Both Ricoh WG-50 and Olympus TG-4 have 16.0 MP resolution sensors but Ricoh WG-50's sensor is 1/2.3" (6.17 x 4.55 mm ) and Olympus TG-4's sensor is 1/2.3 (6.17 x 4.55 mm ).
Since Olympus TG-4'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 Ricoh WG-50.
Below you can see the WG-50 and TG-4 sensor size comparison.
Ricoh WG-50 and Olympus TG-4 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.