Function image::imageops::unsharpen

pub fn unsharpen<I, P, S>(image: &I,
                          sigma: f32,
                          threshold: i32)
                          -> ImageBuffer<P, Vec<S>> where I: GenericImage<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