Sony S2100 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Bionz processor. On the other hand, Olympus TG-4 has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features TruePic VII processor.
Below you can see the S2100 and TG-4 sensor size comparison.
Sony S2100 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. On the other hand, since Sony S2100 has 32% larger pixel area compared to Olympus TG-4, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.