remove mitchell filter. Has no advantages over bicubic

PIL/Image.py

@@ -172,7 +172,6 @@ BOX = 4
 BILINEAR = LINEAR = 2
 HAMMING = 5
 BICUBIC = CUBIC = 3
-MITCHELL = 6
 LANCZOS = ANTIALIAS = 1
 
 # dithers
@@ -1522,8 +1521,7 @@ class Image(object):
         :param resample: An optional resampling filter.  This can be
            one of :py:attr:`PIL.Image.NEAREST`, :py:attr:`PIL.Image.BOX`,
            :py:attr:`PIL.Image.BILINEAR`, :py:attr:`PIL.Image.HAMMING`,
-           :py:attr:`PIL.Image.BICUBIC`, :py:attr:`PIL.Image.MITCHELL` or
+           :py:attr:`PIL.Image.BICUBIC` or :py:attr:`PIL.Image.LANCZOS`.
-           :py:attr:`PIL.Image.LANCZOS`.
            If omitted, or if the image has mode "1" or "P", it is
            set :py:attr:`PIL.Image.NEAREST`.
            See: :ref:`concept-filters`.
@@ -1531,8 +1529,7 @@ class Image(object):
         """
 
         if resample not in (
-                NEAREST, BILINEAR, BICUBIC, LANCZOS,
+                NEAREST, BILINEAR, BICUBIC, LANCZOS, BOX, HAMMING,
-                BOX, HAMMING, MITCHELL,
         ):
             raise ValueError("unknown resampling filter")
 

Tests/test_image_resample.py

@@ -126,16 +126,6 @@ class TestImagingCoreResampleAccuracy(PillowTestCase):
             for channel in case.split():
                 self.check_case(channel, self.make_sample(data, (6, 6)))
 
-    def test_reduce_mitchell(self):
-        for mode in ['RGBX', 'RGB', 'La', 'L']:
-            case = self.make_case(mode, (12, 12), 0xe1)
-            case = case.resize((6, 6), Image.MITCHELL)
-            data = ('e1 e2 cc'
-                    'e2 e3 cd'
-                    'cc cd bb')
-            for channel in case.split():
-                self.check_case(channel, self.make_sample(data, (6, 6)))
-
     def test_reduce_lanczos(self):
         for mode in ['RGBX', 'RGB', 'La', 'L']:
             case = self.make_case(mode, (16, 16), 0xe1)
@@ -187,17 +177,6 @@ class TestImagingCoreResampleAccuracy(PillowTestCase):
             for channel in case.split():
                 self.check_case(channel, self.make_sample(data, (8, 8)))
 
-    def test_enlarge_mitchell(self):
-        for mode in ['RGBX', 'RGB', 'La', 'L']:
-            case = self.make_case(mode, (4, 4), 0xe1)
-            case = case.resize((8, 8), Image.MITCHELL)
-            data = ('e1 e4 e6 b2'
-                    'e4 e7 e9 b3'
-                    'e6 e9 eb b4'
-                    'b2 b3 b5 9a')
-            for channel in case.split():
-                self.check_case(channel, self.make_sample(data, (8, 8)))
-
     def test_enlarge_lanczos(self):
         for mode in ['RGBX', 'RGB', 'La', 'L']:
             case = self.make_case(mode, (6, 6), 0xe1)
@@ -274,7 +253,6 @@ class CoreResampleAlphaCorrectTest(PillowTestCase):
         self.run_levels_case(case.resize((512, 32), Image.BILINEAR))
         self.run_levels_case(case.resize((512, 32), Image.HAMMING))
         self.run_levels_case(case.resize((512, 32), Image.BICUBIC))
-        self.run_levels_case(case.resize((512, 32), Image.MITCHELL))
         self.run_levels_case(case.resize((512, 32), Image.LANCZOS))
 
