第六课：ResNeXt学习
2024-06-04 04:08:42
前言
随着人工智能的不断发展，机器学习这门技术也越来越重要，很多人都开启了学习机器学习，本文就介绍了机器学习的基础内容。来源于哔哩哔哩博主“霹雳吧啦Wz”，博主学习作为笔记记录，欢迎大家一起讨论学习交流。
一、搭建ResNeXt网络
用ResNeXt学习,没训练。
二、代码部分
1.module.py----定义ResNeXt的网络结构
代码如下（示例）：
import torch.nn as nn
import torchclass BasicBlock(nn.Module):expansion = 1def __init__(self, in_channel, out_channel, stride=1, downsample=None, **kwargs):super(BasicBlock, self).__init__()self.conv1 = nn.Conv2d(in_channels=in_channel, out_channels=out_channel,kernel_size=3, stride=stride, padding=1, bias=False)self.bn1 = nn.BatchNorm2d(out_channel)self.relu = nn.ReLU()self.conv2 = nn.Conv2d(in_channels=out_channel, out_channels=out_channel,kernel_size=3, stride=1, padding=1, bias=False)self.bn2 = nn.BatchNorm2d(out_channel)self.downsample = downsampledef forward(self, x):identity = xif self.downsample is not None:identity = self.downsample(x)out = self.conv1(x)out = self.bn1(out)out = self.relu(out)out = self.conv2(out)out = self.bn2(out)out += identityout = self.relu(out)return outclass Bottleneck(nn.Module):"""注意：原论文中，在虚线残差结构的主分支上，第一个1x1卷积层的步距是2，第二个3x3卷积层步距是1。但在pytorch官方实现过程中是第一个1x1卷积层的步距是1，第二个3x3卷积层步距是2，这么做的好处是能够在top1上提升大概0.5%的准确率。可参考Resnet v1.5 https://ngc.nvidia.com/catalog/model-scripts/nvidia:resnet_50_v1_5_for_pytorch"""expansion = 4def __init__(self, in_channel, out_channel, stride=1, downsample=None,groups=1, width_per_group=64):super(Bottleneck, self).__init__()width = int(out_channel * (width_per_group / 64.)) * groupsself.conv1 = nn.Conv2d(in_channels=in_channel, out_channels=width,kernel_size=1, stride=1, bias=False) # squeeze channelsself.bn1 = nn.BatchNorm2d(width)# -----------------------------------------self.conv2 = nn.Conv2d(in_channels=width, out_channels=width, groups=groups,kernel_size=3, stride=stride, bias=False, padding=1)self.bn2 = nn.BatchNorm2d(width)# -----------------------------------------self.conv3 = nn.Conv2d(in_channels=width, out_channels=out_channel*self.expansion,kernel_size=1, stride=1, bias=False) # unsqueeze channelsself.bn3 = nn.BatchNorm2d(out_channel*self.expansion)self.relu = nn.ReLU(inplace=True)self.downsample = downsampledef forward(self, x):identity = xif self.downsample is not None:identity = self.downsample(x)out = self.conv1(x)out = self.bn1(out)out = self.relu(out)out = self.conv2(out)out = self.bn2(out)out = self.relu(out)out = self.conv3(out)out = self.bn3(out)out += identityout = self.relu(out)return outclass ResNet(nn.Module):def __init__(self,block,blocks_num,num_classes=1000,include_top=True,groups=1,width_per_group=64):super(ResNet, self).__init__()self.include_top = include_topself.in_channel = 64self.groups = groupsself.width_per_group = width_per_groupself.conv1 = nn.Conv2d(3, self.in_channel, kernel_size=7, stride=2,padding=3, bias=False)self.bn1 = nn.BatchNorm2d(self.in_channel)self.relu = nn.ReLU(inplace=True)self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)self.layer1 = self._make_layer(block, 64, blocks_num[0])self.layer2 = self._make_layer(block, 128, blocks_num[1], stride=2)self.layer3 = self._make_layer(block, 256, blocks_num[2], stride=2)self.layer4 = self._make_layer(block, 512, blocks_num[3], stride=2)if self.include_top:self.avgpool = nn.AdaptiveAvgPool2d((1, 1)) # output size = (1, 1)self.fc = nn.Linear(512 * block.expansion, num_classes)for m in self.modules():if isinstance(m, nn.Conv2d):nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')def _make_layer(self, block, channel, block_num, stride=1):downsample = Noneif stride != 1 or self.in_channel != channel * block.expansion:downsample = nn.Sequential(nn.Conv2d(self.in_channel, channel * block.expansion, kernel_size=1, stride=stride, bias=False),nn.BatchNorm2d(channel * block.expansion))layers = []layers.append(block(self.in_channel,channel,downsample=downsample,stride=stride,groups=self.groups,width_per_group=self.width_per_group))self.in_channel = channel * block.expansionfor _ in range(1, block_num):layers.append(block(self.in_channel,channel,groups=self.groups,width_per_group=self.width_per_group))return nn.Sequential(*layers)def forward(self, x):x = self.conv1(x)x = self.bn1(x)x = self.relu(x)x = self.maxpool(x)x = self.layer1(x)x = self.layer2(x)x = self.layer3(x)x = self.layer4(x)if self.include_top:x = self.avgpool(x)x = torch.flatten(x, 1)x = self.fc(x)return xdef resnet34(num_classes=1000, include_top=True):# https://download.pytorch.org/models/resnet34-333f7ec4.pthreturn ResNet(BasicBlock, [3, 4, 6, 3], num_classes=num_classes, include_top=include_top)def resnet50(num_classes=1000, include_top=True):# https://download.pytorch.org/models/resnet50-19c8e357.pthreturn ResNet(Bottleneck, [3, 4, 6, 3], num_classes=num_classes, include_top=include_top)def resnet101(num_classes=1000, include_top=True):# https://download.pytorch.org/models/resnet101-5d3b4d8f.pthreturn ResNet(Bottleneck, [3, 4, 23, 3], num_classes=num_classes, include_top=include_top)def resnext50_32x4d(num_classes=1000, include_top=True):# https://download.pytorch.org/models/resnext50_32x4d-7cdf4587.pthgroups = 32width_per_group = 4return ResNet(Bottleneck, [3, 4, 6, 3],num_classes=num_classes,include_top=include_top,groups=groups,width_per_group=width_per_group)def resnext101_32x8d(num_classes=1000, include_top=True):# https://download.pytorch.org/models/resnext101_32x8d-8ba56ff5.pthgroups = 32width_per_group = 8return ResNet(Bottleneck, [3, 4, 23, 3],num_classes=num_classes,include_top=include_top,groups=groups,width_per_group=width_per_group)
2.train.py----加载数据集并进行训练，训练集计算loss，测试集计算accuracy，保存训练好的网络参数
代码如下（示例）：
import os
import sys
import jsonimport torch
import torch.nn as nn
import torch.optim as optim
from torchvision import transforms, datasets
from tqdm import tqdmfrom model import resnet34def main():device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")print("using {} device.".format(device))data_transform = {"train": transforms.Compose([transforms.RandomResizedCrop(224),transforms.RandomHorizontalFlip(),transforms.ToTensor(),transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])]),"val": transforms.Compose([transforms.Resize(256),transforms.CenterCrop(224),transforms.ToTensor(),transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])])}data_root = os.path.abspath(os.path.join(os.getcwd(), "../..")) # get data root pathimage_path = os.path.join(data_root, "data_set", "flower_data") # flower data set pathassert os.path.exists(image_path), "{} path does not exist.".format(image_path)train_dataset = datasets.ImageFolder(root=os.path.join(image_path, "train"),transform=data_transform["train"])train_num = len(train_dataset)# {'daisy':0, 'dandelion':1, 'roses':2, 'sunflower':3, 'tulips':4}flower_list = train_dataset.class_to_idxcla_dict = dict((val, key) for key, val in flower_list.items())# write dict into json filejson_str = json.dumps(cla_dict, indent=4)with open('class_indices.json', 'w') as json_file:json_file.write(json_str)batch_size = 16nw = min([os.cpu_count(), batch_size if batch_size > 1 else 0, 8]) # number of workersprint('Using {} dataloader workers every process'.format(nw))train_loader = torch.utils.data.DataLoader(train_dataset,batch_size=batch_size, shuffle=True,num_workers=nw)validate_dataset = datasets.ImageFolder(root=os.path.join(image_path, "val"),transform=data_transform["val"])val_num = len(validate_dataset)validate_loader = torch.utils.data.DataLoader(validate_dataset,batch_size=batch_size, shuffle=False,num_workers=nw)print("using {} images for training, {} images for validation.".format(train_num,val_num))net = resnet34()# load pretrain weights# download url: https://download.pytorch.org/models/resnet34-333f7ec4.pthmodel_weight_path = "./resnet34-pre.pth"assert os.path.exists(model_weight_path), "file {} does not exist.".format(model_weight_path)net.load_state_dict(torch.load(model_weight_path, map_location='cpu'))# for param in net.parameters():# param.requires_grad = False# change fc layer structurein_channel = net.fc.in_featuresnet.fc = nn.Linear(in_channel, 5)net.to(device)# define loss functionloss_function = nn.CrossEntropyLoss()# construct an optimizerparams = [p for p in net.parameters() if p.requires_grad]optimizer = optim.Adam(params, lr=0.0001)epochs = 3best_acc = 0.0save_path = './resNet34.pth'train_steps = len(train_loader)for epoch in range(epochs):# trainnet.train()running_loss = 0.0train_bar = tqdm(train_loader, file=sys.stdout)for step, data in enumerate(train_bar):images, labels = dataoptimizer.zero_grad()logits = net(images.to(device))loss = loss_function(logits, labels.to(device))loss.backward()optimizer.step()# print statisticsrunning_loss += loss.item()train_bar.desc = "train epoch[{}/{}] loss:{:.3f}".format(epoch + 1,epochs,loss)# validatenet.eval()acc = 0.0 # accumulate accurate number / epochwith torch.no_grad():val_bar = tqdm(validate_loader, file=sys.stdout)for val_data in val_bar:val_images, val_labels = val_dataoutputs = net(val_images.to(device))# loss = loss_function(outputs, test_labels)predict_y = torch.max(outputs, dim=1)[1]acc += torch.eq(predict_y, val_labels.to(device)).sum().item()val_bar.desc = "valid epoch[{}/{}]".format(epoch + 1,epochs)val_accurate = acc / val_numprint('[epoch %d] train_loss: %.3f val_accuracy: %.3f' %(epoch + 1, running_loss / train_steps, val_accurate))if val_accurate > best_acc:best_acc = val_accuratetorch.save(net.state_dict(), save_path)print('Finished Training')if __name__ == '__main__':main()
3.predict.py——得到训练好的网络参数后，用自己找的图像进行分类测试
import os
import jsonimport torch
from PIL import Image
from torchvision import transforms
import matplotlib.pyplot as pltfrom model import resnet34def main():device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")data_transform = transforms.Compose([transforms.Resize(256),transforms.CenterCrop(224),transforms.ToTensor(),transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])])# load imageimg_path = "../tulip.jpg"assert os.path.exists(img_path), "file: '{}' dose not exist.".format(img_path)img = Image.open(img_path)plt.imshow(img)# [N, C, H, W]img = data_transform(img)# expand batch dimensionimg = torch.unsqueeze(img, dim=0)# read class_indictjson_path = './class_indices.json'assert os.path.exists(json_path), "file: '{}' dose not exist.".format(json_path)with open(json_path, "r") as f:class_indict = json.load(f)# create modelmodel = resnet34(num_classes=5).to(device)# load model weightsweights_path = "./resNet34.pth"assert