Function image::imageops::unsharpen

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

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