update tests and docs

Tests/test_image_resample.py

@@ -309,6 +309,8 @@ class TestCoreResampleAlphaCorrect:
         self.run_levels_case(case.resize((512, 32), Image.Resampling.HAMMING))
         self.run_levels_case(case.resize((512, 32), Image.Resampling.BICUBIC))
         self.run_levels_case(case.resize((512, 32), Image.Resampling.LANCZOS))
+        self.run_levels_case(case.resize((512, 32), Image.Resampling.MKS2013))
+        self.run_levels_case(case.resize((512, 32), Image.Resampling.MKS2021))
 
     @pytest.mark.xfail(reason="Current implementation isn't precise enough")
     def test_levels_la(self) -> None:
@@ -318,6 +320,8 @@ class TestCoreResampleAlphaCorrect:
         self.run_levels_case(case.resize((512, 32), Image.Resampling.HAMMING))
         self.run_levels_case(case.resize((512, 32), Image.Resampling.BICUBIC))
         self.run_levels_case(case.resize((512, 32), Image.Resampling.LANCZOS))
+        self.run_levels_case(case.resize((512, 32), Image.Resampling.MKS2013))
+        self.run_levels_case(case.resize((512, 32), Image.Resampling.MKS2021))
 
     def make_dirty_case(
         self, mode: str, clean_pixel: tuple[int, ...], dirty_pixel: tuple[int, ...]
@@ -360,6 +364,12 @@ class TestCoreResampleAlphaCorrect:
         self.run_dirty_case(
             case.resize((20, 20), Image.Resampling.LANCZOS), (255, 255, 0)
         )
+        self.run_dirty_case(
+            case.resize((20, 20), Image.Resampling.MKS2013), (255, 255, 0)
+        )
+        self.run_dirty_case(
+            case.resize((20, 20), Image.Resampling.MKS2021), (255, 255, 0)
+        )
 
     def test_dirty_pixels_la(self) -> None:
         case = self.make_dirty_case("LA", (255, 128), (0, 0))
@@ -368,6 +378,8 @@ class TestCoreResampleAlphaCorrect:
         self.run_dirty_case(case.resize((20, 20), Image.Resampling.HAMMING), (255,))
         self.run_dirty_case(case.resize((20, 20), Image.Resampling.BICUBIC), (255,))
         self.run_dirty_case(case.resize((20, 20), Image.Resampling.LANCZOS), (255,))
+        self.run_dirty_case(case.resize((20, 20), Image.Resampling.MKS2013), (255,))
+        self.run_dirty_case(case.resize((20, 20), Image.Resampling.MKS2021), (255,))
 
 
 class TestCoreResamplePasses:
@@ -453,6 +465,8 @@ class TestCoreResampleBox:
             Image.Resampling.HAMMING,
             Image.Resampling.BICUBIC,
             Image.Resampling.LANCZOS,
+            Image.Resampling.MKS2013,
+            Image.Resampling.MKS2021,
         ),
     )
     def test_wrong_arguments(self, resample: Image.Resampling) -> None:

Tests/test_image_resize.py

@@ -72,6 +72,8 @@ class TestImagingCoreResize:
             Image.Resampling.HAMMING,
             Image.Resampling.BICUBIC,
             Image.Resampling.LANCZOS,
+            Image.Resampling.MKS2013,
+            Image.Resampling.MKS2021,
         ),
     )
     def test_reduce_filters(self, resample: Image.Resampling) -> None:
@@ -88,6 +90,8 @@ class TestImagingCoreResize:
             Image.Resampling.HAMMING,
             Image.Resampling.BICUBIC,
             Image.Resampling.LANCZOS,
+            Image.Resampling.MKS2013,
+            Image.Resampling.MKS2021,
         ),
     )
     def test_enlarge_filters(self, resample: Image.Resampling) -> None:
@@ -104,6 +108,8 @@ class TestImagingCoreResize:
             Image.Resampling.HAMMING,
             Image.Resampling.BICUBIC,
             Image.Resampling.LANCZOS,
+            Image.Resampling.MKS2013,
+            Image.Resampling.MKS2021,
         ),
     )
     @pytest.mark.parametrize(
@@ -154,6 +160,8 @@ class TestImagingCoreResize:
             Image.Resampling.HAMMING,
             Image.Resampling.BICUBIC,
             Image.Resampling.LANCZOS,
+            Image.Resampling.MKS2013,
+            Image.Resampling.MKS2021,
         ),
     )
     def test_enlarge_zero(self, resample: Image.Resampling) -> None:

docs/handbook/concepts.rst

@@ -195,6 +195,23 @@ pixel, the Python Imaging Library provides different resampling *filters*.
 
