diff --git a/src/lib.rs b/src/lib.rs
index 43919b6..c445cf6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,14 +1,15 @@
 extern crate image;
 
-use image::{Pixel, GenericImage, ImageResult, ImageError};
+use image::{Pixel, GenericImage, ImageResult};
 
-pub fn psnr<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img1: &T, img2: &T) -> ImageResult<f64> {
+/// Compute a PSNR between two images.
+///
+/// Will panic an error if the two images don't have the same size.
+pub fn psnr<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img1: &T, img2: &T) -> f64 {
 
-    let twenty_log10_max: f64 = 20.0 * (std::u32::MAX as f64).log10();
+    let twenty_log10_max: f64 = 20.0 * (std::u8::MAX as f64).log10();
 
-    if img1.dimensions() != img2.dimensions() {
-        return Err(ImageError::DimensionError);
-    }
+    assert_eq!(img1.dimensions(), img2.dimensions());
 
     let mut mse = 0.0;
 
@@ -31,11 +32,11 @@ pub fn psnr<P: Pixel<Subpixel=u8>, T: GenericImage<Pixel=P>>(img1: &T, img2: &T)
     }
 
     mse /= (img1.dimensions().0 * img1.dimensions().1 * 3) as f64;
-    Ok(twenty_log10_max - 10.0 * mse.log10())
+    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)
+    Ok(psnr(&img1, &img2))
 }