This patch matches the size of the Fast Gaussian mode of blur with the standard Gaussian mode. The sigma value was computed as half the radius, while it should be third of the radius, since Blender's Gaussian function is truncated at 3 of the standard deviation of the unit Gaussian. The patch include versioning to adjust the size of existing files. Pull Request: https://projects.blender.org/blender/blender/pulls/121211