Added ImageOps pad method

Tests/test_imageops.py

@@ -24,6 +24,9 @@ class TestImageOps(PillowTestCase):
         ImageOps.colorize(hopper("L"), (0, 0, 0), (255, 255, 255))
         ImageOps.colorize(hopper("L"), "black", "white")
 
+        ImageOps.pad(hopper("L"), (128, 128))
+        ImageOps.pad(hopper("RGB"), (128, 128))
+
         ImageOps.crop(hopper("L"), 1)
         ImageOps.crop(hopper("RGB"), 1)
 
@@ -70,6 +73,27 @@ class TestImageOps(PillowTestCase):
         newimg = ImageOps.fit(hopper("RGB").resize((100, 1)), (35, 35))
         self.assertEqual(newimg.size, (35, 35))
 
+    def test_pad(self):
+        # Same ratio
+        im = hopper()
+        new_size = (im.width * 2, im.height * 2)
+        new_im = ImageOps.pad(im, new_size)
+        self.assertEqual(new_im.size, new_size)
+
+        for label, color, new_size in [
+            ("h", None, (im.width * 4, im.height * 2)),
+            ("v", "#f00", (im.width * 2, im.height * 4))
+        ]:
+            for i, centering in enumerate([(0,0), (0.5, 0.5), (1, 1)]):
+                new_im = ImageOps.pad(im, new_size,
+                                      color=color, centering=centering)
+                self.assertEqual(new_im.size, new_size)
+
+                target = Image.open(
+                    "Tests/images/imageops_pad_"+label+"_"+str(i)+".jpg")
+                self.assert_image_similar(new_im, target, 6)
+
+
     def test_pil163(self):
         # Division by zero in equalize if < 255 pixels in image (@PIL163)
 

src/PIL/ImageOps.py

@@ -221,6 +221,50 @@ def colorize(image, black, white, mid=None, blackpoint=0,
     return _lut(image, red + green + blue)
 
 
+def pad(image, size, method=Image.NEAREST, 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.
+
+    :param image: The image to size and crop.
+    :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`.
+    :param color: The background color of the padded image.
+    :param centering: Control the position of the original image within the
+                      padded version.
+                          (0.5, 0.5) will keep the image centered
+                          (0, 0) will keep the image aligned to the top left
+                          (1, 1) will keep the image aligned to the bottom
+                          right
+    :return: An image.
+    """
+
+    im_ratio = image.width / image.height
+    dest_ratio = float(size[0]) / size[1]
+
+    if im_ratio == dest_ratio:
+        out = image.resize(size, resample=method)
+    else:
+        out = Image.new(image.mode, size, color)
+        if im_ratio > dest_ratio:
+            new_height = int(image.height / image.width * size[0])
+            if new_height != size[1]:
+                image = image.resize((size[0], new_height), resample=method)
+
+            y = int((size[1] - new_height) * max(0, min(centering[1], 1)))
+            out.paste(image, (0, y))
+        else:
+            new_width = int(image.width / image.height * size[1])
+            if new_width != size[0]:
+                image = image.resize((new_width, size[1]), resample=method)
+
+            x = int((size[0] - new_width) * max(0, min(centering[0], 1)))
+            out.paste(image, (x, 0))
+    return out
+
+
 def crop(image, border=0):
     """
     Remove border from image.  The same amount of pixels are removed