Function `unsharpen`

fn unsharpen<I, P, S>(image: &I, sigma: f32, threshold: i32) -> ImageBuffer<P, Vec<S>>
where
    I: GenericImageView<Pixel = P>,
    P: Pixel<Subpixel = S> + 'static,
    S: Primitive + 'static

Performs an unsharpen mask on the supplied image. sigma is the amount to blur the image by. threshold is the threshold for minimal brightness change that will be sharpened.

See https://en.wikipedia.org/wiki/Unsharp_masking#Digital_unsharp_masking