FujiFilm S2800HD has a 14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Canon SX170 IS has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor.
Below you can see the S2800HD and SX170 IS sensor size comparison.
FujiFilm S2800HD and Canon SX170 IS 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 FujiFilm S2800HD has 15% larger pixel area compared to Canon SX170 IS, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.