Edge Detection & Gradients

Gradients and edge maps highlight structural changes and borders within images. Iris provides standard first and second-order image derivative approximations, plus geometric shape detectors.

Gradient Operators

Sobel

Calculates first-order derivatives along the X and Y axes. Returns a single gradient magnitude image.

// Compute Sobel gradient magnitude
let edges = image.sobel()?;

Scharr

Provides more accurate derivative estimations compared to the Sobel operator.

// Compute Scharr gradient magnitude
let scharr_img = image.scharr()?;

Laplacian

Calculates the second-order derivative (sum of second spatial derivatives), emphasizing high-frequency regions.

// Compute Laplacian
let laplacian = image.laplacian()?;

Canny Edge Detection

Canny edge detection is a multi-stage process that reduces noise, computes gradients, performs non-maximum suppression, and uses hysteresis thresholding.

// Run Canny edge detector with low/high thresholds
let edges = image.canny(0.1, 0.3)?;

Hough Transforms

Probabilistic Hough Line Transform

Detects line segments in a binary edge image. Returns a vector of LineSegment as ((x1,y1), (x2,y2)).

let lines = edges.hough_lines_p(
    1.0,                            // rho: distance resolution
    std::f32::consts::PI / 180.0,   // theta: angle resolution
    50,                             // threshold: minimum votes
    50,                             // min_line_length
    10,                             // max_line_gap
)?;
for ((x1, y1), (x2, y2)) in lines {
    println!("Line from ({}, {}) to ({}, {})", x1, y1, x2, y2);
}

Hough Circle Transform

Detects circles in a grayscale image. Returns circles as (center_x, center_y, radius).

let circles = image.hough_circles(
    1.0,    // dp: accumulator resolution ratio
    20.0,   // min_dist: minimum distance between circles
    50.0,   // param1: upper Canny threshold
    30.0,   // param2: accumulator threshold
    10,     // min_radius
    100,    // max_radius
)?;
for (cx, cy, r) in circles {
    println!("Circle at ({}, {}) with radius {}", cx, cy, r);
}