Function normalize_image 

pub fn normalize_image(
    image: &Tensor,
    mean: &[f32],
    std: &[f32],
) -> Result<Tensor, ImgProcError>

Normalize u8 image to [0, 1] f32 then apply mean/std normalization. Per-channel normalization: (pixel - mean[c]) / std[c] for an HWC image.