Filtering and resampling

# to run in google colab
import sys
if 'google.colab' in sys.modules:
    import subprocess
    subprocess.call('apt-get install subversion'.split())
    subprocess.call('svn export https://github.com/YoniChechik/AI_is_Math/trunk/c_02b_filtering_and_resampling/Tour_Eiffel.jpg'.split())

import numpy as np
import cv2
from matplotlib import pyplot as plt

figsize = (10,10)

def plot_im(img, title):
    plt.figure(figsize=figsize)
    plt.imshow(img)
    plt.title(title)
    plt.xticks([])
    plt.yticks([])
    plt.show()

img = cv2.imread("Tour_Eiffel.jpg")
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
plot_im(img, "original image")

def mean_kernel_smoothing(img, sz):
    kernel = np.ones((sz, sz))/(sz**2)
    dst = cv2.filter2D(img, -1, kernel)

    plot_im(dst, str(sz)+'X'+str(sz)+" mean kernel")


mean_kernel_smoothing(img, 5)
mean_kernel_smoothing(img, 10)
mean_kernel_smoothing(img, 20)

def gauss_blur(img, k_sz, sigma=-1, is_plot_kernel=False):
    blur = cv2.GaussianBlur(img, (k_sz, k_sz), sigma)
    plot_im(blur, "gaussian kernel with kernel_size="
            + str(k_sz)+r", $\sigma$=" + str(sigma))
    if is_plot_kernel:
        # sigma=-1 will set the sigma size automatically 
        gauss_ker = cv2.getGaussianKernel(k_sz, sigma)
        plt.figure(figsize=(figsize[0]/2, figsize[1]/2))
        plt.plot(gauss_ker)
        plt.title("corresponding gaussian kernel")
        plt.show()

gauss_blur(img, 5, is_plot_kernel=True)
gauss_blur(img, 21, is_plot_kernel=True)
gauss_blur(img, 21, 1, is_plot_kernel=True)