Nikon S620 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Samsung NX20 has a
20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor .
Samsung NX20's sensor provides 8MP more than Nikon S620's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the S620 and NX20 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon S620 and Samsung NX20 Cameras
As seen above, Samsung NX20 has a 13.3x Larger sensor area than Nikon S620. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in 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 S620
or the
Samsung NX20 ,
including hyperfocal distance.
One thing to watch when comparing these two: they have different sensor sizes
(1/2.3-inch versus APS-C),
so compare them at the same framing rather than the same focal length.
Put the same focal length on the smaller sensor and it will show less depth of
field, not more, because it also crops tighter. The calculator shows the
full frame equivalent focal length for each body so you can match the framing.