In the last blog post I showed how the line detector could be used with a Sobel filter. In this post I will show how Canny edge detection https://en.wikipedia.org/wiki/Canny_edge_detector can provide a better input to the line detector.
The latest cookbook http://sound-analysis.com/imaging-whiteboard-3-0/ shows how to use the Line Detector Control with a Sobel filter, and, how to perform Canny edge detection. This post will show how to combine both.
First, we prepare the image; repeat will help making the adjustments to the Canny edge detection, Set region will limit the entire process to a specific region. Monochrome because the Hough transform is a monochrome process.
Next, we filter the image to remove noise, and perform the initial edge detection using a full Sobel filter (includes edge direction) and gradient thresholding.
Next, we complete the Canny edge detection with double thresholding and edge hysteresis.
Finally, we use the Edge Detector to identify the most prominent lines.