     @unittest.skip("current implementation isn't precise enough")
@@ -284,7 +262,6 @@ class CoreResampleAlphaCorrectTest(PillowTestCase):
         self.run_levels_case(case.resize((512, 32), Image.BILINEAR))
         self.run_levels_case(case.resize((512, 32), Image.HAMMING))
         self.run_levels_case(case.resize((512, 32), Image.BICUBIC))
-        self.run_levels_case(case.resize((512, 32), Image.MITCHELL))
         self.run_levels_case(case.resize((512, 32), Image.LANCZOS))
 
     def make_dity_case(self, mode, clean_pixel, dirty_pixel):
@@ -312,7 +289,6 @@ class CoreResampleAlphaCorrectTest(PillowTestCase):
         self.run_dity_case(case.resize((20, 20), Image.BILINEAR), (255, 255, 0))
         self.run_dity_case(case.resize((20, 20), Image.HAMMING), (255, 255, 0))
         self.run_dity_case(case.resize((20, 20), Image.BICUBIC), (255, 255, 0))
-        self.run_dity_case(case.resize((20, 20), Image.MITCHELL), (255, 255, 0))
         self.run_dity_case(case.resize((20, 20), Image.LANCZOS), (255, 255, 0))
 
     def test_dirty_pixels_la(self):
@@ -321,7 +297,6 @@ class CoreResampleAlphaCorrectTest(PillowTestCase):
         self.run_dity_case(case.resize((20, 20), Image.BILINEAR), (255,))
         self.run_dity_case(case.resize((20, 20), Image.HAMMING), (255,))
         self.run_dity_case(case.resize((20, 20), Image.BICUBIC), (255,))
-        self.run_dity_case(case.resize((20, 20), Image.MITCHELL), (255,))
         self.run_dity_case(case.resize((20, 20), Image.LANCZOS), (255,))
 
 

libImaging/Imaging.h

@@ -233,7 +233,6 @@ extern void ImagingError_Clear(void);
 #define IMAGING_TRANSFORM_BILINEAR 2
 #define IMAGING_TRANSFORM_HAMMING 5
 #define IMAGING_TRANSFORM_BICUBIC 3
-#define IMAGING_TRANSFORM_MITCHELL 6
 #define IMAGING_TRANSFORM_LANCZOS 1
 
 typedef int (*ImagingTransformMap)(double* X, double* Y,

libImaging/Resample.c

@@ -50,27 +50,6 @@ static inline double bicubic_filter(double x)
 #undef a
 }
 
-static inline double mitchell_filter(double x)
-{
-    double fB = 1.f / 3.f;
-    double fC = 1.f / 3.f;
-    double fA1 = -fB - 6*fC;
-    double fB1 = 6*fB + 30*fC;
-    double fC1 = -12*fB - 48*fC;
-    double fD1 = 8*fB + 24*fC;
-    double fA2 = 12 - 9*fB - 6*fC;
-    double fB2 = -18 + 12*fB + 6*fC;
-    double fD2 = 6 - 2*fB;
-
-    if (x < 0.0)
-        x = -x;
-    if (x < 1.0)
-        return ((fA2 * x + fB2) * x*x + fD2) * (1.f/6.f);
-    if (x < 2.0)
-        return (((fA1 * x + fB1) * x + fC1) * x + fD1) * (1.f/6.f);
-    return 0.0;
-}
-
 static inline double sinc_filter(double x)
 {
     if (x == 0.0)
@@ -91,7 +70,6 @@ static struct filter BOX = { box_filter, 0.5 };
 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 MITCHELL = { mitchell_filter, 2.0 };
 static struct filter LANCZOS = { lanczos_filter, 3.0 };
 
 
@@ -575,9 +553,6 @@ ImagingResample(Imaging imIn, int xsize, int ysize, int filter)
     case IMAGING_TRANSFORM_BICUBIC:
         filterp = &BICUBIC;
         break;
-    case IMAGING_TRANSFORM_MITCHELL:
-        filterp = &MITCHELL;
-        break;
     case IMAGING_TRANSFORM_LANCZOS:
         filterp = &LANCZOS;
         break;