Draw circles on the image after applying hough transform?

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I'm using HoughCircleTransformation class of AForge to detect circles. I want to draw circles on the image where the circles are detected (to highlight the circles on the original image). How can i modify the 'foreach loop' to do that?

C#

public Bitmap hough(Bitmap bmp)
   {
       HoughCircleTransformation circleTransform = new HoughCircleTransformation(35);
       // apply Hough circle transform
       circleTransform.ProcessImage(bmp);
       Bitmap houghCirlceImage = circleTransform.ToBitmap();
       // get circles using relative intensity
       HoughCircle[] circles = circleTransform.GetCirclesByRelativeIntensity(0.5);
       int numCircles = circleTransform.CirclesCount;
       MessageBox.Show("Number of circles found : " + numCircles.ToString());
       foreach (HoughCircle circle in circles)
       {

         //code to draw circle
       }
       return bmp;
   }

Posted 2-Apr-14 23:59pm

AmnaRahman

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2 solutions

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lukeer · Accepted Answer · 2014-04-03T00:10:00

Solution 1

You need a Graphics[^] object to draw someting. When you have it, use it to draw:

C#

MessageBox.Show("Number of circles found : " + numCircles.ToString());
System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp);
foreach (HoughCircle circle in circles)
{
    g.DrawEllipse(Pens.Green, circle.GetTheThingsCoordinates());
    //code to draw circle
}

Posted 3-Apr-14 0:10am

lukeer

Comments

lukeer 3-Apr-14 8:02am

Come on, I've never touched the AForge library and still came to find the HoughCircle documentation within minutes. The class has members named "X", "Y", and "Radius". That's very close to what you need.

[Edit]Where is that comment I replied to?[/Edit]

AmnaRahman 3-Apr-14 13:03pm

i did it thanks

AmnaRahman · Accepted Answer · 2014-04-03T07:05:00

Solution 2

foreach (HoughCircle circle in circles)
{
Pen redPen = new Pen(Color.Red, 1);
using (var graphics = Graphics.FromImage(bmp2))
{
graphics.DrawEllipse(redPen, circle.X, circle.Y, circle.Radius, circle.Radius);

}

}

Posted 3-Apr-14 7:05am

AmnaRahman

Comments

lukeer 4-Apr-14 2:27am

You got it to work. That's great!
Let me add a few hints:
Depending on the number of detected circles, this approach might degrade performance more than necessary because it's creating new graphics and pen objects for each circle.
If drawing seems too slow, create the graphics object outside the loop (as suggested in my solution). Same for the pen.

AmnaRahman 4-Apr-14 9:59am

ok i will try it this way. thanks