Function canny 

pub fn canny<T: Into<DynamicImage>>(
    image: T,
    sigma: f32,
    strong_threshold: f32,
    weak_threshold: f32,
) -> Detection

Computes the canny edges of an image.

The variable sigma determines the size of the filter kernel which affects the precision and SNR of the computation:

• A small sigma (3.0<) creates a kernel which is able to discern fine details but is more prone to noise.
• Larger values result in detail being lost and are thus best used for detecting large features. Computation time also increases.

The weak_threshold and strong_threshold determine what detected pixels are to be regarded as edges and which should be discarded. They are compared with the absolute magnitude of the change in brightness.

Panics:

• If either strong_threshold or weak_threshold are outisde the range of 0 to 1 inclusive.
• If strong_threshold is less than weak_threshold.
• If image contains no pixels (either it’s width or height is 0).