Re: [GRASS-user] output values of r.composite
Thanks for clarifying. We always have to answer claims such as: "...but Arc* does like this...". We noticed the problem when compositing Landsat tiles in an area with very uniform landscape. The slight shift in RGB values with the default level=32 led to many adjacent pixels getting the same color value, and the result looked very "blocky". On 30-Jan-15 2:33 PM, Glynn Clements wrote: Markus Metz wrote: On Wed, Jan 28, 2015 at 10:34 PM, Micha Silver wrote: 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? Because the number of levels to be used for each component is by default 32, not 256 [0]. You can use levels=256 if you want 256 levels. But the resulting map will have a very large colour table (65536 rules), which will negatively affect the performance of anything which reads the colour table. Which is why the default is 32 levels rather than 256. -- Moshav Idan D.N. Arava, 86840 cell: 0523-665918 http://www.surfaces.co.il ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] output values of r.composite
Markus Metz wrote: > On Wed, Jan 28, 2015 at 10:34 PM, Micha Silver wrote: > > 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? > > Because the number of levels to be used for each component is by > default 32, not 256 [0]. You can use levels=256 if you want 256 levels. But the resulting map will have a very large colour table (65536 rules), which will negatively affect the performance of anything which reads the colour table. Which is why the default is 32 levels rather than 256. -- Glynn Clements ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] output values of r.composite
Hi Markus: Thanks for the quick reply. That indeed was my problem: misunderstanding the implications of the levels param. Best, Micha On 29-Jan-15 12:28 PM, Markus Metz wrote: On Wed, Jan 28, 2015 at 10:34 PM, Micha Silver wrote: 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? Because the number of levels to be used for each component is by default 32, not 256 [0]. Markus M [0] http://grass.osgeo.org/grass70/manuals/r.composite.html 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 ... 100% r.composite complete. Raster map 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=60; y=90 # 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 60|90||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 60|90||12712|065:106:098<< GRASS 7.0.0svn (UTM33N):~/Downloads > Thanks, Micha ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user This mail was received via Mail-SeCure System. -- Moshav Idan D.N. Arava, 86840 cell: 0523-665918 http://www.surfaces.co.il ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] output values of r.composite
On Wed, Jan 28, 2015 at 10:34 PM, Micha Silver wrote: > 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? Because the number of levels to be used for each component is by default 32, not 256 [0]. Markus M [0] http://grass.osgeo.org/grass70/manuals/r.composite.html > > 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 ... > 100% > r.composite complete. Raster map 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=60; y=90 > > # 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 > 60|90||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 > 60|90||12712|065:106:098<< > GRASS 7.0.0svn (UTM33N):~/Downloads > > > Thanks, > Micha > > > ___ > grass-user mailing list > grass-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
[GRASS-user] output values of r.composite
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? 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 ... 100% r.composite complete. Raster map 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=60; y=90 # 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 60|90||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 60|90||12712|065:106:098<< GRASS 7.0.0svn (UTM33N):~/Downloads > Thanks, Micha ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user