Extract bw stuff to new module

src/bw.rs

@@ -0,0 +1,61 @@
+use image::RgbaImage;
+use palette::{Hsl, Hsv, IntoColor, Lab, LinSrgb, Oklab, Srgb};
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum Method {
+    SrgbAverage,
+    LinSrgbAverage,
+    Hsl,
+    Hsv,
+    Cielab,
+    Oklab,
+}
+
+impl Method {
+    fn to_bw(self, pixel: Srgb) -> Srgb {
+        match self {
+            Self::SrgbAverage => {
+                let value = (pixel.red + pixel.green + pixel.blue) / 3.0;
+                Srgb::new(value, value, value)
+            }
+            Self::LinSrgbAverage => {
+                let pixel: LinSrgb = pixel.into_color();
+                let value = (pixel.red + pixel.green + pixel.blue) / 3.0;
+                LinSrgb::new(value, value, value).into_color()
+            }
+            Self::Hsl => {
+                let mut pixel: Hsl = pixel.into_color();
+                pixel.saturation = 0.0;
+                pixel.into_color()
+            }
+            Self::Hsv => {
+                let mut pixel: Hsv = pixel.into_color();
+                pixel.saturation = 0.0;
+                pixel.into_color()
+            }
+            Self::Cielab => {
+                let mut pixel: Lab = pixel.into_color();
+                pixel.a = 0.5;
+                pixel.b = 0.5;
+                pixel.into_color()
+            }
+            Self::Oklab => {
+                let mut pixel: Oklab = pixel.into_color();
+                pixel.a = 0.0;
+                pixel.b = 0.0;
+                pixel.into_color()
+            }
+        }
+    }
+}
+
+pub fn bw(image: &mut RgbaImage, method: Method) {
+    for pixel in image.pixels_mut() {
+        let [r, g, b, _] = pixel.0;
+        let srgb = Srgb::new(r, g, b).into_format::<f32>();
+        let srgb = method.to_bw(srgb).into_format::<u8>();
+        pixel.0[0] = srgb.red;
+        pixel.0[1] = srgb.green;
+        pixel.0[2] = srgb.blue;
+    }
+}