'SSD preprocessing.
Maps pixel values to the range [-1, 1].
Args:
resized_inputs: a [batch, height, width, channels] float tensor
representing a batch of images.
Returns:
preprocessed_inputs: a [batch, height, width, channels] float tensor
representing a batch of images.'

def preprocess(self, resized_inputs):

    return (((2.0 / 255.0) * resized_inputs) - 1.0)
