Better thumbnail aspect ratio preservation

[homm]

If the source image is 256×162, it's aspect ratio is 1.58. Before, after thumbnailing, for example, the resulting image had 33×20 size, which aspect ratio is 1.65. Now thumbnail returns 33×21 image, with aspect ration 1.57, which is much closer.

[hugovk]

So using round to round to the nearest integer, instead of int to round down to an integer.

>>> int(1.1)
1
>>> int(1.9)
1
>>> round(1.1)
1
>>> round(1.9)
2

Let's also add this to the release notes.

[radarhere]

Just to be aware - by removing the int rounding on these second lines, if someone had existing code im.thumbnail((150.2, 150.2)), it would now break.

That's not unreasonable though.

[hugovk]

Example:

from PIL import Image

im = Image.open("Tests/images/hopper.png")
print(im.size)

im.thumbnail((15.2, 15.2))
print(im.size)

im.thumbnail((10, 10))
print(im.size)

On 6.2.1:

(128, 128)
(15, 15)
(10, 10)

On master with this PR:

(128, 128)
Traceback (most recent call last):
  File "1.py", line 6, in <module>
    im.thumbnail((15.2, 15.2))
  File "/Users/hugo/github/Pillow/src/PIL/Image.py", line 2153, in thumbnail
    im = self.resize(size, resample)
  File "/Users/hugo/github/Pillow/src/PIL/Image.py", line 1822, in resize
    return self._new(self.im.resize(size, resample, box))
TypeError: integer argument expected, got float

Should we fix it something like this?

diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index 613b3a36..981c8c81 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -2138,10 +2138,10 @@ class Image:
         x, y = self.size
         if x > size[0]:
             y = max(round(y * size[0] / x), 1)
-            x = size[0]
+            x = round(size[0])
         if y > size[1]:
             x = max(round(x * size[1] / y), 1)
-            y = size[1]
+            y = round(size[1])
         size = x, y

         if size == self.size:

(128, 128)
(15, 15)
(10, 10)

[radarhere]

Okay, I've created PR #4272