Merge pull request #4255 from uploadcare/default-resample-filter

Change default resize resampling filter from NEAREST to BICUBIC

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 +47,17 @@ 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 resampling filter
+^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The default resampling filter has been changed to the high-quality convolution
+``Image.BICUBIC`` instead of ``Image.NEAREST``, for the :py:meth:`~PIL.Image.Image.resize`
+method and the :py:meth:`~PIL.ImageOps.pad``, :py:meth:`~PIL.ImageOps.scale``
+and :py:meth:`~PIL.ImageOps.fit`` functions.
+``Image.NEAREST`` is still always used for images in "P" and "1" modes.
+See :ref:`concept-filters` to learn the difference. In short,
+``Image.NEAREST`` is a very fast filter, but simple and low-quality.
+
 
 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
+           Default filter is :py:attr:`PIL.Image.BICUBIC`.
-           set :py:attr:`PIL.Image.NEAREST`.
+           If the image has mode "1" or "P", it is
+           always set to :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.
@@ -1842,7 +1843,7 @@ class Image:
            environment), or :py:attr:`PIL.Image.BICUBIC`
            (cubic spline interpolation in a 4x4 environment).
            If omitted, or if the image has mode "1" or "P", it is
-           set :py:attr:`PIL.Image.NEAREST`. See :ref:`concept-filters`.
+           set to :py:attr:`PIL.Image.NEAREST`. See :ref:`concept-filters`.
         :param expand: Optional expansion flag.  If true, expands the output
            image to make it large enough to hold the entire rotated image.
            If false or omitted, make the output image the same size as the

src/PIL/ImageOps.py

@@ -221,7 +221,7 @@ def colorize(image, black, white, mid=None, blackpoint=0, whitepoint=255, midpoi
     return _lut(image, red + green + blue)
 
 
-def pad(image, size, method=Image.NEAREST, color=None, centering=(0.5, 0.5)):
+def pad(image, size, method=Image.BICUBIC, color=None, centering=(0.5, 0.5)):
     """
     Returns a sized and padded version of the image, expanded to fill the
     requested aspect ratio and size.
@@ -230,7 +230,7 @@ def pad(image, size, method=Image.NEAREST, color=None, centering=(0.5, 0.5)):
     :param size: The requested output size in pixels, given as a
                  (width, height) tuple.
     :param method: What resampling method to use. Default is
-                   :py:attr:`PIL.Image.NEAREST`.
+                   :py:attr:`PIL.Image.BICUBIC`. See :ref:`concept-filters`.
     :param color: The background color of the padded image.
     :param centering: Control the position of the original image within the
                       padded version.
@@ -280,7 +280,7 @@ def crop(image, border=0):
     return image.crop((left, top, image.size[0] - right, image.size[1] - bottom))
 
 
-def scale(image, factor, resample=Image.NEAREST):
+def scale(image, factor, resample=Image.BICUBIC):
     """
     Returns a rescaled image by a specific factor given in parameter.
     A factor greater than 1 expands the image, between 0 and 1 contracts the
@@ -288,8 +288,8 @@ def scale(image, factor, resample=Image.NEAREST):
 
     :param image: The image to rescale.
     :param factor: The expansion factor, as a float.
-    :param resample: An optional resampling filter. Same values possible as
+    :param resample: What resampling method to use. Default is
-       in the PIL.Image.resize function.
+                     :py:attr:`PIL.Image.BICUBIC`. See :ref:`concept-filters`.
     :returns: An :py:class:`~PIL.Image.Image` object.
     """
     if factor == 1:
@@ -363,7 +363,7 @@ def expand(image, border=0, fill=0):
     return out
 
 
-def fit(image, size, method=Image.NEAREST, bleed=0.0, centering=(0.5, 0.5)):
+def fit(image, size, method=Image.BICUBIC, bleed=0.0, centering=(0.5, 0.5)):
     """
     Returns a sized and cropped version of the image, cropped to the
     requested aspect ratio and size.
@@ -374,7 +374,7 @@ def fit(image, size, method=Image.NEAREST, bleed=0.0, centering=(0.5, 0.5)):
     :param size: The requested output size in pixels, given as a
                  (width, height) tuple.
     :param method: What resampling method to use. Default is
-                   :py:attr:`PIL.Image.NEAREST`.
+                   :py:attr:`PIL.Image.BICUBIC`. See :ref:`concept-filters`.
     :param bleed: Remove a border around the outside of the image from all
                   four edges. The value is a decimal percentage (use 0.01 for
                   one percent). The default value is 0 (no border).