Kinect SDK 1 - Skeletons

Written by Mike James

Article Index
Kinect SDK 1 - Skeletons
Using the GDI
Joints
From 3D to 2D

Page 4 of 4

From 3D to 2D

First we need to convert the 3D skeleton co-ordinates into 2D color image co-ordinates:

ColorImagePoint Cloc = 
 sensor.MapSkeletonPointToColor(Sloc, 
  ColorImageFormat.RgbResolution640x480Fps30);

We now have the x,y pixel co-ordinate of the Head in the video bitmap stored as properties of the ColorImagePoint.

Assuming we have a method called markAtPoint(ColorImagePoint p, Bitmap bmp)

which will draw an ellipse centered at the location, we can complete the program with:

  markAtPoint(Cloc, bmap);
 }
}

The MarkAtPoint method simply uses the GDI to draw an ellipse:

void markAtPoint(ColorImagePoint p, 
                              Bitmap bmp)
{
 Graphics g = Graphics.FromImage(bmp);
 g.DrawEllipse(Pens.Red, 
  new Rectangle(p.X - 20, p.Y - 20, 40, 40));
}

Now if you run the program you should see a small red ellipses appear to mark the head of the players.

sample

The complete FrameReady event handler is:

void FramesReady(object sender, 
                 AllFramesReadyEventArgs e)
{
 ColorImageFrame VFrame = 
                     e.OpenColorImageFrame();
 if (VFrame == null) return;
 Bitmap bmap = ImageToBitmap(VFrame);
 SkeletonFrame SFrame = e.OpenSkeletonFrame();
 if (SFrame == null) return;
 Skeleton[] Skeletons = 
    new Skeleton[SFrame.SkeletonArrayLength];
 SFrame.CopySkeletonDataTo(Skeletons);
 foreach (Skeleton S in Skeletons)
 {
  if (S.TrackingState == 
            SkeletonTrackingState.Tracked)
  {
   SkeletonPoint Sloc = 
         S.Joints[JointType.Head].Position;
   ColorImagePoint Cloc = 
     sensor.MapSkeletonPointToColor(Sloc, 
      ColorImageFormat.RgbResolution640x480Fps30);
   markAtPoint(Cloc, bmap);
  }
 }
 pictureBox1.Image = bmap;
}

Once you have seen how to track a head the rest of the body is no problem and you will be surprised at how rarely you actually need to draw a skeleton corresponding to where the player is - which is the topic of the next chapter.

You can download the code for the Windows Forms version of this program from the CodeBin (note you have to register first).

Practical Windows Kinect in C#
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From 3D to 2D

Practical Windows Kinect in C#Chapter List

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Further reading:

Practical Windows Kinect in C#
Chapter List