前言：本篇主要偏向图像分类实战部分，使用MMclassification工具进行代码应用，最后对水果分类进行实战演示，本次环境和代码配置部分省略，具体内容建议参考前一篇文章：计算机视觉框架OpenMMLab开源学习（二）：图像分类

计算机视觉框架OpenMMLab开源学习（三）：图像分类实战

一、安装OpenMMLab v2.0

Step 1. Install MMCV

mim install "mmcv>=2.0.0rc0"

Step 2. Install MMClassification and MMDetection

mim install "mmcls>=1.0.0rc0" "mmdet>=3.0.0rc0"

代码模版讲解：

model = dict(type='ImageClassifier',     # 分类器类型backbone=dict(type='ResNet',          # 主干网络类型depth=50,               # 主干网网络深度， ResNet 一般有18, 34, 50, 101, 152 可以选择num_stages=4,           # 主干网络状态(stages)的数目，这些状态产生的特征图作为后续的 head 的输入。out_indices=(3, ),      # 输出的特征图输出索引。越远离输入图像，索引越大frozen_stages=-1,       # 网络微调时，冻结网络的stage（训练时不执行反相传播算法），若num_stages=4，backbone包含stem 与 4 个 stages。frozen_stages为-1时，不冻结网络； 为0时，冻结 stem； 为1时，冻结 stem 和 stage1； 为4时，冻结整个backbonestyle='pytorch'),       # 主干网络的风格，'pytorch' 意思是步长为2的层为 3x3 卷积， 'caffe' 意思是步长为2的层为 1x1 卷积。neck=dict(type='GlobalAveragePooling'),    # 颈网络类型head=dict(type='LinearClsHead',     # 线性分类头，num_classes=1000,         # 输出类别数，这与数据集的类别数一致in_channels=2048,         # 输入通道数，这与 neck 的输出通道一致loss=dict(type='CrossEntropyLoss', loss_weight=1.0), # 损失函数配置信息topk=(1, 5),              # 评估指标，Top-k 准确率， 这里为 top1 与 top5 准确率))

二、Pytorch图像分类任务

本次任务训练数据为FashionMNIST，完整代码如下：

# https://pytorch.org/tutorials/beginner/basics/quickstart_tutorial.htmlimport torch
from torch import nn
from torch.utils.data import DataLoader
from torchvision import datasets
from torchvision.transforms import ToTensor# Training## Construct Dataset and Dataloader
training_data = datasets.FashionMNIST(root="data",train=True,download=True,transform=ToTensor(),
)
test_data = datasets.FashionMNIST(root="data",train=False,download=True,transform=ToTensor(),
)batch_size = 64train_dataloader = DataLoader(training_data, batch_size=batch_size)
test_dataloader = DataLoader(test_data, batch_size=batch_size)## Define model
class NeuralNetwork(nn.Module):def __init__(self):super(NeuralNetwork, self).__init__()self.flatten = nn.Flatten()self.linear_relu_stack = nn.Sequential(nn.Linear(28*28, 512),nn.ReLU(),nn.Linear(512, 512),nn.ReLU(),nn.Linear(512, 10))def forward(self, x):x = self.flatten(x)logits = self.linear_relu_stack(x)return logitsdevice = "cuda" if torch.cuda.is_available() else "cpu"
model = NeuralNetwork().to(device)## Define loss function and Optimizer
loss_fn = nn.CrossEntropyLoss()
optimizer = torch.optim.SGD(model.parameters(), lr=1e-3)## Inner loop for training
def train(dataloader, model, loss_fn, optimizer):size = len(dataloader.dataset)model.train()for batch, (X, y) in enumerate(dataloader):X, y = X.to(device), y.to(device)# Compute prediction errorpred = model(X)loss = loss_fn(pred, y)# Backpropagationoptimizer.zero_grad()loss.backward()optimizer.step()# Output Logsif batch % 100 == 0:loss, current = loss.item(), batch * len(X)print(f"loss: {loss:>7f}  [{current:>5d}/{size:>5d}]")## Inner loop for test
def test(dataloader, model, loss_fn):size = len(dataloader.dataset)num_batches = len(dataloader)model.eval()test_loss, correct = 0, 0with torch.no_grad():for X, y in dataloader:X, y = X.to(device), y.to(device)pred = model(X)test_loss += loss_fn(pred, y).item()correct += (pred.argmax(1) == y).type(torch.float).sum().item()test_loss /= num_batchescorrect /= sizeprint(f"Test Error: \n Accuracy: {(100*correct):>0.1f}%, Avg loss: {test_loss:>8f} \n")## Launch training / test loops#
epochs = 5
for t in range(epochs):print(f"Epoch {t+1}\n-------------------------------")train(train_dataloader, model, loss_fn, optimizer)test(test_dataloader, model, loss_fn)
print("Done!")## Saving Modelstorch.save(model.state_dict(), "model.pth")
print("Saved PyTorch Model State to model.pth")# Deployment## Loading Models
model = NeuralNetwork()
model.load_state_dict(torch.load("model.pth"))# Predict new imagesclasses = ["T-shirt/top","Trouser","Pullover","Dress","Coat","Sandal","Shirt","Sneaker","Bag","Ankle boot",
]model.eval()
x, y = test_data[0][0], test_data[0][1]
with torch.no_grad():pred = model(x)predicted, actual = classes[pred[0].argmax(0)], classes[y]print(f'Predicted: "{predicted}", Actual: "{actual}"')

