The dataset is composed of D -> F sets (not pairs, because there are many underexposed images) of Dark to Fully-illuminated images. Yes, the net is "dreaming"

The dataset is composed of D -> F sets (not pairs, because there are many underexposed images) of Dark to Fully-illuminated images. Yes, the net is "dreaming" the details, based on what it learns from those mappings. I'd say this nets are very specialised on the sensor, and maybe even lens choice. Simply put, what they did is compressing a full pipeline of processing into a deep net that consumes RAW files and spits out natural looking images.