二分类的 DiceLoss 损失函数
二分类 Dice 系数计算
假设模型输出的预测值 preds 经过 sigmoid 后,得到 logits 如下所示
该 logits 对应的标签 label 如下所示,0 表示不属于某一类,1 表示属于某一类:
根据 DiceLoss 系数的定义有:
∣X∩Y∣=[0.53220.49320.17640.31070.52970.16040.38410.35370.35740.33230.83010.6436]⋆[000000111111]=[0.00000.00000.00000.00000.00000.00000.38410.35370.35740.33230.83010.6436]→2.9012(求和)
\begin{aligned}
|X \cap Y| &=\begin{bmatrix} 0.5322&0.4932&0.1764\\
0.3107&0.5297&0.1604\\
0.3841&0.3537&0.3574\\
0.3323&0.8301&0.6436 \end{bmatrix} \star \begin{bmatrix} 0&0&0\\
0&0&0\\
1&1&1\\
1&1&1
\end{bmatrix} \\&= \begin{bmatrix} 0.0000&0.0000&0.0000\\
0.0000&0.0000&0.0000\\
0.3841&0.3537&0.3574\\
0.3323&0.8301&0.6436 \end{bmatrix} \rightarrow 2.9012 (求和)
\end{aligned}
∣X∣=[0.53220.49320.17640.31070.52970.16040.38410.35370.35740.33230.83010.6436]→5.1038
|X| = \begin{bmatrix} 0.5322&0.4932&0.1764\\
0.3107&0.5297&0.1604\\
0.3841&0.3537&0.3574\\
0.3323&0.8301&0.6436 \end{bmatrix} \rightarrow 5.1038
∣Y∣=[000000111111]→8
|Y| = \begin{bmatrix} 0&0&0\\
0&0&0\\
1&1&1\\
1&1&1 \end{bmatrix} \rightarrow 8
所以 Dice 系数为
D=2∗∣X∩Y∣+1∣X∣+∣Y∣+1=2∗2.9012+15.1038+8+1=0.5901
D = \frac{2 * |X\cap Y| +1}{|X| + |Y | + 1} = \frac{2 * 2.9012 + 1}{ 5.1038 + 8+1}=0.5901
所以 Dice 损失 L=1−D=0.4099L = 1-D=0.4099
这是二分类一个批次只有一张图的情况,当一个批次有 NN 张图片时,可以将图片压缩为一维向量,如下所示:
对应的 label 也做相应的变换,最后一起计算 NN 张图片的 Dice 系数 和 Loss。
上面这个过程的 pytorch 代码实现如下所示;
import torch
import torch.nn as nn
class BinaryDiceLoss(nn.Model):
def __init__(self):
super(BinaryDiceLoss, self).__init__()
def forward(self, input, targets):
# 获取每个批次的大小 N
N = targets.size()[0]
# 平滑变量
smooth = 1
# 将宽高 reshape 到同一纬度
input_flat = input.view(N, -1)
targets_flat = targets.view(N, -1)
# 计算交集
intersection = input_flat * targets_flat
N_dice_eff = (2 * intersection.sum(1) + smooth) / (input_flat.sum(1) + targets_flat.sum(1) + smooth)
# 计算一个批次中平均每张图的损失
loss = 1 - dice_eff.sum() / N
return loss
多分类 DiceLoss 损失函数
当有多个分类时,label 通过 one hot 转化为多个二分类,如下图所示:
每个channel 切面,可以看作是一个二分类问题,所以多分类 DiceLoss 损失函数,可以通过计算每个类别的二分类 DiceLoss 损失,最后再求均值得到。pytorch 代码如下所示:
import torch
import torch.nn as nn
class MultiClassDiceLoss(nn.Module):
def __init__(self, weight=None, ignore_index=None, **kwargs):
super(MultiClassDiceLoss, self).__init__()
self.weight = weight
self.ignore_index = ignore_index
self.kwargs = kwargs
def forward(self, input, target):
"""
input tesor of shape = (N, C, H, W)
target tensor of shape = (N, C, H, W)
"""
assert input.shape == target.shape, "predict & target shape do not match"
binaryDiceLoss = BinaryDiceLoss()
total_loss = 0
# 归一化输出
logits = F.softmax(input, dim=1)
C = target.shape[1]
# 遍历 channel,得到每个类别的二分类 DiceLoss
for i in range(C):
dice_loss = binaryDiceLoss(logits[:, i], target[:, i])
total_loss += dice_loss
# 每个类别的平均 dice_loss
return total_loss / C
本文地址:https://blog.csdn.net/liangjiu2009/article/details/107352164