fix: check bounds when adding to stack in hysteresis

src/edges.rs

@@ -129,9 +129,11 @@ fn hysteresis(input: &Image<Luma<f32>>, low_thresh: f32, high_thresh: f32) -> Im
                 // Track neighbors until no neighbor is >= low_thresh.
                 while let Some((nx, ny)) = edges.pop() {
                     let neighbor_indices = [
+                        (nx + 1, ny - 1),
                         (nx + 1, ny),
                         (nx + 1, ny + 1),
                         (nx, ny + 1),
+                        (nx, ny - 1),
                         (nx - 1, ny - 1),
                         (nx - 1, ny),
                         (nx - 1, ny + 1),
@@ -142,6 +144,13 @@ fn hysteresis(input: &Image<Luma<f32>>, low_thresh: f32, high_thresh: f32) -> Im
                         let out_neighbor = *out.get_pixel(neighbor_idx.0, neighbor_idx.1);
                         if in_neighbor[0] >= low_thresh && out_neighbor[0] == 0 {
                             out.put_pixel(neighbor_idx.0, neighbor_idx.1, max_brightness);
+                            if neighbor_idx.0 == 0
+                                || neighbor_idx.0 >= input.width() - 1
+                                || neighbor_idx.1 == 0
+                                || neighbor_idx.1 >= input.height() - 1
+                            {
+                                continue;
+                            }
                             edges.push((neighbor_idx.0, neighbor_idx.1));
                         }
                     }

src/filter/mod.rs

@@ -810,6 +810,19 @@ mod tests {
         let image2 = gaussian_blur_f32(&image, 6f32);
         assert_pixels_eq_within!(image2, image, 1e-6);
     }
+
+    #[test]
+    fn test_canny_zero_threshold_panic() {
+        let image = image::GrayImage::new(10, 10);
+        _ = crate::edges::canny(&image, 0.0, 0.0);
+    }
+
+    #[test]
+    fn test_canny_one_border_pixel_panic() {
+        let mut image = image::GrayImage::new(10, 10);
+        *image.get_pixel_mut(9, 0) = Luma([255u8]);
+        _ = crate::edges::canny(&image, 0.0, 100.0);
+    }
 }
 
 #[cfg(not(miri))]