目录
一、构建数据集
1. 对Dataset和DataLoader的理解
Pytorch提供了一种十分方便的数据读取机制，即使用Dataset与DataLoader组合得到数据迭代器。在每次训练时，利用这个迭代器输出每一个batch的数据，并能在输出时对数据进行相应的预处理或数据增广操作。
-
我们如果要自定义数据读取的方法，就需要继承torch.utils.data.Dataset，并将其封装到torch.utils.data.DataLoader中。
-
torch.utils.data.Dataset表示该数据集，继承该类可以重载其中的方法，实现多种数据读取及数据预处理。
-
torch.utils.data.DataLoader 封装了Data对象，实现单（多）进程迭代器输出数据集。
2. torch.utils.data.Dataset
torch.utils.data.Dataset是代表自定义数据集方法的类，用户可以通过继承该类来自定义自己的数据集类，在继承时要求用户重载__len__()和__getitem__()这两个方法。
-
__len__()：返回的是数据集的大小。 -
__getitem__()：实现索引数据集中的某一个数据。此外，可以在__getitem__()中实现数据预处理。
3. torch.utils.data.DataLoader
-
DataLoader将Dataset对象或自定义数据类的对象封装成一个迭代器；
-
这个迭代器可以迭代输出Dataset的内容；
-
同时可以实现多进程、shuffle、不同采样策略，数据校对等等处理过程。
4. 代码分块解析
- 自定义的数据集类为NYUv2_Dataset，继承自torch.utils.data.Dataset
class NYUv2_Dataset(Dataset):
def __init__(self, data_root, img_transforms):
self.data_root = data_root
self.img_transforms = img_transforms
data_list, label_list = read_image_path(root=self.data_root)
self.data_list = data_list
self.label_list = label_list
def __len__(self):
return len(self.data_list)
def __getitem__(self, item):
img = self.data_list[item]
label = self.label_list[item]
img = cv2.imread(img)
label = cv2.imread(label)
img, label = self.img_transforms(img, label)
return img,label
- 在NYUv2_Dataset类中，使用到了read_image_path()函数，输入为数据集的路径，输出为数据和标签的地址列表。
# 定义需要读取的数据路径的函数
def read_image_path(root=r"C:\Users\22476\Desktop\VOC_format_dataset\ImageSet\train.txt"):
# 原始图像路径输出为data，标签图像路径输出为label
image = np.loadtxt(root, dtype=str)
n =len(image)
data, label = [None]*n, [None]*n
for i,fname in enumerate(image):
data[i] = r"C:\Users\22476\Desktop\VOC_format_dataset\JPEGImages\%s.jpg" % (fname)
label[i] = r"C:\Users\22476\Desktop\VOC_format_dataset\Segmentation_40\%s.png" % (fname)
return data, label
- 在NYUv2_Dataset类中，还使用到了img_transforms()函数，用来将原始图像和类别标签转变为Tensor格式，并将标签转化为每个像素值为一类数据。
def image2label(image, colormap):
# 将标签转化为每个像素值为一类数据
cm2lbl = np.zeros(256**3)
for i,cm in enumerate(colormap):
cm2lbl[(cm[0]*256+cm[1]*256+cm[2])] = i
# 对一张图像转换
image = np.array(image, dtype="int64")
ix = (image[:,:,0]*256+image[:,:,1]*256+image[:,:,2])
image2 = cm2lbl[ix]
return image2
def img_transforms(data, label):
# 将标记图像数据进行二维标签化的操作
# 输出原始图像和类别标签的张量数据
data_tfs = transforms.Compose([
transforms.ToTensor(),
])
data = data_tfs(data)
label = torch.from_numpy(image2label(label, colormap)) # 把数组转换成张量，且二者共享内存，对张量进行修改比如重新赋值，那么原始数组也会相应发生改变
return data, label
5. 完整代码
下面展示了构建NYUv2数据集的全部代码，其中colormap是NYUv2数据集中分割标签的像素值（即类别），该部分代码实现了读取数据、数据处理、创建数据加载器dataloader。
colormap = [[0, 0, 0],
[1, 1, 1],
