0|前言
YOLOv5为兼顾速度与性能的目标检测算法。笔者将在近期更新一系列YOLOv5的代码导读博客。YOLOv5为2021.1.5日发布的4.0版本。
YOLOv5开源项目github网址
本博客导读的代码为utils文件夹下的metrics.py
metrics.py
此文件为模型验证指标，作用主要是获得到的预测结果与ground truth表现计算指标P、R、F1-score、AP、不同阈值下的mAP等。同时，该文件将上述指标进行了可视化，绘制了混淆矩阵以及P-R曲线。
这里为了对比阅读，附上模型验证指标的全部代码，以供读者阅读：
# Model validation metrics
from pathlib import Path
import matplotlib.pyplot as plt
import numpy as np
import torch
from . import general
def fitness(x):
# Model fitness as a weighted combination of metrics
w = [0.0, 0.0, 0.1, 0.9] # weights for [P, R, mAP@0.5, mAP@0.5:0.95]
return (x[:, :4] * w).sum(1)
def ap_per_class(tp, conf, pred_cls, target_cls, plot=False, save_dir='precision-recall_curve.png', names=[]):
""" Compute the average precision, given the recall and precision curves.
Source: https://github.com/rafaelpadilla/Object-Detection-Metrics.
# Arguments
tp: True positives (nparray, nx1 or nx10).
conf: Objectness value from 0-1 (nparray).
pred_cls: Predicted object classes (nparray).
target_cls: True object classes (nparray).
plot: Plot precision-recall curve at mAP@0.5
save_dir: Plot save directory
# Returns
The average precision as computed in py-faster-rcnn.
"""
# Sort by objectness
i = np.argsort(-conf)
tp, conf, pred_cls = tp[i], conf[i], pred_cls[i]
# Find unique classes
unique_classes = np.unique(target_cls)
# Create Precision-Recall curve and compute AP for each class
px, py = np.linspace(0, 1, 1000), [] # for plotting
pr_score = 0.1 # score to evaluate P and R https://github.com/ultralytics/yolov3/issues/898
s = [unique_classes.shape[0], tp.shape[1]] # number class, number iou thresholds (i.e. 10 for mAP0.5...0.95)
ap, p, r = np.zeros(s), np.zeros(s), np.zeros(s)
for ci, c in enumerate(unique_classes):
i = pred_cls == c
n_l = (target_cls == c).sum() # number of labels
n_p = i.sum() # number of predictions
if n_p == 0 or n_l == 0:
continue
else:
# Accumulate FPs and TPs
fpc = (1 - tp[i]).cumsum(0)
tpc = tp[i].cumsum(0)
# Recall
recall = tpc / (n_l + 1e-16) # recall curve
r[ci] = np.interp(-pr_score, -conf[i], recall[:, 0]) # r at pr_score, negative x, xp because xp decreases
# Precision
precision = tpc / (tpc + fpc) # precision curve
p[ci] = np.interp(-pr_score, -conf[i], precision[:, 0]) # p at pr_score
# AP from recall-precision curve
for j in range(tp.shape[1]):
ap[ci, j], mpre, mrec = compute_ap(recall[:, j], precision[:, j])
if plot and (j == 0):
py.append(np.interp(px, mrec, mpre)) # precision at mAP@0.5
# Compute F1 score (harmonic mean of precision and recall)
f1 = 2 * p * r / (p + r + 1e-16)
if plot:
plot_pr_curve(px, py, ap, save_dir, names)
return p, r, ap, f1, unique_classes.astype('int32')
def compute_ap(recall, precision):
""" Compute the average precision, given the recall and precision curves
# Arguments
recall: The recall curve (list)
precision: The precision curve (list)
# Returns
Average precision, precision curve, recall curve
"""
# Append sentinel values to beginning and end
mrec = np.concatenate(([0.], recall, [recall[-1] + 0.01]))
mpre = np.concatenate(([1.], precision, [0.]))