     .. versionadded:: 1.1.3
 
+.. data:: Resampling.MKS2013
+    :noindex:
+
+    Calculate the output pixel value using the Magic Kernel Sharp 2013 filter
+    (a quadratic B-spline composed with a sharpening kernel) on all pixels that
+    may contribute to the output value. This filter can only be used with the
+    :py:meth:`~PIL.Image.Image.resize` and :py:meth:`~PIL.Image.Image.thumbnail`
+    methods.
+
+.. data:: Resampling.MKS2021
+    :noindex:
+
+    Calculate the output pixel value using the Magic Kernel Sharp 2021 filter
+    (a quadratic B-spline composed with a sharpening kernel) on all pixels that
+    may contribute to the output value. This filter can only be used with the
+    :py:meth:`~PIL.Image.Image.resize` and :py:meth:`~PIL.Image.Image.thumbnail`
+    methods.
 
 Filters comparison table
 ~~~~~~~~~~~~~~~~~~~~~~~~
@@ -215,3 +232,7 @@ Filters comparison table
 +---------------------------+-------------+-----------+-------------+
 |:data:`Resampling.LANCZOS` | ⭐⭐⭐⭐    | ⭐⭐⭐⭐  | ⭐          |
 +---------------------------+-------------+-----------+-------------+
+|:data:`Resampling.MKS2013` | ⭐⭐⭐⭐    | ⭐⭐⭐⭐  | ⭐          |
++---------------------------+-------------+-----------+-------------+
+|:data:`Resampling.MKS2021` | ⭐⭐⭐⭐⭐  | ⭐⭐⭐⭐⭐ | ⭐          |
++---------------------------+-------------+-----------+-------------+

src/PIL/Image.py

@@ -169,7 +169,8 @@ class Resampling(IntEnum):
     HAMMING = 5
     BICUBIC = 3
     LANCZOS = 1
-    MKS2021 = 6
+    MKS2013 = 6
+    MKS2021 = 7
 
 
 _filters_support = {
@@ -178,6 +179,7 @@ _filters_support = {
     Resampling.HAMMING: 1.0,
     Resampling.BICUBIC: 2.0,
     Resampling.LANCZOS: 3.0,
+    Resampling.MKS2013: 2.5,
     Resampling.MKS2021: 4.5,
 }
 
@@ -2209,7 +2211,8 @@ class Image:
         :param resample: An optional resampling filter.  This can be
            one of :py:data:`Resampling.NEAREST`, :py:data:`Resampling.BOX`,
            :py:data:`Resampling.BILINEAR`, :py:data:`Resampling.HAMMING`,
-           :py:data:`Resampling.BICUBIC` or :py:data:`Resampling.LANCZOS`.
+           :py:data:`Resampling.BICUBIC`, :py:data:`Resampling.LANCZOS`,
+           :py:data:`Resampling.MKS2013`, or :py:data:`Resampling.MKS2021`.
            If the image has mode "1" or "P", it is always set to
            :py:data:`Resampling.NEAREST`. If the image mode is "BGR;15",
            "BGR;16" or "BGR;24", then the default filter is
@@ -2244,6 +2247,7 @@ class Image:
             Resampling.LANCZOS,
             Resampling.BOX,
             Resampling.HAMMING,
+            Resampling.MKS2013,
             Resampling.MKS2021,
         ):
             msg = f"Unknown resampling filter ({resample})."
@@ -2257,6 +2261,7 @@ class Image:
                     (Resampling.BICUBIC, "Image.Resampling.BICUBIC"),
                     (Resampling.BOX, "Image.Resampling.BOX"),
                     (Resampling.HAMMING, "Image.Resampling.HAMMING"),
+                    (Resampling.MKS2013, "Image.Resampling.MKS2013"),
                     (Resampling.MKS2021, "Image.Resampling.MKS2021"),
                 )
             ]
@@ -2694,7 +2699,8 @@ class Image:
