Olympus TG-4 has a 16.0MP 1/2.3" (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features TruePic VII processor. On the other hand, Olympus XZ-10 has a 12.0MP 1/2.3" (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the TG-4 and XZ-10 sensor size comparison.
Olympus TG-4 and Olympus XZ-10 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 Olympus XZ-10 has 35% larger pixel area (2.38µm2 vs 1.76µm2) compared to Olympus TG-4, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.