Hi  @ptrblck  I am following tutorial of FINETUNING TORCHVISION MODELS to test my data. https://pytorch.org/tutorials/beginner/finetuning_torchvision_models_tutorial.html#finetuning-torchvision-models
But the accuracy of transfer learning method and a model trained from scratch is the same in my dataset as shown in the figure

The goal of my code is to detect there is woman people in the images (1: have woman, 0: No woman in the image).
The size of each image is different: some are 300200, 1200 500, 350* 280 .
The code is a little change (data loader part)of the tutorial, but most of part is the same.
from __future__ import print_function
from torchvision import datasets, models, transforms
import matplotlib.pyplot as plt
import time
import os
import copy
import torch
import torchvision
import torchvision.transforms as transforms
import imagehash
import time
import pandas as pd
import os
import torch.nn as nn
import torch.optim as optim


from PIL import Image

from torch.utils.data import Dataset, DataLoader
from torchvision import transforms
from PIL import Image
import torch
import csv
import os
import cv2

class bannerDataset(Dataset):
    def __init__(self, dataPath, label_name, df_labels,  transform=None):
        self.dataPath=dataPath     #the path to the data directory
        self.transform = transform  #a transform object   
        self.labels = list(df_labels[label_name])
        self.image_id = list(df_labels['image_id'])
        
    def __len__(self):
        return len(self.labels)
    
    def __getitem__(self, idx):
        imageName, imageLabel=self.image_id[idx], self.labels[idx]
        imagePath =  os.path.join(self.dataPath, imageName)
        image = cv2.imread(imagePath)
        image = Image.fromarray(image)  
        
        return  image, imageLabel
class DatasetTransformer(torch.utils.data.Dataset):

    def __init__(self, base_dataset, transform):
        self.base_dataset = base_dataset
        self.transform = transform

    def __getitem__(self, index):
        img, target = self.base_dataset[index]
        return self.transform(img), target

    def __len__(self):
        return len(self.base_dataset)
import numpy as np
bannerdata= bannerDataset(path2, 'woman', df_tag_repeat_del_woman)
batch_size = 16
validation_split = .1
shuffle_dataset = True
random_seed= 42
dataset_size = len(bannerdata)


valid_ratio = 0.1
# Split it into training and validation sets
nb_train = int((1.0 - valid_ratio) * len(bannerdata))
nb_valid =  int(valid_ratio * len(bannerdata))
train_dataset, valid_dataset = torch.utils.data.dataset.random_split(bannerdata, [nb_train, nb_valid])

train_dataset = DatasetTransformer(train_dataset, banner_transforms_train)
valid_dataset = DatasetTransformer(valid_dataset, banner_transforms_test)

num_threads = 4
batch_size  = 32
train_loader = torch.utils.data.DataLoader(dataset=train_dataset,
                                          batch_size=batch_size,
                                          shuffle=True,                # <-- this reshuffles the data at every epoch
                                          num_workers=num_threads)
valid_loader = torch.utils.data.DataLoader(dataset=valid_dataset,
                                          batch_size=batch_size, 
                                          shuffle=False,
                                          num_workers=num_threads)
dataloader = {'train': train_loader, 'val':valid_loader}
dataset_sizes = {'train': nb_train, 'val':nb_valid}

def train_model(dataloader, model, criterion, optimizer,num_epochs=25, is_inception=False):
    since = time.time()
    val_acc_history = []
    best_model_wts = copy.deepcopy(model.state_dict())
    best_acc = 0.0

    for epoch in range(num_epochs):
        print('Epoch {}/{}'.format(epoch, num_epochs - 1))
        print('-' * 10)

        # Each epoch has a training and validation phase
        for phase in ['train', 'val']:
            if phase == 'train':
                model.train()  # Set model to training mode
            else:
                model.eval()   # Set model to evaluate mode

            running_loss = 0.0
            running_corrects = 0
            for inputs, labels in dataloader[phase]:
                inputs = inputs.to(device)
                labels = labels.to(device)
#                 print('labels:', labels)

                # zero the parameter gradients
                optimizer.zero_grad()

                # forward
                # track history if only in train
                with torch.set_grad_enabled(phase == 'train'):
                    if is_inception and phase == 'train':
                        outputs, aux_outputs = model(inputs)
                        loss1 = criterion(outputs, labels)
                        loss2 = criterion(aux_outputs, labels)
                        loss = loss1 + 0.4*loss2
                    else:
                        outputs = model(inputs)
                        loss = criterion(outputs, labels)
                    _, preds = torch.max(outputs, 1)
                    # backward + optimize only if in training phase
                    if phase == 'train':
                        loss.backward()
                        optimizer.step()

                # statistics
                running_loss += loss.item() * inputs.size(0)
                running_corrects += torch.sum(preds == labels.data)

            epoch_loss = running_loss / dataset_sizes[phase]
            epoch_acc = running_corrects.double() / dataset_sizes[phase]

            print('{} Loss: {:.4f} Acc: {:.4f}'.format(
                phase, epoch_loss, epoch_acc))

            # deep copy the model
            if phase == 'val' and epoch_acc > best_acc:
                best_acc = epoch_acc
                best_model_wts = copy.deepcopy(model.state_dict())
            if phase == 'val':
                val_acc_history.append(epoch_acc)

        print()

    time_elapsed = time.time() - since
    print('Training complete in {:.0f}m {:.0f}s'.format(
        time_elapsed // 60, time_elapsed % 60))
    print('Best val Acc: {:4f}'.format(best_acc))