# Compute the precision envelope
mpre = np.flip(np.maximum.accumulate(np.flip(mpre)))
# Integrate area under curve
method = 'interp' # methods: 'continuous', 'interp'
if method == 'interp':
x = np.linspace(0, 1, 101) # 101-point interp (COCO)
ap = np.trapz(np.interp(x, mrec, mpre), x) # integrate
else: # 'continuous'
i = np.where(mrec[1:] != mrec[:-1])[0] # points where x axis (recall) changes
ap = np.sum((mrec[i + 1] - mrec[i]) * mpre[i + 1]) # area under curve
return ap, mpre, mrec
class ConfusionMatrix:
# Updated version of https://github.com/kaanakan/object_detection_confusion_matrix
def __init__(self, nc, conf=0.25, iou_thres=0.45):
self.matrix = np.zeros((nc + 1, nc + 1))
self.nc = nc # number of classes
self.conf = conf
self.iou_thres = iou_thres
def process_batch(self, detections, labels):
"""
Return intersection-over-union (Jaccard index) of boxes.
Both sets of boxes are expected to be in (x1, y1, x2, y2) format.
Arguments:
detections (Array[N, 6]), x1, y1, x2, y2, conf, class
labels (Array[M, 5]), class, x1, y1, x2, y2
Returns:
None, updates confusion matrix accordingly
"""
detections = detections[detections[:, 4] > self.conf]
gt_classes = labels[:, 0].int()
detection_classes = detections[:, 5].int()
iou = general.box_iou(labels[:, 1:], detections[:, :4])
x = torch.where(iou > self.iou_thres)
if x[0].shape[0]:
matches = torch.cat((torch.stack(x, 1), iou[x[0], x[1]][:, None]), 1).cpu().numpy()
if x[0].shape[0] > 1:
matches = matches[matches[:, 2].argsort()[::-1]]
matches = matches[np.unique(matches[:, 1], return_index=True)[1]]
matches = matches[matches[:, 2].argsort()[::-1]]
matches = matches[np.unique(matches[:, 0], return_index=True)[1]]
else:
matches = np.zeros((0, 3))
n = matches.shape[0] > 0
m0, m1, _ = matches.transpose().astype(np.int16)
for i, gc in enumerate(gt_classes):
j = m0 == i
if n and sum(j) == 1:
self.matrix[gc, detection_classes[m1[j]]] += 1 # correct
else:
self.matrix[gc, self.nc] += 1 # background FP
if n:
for i, dc in enumerate(detection_classes):
if not any(m1 == i):
self.matrix[self.nc, dc] += 1 # background FN
def matrix(self):
return self.matrix
def plot(self, save_dir='', names=()):
try:
import seaborn as sn
array = self.matrix / (self.matrix.sum(0).reshape(1, self.nc + 1) + 1E-6) # normalize
array[array < 0.005] = np.nan # don't annotate (would appear as 0.00)
fig = plt.figure(figsize=(12, 9), tight_layout=True)
sn.set(font_scale=1.0 if self.nc < 50 else 0.8) # for label size
labels = (0 < len(names) < 99) and len(names) == self.nc # apply names to ticklabels
sn.heatmap(array, annot=self.nc < 30, annot_kws={"size": 8}, cmap='Blues', fmt='.2f', square=True,
xticklabels=names + ['background FN'] if labels else "auto",
yticklabels=names + ['background FP'] if labels else "auto").set_facecolor((1, 1, 1))
fig.axes[0].set_xlabel('True')
fig.axes[0].set_ylabel('Predicted')
fig.savefig(Path(save_dir) / 'confusion_matrix.png', dpi=250)
except Exception as e:
pass
def print(self):
for i in range(self.nc + 1):
print(' '.join(map(str, self.matrix[i])))
# Plots ----------------------------------------------------------------------------------------------------------------
def plot_pr_curve(px, py, ap, save_dir='.', names=()):
fig, ax = plt.subplots(1, 1, figsize=(9, 6), tight_layout=True)
py = np.stack(py, axis=1)
if 0 < len(names) < 21: # show mAP in legend if < 10 classes
for i, y in enumerate(py.T):
ax.plot(px, y, linewidth=1, label=f'{names[i]} %.3f' % ap[i, 0]) # plot(recall, precision)
else:
ax.plot(px, py, linewidth=1, color='grey') # plot(recall, precision)
ax.plot(px, py.mean(1), linewidth=3, color='blue', label='all classes %.3f mAP@0.5' % ap[:, 0].mean())
ax.set_xlabel('Recall')
ax.set_ylabel('Precision')
ax.set_xlim(0, 1)
ax.set_ylim(0, 1)
plt.legend(bbox_to_anchor=(1.04, 1), loc="upper left")
fig.savefig(Path(save_dir) / 'precision_recall_curve.png', dpi=250)
1) 首先欣赏一下导入模块
from pathlib import path #调用路径操作模块
import matplotlib.pyplot as plt #matplotlib 画图模块
import numpy as np # numpy矩阵处理模块
import torch # pytorch模块
from . import general #从当前文件所处的相对路径中调用general.py
2) fitness函数： 通过指标加权的形式返回适应度
def fitness(x):
# 以矩阵的加权组合作为模型的适应度
w = [0.0, 0.0, 0.1, 0.9] # 每个变量对应的权重 [P, R, mAP@0.5, mAP@0.5:0.95]
# (torch.tensor).sum(1) 每一行求和tensor为二维时返回一个以每一行求和为结果的行向量
return (x[:, :4] * w).sum(1)
3) ap_per_class函数：计算每个类的AP指标
# ap_per_class函数：计算每个类别的AP指标
def ap_per_class(tp, conf, pred_cls, target_cls, plot=False, save_dir='precision-recall_curve.png', names=[]):
""" Compute the average precision, given the recall and precision curves.
