https://github.com/kohya-ss/sd-scripts/pull/1741

[2] aspect ratios compared in log-space have the desirable property that a 1:1 aspect ratio can be equidistant
from buckets 2:1 and 1:2, each of which fit an equal proportion of its area. - https://arxiv.org/abs/2409.15997

library/train_util.py

@@ -271,7 +271,7 @@ def select_bucket(self, image_width, image_height):
             if reso in self.predefined_resos_set:
                 pass
             else:
-                ar_errors = self.predefined_aspect_ratios - aspect_ratio
+                ar_errors = np.log(self.predefined_aspect_ratios) - np.log(aspect_ratio)
                 predefined_bucket_id = np.abs(ar_errors).argmin()  # 当該解像度以外でaspect ratio errorが最も少ないもの
                 reso = self.predefined_resos[predefined_bucket_id]