Samsung ST600 has a
14.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Canon Elph 115 IS has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 5 processor.
Below you can see the ST600 and Elph 115 IS sensor size comparison.
Samsung ST600 and Canon Elph 115 IS 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.