Casio EX-G1 has a 12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Sony WX220 has a 18.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Bionz X processor.
Sony WX220's sensor provides 6MP more than Casio EX-G1's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the EX-G1 and WX220 sensor size comparison.
Casio EX-G1 and Sony WX220 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-G1 has 49% larger pixel area compared to Sony WX220, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.