tracking.js Rectangle detection.

Hi,

is it possible to do rectangle detection with the framework, is it something you think about? maybe implementation of hough transform.

Thanks!

Nov 12 '17 14:11 boazgarty

@eduardolundgren , What would be the best approach for doing document edge detection and perspective correction for js/cordova/hrml5?

Nov 20 '17 06:11 dev-fJ-del

@boazgarty

hough transform is used to find circles. if you are after edge detection you can use sobel function

  <div class="demo-frame">
    <div class="demo-container">
      < img id="image" width="250" height="250" src="assets/chess.png" /> 
      < canvas id="canvas" width="250" height="250"></canvas> 
    </div>
  </div>

  <script>
  
    window.onload = function() {
      var width = 225;
      var height = 225;
      var canvas = document.getElementById('canvas');
      var context = canvas.getContext('2d');
      var image = document.getElementById('image');

      var doFindFeatures = function() {

        context.drawImage(image, 0, 0, width, height);
        var imageData = context.getImageData(0, 0, width, height);

        var gray = tracking.Image.sobel(imageData.data, width, height);
     
        for (var i=0; i<gray.length; i++) {
          imageData.data[i] = gray[i];
        }        

        context.clearRect(0, 0, canvas.width, canvas.height);
        context.putImageData(imageData, 0, 0);

      }

      doFindFeatures();

    }

  </script>

screenshot from 2017-12-16 22-04-29

Dec 16 '17 22:12 murat-aka

@murat-aka Thanks for your example. I'm trying to do something similar (identify a rectangle and extract it). After using the sobel filter, would you have any suggestions for how to (efficiently) detect whether the image contains a rectangle?

Jul 05 '18 17:07 pmulac

Instead of a chess board, which has well-defined areas of contrasting colors, the edge of a floor, where there is lots of "noise" that will give rise to many features which just approximate a straight line, from which we want to then derive the straight line, which as I understand it is the whole point of the Hough transform, or am I misunderstanding what Sobel does?