use 0.0 comparisions instead of f64::epsilon for kapur

.github/workflows/deploy-github-pages.yml

@@ -29,7 +29,7 @@ jobs:
             ~/.cargo/git
             ~/.cargo/registry
             **/target
-          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/Cargo.lock') }}
+          key: ${{ runner.os }}-build-${{ hashFiles('**/Cargo.lock') }}
 
       - name: Install dependencies
         run: |

src/image_helpers.rs

@@ -33,11 +33,11 @@ fn kapur_level(img: &GrayImage) -> u8 {
     // The H_s in the article. These are the entropies attached to the
     // distributions p[0],...,p[s].
     let mut h = [0.0f64; 256];
-    if p[0] > f64::EPSILON {
+    if p[0] > 0.0 {
         h[0] = -p[0] * p[0].ln();
     }
     for s in 1..=255 {
-        if p[s] > f64::EPSILON {
+        if p[s] > 0.0 {
             h[s] = h[s - 1] - p[s] * p[s].ln();
         } else {
             h[s] = h[s - 1]
@@ -48,12 +48,15 @@ fn kapur_level(img: &GrayImage) -> u8 {
     let mut best_threshold = usize::MIN;
 
     for s in 0..=255 {
+        let pq = (cum_p[s]) * (1.0 - cum_p[s]);
+        if pq <= 0.0 {
+            continue;
+        }
+
         // psi_s is the total entropy of foreground and background at threshold
         // level s. Instead of computing them separately, equation (18) in the
         // article, which simplifies this to this:
-        let psi_s = (cum_p[s] * (1.0 - cum_p[s])).ln()
-            + h[s] / cum_p[s]
-            + (h[255] - h[s]) / (1.0 - cum_p[s]);
+        let psi_s = pq.ln() + h[s] / cum_p[s] + (h[255] - h[s]) / (1.0 - cum_p[s]);
 
         if psi_s > max_entropy {
             max_entropy = psi_s;