[GRASS-user] Extracting grey features from an image

[Christian Schwartze]

Use r.mask as already done to identify your grey values only, then apply 
r.mapcalc "new_raster=if(MASK,orig_raster,null())".

Christian.

--------------------------------------------------
From: "baobazz" <baobazz at hotmail.fr>
Sent: Thursday, May 27, 2010 11:59 AM
To: <grass-user at lists.osgeo.org>
Subject: [GRASS-user] Extracting grey features from an image

>
> Hello
>
> I've got a black and white image with some grey features on it
>
> I'd like to create a new image containing only these features so I can
> vectorize them
>
> i think that I have to use
> r.mask
> r.mapcalc
> or
> r.reclass
>
> r.describe raster
> returns me
> 0-121 123 125-127 132-255
>
> I created a mask of my image
> r.mask input=image maskcats="0 thru 121" -i
> -i to invert the maskcats range
>
> Only the grey features appear.
>
> So, my grey features seem to have the 0-121 range category of values.
>
> Considering that, how can I manage to create a raster map based only on
> these values.
>
> I used r.reclass like this:
> r.reclass input=raster output=rasterRec
>>0 thru 121=1 black
>>*=NULL
> But I didn't get any good result...
>
> Any help would be greatly appreciated!
>
>
>
> -- 
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> http://osgeo-org.1803224.n2.nabble.com/Extracting-grey-features-from-an-image-tp5107822p5107822.html
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