# Ultralytics YOLO 🚀, AGPL-3.0 license
import torch
import torchvision
from ultralytics.data import ClassificationDataset, build_dataloader
from ultralytics.engine.trainer import BaseTrainer
from ultralytics.models import yolo
from ultralytics.nn.tasks import ClassificationModel, attempt_load_one_weight
from ultralytics.utils import DEFAULT_CFG, LOGGER, RANK, colorstr
from ultralytics.utils.plotting import plot_images, plot_results
from ultralytics.utils.torch_utils import is_parallel, strip_optimizer, torch_distributed_zero_first
class ClassificationTrainer(BaseTrainer):
"""
A class extending the BaseTrainer class for training based on a classification model.
Notes:
- Torchvision classification models can also be passed to the 'model' argument, i.e. model='resnet18'.
Example:
```python
from ultralytics.models.yolo.classify import ClassificationTrainer
args = dict(model='yolov8n-cls.pt', data='imagenet10', epochs=3)
trainer = ClassificationTrainer(overrides=args)
trainer.train()
```
"""
def __init__(self, cfg=DEFAULT_CFG, overrides=None, _callbacks=None):
"""Initialize a ClassificationTrainer object with optional configuration overrides and callbacks."""
if overrides is None:
overrides = {}
overrides['task'] = 'classify'
if overrides.get('imgsz') is None:
overrides['imgsz'] = 224
super().__init__(cfg, overrides, _callbacks)
def set_model_attributes(self):
"""Set the YOLO model's class names from the loaded dataset."""
self.model.names = self.data['names']
def get_model(self, cfg=None, weights=None, verbose=True):
"""Returns a modified PyTorch model configured for training YOLO."""
model = ClassificationModel(cfg, nc=self.data['nc'], verbose=verbose and RANK == -1)
if weights:
model.load(weights)
for m in model.modules():
if not self.args.pretrained and hasattr(m, 'reset_parameters'):
m.reset_parameters()
if isinstance(m, torch.nn.Dropout) and self.args.dropout:
m.p = self.args.dropout # set dropout
for p in model.parameters():
p.requires_grad = True # for training
return model
def setup_model(self):
"""Load, create or download model for any task."""
if isinstance(self.model, torch.nn.Module): # if model is loaded beforehand. No setup needed
return
model, ckpt = str(self.model), None
# Load a YOLO model locally, from torchvision, or from Ultralytics assets
if model.endswith('.pt'):
self.model, ckpt = attempt_load_one_weight(model, device='cpu')
for p in self.model.parameters():
p.requires_grad = True # for training
elif model.split('.')[-1] in ('yaml', 'yml'):
self.model = self.get_model(cfg=model)
elif model in torchvision.models.__dict__:
self.model = torchvision.models.__dict__[model](weights='IMAGENET1K_V1' if self.args.pretrained else None)
else:
FileNotFoundError(f'ERROR: model={model} not found locally or online. Please check model name.')
ClassificationModel.reshape_outputs(self.model, self.data['nc'])
return ckpt
def build_dataset(self, img_path, mode='train', batch=None):
"""Creates a ClassificationDataset instance given an image path, and mode (train/test etc.)."""
return ClassificationDataset(root=img_path, args=self.args, augment=mode == 'train', prefix=mode)
def get_dataloader(self, dataset_path, batch_size=16, rank=0, mode='train'):
"""Returns PyTorch DataLoader with transforms to preprocess images for inference."""
with torch_distributed_zero_first(rank): # init dataset *.cache only once if DDP
dataset = self.build_dataset(dataset_path, mode)
loader = build_dataloader(dataset, batch_size, self.args.workers, rank=rank)
# Attach inference transforms
if mode != 'train':
if is_parallel(self.model):
self.model.module.transforms = loader.dataset.torch_transforms
else:
self.model.transforms = loader.dataset.torch_transforms
return loader
def preprocess_batch(self, batch):
"""Preprocesses a batch of images and classes."""
batch['img'] = batch['img'].to(self.device)
batch['cls'] = batch['cls'].to(self.device)
return batch
def progress_string(self):
"""Returns a formatted string showing training progress."""
return ('\n' + '%11s' * (4 + len(self.loss_names))) % \
('Epoch', 'GPU_mem', *self.loss_names, 'Instances', 'Size')
def get_validator(self):
"""Returns an instance of ClassificationValidator for validation."""
self.loss_names = ['loss']
return yolo.classify.ClassificationValidator(self.test_loader, self.save_dir, _callbacks=self.callbacks)
def label_loss_items(self, loss_items=None, prefix='train'):
"""
Returns a loss dict with labelled training loss items tensor.
Not needed for classification but necessary for segmentation & detection
"""
keys = [f'{prefix}/{x}' for x in self.loss_names]
if loss_items is None:
return keys
loss_items = [round(float(loss_items), 5)]
return dict(zip(keys, loss_items))
def plot_metrics(self):
"""Plots metrics from a CSV file."""
plot_results(file=self.csv, classify=True, on_plot=self.on_plot) # save results.png
def final_eval(self):
"""Evaluate trained model and save validation results."""
for f in self.last, self.best:
if f.exists():
strip_optimizer(f) # strip optimizers
if f is self.best:
LOGGER.info(f'\nValidating {f}...')
self.validator.args.data = self.args.data
self.validator.args.plots = self.args.plots
self.metrics = self.validator(model=f)
self.metrics.pop('fitness', None)
self.run_callbacks('on_fit_epoch_end')
LOGGER.info(f"Results saved to {colorstr('bold', self.save_dir)}")
def plot_training_samples(self, batch, ni):
"""Plots training samples with their annotations."""
plot_images(
images=batch['img'],
batch_idx=torch.arange(len(batch['img'])),
cls=batch['cls'].view(-1), # warning: use .view(), not .squeeze() for Classify models
fname=self.save_dir / f'train_batch{ni}.jpg',
on_plot=self.on_plot)