# Removing Duplicate Objects This recipe demonstrates a simple workflow for finding and removing duplicate objects in your FiftyOne datasets using [intersection over union (IoU)](https://en.wikipedia.org/wiki/Jaccard_index). Specificially, it covers: - Using the [compute_max_ious()](https://voxel51.com/docs/fiftyone/api/fiftyone.utils.iou.html#fiftyone.utils.iou.compute_max_ious) utility to compute overlap between spatial objects - Using the [App’s tagging UI](https://voxel51.com/docs/fiftyone/user_guide/app.html#tags-and-tagging) to review and delete duplicate labels - Using FiftyOne’s [CVAT integration](https://voxel51.com/docs/fiftyone/integrations/cvat.html) to edit duplicate labels - Using the [find_duplicates()](https://voxel51.com/docs/fiftyone/api/fiftyone.utils.iou.html#fiftyone.utils.iou.find_duplicates) utility to automatically detect duplicate objects Also, check out [our blog post](https://towardsdatascience.com/iou-a-better-detection-evaluation-metric-45a511185be1) for more information about using IoU to evaluate your object detection models. ## Setup If you haven’t already, install FiftyOne: ## Load a dataset In this recipe, we’ll work with the validation split of the [COCO dataset](https://cocodataset.org/#home), which is conveniently available for download via the [FiftyOne Dataset Zoo](https://voxel51.com/docs/fiftyone/user_guide/dataset_zoo/datasets.html#coco-2017). The snippet below downloads and loads a subset of the validation split into FiftyOne: Let’s print the dataset to see what we downloaded: ## Finding duplicate objects Now let’s use the [compute_max_ious()](https://voxel51.com/docs/fiftyone/api/fiftyone.utils.iou.html#fiftyone.utils.iou.compute_max_ious) utility to compute the maximum IoU between each object in the `ground_truth` field with another object of the same class (`classwise=True`) within the same image. The max IOU will be stored in a `max_iou` attribute of each object, and the idea here is that duplicate objects will necessarily have high [IoU](https://en.wikipedia.org/wiki/Jaccard_index) with another object. Note that [compute_max_ious()](https://voxel51.com/docs/fiftyone/api/fiftyone.utils.iou.html#fiftyone.utils.iou.compute_max_ious) provides an optional `other_field` parameter if you would like to compute IoUs between objects in different fields instead. In any case, let’s [create a view](https://voxel51.com/docs/fiftyone/user_guide/using_views.html#filtering-sample-contents) that contains only labels with a max IoU > 0.75: and load it in the App: ## Removing duplicates in the App One simple approach to removing the duplicate labels is to review them in the App and [assign label tags](https://voxel51.com/docs/fiftyone/user_guide/app.html#tags-and-tagging) to the labels that we deem to be duplicates: Then we can simply delete the labels with the duplicate tag that we populated: ## Removing duplicates in CVAT Another approach to resolve the duplicate labegls is to use FiftyOne’s [CVAT integration](https://voxel51.com/docs/fiftyone/integrations/cvat.html) to upload the duplicate labels to CVAT for review, editing, and/or deletion: ![cvat-remove-dups](recipes/images/cvat_remove_dups.jpg) Once we’re finished editing in CVAT, we simply load the results back into FiftyOne: and refresh the App to verify that the duplicates have been properly addressed: ## Automatically finding duplicates A third approach is to use the [find_duplicates()](https://voxel51.com/docs/fiftyone/api/fiftyone.utils.iou.html#fiftyone.utils.iou.find_duplicates) utility to automatically retrieve the IDs of duplicate labels: Of course, when dealing with duplicate labels, there is inherent ambiguity: which one is “correct” and which one(s) are “duplicate”? By default, [find_duplicates()](https://voxel51.com/docs/fiftyone/api/fiftyone.utils.iou.html#fiftyone.utils.iou.find_duplicates) will simply iterate through the labels in each sample and flag any label whose IoU with a previous label exceeds the chosen threshold as a duplicate. Alternatively, you can pass the `method="greedy"` option to instead use a greedy approach to mark the fewest number of labels as duplicate such that no non-duplicate labels have IoU greater than the specified threshold with each other. In either case, it is recommended to visualize the duplicates in the App before taking any action. One convenient way to do this is to first tag the duplicates: Then, use [match_labels()](https://voxel51.com/docs/fiftyone/api/fiftyone.core.collections.html#fiftyone.core.collections.SampleCollection.match_labels) to load the samples containing at least one duplicate label in the App and use the `duplicate` tag you added to conveniently isolate and evaluate the duplicates. If you see any erroneous duplicates, simply remove the `duplicate` tag in the App: When you’re ready to act, you can then easily delete the duplicate labels as follows: