版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/jacke121/article/details/82795272
import torch
import numpy as np
import collections
import torch
import itertools
from typing import List
import math
def convert_locations_to_boxes(locations, priors, center_variance,
size_variance):
"""Convert regressional location results of SSD into boxes in the form of (center_x, center_y, h, w).
The conversion:
$$predicted\_center * center_variance = \frac {real\_center - prior\_center} {prior\_hw}$$
$$exp(predicted\_hw * size_variance) = \frac {real\_hw} {prior\_hw}$$
We do it in the inverse direction here.
Args:
locations (batch_size, num_priors, 4): the regression output of SSD. It will contain the outputs as well.
priors (num_priors, 4) or (batch_size/1, num_priors, 4): prior boxes.
center_variance: a float used to change the scale of center.
size_variance: a float used to change of scale of size.
Returns:
boxes: priors: [[center_x, center_y, h, w]]. All the values
are relative to the image size.
"""
# priors can have one dimension less.
if priors.dim() + 1 == locations.dim():
priors = priors.unsqueeze(0)
return torch.cat([
locations[..., :2] * center_variance * priors[..., 2:] + priors[..., :2],
torch.exp(locations[..., 2:] * size_variance) * priors[..., 2:]
], dim=locations.dim() - 1)
def convert_boxes_to_locations(center_form_boxes, center_form_priors, center_variance, size_variance):
# priors can have one dimension less
if center_form_priors.dim() + 1 == center_form_boxes.dim():
center_form_priors = center_form_priors.unsqueeze(0)
return torch.cat([
(center_form_boxes[..., :2] - center_form_priors[..., :2]) / center_form_priors[..., 2:] / center_variance,
torch.log(center_form_boxes[..., 2:] / center_form_priors[..., 2:]) / size_variance
], dim=center_form_boxes.dim() - 1)
def area_of(left_top, right_bottom) -> torch.Tensor:
"""Compute the areas of rectangles given two corners.
Args:
left_top (N, 2): left top corner.
right_bottom (N, 2): right bottom corner.
Returns:
area (N): return the area.
"""
hw = torch.clamp(right_bottom - left_top, min=0.0)
return hw[..., 0] * hw[..., 1]
def iou_of(boxes0, boxes1, eps=1e-5):
"""Return intersection-over-union (Jaccard index) of boxes.
Args:
boxes0 (N, 4): ground truth boxes.
boxes1 (N or 1, 4): predicted boxes.
eps: a small number to avoid 0 as denominator.
Returns:
iou (N): IoU values.
"""
overlap_left_top = torch.max(boxes0[..., :2], boxes1[..., :2])
overlap_right_bottom = torch.min(boxes0[..., 2:], boxes1[..., 2:])
overlap_area = area_of(overlap_left_top, overlap_right_bottom)
area0 = area_of(boxes0[..., :2], boxes0[..., 2:])
area1 = area_of(boxes1[..., :2], boxes1[..., 2:])
return overlap_area / (area0 + area1 - overlap_area + eps)
def assign_priors(gt_boxes, gt_labels, corner_form_priors,
iou_threshold):
"""Assign ground truth boxes and targets to priors.
Args:
gt_boxes (num_targets, 4): ground truth boxes.
gt_labels (num_targets): labels of targets.
priors (num_priors, 4): corner form priors
Returns:
boxes (num_priors, 4): real values for priors.
labels (num_priros): labels for priors.
"""
# size: num_priors x num_targets
ious = iou_of(gt_boxes.unsqueeze(0), corner_form_priors.unsqueeze(1))
# size: num_priors
best_target_per_prior, best_target_per_prior_index = ious.max(1)
# size: num_targets
best_prior_per_target, best_prior_per_target_index = ious.max(0)
for target_index, prior_index in enumerate(best_prior_per_target_index):
best_target_per_prior_index[prior_index] = target_index
# 2.0 is used to make sure every target has a prior assigned
best_target_per_prior.index_fill_(0, best_prior_per_target_index, 2)
# size: num_priors
labels = gt_labels[best_target_per_prior_index]
labels[best_target_per_prior < iou_threshold] = 0 # the backgournd id
boxes = gt_boxes[best_target_per_prior_index]
return boxes, labels
def hard_negative_mining(loss, labels, neg_pos_ratio):
"""
It used to suppress the presence of a large number of negative prediction.
