The program I use is a spatial filter which does Fourier analysis. If either of those things mean much then ill talk about it and share filters as it can be indispensable but otherwise its a hard technique to use.
I am using a high pass filter but I am keeping the average or DC component. The program allows you to set how much of the high pass to keep. I am only knocking out a little of the low pass - just enough to even out the brightness.
In theory if you use a high pass and a very very large blur - enough to average the whole image to a single shade and then add the two together then it should produce the same effect. Generally tho, most paint packages clip the high pass or center it around the mid grey mark so that when you add them it would not look right.