• Kinect for Windows Product Blog

    Using Kinect Background Removal with Multiple Users


    Introduction: Background Removal in Kinect for Windows

    The 1.8 release of the Kinect for Windows Developer Toolkit includes a component for isolating a user from the background of the scene. The component is called the BackgroundRemovedColorStream. This capability has many possible uses, such as simulating chroma-key or “green-screen” replacement of the background – without needing to use an actual green screen; compositing a person’s image into a virtual environment; or simply blurring out the background, so that video conference participants can’t see how messy your office really is.


    To use this feature in an application, you create the BackgroundRemovedColorStream, and then feed it each incoming color, depth, and skeleton frame when they are delivered by your Kinect for Windows sensor. You also specify which user you want to isolate, using their skeleton tracking ID. The BackgroundRemovedColorStream produces a sequence of color frames, in BGRA (blue/green/red/alpha) format. These frames are identical in content to the original color frames from the sensor, except that the alpha channel is used to distinguish foreground pixels from background pixels. Pixels that the background removal algorithm considers part of the background will have an alpha value of 0 (fully transparent), while foreground pixels will have their alpha at 255 (fully opaque). The foreground region is given a smoother edge by using intermediate alpha values (between 0 and 255) for a “feathering” effect. This image format makes it easy to combine the background-removed frames with other images in your application.

    As a developer, you get the choice of which user you want in the foreground. The BackgroundRemovalBasics-WPF sample has some simple logic that selects the user nearest the sensor, and then continues to track the same user until they are no longer visible in the scene.

    private void ChooseSkeleton()
        var isTrackedSkeltonVisible = false;
        var nearestDistance = float.MaxValue;
        var nearestSkeleton = 0;
        foreach (var skel in this.skeletons)
            if (null == skel)
            if (skel.TrackingState != SkeletonTrackingState.Tracked)
            if (skel.TrackingId == this.currentlyTrackedSkeletonId)
                isTrackedSkeltonVisible = true;
            if (skel.Position.Z < nearestDistance)
                nearestDistance = skel.Position.Z;
                nearestSkeleton = skel.TrackingId;
        if (!isTrackedSkeltonVisible && nearestSkeleton != 0)
            this.currentlyTrackedSkeletonId = nearestSkeleton;

    Wait, only one person?

    If you wanted to select more than one person from the scene to appear in the foreground, it would seem that you’re out of luck, because the BackgroundRemovedColorStream’s SetTrackedPlayer method accepts only one tracking ID. But you can work around this limitation by running two separate instances of the stream, and sending each one a different tracking ID. Each of these streams will produce a separate color image, containing one of the users. These images can then be combined into a single image, or used separately, depending on your application’s needs.

    Wait, only two people?

    In the most straightforward implementation of the multiple stream approach, you’d be limited to tracking just two people, due to an inherent limitation in the skeleton tracking capability of Kinect for Windows. Only two skeletons at a time can be tracked with full joint-level fidelity. The joint positions are required by the background removal implementation in order to perform its job accurately.

    However, there is an additional trick we can apply, to escape the two-skeleton limit. This trick relies on an assumption that the people in the scene will not be moving at extremely high velocities (generally a safe bet). If a particular skeleton is not fully tracked for a frame or two, we can instead reuse the most recent frame in which that skeleton actually was fully tracked. Since the skeleton tracking API lets us choose which two skeletons to track at full fidelity, we can choose a different pair of skeletons each frame, cycling through up to six skeletons we wish to track, over three successive frames.

    Each additional instance of BackgroundRemovedColor stream will place increased demands on CPU and memory. Depending on your own application’s needs and your hardware configuration, you may need to dial back the number of simultaneous users you can process in this way.

    Wait, only six people?

    Demanding, aren’t we? Sorry, the Kinect for Windows skeleton stream can monitor at most six people simultaneously (two at full fidelity, and four at lower fidelity). This is a hard limit.

    Introducing a multi-user background removal sample

    We’ve created a new sample application, called BackgroundRemovalMultiUser-WPF, to demonstrate how to use the technique described above to perform background removal on up to six people. We started with the code from the BackgroundRemovalBasics-WPF sample, and changed it to support multiple streams, one per user. The output from each stream is then overlaid on the backdrop image.


    Factoring the code: TrackableUser

    The largest change to the original sample was refactoring the application code that interacts the BackgroundRemovedColorStream, so that we can have multiple copies of it running simultaneously. This code, in the new sample, resides in a new class named TrackableUser. Let’s take a brief tour of the interesting parts of this class.

    The application can instruct TrackableUser to track a specific user by setting the TrackingId property appropriately.

    public int TrackingId
            return this.trackingId;
            if (value != this.trackingId)
                if (null != this.backgroundRemovedColorStream)
                    if (InvalidTrackingId != value)
                        this.Timestamp = DateTime.UtcNow;
                        // Hide the last frame that was received for this user.
                        this.imageControl.Visibility = Visibility.Hidden;      
                        this.Timestamp = DateTime.MinValue;
                this.trackingId = value;

    The Timestamp property indicates when the TrackingId was most recently set to a valid value. We’ll see later how this property is used by the sample application’s user-selection logic.

    public DateTime Timestamp { get; private set; }

    Whenever the application is notified that the default Kinect sensor has changed (at startup time, or when the hardware is plugged in or unplugged), it passes this information along to each TrackableUser by calling OnKinectSensorChanged. The TrackableUser, in turn, sets up or tears down its BackgroundRemovedColorStream accordingly.

    public void OnKinectSensorChanged(KinectSensor oldSensor, KinectSensor newSensor)
        if (null != oldSensor)
            // Remove sensor frame event handler.
            oldSensor.AllFramesReady -= this.SensorAllFramesReady;
            // Tear down the BackgroundRemovedColorStream for this user.
            this.backgroundRemovedColorStream.BackgroundRemovedFrameReady -=
            this.backgroundRemovedColorStream = null;
            this.TrackingId = InvalidTrackingId;
        this.sensor = newSensor;
        if (null != newSensor)
            // Setup a new BackgroundRemovedColorStream for this user.
            this.backgroundRemovedColorStream = new BackgroundRemovedColorStream(newSensor);
            this.backgroundRemovedColorStream.BackgroundRemovedFrameReady +=
            // Add an event handler to be called when there is new frame data from the sensor.
            newSensor.AllFramesReady += this.SensorAllFramesReady;

    Each time the Kinect sensor produces a matched set of depth, color, and skeleton frames, we forward each frame’s data along to the BackgroundRemovedColorStream.

    private void SensorAllFramesReady(object sender, AllFramesReadyEventArgs e)
            if (this.IsTracked)
                using (var depthFrame = e.OpenDepthImageFrame())
                    if (null != depthFrame)
                         // Process depth data for background removal.
                using (var colorFrame = e.OpenColorImageFrame())      
                    if (null != colorFrame)      
                        // Process color data for background removal.
                using (var skeletonFrame = e.OpenSkeletonFrame())
                    if (null != skeletonFrame)
                        // Save skeleton frame data for subsequent processing.
                        // Locate the most recent data in which this user was fully tracked.
                        bool isUserPresent = UpdateTrackedSkeletonsArray();
                        // If we have an array in which this user is fully tracked,
                        // process the skeleton data for background removal.
                        if (isUserPresent && null != this.skeletonsTracked)

