Is there a way to do reclassify a raster image to Qgis?
In Arcgis you can do that in Spatial analyst Tools-->Reclass-->Reclassify
Using GRASS and the r.reclass module, yes. However, you actually need to use the keyword "thru".
Example: For a raster elevation grid, to be reclassified into values based on 100m-intervals:
500 thru 599.99 = 500
600 thru 699.99 = 600
700 thru 799.99 = 700
Etc.. And you save that into a notepad text document(with no spaces between lines). Then when opening the r.reclass module, you will simply load that rulefile into the gui and away you go.
Experience: I just performed a reclassification on a DEM for my thesis project in Tajikistan over the weekend using this method and it worked a treat.
*Note(caveat): You might look into modeling this process or even using GDAL to output a *.prj file alongside the output for use in Arc, as the outputs I've seen from this thus far contain no projection definition readable by Arc. If you're sticking with QGIS, tho, then you should be good-to-go.
One more thing, as with any QGIS/GRASS/GDAL processes, ensure you have downloaded the OSGeo4W Installer which ensures you have everything up-to-date: http://trac.osgeo.org/osgeo4w/
Hope this helps.
The easier way is to use GRASS (also using the QGIS/GRASS plugin) and the r.reclass module.
You will need to create a reclassification rule file, where you can use the keyword "through" or the wildcard "*" to reclassify multiple values in one rule.