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Verify if there are really no instances of the target labels present in the image(s) or ROI(s). Try to add images or ROI(s) that have a similar appearance to the ones containing false-positive predictions.
Have a look at the annotations in your validation images in cases where the app has performed a segmentation task and check whether the annotations are complete. If annotations are correct and complete, then you can improve your trained model by adding new images or ROI(s) without any instances to the training set.
You will get the optimal improvements by adding images or ROI(s) containing instances with a similar appearance as the areas that have been detected by the algorithm model in the validation images.
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