diff --git a/Tests/benchmarks.py b/Tests/benchmarks.py
index 9d7439d321b..cf692f98d4a 100644
--- a/Tests/benchmarks.py
+++ b/Tests/benchmarks.py
@@ -135,17 +135,28 @@ def test_box_blur(
 
 
 @pytest.mark.benchmark(group="composition")
+@pytest.mark.parametrize("alpha", ["opaque", "transparent", "mixed"])
 @pytest.mark.parametrize("mode", ALPHA_MODES)
 @pytest.mark.parametrize("size", SIZES, ids=_format_size)
-def test_alpha_composition(
+def test_alpha_composite(
     bench: BenchmarkFixture,
     mode: str,
     size: tuple[int, int],
+    alpha: str,
 ) -> None:
-    im = make_pillow_image(mode, size)
-    second = im.copy()
-    bench.extra_info["label"] = ["Composition"]
-    bench(Image.alpha_composite, im, second)
+    im1 = make_pillow_image(mode, size)
+    im2 = make_pillow_image(mode, size, pattern_offset=1024)
+    if alpha == "opaque":
+        im2.putalpha(255)
+    elif alpha == "transparent":
+        im2.putalpha(0)
+    else:  # "mixed"
+        width, height = size
+        gradient = bytes((x * 256) // width for x in range(width)) * height
+        im2.putalpha(Image.frombytes("L", size, gradient))
+    bench.extra_info["label"] = ["Composition", alpha]
+    result = bench(Image.alpha_composite, im1, im2)
+    assert result.size == im1.size
 
 
 @pytest.mark.benchmark(group="convert")
diff --git a/src/libImaging/AlphaComposite.c b/src/libImaging/AlphaComposite.c
index 280277e835a..d1a1e7ad34a 100644
--- a/src/libImaging/AlphaComposite.c
+++ b/src/libImaging/AlphaComposite.c
@@ -22,7 +22,6 @@ typedef struct {
 Imaging
 ImagingAlphaComposite(Imaging imDst, Imaging imSrc) {
     Imaging imOut;
-    int x, y;
 
     /* Check arguments */
     if (!imDst || !imSrc ||
@@ -40,12 +39,17 @@ ImagingAlphaComposite(Imaging imDst, Imaging imSrc) {
         return NULL;
     }
 
-    for (y = 0; y < imDst->ysize; y++) {
-        rgba8 *dst = (rgba8 *)imDst->image[y];
-        rgba8 *src = (rgba8 *)imSrc->image[y];
-        rgba8 *out = (rgba8 *)imOut->image[y];
+    // Invariant over the loop.
+    int xsize = imDst->xsize;
+    int ysize = imDst->ysize;
 
-        for (x = 0; x < imDst->xsize; x++) {
+    for (int y = 0; y < ysize; y++) {
+        // restrict safe: imDst/imSrc are read-only, imOut is a fresh allocation.
+        rgba8 *restrict dst = (rgba8 *)imDst->image[y];
+        rgba8 *restrict src = (rgba8 *)imSrc->image[y];
+        rgba8 *restrict out = (rgba8 *)imOut->image[y];
+
+        for (int x = 0; x < xsize; x++) {
             if (src->a == 0) {
                 // Copy 4 bytes at once.
                 *out = *dst;
diff --git a/src/libImaging/Imaging.h b/src/libImaging/Imaging.h
index 713eab48b81..472bda5d0fd 100644
--- a/src/libImaging/Imaging.h
+++ b/src/libImaging/Imaging.h
@@ -307,7 +307,7 @@ ImagingConvert(Imaging im, ModeID mode, ImagingPalette palette, int dither);
 extern Imaging
 ImagingConvertInPlace(Imaging im, ModeID mode);
 extern Imaging
-ImagingConvertMatrix(Imaging im, ModeID mode, float m[]);
+ImagingConvertMatrix(Imaging im, ModeID mode, const float m[12]);
 extern Imaging
 ImagingConvertTransparent(Imaging im, ModeID mode, int r, int g, int b);
 extern Imaging
diff --git a/src/libImaging/Matrix.c b/src/libImaging/Matrix.c
index d63ba8be880..02676c9e31a 100644
--- a/src/libImaging/Matrix.c
+++ b/src/libImaging/Matrix.c
@@ -18,9 +18,8 @@
 #define CLIPF(v) ((v <= 0.0) ? 0 : (v >= 255.0F) ? 255 : (UINT8)v)
 