计算平均精度（AP）,并绘制P-R曲线，代码来源如下
Source: https://github.com/rafaelpadilla/Object-Detection-Metrics.
# Arguments (变量)
tp: True positives (nparray, nx1 or nx10). 真阳
conf: Objectness value from 0-1 (nparray). 目标的置信度取值为0-1.
pred_cls: Predicted object classes (nparray). 预测目标的类别
target_cls: True object classes (nparray). 真实目标的类别
plot: Plot precision-recall curve at mAP@0.5 是否绘制P-R曲线，在mAP@0.5的情况下
save_dir: Plot save directory P-R曲线图的保存路径
# Returns (返回值)
像faster-rcnn 那种方式计算AP (这里涉及计算AP的两种不同方式，建议查询)
The average precisi on as computed in py-faster-rcnn.
"""
# Sort by objectness 将目标进行排序
# np.argsort(-conf)函数返回一个索引数组 其中每一个数按照conf(目标的置信度)中的元素从大到小置为0,1,2,...n排序
i = np.argsort(-conf)
# tp(真阳), conf(置信度) pred_cls(预测类别) 三个矩阵均按照置信度从大到小进行排列
tp, conf, pred_cls = tp[i], conf[i], pred_cls[i]
# Find unique classes 找到各个独立的类别
# np.unique()会返回输入array中出现至少一次的变量 这里返回所有独立的类别
unique_classes = np.unique(target_cls)
# Create Precision-Recall curve and compute AP for each class
# 创建P-R曲线， 并计算每一个类别的AP
px, py = np.linspace(0, 1, 1000), [] # for plotting
pr_score = 0.1 # 评估P和R的分数 参考 https://github.com/ultralytics/yolov3/issues/898
# 第一个为类别数， 第二为IOU loss阈值的类别
s = [unique_classes.shape[0], tp.shape[1]] # number class, number iou thresholds (i.e. 10 for mAP0.5...0.95)
# 初始化 对每一个类别在每一个IOU阈值下面 计算P R AP参数
ap, p, r = np.zeros(s), np.zeros(s), np.zeros(s)
for ci, c in enumerate(unique_classes): # ci:类别对应的索引；c具体的类别
# i为一个包含True/False的列表 代表pred_cls array 各元素是否与类别C相同
i = pred_cls == c # 预测为类别C的列表
n_l = (target_cls == c).sum() # number of labels ground truth中 类别C的个数 all_results
n_p = i.sum() # number of predictions # 预测为类别C的列表中Ture的个数
if n_p == 0 or n_l == 0: #如果没有预测到 或者 ground truth中没有标注 则略过类别C
continue
else:
# Accumulate FPs and TPs
'''
计算FP（False Positive）和TP（True Positive）
tp[i] 会根据i中对应位置是否为False来决定是否删除这一位的内容，如下所示：
a = np.array([0,1,0,1]) i = np.array([Truee,False,False,True]) b = a[i]
则b为：[0,1]
而。cumsum(0)函数会按照对象进行累加操作，如下所示：
a = np.array([0,1,0,1]) b = a.cumsum(0)
则b为：[0,1,1,2]
(FP+TP = all_detections 所以有fp[i] = 1 - tp[i])
所以fpc为 类别c 按照置信度从大到小排列 截止到每一位的FP数目
tpc为 类别c 按照置信度从大到小排列 截止到每一位的TP数目
recall 和 precision 均按照元素从小到大排列
'''
fpc = (1 - tp[i]).cumsum(0)
tpc = tp[i].cumsum(0)
# Recall 召回率
# Recall = TP /(TP+FN) = TP/ all_results = TP / n_l
recall = tpc / (n_l + 1e-16) # recall curve
'''
np.interp()函数第一个输入值为数值， 第二、第三个变量为一组x,y坐标； 返回结果为一个数值
这个数值为 找寻该数值左右两边的x值， 并将两者对应的y值取平均 如果在左侧或右侧 则取边界值】
如果第一个输入为数组 则返回一个数组 其中每一个元素按照上述计算规则产生
'''
r[ci] = np.interp(-pr_score, -conf[i], recall[:, 0]) # pr_score处的y值
# Precision
# Precision = TP/(TP+FP) = TP/ all_detections
precision = tpc / (tpc + fpc) # precision curve
p[ci] = np.interp(-pr_score, -conf[i], precision[:, 0]) # p at pr_score
