May 13, 2021
Thanks! Sorry for the late reply.
1. This is done to bring the center of the landmarks to the origin for rotation. The landmarks have been mapped between [0, 1]. So, 0.5 is the center value.
2. By dividing the landmarks by the image dimensions, we map them between 0 to 1. This allows us to use a sigmoid function at the output layer.
3. We normalize the image to get the pixel values in the range of [-1, 1] or [0, 1]. This leads to a stable training.