Panasonic ZS3 has a 10.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Sony TX20 has a 16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features BIONZ processor.
Sony TX20's sensor provides 6MP more than Panasonic ZS3'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 ZS3 and TX20 sensor size comparison.
![Panasonic ZS3 vs Sony TX20 Sensor Size Comparison]()
Sensor Size and Resolution Comparison image of Panasonic ZS3 and Sony TX20 Cameras
Panasonic ZS3 and Sony TX20 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.