fn gaussian_baseline_rgb<I>(image: &I, stdev: f32) -> Image<Rgb<u8>>
    where
        I: GenericImage<Pixel = Rgb<u8>>,
    {
        blur(image, stdev)
    }
Baseline implementation of Gaussian blur is that provided by image::imageops.
We can also use this to validate correctness of any implementations we add here.
src/filter/mod.rs