diff --git a/benches/reductions.rs b/benches/reductions.rs
index 774c346a..be9b6e06 100644
--- a/benches/reductions.rs
+++ b/benches/reductions.rs
@@ -75,6 +75,66 @@ fn reductions_2_to_1_bits(b: &mut Bencher) {
     b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
 }
 
+#[bench]
+fn reductions_grayscale_8_to_4_bits(b: &mut Bencher) {
+    let input = test::black_box(PathBuf::from(
+        "tests/files/grayscale_8_should_be_grayscale_4.png",
+    ));
+    let png = PngData::new(&input, false).unwrap();
+
+    b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
+}
+
+#[bench]
+fn reductions_grayscale_8_to_2_bits(b: &mut Bencher) {
+    let input = test::black_box(PathBuf::from(
+        "tests/files/grayscale_8_should_be_grayscale_2.png",
+    ));
+    let png = PngData::new(&input, false).unwrap();
+
+    b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
+}
+
+#[bench]
+fn reductions_grayscale_8_to_1_bits(b: &mut Bencher) {
+    let input = test::black_box(PathBuf::from(
+        "tests/files/grayscale_8_should_be_grayscale_1.png",
+    ));
+    let png = PngData::new(&input, false).unwrap();
+
+    b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
+}
+
+#[bench]
+fn reductions_grayscale_4_to_2_bits(b: &mut Bencher) {
+    let input = test::black_box(PathBuf::from(
+        "tests/files/grayscale_4_should_be_grayscale_2.png",
+    ));
+    let png = PngData::new(&input, false).unwrap();
+
+    b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
+}
+
+#[bench]
+fn reductions_grayscale_4_to_1_bits(b: &mut Bencher) {
+    let input = test::black_box(PathBuf::from(
+        "tests/files/grayscale_4_should_be_grayscale_1.png",
+    ));
+    let png = PngData::new(&input, false).unwrap();
+
+    b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
+}
+
+#[bench]
+fn reductions_grayscale_2_to_1_bits(b: &mut Bencher) {
+    let input = test::black_box(PathBuf::from(
+        "tests/files/grayscale_2_should_be_grayscale_1.png",
+    ));
+    let png = PngData::new(&input, false).unwrap();
+
+    b.iter(|| bit_depth::reduce_bit_depth(&png.raw, 1));
+}
+
 #[bench]
 fn reductions_rgba_to_rgb_16(b: &mut Bencher) {
     let input = test::black_box(PathBuf::from("tests/files/rgba_16_should_be_rgb_16.png"));
diff --git a/tests/files/grayscale_2_should_be_grayscale_1.png b/tests/files/grayscale_2_should_be_grayscale_1.png
new file mode 100644
index 00000000..c614d443
Binary files /dev/null and b/tests/files/grayscale_2_should_be_grayscale_1.png differ
diff --git a/tests/files/grayscale_4_should_be_grayscale_1.png b/tests/files/grayscale_4_should_be_grayscale_1.png
new file mode 100644
index 00000000..12d05931
Binary files /dev/null and b/tests/files/grayscale_4_should_be_grayscale_1.png differ
diff --git a/tests/files/grayscale_4_should_be_grayscale_2.png b/tests/files/grayscale_4_should_be_grayscale_2.png
new file mode 100644
index 00000000..eb4570ff
Binary files /dev/null and b/tests/files/grayscale_4_should_be_grayscale_2.png differ
diff --git a/tests/files/grayscale_8_should_be_grayscale_1.png b/tests/files/grayscale_8_should_be_grayscale_1.png
new file mode 100644
index 00000000..89248c61
Binary files /dev/null and b/tests/files/grayscale_8_should_be_grayscale_1.png differ
diff --git a/tests/files/grayscale_8_should_be_grayscale_2.png b/tests/files/grayscale_8_should_be_grayscale_2.png
new file mode 100644
index 00000000..a3e063c9
Binary files /dev/null and b/tests/files/grayscale_8_should_be_grayscale_2.png differ
diff --git a/tests/files/grayscale_8_should_be_grayscale_4.png b/tests/files/grayscale_8_should_be_grayscale_4.png
new file mode 100644
index 00000000..c561432e
Binary files /dev/null and b/tests/files/grayscale_8_should_be_grayscale_4.png differ
diff --git a/tests/reduction.rs b/tests/reduction.rs
index e6ec5a2a..f3afdb88 100644
--- a/tests/reduction.rs
+++ b/tests/reduction.rs
@@ -718,6 +718,78 @@ fn grayscale_8_should_be_grayscale_8() {
     );
 }
 
+#[test]
+fn grayscale_8_should_be_grayscale_4() {
+    test_it_converts(
+        "tests/files/grayscale_8_should_be_grayscale_4.png",
+        false,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+        ColorType::Grayscale,
+        BitDepth::Four,
+    );
+}
+
+#[test]
+fn grayscale_8_should_be_grayscale_2() {
+    test_it_converts(
+        "tests/files/grayscale_8_should_be_grayscale_2.png",
+        false,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+        ColorType::Grayscale,
+        BitDepth::Two,
+    );
+}
+
+#[test]
+fn grayscale_4_should_be_grayscale_2() {
+    test_it_converts(
+        "tests/files/grayscale_4_should_be_grayscale_2.png",
+        false,
+        ColorType::Grayscale,
+        BitDepth::Four,
+        ColorType::Grayscale,
+        BitDepth::Two,
+    );
+}
+
+#[test]
+fn grayscale_8_should_be_grayscale_1() {
+    test_it_converts(
+        "tests/files/grayscale_8_should_be_grayscale_1.png",
+        false,
+        ColorType::Grayscale,
+        BitDepth::Eight,
+        ColorType::Grayscale,
+        BitDepth::One,
+    );
+}
+
+#[test]
+fn grayscale_4_should_be_grayscale_1() {
+    test_it_converts(
+        "tests/files/grayscale_4_should_be_grayscale_1.png",
+        false,
+        ColorType::Grayscale,
+        BitDepth::Four,
+        ColorType::Grayscale,
+        BitDepth::One,
+    );
+}
+
+#[test]
+fn grayscale_2_should_be_grayscale_1() {
+    test_it_converts(
+        "tests/files/grayscale_2_should_be_grayscale_1.png",
+        false,
+        ColorType::Grayscale,
+        BitDepth::Two,
+        ColorType::Grayscale,
+        BitDepth::One,
+    );
+}
+
 #[test]
 fn grayscale_alpha_16_should_be_grayscale_trns_16() {
     test_it_converts(