Convolutionfilter: how to create crystallize effect?

I’m just wondering how to achieve an effect similar to the crystallize filter in photoshop, using the ConvolutionFilter.

Basically I don’t really understand how a convolutionfilter works exactly and what the different parameters do. And I’m afraid the Help isn’t really… well helpfull to me :sigh:

Could anyone point me in the right direction on this one?