Sigma Quattro has a
29.0MP APS-C (23.5 x 15.6 mm ) sized CMOS (Foveon X3) sensor and features Dual TRUE III processor. On the other hand, Samsung NX500 has a
28.0MP APS-C (23.5 x 15.7 mm ) sized BSI-CMOS sensor and features DRIMe 5 processor.
Another similarity between these two cameras is that both Samsung NX500 and Sigma Quattro sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the Quattro and NX500 sensor size comparison.
Sigma Quattro and Samsung NX500 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.