Add at() method to Image

src/image.rs

@@ -95,6 +95,10 @@ impl<P: Pixel> Image<P> {
         Self { extent, pixels }
     }
 
+    pub fn at(&self, x: usize, y: usize) -> P {
+        self.pixels[y * self.extent.x + x]
+    }
+
     pub fn for_each<F>(&mut self, f: F)
     where
         F: Fn(usize, usize, &mut P) + Send + Sync,
@@ -117,9 +121,7 @@ impl<P: Pixel> Image<P> {
         Q: Pixel,
     {
         let mut img = Image::with_extent(self.extent);
-        img.for_each(|x, y, p| {
+        img.for_each(|x, y, p| *p = f(self.at(x, y)));
-            *p = f(self.pixels[self.extent.x * y + x]);
-        });
         img
     }