Cosmic Techie

Image to Pencil Sketch using Python and OpenCV

We will go through a program to get a pencil sketch from an image using python and OpenCV.  The complete program can be found at the end.(Note: The steps demonstrated have been for the understanding.)

Step 1: 

To use OpenCV, import the library.
import cv2

Step 2:

Read the Image.
image = cv2.imread("vegeta.png")
cv2.imshow("Vegeta",image)
cv2.waitKey(0)

Step 3:

Create a new image by converting the original image to grayscale.
gray_image = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
cv2.imshow("GrayVegeta",gray_image)
cv2.waitKey(0)

Step 4:

Invert the grayscale image. We can invert images simply by subtracting from 255, as grayscale images are 8 bit images or have a maximum of 256 tones.
inverted_image = 255-gray_image
cv2.imshow("InvertedVegeta",inverted_image)
cv.waitKey(0)

Step 5:

Blur the inverted image using GaussianBlur method in OpenCV library and invert the blurred image. 
blurred = cv2.GaussianBlur(inverted_image,(21,21),0)
inverted_blurred = 255-blurred
cv2.imshow("InvertedBlurredVegeta",inverted_blurred)
cv2.waitkey(0)

Step 6:

Divide the grayscale values of the image by the values of image received from step-5 (Note: We inverted the grayscale image and we blurred this image and then again inverted it). Dividing an image from its smoothened form will highlight the edges and we get the image like Pencil Sketch.
pencil_sketch = cv2.divide(gray_image,inverted_blurred, scale=256.0)
cv2.imshow("VegetaSketch",pencil_sketch)
cv2.waitKey(0)

Steps Illustration:

Complete Program to get a sketch from an Image