Sorry for the late reply, I've been Hubski'ing on mobile and wanted to write a proper response . I'm intrigued by the tutorial you mention, I'd love to see it! I'm curious though, is it that the photographer has taken a photo, done a secondary identical layer and played with the levels? I've been wanting to get into light painting, long exposures etc, but haven't found what I want to capture. This might just be the inspiration to kick my butt into gear. This might sound a crazy, so let me know if so: There are apps and devices that graphically display WiFi signal strength with graphical displays (eg an oscilloscope). If you took one of those, and read the signals in a location that you photographed, could you then convert the oscilloscope signals into a color representation, then layer that image over the top of the visual photo layer? Apologies if that makes zero sense, I may have had some liquid inspiration in coming up with it.