Backport zoom transformation performance improvement, GitLab issue #334. Thanks to @startmat for the patch.

docs/releases/2.1.5.rst

@@ -12,11 +12,15 @@ This is a bug-fix release and all users are encouraged to upgrade.
 Other changes
 -------------
 
+- Backport resize transformation math operation fix (GitLab #319).
 - Update Pillow to 3.1.2
 
     - https://pillow.readthedocs.io/en/3.4.x/releasenotes/3.1.1.html
     - https://pillow.readthedocs.io/en/3.4.x/releasenotes/3.1.2.html
 
+- Backport zoom performance improvement (GitLab #334).
+
+
 Removals
 --------
 * None
@@ -70,6 +74,7 @@ Backward incompatible changes
 Bugs fixed or issues closed
 ===========================
 
-* `GitLab issue #311 <https://gitlab.com/mayan-edms/mayan-edms/issues/311>`_ acl page return ContentType:Document
+* `GitLab issue #319 <https://gitlab.com/mayan-edms/mayan-edms/issues/319>`_ TransformationResize issue with very "long" image
+* `GitLab issue #334 <https://gitlab.com/mayan-edms/mayan-edms/issues/334>`_ Perfomance improvment: prevent unnecessary image.resize in TransformationZoom
 
 .. _PyPI: https://pypi.python.org/pypi/mayan-edms/