Panasonic ZS99 has a
20.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Venus Engine processor. On the other hand, Panasonic FZ28 has a
10.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor .
Panasonic ZS99's sensor provides 10MP more than Panasonic FZ28'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 ZS99 and FZ28 sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic ZS99 and Panasonic FZ28 Cameras
Panasonic ZS99 and Panasonic FZ28 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
Panasonic ZS99
or the
Panasonic FZ28 ,
including hyperfocal distance.