Panasonic S5 has a 24.0MP Full frame
(35.6 x 23.8 mm ) sized CMOS sensor and features Venus Engine processor. On the other hand, Canon 300D has a 6.0MP APS-C
(22.7 x 15.1 mm ) sized CMOS sensor .
Panasonic S5's sensor provides 18MP more than Canon 300D'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.
Another difference between these two cameras is that Panasonic S5's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the S5 and 300D sensor size comparison.
As seen above, Panasonic S5 has a 2.5x Larger sensor area than Canon 300D. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.
DxOMark Sensor Scores
Both Panasonic S5 and Canon 300D sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, S5 has scored 94, 39 points higher than 300D.