You can disable filtering (and thus blurring) completely in native bitmap loader by choosing
none as filtering option. My guess, it's the same, or nearly the same, as choosing
nearest neighbour in Corona bitmap and setting blurring to 0,01
Why?
I just saw that you're changing filtering in native bitmap, but sticking to default in Corona bitmap, so i thought it would be fair to either leave default filtering in both loaders and change only blurring, or test all possible combinations.