Sony HX300 has a
20.0MP 1/2.3-inch (6.16 x 4.62 mm ) sized BSI-CMOS sensor . On the other hand, Panasonic FZ200 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CMOS sensor and features Venus Engine VII FHD processor.
Sony HX300's sensor provides 8MP more than Panasonic FZ200'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 HX300 and FZ200 sensor size comparison.
Sensor Size and Resolution Comparison image of Sony HX300 and Panasonic FZ200 Cameras
Sony HX300 and Panasonic FZ200 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Sony HX300
or the
Panasonic FZ200 ,
including hyperfocal distance.