Read only data within ROI from file

[NichtJens]

A nice to have feature would be the ability to read only the data within an ROI from the file.

This is in contrast to: Read the whole image and THEN apply the ROI.

I would imagine this to work like this: Use the (somehow reversed!) module map to find where in the raw file the ROI actually is, read only these values to memory, and finally assemble only the ROI'ed image.