Canon SX20 IS has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor. On the other hand, Fujifilm S1 has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor .
Below you can see the SX20 IS and S1 sensor size comparison.
Canon SX20 IS and Fujifilm S1 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 Canon SX20 IS has 32% larger pixel area compared to Fujifilm S1, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.