Hello to the GRASS users,
Does anybody know how to equalize, or stretch, the histogram of a raster? 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! Thank you!
Greetings,
Adrian Kirilov
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:
<http://grass.osgeo.org/grass70/manuals/r.colors.html>\).
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
Adrian wrote:
> 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!
Nikos:
I don't know what the "...with a saturation of minimum"
means. Maybe someone else that understands this stuff better
can help.
the "stretch" sounds a bit like linear 0.0-1.0 normalization to me.
for an application, see also the i.landsat.rgb module.
Hamish
Adrian wrote:
> > 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!
Nikos:
> I don't know what the "...with a saturation of minimum"
> means. Maybe someone else that understands this stuff better
> can help.
Hamish:
the "stretch" sounds a bit like linear 0.0-1.0 normalization to me.
for an application, see also the i.landsat.rgb module.
Also, there is "r.rescale.eq". Maybe also of interest here? @Adrian,
r.rescale.eq will operate on the actual pixel values and create a new raster
map as requested, e.g.:
r.rescale.eq input=InputMap output=RescaledMap to=0.0,1.0
Best, Nikos