Both Olympus TG-830 iHS and Olympus TG-860 have 16.0 MP resolution sensors but Olympus TG-830 iHS's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Olympus TG-860's sensor is (1/2. ).
Since Olympus TG-830 iHS'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-860.
Below you can see the TG-830 iHS and TG-860 sensor size comparison.
As seen above, Olympus TG-830 iHS has a infx Larger sensor area than Olympus TG-860. 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.