# AP from recall-precision curve 从P-R曲线中计算AP ci: 为类别索引， tp: 为真阳
for j in range(tp.shape[1]): # 这里对每一个IOU阈值下的参数进行计算
ap[ci, j], mpre, mrec = compute_ap(recall[:, j], precision[:, j]) # 取每一个阈值计算AP
if plot and (j == 0):
py.append(np.interp(px, mrec, mpre)) # precision at mAP@0.5 mAP@0.5处的p
# Compute F1 score (harmonic mean of precision and recall)
# 计算F1分数P和R的调和平均值
f1 = 2 * p * r / (p + r + 1e-16)
if plot:
plot_pr_curve(px, py, ap, save_dir, names) # plot函数在本代码的末尾
return p, r, ap, f1, unique_classes.astype('int32') # 返回值：P,r，ap, f1，
4) compute_ap: 通过输入P和R的值计算AP
def compute_ap(recall, precision):
""" Compute the average precision, given the recall and precision curves
通过P和R来计算AP
Source: https://github.com/rbgirshick/py-faster-rcnn.
# Arguments(变量)
recall: The recall curve (list)
precision: The precision curve (list)
# Returns
Average precision, precision curve, recall curve
"""
# Append sentinel values to beginning and end
# 在开头和末尾添加保护值 防止全零的情况出现
mrec = np.concatenate(([0.], recall, [recall[-1] + 0.01]))
mpre = np.concatenate(([1.], precision, [0.]))
'''
此处需要关注precision列表输入时元素为从小到大排列（由上一个函数）
np.filp()函数会把一维数组每个元素的顺序进行翻转 第一个翻转成为最后一个
np.maximum.accumulate()函数会返回输入
mpre = np.filp(np.maximum.accumulate(np.flip(recall)))
Q?：此处mpre返回的是是否由输入数组中最大的元素组成的数组如
recall = np.array([0.1,0.2,0.2,0.3,0.4])
final_1 = np.flip(np.maximum.accumulate(np.flip(recall)))
final_2 = np.flip(np.maximum.accumulate(recall))
final_1：[0.4 0.4 0.4 0.4 0.4]
final_2：[0.4 0.3 0.2 0.2 0.1]
'''
# Compute the precision envelope
mpre = np.flip(np.maximum.accumulate(np.flip(mpre)))
# Integrate area under curve
method = 'interp' # methods: 'continuous', 'interp'
if method == 'interp': # 计算AP的方法为间断性的
# x 为0-1的101个点组成的等差数列的数组 为间断点
x = np.linspace(0, 1, 101) # 101-point interp (COCO)
# np.trapz(list, list) 计算两个list对应点与点之间四边形的面积 以定积分形式估算AP
# 按照P-R曲线的定义 R近似为递增数组 P为近似递减数组 如上中final_2结果
ap = np.trapz(np.interp(x, mrec, mpre), x) # 前一个数组为纵坐标， 第二个为横坐标
else: # 'continuous' 采用连续的方法计算AP
'''
通过错位的方式 判断哪个点发生了改变并通过 ！=判断 返回一个布尔数组
在通过np.where()函数找出mrec中对应发生的改变点 i为一个数组 每一个元素代表当前位置到下一个位置发生改变
'''
i = np.where(mrec[1:] != mrec[:-1])[0] # points where x axis (recall) changes
ap = np.sum((mrec[i + 1] - mrec[i]) * mpre[i + 1]) # area under curve
return ap, mpre, mrec
5) ConfusionMatrix类：求解混淆矩阵并进行绘图
class ConfusionMatrix: # nc: 训练的类别； conf: 置信度； iou_thres: IOU loss的阈值
# Updated version of https://github.com/kaanakan/object_detection_confusion_matrix
def __init__(self, nc, conf=0.25, iou_thres=0.45):
self.matrix = np.zeros((nc + 1, nc + 1))
self.nc = nc # number of classes
self.conf = conf
self.iou_thres = iou_thres
def process_batch(self, detections, labels):
"""
Return intersection-over-union (Jaccard index) of boxes.
