diff --git a/src/filter.rs b/src/filter.rs
index 8d787df..408da3b 100644
--- a/src/filter.rs
+++ b/src/filter.rs
@@ -1,5 +1,8 @@
 pub mod canny;
 pub mod sobel;
+pub mod threshold;
 
 pub use canny::canny;
 pub use sobel::sobel;
+pub use threshold::threshold;
+pub use threshold::threshold_auto;
diff --git a/src/filter/canny/double_threshold.rs b/src/filter/canny/double_threshold.rs
index c7b313e..9dff3f2 100644
--- a/src/filter/canny/double_threshold.rs
+++ b/src/filter/canny/double_threshold.rs
@@ -1,4 +1,5 @@
 use crate::image::*;
+use crate::*;
 
 #[derive(Clone, Copy, PartialEq)]
 pub enum Candidate {
@@ -14,72 +15,16 @@ impl Default for Candidate {
 }
 
 pub fn double_threshold(img: Image<f32>) -> Image<Candidate> {
-    let t = otsu::<20>(&img.pixels);
-    let mut result = Image::<Candidate>::with_extent(img.extent);
-    result.for_each(|x, y, p| {
-        let value = img.at(x, y);
-        *p = if value < t / 2.0 {
+    let t = filter::threshold::otsu::<20, _>(
+        (&img.pixels).into_iter().map(|p| *p),
+    );
+    img.map(|p| {
+        if p < t / 2.0 {
             Candidate::None
-        } else if value < t {
+        } else if p < t {
             Candidate::Weak
         } else {
             Candidate::Strong
         }
-    });
-    result
-}
-
-fn otsu<const N: usize>(values: &Vec<f32>) -> f32 {
-    let mut hist = [0.0; N];
-    for x in values {
-        let bin = std::cmp::min(N - 1, (*x * (N as f32)) as usize);
-        hist[bin] += 1.0;
-    }
-    for i in 0..N {
-        hist[i] /= values.len() as f32;
-    }
-
-    let mut max = 0.0;
-    let mut res = 0;
-    for t in 0..N {
-        let var = variance(t, hist);
-        if var > max {
-            res = t;
-            max = var;
-        }
-    }
-
-    res as f32 / N as f32
-}
-
-fn variance<const N: usize>(t: usize, hist: [f32; N]) -> f32 {
-    let omega_0 = omega(0, t, hist);
-    let omega_1 = omega(t, N, hist);
-
-    let mu_0 = mu(0, t, hist, omega_0);
-    let mu_1 = mu(t, N, hist, omega_1);
-
-    omega_0 * omega_1 * (mu_0 - mu_1).powf(2.0)
-}
-
-fn omega<const N: usize>(from: usize, to: usize, hist: [f32; N]) -> f32 {
-    let mut sum = 0.0;
-    for i in from..to {
-        sum += hist[i];
-    }
-    sum
-}
-
-fn mu<const N: usize>(
-    from: usize,
-    to: usize,
-    hist: [f32; N],
-    omega: f32,
-) -> f32 {
-    let mut sum = 0.0;
-    for i in from..to {
-        let bin_centre = (i as f32 + 0.5) / N as f32;
-        sum += bin_centre * hist[i];
-    }
-    sum / omega
+    })
 }
diff --git a/src/filter/threshold.rs b/src/filter/threshold.rs
new file mode 100644
index 0000000..cdb3c1f
--- /dev/null
+++ b/src/filter/threshold.rs
@@ -0,0 +1,73 @@
+use crate::image::*;
+
+pub fn threshold_auto(img: Image<Luminance>) -> Image<Luminance> {
+    let t = otsu::<20, _>((&img.pixels).into_iter().map(|p| p.y));
+	threshold(t, img)
+}
+
+pub fn threshold(t: f32, mut img: Image<Luminance>) -> Image<Luminance> {
+    img.for_each(|_, _, p| {
+        p.y = if p.y >= t { 1.0 } else { 0.0 };
+    });
+    img
+}
+
+pub fn otsu<const N: usize, I>(values: I) -> f32
+where
+    I: Iterator<Item = f32>,
+{
+    let mut hist = [0.0; N];
+    let mut n = 0;
+    for x in values {
+        let bin = std::cmp::min(N - 1, (x * (N as f32)) as usize);
+        hist[bin] += 1.0;
+        n += 1;
+    }
+    for i in 0..N {
+        hist[i] /= n as f32;
+    }
+
+    let mut max = 0.0;
+    let mut res = 0;
+    for t in 0..N {
+        let var = variance(t, hist);
+        if var > max {
+            res = t;
+            max = var;
+        }
+    }
+
+    res as f32 / N as f32
+}
+
+fn variance<const N: usize>(t: usize, hist: [f32; N]) -> f32 {
+    let omega_0 = omega(0, t, hist);
+    let omega_1 = omega(t, N, hist);
+
+    let mu_0 = mu(0, t, hist, omega_0);
+    let mu_1 = mu(t, N, hist, omega_1);
+
+    omega_0 * omega_1 * (mu_0 - mu_1).powf(2.0)
+}
+
+fn omega<const N: usize>(from: usize, to: usize, hist: [f32; N]) -> f32 {
+    let mut sum = 0.0;
+    for i in from..to {
+        sum += hist[i];
+    }
+    sum
+}
+
+fn mu<const N: usize>(
+    from: usize,
+    to: usize,
+    hist: [f32; N],
+    omega: f32,
+) -> f32 {
+    let mut sum = 0.0;
+    for i in from..to {
+        let bin_centre = (i as f32 + 0.5) / N as f32;
+        sum += bin_centre * hist[i];
+    }
+    sum / omega
+}
diff --git a/src/lib.rs b/src/lib.rs
index bd26a13..8e343a3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,3 @@
+pub mod filter;
 pub mod image;
 pub mod kernel;
-pub mod filter;