Both Olympus TG-2 iHS and Samsung SL620 have 1/2.3-inch sized 12.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Below you can see the TG-2 iHS and SL620 sensor size comparison.
Sensor Size and Resolution Comparison image of Olympus TG-2 iHS and Samsung SL620 Cameras
Olympus TG-2 iHS and Samsung SL620 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Olympus TG-2 iHS
or the
Samsung SL620 ,
including hyperfocal distance.