Okay, so this does something a little different than removing the mean, but suffice it to say it is not sufficiently general. Having a hard-coded constant in there is not useful. What it could or should do should be to take the min and the max of the pixels in the training data and subtract `min + (max - min)/2`. Subtracting the min makes the values be between 0 to `(max - min)`, then subtracting (max - min)/2 centers the values around 0.