[2, 2, 2],
[3, 3, 3],
[4, 4, 4],
[5, 5, 5],
[6, 6, 6],
[7, 7, 7],
[8, 8, 8],
[9, 9, 9],
[10, 10, 10],
[11, 11, 11],
[12, 12, 12],
[13, 13, 13],
[14, 14, 14],
[15, 15, 15],
[16, 16, 16],
[17, 17, 17],
[18, 18, 18],
[19, 19, 19],
[20, 20, 20],
[21, 21, 21],
[22, 22, 22],
[23, 23, 23],
[24, 24, 24],
[25, 25, 25],
[26, 26, 26],
[27, 27, 27],
[28, 28, 28],
[29, 29, 29],
[30, 30, 30],
[31, 31, 31],
[32, 32, 32],
[33, 33, 33],
[34, 34, 34],
[35, 35, 35],
[36, 36, 36],
[37, 37, 37],
[38, 38, 38],
[39, 39, 39],
[40, 40, 40]]
# 定义计算设备
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
def image2label(image, colormap):
# 将标签转化为每个像素值为一类数据
cm2lbl = np.zeros(256**3)
for i,cm in enumerate(colormap):
cm2lbl[(cm[0]*256+cm[1]*256+cm[2])] = i
# 对一张图像转换
image = np.array(image, dtype="int64")
ix = (image[:,:,0]*256+image[:,:,1]*256+image[:,:,2])
image2 = cm2lbl[ix]
return image2
# 定义需要读取的数据路径的函数
def read_image_path(root=r"C:\Users\22476\Desktop\VOC_format_dataset\ImageSet\train.txt"):
# 原始图像路径输出为data，标签图像路径输出为label
image = np.loadtxt(root, dtype=str)
n =len(image)
data, label = [None]*n, [None]*n
for i,fname in enumerate(image):
data[i] = r"C:\Users\22476\Desktop\VOC_format_dataset\JPEGImages\%s.jpg" % (fname)
label[i] = r"C:\Users\22476\Desktop\VOC_format_dataset\Segmentation_40\%s.png" % (fname)
return data, label
# 单组图像的转换操作
def img_transforms(data, label):
# 将输入图像进行亮度、对比度、饱和度、色相的改变；将标记图像数据进行二维标签化的操作
# 输出原始图像和类别标签的张量数据
data_tfs = transforms.Compose([
transforms.ToTensor(),
])
data = data_tfs(data)
label = torch.from_numpy(image2label(label, colormap)) # 把数组转换成张量，且二者共享内存，对张量进行修改比如重新赋值，那么原始数组也会相应发生改变
return data, label
class NYUv2_Dataset(Dataset):
def __init__(self, data_root, img_transforms):
self.data_root = data_root
self.img_transforms = img_transforms
data_list, label_list = read_image_path(root=self.data_root)
self.data_list = data_list
self.label_list = label_list
def __len__(self):
return len(self.data_list)
def __getitem__(self, item):
img = self.data_list[item]
label = self.label_list[item]
img = cv2.imread(img)
label = cv2.imread(label)
img, label = self.img_transforms(img, label)
return img,label
nyuv2_train = NYUv2_Dataset(r"C:\Users\22476\Desktop\VOC_format_dataset\ImageSet\train.txt", img_transforms)
nyuv2_val = NYUv2_Dataset(r"C:\Users\22476\Desktop\VOC_format_dataset\ImageSet\val.txt", img_transforms)
# 创建数据加载器每个batch使用4张图像
train_loader = Data.DataLoader(nyuv2_train, batch_size=2, shuffle=True, num_workers=0, pin_memory=True)
val_loader = Data.DataLoader(nyuv2_val, batch_size=2, shuffle=True, num_workers=0, pin_memory=True)