 Imaging
-ImagingConvertMatrix(Imaging im, const ModeID mode, float m[]) {
+ImagingConvertMatrix(Imaging im, const ModeID mode, const float m[12]) {
     Imaging imOut;
-    int x, y;
     ImagingSectionCookie cookie;
 
     /* Assume there's enough data in the buffer */
@@ -34,12 +33,16 @@ ImagingConvertMatrix(Imaging im, const ModeID mode, float m[]) {
             return NULL;
         }
 
+        // Invariant over the loop.
+        int xsize = im->xsize, ysize = im->ysize;
+
         ImagingSectionEnter(&cookie);
-        for (y = 0; y < im->ysize; y++) {
-            UINT8 *in = (UINT8 *)im->image[y];
-            UINT8 *out = (UINT8 *)imOut->image[y];
+        for (int y = 0; y < ysize; y++) {
+            // restrict safe: im is read-only, imOut is a fresh allocation.
+            UINT8 *restrict in = (UINT8 *)im->image[y];
+            UINT8 *restrict out = (UINT8 *)imOut->image[y];
 
-            for (x = 0; x < im->xsize; x++) {
+            for (int x = 0; x < xsize; x++) {
                 float v = m[0] * in[0] + m[1] * in[1] + m[2] * in[2] + m[3] + 0.5;
                 out[x] = CLIPF(v);
                 in += 4;
@@ -52,12 +55,16 @@ ImagingConvertMatrix(Imaging im, const ModeID mode, float m[]) {
             return NULL;
         }
 
-        for (y = 0; y < im->ysize; y++) {
-            UINT8 *in = (UINT8 *)im->image[y];
-            UINT8 *out = (UINT8 *)imOut->image[y];
+        // Invariant over the loop.
+        int xsize = im->xsize, ysize = im->ysize;
+
+        for (int y = 0; y < ysize; y++) {
+            // restrict safe: im is read-only, imOut is a fresh allocation.
+            UINT8 *restrict in = (UINT8 *)im->image[y];
+            UINT8 *restrict out = (UINT8 *)imOut->image[y];
 
             ImagingSectionEnter(&cookie);
-            for (x = 0; x < im->xsize; x++) {
+            for (int x = 0; x < xsize; x++) {
                 float v0 = m[0] * in[0] + m[1] * in[1] + m[2] * in[2] + m[3] + 0.5;
                 float v1 = m[4] * in[0] + m[5] * in[1] + m[6] * in[2] + m[7] + 0.5;
                 float v2 = m[8] * in[0] + m[9] * in[1] + m[10] * in[2] + m[11] + 0.5;
diff --git a/src/libImaging/Negative.c b/src/libImaging/Negative.c
index 70b96c39772..114e8608e87 100644
--- a/src/libImaging/Negative.c
+++ b/src/libImaging/Negative.c
@@ -32,9 +32,15 @@ ImagingNegative(Imaging im) {
         return NULL;
     }
 
-    for (y = 0; y < im->ysize; y++) {
-        for (x = 0; x < im->linesize; x++) {
-            imOut->image[y][x] = ~im->image[y][x];
+    // ysize and linesize are loop-invariant.
+    int ysize = im->ysize, linesize = im->linesize;
+
+    for (y = 0; y < ysize; y++) {
+        // restrict safe: im is read-only, imOut is a fresh allocation.
+        UINT8 *restrict in = (UINT8 *)im->image[y];
+        UINT8 *restrict out = (UINT8 *)imOut->image[y];
+        for (x = 0; x < linesize; x++) {
+            out[x] = ~in[x];
         }
     }
 
diff --git a/src/libImaging/Quant.c b/src/libImaging/Quant.c
index 46cff5b8b3c..99c2dbac3af 100644
--- a/src/libImaging/Quant.c
+++ b/src/libImaging/Quant.c
@@ -1696,11 +1696,14 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         return ImagingError_ModeError();
     }
 
