Color　imaging　in　low-light　conditions　is　often　significantly　degraded　by　insufficient　lighting　and　color　cast.　In　this　paper,　we　present　a　novel　color　constancy-based　method　to　enhance　the　visibility　of　low-light　images.　Due　to　the　occurrence　of　the　scene　illuminant　or　specular　highlights,　inhomogeneous　illumination　affects　the　estimation　of　the　illuminant　color　across　the　scene.　Thus　in　the　image,　an　active　set　of　pixel　values　is　defined　to　reduce　their　effects.　We　then　propose　an　improvement　on　the　gray-pixel　assumption　imposed　by　the　shades-of-gray　algorithm　using　the　active　set.　The　improved　shades-of-gray　algorithm　is　applied　to　low-light　image　visibility　enhancement　for　cast　removal.　Limits　of　histogram　clipping　are　found　in　the　active　set　in　the　post-processing　step　that　is　added　to　render　the　resulting　image　with　a　good　lightness　and　contrast　range.　Results　on　a　variety　of　low-light　images　demonstrate　that　the　proposed　method　can　achieve　a　good　correction　for　lightness,　contrast　and　color　fidelity　without　local　graying-out　artifacts　or　halo　artifacts　intrinsic　to　Retinex　approaches.　Copyright　©　2011　Acta　Automatica　Sinica.