Skip extra evaluation when identical

Author: andrews05

src/reduction/mod.rs

@@ -143,22 +143,23 @@ pub(crate) fn perform_reductions(
 
     // Attempt to reduce to a lower bit depth
     if opts.bit_depth_reduction && !deadline.passed() {
-        // First try reducing the `png` var (could be grayscale or indexed)
+        // First try the `png` var
         let reduced = reduced_bit_depth_8_or_less(&png);
-        // It's possible that an indexed version will be smaller (it might reach a lower depth),
-        // but grayscale is usually better so we'll skip it if we're doing cheap evaluations and
-        // already have a reduced image.
-        let try_indexed = !cheap || reduced.is_none();
+        // Then try the `indexed` var, unless we're doing cheap evaluations and already have a reduction
+        if (!cheap || reduced.is_none()) && !deadline.passed() {
+            if let Some(indexed) = indexed.and_then(|png| reduced_bit_depth_8_or_less(&png)) {
+                // Only evaluate this if it's different from the first result (which must be grayscale if it exists)
+                if reduced.as_ref().map_or(true, |r| r.data != indexed.data) {
+                    eval.try_image(Arc::new(indexed));
+                    evaluation_added = true;
+                }
+            }
+        }
+        // Enter the first result into the evaluator
         if let Some(reduced) = reduced {
             eval.try_image(Arc::new(reduced));
             evaluation_added = true;
         }
-        if try_indexed && !deadline.passed() {
-            if let Some(reduced) = indexed.and_then(|png| reduced_bit_depth_8_or_less(&png)) {
-                eval.try_image(Arc::new(reduced));
-                evaluation_added = true;
-            }
-        }
     }
 
     if evaluation_added {