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It's an outline of a particular area within an image presenting one or more features.
📑 How to manage ROI(s)?
Draw ROI
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(s)
Switch to “Region of Interest drawing mode” 
in the Image Editor from the right-hand toolbar.
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By selecting one of these tools you can draw your ROI on the image by clicking and dragging your mouse cursor.
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Modify ROI
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(s)
Previously drawn ROI shapes can be modified:
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