Canon Elph 115 IS has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 5 processor. On the other hand, Nikon S4100 has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Expeed C2 processor.
Below you can see the Elph 115 IS and S4100 sensor size comparison.
Canon Elph 115 IS and Nikon S4100 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 Nikon S4100 has 14% larger pixel area (2.01µm2 vs 1.76µm2) compared to Canon Elph 115 IS, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.