Sony TX20 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features BIONZ processor. On the other hand, Nikon S230 has a
10.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Sony TX20's sensor provides 6MP more than Nikon S230'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 TX20 and S230 sensor size comparison.
Sony TX20 and Nikon S230 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 S230 has 59% larger pixel area (2.81µm2 vs 1.76µm2) compared to Sony TX20, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.