The overlay type tag is used with value "G" - Graphics when needed to
draw overlays on an image or when using shutter.
I don't know in which cases should this tag have the value "R" - ROI.
I found in the standard that when overlay type is "R", the overlay bits
corresponding to all
the pixels included in the ROI shall be set to 1. All other bits are
set to 0. What is the difference between this representation and
Thank you for your help.