It works on image level not batch level.
For any example/image, it keeps all the positive predictions and
cut the number of negative predictions to make sure the ratio
between the negative examples and positive examples is no more
the given ratio for an image.
Args:
loss (N, num_priors): the loss for each example.
labels (N, num_priors): the labels.
neg_pos_ratio: the ratio between the negative examples and positive examples.
"""
pos_mask = labels > 0
num_pos = pos_mask.long().sum(dim=1, keepdim=True)
num_neg = num_pos * neg_pos_ratio
loss[pos_mask] = -math.inf
_, indexes = loss.sort(dim=1, descending=True)
_, orders = indexes.sort(dim=1)
neg_mask = orders < num_neg
return pos_mask | neg_mask
def center_form_to_corner_form(locations):
return torch.cat([locations[..., :2] - locations[..., 2:]/2,
locations[..., :2] + locations[..., 2:]/2], locations.dim() - 1)
def corner_form_to_center_form(boxes):
return torch.cat([
(boxes[..., :2] + boxes[..., 2:]) / 2,
boxes[..., 2:] - boxes[..., :2]
], boxes.dim() - 1)
def hard_nms(box_scores, iou_threshold, top_k=-1, candidate_size=200):
"""
Args:
box_scores (N, 5): boxes in corner-form and probabilities.
iou_threshold: intersection over union threshold.
top_k: keep top_k results. If k <= 0, keep all the results.
candidate_size: only consider the candidates with the highest scores.
Returns:
picked: a list of indexes of the kept boxes
"""
scores = box_scores[:, -1]
boxes = box_scores[:, :-1]
picked = []
_, indexes = scores.sort(descending=True)
indexes = indexes[:candidate_size]
while len(indexes) > 0:
current = indexes[0]
picked.append(current.item())
if 0 < top_k == len(picked) or len(indexes) == 1:
break
current_box = boxes[current, :]
indexes = indexes[1:]
rest_boxes = boxes[indexes, :]
iou = iou_of(
rest_boxes,
current_box.unsqueeze(0),
)
indexes = indexes[iou <= iou_threshold]
return box_scores[picked, :]
def nms(box_scores, nms_method=None, score_threshold=None, iou_threshold=None,
sigma=0.5, top_k=-1, candidate_size=200):
if nms_method == "soft":
return soft_nms(box_scores, score_threshold, sigma, top_k)
else:
return hard_nms(box_scores, iou_threshold, top_k, candidate_size=candidate_size)
def soft_nms(box_scores, score_threshold, sigma=0.5, top_k=-1):
"""Soft NMS implementation.
References:
https://arxiv.org/abs/1704.04503
https://github.com/facebookresearch/Detectron/blob/master/detectron/utils/cython_nms.pyx
Args:
box_scores (N, 5): boxes in corner-form and probabilities.
score_threshold: boxes with scores less than value are not considered.
sigma: the parameter in score re-computation.
scores[i] = scores[i] * exp(-(iou_i)^2 / simga)
top_k: keep top_k results. If k <= 0, keep all the results.
Returns:
picked_box_scores (K, 5): results of NMS.
"""
picked_box_scores = []
while box_scores.size(0) > 0:
max_score_index = torch.argmax(box_scores[:, 4])
cur_box_prob = torch.tensor(box_scores[max_score_index, :])
picked_box_scores.append(cur_box_prob)
if len(picked_box_scores) == top_k > 0 or box_scores.size(0) == 1:
break
cur_box = cur_box_prob[:-1]
box_scores[max_score_index, :] = box_scores[-1, :]
box_scores = box_scores[:-1, :]
ious = iou_of(cur_box.unsqueeze(0), box_scores[:, :-1])
box_scores[:, -1] = box_scores[:, -1] * torch.exp(-(ious * ious) / sigma)
box_scores = box_scores[box_scores[:, -1] > score_threshold, :]
if len(picked_box_scores) > 0:
return torch.stack(picked_box_scores)
else:
return torch.tensor([])
if __name__ == '__main__':
# 80 10 5 3:4
# 80 3 11 11
a = torch.linspace(1, 10, steps=10).view(2,5)
# b = torch.FloatTensor(0.5).seqence()
# print(b)
print(soft_nms(a,6))