6. 可视化
通过可视化一个batch的数据，检查数据预处理是否正确
# 检查训练数据集的一个batch的样本的维度是否正确
for step,(b_x,b_y) in enumerate(train_loader):
if step > 0:
break
# 输出训练图像的尺寸和标签的尺寸，以及接受类型
# print("Train数据：",b_x)
# print("Train标签：",b_y)
#
# print("b_x.shape:",b_x.shape)
# print("b_y.shape:",b_y.shape)
# 可视化一个batch的图像，检查数据预处理是否正确
b_x_numpy = b_x.data.numpy()
b_x_numpy = b_x_numpy.transpose(0,2,3,1)
plt.imshow(b_x_numpy[1])
plt.show()
b_y_numpy = b_y.data.numpy()
plt.imshow(b_y_numpy[1])
plt.show()
二、模型搭建
本文以预训练好的VGG19模型作为Backbone，然后自己搭建上采样部分网络，从而完成整个语义分割网络的模型搭建。
high, width = 320, 480
# 使用预训练好的VGG19网络作为backbone
model_vgg19 = vgg19(pretrained=True)
# 不使用VGG19网络后面的AdaptiveAvgPool2d和Linear层
base_model = model_vgg19.features
base_model = base_model.cuda()
# summary(base_model,input_size=(3, high, width))
# 定义FCN语义分割网络
class FCN8s(nn.Module):
def __init__(self, num_classes):
super().__init__()
self.num_classes = num_classes
model_vgg19 = vgg19(pretrained=True)
# 不使用VGG19网络后面的AdaptiveAvgPool2d和Linear层
self.base_model = model_vgg19.features
# 定义几个需要的层操作，并且使用转置卷积将特征映射进行升维
self.relu = nn.ReLU(inplace=True)
self.deconv1 = nn.ConvTranspose2d(512, 512, kernel_size=3, stride=2, padding=1, dilation=1, output_padding=1)
self.bn1 = nn.BatchNorm2d(512)
self.deconv2 = nn.ConvTranspose2d(512, 256, 3, 2, 1, 1, 1)
self.bn2 = nn.BatchNorm2d(256)
self.deconv3 = nn.ConvTranspose2d(256, 128, 3, 2, 1, 1, 1)
self.bn3 = nn.BatchNorm2d(128)
self.deconv4 = nn.ConvTranspose2d(128, 64, 3, 2, 1, 1, 1)
self.bn4 = nn.BatchNorm2d(64)
self.deconv5 = nn.ConvTranspose2d(64, 32, 3, 2, 1, 1, 1)
self.bn5 = nn.BatchNorm2d(32)
self.classifier = nn.Conv2d(32, num_classes, kernel_size=1)
## VGG19中MaxPool2d所在的层
self.layers = {"4":"maxpool_1","9":"maxpool_2",
"18": "maxpool_3", "27": "maxpool_4",
"36": "maxpool_5"}
def forward(self, x):
output ={}
for name, layer in self.base_model._modules.items():
## 从第一层开始获取图像的特征
x = layer(x)
## 如果是layers参数指定的特征，那就保存到output中
if name in self.layers:
output[self.layers[name]] = x
x5 = output["maxpool_5"] ## size = (N, 512, x.H/32, x.W/32)
x4 = output["maxpool_4"] ## size = (N, 512, x.H/16, x.W/16)
x3 = output["maxpool_3"] ## size = (N, 512, x.H/8, x.W/8)
## 对特征进行相关的转置卷积操作，逐渐将图像放大到原始图像大小
## size = (N, 512, x.H/16, x.W/16)
score = self.relu(self.deconv1(x5))
## 对应元素相加，size = (N, 512, x.H/16, x.W/16)
score = self.bn1(score + x4)
## size = (N, 256, x.H/8, x.W/8)
score = self.relu(self.deconv2(score))
## 对应元素相加，size = (N, 256, x.H/8, x.W/8)
score = self.bn2(score + x3)
## size = (N, 128, x.H/4, x.W/4)
score = self.bn3(self.relu(self.deconv3(score)))
