code: def subtract_imagenet_mean_preprocess_batch(batch):
      
      batch = F.swapaxes(batch,0, 1)
      (r, g, b) = F.split(batch, num_outputs=3, axis=0)
      r = r - 123.680
      g = g - 116.779
      b = b - 103.939
      batch = F.concat(b, g, r, dim=0)
      batch = F.swapaxes(batch,0, 1)
      return batch
docs: Subtract ImageNet mean pixel-wise from a BGR image.