    The UpdateTrackedSkeletonsArray method implements the logic to reuse skeleton data from an older frame when the newest frame contains the user’s skeleton, but not in a fully-tracked state. It also informs the caller whether the user with the requested tracking ID is still present in the scene.

    private bool UpdateTrackedSkeletonsArray()
        // Determine if this user is still present in the scene.
        bool isUserPresent = false;
        foreach (var skeleton in this.skeletonsNew)
            if (skeleton.TrackingId == this.TrackingId)
                isUserPresent = true;
                if (skeleton.TrackingState == SkeletonTrackingState.Tracked)
                    // User is fully tracked: save the new array of skeletons,
                    // and recycle the old saved array for reuse next time.
                    var temp = this.skeletonsTracked;
                    this.skeletonsTracked = this.skeletonsNew;
                    this.skeletonsNew = temp;
        if (!isUserPresent)
            // User has disappeared; stop trying to track.
            this.TrackingId = TrackableUser.InvalidTrackingId;
        return isUserPresent;

    Whenever the BackgroundRemovedColorStream produces a frame, we copy its BGRA data to the bitmap that is the underlying Source for an Image element in the MainWindow. This causes the updated frame to appear within the application’s window, overlaid on the background image.

    private void BackgroundRemovedFrameReadyHandler(
        object sender,
        BackgroundRemovedColorFrameReadyEventArgs e)
        using (var backgroundRemovedFrame = e.OpenBackgroundRemovedColorFrame())
             if (null != backgroundRemovedFrame && this.IsTracked)
                 int width = backgroundRemovedFrame.Width;
                 int height = backgroundRemovedFrame.Height;
                 WriteableBitmap foregroundBitmap =
                    this.imageControl.Source as WriteableBitmap;
                // If necessary, allocate new bitmap. Set it as the source of the Image
                // control.
                if (null == foregroundBitmap ||
                    foregroundBitmap.PixelWidth != width ||
                    foregroundBitmap.PixelHeight != height)
                    foregroundBitmap = new WriteableBitmap(
                    this.imageControl.Source = foregroundBitmap;
                // Write the pixel data into our bitmap.
                    new Int32Rect(0, 0, width, height),
                    width * sizeof(uint),
                // A frame has been delivered; ensure that it is visible.
                this.imageControl.Visibility = Visibility.Visible;

    Limiting the number of users to track

    As mentioned earlier, the maximum number of trackable users may have a practical limit, depending on your hardware. To specify the limit, we define a constant in the MainWindow class:

    private const int MaxUsers = 6;

    You can modify this constant to have any value from 2 to 6. (Values larger than 6 are not useful, as Kinect for Windows does not track more than 6 users.)

    Selecting users to track: The User View

    We want to provide a convenient way to choose which users will be tracked for background removal. To do this, we present a view of the detected users in a small inset. By clicking on the users displayed in this inset, we can select which of those users are associated with our TrackableUser objects, causing them to be included in the foreground.


    We update the user view each time a depth frame is received by the sample’s main window.

    private void UpdateUserView(DepthImageFrame depthFrame)
        // Store the depth data.
        // Write the per-user colors into the user view bitmap, one pixel at a time.
            uint* userViewBits = (uint*)this.userViewBitmap.BackBuffer;
            fixed (uint* userColors = &this.userColors[0])
                // Walk through each pixel in the depth data.
                fixed (DepthImagePixel* depthData = &this.depthData[0])      
                    DepthImagePixel* depthPixel = depthData;
                    DepthImagePixel* depthPixelEnd = depthPixel + this.depthData.Length;
                    while (depthPixel < depthPixelEnd)
                        // Lookup a pixel color based on the player index.
                        // Store the color in the user view bitmap's buffer.
                        *(userViewBits++) = *(userColors + (depthPixel++)->PlayerIndex);
        this.userViewBitmap.AddDirtyRect(new Int32Rect(0, 0, width, height));

    This code fills the user view bitmap with solid-colored regions representing each of the detected users, as distinguished by the value of the PlayerIndex field at each pixel in the depth frame.

    The main window responds to a mouse click within the user view by locating the corresponding pixel in the most recent depth frame, and using its PlayerIndex to look up the user’s TrackingId in the most recent skeleton data. The TrackingID is passed along to the ToggleUserTracking method, which will attempt to toggle the tracking of that TrackingID between the tracked and untracked states.

    private void UserViewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        // Determine which pixel in the depth image was clicked.
        Point p = e.GetPosition(this.UserView);
        int depthX =
            (int)(p.X * this.userViewBitmap.PixelWidth / this.UserView.ActualWidth);
        int depthY =
            (int)(p.Y * this.userViewBitmap.PixelHeight / this.UserView.ActualHeight);
        int pixelIndex = (depthY * this.userViewBitmap.PixelWidth) + depthX;
        if (pixelIndex >= 0 && pixelIndex < this.depthData.Length)
            // Find the player index in the depth image. If non-zero, toggle background
            // removal for the corresponding user.
            short playerIndex = this.depthData[pixelIndex].PlayerIndex;
            if (playerIndex > 0)
                // playerIndex is 1-based, skeletons array is 0-based, so subtract 1.
                this.ToggleUserTracking(this.skeletons[playerIndex - 1].TrackingId);

    Picking which users will be tracked

    When MaxUsers is less than 6, we need some logic to handle a click on an untracked user, and we are already tracking the maximum number of users. We choose to stop tracking the user who was tracked earliest (based on timestamp), and start tracking the newly chosen user immediately. This logic is implemented in ToggleUserTracking.

    private void ToggleUserTracking(int trackingId)
        if (TrackableUser.InvalidTrackingId != trackingId)
            DateTime minTimestamp = DateTime.MaxValue;
            TrackableUser trackedUser = null;
            TrackableUser staleUser = null;
            // Attempt to find a TrackableUser with a matching TrackingId.
            foreach (var user in this.trackableUsers)
                if (user.TrackingId == trackingId)
                    // Yes, this TrackableUser has a matching TrackingId.
                    trackedUser = user;
                // Find the "stale" user (the trackable user with the earliest timestamp).
                if (user.Timestamp < minTimestamp)
                    staleUser = user;
                    minTimestamp = user.Timestamp;
            if (null != trackedUser)
                // User is being tracked: toggle to not tracked.
                trackedUser.TrackingId = TrackableUser.InvalidTrackingId;
                // User is not currently being tracked: start tracking, by reusing
                // the "stale" trackable user.
                staleUser.TrackingId = trackingId;

    Once we’ve determined which users will be tracked by the TrackableUser objects, we need to ensure that those users are being targeted for tracking by the skeleton stream on a regular basis (at least once every three frames). UpdateChosenSkeletons implements this using a round-robin scheme.

