Change default resize resampling filter

Tests/test_file_gif.py

@@ -754,7 +754,7 @@ class TestFileGif(PillowTestCase):
     def test_getdata(self):
         # test getheader/getdata against legacy values
         # Create a 'P' image with holes in the palette
-        im = Image._wedge().resize((16, 16))
+        im = Image._wedge().resize((16, 16), Image.NEAREST)
         im.putpalette(ImagePalette.ImagePalette("RGB"))
         im.info = {"background": 0}
 

Tests/test_image_getdata.py

@@ -1,3 +1,5 @@
+from PIL import Image
+
 from .helper import PillowTestCase, hopper
 
 
@@ -13,7 +15,7 @@ class TestImageGetData(PillowTestCase):
 
     def test_roundtrip(self):
         def getdata(mode):
-            im = hopper(mode).resize((32, 30))
+            im = hopper(mode).resize((32, 30), Image.NEAREST)
             data = im.getdata()
             return data[0], len(data), len(list(data))
 

Tests/test_image_resize.py

@@ -150,3 +150,12 @@ class TestImageResize(PillowTestCase):
         # Test unknown resampling filter
         with hopper() as im:
             self.assertRaises(ValueError, im.resize, (10, 10), "unknown")
+
+    def test_default_filter(self):
+        for mode in "L", "RGB", "I", "F":
+            im = hopper(mode)
+            self.assertEqual(im.resize((20, 20), Image.BICUBIC), im.resize((20, 20)))
+
+        for mode in "1", "P":
+            im = hopper(mode)
+            self.assertEqual(im.resize((20, 20), Image.NEAREST), im.resize((20, 20)))

Tests/test_imagedraw.py

@@ -159,7 +159,8 @@ class TestImageDraw(PillowTestCase):
         # Arrange
         im = Image.new("RGB", (W, H))
         draw = ImageDraw.Draw(im)
-        with Image.open("Tests/images/pil123rgba.png").resize((50, 50)) as small:
+        with Image.open("Tests/images/pil123rgba.png") as small:
+            small = small.resize((50, 50), Image.NEAREST)
 
             # Act
             draw.bitmap((10, 10), small)

Tests/test_imagefile.py

@@ -24,7 +24,7 @@ class TestImageFile(PillowTestCase):
     def test_parser(self):
         def roundtrip(format):
 
-            im = hopper("L").resize((1000, 1000))
+            im = hopper("L").resize((1000, 1000), Image.NEAREST)
             if format in ("MSP", "XBM"):
                 im = im.convert("1")
 

docs/releasenotes/7.0.0.rst

@@ -47,6 +47,13 @@ Setting the size of TIFF images
 Setting the size of a TIFF image directly (eg. ``im.size = (256, 256)``) throws
 an error. Use ``Image.resize`` instead.
 
+Default resize resampling filter
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The default resampling filter for the ``Image.resize`` method is changed to
+high-quality convolution ``Image.BICUBIC`` instead of ``Image.NEAREST``.
+``Image.NEAREST`` is still always used for images in "P" and "1" modes.
+
 
 API Changes
 ===========

src/PIL/Image.py

@@ -1761,7 +1761,7 @@ class Image:
 
         return m_im
 
-    def resize(self, size, resample=NEAREST, box=None):
+    def resize(self, size, resample=BICUBIC, box=None):
         """
         Returns a resized copy of this image.
 
@@ -1771,8 +1771,9 @@ class Image:
            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` or :py:attr:`PIL.Image.LANCZOS`.
-           If omitted, or if the image has mode "1" or "P", it is
-           set :py:attr:`PIL.Image.NEAREST`.
+           Default filter is :py:attr:`PIL.Image.BICUBIC`.
+           If the image has mode "1" or "P", it is
+           always set :py:attr:`PIL.Image.NEAREST`.
            See: :ref:`concept-filters`.
         :param box: An optional 4-tuple of floats giving the region
            of the source image which should be scaled.