Okay, I think I'm going to bust.
The General Technique
- start with some photograph
- copy to new layer
- do something to it, like Mosaic or Crosshatch or whatever
- set blending mode to Linear Light @ 50%
- invert
- favorite method to copy merged and paste
- invert this layer
- turn off the previously inverted layer
- get crazy
What you are left with is the difference. You can now use the difference. I prefer Linear Light @ 50% because it's mathematically correct, but feel free to mix it up.
Using that technique, you can go back and forth between Gauss and High Pass.
Take it another step further.
- copy photograph twice to two new layers
- do something different to each layer
- go through the Linear Light @ 50% thing
This is how you get medium frequencies. Gauss one layer at a decent radius, High Pass another layer at a smaller radius, and then go through the LL@50% thing.
This general technique is also good for a few other things. By extracting the difference in operations, you can tweak further in new ways. You can even rock back-and-forth in a manner. But I'll leave this particular thing to you.
Now, let's mix in Lens Blur.
- start with some photograph
- new Alpha1 channel
- give Alpha1 a simple, random gradient
- new Alpha2 channel
- give Alpha2 a simple, random gradient
- copy photograph to new layer
- use Alpha1 to Lens Blur
- copy original
- use Alpha2 to Lens Blur
- go through LL@50% thing
Once you copy merge and paste that, set final result to LL@50% and turn off both Lens Blurred layers. What you will be left with are variable medium frequencies. Depending, maybe even just variable blurring and variable high pass without the medium frequences.
Instead of just two different gradients, feel free to mix it up with Clouds/Difference Clouds or what have you.
You can use the same operation to blur variably, sharpen variably, and do medium frequencies variably - all in one go. Perfect blending, too.
Now, the trick is in controlling it. Or doing it in a meaningful manner. This gurus just happens to have just the ticket.
