Add convolution with edge saturating

src/kernel.rs

@@ -7,6 +7,32 @@ pub trait Kernel {
     fn convolve<P>(&self, img: &image::Image<P>) -> image::Image<P>
     where
         P: image::Pixel;
+
+    fn convolve_sat<P>(&self, img: &image::Image<P>) -> image::Image<P>
+    where
+        P: image::Pixel;
+}
+
+fn at_sat<P>(x: isize, y: isize, img: &image::Image<P>) -> P
+where
+    P: Copy,
+{
+    img.at(
+        if x < 0 {
+            0
+        } else if x as usize >= img.extent.x {
+            img.extent.x - 1
+        } else {
+            x as usize
+        },
+        if y < 0 {
+            0
+        } else if y as usize >= img.extent.y {
+            img.extent.y - 1
+        } else {
+            y as usize
+        },
+    )
 }
 
 impl<const N: usize> Kernel for [[f32; N]; N] {
@@ -29,6 +55,24 @@ impl<const N: usize> Kernel for [[f32; N]; N] {
         });
         result
     }
+
+    fn convolve_sat<P>(&self, img: &image::Image<P>) -> image::Image<P>
+    where
+        P: image::Pixel,
+    {
+        let l = N as isize / 2;
+        let mut result = image::Image::with_extent(img.extent);
+        result.for_each(|x, y, p| {
+            for i in 0..N {
+                for j in 0..N {
+					let xi = (x + j) as isize - l;
+					let yi = (y + i) as isize - l;
+                    *p += at_sat(xi, yi, img) * self[i][j];
+                }
+            }
+        });
+        result
+    }
 }
 
 #[cfg(test)]