keep only 1 laplacian for simplicity (#745)

Author: cospectrum

src/filter/mod.rs

@@ -440,14 +440,14 @@ where
 /// ```
 #[must_use = "the function does not modify the original image"]
 pub fn laplacian_filter(image: &GrayImage) -> Image<Luma<i16>> {
-    filter_clamped(image, kernel::FOUR_LAPLACIAN_3X3)
+    filter_clamped(image, kernel::LAPLACIAN_3X3)
 }
 
 #[must_use = "the function does not modify the original image"]
 #[cfg(feature = "rayon")]
 #[doc = generate_parallel_doc_comment!("laplacian_filter")]
 pub fn laplacian_filter_parallel(image: &GrayImage) -> Image<Luma<i16>> {
-    filter_clamped_parallel(image, kernel::FOUR_LAPLACIAN_3X3)
+    filter_clamped_parallel(image, kernel::LAPLACIAN_3X3)
 }
 
 #[cfg(test)]

src/kernel.rs

@@ -86,9 +86,5 @@ pub const ROBERTS_HORIZONTAL_2X2: Kernel<'static, i32> = Kernel::new(&[1, 0, 0,
 /// The roberts vertical 3x3 kernel.
 pub const ROBERTS_VERTICAL_2X2: Kernel<'static, i32> = Kernel::new(&[0, 1, -1, -0], 2, 2);
 
-/// The 4-connectivity laplacian 3x3 kernel.
-pub const FOUR_LAPLACIAN_3X3: Kernel<'static, i16> =
-    Kernel::new(&[0, 1, 0, 1, -4, 1, 0, 1, 0], 3, 3);
-/// The 8-connectivity laplacian 3x3 kernel.
-pub const EIGHT_LAPLACIAN_3X3: Kernel<'static, i16> =
-    Kernel::new(&[1, 1, 1, 1, -8, 1, 1, 1, 1], 3, 3);
+/// The laplacian 3x3 kernel.
+pub const LAPLACIAN_3X3: Kernel<'static, i16> = Kernel::new(&[0, 1, 0, 1, -4, 1, 0, 1, 0], 3, 3);