Both Samsung NX300 and Olympus E-M1X have 20.0 MP resolution sensors but Samsung NX300's sensor is APS-C (23.5 x 15.7 mm ) and Olympus E-M1X's sensor is Four Thirds (17.4 x 13 mm ).
Since Samsung NX300'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 Olympus E-M1X.
Below you can see the NX300 and E-M1X sensor size comparison.
As seen above, Samsung NX300 has a 1.6x Larger sensor area than Olympus E-M1X. 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.