White blob detection

Question

I'm trying to use AForge.NET to detect a thick white line across an Image.

It's like pipe that I get and is my desired result after applying a Threshold filter.

I know how to detect shapes and I'm doing that, already, but this doesn't match under any shape since it has no edges and isn't a circle.

I have sample code from detecting equilateral shapes, but I don't know if that's relevant.

public void DetectQuadrilateralType(Bitmap bitmap)
{
    BlobCounter blobCounter = new BlobCounter();
    blobCounter.ProcessImage(bitmap);
    Blob[] blobs = blobCounter.GetObjectsInformation();
    //Graphics object to draw
    Pen pen;
    Graphics g = Graphics.FromImage(bitmap);
    SimpleShapeChecker shapeChecker = new SimpleShapeChecker();

    for (int i = 0; i < blobs.Length; i++)
    {
        List<IntPoint> edgePoints = blobCounter.GetBlobsEdgePoints(blobs[i]);
        List<IntPoint> corners;

        if (i < edgePoints.ToArray().Length && i > -1)
        {
            try
            {
                if (shapeChecker.IsConvexPolygon(edgePoints, out corners))
                {
                    PolygonSubType subType = shapeChecker.CheckPolygonSubType(corners);

                    pen = new Pen(colors[subType], 2);
                    g.DrawPolygon(pen, ToPointsArray(corners));
                    pen.Dispose();
                }
            }
            catch (Exception e) { }
        }
    }
    g.Dispose();
}

Here's the image i'm trying to detect:

If anybody has any idea how I can detect that white blob with AForge or otherwise using C#/.NET i'd really appreciate it.

The code above only detects edges, so it'll only detect the shape if it has a sharp edge, which will rarely be the case.

EDIT

I sort of have it working with the following method

public void DetectBigBlobs(Bitmap bitmap)
{
    BlobCounter blobCounter = new BlobCounter();
    blobCounter.ProcessImage(bitmap);
    Rectangle[] rects = blobCounter.GetObjectsRectangles();
    //Graphics object to draw
    Pen pen = new Pen(Color.Red, 2);
    Graphics g = Graphics.FromImage(bitmap);

    foreach (Rectangle rect in rects)
    {
        if (rect.Width > 200 && rect.Height > 150)
        {
            g.DrawRectangle(pen, rect);
        }
    }

    pen.Dispose();
    g.Dispose();
}

There must be a better way than using fixed widths (because they could vary greatly)

Answer 1

if you want to get a marked blob you can use this code

public void DetectBigBlobs(Bitmap bitmap)
    {
        BlobCounter blobCounter = new BlobCounter();

        Graphics g = Graphics.FromImage(bitmap);

        //filtering the blobs before searching for blobs 
        blobCounter.FilterBlobs = true;
        blobCounter.MinHeight = bitmap.Height/3;
        blobCounter.MinWidth = bitmap.Width/3;

        blobCounter.ProcessImage(bitmap);
        Blob[] blobs = blobCounter.GetObjectsInformation();

        foreach (Blob b in blobs)
        { 
            //getting the found blob edgepoints 
            List<IntPoint> edgePoints = blobCounter.GetBlobsEdgePoints(b);
            //if you want to mark every edge point RED 
            foreach (IntPoint point in edgePoints)
                bitmap.SetPixel(point.X, point.Y, Color.Red);
            //if you want to draw a rectangle around the blob 
            g.DrawRectangle(Pens.Blue,b.Rectangle);

        }

        g.Dispose();
    }

ask me if you want something differing i will help as much as i can :)