Kinect & Processing: A Beginner's Tutorial

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Kinect and Processing Tutorial

Hey guys! Ever wanted to create interactive art or cool projects using your body movements? Well, you're in the right place! This tutorial will guide you through the basics of using the Kinect with Processing, a super flexible and easy-to-learn programming language for visual design. Get ready to dive into the exciting world of motion tracking and creative coding!

What You'll Need

Before we get started, make sure you have these things ready:

  • Kinect Sensor: Obviously! Any version of the Kinect (v1 or v2) will work, but this tutorial is geared towards the original Kinect (v1).
  • Processing: Download and install the latest version of Processing from processing.org. It's free!
  • Simple OpenNI: You'll need this Processing library to interface with the Kinect. We'll cover how to install it in the next section.
  • Kinect Drivers: Make sure your Kinect is properly recognized by your computer. You might need to install drivers depending on your operating system.

Setting Up Processing and Simple OpenNI

Okay, let's get Processing ready to talk to your Kinect. Follow these steps carefully:

  1. Install Processing: If you haven't already, download and install Processing from the official website. Just follow the instructions for your operating system.
  2. Install Simple OpenNI Library:
    • Open Processing.
    • Go to Sketch > Import Library > Add Library.
    • Search for "Simple OpenNI" and install it. If you don't see it, make sure you're connected to the internet.

Diving Deeper into Processing Setup

Alright, let's break down this setup process a little further to ensure everyone's on the same page. Setting up Processing and the Simple OpenNI library is a foundational step, and getting it right ensures a smoother ride ahead. When you first install Processing, take a moment to familiarize yourself with the interface. You'll notice the code editor where you'll be writing your sketches (Processing programs), the console for displaying messages and errors, and the toolbar with essential functions like Run, Stop, and Save. The 'Sketch' menu is your go-to for managing your projects and importing libraries. Now, about that Simple OpenNI library, it's essentially a bridge that allows Processing to understand and utilize the data coming from your Kinect sensor. Without it, Processing wouldn't know what to do with the Kinect's input. That's why installing it correctly is super important. When you go to Sketch > Import Library > Add Library, Processing opens up a Library Manager. This is a handy tool that lets you search for and install libraries contributed by the Processing community. Typing "Simple OpenNI" in the search bar should bring up the library. Make sure you select the correct one (usually the one with the most downloads and a clear description) and click 'Install'. Processing will then download and install the library, making it available for your sketches. Once installed, you might want to restart Processing just to be sure everything is loaded correctly. To confirm that Simple OpenNI is properly installed, you can try running a simple example sketch that uses the library. We'll cover an example later in this tutorial, but for now, just knowing that the library is installed and ready to go is a great first step. Remember, if you encounter any issues during the installation process, the Processing website and the Simple OpenNI library page are excellent resources for troubleshooting. Don't hesitate to consult them or ask for help in the Processing community forums. With Processing and Simple OpenNI set up correctly, you're well on your way to creating some amazing interactive projects with your Kinect.

Basic Kinect Code in Processing

Now for the fun part! Let's write some code to get data from the Kinect. Here's a basic sketch that initializes the Kinect and displays the raw depth data:

import SimpleOpenNI.*;

SimpleOpenNI kinect;

void setup() {
  size(640, 480);
  kinect = new SimpleOpenNI(this);
  kinect.enableDepth();
  kinect.init();
}

void draw() {
  kinect.update();
  int[] depthData = kinect.depthMap();

  for (int i = 0; i < depthData.length; i++) {
    int depth = depthData[i];
    int brightness = map(depth, 0, 2000, 255, 0); // Adjust range as needed
    brightness = constrain(brightness, 0, 255);
    int x = i % 640;
    int y = i / 640;
    stroke(brightness);
    point(x, y);
  }
}

Copy and paste this code into your Processing editor and run it. You should see a grayscale image representing the depth data from the Kinect. Closer objects will appear brighter, and farther objects will be darker.

