Add changelog entry

dstansby · dstansby · commit d38e82ce845c · 2021-12-28T10:49:58.000Z
diff --git a/doc/api/next_api_changes/behavior/19368-DS.rst b/doc/api/next_api_changes/behavior/19368-DS.rst
@@ -0,0 +1,8 @@
+Large ``imshow`` images are now downsampled
+-------------------------------------------
+When showing an image using `~matplotlib.axes.Axes.imshow ` that has more than
+:math:`2^{24}` columns or :math:`2^{23}` rows, the image will now be downsampled
+to below this resolution before being resampled for display by the AGG renderer.
+Previously such a large image would be shown incorrectly. To prevent this
+downsampling and the warning it raises, manually downsample your data before
+handing it to `~matplotlib.axes.Axes.imshow`
