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#!/usr/bin/env python3
# Copyright 2004-present Facebook. All Rights Reserved.
import copy
import numpy as np
from typing import List
import torch
from detectron2.config import configurable
from detectron2.structures import Boxes, Instances
from detectron2.structures.boxes import pairwise_iou
from ..config.config import CfgNode as CfgNode_
from .base_tracker import TRACKER_HEADS_REGISTRY, BaseTracker
@TRACKER_HEADS_REGISTRY.register()
class BBoxIOUTracker(BaseTracker):
"""
A bounding box tracker to assign ID based on IoU between current and previous instances
"""
@configurable
def __init__(
self,
*,
video_height: int,
video_width: int,
max_num_instances: int = 200,
max_lost_frame_count: int = 0,
min_box_rel_dim: float = 0.02,
min_instance_period: int = 1,
track_iou_threshold: float = 0.5,
**kwargs,
):
"""
Args:
video_height: height the video frame
video_width: width of the video frame
max_num_instances: maximum number of id allowed to be tracked
max_lost_frame_count: maximum number of frame an id can lost tracking
exceed this number, an id is considered as lost
forever
min_box_rel_dim: a percentage, smaller than this dimension, a bbox is
removed from tracking
min_instance_period: an instance will be shown after this number of period
since its first showing up in the video
track_iou_threshold: iou threshold, below this number a bbox pair is removed
from tracking
"""
super().__init__(**kwargs)
self._video_height = video_height
self._video_width = video_width
self._max_num_instances = max_num_instances
self._max_lost_frame_count = max_lost_frame_count
self._min_box_rel_dim = min_box_rel_dim
self._min_instance_period = min_instance_period
self._track_iou_threshold = track_iou_threshold
@classmethod
def from_config(cls, cfg: CfgNode_):
"""
Old style initialization using CfgNode
Args:
cfg: D2 CfgNode, config file
Return:
dictionary storing arguments for __init__ method
"""
assert "VIDEO_HEIGHT" in cfg.TRACKER_HEADS
assert "VIDEO_WIDTH" in cfg.TRACKER_HEADS
video_height = cfg.TRACKER_HEADS.get("VIDEO_HEIGHT")
video_width = cfg.TRACKER_HEADS.get("VIDEO_WIDTH")
max_num_instances = cfg.TRACKER_HEADS.get("MAX_NUM_INSTANCES", 200)
max_lost_frame_count = cfg.TRACKER_HEADS.get("MAX_LOST_FRAME_COUNT", 0)
min_box_rel_dim = cfg.TRACKER_HEADS.get("MIN_BOX_REL_DIM", 0.02)
min_instance_period = cfg.TRACKER_HEADS.get("MIN_INSTANCE_PERIOD", 1)
track_iou_threshold = cfg.TRACKER_HEADS.get("TRACK_IOU_THRESHOLD", 0.5)
return {
"_target_": "detectron2.tracking.bbox_iou_tracker.BBoxIOUTracker",
"video_height": video_height,
"video_width": video_width,
"max_num_instances": max_num_instances,
"max_lost_frame_count": max_lost_frame_count,
"min_box_rel_dim": min_box_rel_dim,
"min_instance_period": min_instance_period,
"track_iou_threshold": track_iou_threshold,
}
def update(self, instances: Instances) -> Instances:
"""
See BaseTracker description
"""
instances = self._initialize_extra_fields(instances)
if self._prev_instances is not None:
# calculate IoU of all bbox pairs
iou_all = pairwise_iou(
boxes1=instances.pred_boxes,
boxes2=self._prev_instances.pred_boxes,
)
# sort IoU in descending order
bbox_pairs = self._create_prediction_pairs(instances, iou_all)
# assign previous ID to current bbox if IoU > track_iou_threshold
self._reset_fields()
for bbox_pair in bbox_pairs:
idx = bbox_pair["idx"]
prev_id = bbox_pair["prev_id"]
if (
idx in self._matched_idx
or prev_id in self._matched_ID
or bbox_pair["IoU"] < self._track_iou_threshold
):
continue
instances.ID[idx] = prev_id
instances.ID_period[idx] = bbox_pair["prev_period"] + 1
instances.lost_frame_count[idx] = 0
self._matched_idx.add(idx)
self._matched_ID.add(prev_id)
self._untracked_prev_idx.remove(bbox_pair["prev_idx"])
instances = self._assign_new_id(instances)
instances = self._merge_untracked_instances(instances)
self._prev_instances = copy.deepcopy(instances)
return instances
def _create_prediction_pairs(self, instances: Instances, iou_all: np.ndarray) -> List:
"""
For all instances in previous and current frames, create pairs. For each
pair, store index of the instance in current frame predcitions, index in
previous predictions, ID in previous predictions, IoU of the bboxes in this
pair, period in previous predictions.
Args:
instances: D2 Instances, for predictions of the current frame
iou_all: IoU for all bboxes pairs
Return:
A list of IoU for all pairs
"""
bbox_pairs = []
for i in range(len(instances)):
for j in range(len(self._prev_instances)):
bbox_pairs.append(
{
"idx": i,
"prev_idx": j,
"prev_id": self._prev_instances.ID[j],
"IoU": iou_all[i, j],
"prev_period": self._prev_instances.ID_period[j],
}
)
return bbox_pairs
def _initialize_extra_fields(self, instances: Instances) -> Instances:
"""
If input instances don't have ID, ID_period, lost_frame_count fields,
this method is used to initialize these fields.
Args:
instances: D2 Instances, for predictions of the current frame
Return:
D2 Instances with extra fields added
"""
if not instances.has("ID"):
instances.set("ID", [None] * len(instances))
if not instances.has("ID_period"):
instances.set("ID_period", [None] * len(instances))
if not instances.has("lost_frame_count"):
instances.set("lost_frame_count", [None] * len(instances))
if self._prev_instances is None:
instances.ID = list(range(len(instances)))
self._id_count += len(instances)
instances.ID_period = [1] * len(instances)
instances.lost_frame_count = [0] * len(instances)
return instances
def _reset_fields(self):
"""
Before each uodate call, reset fields first
"""
self._matched_idx = set()
self._matched_ID = set()
self._untracked_prev_idx = set(range(len(self._prev_instances)))
def _assign_new_id(self, instances: Instances) -> Instances:
"""
For each untracked instance, assign a new id
Args:
instances: D2 Instances, for predictions of the current frame
Return:
D2 Instances with new ID assigned
"""
untracked_idx = set(range(len(instances))).difference(self._matched_idx)
for idx in untracked_idx:
instances.ID[idx] = self._id_count
self._id_count += 1
instances.ID_period[idx] = 1
instances.lost_frame_count[idx] = 0
return instances
def _merge_untracked_instances(self, instances: Instances) -> Instances:
"""
For untracked previous instances, under certain condition, still keep them
in tracking and merge with the current instances.
Args:
instances: D2 Instances, for predictions of the current frame
Return:
D2 Instances merging current instances and instances from previous
frame decided to keep tracking
"""
untracked_instances = Instances(
image_size=instances.image_size,
pred_boxes=[],
pred_classes=[],
scores=[],
ID=[],
ID_period=[],
lost_frame_count=[],
)
prev_bboxes = list(self._prev_instances.pred_boxes)
prev_classes = list(self._prev_instances.pred_classes)
prev_scores = list(self._prev_instances.scores)
prev_ID_period = self._prev_instances.ID_period
if instances.has("pred_masks"):
untracked_instances.set("pred_masks", [])
prev_masks = list(self._prev_instances.pred_masks)
if instances.has("pred_keypoints"):
untracked_instances.set("pred_keypoints", [])
prev_keypoints = list(self._prev_instances.pred_keypoints)
if instances.has("pred_keypoint_heatmaps"):
untracked_instances.set("pred_keypoint_heatmaps", [])
prev_keypoint_heatmaps = list(self._prev_instances.pred_keypoint_heatmaps)
for idx in self._untracked_prev_idx:
x_left, y_top, x_right, y_bot = prev_bboxes[idx]
if (
(1.0 * (x_right - x_left) / self._video_width < self._min_box_rel_dim)
or (1.0 * (y_bot - y_top) / self._video_height < self._min_box_rel_dim)
or self._prev_instances.lost_frame_count[idx] >= self._max_lost_frame_count
or prev_ID_period[idx] <= self._min_instance_period
):
continue
untracked_instances.pred_boxes.append(list(prev_bboxes[idx].numpy()))
untracked_instances.pred_classes.append(int(prev_classes[idx]))
untracked_instances.scores.append(float(prev_scores[idx]))
untracked_instances.ID.append(self._prev_instances.ID[idx])
untracked_instances.ID_period.append(self._prev_instances.ID_period[idx])
untracked_instances.lost_frame_count.append(
self._prev_instances.lost_frame_count[idx] + 1
)
if instances.has("pred_masks"):
untracked_instances.pred_masks.append(prev_masks[idx].numpy().astype(np.uint8))
if instances.has("pred_keypoints"):
untracked_instances.pred_keypoints.append(
prev_keypoints[idx].numpy().astype(np.uint8)
)
if instances.has("pred_keypoint_heatmaps"):
untracked_instances.pred_keypoint_heatmaps.append(
prev_keypoint_heatmaps[idx].numpy().astype(np.float32)
)
untracked_instances.pred_boxes = Boxes(torch.FloatTensor(untracked_instances.pred_boxes))
untracked_instances.pred_classes = torch.IntTensor(untracked_instances.pred_classes)
untracked_instances.scores = torch.FloatTensor(untracked_instances.scores)
if instances.has("pred_masks"):
untracked_instances.pred_masks = torch.IntTensor(untracked_instances.pred_masks)
if instances.has("pred_keypoints"):
untracked_instances.pred_keypoints = torch.IntTensor(untracked_instances.pred_keypoints)
if instances.has("pred_keypoint_heatmaps"):
untracked_instances.pred_keypoint_heatmaps = torch.FloatTensor(
untracked_instances.pred_keypoint_heatmaps
)
return Instances.cat(
[
instances,
untracked_instances,
]
)
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