class_docstr: subtract pixel_mean from data at `index`.  Assumes data is in CxHxWxN
code: def __init__(
      self,
      dataloader,
      index,
      pixel_mean=[127, 119, 104],
      *args,
      **kwargs,
  ):
      super(BGRMeanSubtract, self).__init__(
          dataloader, index=index, *args, **kwargs
      )
  
      pixel_mean = np.asarray(pixel_mean)
      self.pixel_mean = self.be.array(pixel_mean[:, np.newaxis])
  
imports: from __future__ import division
  import numpy
  from neon import NervanaObject
label_desc: Use image node_id 1 to create a new BGRMeanSubtract object from inherited base classes: DataLoaderTransformer with example: obj = BGRMeanSubtract(dataloader, index, pixel_mean)