    private void UpdateChosenSkeletons()
        KinectSensor sensor = this.sensorChooser.Kinect;
        if (null != sensor)
            // Choose which of the users will be tracked in the next frame.
            int trackedUserCount = 0;
            for (int i = 0; i < MaxUsers && trackedUserCount < this.trackingIds.Length; ++i)
                // Get the trackable user for consideration.
                var trackableUser = this.trackableUsers[this.nextUserIndex];
                if (trackableUser.IsTracked)
                    // If this user is currently being tracked, copy its TrackingId to the
                    // array of chosen users.
                    this.trackingIds[trackedUserCount++] = trackableUser.TrackingId;
                // Update the index for the next user to be considered.
                this.nextUserIndex = (this.nextUserIndex + 1) % MaxUsers;
            // Fill any unused slots with InvalidTrackingId.
            for (int i = trackedUserCount; i < this.trackingIds.Length; ++i)
                this.trackingIds[i] = TrackableUser.InvalidTrackingId;
            // Pass the chosen tracking IDs to the skeleton stream.
            sensor.SkeletonStream.ChooseSkeletons(this.trackingIds[0], this.trackingIds[1]);

    Combining multiple foreground images

    Now that we can have multiple instances of TrackableUser, each producing a background-removed image of a user, we need to combine those images on-screen. We do this by creating multiple overlapping Image elements (one per trackable user), each parented by the MaskedColorImages element, which itself is a sibling of the Backdrop element. Wherever the background has been removed from each image, the backdrop image will show through.

    As each image is created, we associate it with its own TrackableUser.

    public MainWindow()
        // Create one Image control per trackable user.
        for (int i = 0; i < MaxUsers; ++i)
            Image image = new Image();
            this.trackableUsers[i] = new TrackableUser(image);

    To capture and save a snapshot of the current composited image, we create two VisualBrush objects, one for the Backdrop, and one for MaskedColorImages. We draw rectangles with each of these brushes, into a bitmap, and then write the bitmap to a file.

    private void ButtonScreenshotClick(object sender, RoutedEventArgs e)
        var dv = new DrawingVisual();
        using (var dc = dv.RenderOpen())
            // Render the backdrop.
            var backdropBrush = new VisualBrush(Backdrop);      
                new Rect(new Point(), new Size(colorWidth, colorHeight)));
            // Render the foreground.
            var colorBrush = new VisualBrush(MaskedColorImages);      
                new Rect(new Point(), new Size(colorWidth, colorHeight)));


    While the BackgroundRemovedColorStream is limited to tracking only one user at a time, the new BackgroundRemovalMultiUser-WPF sample demonstrates that you can run multiple stream instances to track up to six users simultaneously. When using this technique, you should consider – and measure – the increased resource demands (CPU and memory) that the additional background removal streams will have, and determine for yourself how many streams your configuration can handle.

    We hope that this sample opens up new possibilities for using background removal in your own applications.

    John Elsbree
    Principal Software Development Engineer
    Kinect for Windows

  • Kinect for Windows Product Blog

    Enabling retailers to drive business in new, innovative ways


    It is essential for retailers to find ways to attract and connect with customers—and to stand out from the competition. To help them do so, the industry is grappling with how to build interactive experiences at scale that engage and truly help customers make satisfying purchasing decisions while also using retail space strategically to provide the best possible experience.

    To get a deeper understanding of what this means, we did extensive first-hand research with dozens of retailers and big brands . We learned how retailers think about implementing natural user interface technology (NUI) and how they see these experiences helping propel their businesses forward.

    What we heard:

    • NUI offers one of the best ways to interact with large screens in stores.
    • Exploring virtual merchandise by gesturing naturally is easy, engaging, and fun for customers.
    • Immersive experiences can improve the purchase process and are an impactful way to market and sell to customers.

    We agree. And we believe it’s important for us to bring these findings back into Kinect for Windows by delivering features that facilitate the best retail innovations. To help support this, we recently released an update to our SDK (Kinect for Windows SDK 1.8) that includes new features specifically designed to enable the development of higher-quality digital signage applications. Key features include the ability to remove backgrounds, an adaptive UI sample, and an HTML interaction sample.

    To help illustrate what this all means, our team developed the following three videos. They show how Kinect for Windows experiences can help retailers attract new customers and engage customers in deeper ways. They offer examples of ways that digital signs powered by Kinect for Windows can draw customers into the business—making it possible for retailers to share offerings, cross-sell and upsell merchandise, bring the “endless aisle” concept to life, and, ultimately, inspire shoppers to purchase. And all of this is accomplished in a beautiful way that feels natural to the customer.

    This enjoyable and easy-to-use application engages new customers by helping them understand and experience the resort, while also providing them with an offer to receive a discount on future stays.

    This digital sign application is powered by Kinect for Windows and makes it easy for shoppers to engage with products, try them on, and purchase them. It also incorporates social media for additional marketing reach.

    This last video demonstrates the ability to welcome a person or people into an immersive real-time experience with the store’s merchandise. It demonstrates the Kinect Fusion scanning features that can be used as part of this and many other retail experiences.

    These videos highlight some of the core benefits retailers tell us Kinect for Windows offers them:

    • Capture a customer's attention
    • Educate customers about products
    • Move a customer through the decision-making cycle to close a sale

    Kinect for Windows does this by optimizing interactions with existing large screens and enhancing the overall retail space—using gesture and voice control, background removal, proximity-based interface, and more.

    So many companies have already created exciting retail experiences with Kinect for Windows: Bloomingdales, Build-a-Bear, Coca-Cola, Mattel, Nissan, Pepsi, and others. We are excited to see the new ways that Kinect for Windows is being applied in retail. The dramatic shifts in consumer shopping behaviors, preferences, and expectations in retail today are driving innovation to new levels. The possibilities are endless when we use the latest technology to put the customer at the heart of the business.

    Kinect for Windows Team

    Key links




  • Kinect for Windows Product Blog

    Using Kinect Webserver to Expose Speech Events to Web Clients


    In our 1.8 release, we made it easy to create Kinect-enabled HTML5 web applications. This is possible because we added an extensible webserver for Kinect data along with a Javascript API which gives developers some great functionality right out of the box:

    • Interactions : hand pointer movements, press and grip events useful for controlling a cursor, buttons and other UI
    • User Viewer: visual representation of the users currently visible to Kinect sensor. Uses different colors to indicate different user states
    • Background Removal: “Green screen” image stream for a single person at a time
    • Skeleton: standard skeleton data such as tracking state, joint positions, joint orientations, etc.
    • Sensor Status: Events corresponding to sensor connection/disconnection

    This is enough functionality to write a compelling application but it doesn’t represent the whole range of Kinect sensor capabilities. In this article I will show you step-by-step how to extend the WebserverBasics-WPF sample (see C# code in CodePlex  or documentation in MSDN) available from Kinect Toolkit Browser to enable web applications to respond to speech commands, where the active speech grammar is configurable by the web client.