## size = (N, 64, x.H/2, x.W/2)
score = self.bn4(self.relu(self.deconv4(score)))
## size = (N, 32, x.H, x.W)
score = self.bn5(self.relu(self.deconv5(score)))
score = self.classifier(score)
return score ## size = (N, n_class, x.H/1, x.W/1)
fcn8s = FCN8s(41).to(device)
summary(fcn8s, input_size=(3, high, width))
模型结构如下表所示：
| Layer (type) | Output Shape | Param |
|---|---|---|
| Conv2d-1 | [-1, 64, 320, 480] | 1,792 |
| ReLU-2 | [-1, 64, 320, 480] | 0 |
| Conv2d-3 | [-1, 64, 320, 480] | 36,928 |
| ReLU-4 | [-1, 64, 320, 480] | 0 |
| MaxPool2d-5 | [-1, 64, 160, 240] | 0 |
| Conv2d-6 | [-1, 128, 160, 240] | 73,856 |
| ReLU-7 | [-1, 128, 160, 240] | 0 |
| Conv2d-8 | [-1, 128, 160, 240] | 147,584 |
| ReLU-9 | [-1, 128, 160, 240] | 0 |
| MaxPool2d-10 | [-1, 128, 80, 120] | 0 |
| Conv2d-11 | [-1, 256, 80, 120] | 295,168 |
| ReLU-12 | [-1, 256, 80, 120] | 0 |
| Conv2d-13 | [-1, 256, 80, 120] | 590,080 |
| ReLU-14 | [-1, 256, 80, 120] | 0 |
| Conv2d-15 | [-1, 256, 80, 120] | 590,080 |
| ReLU-16 | [-1, 256, 80, 120] | 0 |
| Conv2d-17 | [-1, 256, 80, 120] | 590,080 |
| ReLU-18 | [-1, 256, 80, 120] | 0 |
| MaxPool2d-19 | [-1, 256, 40, 60] | 0 |
| Conv2d-20 | [-1, 512, 40, 60] | 1,180,160 |
| ReLU-21 | [-1, 512, 40, 60] | 0 |
| Conv2d-22 | [-1, 512, 40, 60] | 2,359,808 |
| ReLU-23 | [-1, 512, 40, 60] | 0 |
| Conv2d-24 | [-1, 512, 40, 60] | 2,359,808 |
| ReLU-25 | [-1, 512, 40, 60] | 0 |
| Conv2d-26 | [-1, 512, 40, 60] | 2,359,808 |
| ReLU-27 | [-1, 512, 40, 60] | 0 |
| MaxPool2d-28 | [-1, 512, 20, 30] | 0 |
| Conv2d-29 | [-1, 512, 20, 30] | 2,359,808 |
| ReLU-30 | [-1, 512, 20, 30] | 0 |
| Conv2d-31 | [-1, 512, 20, 30] | 2,359,808 |
| ReLU-32 | [-1, 512, 20, 30] | 0 |
| Conv2d-33 | [-1, 512, 20, 30] | 2,359,808 |
| ReLU-34 | [-1, 512, 20, 30] | 0 |
| Conv2d-35 | [-1, 512, 20, 30] | 2,359,808 |
| ReLU-36 | [-1, 512, 20, 30] | 0 |
| MaxPool2d-37 | [-1, 512, 10, 15] | 0 |
| ConvTranspose2d-38 | [-1, 512, 20, 30] | 2,359,808 |
| ReLU-39 | [-1, 512, 20, 30] | 0 |
| BatchNorm2d-40 | [-1, 512, 20, 30] | 1,024 |
| ConvTranspose2d-41 | [-1, 256, 40, 60]] | 1,179,904 |
| ReLU-42 | [-1, 256, 40, 60] | 0 |
| BatchNorm2d-43 | [-1, 256, 40, 60] | 512 |
| ConvTranspose2d-44 | [-1, 128, 80, 120] | 295,040 |
| ReLU-45 | [-1, 128, 80, 120] | 0 |
| BatchNorm2d-46 | [-1, 128, 80, 120] | 256 |
| ConvTranspose2d-47 | [-1, 64, 160, 240] | 73,792 |
| ReLU-48 | [-1, 64, 160, 240] | 0 |
| BatchNorm2d-49 | [-1, 64, 160, 240] | 128 |
| ConvTranspose2d-50 | [-1, 32, 320, 480] | 18,464 |
| ReLU-51 | [-1, 32, 320, 480] | 0 |
| BatchNorm2d-52 | [-1, 32, 320, 480] | 64 |
