Kodak FZ55 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor . On the other hand, Nikon S640 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Expeed processor.
Below you can see the FZ55 and S640 sensor size comparison.
Sensor Size and Resolution Comparison image of Kodak FZ55 and Nikon S640 Cameras
Kodak FZ55 and Nikon S640 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
Kodak FZ55
or the
Nikon S640 ,
including hyperfocal distance.