src/application/image/model_detection.py

from sklearn.metrics import roc_auc_score
from torchmetrics import Accuracy, Recall
import pytorch_lightning as pl
import timm  
import torch
import torch.nn.functional as F
import logging
from PIL import Image
import torchvision.transforms as transforms
from torchvision.transforms import v2

logging.basicConfig(filename='training.log',filemode='w',level=logging.INFO, force=True)
CHECKPOINT = "models/image_classifier/image-classifier-step=8008-val_loss=0.11.ckpt"

class ImageClassifier(pl.LightningModule):
    def __init__(self, lmd=0):
        super().__init__()
        self.model = timm.create_model('resnet50', pretrained=True, num_classes=1)
        self.accuracy = Accuracy(task='binary', threshold=0.5)
        self.recall = Recall(task='binary', threshold=0.5)  
        self.validation_outputs = []
        self.lmd = lmd

    def forward(self, x):
        return self.model(x)

    def training_step(self, batch):
        images, labels, _ = batch
        outputs = self.forward(images).squeeze()
        
        print(f"Shape of outputs (training): {outputs.shape}")
        print(f"Shape of labels (training): {labels.shape}")
        
        loss = F.binary_cross_entropy_with_logits(outputs, labels.float())
        logging.info(f"Training Step - ERM loss: {loss.item()}")
        loss += self.lmd * (outputs ** 2).mean() # SD loss penalty
        logging.info(f"Training Step - SD loss: {loss.item()}")
        return loss

    def validation_step(self, batch):
        images, labels, _ = batch
        outputs = self.forward(images).squeeze()

        if outputs.shape == torch.Size([]):
            return
        
        print(f"Shape of outputs (validation): {outputs.shape}")
        print(f"Shape of labels (validation): {labels.shape}")

        loss = F.binary_cross_entropy_with_logits(outputs, labels.float())
        preds = torch.sigmoid(outputs)
        self.log('val_loss', loss, prog_bar=True, sync_dist=True)
        self.log('val_acc', self.accuracy(preds, labels.int()), prog_bar=True, sync_dist=True)
        self.log('val_recall', self.recall(preds, labels.int()), prog_bar=True, sync_dist=True)
        output = {"val_loss": loss, "preds": preds, "labels": labels}
        self.validation_outputs.append(output)
        logging.info(f"Validation Step - Batch loss: {loss.item()}")
        return output
    
    def predict_step(self, batch):
        images, label, domain = batch
        outputs = self.forward(images).squeeze()
        preds = torch.sigmoid(outputs)
        return preds, label, domain

    def on_validation_epoch_end(self):
        if not self.validation_outputs:
            logging.warning("No outputs in validation step to process")
            return
        preds = torch.cat([x['preds'] for x in self.validation_outputs])
        labels = torch.cat([x['labels'] for x in self.validation_outputs])
        if labels.unique().size(0) == 1:
            logging.warning("Only one class in validation step")
            return
        auc_score = roc_auc_score(labels.cpu(), preds.cpu())
        self.log('val_auc', auc_score, prog_bar=True, sync_dist=True)
        logging.info(f"Validation Epoch End - AUC score: {auc_score}")
        self.validation_outputs = []

    def configure_optimizers(self):
        optimizer = torch.optim.Adam(self.model.parameters(), lr=0.0005)
        return optimizer



def load_image(image_path, transform=None):
    image = Image.open(image_path).convert('RGB')
    
    if transform:
        image = transform(image)
    
    return image


def predict_single_image(image_path, model, transform=None):
    image = load_image(image_path, transform) 
    
    device = torch.device('cuda' if torch.cuda.is_available() else 'cpu')
    
    model.to(device)
    
    image = image.to(device)

    model.eval()
    
    with torch.no_grad():
        image = image.unsqueeze(0)  
        output = model(image).squeeze() 
        prediction = torch.sigmoid(output).item()  
    
    return prediction


def image_generation_detection(image_path):
    model = ImageClassifier.load_from_checkpoint(CHECKPOINT)

    transform = v2.Compose([
        transforms.ToTensor(),
        v2.CenterCrop((256, 256)),
    ])    

    prediction = predict_single_image(image_path, model, transform) 
    
    result = ""
    if prediction <= 0.2:
        result += "Most likely human"
        image_prediction_label = "HUMAN"
    else:
        result += "Most likely machine"
        image_prediction_label = "MACHINE"
    image_confidence = min(1, 0.5 + abs(prediction - 0.2))
    result += f" with confidence = {round(image_confidence * 100, 2)}%"
    image_confidence = round(image_confidence * 100, 2)
    return image_prediction_label, image_confidence


if __name__ == "__main__":  
    image_path = "path_to_your_image.jpg"  # Replace with your image path
    image_prediction_label, image_confidence = image_generation_detection(
        image_path,
        )