Unexpected Feature Behavior

[JohnMcLear]

So I may be barking up the wrong tree here but I was using the feature detection just to do some basic edge detection of an object and I guess maybe I took the wrong approach to the problem but I expected the edges of the object to be "features" and not minor details inside of the feature.. I tried different thresholds to no avail..

http://i.imgur.com/k2V3Pz6.png <-- Note a lot of "Edges" are not shown as features despite the threshold being low (5).

[eduardolundgren]

Fast feature detector is meant to detect corners not edges. You may want to give a try with Sobel for detecting the edges:

tracking.Image.sobel(pixels, width, height);

[eduardolundgren]

Did Sobel work for what you were looking for?

[JohnMcLear]

Should this work?

      window.fastThreshold = 10;

      var doFindFeatures = function() {
        tracking.Fast.THRESHOLD = window.fastThreshold;
        context.drawImage(image, 0, 0, width, height);

        var imageData = context.getImageData(0, 0, width, height);
        var gray = tracking.Image.grayscale(imageData.data, width, height);
        var edges = tracking.Image.sobel(gray, width, height);

        for (var i = 0; i < edges.length; i += 2) {
          context.fillStyle = '#f00';
          context.fillRect(edges[i], edges[i + 1], 3, 3);
        }
      };

      doFindFeatures();

The output is just two lines across the screen ;\

[JohnMcLear]

@eduardolundgren any thoughts on this?

[eduardolundgren]

Hello @JohnMcLear, sorry for delaying this answer, I have been traveling in a project.

Hey @thiago-rocha, @pablocp could you help @JohnMcLear here?

[alx-1]

@JohnMcLear, @eduardolundgren did you get it working? I get two similar lines, one horizontal and another oblique starting from the upper left corner of the image.

[alx-1]

Here are the first few values of the array of pixels produced by sobel : 8.9442720413208,8.9442720413208, 8.9442720413208, 255, 5.656854152679443, 5.656854152679443, 5.656854152679443, 255, 17.262676239013672, 17.262676239013672, 17.262676239013672, 255, 18, 18, 18, 255, 3.1622776985168457... It might look like r,g,b,a values but I don't get the coords. It does explain the origin of those two lines. I suspect it is simply me not passing the imageData.data values it needs. Is there an example for the sobel function?

[hydrococcous]

Hello @JohnMcLear, @eduardolundgren, @JohnMcLear,

i have exactly the same problem. @JohnMcLear did you have a solution? Is there an example for the sobel function?