Hot answers tagged rgb
Your fire hydrants will have a very unique spectral signature, therefore I would use supervised maximum likelihood classification to classify your raster. An alternative is to run an ISODATA algorithm for an unsupervised approach. Try the following (partial) workflow: Open Iso Cluster Unsupervised Classification in ArcGIS Enter ALL 3 bands (i.e. R, G, B) ...
Vegetation extraction is a bit more complex than running the spatial analysis tools that you named. For better results I would suggest the following: run analysis on a 4 band image (e.g. R,G,B,NIR) change image to be symbolized as 432 for RGB not 321 create training samples that represent vegetation and run a supervised classification These steps will ...
Herein lies a misunderstanding: "...that is done separately for each band and not for a specific colour." "Each band" and "specific colour" are in fact the same thing. That is, it is the values in each band that, when combined together, make a specific colour. For example the RGB triplet 255,0,0 is the specific colour of pure red, comprised of band-red at ...
Seems the bugs you mention with GRASS are a known issue with the standalone version. Nothing to do with mapcalc... this was a packaging issue that has been solved on osgeo4w and now is just needed to wait for updated standalone installers. Réf : https://hub.qgis.org/issues/8529
I am guessing those mysterious spaces after G:\ are your attempt to make your file path anonymous? Your output file name is invalid. "cml.tif&_nred" is not a valid file geodatabase name. You cannot have symbols like "." or "&" in the raster name. A valid name would by something like "cml_tif_nred". Have a look at the model only Parse Path tool.
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