High Pass Filter

Being a student studying electrical and computer engineering, I got quite curious about how photoshop's High Pass Filter works.

You see in analog and digital communication systems a high pass filter will remove low frequency components of a signal, and pass the high frequencies. A HPF is actually a simple circuit, and looks something like this:

But photoshop's HPF is clearly not a circuit so since I'm always reading SOMETHING while I enjoy my breakfast, I decided to explore how this high pass filter concept applies to image processing. I won't bore you will all the gory details - but according to this informative site: "The kernel of the high pass filter is designed to increase the brightness of the center pixel relative to neighboring pixels. The kernel array usually contains a single positive value at its center, which is completely surrounded by negative values."  


I decided to apply a high pass filter to a picture of breakfast. 

Turns out that the settings I have it on just make the air look a bit smokey - I swear I didn't burn my toast... :)


What are your favorite photoshop filters?