[GRASS-user] Extracting grey features from an image

[baobazz]

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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