Add parallelized sharpen3x3

src/filter/mod.rs

@@ -386,6 +386,9 @@ where
 
 /// Returns 2d correlation of an image with a row-major kernel. Intermediate calculations are
 /// performed at type K, and the results clamped to subpixel type S. Pads by continuity.
+///
+/// A parallelized version of this function exists with [`filter_clamped_parallel`] when
+/// the crate `rayon` feature is enabled.
 pub fn filter_clamped<P, K, S>(image: &Image<P>, kernel: Kernel<K>) -> Image<ChannelMap<P, S>>
 where
     P::Subpixel: Into<K>,

src/filter/sharpen.rs

@@ -1,3 +1,5 @@
+#[cfg(feature = "rayon")]
+use super::filter_clamped_parallel;
 use super::{filter_clamped, gaussian_blur_f32};
 use crate::{
     definitions::{Clamp, Image},
@@ -13,6 +15,16 @@ pub fn sharpen3x3(image: &GrayImage) -> GrayImage {
     filter_clamped(image, identity_minus_laplacian)
 }
 
+/// Sharpens a grayscale image by applying a 3x3 approximation to the Laplacian.
+/// This version uses rayon to parallelize the computation.
+#[must_use = "the function does not modify the original image"]
+#[cfg(feature = "rayon")]
+#[cfg_attr(docsrs, doc(cfg(feature = "rayon")))]
+pub fn sharpen3x3_parallel(image: &GrayImage) -> GrayImage {
+    let identity_minus_laplacian = Kernel::new(&[0, -1, 0, -1, 5, -1, 0, -1, 0], 3, 3);
+    filter_clamped_parallel(image, identity_minus_laplacian)
+}
+
 /// Sharpens a grayscale image using a Gaussian as a low-pass filter.
 ///
 /// * `sigma` is the standard deviation of the Gaussian filter used.