From 791d1a2846e28955e964cfa38ac4632fc457fa30 Mon Sep 17 00:00:00 2001
From: Alexander <homm86@gmail.com>
Date: Sat, 7 Dec 2019 20:07:27 +0300
Subject: [PATCH] Better thumbnail aspect ratio preservation

---
 Tests/test_image_thumbnail.py | 40 ++++++++++++++++++++---------------
 src/PIL/Image.py              |  8 +++----
 2 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/Tests/test_image_thumbnail.py b/Tests/test_image_thumbnail.py
index d1224f075..30fe25557 100644
--- a/Tests/test_image_thumbnail.py
+++ b/Tests/test_image_thumbnail.py
@@ -5,37 +5,43 @@ from .helper import PillowTestCase, hopper
 
 class TestImageThumbnail(PillowTestCase):
     def test_sanity(self):
-
         im = hopper()
-        im.thumbnail((100, 100))
+        self.assertIsNone(im.thumbnail((100, 100)))
 
-        self.assert_image(im, im.mode, (100, 100))
+        self.assertEqual(im.size, (100, 100))
 
     def test_aspect(self):
-
-        im = hopper()
+        im = Image.new("L", (128, 128))
         im.thumbnail((100, 100))
-        self.assert_image(im, im.mode, (100, 100))
+        self.assertEqual(im.size, (100, 100))
 
-        im = hopper().resize((128, 256))
+        im = Image.new("L", (128, 256))
         im.thumbnail((100, 100))
-        self.assert_image(im, im.mode, (50, 100))
+        self.assertEqual(im.size, (50, 100))
 
-        im = hopper().resize((128, 256))
+        im = Image.new("L", (128, 256))
         im.thumbnail((50, 100))
-        self.assert_image(im, im.mode, (50, 100))
+        self.assertEqual(im.size, (50, 100))
 
-        im = hopper().resize((256, 128))
+        im = Image.new("L", (256, 128))
         im.thumbnail((100, 100))
-        self.assert_image(im, im.mode, (100, 50))
+        self.assertEqual(im.size, (100, 50))
 
-        im = hopper().resize((256, 128))
+        im = Image.new("L", (256, 128))
         im.thumbnail((100, 50))
-        self.assert_image(im, im.mode, (100, 50))
+        self.assertEqual(im.size, (100, 50))
 
-        im = hopper().resize((128, 128))
+        im = Image.new("L", (128, 128))
         im.thumbnail((100, 100))
-        self.assert_image(im, im.mode, (100, 100))
+        self.assertEqual(im.size, (100, 100))
+
+        im = Image.new("L", (256, 162))  # ratio is 1.5802469136
+        im.thumbnail((33, 33))
+        self.assertEqual(im.size, (33, 21))  # ratio is 1.5714285714
+
+        im = Image.new("L", (162, 256))  # ratio is 0.6328125
+        im.thumbnail((33, 33))
+        self.assertEqual(im.size, (21, 33))  # ratio is 0.6363636364
 
     def test_no_resize(self):
         # Check that draft() can resize the image to the destination size
@@ -46,4 +52,4 @@ class TestImageThumbnail(PillowTestCase):
         # Test thumbnail(), where only draft() is necessary to resize the image
         with Image.open("Tests/images/hopper.jpg") as im:
             im.thumbnail((64, 64))
-            self.assert_image(im, im.mode, (64, 64))
+            self.assertEqual(im.size, (64, 64))
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 96ec314bc..613b3a361 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2137,11 +2137,11 @@ class Image:
         # preserve aspect ratio
         x, y = self.size
         if x > size[0]:
-            y = int(max(y * size[0] / x, 1))
-            x = int(size[0])
+            y = max(round(y * size[0] / x), 1)
+            x = size[0]
         if y > size[1]:
-            x = int(max(x * size[1] / y, 1))
-            y = int(size[1])
+            x = max(round(x * size[1] / y), 1)
+            y = size[1]
         size = x, y
 
         if size == self.size: