Weighted boxes fusion

Repository contains Python implementation of several methods for ensembling boxes from object detection models:

• Non-maximum Suppression (NMS)
• Soft-NMS [1]
• Non-maximum weighted (NMW) [2]
• Weighted boxes fusion (WBF) [3] - new method which gives better results comparing to others

Requirements

Python 3.*, Numpy

Installation

pip install ensemble-boxes

Usage examples

Coordinates for boxes expected to be normalized e.g in range [0; 1]. Order: x1, y1, x2, y2.

Example of boxes ensembling for 2 models below.

• First model predicts 5 boxes, second model predicts 4 boxes.
• Confidence scores for each box model 1: [0.9, 0.8, 0.2, 0.4, 0.7]
• Confidence scores for each box model 2: [0.5, 0.8, 0.7, 0.3]
• Labels (classes) for each box model 1: [0, 1, 0, 1, 1]
• Labels (classes) for each box model 2: [1, 1, 1, 0]
• We set weight for 1st model to be 2, and weight for second model to be 1.
• We set intersection over union for boxes to be match: iou_thr = 0.5
• We skip boxes with confidence lower than skip_box_thr = 0.0001

from ensemble_boxes import *

boxes_list = [[
    [0.00, 0.51, 0.81, 0.91],
    [0.10, 0.31, 0.71, 0.61],
    [0.01, 0.32, 0.83, 0.93],
    [0.02, 0.53, 0.11, 0.94],
    [0.03, 0.24, 0.12, 0.35],
],[
    [0.04, 0.56, 0.84, 0.92],
    [0.12, 0.33, 0.72, 0.64],
    [0.38, 0.66, 0.79, 0.95],
    [0.08, 0.49, 0.21, 0.89],
]]
scores_list = [[0.9, 0.8, 0.2, 0.4, 0.7], [0.5, 0.8, 0.7, 0.3]]
labels_list = [[0, 1, 0, 1, 1], [1, 1, 1, 0]]
weights = [2, 1]

iou_thr = 0.5
skip_box_thr = 0.0001
sigma = 0.1

boxes, scores, labels = nms(boxes_list, scores_list, labels_list, weights=weights, iou_thr=iou_thr)
boxes, scores, labels = soft_nms(boxes_list, scores_list, labels_list, weights=weights, iou_thr=iou_thr, sigma=sigma, thresh=skip_box_thr)
boxes, scores, labels = non_maximum_weighted(boxes_list, scores_list, labels_list, weights=weights, iou_thr=iou_thr, skip_box_thr=skip_box_thr)
boxes, scores, labels = weighted_boxes_fusion(boxes_list, scores_list, labels_list, weights=weights, iou_thr=iou_thr, skip_box_thr=skip_box_thr)

Single model

If you need to apply NMS or any other method to single model predictions you can call function like that:

from ensemble_boxes import *
# Merge boxes for single model predictions
boxes, scores, labels = weighted_boxes_fusion([boxes_list], [scores_list], [labels_list], weights=None, method=method, iou_thr=iou_thr, thresh=thresh)

More examples can be found in example.py

Accuracy and speed comparison

Comparison was made for ensemble of 5 different object detection models predictions trained on Open Images Dataset (500 classes).

Model scores at local validation:

• Model 1: mAP(0.5) 0.5164
• Model 2: mAP(0.5) 0.5019
• Model 3: mAP(0.5) 0.5144
• Model 4: mAP(0.5) 0.5152
• Model 5: mAP(0.5) 0.4910

Method	mAP(0.5) Result	Best params	Elapsed time (sec)
NMS	0.5642	IOU Thr: 0.5	47
Soft-NMS	0.5616	Sigma: 0.1, Confidence Thr: 0.001	88
NMW	0.5667	IOU Thr: 0.5	171
WBF	0.5982	IOU Thr: 0.6	249

You can download model predictions as well as ground truth labels from here: test_data.zip

Ensemble script for them is available here: example_oid.py

Description of WBF method

• https://arxiv.org/abs/1910.13302