三、利用MMClassification提供的预训练模型推理：

安装环境：

pip install openmim, mmengine
mim install mmcv-full mmcls

Inference using high-level API

from mmcls.apis import init_model, inference_modelmodel = init_model('mobilenet-v2_8xb32_in1k.py', 'mobilenet_v2_batch256_imagenet_20200708-3b2dc3af.pth', device='cuda:0')
load checkpoint from local path: mobilenet_v2_batch256_imagenet_20200708-3b2dc3af.pth
result = inference_model(model, 'banana.png')
result
{'pred_label': 954, 'pred_score': 0.9999284744262695, 'pred_class': 'banana'}
from mmcls.apis import show_result_pyplotshow_result_pyplot(model, 'banana.png', result)

PyTorch codes under the hood

Let write some raw PyTorch codes to do the same thing.

These are actual codes wrapped in high-level APIs.

construct an ImageClassifier

Note: current implementation only allow configs of backbone, neck and classification head instead of Python objects.

from mmcls.models import ImageClassifierclassifier = ImageClassifier(backbone=dict(type='MobileNetV2', widen_factor=1.0),neck=dict(type='GlobalAveragePooling'),head=dict(type='LinearClsHead',num_classes=1000,in_channels=1280)
)

Load trained parameters

import torchckpt = torch.load('mobilenet_v2_batch256_imagenet_20200708-3b2dc3af.pth')
classifier.load_state_dict(ckpt['state_dict'])

Construct data preprocessing pipeline

Important: A models work only if image preprocessing pipelines is correct.

from mmcls.datasets.pipelines import Composetest_pipeline = Compose([dict(type='LoadImageFromFile'),dict(type='Resize', size=(256, -1), backend='pillow'),dict(type='CenterCrop', crop_size=224),dict(type='Normalize',mean=[123.675, 116.28, 103.53],std=[58.395, 57.12, 57.375],to_rgb=True),dict(type='ImageToTensor', keys=['img']),dict(type='Collect', keys=['img'])
])

data = dict(img_info=dict(filename='banana.png'), img_prefix=None)
data = test_pipeline(data)
data

{'img_metas': DataContainer({'filename': 'banana.png', 'ori_filename': 'banana.png', 'ori_shape': (403, 393, 3), 'img_shape': (224, 224, 3), 'img_norm_cfg': {'mean': array([123.675, 116.28 , 103.53 ], dtype=float32), 'std': array([58.395, 57.12 , 57.375], dtype=float32), 'to_rgb': True}}),'img': tensor([[[ 0.3309,  0.2967,  0.3138,  ...,  2.0263,  2.0092,  1.9920],[ 0.3481,  0.3309,  0.2282,  ...,  2.0263,  2.0092,  1.9920],[ 0.2796,  0.2967,  0.2967,  ...,  1.9920,  2.0263,  1.9749],...,[ 0.1939,  0.1768,  0.2282,  ...,  0.3994,  0.3309,  0.3823],[ 0.1426,  0.1254,  0.2111,  ...,  0.5878,  0.5364,  0.5536],[-0.0116, -0.0801,  0.1597,  ...,  0.5707,  0.5536,  0.5364]],[[ 0.3803,  0.3803,  0.3803,  ...,  2.1660,  2.1485,  2.1134],[ 0.4153,  0.4153,  0.3102,  ...,  2.1835,  2.1310,  2.1134],[ 0.3452,  0.3803,  0.3803,  ...,  2.1134,  2.1485,  2.1134],...,[ 0.2752,  0.2577,  0.3102,  ...,  0.5028,  0.4328,  0.4328],[ 0.2227,  0.1877,  0.3102,  ...,  0.6604,  0.6254,  0.5728],[ 0.0301, -0.0049,  0.2402,  ...,  0.6604,  0.6254,  0.5728]],[[ 0.5485,  0.5485,  0.5485,  ...,  2.3437,  2.3263,  2.2914],[ 0.5834,  0.5834,  0.4788,  ...,  2.3611,  2.3088,  2.2914],[ 0.5136,  0.5485,  0.5485,  ...,  2.3088,  2.3437,  2.3088],...,[ 0.4091,  0.3916,  0.4439,  ...,  0.5834,  0.5136,  0.5311],[ 0.3568,  0.3045,  0.4265,  ...,  0.7576,  0.7228,  0.7054],[ 0.1651,  0.1128,  0.3742,  ...,  0.7576,  0.7402,  0.7054]]])}

equivalent in torchvision

from PIL import Image
from torchvision.transforms import Compose, Resize, CenterCrop, Normalize, ToTensortv_transform = Compose([Resize(256), CenterCrop(224), ToTensor(),Normalize([0.485, 0.456, 0.406], [0.229, 0.224, 0.225])])image = Image.open('banana.png').convert('RGB')
tv_data = tv_transform(image)

