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Rishi Saxena
Rishi Saxena

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Frequency Domain Filtering Using OpenCV

#python #opencv #jupyter

What we need to get started with OpenCv...

We need to import few libraries given below and are available in Google Colab, independent installations may be required for other platforms.

1. Imports required 

 import cv2 from google.colab.patches import cv2_imshow import numpy as np import matplotlib.pyplot as plt
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2. Next we import an image and use a simple Edge Preserving Filter.

Domain Filtering - Frequency Domain Filters are used for smoothing and sharpening of image by removal of high or low frequency components. Sometimes it is possible of removal of very high and very low frequency.

 #read image src = cv2.imread(r'/content/P.png', cv2.IMREAD_UNCHANGED) DF = cv2.edgePreservingFilter(src, flags=1, sigma_s=60, sigma_r=0.4) print("Domain Filter - Cartoonify") cv2_imshow(numpy.hstack((src, DF)))
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Cartoonify Filter

3. A- Smoothing of Image and other Domain Filters.

Frequency Domain Filters are used for smoothing and sharpening of images by removal of high or low-frequency components.
Gaussian blur (also known as Gaussian smoothing) is the result of blurring an image by a Gaussian function.

 #apply guassian blur on src image dst = cv2.GaussianBlur(src,(5,5),cv2.BORDER_DEFAULT) print("Gaussian Smoothing") cv2_imshow(numpy.hstack((src, dst)))
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Gaussian Smoothing Blur

Mean Filter 

 kernel = np.ones((10,10),np.float32)/25 dst2 = cv2.filter2D(src,-1,kernel) print("Mean Filter") cv2_imshow(numpy.hstack((src, dst2)))
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Mean Filter

Median Filter

 #Median Filter dst3 = cv2.medianBlur(src,5) print("Median Filter") cv2_imshow(numpy.hstack((src, dst3)))
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Median Filter

4. B- Sharpening Filter -

Bilateral filter 

 #Bilateral filter print("Bilateral Filter") dst4 = cv2.bilateralFilter(src, 60, 60, 60) cv2_imshow(numpy.hstack((src, dst4)))
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Bilateral Filer Sharpening

5. C- Frequency Band Filter

Low Pass 

 #low pass filter Lp = cv2.filter2D(src,-1, kernel) Lp = src - Lp print("Low Pass") cv2_imshow(numpy.hstack((src, Lp)))
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Low Pass

High Pass

 Hp = src - dst filtered = filtered + 127*numpy.ones(src.shape, numpy.uint8) print("High Pass") cv2_imshow(numpy.hstack((src, Hp)))
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High Pass

Frequency filters process an image in the frequency domain. The image is Fourier transformed, multiplied with the filter function and then re-transformed into the spatial domain. Attenuating high frequencies results in a smoother image in the spatial domain, attenuating low frequencies enhances the edges.

Any frequency filter can be implemented in the spatial domain and, if there exists a simple kernel for the desired filter effect.

If you missed the first part

LINK

alcatraz714

OpenCV image processing using Python

Rishi Saxena ・ Sep 9 '21

#python #jupyter #opencv

Thanks for Reading...

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