🐛 Bug Report

How To Reproduce

As part of #4087, the perceptual image hash images have been updated to account for the associated changes within iris from the recent release of matplotlib 3.4.1.

As part of #4087, SciTools/test-iris-imagehash#39 was raised to update the test-iris-imagehash archive.

Consequently, there appears to be a regression for one the graphical test iris.tests.test_mapping.TestLimitedAreaCube.test_grid.0, see here for further details.

Steps to reproduce the behaviour:

From the root directory of iris:

1. git checkout 7fd7960e25cefc48c49a6e518cfd02f42fa860ea
2. pip install --no-deps --editable .
3. python setup.py test
4. python lib/iris/tests/idiff.py --results iris_image_test_output

Environment

• Iris Version: as per the iris commit SHA
• Matplotlib Version: 3.4.1

Additional context

Add additional verbose information in a collapsible section.