7. The method of claim 6 , wherein the confidence loss term for the particular set of assignments is further based on, for each candidate bounding box that is not assigned to any of the object locations by the particular set of assignments, how close the confidence score for the candidate bounding box is to a second target confidence score for candidate bounding boxes that are not assigned to object locations, wherein the second target confidence score is lower than the first target confidence score.
6. The method of claim 3 , wherein the confidence loss term for a particular set of assignments is based on, for each candidate bounding box that is assigned to any of the object locations by the particular set of assignments, how close the confidence score for the candidate bounding box is to a first target confidence score for candidate bounding boxes that are assigned to object locations.