Fujifilm S4500 has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Fujifilm S8600 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the S4500 and S8600 sensor size comparison.
Fujifilm S4500 and Fujifilm S8600 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 Fujifilm S4500 has 15% larger pixel area compared to Fujifilm S8600, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.