    A solution containing the full, final sample code is available on CodePlex. To compile this sample you will also need Microsoft.Samples.Kinect.Webserver (available via CodePlex and Toolkit Browser) and Microsoft.Kinect.Toolkit components (available via Toolkit Browser).

    Getting Started

    To follow along step-by-step:

    1. If you haven’t done so already, install the Kinect for Windows v1.8 SDK and Toolkit
    2. Launch the Kinect Toolkit Browser
    3. Install WebserverBasics-WPF sample in a local directory
    4. Open the WebserverBasics-WPF.sln solution in Visual Studio
    5. Go to line 136 in MainWindow.xaml.cs file

    You should see the following TODO comment which describes exactly how we’re going to expose speech recognition functionality:

    //// TODO: Optionally add factories here for custom handlers:
    ////       this.webserver.SensorStreamHandlerFactories.Add(new MyCustomSensorStreamHandlerFactory());
    //// Your custom factory would implement ISensorStreamHandlerFactory, in which the
    //// CreateHandler method would return a class derived from SensorStreamHandlerBase
    //// which overrides one or more of its virtual methods.

    We will replace this comment with the functionality described below.

    So, What Functionality Are We Implementing?


    More specifically, on the server side we will:

    1. Create a speech recognition engine
    2. Bind the engine to a Kinect sensor’s audio stream whenever sensor gets connected/disconnected
    3. Allow a web client to specify the speech grammar to be recognized
    4. Forward speech recognition events generated by engine to web client
    5. Registering a factory for the speech stream handler with the Kinect webserver

    This will be accomplished by creating a class called SpeechStreamHandler, derived fromMicrosoft.Samples.Kinect.Webserver.Sensor.SensorStreamHandlerBase. SensorStreamHandlerBase is an implementation of ISensorStreamHandler that frees us from writing boilerplate code. ISensorStreamHandler is an abstraction that gets notified whenever a Kinect sensor gets connected/disconnected, when color, depth and skeleton frames become available and when web clients request to view or update configuration values. In response, our speech stream handler will send event messages to web clients.

    On the web client side we will:

    1. Configure speech recognition stream (enable and specify the speech grammar to be recognized)
    2. Modify the web UI in response to recognized speech events

    All new client-side code is in SamplePage.html

    Creating a Speech Recognition Engine

    In the constructor for SpeechStreamHandler you’ll see the following code:

    RecognizerInfo ri = GetKinectRecognizer();
    if (ri != null)
        this.speechEngine = new SpeechRecognitionEngine(ri.Id);

        if (this.speechEngine != null)
            // disable speech engine adaptation feature
            this.speechEngine.UpdateRecognizerSetting("AdaptationOn", 0);
            this.speechEngine.UpdateRecognizerSetting("PersistedBackgroundAdaptation", 0);
            this.speechEngine.AudioStateChanged += this.AudioStateChanged;
            this.speechEngine.SpeechRecognitionRejected += this.SpeechRecognitionRejected;
            this.speechEngine.SpeechRecognized += this.SpeechRecognized;

    This code snippet will be familiar if you’ve looked at some of our other speech samples such as SpeechBasics-WPF. Basically, we’re getting the metadata corresponding to the Kinect acoustic model (GetKinectRecognizer is hardcoded to use English language acoustic model in this sample, but this can be changed by installing additional language packs and modifying GetKinectRecognizer to look for the desired culture name), using it to create a speech engine, turning off some settings related to audio adaptation feature (which makes speech engine better suited for long-running scenarios) and registering to receive events when speech is recognized or rejected, or when audio state (e.g.: silence vs someone speaking) changes.

    Binding the Speech Recognition Engine to a Kinect Sensor’s Audio Stream

    In order to do this, we override SensorStreamHandlerBase’s implementation of OnSensorChanged, so we can find out about sensors connecting and disconnecting.

    public override void OnSensorChanged(KinectSensor newSensor)
        if (this.sensor != null)
            if (this.speechEngine != null)

        this.sensor = newSensor;
        if (newSensor != null)
            if (this.speechEngine != null)
                    newSensor.AudioSource.Start(), new SpeechAudioFormatInfo(EncodingFormat.Pcm, 16000, 16, 1, 32000, 2, null));

    The main thing we need to do here is Start the AudioSource of the newly connected Kinect sensor in order to get an audio stream that we can hook up as the input to the speech engine. We also need to specify the format of the audio stream, which is a single-channel, 16-bits per sample, Pulse Code Modulation (PCM) stream, sampled at 16kHz.

    Allow Web Clients to Specify Speech Grammar

    We will let clients send us the whole speech grammar that they want recognized, as XML that conforms to the W3C Speech Recognition Grammar Specification format version 1.0. To do this, we will expose a configuration property called “grammarXml”.

    Let’s backtrack a little bit because earlier we glossed over the bit of code in the SpeechStreamHandler constructor where we register the handlers for getting and setting stream configuration properties:

    this.AddStreamConfiguration(SpeechEventCategory, new StreamConfiguration(this.GetProperties, this.SetProperty));

    Now, in the SetProperty method we call LoadGrammarXml method whenever a client sets the “grammarXml” property:

    case GrammarXmlPropertyName:

    And in the LoadGrammarXml method we do the real work of updating the speech grammar:

    private void LoadGrammarXml(string grammarXml)

        if (!string.IsNullOrEmpty(grammarXml))
            using (var memoryStream = new MemoryStream(Encoding.UTF8.GetBytes(grammarXml)))
                Grammar newGrammar;
                    newGrammar = new Grammar(memoryStream);
                catch (ArgumentException e)
                    throw new InvalidOperationException("Requested grammar might not contain a root rule", e);
                catch (FormatException e)
                    throw new InvalidOperationException("Requested grammar was specified with an invalid format", e);


    We first stop the speech recognition because we don’t yet know if the specified grammar is going to be valid or not, then we try to create a new Microsoft.Speech.Recognition.Grammar object from the specified property value. If the property value does not represent a valid grammar, newGrammar variable will remain null. Finally, we call StartRecognition method, which loads the grammar into the speech engine (if grammar is valid), and tells the speech engine to start recognizing and keep recognizing speech phrases until we explicitly tell it to stop.

    private void StartRecognition(Grammar g)
        if ((this.sensor != null) && (g != null))

        this.grammar = g;

    Send Speech Recognition Events to Web Client

    When we created the speech recognition engine, we registered for 3 events: AudioStateChanged, SpeechRecognized and SpeechRecognitionRejected. Whenever any of these events happen we just want to forward the event to the web client. Since the code ends up being very similar, we will focus on the SpeechRecognized event handler:

    private async void SpeechRecognized(object sender, SpeechRecognizedEventArgs args)
        var message = new RecognizedSpeechMessage(args);
        await this.ownerContext.SendEventMessageAsync(message);

    To send messages to web clients we use functionality exposed by ownerContext, which is an instance of the SensorStreamHandlerContext class which was passed to us in the constructor. The messages are sent to clients using a web socket channel, and could be

    • Stream messages: Messages that are generated continuously, at a predictable rate (e.g.: 30 skeleton stream frames are generated every second), where the data from each message replaces the data from the previous message. If we drop one of these messages every so often there is no major consequence because another will arrive shortly thereafter with more up-to-date data, so the framework might decide to drop one of these messages if it detects a bottleneck in the web socket channel.
    • Event messages: Messages that are generated sporadically, at an unpredictable rate, where each event represents an isolated incident. As such, it is not desirable to drop any one of these kind of messages.

