Laser Gesture Recognition

• Download source files - 177 Kb
• Download demo project - 104 Kb

Introduction

Wouldn't it be great if we could somehow give visual commands to our computer without touching the keyboard or mouse? In this article, we will put together a simple laser gesture recognition application and use it to control Windows Media Player. This is far more comfortable than using a remote control because you don't have to look for the correct buttons in the dark. All you have to do is make a few simple gestures anywhere in the camera's field of view with a laser pointer, and that's it! This program recognizes simple gestures made on a wall with a laser pointer such as left, right, up, down, two downward and two upward diagonals. This program could be modified to recognize some more gestures; however, it cannot recognize complex gestures since I haven't taken a neural network approach for image recognition.

Video

Our first step is to get a video feed into our application from a webcam. We can use DirectX's component DirectShow for accomplishing this. I have directly used Andrew Kirillov's Motion Detection code[^] (with permission) for image acquisition. I modified the code in MotionDetector1.cs to perform laser gesture recognition.

Recognition

The program searches for the brightest pixel in its field of view (which is a laser dot, in our case) with luminance above a certain threshold value. Luminance of a pixel can be calculated using its RGB values, with a simple formula:

Luminance = (299 * red + 587 * green + 114 * blue) / 1000

After it finds the pixel, it analyzes how much that point moved along the x and y axes. Based on these parameters, the program tries to recognize the movement. For example, if the laser dot's movement along the x-axis is much more than its movement along the y-axis, the program will determine that it was more or less a horizontal movement. Then, based on the initial and final position of the laser dot, it will determine if the movement was towards the left or towards the right. It uses a similar technique to detect upward, downward, and diagonal movements.

Controlling Windows Media Player

For controlling the Windows Media Player, the program simply simulates some of the keyboard shortcuts used by Media Player. This code can skip to the next/previous track, or play, pause, stop a track based on the gesture the program recognizes:

// Get a handle to an application window.
[DllImport("USER32.DLL")]
private static extern IntPtr FindWindow(string lpClassName,
    string lpWindowName);

// Activate an application window.
[DllImport("USER32.DLL")]
private static extern bool SetForegroundWindow(IntPtr hWnd);


private void ControlMediaPlayer(string gesture)
{
    IntPtr mediaPlayerHandle = 
           FindWindow("WMPlayerApp", "Windows Media Player");

    // Verify that WMP is a running process.
    if (mediaPlayerHandle == IntPtr.Zero)
    {
        System.Windows.Forms.MessageBox.Show("WMP is not running.");
        return;
    }

    switch (gesture)
    {        
        case "LEFT":
            SetForegroundWindow(mediaPlayerHandle);
            SendKeys.SendWait("^b");
            break;

        case "RIGHT":
            SetForegroundWindow(mediaPlayerHandle);
            SendKeys.SendWait("^f");
            break;

        case "UP":
            SetForegroundWindow(mediaPlayerHandle);
            SendKeys.SendWait("^s");
            break;

        case "DOWN":
            SetForegroundWindow(mediaPlayerHandle);
            SendKeys.SendWait("^p");
            break;
    }
}

Using the program

Since the program searches for the brightest pixel in the camera's field of view, the lighting conditions of your room can affect its performance. So, adjust the brightness threshold and lighting conditions so that nothing (except the laser) exceeds the brightness threshold.

In the sample program I've provided with this article, the gestures for controlling Windows Media Player are:

• Up – Stop
• Down – Play/Pause
• Left – Previous Track
• Right – Next Track

You can also easily modify the code and use diagonal gestures for volume control. :)

Conclusion

We have reached the end of this article. I might update this program to perform more complex gesture recognition later on. However, for now, have fun with it! You can find some videos of this application being used to control Media Player on my blog[^]. You can also easily modify the code to make this program do much more than just controlling Windows Media Player. Have fun!

History

• [13-JAN-2007] - Minor corrections
• [09-JAN-2007] - Initial publication