Function scharr 

pub fn scharr<T, const CHANNELS: usize>(
    input: ImageView<'_, T, CHANNELS>,
    dx: usize,
    dy: usize,
    scale: f64,
    delta: f64,
    border: BorderMode<T, CHANNELS>,
) -> Result<Image<f32, CHANNELS>, VisionError>
where
    T: PixelComponent,

Computes a 3×3 Scharr first derivative as signed f32 values.