From 5b0d565ff1941b828eaf568fd5fbe18505f169c3 Mon Sep 17 00:00:00 2001
From: Aarni Koskela <akx@iki.fi>
Date: Wed, 16 Sep 2026 10:00:11 +0300
Subject: [PATCH 1/2] Quantize benchmark: spell out quantization methods

---
 Tests/benchmarks.py | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/Tests/benchmarks.py b/Tests/benchmarks.py
index 11ed3cf743b..6e6492a56bc 100644
--- a/Tests/benchmarks.py
+++ b/Tests/benchmarks.py
@@ -818,12 +818,27 @@ def test_font_getmask(bench: BenchmarkFixture, mode: str) -> None:
 
 
 @pytest.mark.benchmark(group="quantize")
-@pytest.mark.parametrize("mode", [m for m in MODES if m in ("L", "RGB", "RGBA")])
+@pytest.mark.parametrize(
+    "mode, method",
+    [
+        ("L", Image.Quantize.MEDIANCUT),
+        ("L", Image.Quantize.MAXCOVERAGE),
+        ("RGB", Image.Quantize.MEDIANCUT),
+        ("RGB", Image.Quantize.MAXCOVERAGE),
+        ("RGBA", Image.Quantize.FASTOCTREE),
+    ],
+    ids=lambda p: getattr(p, "name", p),
+)
 @pytest.mark.parametrize("size", SIZES, ids=_format_size)
-def test_quantize(bench: BenchmarkFixture, mode: str, size: tuple[int, int]) -> None:
+def test_quantize(
+    bench: BenchmarkFixture,
+    mode: str,
+    method: Image.Quantize,
+    size: tuple[int, int],
+) -> None:
     im = make_pillow_image(mode, size)
-    bench.extra_info["label"] = [f"quantize {mode}"]
-    result = bench(im.quantize, 256)
+    bench.extra_info["label"] = [f"quantize {mode} {method.name}"]
+    result = bench(im.quantize, 256, method=method)
     assert result.mode == "P"
 
 

From b94592001c3a4a8732bec1b1823e30d838601ce0 Mon Sep 17 00:00:00 2001
From: Aarni Koskela <akx@iki.fi>
Date: Wed, 16 Sep 2026 09:39:13 +0300
Subject: [PATCH 2/2] Apply restrict optimizations to ImagingQuantize's output
 loop

---
 src/libImaging/Quant.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/libImaging/Quant.c b/src/libImaging/Quant.c
index 5712f6bd39c..a0796763751 100644
--- a/src/libImaging/Quant.c
+++ b/src/libImaging/Quant.c
@@ -1831,10 +1831,15 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         }
         ImagingSectionEnter(&cookie);
 
+        // restrict safe: imOut is a fresh allocation and
+        //                newData was just allocated by the quantizer.
         for (i = y = 0; y < ysize; y++) {
+            UINT8 *restrict out = imOut->image8[y];
+            const uint32_t *restrict in = newData + i;
             for (x = 0; x < xsize; x++) {
-                imOut->image8[y][x] = (unsigned char)newData[i++];
+                out[x] = (UINT8)in[x];
             }
+            i += xsize;
         }
 
         free(newData);