Quote Originally Posted by DavidEccleston View Post
All Canon cameras have a high-ISO noise reduction option that records with the shutter closed for as long as it recorded with the shutter open, and subtracts the sensor-specific read noise from the actual image data. It's not that it's taking 30 seconds to process the image, it's that it takes 30 seconds to re-create 30 seconds worth of noise.

edit: I'm going to edit... perhaps not *all* Canon cameras have this option. Many do. Perhaps all, but I don't know for sure.
You're describing long exposure noise reduction (LENR), which is different than high ISO NR. It's an important distinction since LENR affects RAW image capture, whereas high ISO NR and most other settings do not.