What does the ndc transforming means when the rendered image' h and w are different?

[chenerg]

The following is copied from pytorch camera documentation

The relationship between screen and NDC specifications of a camera's focal_length and principal_point is given by the following equations, where s = min(image_width, image_height). The transformation of x and y coordinates between screen and NDC is exactly the same as for px and py.

` fx_ndc = fx_screen * 2.0 / s fy_ndc = fy_screen * 2.0 / s

px_ndc = - (px_screen - image_width / 2.0) * 2.0 / s py_ndc = - (py_screen - image_height / 2.0) * 2.0 / s`

I'm confused why the s is min(image_width, image_height). I think this will cause the NDC coordinate of x or y to be greater than 1, is that ok?