返回 各个box之间的交并比（IOU）
Both sets of boxes are expected to be in (x1, y1, x2, y2) format.
每一个box的集合都被期望使用(x1,y1,x2,y2)的形式 这两点为box的对角顶点
Arguments: detections 和 labels的数据结构
detections (Array[N, 6]), x1, y1, x2, y2, conf, class
labels (Array[M, 5]), class, x1, y1, x2, y2
Returns:
None, updates confusion matrix accordingly
无返回 更新混淆矩阵
"""
# dect=ections (Array[N,6]), x1,y1,x2,y2, conf, class
detections = detections[detections[:, 4] > self.conf] # 返回检测大于阈值的框
gt_classes = labels[:, 0].int() # 返回ground truth的类别
detection_classes = detections[:, 5].int() # 返回检测到的类别
'''
iou计算 box1 (Array[N,4]), x1,y1,x2,y2
box2 (Array[M,4]), x1,y1,x2,y2
iou (Tensor[N,M]) NxM矩阵包含了box1中每一个框和box2中每一个框的iou值
非常重要！iou中坐标(n1,m1) 代表 第n1个ground truth框 和 第m1个预测框的
'''
iou = general.box_iou(labels[:, 1:], detections[:, :4]) # 调用general中计算iou的方式计算
# x为一个含有两个tensor的tuple表示iou中大于阈值的值的坐标，第一个tensor为第几行，第二个为第几列
x = torch.where(iou > self.iou_thres) # 找到iou中大于阈值的那部分并提取
if x[0].shape[0]:
'''
torch.cat(inputs, dimension=0)为指定的维度对张量inputs进行堆叠
二维情况下 0代表按照行 1代表按照列 0时会增加行 1时会增加列
torch.stack(x,1) 当x为二维张量的时候， 本质上是对x做转置操作
.cpu()是将变量转移到cpu上进行运算 .numpy()是转换为numpy数组
matches (Array[N,3]), row，col, iou_value ！！！
row为大于阈值的iou张量中点的横坐标 col为纵坐标 iou_value为对应的iouz值
'''
matches = torch.cat((torch.stack(x, 1), iou[x[0], x[1]][:, None]), 1).cpu().numpy()
if x[0].shape[0] > 1: # 当box个数大于1时进行一下过程 此处matches的过滤过程见下文 补充部分
matches = matches[matches[:, 2].argsort()[::-1]]
matches = matches[np.unique(matches[:, 1], return_index=True)[1]]
matches = matches[matches[:, 2].argsort()[::-1]]
matches = matches[np.unique(matches[:, 0], return_index=True)[1]]
else:
matches = np.zeros((0, 3)) # 这里返回一个0行3列全0的二维数组？ 因为没有一个例子满足这个要求
n = matches.shape[0] > 0 # 这里n为True 或 False 用于判断是否存在满足阈值要求的对象是否至少有一个
'''
a.transpose()是numpy中轮换维度索引的方法 对二维数组表示为转置
此处matches (Array[N,3]), row，col, iou_value
物理意义：在大于阈值的前提下，N*M种label与预测框的组合可能下， 每一种预测框与所有label框iou值最大的那个
mo, m1 (Array[1,N])
m0代表: 满足上述条件的第i个label框 (也即类别)
m1代表：满足上述条件的第j个predict框 (也即类别)
'''
m0, m1, _ = matches.transpose().astype(np.int16)
for i, gc in enumerate(gt_classes): # 解析ground truth中的类别
j = m0 == i
if n and sum(j) == 1: # 检测到的目标至少有1个且ground truth 对应只有一个
self.matrix[gc, detection_classes[m1[j]]] += 1 # correct 判断正确的数目加1
else:
self.matrix[gc, self.nc] += 1 # background FP 背景FP(false positive) 个数加1 背景被误认为目标
if n: # 当目标不止一个时
for i, dc in enumerate(detection_classes): # i为索引 dc为每一个目标检测得的类别
