Canon SD780 IS has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Fujifilm XP120 has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the SD780 IS and XP120 sensor size comparison.
Canon SD780 IS and Fujifilm XP120 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 SD780 IS has 32% larger pixel area compared to Fujifilm XP120, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.