The Alpha Filter
Adjusts the opacity of the content of the object

Here is original picture - no filter applied. This is what your viewers will see if their browser does not support these filters.

Below is same picture with Alpha Filter, Style 0 (uniform) applied, with Opacity of 50

Here we have Style 1 (Linear)
Opacity=100, FinishOpacity=50
StartY=40, FinishY=80

Here we have Style 2 (Radial)
Opacity=100, FinishOpacity=50

Below is  Style 3 (Rectangular)
Opacity=40, FinishOpacity=100