code: def psnr(img1, img2):
      mse = (
          (((img1 - img2)) ** 2)
          .view(img1.shape[0], -1)
          .mean(1, keepdim=True)
      )
      return 20 * torch.log10(1.0 / torch.sqrt(mse))
  
label_desc: Use image node_id 2 for calling a global function with example usage: psnr(img1, img2) and returns: unknown