-    if (im->xsize > INT_MAX / im->ysize) {
+    // Hoisted here as these are invariant over the loops below.
+    int xsize = im->xsize, ysize = im->ysize;
+
+    if (xsize > INT_MAX / ysize) {
         return ImagingError_MemoryError();
     }
     /* malloc check ok, using calloc for final overflow, x*y above */
-    p = calloc(im->xsize * im->ysize, sizeof(Pixel));
+    p = calloc(xsize * ysize, sizeof(Pixel));
     if (!p) {
         return ImagingError_MemoryError();
     }
@@ -1716,9 +1719,10 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         /* FIXME: converting a "L" image to "P" with 256 colors
            should be done by a simple copy... */
 
-        for (i = y = 0; y < im->ysize; y++) {
-            for (x = 0; x < im->xsize; x++, i++) {
-                p[i].c.r = p[i].c.g = p[i].c.b = im->image8[y][x];
+        for (i = y = 0; y < ysize; y++) {
+            UINT8 *in = im->image8[y];
+            for (x = 0; x < xsize; x++, i++) {
+                p[i].c.r = p[i].c.g = p[i].c.b = in[x];
                 p[i].c.a = 255;
             }
         }
@@ -1728,9 +1732,10 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
 
         pp = im->palette->palette;
 
-        for (i = y = 0; y < im->ysize; y++) {
-            for (x = 0; x < im->xsize; x++, i++) {
-                v = im->image8[y][x];
+        for (i = y = 0; y < ysize; y++) {
+            UINT8 *in = im->image8[y];
+            for (x = 0; x < xsize; x++, i++) {
+                v = in[x];
                 p[i].c.r = pp[v * 4 + 0];
                 p[i].c.g = pp[v * 4 + 1];
                 p[i].c.b = pp[v * 4 + 2];
@@ -1744,9 +1749,10 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         withAlpha = im->mode == IMAGING_MODE_RGBA;
         int transparency = 0;
         unsigned char r = 0, g = 0, b = 0;
-        for (i = y = 0; y < im->ysize; y++) {
-            for (x = 0; x < im->xsize; x++, i++) {
-                p[i].v = im->image32[y][x];
+        for (i = y = 0; y < ysize; y++) {
+            INT32 *in = im->image32[y];
+            for (x = 0; x < xsize; x++, i++) {
+                p[i].v = in[x];
                 if (withAlpha) {
                     if (p[i].c.a == 0) {
                         if (transparency == 0) {
@@ -1779,49 +1785,24 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         case 0:
             /* median cut */
             result = quantize(
-                p,
-                im->xsize * im->ysize,
-                colors,
-                &palette,
-                &paletteLength,
-                &newData,
-                kmeans
+                p, xsize * ysize, colors, &palette, &paletteLength, &newData, kmeans
             );
             break;
         case 1:
             /* maximum coverage */
             result = quantize2(
-                p,
-                im->xsize * im->ysize,
-                colors,
-                &palette,
-                &paletteLength,
-                &newData,
-                kmeans
+                p, xsize * ysize, colors, &palette, &paletteLength, &newData, kmeans
             );
             break;
         case 2:
             result = quantize_octree(
-                p,
-                im->xsize * im->ysize,
-                colors,
-                &palette,
-                &paletteLength,
-                &newData,
-                withAlpha
+                p, xsize * ysize, colors, &palette, &paletteLength, &newData, withAlpha
             );
             break;
         case 3:
 #ifdef HAVE_LIBIMAGEQUANT
             result = quantize_pngquant(
-                p,
-                im->xsize,
-                im->ysize,
-                colors,
-                &palette,
-                &paletteLength,
-                &newData,
-                withAlpha
+                p, xsize, ysize, colors, &palette, &paletteLength, &newData, withAlpha
             );
 #else
             result = -1;
@@ -1836,7 +1817,7 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
     ImagingSectionLeave(&cookie);
 
     if (result > 0) {
-        imOut = ImagingNewDirty(IMAGING_MODE_P, im->xsize, im->ysize);
+        imOut = ImagingNewDirty(IMAGING_MODE_P, xsize, ysize);
         if (!imOut) {
             free(newData);
             free(palette);
@@ -1844,8 +1825,8 @@ ImagingQuantize(Imaging im, int colors, int mode, int kmeans) {
         }
         ImagingSectionEnter(&cookie);
 
-        for (i = y = 0; y < im->ysize; y++) {
-            for (x = 0; x < im->xsize; x++) {
+        for (i = y = 0; y < ysize; y++) {
+            for (x = 0; x < xsize; x++) {
                 imOut->image8[y][x] = (unsigned char)newData[i++];
             }
         }