diff --git a/src/reduction/bit_depth.rs b/src/reduction/bit_depth.rs
index 262357b0..6f04ec86 100644
--- a/src/reduction/bit_depth.rs
+++ b/src/reduction/bit_depth.rs
@@ -4,24 +4,28 @@ use crate::png::PngImage;
 use bit_vec::BitVec;
 
 const ONE_BIT_PERMUTATIONS: [u8; 2] = [0b0000_0000, 0b1111_1111];
-const TWO_BIT_PERMUTATIONS: [u8; 5] = [
+const TWO_BIT_PERMUTATIONS: [u8; 4] = [
     0b0000_0000,
-    0b0000_1111,
-    0b0011_1100,
-    0b1111_0000,
+    0b0101_0101,
+    0b1010_1010,
     0b1111_1111,
 ];
-const FOUR_BIT_PERMUTATIONS: [u8; 11] = [
+const FOUR_BIT_PERMUTATIONS: [u8; 16] = [
     0b0000_0000,
-    0b0000_0011,
-    0b0000_1100,
-    0b0011_0000,
-    0b1100_0000,
-    0b0000_1111,
-    0b0011_1100,
-    0b1111_0000,
-    0b0011_1111,
-    0b1111_1100,
+    0b0001_0001,
+    0b0010_0010,
+    0b0011_0011,
+    0b0100_0100,
+    0b0101_0101,
+    0b0110_0110,
+    0b0111_0111,
+    0b1000_1000,
+    0b1001_1001,
+    0b1010_1010,
+    0b1011_1011,
+    0b1100_1100,
+    0b1101_1101,
+    0b1110_1110,
     0b1111_1111,
 ];