Load an image into your favourite editor. Create two duplicates of it on new layers, set the top layer to SCREEN and merge it with the middle layer.
Duplicate the middle layer, and BLUR the new top layer. For a 6mpixel image a Gaussian blur of 15 works well. Now, change the new blur layer to MULTIPLY.
Now tweak the layers to your heart's content.
I'm gonna give it a shot.