"""
================================================================
Removing small objects in grayscale images with a top hat filter
================================================================

This example shows how to remove small objects from grayscale images.
The top-hat transform [1]_ is an operation that extracts small elements and
details from given images. Here we use a white top-hat transform, which is
defined as the difference between the input image and its
(mathematical morphology) opening.

.. [1] https://en.wikipedia.org/wiki/Top-hat_transform

"""

import numpy as np
import matplotlib.pyplot as plt

from skimage import data
from skimage import color, morphology

image = color.rgb2gray(data.hubble_deep_field())[:500, :500]

selem =  morphology.disk(1)
res = morphology.white_tophat(image, selem)

fig, ax = plt.subplots(ncols=3, figsize=(20, 8))
ax[0].set_title('Original')
ax[0].imshow(image, cmap='gray')
ax[1].set_title('White tophat')
ax[1].imshow(res, cmap='gray')
ax[2].set_title('Complementary')
ax[2].imshow(image - res, cmap='gray')

plt.show()