Function filter3x3

pub fn filter3x3<P, K, S>(
    image: &Image<P>,
    kernel: &[K],
) -> Image<ChannelMap<P, S>>
where
    P::Subpixel: ValueInto<K>,
    S: Clamp<K> + Primitive,
    P: WithChannel<S>,
    K: Num + Copy,

Returns 2d correlation of an image with a 3x3 row-major kernel. Intermediate calculations are performed at type K, and the results clamped to subpixel type S. Pads by continuity.