[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! -- View this message in context: http://osgeo-org.1803224.n2.nabble.com/Extracting-grey-features-from-an-image-tp5107822p5107822.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Extracting grey features from an image
On 05/27/2010 12:59 PM, baobazz wrote: 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 If I understand you correctly, you have a grey-scale raster (values from 0-255) which is displayed in three colors, black, grey and white? From the above there are cells with values from 0-255, the only values that do *not* appear are 122, 124, and 128-131. Perhaps you can run r.describe -1 ( or r.stats -ap ) to output all the categories, one per line, to have a clear idea of what the original contains. Now, if you need to separate out raster cells with certain category values, then vectorize it, you could do, i.e.: # extract only values between 125 and 127 r.mapcalc grey_raster=if(orig_rast=125 and orig_rast=127, 1, null() ) # All cells from 125-127 get the value '1' in the new raster. All others are null. # convert to vector r.to.vect in=grey_raster out=grey_polygons feature=area This will clump together into a vector of polygons all raster cells that have values 125,126, or 127. HTH -- Micha 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! -- Micha Silver http://www.surfaces.co.il/ Arava Development Co. +972-52-3665918 ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
Re: [GRASS-user] Extracting grey features from an image
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 baob...@hotmail.fr Sent: Thursday, May 27, 2010 11:59 AM To: grass-user@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! -- View this message in context: http://osgeo-org.1803224.n2.nabble.com/Extracting-grey-features-from-an-image-tp5107822p5107822.html Sent from the Grass - Users mailing list archive at Nabble.com. ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user ___ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
