'Constructor.
Args:
image_diff_list: A list of (image, diff) tuples, with shape
[batch_size, image_size, image_size, 3] and image_sizes as
[32, 64, 128, 256].
params: Dict of parameters.'

def __init__(self, image_diff_list, params):

    self.images = [i for (i, _) in image_diff_list]
    self.diffs = [((d + params['scale']) / 2) for (i, d) in image_diff_list]
    self.params = params
