Ok, so after reading this it got me thinking... After back and forth of whether ISO increases/decreases noise, does it actually do just that? As explained, the ISO in the camera turns up the amplitude of the signal (I'm not actually sure when, but I think it's after the light has hit the sensor) which carries noise along with it.
There were examples of low ISOs producing higher noise, but this was all after processing in Photoshop/Lightroom. The low ISO would have been very underexposed so would need a lot of processing to get it "properly" exposed. But it seems that doing that process is very similar to raising the ISO on your camera, it turns up the amplitude of the (well in the case of post processing) pixel (not signal because the picture has already been taken).
It seems to me that post processing just does a worse job at raising the "amplitude" because it hasn't got the raw data to process. But, it essentially does the same thing and results in, more noise.
So, what are the technicalities of exposure compensation for an underexposed image in post processing?
EDIT: Just to explain a little better, does anyone know of any algorithms or explain mathematically how brightness (or EV) is processed (in post-processing). Does it adjust the level of brightness/RBG/contrast for each pixel? Does it relate to the histogram?