Introduction to Morphological Operators¶

In this tutorial you are gonna explore kornia.morphology, that’s Kornia’s module for differentiable Morphological Operators.

By the end, you will be able to use morphological operations as easy as:

new_image = morph.operation(original_image, structuring_element)

But first things first, let’s prepare the environment.

Download Kornia¶

If you don’t have Kornia installed, you can download it using pip.

%%capture
!pip install git+https://github.com/kornia/kornia

Prepare the image¶

With kornia.morphology, you can apply morphological operators in 3 channel color images. Besides, all operators are differentiable. Let’s download and read an image.

%%capture
!wget 'https://image.shutterstock.com/image-photo/portrait-surprised-cat-scottish-straight-260nw-499196506.jpg' -O img.jpg

We can use can use OpenCV to load the image.

import cv2
 
img = cv2.imread("img.jpg") # Download Image
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB) # Define RGB

Structuring element¶

We have the original image ready to go, now we need the second part in the operation, the structuring element (aka Kernel).

The kernel must be a 2-dim tensor with odd sides, i.e. 3x3.

import torch
import kornia as K

device = 'cpu' # 'cuda:0' for GPU
kernel = torch.tensor([[0, 1, 0],[1, 1, 1],[0, 1, 0]]).to(device)

# to torch.tensor
img_t = K.image_to_tensor(img, keepdim=False)
img_t = img_t.float() / 255.

Making plots!¶

In this tutorial we are gonna compare the images before and after transforming them.

It make sense to create a function to plot and see the changes!

import matplotlib.pyplot as plt
from matplotlib import rcParams

def plot_morph_image(tensor):

  # kornia.tensor_to_image
  image = K.tensor_to_image(tensor.squeeze(0)) # Tensor to image

  # Plot before-after
  rcParams['figure.figsize'] = 20 ,20
  fig, ax = plt.subplots(1,2)
  ax[0].axis('off')
  ax[0].imshow(img)
  ax[1].axis('off')
  ax[1].imshow(image)

Morphology¶

The main goal of kornia.morphology is that you could easily implement several morphological operator as follows:

new_image = morph.operation(original_image, structuring_element)

Let’s check them all!

Dilation¶

from kornia import morphology as morph

dilated_image = morph.dilation(img_t, kernel) # Dilation
plot_morph_image(dilated_image) # Plot

Erosion¶

eroded_image = morph.erosion(img_t, kernel) # Erosion
plot_morph_image(eroded_image) # Plot

Open¶

opened_image = morph.opening(img_t, kernel) # Open
plot_morph_image(opened_image)

Close¶

closed_image = morph.closing(img_t, kernel) # Close
plot_morph_image(closed_image) # Plot

Morphological Gradient¶

graded_image = morph.gradient(img_t, kernel) # Morphological gradient
plot_morph_image(1. - graded_image)

Bottom Hat¶

bottom_image = morph.bottom_hat(img_t, kernel) # Black Hat
plot_morph_image(1. - bottom_image)

Top Hat¶

toph_image = morph.top_hat(img_t, kernel) # Top Hat
plot_morph_image(1. - toph_image)

Conclusion¶

And that’s it!

Now you know how to use Kornia to apply differentiable morphological operations in your PyTorch pipeline.

Many thanks for using Kornia, and have fun!