Merge pull request #4088 from radarhere/fit

Do not calculate the crop width in Image.fit if it is already known

Tests/test_imageops.py

@@ -81,6 +81,16 @@ def test_1pxfit(self):
         newimg = ImageOps.fit(hopper("RGB").resize((100, 1)), (35, 35))
         self.assertEqual(newimg.size, (35, 35))
 
+    def test_fit_same_ratio(self):
+        # The ratio for this image is 1000.0 / 755 = 1.3245033112582782
+        # If the ratios are not acknowledged to be the same,
+        # and Pillow attempts to adjust the width to
+        # 1.3245033112582782 * 755 = 1000.0000000000001
+        # then centering this greater width causes a negative x offset when cropping
+        with Image.new("RGB", (1000, 755)) as im:
+            new_im = ImageOps.fit(im, (1000, 755))
+            self.assertEqual(new_im.size, (1000, 755))
+
     def test_pad(self):
         # Same ratio
         im = hopper()

src/PIL/ImageOps.py

@@ -426,7 +426,11 @@ def fit(image, size, method=Image.NEAREST, bleed=0.0, centering=(0.5, 0.5)):
     output_ratio = float(size[0]) / size[1]
 
     # figure out if the sides or top/bottom will be cropped off
-    if live_size_ratio >= output_ratio:
+    if live_size_ratio == output_ratio:
+        # live_size is already the needed ratio
+        crop_width = live_size[0]
+        crop_height = live_size[1]
+    elif live_size_ratio >= output_ratio:
         # live_size is wider than what's needed, crop the sides
         crop_width = output_ratio * live_size[1]
         crop_height = live_size[1]