Mastering OpenCV 4 - Third Edition

Generating a black and white sketch

To obtain a sketch (black and white drawing) of the camera frame, we will use an edge detection filter, whereas to obtain a color painting, we will use an edge preserving filter (bilateral filter) to further smooth the flat regions while keeping edges intact. By overlaying the sketch drawing on top of the color painting, we obtain a cartoon effect, as shown earlier in the screenshot of the final app.

There are many different edge detection filters, such as Sobel, Scharr, and Laplacian filters, or a Canny edge detector. We will use a Laplacian edge filter since it produces edges that look most similar to hand sketches compared to Sobel or Scharr, and is quite consistent compared to a Canny edge detector, ...