    Given the nature of speech recognition, we chose to communicate with clients using event messages. Specifically, we created the RecognizedSpeechMessage class, which is a subclass of EventMessage that serves as a representation of SpeechRecognizedEventArgs which can be easily serialized as JSON and follows the JavaScript naming conventions.

    You might have noticed the usage of the “async” and “await” keywords in this snippet. They are described in much more detail in MSDN but, in summary, they enable an asynchronous programming model so that long-running operations don’t block thread execution while not necessarily using more than one thread. The Kinect webserver uses a single thread to schedule tasks so the consequence for you is that ISensorStreamHandler implementations don’t need to be thread-safe, but should be aware of potential re-entrancy due to asynchronous behavior.

    Registering a Speech Stream Handler Factory with the Kinect Webserver

    The Kinect webserver can be started, stopped and restarted, and each time it is started it creates ISensorStreamHandler instances in a thread dedicated to Kinect data handling, which is the only thread that ever calls these objects. To facilitate this behavior, the server doesn’t allow for direct registration of ISensorStreamHandler instances and instead expects ISensorStreamHandlerFactory instances to be registered in KinectWebserver.SensorStreamHandlerFactories property.

    For the purposes of this sample, we declared a private factory class that is exposed as a static singleton instance directly from the SpeechStreamHandler class:

    public class SpeechStreamHandler : SensorStreamHandlerBase, IDisposable

        static SpeechStreamHandler()
            Factory = new SpeechStreamHandlerFactory();

        public static ISensorStreamHandlerFactory Factory { get; private set; }

        private class SpeechStreamHandlerFactory : ISensorStreamHandlerFactory
            public ISensorStreamHandler CreateHandler(SensorStreamHandlerContext context)
                return new SpeechStreamHandler(context);

    Finally, back in line 136 of MainWindow.xaml.cs, we replace the TODO comment mentioned above with

    // Add speech stream handler to the list of available handlers, so web client
    // can configure speech grammar and receive speech events

    Configure Speech Recognition Stream in Web Client

    The sample web client distributed with WebserverBasics-WPF is already configuring a couple of other streams in the function called updateUserState in SamplePage.html, so we will add the following code to this function:

    var speechGrammar = '\
    <grammar version="1.0" xml:lang="en-US" tag-format="semantics/1.0-literals" root="DefaultRule" xmlns="\' data-mce-href=">\'>\'>\'>\'>http://www.w3.org/2001/06/grammar">\
        <rule id="DefaultRule" scope="public">\
                    <one-of><item>Show Panel</item><item>Show</item></one-of>\
                    <one-of><item>Hide Panel</item><item>Hide</item></one-of>\

    immediateConfig["speech"] = { "enabled": true, "grammarXml": speechGrammar };

    This code enables the speech stream and specifies a grammar that

    • triggers a recognition event with “SHOW” as semantic value whenever a user utters the phrases “Show” or “Show Panel”
    • triggers a recognition event with “HIDE” as semantic value whenever a user utters the phrases “Hide” or “Hide Panel”

    Modify the web UI in response to recognized speech events

    The sample web client already registers an event handler function, so we just need to update it to respond to speech events in addition to user state events:

    function onSpeechRecognized(recognizedArgs) {
        if (recognizedArgs.confidence > 0.7) {
            switch (recognizedArgs.semantics.value) {
                case "HIDE":
                case "SHOW":

    sensor.addEventHandler(function (event) {
        switch (event.category) {
            case "speech":
                switch (event.eventType) {
                    case "recognized":

    Party Time!

    At this point you can rebuild the updated solution and run it to see the server UI. From this UI you can click on the link that reads “Open sample page in default browser” and play with the sample UI. It will look the same as before the code changes, but will respond to the speech phrases “Show”, “Show Panel”, “Hide” and “Hide Panel”. Now try changing the grammar to include more phrases and update the UI in different ways in response to speech events.

    Happy coding!

    Additional Resources

  • Kinect for Windows Product Blog

    Updated SDK, with HTML5, Kinect Fusion improvements, and more


    I am pleased to announce that we released the Kinect for Windows software development kit (SDK) 1.8 today. This is the fourth update to the SDK since we first released it commercially one and a half years ago. Since then, we’ve seen numerous companies using Kinect for Windows worldwide, and more than 700,000 downloads of our SDK.

    We build each version of the SDK with our customers in mind—listening to what the developer community and business leaders tell us they want and traveling around the globe to see what these dedicated teams do, how they do it, and what they most need out of our software development kit.

    The new background removal API is useful for advertising, augmented reality gaming, training and simulation, and more.
    The new background removal API is useful for advertising, augmented reality gaming, training
     and simulation, and more.

    Kinect for Windows SDK 1.8 includes some key features and samples that the community has been asking for, including:

    • New background removal. An API removes the background behind the active user so that it can be replaced with an artificial background. This green-screening effect was one of the top requests we’re heard in recent months. It is especially useful for advertising, augmented reality gaming, training and simulation, and other immersive experiences that place the user in a different virtual environment.
    • Realistic color capture with Kinect Fusion. A new Kinect Fusion API scans the color of the scene along with the depth information so that it can capture the color of the object along with its three-dimensional (3D) model. The API also produces a texture map for the mesh created from the scan. This feature provides a full fidelity 3D model of a scan, including color, which can be used for full color 3D printing or to create accurate 3D assets for games, CAD, and other applications.
    • Improved tracking robustness with Kinect Fusion. This algorithm makes it easier to scan a scene. With this update, Kinect Fusion is better able to maintain its lock on the scene as the camera position moves, yielding a more reliable and consistent scanning.
    • HTML interaction sample. This sample demonstrates implementing Kinect-enabled buttons, simple user engagement, and the use of a background removal stream in HTML5. It allows developers to use HTML5 and JavaScript to implement Kinect-enabled user interfaces, which was not possible previously—making it easier for developers to work in whatever programming languages they prefer and integrate Kinect for Windows into their existing solutions.
    • Multiple-sensor Kinect Fusion sample. This sample shows developers how to use two sensors simultaneously to scan a person or object from both sides—making it possible to construct a 3D model without having to move the sensor or the object! It demonstrates the calibration between two Kinect for Windows sensors, and how to use Kinect Fusion APIs with multiple depth snapshots. It is ideal for retail experiences and other public kiosks that do not include having an attendant available to scan by hand.
    • Adaptive UI sample. This sample demonstrates how to build an application that adapts itself depending on the distance between the user and the screen—from gesturing at a distance to touching a touchscreen. The algorithm in this sample uses the physical dimensions and positions of the screen and sensor to determine the best ergonomic position on the screen for touch controls as well as ways the UI can adapt as the user approaches the screen or moves further away from it. As a result, the touch interface and visual display adapt to the user’s position and height, which enables users to interact with large touch screen displays comfortably. The display can also be adapted for more than one user.