| Conv2d-53 | [-1, 41, 320, 480] | 1,353 |
三、定义损失函数和优化器
# 定义损失函数和优化器
LR = 0.0003
criterion = nn.NLLLoss()
optimizer = optim.Adam(fcn8s.parameters(), lr=LR,weight_decay=1e-4)
四、迭代训练
# 对模型进行迭代训练，对所有的数据训练epoch轮
fcn8s,train_process = train_model(
fcn8s,criterion,optimizer,train_loader,
val_loader, num_epochs=200)
## 保存训练好的模型fcn8s
torch.save(fcn8s,"fcnNYUv2.pt")
def train_model(model, criterion, optimizer, traindataloader, valdataloader, num_epochs = 25):
"""
:param model: 网络模型
:param criterion: 损失函数
:param optimizer: 优化函数
:param traindataloader: 训练的数据集
:param valdataloader: 验证的数据集
:param num_epochs: 训练的轮数
"""
since = time.time()
best_model_wts = copy.deepcopy(model.state_dict())
best_loss = 1e10
train_loss_all = []
train_acc_all = []
val_loss_all = []
val_acc_all = []
since = time.time()
for epoch in range(num_epochs):
print('Epoch {}/{}'.format(epoch, num_epochs-1))
print('-' * 10)
train_loss = 0.0
train_num = 0
val_loss = 0.0
val_num = 0
## 每个epoch包括训练和验证阶段
model.train() ## 设置模型为训练模式
for step,(b_x,b_y) in enumerate(traindataloader):
optimizer.zero_grad()
b_x = b_x.float().to(device)
b_y = b_y.long().to(device)
out = model(b_x)
out = F.log_softmax(out, dim=1)
pre_lab = torch.argmax(out,1) ## 预测的标签
loss = criterion(out, b_y) ## 计算损失函数值
loss.backward()
optimizer.step()
train_loss += loss.item() * len(b_y)
train_num += len(b_y)
## 计算一个epoch在训练集上的损失和精度
train_loss_all.append(train_loss / train_num)
print('{} Train loss: {:.4f}'.format(epoch, train_loss_all[-1]))
## 计算一个epoch训练后在验证集上的损失
model.eval() ## 设置模型为验证模式
for step,(b_x,b_y) in enumerate(valdataloader):
b_x = b_x.float().to(device)
b_y = b_y.long().to(device)
out = model(b_x)
out = F.log_softmax(out, dim=1)
pre_lab = torch.argmax(out,1) ## 预测的标签
loss = criterion(out, b_y) ## 计算损失函数值
val_loss += loss.item() * len(b_y)
val_num += len(b_y)
## 计算一个epoch在验证集上的损失和精度
val_loss_all.append(val_loss / val_num)
print('{} Val loss: {:.4f}'.format(epoch, val_loss_all[-1]))
## 保存最好的网络参数
if val_loss_all[-1] < best_loss:
best_loss = val_loss_all[-1]
best_model_wts = copy.deepcopy(model.state_dict())
## 每个epoch花费的时间
time_use = time.time() - since
print("Train and val complete in {:.0f}m {:.0f}s".format(time_use // 60, time_use %60))
train_process = pd.DataFrame(
data = {"epoch":range(num_epochs),
"train_loss_all":train_loss_all,
"val_loss_all":val_loss_all})
## 输出最好的模型
model.load_state_dict(best_model_wts)
return model,train_process
参考文章
Pytorch构建数据集——torch.utils.data.Dataset()和torch.utils.dataDataLoader()
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