diff --git a/Cargo.toml b/Cargo.toml
index 68b093c..4a89f8e 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -5,3 +5,7 @@ authors = ["Thomas Forgione <thomas@tforgione.fr>"]
 
 [dependencies]
 image = "*"
+
+[[bin]]
+name = "psnr"
+path = "src/main.rs"
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..43919b6
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,41 @@
+extern crate image;
+
+use image::{Pixel, GenericImage, ImageResult, ImageError};
+
+pub fn psnr<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img1: &T, img2: &T) -> ImageResult<f64> {
+
+    let twenty_log10_max: f64 = 20.0 * (std::u32::MAX as f64).log10();
+
+    if img1.dimensions() != img2.dimensions() {
+        return Err(ImageError::DimensionError);
+    }
+
+    let mut mse = 0.0;
+
+    for x in 0 .. img1.dimensions().0 {
+        for y in 0 .. img1.dimensions().1 {
+
+            let p1 = img1.get_pixel(x, y).to_rgba();
+            let p2 = img2.get_pixel(x, y).to_rgba();
+
+            let dx = p1.data[0] as f64 - p2.data[0] as f64;
+            let dy = p1.data[1] as f64 - p2.data[1] as f64;
+            let dz = p1.data[2] as f64 - p2.data[2] as f64;
+
+            let dx = dx * dx;
+            let dy = dy * dy;
+            let dz = dz * dz;
+
+            mse += dx + dy + dz;
+        }
+    }
+
+    mse /= (img1.dimensions().0 * img1.dimensions().1 * 3) as f64;
+    Ok(twenty_log10_max - 10.0 * mse.log10())
+}
+
+pub fn psnr_files(path1: &str, path2: &str) -> ImageResult<f64> {
+    let img1 = image::open(path1)?;
+    let img2 = image::open(path2)?;
+    psnr(&img1, &img2)
+}
diff --git a/src/main.rs b/src/main.rs
index ca40023..c9234cd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,50 +1,13 @@
 extern crate image;
+extern crate psnr;
 
 use std::env::args;
 use std::fs;
 
-use image::{ImageResult, ImageError};
+use image::ImageResult;
+use psnr::psnr_files;
 
-const MAX: u32 = 255;
-
-fn mse_files(path1: &str, path2: &str) -> ImageResult<f64> {
-
-    let twenty_log10_max: f64 = 20.0 * (MAX as f64).log10();
-
-    let img1 = image::open(path1)?;
-    let img2 = image::open(path2)?;
-
-    use image::GenericImage;
-
-    if img1.dimensions() != img2.dimensions() {
-        return Err(ImageError::DimensionError);
-    }
-
-    let mut mse = 0.0;
-
-    for x in 0 .. img1.dimensions().0 {
-        for y in 0 .. img1.dimensions().1 {
-            let p1 = img1.get_pixel(x, y);
-            let p2 = img2.get_pixel(x, y);
-
-            let dx = p1[0] as f64 - p2[0] as f64;
-            let dy = p1[1] as f64 - p2[1] as f64;
-            let dz = p1[2] as f64 - p2[2] as f64;
-
-            let dx = dx * dx;
-            let dy = dy * dy;
-            let dz = dz * dz;
-
-            mse += dx + dy + dz;
-        }
-    }
-
-    mse /= (img1.dimensions().0 * img1.dimensions().1 * 3) as f64;
-
-    Ok(twenty_log10_max - 10.0 * mse.log10())
-}
-
-fn mse_dir(path1: &str, path2: &str) -> Vec<(String, ImageResult<f64>)> {
+fn psnr_dir(path1: &str, path2: &str) -> Vec<(String, ImageResult<f64>)> {
     let mut dirs1: Vec<_> = fs::read_dir(path1).unwrap()
         .map(|x|x.unwrap())
         .filter(|x| x.file_name().into_string().unwrap().ends_with(".png"))
@@ -63,9 +26,9 @@ fn mse_dir(path1: &str, path2: &str) -> Vec<(String, ImageResult<f64>)> {
     for file in dirs1 {
         let p1 = path1.to_owned() + &file.file_name().to_owned().into_string().unwrap();
         let p2 = path2.to_owned() + &file.file_name().to_owned().into_string().unwrap();
-        let mse = mse_files(&p1, &p2);
+        let psnr = psnr_files(&p1, &p2);
 
-        let elt = (file.file_name().to_owned().into_string().unwrap(), mse.unwrap());
+        let elt = (file.file_name().to_owned().into_string().unwrap(), psnr.unwrap());
         println!("{} {}", elt.0, elt.1);
         res.push((elt.0, Ok(elt.1)));
     }
@@ -77,5 +40,5 @@ fn main() {
     let path1 = args().nth(1).unwrap();
     let path2 = args().nth(2).unwrap();
 
-    let _ = mse_dir(&path1, &path2);
+    let _ = psnr_dir(&path1, &path2);
 }