Merge pull request #2011 from vlmath/master

Add ImageOps.scale to expand or contract a PIL image by a factor

PIL/ImageOps.py

@@ -178,6 +178,27 @@ def crop(image, border=0):
         )
 
 
+def scale(image, factor, resample=Image.NEAREST):
+    """
+    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
+    image.
+
+    :param factor: The expansion factor, as a float.
+    :param resample: An optional resampling filter. Same values possible as
+       in the PIL.Image.resize function.
+    :returns: An :py:class:`~PIL.Image.Image` object.
+    """
+    if factor == 1:
+        return image.copy()
+    elif factor <= 0:
+        raise ValueError("the factor must be greater than 0")
+    else:
+        size = (int(round(factor * image.width)),
+                int(round(factor * image.height)))
+        return image.resize(size, resample)
+
+
 def deform(image, deformer, resample=Image.BILINEAR):
     """
     Deform the image.

Tests/test_imageops.py

@@ -78,6 +78,22 @@ class TestImageOps(PillowTestCase):
         ImageOps.equalize(i.convert("P"))
         ImageOps.equalize(i.convert("RGB"))
 
+    def test_scale(self):
+        # Test the scaling function
+        i = hopper("L").resize((50, 50))
+        
+        with self.assertRaises(ValueError):
+            ImageOps.scale(i, -1)
+
+        newimg = ImageOps.scale(i, 1)
+        self.assertEqual(newimg.size, (50, 50))
+
+        newimg = ImageOps.scale(i, 2)
+        self.assertEqual(newimg.size, (100, 100))
+
+        newimg = ImageOps.scale(i, 0.5)
+        self.assertEqual(newimg.size, (25, 25))
+
 
 if __name__ == '__main__':
     unittest.main()