         :param resample: Optional resampling filter.  This can be one
            of :py:data:`Resampling.NEAREST`, :py:data:`Resampling.BOX`,
            :py:data:`Resampling.BILINEAR`, :py:data:`Resampling.HAMMING`,
-           :py:data:`Resampling.BICUBIC` or :py:data:`Resampling.LANCZOS`.
+           :py:data:`Resampling.BICUBIC`, :py:data:`Resampling.LANCZOS`,
+           :py:data:`Resampling.MKS2013`, or :py:data:`Resampling.MKS2021`.
            If omitted, it defaults to :py:data:`Resampling.BICUBIC`.
            (was :py:data:`Resampling.NEAREST` prior to version 2.5.0).
            See: :ref:`concept-filters`.
@@ -2912,12 +2918,14 @@ class Image:
                 Resampling.BOX,
                 Resampling.HAMMING,
                 Resampling.LANCZOS,
+                Resampling.MKS2013,
                 Resampling.MKS2021,
             ):
                 unusable: dict[int, str] = {
                     Resampling.BOX: "Image.Resampling.BOX",
                     Resampling.HAMMING: "Image.Resampling.HAMMING",
                     Resampling.LANCZOS: "Image.Resampling.LANCZOS",
+                    Resampling.MKS2013: "Image.Resampling.MKS2013",
                     Resampling.MKS2021: "Image.Resampling.MKS2021",
                 }
                 msg = unusable[resample] + f" ({resample}) cannot be used."

src/libImaging/Imaging.h

@@ -269,7 +269,8 @@ ImagingError_Clear(void);
 #define IMAGING_TRANSFORM_HAMMING 5
 #define IMAGING_TRANSFORM_BICUBIC 3
 #define IMAGING_TRANSFORM_LANCZOS 1
-#define IMAGING_TRANSFORM_MKS2021 6
+#define IMAGING_TRANSFORM_MKS2013 6
+#define IMAGING_TRANSFORM_MKS2021 7
 
 typedef int (*ImagingTransformMap)(double *X, double *Y, int x, int y, void *data);
 typedef int (*ImagingTransformFilter)(void *out, Imaging im, double x, double y);

src/libImaging/Resample.c

@@ -79,6 +79,20 @@ lanczos_filter(double x) {
     return 0.0;
 }
 
+static inline double
+mks_2013_filter(double x) {
+    /* https://johncostella.com/magic/ */
+    if (x < 0.0)
+        x = -x;
+    if (x < 0.5)
+        return 17.0 / 16.0 - 7.0 / 4.0 * pow(x, 2.0);
+    if (x < 1.5)
+        return (1.0 - x) * (7.0/4.0 - x);
+    if (x < 2.5)
+        return -1.0 / 8.0 * pow(x - 5.0 / 2.0, 2.0);
+    return (0.0);
+}
+
 static inline double
 mks_2021_filter(double x) {
     /* https://johncostella.com/magic/ */
@@ -102,6 +116,7 @@ static struct filter BILINEAR = {bilinear_filter, 1.0};
 static struct filter HAMMING = {hamming_filter, 1.0};
 static struct filter BICUBIC = {bicubic_filter, 2.0};
 static struct filter LANCZOS = {lanczos_filter, 3.0};
+static struct filter MKS2013 = {mks_2013_filter, 2.5};
 static struct filter MKS2021 = {mks_2021_filter, 4.5};
 
 /* 8 bits for result. Filter can have negative areas.
@@ -712,6 +727,9 @@ ImagingResample(Imaging imIn, int xsize, int ysize, int filter, float box[4]) {
         case IMAGING_TRANSFORM_LANCZOS:
             filterp = &LANCZOS;
             break;
+        case IMAGING_TRANSFORM_MKS2013:
+            filterp = &MKS2013;
+            break;
         case IMAGING_TRANSFORM_MKS2021:
             filterp = &MKS2021;
             break;