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from typing import Optional
import numpy as np
def w_np_non_max_suppression(
prediction,
conf_thresh: float = 0.25,
iou_thresh: float = 0.45,
class_agnostic: bool = False,
max_detections: int = 300,
max_candidate_detections: int = 3000,
timeout_seconds: Optional[int] = None,
num_masks: int = 0,
box_format: str = "xywh",
):
"""Applies non-maximum suppression to predictions.
Args:
prediction (np.ndarray): Array of predictions. Format for single prediction is
[bbox x 4, max_class_confidence, (confidence) x num_of_classes, additional_element x num_masks]
conf_thresh (float, optional): Confidence threshold. Defaults to 0.25.
iou_thresh (float, optional): IOU threshold. Defaults to 0.45.
class_agnostic (bool, optional): Whether to ignore class labels. Defaults to False.
max_detections (int, optional): Maximum number of detections. Defaults to 300.
max_candidate_detections (int, optional): Maximum number of candidate detections. Defaults to 3000.
timeout_seconds (Optional[int], optional): Timeout in seconds. Defaults to None.
num_masks (int, optional): Number of masks. Defaults to 0.
box_format (str, optional): Format of bounding boxes. Either 'xywh' or 'xyxy'. Defaults to 'xywh'.
Returns:
list: List of filtered predictions after non-maximum suppression. Format of a single result is:
[bbox x 4, max_class_confidence, max_class_confidence, id_of_class_with_max_confidence,
additional_element x num_masks]
"""
num_classes = prediction.shape[2] - 5 - num_masks
np_box_corner = np.zeros(prediction.shape)
if box_format == "xywh":
np_box_corner[:, :, 0] = prediction[:, :, 0] - prediction[:, :, 2] / 2
np_box_corner[:, :, 1] = prediction[:, :, 1] - prediction[:, :, 3] / 2
np_box_corner[:, :, 2] = prediction[:, :, 0] + prediction[:, :, 2] / 2
np_box_corner[:, :, 3] = prediction[:, :, 1] + prediction[:, :, 3] / 2
prediction[:, :, :4] = np_box_corner[:, :, :4]
elif box_format == "xyxy":
pass
else:
raise ValueError(
"box_format must be either 'xywh' or 'xyxy', got {}".format(box_format)
)
batch_predictions = []
for np_image_i, np_image_pred in enumerate(prediction):
filtered_predictions = []
np_conf_mask = (np_image_pred[:, 4] >= conf_thresh).squeeze()
np_image_pred = np_image_pred[np_conf_mask]
if np_image_pred.shape[0] == 0:
batch_predictions.append(filtered_predictions)
continue
np_class_conf = np.max(np_image_pred[:, 5 : num_classes + 5], 1)
np_class_pred = np.argmax(np_image_pred[:, 5 : num_classes + 5], 1)
np_class_conf = np.expand_dims(np_class_conf, axis=1)
np_class_pred = np.expand_dims(np_class_pred, axis=1)
np_mask_pred = np_image_pred[:, 5 + num_classes :]
np_detections = np.append(
np.append(
np.append(np_image_pred[:, :5], np_class_conf, axis=1),
np_class_pred,
axis=1,
),
np_mask_pred,
axis=1,
)
np_unique_labels = np.unique(np_detections[:, 6])
if class_agnostic:
np_detections_class = sorted(
np_detections, key=lambda row: row[4], reverse=True
)
filtered_predictions.extend(
non_max_suppression_fast(np.array(np_detections_class), iou_thresh)
)
else:
for c in np_unique_labels:
np_detections_class = np_detections[np_detections[:, 6] == c]
np_detections_class = sorted(
np_detections_class, key=lambda row: row[4], reverse=True
)
filtered_predictions.extend(
non_max_suppression_fast(np.array(np_detections_class), iou_thresh)
)
filtered_predictions = sorted(
filtered_predictions, key=lambda row: row[4], reverse=True
)
batch_predictions.append(filtered_predictions[:max_detections])
return batch_predictions
# Malisiewicz et al.
def non_max_suppression_fast(boxes, overlapThresh):
"""Applies non-maximum suppression to bounding boxes.
Args:
boxes (np.ndarray): Array of bounding boxes with confidence scores.
overlapThresh (float): Overlap threshold for suppression.
Returns:
list: List of bounding boxes after non-maximum suppression.
"""
# if there are no boxes, return an empty list
if len(boxes) == 0:
return []
# if the bounding boxes integers, convert them to floats --
# this is important since we'll be doing a bunch of divisions
if boxes.dtype.kind == "i":
boxes = boxes.astype("float")
# initialize the list of picked indexes
pick = []
# grab the coordinates of the bounding boxes
x1 = boxes[:, 0]
y1 = boxes[:, 1]
x2 = boxes[:, 2]
y2 = boxes[:, 3]
conf = boxes[:, 4]
# compute the area of the bounding boxes and sort the bounding
# boxes by the bottom-right y-coordinate of the bounding box
area = (x2 - x1 + 1) * (y2 - y1 + 1)
idxs = np.argsort(conf)
# keep looping while some indexes still remain in the indexes
# list
while len(idxs) > 0:
# grab the last index in the indexes list and add the
# index value to the list of picked indexes
last = len(idxs) - 1
i = idxs[last]
pick.append(i)
# find the largest (x, y) coordinates for the start of
# the bounding box and the smallest (x, y) coordinates
# for the end of the bounding box
xx1 = np.maximum(x1[i], x1[idxs[:last]])
yy1 = np.maximum(y1[i], y1[idxs[:last]])
xx2 = np.minimum(x2[i], x2[idxs[:last]])
yy2 = np.minimum(y2[i], y2[idxs[:last]])
# compute the width and height of the bounding box
w = np.maximum(0, xx2 - xx1 + 1)
h = np.maximum(0, yy2 - yy1 + 1)
# compute the ratio of overlap
overlap = (w * h) / area[idxs[:last]]
# delete all indexes from the index list that have
idxs = np.delete(
idxs, np.concatenate(([last], np.where(overlap > overlapThresh)[0]))
)
# return only the bounding boxes that were picked using the
# integer data type
return boxes[pick].astype("float")
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