    We also have updated our Human Interface Guidelines (HIG) with guidance to complement the new Adaptive UI sample, including the following:

    Design a transition that reveals or hides additional information without obscuring the anchor points in the overall UI.
    Design a transition that reveals or hides additional information
    without obscuring the anchor points in the overall UI.

    Design UI where users can accomplish all tasks for each goal within a single range.
    Design UI where users can accomplish all tasks for each goal
    within a single range.

    My team and I believe that communicating naturally with computers means being able to gesture and speak, just like you do when communicating with people. We believe this is important to the evolution of computing, and are committed to helping this future come faster by giving our customers the tools they need to build truly innovative solutions. There are many exciting applications being created with Kinect for Windows, and we hope these new features will make those applications better and easier to build. Keep up the great work, and keep us posted!

    Bob Heddle, Director
    Kinect for Windows

    Key links

  • Kinect for Windows Product Blog

    Announcing the 1.8 SDK


    Today we are happy to announce the release of our 1.8 SDK!  Web developers can now bring the interactivity of Kinect for Windows to their world by using our new HTML5/JavaScript app model.  We've also added color to Kinect Fusion (which is mind blowing to see), created a new API for background removal, and added some other improvements and new samples too.  Our product blog has all the deets or, if you are impatient, you can just download the new bits.


    @benlower | kinectninja@microsoft.com | mobile: +1 (206) 659-NINJA (6465)

  • Kinect for Windows Product Blog

    Dev Kit Program Update


    Back in June at the Build Conference we announced and started taking applications for our upcoming developer kit program.

    The response & interest we’ve seen has been tremendous: thousands of developers from 74 different countries applied.

    Mea Culpa

    When we announced the program we said we’d start notifying successful applicants in August. Many people interpreted that to mean that we’d be done with notifications in August. I apologize for not being clearer on this. We never intended to have all the notifications done in August. While we did start in August and have notified many developers of their acceptance to the program, there are still many more applicants to be notified.

    Over the coming weeks we will continue to let applicants know if they are admitted to the program, denied admission, or waitlisted (just like college :-)). Every applicant will hear something from us by the end of September. Anyone who is waitlisted will have a final decision by the end of the year.

    We are still planning to start sending out the developer kits in late November to all program participants.

    Again, apologies for any confusion. Please stay tuned…you will hear something from us soon!


    @benlower | kinectninja@microsoft.com | mobile: +1 (206) 659-NINJA (6465)

  • Kinect for Windows Product Blog

    Joshua Blake on Kinect for Windows and the Natural User Interface Revolution (Part 3)



    The following blog post was guest authored by Kinect for Windows (K4W) MVP, Joshua Blake. Josh is the Technical Director of the InfoStrat Advanced Technology Group in Washington, D.C. where he and his team work on cutting-edge Kinect and NUI projects for their clients. You can find him on twitter @joshblake or at his blog, http://nui.joshland.org.

    Josh recently recorded several videos for our Kinect for Windows Developer Center. This is the third of three posts he will be contributing this month to the blog.


    In part 1, I shared videos covering the core natural user interface concepts and a sample application that I use to control presentations called Kinect PowerPoint Control. In part 2, I shared two more advanced sample applications: Kinect Weather Map and Face Fusion. In this post, I’m going to share videos that show some of the real-life applications that my team and I created for one of our clients. I’ll also provide some additional detail about how and why we created a custom object tracking interaction. These applications put my NUI concepts into action and show what is possible with Kinect for Windows.


    Making it fun to learn

    Our client, Kaplan Early Learning Company, sells teaching resources focused on early childhood education. Kaplan approached us with an interest in creating a series of educational applications for preschool and kindergarten-aged children designed to teach one of several core skills such as basic patterns, spelling simple words, shapes, and spatial relationships. While talking to Kaplan, we learned they had a goal of improving student engagement and excitement while making core skills fun to learn.

    We suggested using Kinect for Windows because it would allow the students to not just interact with the activity but also be immersed in virtual worlds and use their bodies and physical objects for interacting. Kaplan loved the idea and we began creating the applications. After a few iterations of design and development, testing with real students, and feedback, we shipped the final builds of four applications to Kaplan earlier this summer. Kaplan is now selling these applications bundled with a Kinect for Windows sensor in their catalog as Kaplan Move-NG.

    The Kinect for Windows team and I created the videos embedded below to discuss our approach to addressing challenges involved in designing these applications and to demonstrate the core parts of three of the Move-NG applications.


    Designing early childhood education apps for Kaplan

    In the video below, I discuss InfoStrat’s guiding principles to creating great applications for Kinect as well as some of the specific challenges we faced creating applications that are fun and exciting for young children while being educational and fitting in a classroom environment. In the next section below the video, read on for additional discussion and three more videos showing the actual applications.


    Real-world K4W apps: Designing early childhood education apps for Kaplan (7:32)




    One of the key points covered in this video is that when designing a NUI application, we have to consider the context in which the application will be used. In the education space, especially in early childhood education, this context often includes both teachers and students, so we have to design the applications with both types of users in mind. Here are a few of the questions we thought about while designing these apps for Kaplan:

    • When will the teacher use the app and when will the students use the app?
    • Will the teacher be more comfortable using the mouse or the Kinect for specific tasks? Which input device is most appropriate for each task?
    • Will non-technical teachers understand how to set up the space and use the application? Does there need to be a special setup screen to help the teacher configure the classroom space?
    • How will the teachers and students interact while the application is running?
    • How long would it take to give every student a turn in a typical size classroom?
    • What is the social context in the classroom, and what unwritten social behavior rules can we take into account to simplify the application design?
    • Will the user interaction work with both adults and the youngest children?
    • Will the user interaction work across the various ways children respond to visual cues and voice prompts?
    • Is the application fun?
    • Do students across the entire target age group understand what to do with minimal or no additional prompts from the teacher?


    And most importantly:

    • Does the design satisfy the educational goals set for the application?


    As you can imagine, finding a solution to all of these questions was quite a challenge. We took an iterative approach and tested with real children in the target age range as often as possible. Fortunately, my three daughters are in the target age range so I could do quick tests at home almost daily and get feedback. We also sent early builds to Kaplan to get a broader range of feedback from their educators and additional children.

    In several cases, we created a prototype of a design or interaction that worked well for ourselves as adults, but failed completely when tested with children. Sometimes the problem was the data from the children’s smaller bodies had more noise. Other times the problem was that the children just didn’t understand what they were supposed to do, even with prompting, guidance, or demonstration. It was particularly challenging when a concept worked with older kindergarten kids but was too complex for the youngest of the preschooler age range. In those cases there was a cognitive development milestone in the age range that the design relied upon and we simply had to find another solution. I will share an example of this near the end of this post.


