napari is an image viewer and graphical image processing environment. Writing a plugin for napari involves annotating a Python function with image types provided by this package. As an example, if you provide the following in a module:
from typing import Union as U, Tuple as Tup
from imtypes import Image
def gaussian_filter(image : Image, sigma : U[float, Tup[float, ...]], *,
multichannel : bool = True) -> Image:
...Then napari can ingest the module and make the gaussian filter available to users from its graphical user interface.