Extract a function into a submodule

src/colors.rs

@@ -44,6 +44,16 @@ impl ColorType {
             ColorType::RGBA => 6,
         }
     }
+
+    #[inline]
+    pub fn channels_per_pixel(&self) -> u8 {
+        match *self {
+            ColorType::Grayscale | ColorType::Indexed => 1,
+            ColorType::GrayscaleAlpha => 2,
+            ColorType::RGB => 3,
+            ColorType::RGBA => 4,
+        }
+    }
 }
 
 #[derive(Debug, PartialEq, Clone, Copy)]

src/png/mod.rs

@@ -172,12 +172,7 @@ impl PngData {
     /// Return the number of channels in the image, based on color type
     #[inline]
     pub fn channels_per_pixel(&self) -> u8 {
-        match self.ihdr_data.color_type {
+        self.ihdr_data.color_type.channels_per_pixel()
-            ColorType::Grayscale | ColorType::Indexed => 1,
-            ColorType::GrayscaleAlpha => 2,
-            ColorType::RGB => 3,
-            ColorType::RGBA => 4,
-        }
     }
 
     /// Format the `PngData` struct into a valid PNG bytestream