Add Non-Maximum Merging (NMM) to Detections

supervision/__init__.py

@@ -44,6 +44,7 @@
 from supervision.detection.tools.smoother import DetectionsSmoother
 from supervision.detection.utils import (
     box_iou_batch,
+    box_non_max_merge,
     box_non_max_suppression,
     calculate_masks_centroids,
     clip_boxes,

supervision/detection/core.py

@@ -8,6 +8,8 @@
 
 from supervision.config import CLASS_NAME_DATA_FIELD, ORIENTED_BOX_COORDINATES
 from supervision.detection.utils import (
+    box_iou_batch,
+    box_non_max_merge,
     box_non_max_suppression,
     calculate_masks_centroids,
     extract_ultralytics_masks,
@@ -1150,3 +1152,193 @@ def with_nms(
             )
 
         return self[indices]
+
+    def with_nmm(
+        self, threshold: float = 0.5, class_agnostic: bool = False
+    ) -> Detections:
+        """
+        Perform non-maximum merging on the current set of object detections.
+
+        Args:
+            threshold (float, optional): The intersection-over-union threshold
+                to use for non-maximum merging. Defaults to 0.5.
+            class_agnostic (bool, optional): Whether to perform class-agnostic
+                non-maximum merging. If True, the class_id of each detection
+                will be ignored. Defaults to False.
+
+        Returns:
+            Detections: A new Detections object containing the subset of detections
+                after non-maximum merging.
+
+        Raises:
+            AssertionError: If `confidence` is None or `class_id` is None and
+                class_agnostic is False.
+        """
+        if len(self) == 0:
+            return self
+
+        assert (
+            self.confidence is not None
+        ), "Detections confidence must be given for NMM to be executed."
+
+        if class_agnostic:
+            predictions = np.hstack((self.xyxy, self.confidence.reshape(-1, 1)))
+        else:
+            assert self.class_id is not None, (
+                "Detections class_id must be given for NMM to be executed. If you"
+                " intended to perform class agnostic NMM set class_agnostic=True."
+            )
+            predictions = np.hstack(
+                (
+                    self.xyxy,
+                    self.confidence.reshape(-1, 1),
+                    self.class_id.reshape(-1, 1),
+                )
+            )
+
+        merge_groups = box_non_max_merge(
+            predictions=predictions, iou_threshold=threshold
+        )
+
+        result = []
+        for merge_group in merge_groups:
+            unmerged_detections = [self[i] for i in merge_group]
+            merged_detections = merge_inner_detections_objects(
+                unmerged_detections, threshold
+            )
+            result.append(merged_detections)
+
+        return Detections.merge(result)
+
+
+def merge_inner_detection_object_pair(
+    detections_1: Detections, detections_2: Detections
+) -> Detections:
+    """
+    Merges two Detections object into a single Detections object.
+    Assumes each Detections contains exactly one object.
+
+    A `winning` detection is determined based on the confidence score of the two
+    input detections. This winning detection is then used to specify which
+    `class_id`, `tracker_id`, and `data` to include in the merged Detections object.
+
+    The resulting `confidence` of the merged object is calculated by the weighted
+    contribution of ea detection to the merged object.
+    The bounding boxes and masks of the two input detections are merged into a
+    single bounding box and mask, respectively.
+
+    Args:
+        detections_1 (Detections):
+            The first Detections object
+        detections_2 (Detections):
+            The second Detections object
+
+    Returns:
+        Detections: A new Detections object, with merged attributes.
+
+    Raises:
+        ValueError: If the input Detections objects do not have exactly 1 detected
+            object.
+
+    Example:
+        ```python
+        import cv2
+        import supervision as sv
+        from inference import get_model
+
+        image = cv2.imread(<SOURCE_IMAGE_PATH>)
+        model = get_model(model_id="yolov8s-640")
+
+        result = model.infer(image)[0]
+        detections = sv.Detections.from_inference(result)
+
+        merged_detections = merge_object_detection_pair(
+            detections[0], detections[1])
+        ```
+    """
+    if len(detections_1) != 1 or len(detections_2) != 1:
+        raise ValueError("Both Detections should have exactly 1 detected object.")
+
+    validate_fields_both_defined_or_none(detections_1, detections_2)
+
+    xyxy_1 = detections_1.xyxy[0]
+    xyxy_2 = detections_2.xyxy[0]
+    if detections_1.confidence is None and detections_2.confidence is None:
+        merged_confidence = None
+    else:
+        detection_1_area = (xyxy_1[2] - xyxy_1[0]) * (xyxy_1[3] - xyxy_1[1])
+        detections_2_area = (xyxy_2[2] - xyxy_2[0]) * (xyxy_2[3] - xyxy_2[1])
+        merged_confidence = (
+            detection_1_area * detections_1.confidence[0]
+            + detections_2_area * detections_2.confidence[0]
+        ) / (detection_1_area + detections_2_area)
+        merged_confidence = np.array([merged_confidence])
+
+    merged_x1, merged_y1 = np.minimum(xyxy_1[:2], xyxy_2[:2])
+    merged_x2, merged_y2 = np.maximum(xyxy_1[2:], xyxy_2[2:])
+    merged_xyxy = np.array([[merged_x1, merged_y1, merged_x2, merged_y2]])
+
+    if detections_1.mask is None and detections_2.mask is None:
+        merged_mask = None
+    else:
+        merged_mask = np.logical_or(detections_1.mask, detections_2.mask)
+
+    if detections_1.confidence is None and detections_2.confidence is None:
+        winning_detection = detections_1
+    elif detections_1.confidence[0] >= detections_2.confidence[0]:
+        winning_detection = detections_1
+    else:
+        winning_detection = detections_2
+
+    return Detections(
+        xyxy=merged_xyxy,
+        mask=merged_mask,
+        confidence=merged_confidence,
+        class_id=winning_detection.class_id,
+        tracker_id=winning_detection.tracker_id,
+        data=winning_detection.data,
+    )
+
+
+def merge_inner_detections_objects(
+    detections: List[Detections], threshold=0.5
+) -> Detections:
+    """
+    Given N detections each of length 1 (exactly one object inside), combine them into a
+    single detection object of length 1. The contained inner object will be the merged
+    result of all the input detections.
+
+    For example, this lets you merge N boxes into one big box, N masks into one mask,
+    etc.
+    """
+    detections_1 = detections[0]
+    for detections_2 in detections[1:]:
+        box_iou = box_iou_batch(detections_1.xyxy, detections_2.xyxy)[0]
+        if box_iou < threshold:
+            break
+        detections_1 = merge_inner_detection_object_pair(detections_1, detections_2)
+    return detections_1
+
+
+def validate_fields_both_defined_or_none(
+    detections_1: Detections, detections_2: Detections
+) -> None:
+    """
+    Verify that for each optional field in the Detections, both instances either have
+    the field set to None or both have it set to non-None values.
+
+    `data` field is ignored.
+
+    Raises:
+        ValueError: If one field is None and the other is not, for any of the fields.
+    """
+    attributes = ["mask", "confidence", "class_id", "tracker_id"]
+    for attribute in attributes:
+        value_1 = getattr(detections_1, attribute)
+        value_2 = getattr(detections_2, attribute)
+
+        if (value_1 is None) != (value_2 is None):
+            raise ValueError(
+                f"Field '{attribute}' should be consistently None or not None in both "
+                "Detections."
+            )