    # load best model weights
    model.load_state_dict(best_model_wts)
    return model, val_acc_history

def set_parameter_requires_grad(model, feature_extracting):
    if feature_extracting:
        for param in model.parameters():
            param.requires_grad = False

def initialize_model(model_name, num_classes, feature_extract, use_pretrained=True):
    # Initialize these variables which will be set in this if statement. Each of these
    #   variables is model specific.
    model_ft = None
    input_size = 0

    if model_name == "resnet":
        """ Resnet18
        """
        model_ft = models.resnet18(pretrained=use_pretrained)
        set_parameter_requires_grad(model_ft, feature_extract)
        num_ftrs = model_ft.fc.in_features
        model_ft.fc = nn.Linear(num_ftrs, num_classes)
        input_size = 224

    elif model_name == "alexnet":
        """ Alexnet
        """
        model_ft = models.alexnet(pretrained=use_pretrained)
        set_parameter_requires_grad(model_ft, feature_extract)
        num_ftrs = model_ft.classifier[6].in_features
        model_ft.classifier[6] = nn.Linear(num_ftrs,num_classes)
        input_size = 224

    elif model_name == "vgg":
        """ VGG11_bn
        """
        model_ft = models.vgg11_bn(pretrained=use_pretrained)
        set_parameter_requires_grad(model_ft, feature_extract)
        num_ftrs = model_ft.classifier[6].in_features
        model_ft.classifier[6] = nn.Linear(num_ftrs,num_classes)
        input_size = 224

    elif model_name == "squeezenet":
        """ Squeezenet
        """
        model_ft = models.squeezenet1_0(pretrained=use_pretrained)
        set_parameter_requires_grad(model_ft, feature_extract)
        model_ft.classifier[1] = nn.Conv2d(512, num_classes, kernel_size=(1,1), stride=(1,1))
        model_ft.num_classes = num_classes
        input_size = 224

    elif model_name == "densenet":
        """ Densenet
        """
        model_ft = models.densenet121(pretrained=use_pretrained)
        set_parameter_requires_grad(model_ft, feature_extract)
        num_ftrs = model_ft.classifier.in_features
        model_ft.classifier = nn.Linear(num_ftrs, num_classes)
        input_size = 224

    elif model_name == "inception":
        """ Inception v3
        Be careful, expects (299,299) sized images and has auxiliary output
        """
        model_ft = models.inception_v3(pretrained=use_pretrained)
        set_parameter_requires_grad(model_ft, feature_extract)
        # Handle the auxilary net
        num_ftrs = model_ft.AuxLogits.fc.in_features
        model_ft.AuxLogits.fc = nn.Linear(num_ftrs, num_classes)
        # Handle the primary net
        num_ftrs = model_ft.fc.in_features
        model_ft.fc = nn.Linear(num_ftrs,num_classes)
        input_size = 299
        
    else:
        print("Invalid model name, exiting...")
        exit()

    return model_ft, input_size

# Models to choose from [resnet, alexnet, vgg, squeezenet, densenet, inception]
model_name = "squeezenet"

# Number of classes in the dataset
num_classes = 2

# Batch size for training (change depending on how much memory you have)
batch_size = 8

# Number of epochs to train for
num_epochs = 15

# Flag for feature extracting. When False, we finetune the whole model,
#   when True we only update the reshaped layer params
feature_extract = True

model_ft, input_size = initialize_model(model_name, num_classes, feature_extract, use_pretrained=True)

from torchvision import datasets, models, transforms
import torch.nn as nn
import torch.optim as optim
from torch.optim import lr_scheduler
import copy

device = torch.device("cuda:0" if torch.cuda.is_available() else "cpu")

# Send the model to GPU
model_ft = model_ft.to(device)

# Gather the parameters to be optimized/updated in this run. If we are
#  finetuning we will be updating all parameters. However, if we are
#  doing feature extract method, we will only update the parameters
#  that we have just initialized, i.e. the parameters with requires_grad
#  is True.
params_to_update = model_ft.parameters()
print("Params to learn:")
if feature_extract:
    params_to_update = []
    for name,param in model_ft.named_parameters():
        if param.requires_grad == True:
            params_to_update.append(param)
            print("\t",name)
else:
    for name,param in model_ft.named_parameters():
        if param.requires_grad == True:
            print("\t",name)

# Observe that all parameters are being optimized
optimizer_ft = optim.SGD(params_to_update, lr=0.001, momentum=0.9)

# Setup the loss fxn
criterion = nn.CrossEntropyLoss()

# Train and evaluate
model_ft, hist = train_model(dataloader, model_ft,  criterion, optimizer_ft, num_epochs=num_epochs, is_inception=(model_name=="inception"))

# Initialize the non-pretrained version of the model used for this run
scratch_model,_ = initialize_model(model_name, num_classes, feature_extract=False, use_pretrained=False)
scratch_model = scratch_model.to(device)
scratch_optimizer = optim.SGD(scratch_model.parameters(), lr=0.001, momentum=0.9)
scratch_criterion = nn.CrossEntropyLoss()
_,scratch_hist = train_model(dataloader, scratch_model, scratch_criterion, scratch_optimizer, num_epochs=num_epochs, is_inception=(model_name=="inception"))

# Plot the training curves of validation accuracy vs. number
#  of training epochs for the transfer learning method and
#  the model trained from scratch
ohist = []
shist = []

ohist = [h.cpu().numpy() for h in hist]
shist = [h.cpu().numpy() for h in scratch_hist]

plt.title("Validation Accuracy vs. Number of Training Epochs")
plt.xlabel("Training Epochs")
plt.ylabel("Validation Accuracy")
plt.plot(range(1,num_epochs+1),ohist,label="Pretrained")
plt.plot(range(1,num_epochs+1),shist,label="Scratch")
plt.ylim((0,1.))
plt.xticks(np.arange(1, num_epochs+1, 1.0))
plt.legend()
plt.show()


I don’t why there is not any change of accuracy of two model that there is obvious difference between transfer learning and model trained from scratch in the tutorial.