if not any(m1 == i): # 检测到目标 但是目标与ground truth的iou小于之前要求的阈值则
self.matrix[self.nc, dc] += 1 # background FN 背景FN个数加1 (目标被检测成了背景)
def matrix(self): # 返回matrix变量 该matrix为混淆矩阵
return self.matrix
def plot(self, save_dir='', names=()):
try:
import seaborn as sn # seaborn 为易于可视化的一个模块
array = self.matrix / (self.matrix.sum(0).reshape(1, self.nc + 1) + 1E-6) # normalize 矩阵归一化为0-1
array[array < 0.005] = np.nan # don't annotate (would appear as 0.00) # 小于0.005的值被认为NaN
fig = plt.figure(figsize=(12, 9), tight_layout=True) # 初始化画布
sn.set(font_scale=1.0 if self.nc < 50 else 0.8) # for label size 设置标签的尺寸
labels = (0 < len(names) < 99) and len(names) == self.nc # apply names to ticklabels 用于绘制过程中判断是否应用names
# 绘制热力图 即混淆矩阵可视化
sn.heatmap(array, annot=self.nc < 30, annot_kws={"size": 8}, cmap='Blues', fmt='.2f', square=True,
xticklabels=names + ['background FN'] if labels else "auto",
yticklabels=names + ['background FP'] if labels else "auto").set_facecolor((1, 1, 1))
# 下三行代码为设置figure的横坐标 纵坐标及保存该图片
fig.axes[0].set_xlabel('True')
fig.axes[0].set_ylabel('Predicted')
fig.savefig(Path(save_dir) / 'confusion_matrix.png', dpi=250)
except Exception as e:
pass
def print(self):
for i in range(self.nc + 1):
print(' '.join(map(str, self.matrix[i])))
6) plot_pr_curve函数用于绘制P-R曲线
# Plots ----------plot_pr_curve函数用于绘制P-R曲线------------------------------------------------------------
def plot_pr_curve(px, py, ap, save_dir='.', names=()): # 绘制P-R曲线
fig, ax = plt.subplots(1, 1, figsize=(9, 6), tight_layout=True) # 初始化坐标
py = np.stack(py, axis=1)
if 0 < len(names) < 21: # show mAP in legend if < 10 classes 类别小于10类的时候 写上mAP
for i, y in enumerate(py.T):
ax.plot(px, y, linewidth=1, label=f'{names[i]} %.3f' % ap[i, 0]) # plot(recall, precision) 绘制(recall, precision)
else:
ax.plot(px, py, linewidth=1, color='grey') # 绘制(recall, precision)
# 下一行代码为添加mAP@0.5的信息到图片之中
ax.plot(px, py.mean(1), linewidth=3, color='blue', label='all classes %.3f mAP@0.5' % ap[:, 0].mean())
# 以下四行设置图片x、y坐标轴的标签和刻度
ax.set_xlabel('Recall')
ax.set_ylabel('Precision')
ax.set_xlim(0, 1)
ax.set_ylim(0, 1)
# 把上图移动到整张图片的左上角
plt.legend(bbox_to_anchor=(1.04, 1), loc="upper left")
# 保存图片
fig.savefig(Path(save_dir) / 'precision_recall_curve.png', dpi=250)
7). 补充部分
关于上述四步matches处理的详细解释
import torch
import numpy as np
iou = torch.tensor([[0.16512, 0.04280, 0.7912, 0.06599, 0.0755, 0.4665],
