code: def validation_step(self, batch, batch_idx):
      batch = {
          k: v for k, v in batch.items() if isinstance(v, torch.Tensor)
      }
      input = batch["input"]
      output = self.forward(input)
      batch.update({"output": output})
      val_loss_dict = self.compute_losses(**batch)
  
      self.log_dict(val_loss_dict)
      self.log_images(batch, n_log=1, prefix="val_")
  
      return val_loss_dict["loss"]
  
file_path: BigDL/python/nano/client-application/VideoStylization/litmodels.py
imports: from typing import OrderedDict
  import torch
  import torch.nn
  import torch.nn.functional
  import pytorch_lightning
  from feature_model import FeaturesNet
  from original_models import Discriminator, Generator
label_desc: Use image node_id 6 for calling the LitModel obj's underlying member method code with example usage: obj.validation_step(batch, batch_idx) and returns: val_loss_dict