Creating a vignette filter

Using all the information we have, let's see if we can create a nice vignette filter. The output will look something like the following:

Here is the code to achieve this effect:

import cv2
import numpy as np

img = cv2.imread('input.jpg')
rows, cols = img.shape[:2]

# generating vignette mask using Gaussian kernels
kernel_x = cv2.getGaussianKernel(cols,200)
kernel_y = cv2.getGaussianKernel(rows,200)
kernel = kernel_y * kernel_x.T
mask = 255 * kernel / np.linalg.norm(kernel)
output = np.copy(img)

# applying the mask to each channel in the input image
for i in range(3):
    output[:,:,i] = output[:,:,i] * mask

cv2.imshow('Original', img)
cv2.imshow('Vignette', output)
cv2.waitKey(0)

What's happening underneath?

The Vignette filter basically focuses the brightness on a particular part of the image and the other parts look faded. In order to achieve this, we need to filter out each channel in the image using a Gaussian kernel. OpenCV provides a function to do this, which...