Nikon S570 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Expeed processor. On the other hand, Nikon S6500 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the S570 and S6500 sensor size comparison.
Nikon S570 and Nikon S6500 have the same 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 Nikon S570 has 32% larger pixel area compared to Nikon S6500, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.