Canon S100 has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized CMOS sensor and features Digic 5 processor. On the other hand, Canon S95 has a 10.0MP 1/1.7" (7.44 x 5.58 mm ) sized CCD sensor and features Digic 4 processor.
Below you can see the S100 and S95 sensor size comparison.
Canon S100 and Canon S95 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 S95 has 20% larger pixel area (4.16µm2 vs 3.46µm2) compared to Canon S100, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.
DxOMark Sensor Scores
Both Canon S100 and Canon S95 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, S100 has scored 50, 3 points higher than S95.