Dissecting the Code: A Line-by-Line Explanation

Let's take a closer look at what's happening in this code. Understanding each line will empower you to modify and expand upon it for your own creative projects. First, import SimpleOpenNI.*; imports the Simple OpenNI library, giving you access to all its functions. Think of it as including a toolbox filled with Kinect-related tools. Next, SimpleOpenNI kinect; declares a variable named 'kinect' of type SimpleOpenNI. This is how you'll interact with the Kinect sensor. In the setup() function, which runs once at the beginning of the program, size(640, 480); sets the size of the Processing window to 640x480 pixels, matching the resolution of the Kinect's depth sensor. Then, kinect = new SimpleOpenNI(this); creates a new SimpleOpenNI object and assigns it to the 'kinect' variable. The this keyword refers to the current Processing sketch. kinect.enableDepth(); tells the Kinect to start capturing depth data, which is the distance of objects from the sensor. kinect.init(); initializes the Kinect sensor. This is a crucial step that prepares the Kinect for use. Now, let's move on to the draw() function, which runs repeatedly in a loop. kinect.update(); updates the Kinect's data, grabbing the latest depth information. int[] depthData = kinect.depthMap(); retrieves the depth data as an array of integers. Each integer represents the depth value for a specific pixel in the 640x480 depth image. The loop for (int i = 0; i < depthData.length; i++) iterates through each pixel in the depth image. Inside the loop, int depth = depthData[i]; gets the depth value for the current pixel. int brightness = map(depth, 0, 2000, 255, 0); maps the depth value to a brightness value between 0 and 255. The map() function takes a value within a given range (0 to 2000 in this case, representing the minimum and maximum depth values) and scales it to a new range (255 to 0, representing the brightness levels). The range of 0 to 2000 might need adjusting depending on your environment. brightness = constrain(brightness, 0, 255); ensures that the brightness value stays within the valid range of 0 to 255. int x = i % 640; calculates the x-coordinate of the pixel based on its index in the depthData array. int y = i / 640; calculates the y-coordinate of the pixel. stroke(brightness); sets the drawing color to the calculated brightness value. point(x, y); draws a point at the calculated x and y coordinates with the specified brightness. This process is repeated for each pixel, creating a grayscale representation of the depth image. By understanding the function of each line, you can start experimenting with different ways to visualize and interact with the Kinect's depth data.

Getting User Joint Positions

One of the coolest things about the Kinect is its ability to track human skeletons. Let's see how to get the joint positions of a user:

import SimpleOpenNI.*;

SimpleOpenNI kinect;
int userId = 1; // The ID of the user to track

void setup() {
  size(640, 480);
  kinect = new SimpleOpenNI(this);
  kinect.enableDepth();
  kinect.enableUser();
  kinect.init();

  kinect.setMirror(true); // Mirror the image
}

void draw() {
  kinect.update();
  background(0); // Clear the background

  if (kinect.isTrackingSkeleton(userId)) {
    PVector rightHand = new PVector();
    kinect.getJointPositionSkeleton(userId, SimpleOpenNI.JOINT_RIGHT_HAND, rightHand);

    // Convert to screen coordinates
    PVector screenPos = kinect.convertRealWorldToProjective(rightHand);

    ellipse(screenPos.x, screenPos.y, 20, 20);
  }
}

void userNew(int id) {
  println("New user detected: " + id);
  kinect.startTrackingSkeleton(id);
}

This code tracks the right hand of the first user detected and draws an ellipse at its location. Make sure you are in the Kinect's field of view for it to detect you!

Unpacking the Skeleton Tracking Code

Alright, let's dissect this skeleton tracking code to understand how it works. This example builds upon the previous one and introduces the concept of user tracking and joint positions. First off, we have the familiar import SimpleOpenNI.*; which, as before, imports the necessary library. Then, SimpleOpenNI kinect; declares our Kinect object. A new line int userId = 1; declares an integer variable to hold the ID of the user we want to track. Here, we're assuming the first user detected will be assigned ID 1. It's important to remember that the Kinect can track multiple users, each with a unique ID. In the setup() function, after initializing the Kinect and enabling depth data, we have kinect.enableUser();. This line tells the Kinect to start detecting and tracking users. Following that, kinect.setMirror(true); mirrors the image displayed. This is often preferred as it feels more natural to the user. In the draw() function, kinect.update(); updates the Kinect data, and background(0); clears the background with black on each frame. The core of the skeleton tracking logic lies within the if (kinect.isTrackingSkeleton(userId)) statement. This checks if the Kinect is currently tracking a skeleton with the specified userId. If a skeleton is being tracked, the code proceeds to get the position of the right hand. PVector rightHand = new PVector(); creates a PVector object to store the 3D coordinates of the right hand. kinect.getJointPositionSkeleton(userId, SimpleOpenNI.JOINT_RIGHT_HAND, rightHand); retrieves the 3D position of the right hand joint for the specified user and stores it in the rightHand variable. SimpleOpenNI.JOINT_RIGHT_HAND is a constant that specifies which joint to retrieve. The rightHand variable now contains the 3D coordinates of the right hand in the Kinect's coordinate system. To display this position on the screen, we need to convert these 3D coordinates to 2D screen coordinates. This is done using PVector screenPos = kinect.convertRealWorldToProjective(rightHand);. This line uses the convertRealWorldToProjective() function to project the 3D point onto the 2D screen. ellipse(screenPos.x, screenPos.y, 20, 20); draws an ellipse at the calculated screen coordinates, marking the position of the right hand. Finally, we have the userNew(int id) function. This function is automatically called whenever a new user is detected by the Kinect. Inside this function, `println(