Nikon S640 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Expeed processor. On the other hand, Fujifilm XP70 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor .
Below you can see the S640 and XP70 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon S640 and Fujifilm XP70 Cameras
Nikon S640 and Fujifilm XP70 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Nikon S640
or the
Fujifilm XP70 ,
including hyperfocal distance.