    Kaplan Move-NG application and behind-the scenes videos

    The next three videos each cover one of the Kaplan Move-NG applications. The videos introduce the educational goal of the app and show a demonstration of the core interaction. In addition, I discuss the design challenges mentioned above as well as implementation details such as what parts of the Kinect for Windows SDK we used, how we created a particular interaction, or how feedback from student testing affected the application design. These videos should give you a quick overview of the apps as well as a behind-the-scenes view into what went into the designs.  I hope sharing our experience will help you create better applications which incorporate the interactivity and fun of Kinect.


    Real-world K4W apps: Kaplan Move-NG Patterns (6:28)






    Real-world K4W apps: Kaplan Move-NG Where Am I (5:57)






    Real-world K4W apps: Kaplan Move-NG Word Pop (7:41)





    Object tracking as a natural interaction

    The last video above showed Word Pop, which has the unique feature of letting the user spell words by catching letters with a physical basket (or box). In the video, I showed how we created a custom basket tracker by transforming the Kinect depth data. (My technique was inspired by Kyle McDonald’s work at the Art && Code 2011 conference, as shown at 1:43 in his festival demonstration.) Figure 1 shows the basket tracker developer UI as shown in the Word Pop video. In this section, I’m going to give a little more detail on how this basket tracker works and what led to this design.

    fig1 - box tracking
    Figure 1: The basket tracker developer UI used internally during development of Word Pop. The left image in the interface shows the background removed user and basket, with a rectangle drawn around the basket. The right image shows a visualization of how the application is transforming the depth data.

    To find the basket, we excluded the background and user’s torso from the depth image and then applied the Sobel operator. This produces a gradient value representing the curvature at each point. We mark pixels with low curvature as flat pixels, shown in white in figure 1. The curvature threshold value for determining flat pixels was found empirically.

    The outline of the basket is determined by using histograms of flat pixels across the horizontal and vertical dimensions, shown along the top and left edges of the right image in figure 1. The largest continuous area of flat pixels in each dimension is assumed to be the basket. The basket area is expanded slightly, smoothed across frames, and then the application hit tests this area against the letters falling from the sky to determine when the student has caught a letter.

    In testing, we found this implementation to be robust even when the user moves the basket around quickly or holds it out at the end of one arm. In particular, we did not need to depend upon skeleton tracking, which was often interrupted by the basket itself.

    One of our early Word Pop prototypes used hand-based interaction with skeleton tracking, but this was challenging for the youngest children in the target age range to use or understand. For example, given a prompt of “touch the letter M”, my three-year-old would always run to the computer screen to touch the “M” physically rather than moving her mirror image avatar to touch it. On the other hand, my seven-year-old used the avatar without a problem, illustrating the cognitive development milestone challenge I mentioned earlier. When we added the basket, skeleton tracking data became worse, but we could easily track the interactions of even the youngest children. Since “catching” with the basket has only one physical interpretation – using the avatar image – the younger kids started interacting without trouble.

    The basket in Word Pop was a very simple and natural interaction that the children immediately understood. This may seem like a basic point, but it is a perfect example of what makes Kinect unique and important: Kinect lets the computer see and understand our real world, instead of us having to learn and understand the computer. In this case, the Kinect let the children reuse a skill they already had – catching things in baskets – and focus on the fun and educational aspects of the application, rather than being distracted by learning a complex interface.

    I hope you enjoyed a look behind-the-scenes of our design process and seeing how we approached the challenge of designing fun and educational Kinect applications for young children. Thanks to Ben Lower for giving me the opportunity to record the videos in this post and the previous installments. Please feel free to comment or contact me if you have any questions or feedback on anything in this series. (Don’t forget to check out part 1 and part 2 if you haven’t seen those posts and videos already.)

    Thanks for reading (and watching)!


    @joshblake | joshb@infostrat.com | mobile +1 (703) 946-7176 | http://nui.joshland.org

  • Kinect for Windows Product Blog

    Joshua Blake on Kinect and the Natural User Interface Revolution (Part 2)



    The following blog post was guest authored by K4W MVP, Joshua Blake. Josh is the Technical Director of the InfoStrat Advanced Technology Group in Washington, D.C where he and his team work on cutting-edge Kinect and NUI projects for their clients. You can find him on twitter @joshblake or at his blog, http://nui.joshland.org.

    Josh recently recorded several videos for our Kinect for Windows Developer Center. This is the second of three posts he will be contributing this month to the blog.



    In part 1, I shared videos covering the core natural user interface concepts and a sample application that I use to control presentations called Kinect PowerPoint Control. In this post, I’m going to share videos of two more of my sample applications, one of which is brand new and has never been seen before publicly!

    When I present at conferences or workshops about Kinect, I usually demonstrate several sample applications that I’ve developed. These demos enable me to illustrate how various NUI design scenarios and challenges are addressed by features of the Kinect. This helps the audience see the Kinect in action and gets them thinking about the important design concepts used in NUI. (See the Introduction to Natural User Interfaces and Kinect video in part 1 for more on NUI design concepts.)

    Below, you will find overviews and videos of two of my open source sample applications: Kinect Weather Map and Face Fusion. I use Kinect Weather Map in most developer presentations and will be using the new Face Fusion application for future presentations.

    I must point out that these are still samples - they are perhaps 80% solutions to the problems they approach and lack the polish (and complexity!) of a production system. This means they still have rough edges at certain places but also are easier for a developer to look through and learn from the code.

    Kinect Weather Map

    This application lets you play the role of a broadcast meteorologist and puts your image in front of a live, animated weather map. Unlike a broadcast meteorologist, you won’t need a green screen or any special background due to the magic of the Kinect! The application demonstrates background removal, custom gesture recognition, and a gesture design that is appropriate to this particular scenario. This project source code is available under an open source license at http://kinectweather.codeplex.com/.

    Here are three videos covering different aspects of the Kinect Weather Map sample application:


    Community Sample: Kinect Weather Map – Design (1:45)


    Community Sample: Kinect Weather Map – Code Walkthrough – Gestures (2:40)


    Community Sample: Kinect Weather Map – Code Walkthrough – Background Removal (5:40)


    I made Kinect Weather Map a while ago, but it still works great for presentations and is a good reference for new developers for getting started with real-time image manipulation and background removal. This next application, though, is brand new and I have not shown it publicly until today!


    Face Fusion

    The Kinect for Windows SDK recently added the much-awaited Kinect Fusion feature. Kinect Fusion lets you integrate data across multiple frames to create a 3D model, which can be exported to a 3D editing program or used in a 3D printer. As a side-effect, Kinect Fusion also tracks the position of the Kinect relative to the reconstruction volume, the 3D box in the real-world that is being scanned.

    I wanted to try out Kinect Fusion so I was thinking about what might make an interesting application. Most of the Kinect Fusion demos so far have been variations of scanning a room or small area by moving the Kinect around with your hands. Some demos scanned a person, but required a second person to move the Kinect around. This made me think – what would it take to scan yourself without needing a second person? Voila! Face Fusion is born.