[0.014043, 0.3173, 0.4420, 1.2253, 0.206817, 0.5997],
[ 0.4398, 0.1185, 1.2385, 0.2133, 0.7412, 0.06974],
[ 0.7442, 0.9128, 1.0040, 2.0243, 1.0281, 1.3334],
[ 1.0045, 0.7125, 0.03617, 0.0962, 0.7367, 0.6041]])
iou_thres = 0.2
x = torch.where(iou > iou_thres )
x_stack = torch.stack(x,1)
print("first matches第一列为横坐标（label框） 第二列为纵坐标（predict框） 第三列为iou")
matches = torch.cat((torch.stack(x, 1), iou[x[0], x[1]][:, None]), 1).cpu().numpy()
print(matches)
print(" ")
print("second 按照第三列iou值从大到小对matches各个行重新排列")
matches2 = matches[matches[:, 2].argsort()[::-1]]
print(matches2)
print(" ")
print("third 取第二列中各个框首次出现（此处为不同预测到的框）的行（即每一种预测的框中iou值最大的那个）")
#print(np.unique(matches2[:, 1], return_index=True))
matches3 = matches2[np.unique(matches2[:, 1], return_index=True)[1]]
print(matches3)
print(" ")
print("forth 按照第三列iou值从大到小对matches各个行重新排列")
matches4 = matches3[matches3[:, 2].argsort()[::-1]]
print(matches4)
print(" ")
print("fifth 取第一列中各个框首次出现（此处为不同label的框）的行（即每一种label框中iou值最大的那个）")
matches5 = matches4[np.unique(matches4[:, 0], return_index=True)[1]]
print(matches5)
print("经过这样的处理，最终得到每一种预测框与所有label框iou值最大的那个（在大于阈值的前提下）")
first matches第一列为横坐标（label框） 第二列为纵坐标（predict框） 第三列为iou
[[0. 2. 0.7912 ]
[0. 5. 0.4665 ]
[1. 1. 0.3173 ]
[1. 2. 0.442 ]
[1. 3. 1.2253 ]
[1. 4. 0.206817]
[1. 5. 0.5997 ]
[2. 0. 0.4398 ]
[2. 2. 1.2385 ]
[2. 3. 0.2133 ]
[2. 4. 0.7412 ]
[3. 0. 0.7442 ]
[3. 1. 0.9128 ]
[3. 2. 1.004 ]
[3. 3. 2.0243 ]
[3. 4. 1.0281 ]
[3. 5. 1.3334 ]
[4. 0. 1.0045 ]
[4. 1. 0.7125 ]
[4. 4. 0.7367 ]
[4. 5. 0.6041 ]]
second 按照第三列iou值从大到小对matches各个行重新排列
[[3. 3. 2.0243 ]
[3. 5. 1.3334 ]
[2. 2. 1.2385 ]
[1. 3. 1.2253 ]
[3. 4. 1.0281 ]
[4. 0. 1.0045 ]
[3. 2. 1.004 ]
[3. 1. 0.9128 ]
[0. 2. 0.7912 ]
[3. 0. 0.7442 ]
[2. 4. 0.7412 ]
[4. 4. 0.7367 ]
[4. 1. 0.7125 ]
[4. 5. 0.6041 ]
[1. 5. 0.5997 ]
[0. 5. 0.4665 ]
[1. 2. 0.442 ]
[2. 0. 0.4398 ]
[1. 1. 0.3173 ]
[2. 3. 0.2133 ]
[1. 4. 0.206817]]
third 取第二列中各个框首次出现（此处为不同预测到的框）的行（即每一种预测的框中iou值最大的那个）
[[4. 0. 1.0045]
[3. 1. 0.9128]
[2. 2. 1.2385]
[3. 3. 2.0243]
[3. 4. 1.0281]
[3. 5. 1.3334]]
forth 按照第三列iou值从大到小对matches各个行重新排列
[[3. 3. 2.0243]
[3. 5. 1.3334]
[2. 2. 1.2385]
[3. 4. 1.0281]
[4. 0. 1.0045]
[3. 1. 0.9128]]
fifth 取第一列中各个框首次出现（此处为不同label的框）的行（即每一种label框中iou值最大的那个）
[[2. 2. 1.2385]
[3. 3. 2.0243]
[4. 0. 1.0045]]
经过这样的处理，最终得到每一种预测框与所有label框iou值最大的那个（在大于阈值的前提下）
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