Lode's Computer Graphics Tutorial Fourier Transform

It can be seen that only the high frequency parts of the image are left: subtle gradients and colorchanges are gone, only the edges of objects and especially the cooling fin are still recognisable.Photoshop, instead of adding the DC component, adds grey to the image to make all pixels positive, sothe result of the High Pass filter in Photoshop is something like this:If we use a higher radius for the removed circle, only the very highest frequencies remain, only thecooling fin still looks pretty nice:A high pass filter can also be done by first blurring the image, and then substracting the blurred imagefrom the original.After seeing those pictures you might wonder if there is actually something useful that can be donewith a High Pass Filter? Well, it can for example be used to make better tillable textures, take forexample this grass texture:If you tile it, it looks like this: