[GRASS-user] Sky-view Factor and GeoTiff Histogram equalization (stretch)

Nikos Alexandris nik at nikosalexandris.net
Wed May 15 16:43:47 PDT 2013

Adrian Kirilov wrote:

>      Hello to the GRASS users,

Hello Adrian,

>      Does anybody know how to equalize, or stretch, the histogram of a
> raster?

In general, you can perform histogram equalisation on any GRASS raster map's 
color table by using the "r.colors" module and instruct the "-e" flag. The "-
e" flag (quoting from its manual) "is designed to work with any color table, 
both the floating point and the integer raster maps".

Please have a look in the manual (grass64): 
<http://grass.osgeo.org/grass64/manuals/r.colors.html> (or grass70:  

Note, this will operate on the color table associated with the raster map in 
question. It wont affect the map's actual pixel values.

> The last represents Sky-view Factor based on a DEM model. It is
> well-known visualization technique when looking for archaeological
> structures.
>      I have to do *minimum-maximum stretch of the histogram with saturation
> of minimum*. How to do this in GRASS? Any help will be highly appreciated!

I don't know what the "...with a saturation of minimum" means.  Maybe someone 
else that understands this stuff better can help.

Best, Nikos

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