Both Olympus 1s and Canon SX510 HS have 12.0 MP resolution sensors but Olympus 1s's sensor is 1/1.7' (7.44 x 5.58 mm ) and Canon SX510 HS's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Olympus 1s's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Canon SX510 HS.
Below you can see the 1s and SX510 HS sensor size comparison.
As seen above, Olympus 1s has a 1.5x Larger sensor area than Canon SX510 HS. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.