[GRASS-user] r.colors- transparent, HSB color

Dwight Needels needels at translucida.com
Wed Mar 18 20:33:13 EDT 2009


I have been using r.mapcalc to set various combinations of colors in a  
13-color DRG to null to allow the map to be displayed as a series of  
overlays on top of other maps. It occurs to me that it would be useful  
to be able to accomplish this using r.colors by defining the color of  
specific values (or ranges of values) as transparent. Unfortunately, I  
have not been able to find a way to do this.

Is it possible to define a color as transparent without changing the  
pixels to null pixels?

If not, would this be technically feasible in a future version of GRASS?

Is there a different approach that would allow me to generate multiple  
examples of partially transparent maps without the overhead of  
duplicating the raster map multiple times?

Secondly, is it possible to define colors within GRASS using HSB (or  
HSL) instead of RGB values? There are some kinds of calculations, for  
example reducing the saturation of all colors by a given amount, that  
are easier to accomplish in the HSB domain.



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