Forward through the model

## IMPORTANT: set the classifier to eval mode
classifier.eval()imgs = data['img'].unsqueeze(0)
imgs = tv_data.unsqueeze(0)with torch.no_grad():# class probabilitiesprob = classifier.forward_test(imgs)[0]# featuresfeat = classifier.extract_feat(imgs, stage='neck')[0]print(len(prob))
print(prob.argmax().item())
print(feat.shape)

1000
954
torch.Size([1, 1280])

3.使用MMClassificaiton完整进行水果分类实战：

数据集下载：

GitHub - TommyZihao/MMClassification_Tutorials: Jupyter notebook tutorials for MMClassificationJupyter notebook tutorials for MMClassification. Contribute to TommyZihao/MMClassification_Tutorials development by creating an account on GitHub.https://github.com/TommyZihao/MMClassification_Tutorials

代码框架： 

def main():model = build_classifier(cfg.model)model.init_weights()datasets = [build_dataset(cfg.data.train)]train_model(model,datasets,cfg,distributed=distributed,validate=(not args.no_validate),timestamp=timestamp,device=cfg.device,meta=meta)
mmcls/apis/train_model.pydef train_model(model,dataset,cfg):data_loaders = [build_dataloader(ds, **train_loader_cfg) for ds in dataset]optimizer = build_optimizer(model, cfg.optimizer)runner = build_runner(cfg.runner,default_args=dict(model=model,optimizer=optimizer))runner.register_training_hooks(cfg.lr_config,optimizer_config,cfg.checkpoint_config,cfg.log_config,cfg.get('momentum_config', None),custom_hooks_config=cfg.get('custom_hooks', None))runner.run(data_loaders, cfg.workflow)
mmcv/runner/epoch_based_runner.pyclass EpochBasedRunner(BaseRunner):def run_iter(self, data_batch: Any, train_mode: bool, **kwargs) -> None:if train_mode:outputs = self.model.train_step(data_batch, self.optimizer, **kwargs)else:outputs = self.model.val_step(data_batch, self.optimizer, **kwargs)self.outputs = outputsdef train(self, data_loader, **kwargs):self.model.train()self.data_loader = data_loaderfor i, data_batch in enumerate(self.data_loader):self.run_iter(data_batch, train_mode=True, **kwargs)self.call_hook('after_train_iter')
mmcls/models/classifiers/base.pyclass BaseClassifier(BaseModule, metaclass=ABCMeta):def forward(self, img, return_loss=True, **kwargs):"""Calls either forward_train or forward_test depending on whetherreturn_loss=True.Note this setting will change the expected inputs. When`return_loss=True`, img and img_meta are single-nested (i.e. Tensor andList[dict]), and when `resturn_loss=False`, img and img_meta should bedouble nested (i.e.  List[Tensor], List[List[dict]]), with the outerlist indicating test time augmentations."""if return_loss:return self.forward_train(img, **kwargs)else:return self.forward_test(img, **kwargs)def train_step(self, data, optimizer=None, **kwargs):losses = self(**data)loss, log_vars = self._parse_losses(losses)outputs = dict(loss=loss, log_vars=log_vars, num_samples=len(data['img'].data))return outputs
mmcls/models/classifiers/image.pyclass ImageClassifier(BaseClassifier):def __init__(self,backbone,neck=None,head=None,pretrained=None,train_cfg=None,init_cfg=None):super(ImageClassifier, self).__init__(init_cfg)if pretrained is not None:self.init_cfg = dict(type='Pretrained', checkpoint=pretrained)self.backbone = build_backbone(backbone)if neck is not None:self.neck = build_neck(neck)if head is not None:self.head = build_head(head)def extract_feat(self, img):x = self.backbone(img)if self.with_neck:x = self.neck(x)return xdef forward_train(self, img, gt_label, **kwargs):x = self.extract_feat(img)losses = dict()loss = self.head.forward_train(x, gt_label)losses.update(loss)return losses
mmcv/runner/hooks/optimizer.pyclass OptimizerHook(Hook):def after_train_iter(self, runner):runner.optimizer.zero_grad()runner.outputs['loss'].backward()runner.optimizer.step()

总结：本篇主要偏向图像分类实战部分，使用MMclassification工具进行代码应用，熟悉其框架应用，为后续处理不同场景下分类问题提供帮助。 

本文参考：GitHub - wangruohui/sjtu-openmmlab-tutorial