I want to make the cells which values "1" to null in QGIS with Grass or Saga tools (exactly Saga).
Thanks to Volker Wichmann from SAGA GIS forums. If you want to change the cell values to null you can use Saga reclassify grid values from Sextante. Enter the -99999 which will be null on the option for new values for other values. Saga accepts -99999 value as NoData.