Olympus SH-1 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, Canon A2100 IS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the SH-1 and A2100 IS sensor size comparison.
Olympus SH-1 and Canon A2100 IS have the same 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 Canon A2100 IS has 32% larger pixel area (2.34µm2 vs 1.76µm2) compared to Olympus SH-1, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.