pub fn unletter_norm(b: BoundingBox, lb: [f32; 4]) -> BoundingBoxExpand description
Invert a letterbox: map a BoundingBox normalized over the model input
back to normalized-over-the-crop, given the content bounds
[lx0, ly0, lx1, ly1]. The box is canonicalised first, a degenerate
(zero-span) letterbox axis maps with unit scale (no divide-by-zero), and the
result is clamped to [0, 1].
This is the single home for the inverse-letterbox transform;
edgefirst_image::unletter_bbox is a thin wrapper around it (the image
crate depends on decoder, so the shared math lives here, in the lower
crate).