Both Fujifilm XP90 and Ricoh WG-5 GPS have 16.0 MP resolution sensors but Fujifilm XP90's sensor is 1/2.3 (6.17 x 4.55 mm ) and Ricoh WG-5 GPS's sensor is (1/2. ).
Since Fujifilm XP90'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-5 GPS.
Below you can see the XP90 and WG-5 GPS sensor size comparison.
As seen above, Fujifilm XP90 has a infx Larger sensor area than Ricoh WG-5 GPS. 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.