Both Olympus TG-4 and Fujifilm F800EXR have 16.0 MP resolution sensors but Olympus TG-4's sensor is (1/2. ) and Fujifilm F800EXR's sensor is 1/2-inch (6.4 x 4.8 mm ).
Since Fujifilm F800EXR'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 TG-4.
Below you can see the TG-4 and F800EXR sensor size comparison.
As seen above, Fujifilm F800EXR has a infx Larger sensor area than Olympus TG-4. 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.