os.path.exists(weights_path), "file: '{}' dose not exist.".format(weights_path)model.load_state_dict(torch.load(weights_path, map_location=device))# predictionmodel.eval()with torch.no_grad():# predict classoutput = torch.squeeze(model(img.to(device))).cpu()predict = torch.softmax(output, dim=0)predict_cla = torch.argmax(predict).numpy()print_res = "class: {} prob: {:.3}".format(class_indict[str(predict_cla)],predict[predict_cla].numpy())plt.title(print_res)for i in range(len(predict)):print("class: {:10} prob: {:.3}".format(class_indict[str(i)],predict[i].numpy()))plt.show()if __name__ == '__main__':main()
4.batch_predict.py——批量图像预测脚本
import os
import jsonimport torch
from PIL import Image
from torchvision import transformsfrom model import resnet34def main():device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")data_transform = transforms.Compose([transforms.Resize(256),transforms.CenterCrop(224),transforms.ToTensor(),transforms.Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])])# load image# 指向需要遍历预测的图像文件夹imgs_root = "/data/imgs"assert os.path.exists(imgs_root), f"file: '{imgs_root}' dose not exist."# 读取指定文件夹下所有jpg图像路径img_path_list = [os.path.join(imgs_root, i) for i in os.listdir(imgs_root) if i.endswith(".jpg")]# read class_indictjson_path = './class_indices.json'assert os.path.exists(json_path), f"file: '{json_path}' dose not exist."json_file = open(json_path, "r")class_indict = json.load(json_file)# create modelmodel = resnet34(num_classes=5).to(device)# load model weightsweights_path = "./resNet34.pth"assert os.path.exists(weights_path), f"file: '{weights_path}' dose not exist."model.load_state_dict(torch.load(weights_path, map_location=device))# predictionmodel.eval()batch_size = 8 # 每次预测时将多少张图片打包成一个batchwith torch.no_grad():for ids in range(0, len(img_path_list) // batch_size):img_list = []for img_path in img_path_list[ids * batch_size: (ids + 1) * batch_size]:assert os.path.exists(img_path), f"file: '{img_path}' dose not exist."img = Image.open(img_path)img = data_transform(img)img_list.append(img)# batch img# 将img_list列表中的所有图像打包成一个batchbatch_img = torch.stack(img_list, dim=0)# predict classoutput = model(batch_img.to(device)).cpu()predict = torch.softmax(output, dim=1)probs, classes = torch.max(predict, dim=1)for idx, (pro, cla) in enumerate(zip(probs, classes)):print("image: {} class: {} prob: {:.3}".format(img_path_list[ids * batch_size + idx],class_indict[str(cla.numpy())],pro.numpy()))if __name__ == '__main__':main()
三、额外部分
1.通过计算发现分组卷积的参数会减少，与正常相比，理论上减少了分组数g倍（假设卷积核尺寸是kxk,输入图像的深度是Cin,输出卷积核的深度通道数是n,分组卷积的组数是g)。2.当组卷积的分组数g=输入特征矩阵的深度Cin，比如这里输入是四个通道，g=4意味着分成四组，每一组就是分配了一个chanel为1的卷积，并且输出特征矩阵深度n=输入特征矩阵深度Cin,是组卷积就变成了DW卷积。
上图三个部分是等价的，最右边先是通过1x1卷积将深度从256降为128，然后通过3x3，分组为32的组卷积，最后通过1x1卷积将深度从128升为256。中间是通过将分成32组，每组深度是右图深度除以分组32得到的深度，再进行concatenate.左边是先通过1x1卷积再进行相加，与中间先进行concatenate,再进行1x1卷积一样。
32是分组数group，对应conv2,conv3,conv4,conv5对应的group数都是32，C=32；4d是conv2等一系列卷积所对应的block中组卷积当中每一组所采用的卷积的个数。比如conv2，组卷积是32，C=32.每一组的卷积核个数是4，所以输出是32x4=128.即3x3，128，C=32。
不同分组数C和d的效果，错误率较低。
对于浅层网络，比如Resnet 28，34直接通过两层3x3B=的block结构进行堆叠，论文说只有block层数大于3效果会比较好，所以对于两层网络对他进行拆分，效果可能并不好，甚至增加计算量。
ResNeXt在ResNet基础上变化了组卷积模块，其他类似，所以更改代码部分在ResNet基础上，增加组数；其次，在指定网址上下载预训练权重，在train.py文件导入from model import resnext50_32x4d.预训练权重设置成resnext50_32x4d.pth.保存路径也改为resnext50.pth.预测时候在predict.py文件导入from model import resnext50_32x4d.model=resnext50_32x4d,预训练权重设置成resnext50_32x4d.pth.
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