Nikon S4000 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Expeed C2 processor. On the other hand, Canon ELPH 340 HS has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features DIGIC 4+ processor.
Below you can see the S4000 and ELPH 340 HS sensor size comparison.
Nikon S4000 and Canon ELPH 340 HS 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 S4000 has 32% larger pixel area compared to Canon ELPH 340 HS, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.