Casio EX-Z450 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Canon A4000 IS has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the EX-Z450 and A4000 IS sensor size comparison.
Casio EX-Z450 and Canon A4000 IS have 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 Casio EX-Z450 has 32% larger pixel area compared to Canon A4000 IS, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.