Canon A1200 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 4 with iSAPS technology processor. On the other hand, Canon A1400 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the A1200 and A1400 sensor size comparison.
Canon A1200 and Canon A1400 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 Canon A1200 has 32% larger pixel area compared to Canon A1400, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.