Modular image processing pipeline using OpenCV and Python generators

Next, we define thelist_images function (line 22–34) which will help us to walk through the input directory structure to grab the image paths. For face detection, we use the Viola-Jones algorithm known as Haar cascade (line 40). It was published in 2001 by Paul Viola and Michael Jones. You can learn more about the algorithm from their original paper Rapid Object Detection using a Boosted Cascade of Simple Features or Wikipedia page. It is quite an old algorithm in the era of deep learning and false-positives prone (reporting a face in the place of the image where no face is present). Even though it is quite easy to use for our demonstrative case. The main processing loop goes as follow: we walk through image files (line 49), read them (line 51) one by one, detect the faces (line 55), save them to the prepared directory (line 59–72) and saving a summary report (line 78–82) with faces coordinates.