<div class="moz-cite-prefix">On 29-Jan-15 12:28 PM, Markus Metz
wrote:<br>
</div>
<blockquote
cite="mid:CAG+h=FGP-C_69AJu7Gm92FrBtb5q=kHyhnmuhSZu2BKmc1e_Yg@mail.gmail.com"
type="cite">
<pre wrap="">On Wed, Jan 28, 2015 at 10:34 PM, Micha Silver <a class="moz-txt-link-rfc2396E" href="mailto:micha@arava.co.il"><micha@arava.co.il></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">When I use r.composite to create, i.e., a false_color composite from three
Landsat bands, the RGB values in the composite are slightly different than
the values in the original bands. Why is that?
</pre>
</blockquote>
<pre wrap="">
Because the number of levels to be used for each component is by
default 32, not 256 [0].
Markus M
[0] <a class="moz-txt-link-freetext" href="http://grass.osgeo.org/grass70/manuals/r.composite.html">http://grass.osgeo.org/grass70/manuals/r.composite.html</a>
</pre>
<blockquote type="cite">
<pre wrap="">
Here's an example:
# Import three bands
GRASS 7.0.0svn (UTM33N):~/Downloads > for b in 2 3 4; do r.in.gdal --o
input=LE71830542003069SGS00_B${b}.TIF output=b${b}; done
r.in.gdal complete.
# Create composite
GRASS 7.0.0svn (UTM33N):~/Downloads > r.composite r=b4 g=b3 b=b2
out=false_color --o
Creating color table for output raster map...
100%
Writing raster map <false_color>...
100%
r.composite complete. Raster map <false_color> created.
GRASS 7.0.0svn (UTM33N):~/Downloads > r.info -g false_color
north=1065915
south=856485
east=731415
west=497985
# Choose a point for testing
GRASS 7.0.0svn (UTM33N):~/Downloads > x=600000; y=900000
# and query with r.what
GRASS 7.0.0svn (UTM33N):~/Downloads > r.what -n map=b4,b3,b2 coord=${x},${y}
easting|northing|site_name|b4|b3|b2
600000|900000||67|108|96 <<=============
GRASS 7.0.0svn (UTM33N):~/Downloads > r.what -n -r map=false_color
coord=${x},${y}
easting|northing|site_name|false_color|false_color_color
600000|900000||12712|065:106:098 <<============
GRASS 7.0.0svn (UTM33N):~/Downloads >
Thanks,
Micha
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</pre>
</blockquote>
<pre wrap="">
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</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Moshav Idan
D.N. Arava, 86840
cell: 0523-665918
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il">http://www.surfaces.co.il</a></pre>
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