Relax constraints when downsampling by 2.
Relax constraints when downsampling by 2.

Nazg-Gul/libmv,SoylentGraham/libmv,keir/libmv,rgkoo/libmv-blender,petertsoi/libmv,keir/libmv,Nazg-Gul/libmv,rgkoo/libmv-blender,Nazg-Gul/libmv,keir/libmv,Nazg-Gul/libmv,SoylentGraham/libmv,SoylentGraham/libmv,rgkoo/libmv-blender,petertsoi/libmv,rgkoo/libmv-blender,petertsoi/libmv,keir/libmv,SoylentGraham/libmv,Nazg-Gul/libmv,rgkoo/libmv-blender,petertsoi/libmv