Function compute_rmse 

pub fn compute_rmse(a: &[u8], b: &[u8]) -> f64

Per-pixel RMSE (Root Mean Square Error) between two RGBA8 images.

Both buffers must have the same length (width * height * 4). Returns a value in the range [0.0, 255.0]:

• 0.0 – images are byte-identical.
• < 5.0 – visually indistinguishable (acceptance threshold).
• > 50.0 – significant structural difference.

Panics

Panics if a.len() != b.len() or if the length is zero.