Function sobel_threshold_3x3_u8 

pub fn sobel_threshold_3x3_u8(
    input: ImageView<'_, u8, 1>,
    dx: usize,
    dy: usize,
    threshold: u8,
    border: BorderMode<u8, 1>,
) -> VisionResult<Image<u8, 1>>

Computes a binary edge mask from absolute 3x3 Sobel response.

Pixels whose saturated absolute response is strictly greater than threshold become 255; all others become zero. This matches OpenCV’s Sobel(CV_16S) → convertScaleAbs → THRESH_BINARY pipeline.