Allow the user to specify a smaller subset of the entire frame (a.k.a., a Region of Interest or ROI) to focus all operations on for live stacking. Some ZWO cameras support this natively as well. This allows for less data transfer and higher fps rate as all operations are based on smaller portion of the entire frame only. Also this will increase frame processing speed for stacking and stretching etc. The guiding frame should be unrelated to this adjustment. Support this for all modes, not just video, even for live stacking or single frames. This can be achieved by letting user pull in the sides of the frame from each direction toward the center, the same way a user can crops a photo. Once there, it can be locked on the area for all further operations until cleared (set back to full frame). The feature is useful for smaller objects where most of the data in the frame is wasted.
Once the area is locked, the image will "zoom in" as far as the display goes, showing the same preview object in lower apparent resolution. This will be very useful for smaller objects and planets.
