Sony W220 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Sony W570 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features BIONZ processor.
Below you can see the W220 and W570 sensor size comparison.
Sony W220 and Sony W570 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 Sony W220 has 32% larger pixel area compared to Sony W570, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.