    Face Fusion lets you make a 3D scan of your own head using a fixed Kinect sensor. You don’t need anyone else to help you and you don’t need to move the Kinect at all. All you need to do is turn your head while in view of the sensor. This project source code is available under an open source license at http://facefusion.codeplex.com.

    Here are two videos walking through Face Fusion’s design and important parts of the source code. Watch them first to see what the application does, then join me again below for a more detailed discussion of a few technical and user experience design challenges.


    Community Sample: Face Fusion – Design (2:34)



    Community Sample: Face Fusion – Code Walkthrough (4:29)


    I’m pretty satisfied with how Face Fusion ended up in terms of the ease of use and discoverability. In fact, at one point while setting up to record these videos, I took a break but left the application running. While I wasn’t looking, the camera operator snuck over and started using the application himself and successfully scanned his own head. He wasn’t a Kinect developer and didn’t have any training except watching me practice once or twice. This made me happy for two reasons: it was easy to learn, and it worked for someone besides myself!


    Face Fusion Challenges

    Making the application work well and be easy to use and learn isn’t as easy as it sounds though. In this section I’m going to share a few of the challenges I came across and how I solved them.

    Figure 1: Cropped screenshots from Face Fusion: Left, the depth image showing a user and background, with the head and neck joints highlighted with circles. Right, the Kinect Fusion residual image illustrates which pixels from this depth frame were used in Kinect Fusion.


    Scanning just the head

    Kinect Fusion tracks the movement of the sensor (or the movement of the reconstruction volume – it is all relative!) by matching up the new data to previously scanned data. The position of the sensor relative to the reconstruction volume is critical because that is how it knows where to add the new depth data in the scan. Redundant data from non-moving objects just reinforces the scan and improves the quality. On the other hand, anything that changes or moves during the scan is slowly dissolved and re-scanned in the new position.

    This is great for scanning an entire room when everything is fixed, but doesn’t work if you scan your body and turn your head. Kinect Fusion tends to lock onto your shoulders and torso, or anything else visible around you, while your head just dissolves away and you don’t get fully scanned. The solution here was to reduce the size of the reconstruction volume from “entire room” to “just enough to fit your head” and then center the reconstruction volume on your head using Kinect SDK skeleton tracking.

    Kinect Fusion ignores everything outside of the real-world reconstruction volume, even if it is visible in the depth image. This causes Kinect Fusion to only track the relative motion between your head and the sensor. The sensor can now be left in one location and the user can move more freely and naturally because the shoulders and torso are not in the volume.


    Figure 2: A cropped screenshot of Face Fusion scanning only the user’s head in real-time. The Face Fusion application uses Kinect Fusion to render the reconstruction volume. Colors represent different surface normal directions.


    Controlling the application

    Since the scanning process requires the user to stand (or sit) in view of the sensor rather than at the computer, it is difficult to use mouse or touch to control the scan. This is a perfect scenario for voice control! The user can say “Fusion Start”, “Fusion Pause”, or “Fusion Reset” to control the scan process without needing to look at the screen or be near the computer. (Starting the scan just starts streaming data to Kinect Fusion, while resetting the scan clears the data and resets the reconstruction volume.)

    Voice control was a huge help, but I found that when testing the application, I still tended to try to watch the screen during the scan to see how the scan was doing and if the scan had lost tracking. This affected my ability to turn my head far enough for a good scan. If I ignored the screen and slowly turned all the way around, I would often find the scan had failed early on because I moved too quickly and I wasted all that time for nothing. I realized that in this interaction, we needed to have both control of the scan through voice and feedback on the scan progress and quality through non-visual means. Both channels in the interaction are critical.


    Figure 3: A cropped Face Fusion screenshot showing the application affirming that it heard the user’s command, top left. In the top right, the KinectSensorChooserUI control shows the microphone icon so the user knows the application is listening.


    Providing feedback to the user

    Since I already had voice recognition, one approach might have been to use speech synthesis to let the computer guide the user through the scan. I quickly realized this would be difficult to implement and would be a sub-optimal solution. Speech is discrete but the scan progress is continuous. Mapping the scan progress to speech would be challenging.

    At some point I got the idea of making the computer sing, instead. Maybe the pitch or tonality could provide a continuous audio communication channel. I tried making a sine wave generator using the NAudio open source project and bending the pitch based upon the average error in the Kinect Fusion residual image. After testing a prototype, I figured out that this worked well; it greatly improved my confidence in the scan progress without seeing the screen. Even better, it gave me more feedback than I had before so I knew when to move or hold still, resulting in better scan results!

    Face Fusion plays a pleasant triad chord when it has fully integrated the current view of the user's head, and otherwise continuously slides a single note up to an octave downward based upon the average residual error. This continuous feedback lets me decide how far to turn my head and when I should stop to let it catch up. This is easier to understand when you hear it.  I encourage you to watch the Face Fusion videos above.  Better yet download the code and try it yourself!

    The end result may be a little silly to listen to at first, but if you try it out you’ll find that you are having an interesting non-verbal conversation with the application through the Kinect sensor – you moving your head in specific ways and it responding with sound. It helps you get the job done without needing a second person.

    This continuous audio feedback technique would also be useful for other Kinect Fusion applications where you move the sensor with your hands. It would let you focus on the object being scanned rather than looking away at a display.

    Figure 4: A sequence of three cropped Face Fusion screenshots showing the complete scan. When the user pauses the scan by saying “Kinect Pause”, Face Fusion rotates the scan rendering for user review.


    Keep watching this blog this next week for part three, where I will share one more group of videos that break down the designs of several early-childhood educational applications we created for our client, Kaplan Early Learning Company. Those videos will take you behind-the-scenes on our design process and show you how we approached the various challenging aspects of designing fun and educational Kinect applications for small children.


    @joshblake | joshb@infostrat.com | mobile +1 (703) 946-7176 | http://nui.joshland.org

  • Kinect for Windows Product Blog

    Turn any surface into a touch screen with Ubi Interactive and Kinect for Windows


    The following blog post was guest authored by Anup Chathoth, co-founder and CEO of Ubi Interactive.

    Ubi Interactive is a Seattle startup that was one of 11 companies from around the world selected to take part in a three-month Microsoft Kinect Accelerator program in the spring of 2012. Since then, the company has developed the software with more than 100 users and is now accepting orders for the software.


    Patrick Wirtz, an innovation manager for The Walsh Group, spends most of his time implementing technology that will enhance Walsh’s ability to work with clients. It’s a vital role at The Walsh Group, a general building construction organization founded in 1898 that has invested more than US$450 Million in capital equipment and regularly employs more than 5,000 engineers and skilled tradespeople.

    "It’s a powerful piece of technology," says Patrick Wirtz, shown here using Ubi in The Walsh Group offices."It’s a powerful piece of technology," says Patrick Wirtz, shown here using Ubi in The Walsh Group
    offices. By setting up interactive 3-D blueprints on the walls, Walsh gives clients the ability
    to explore, virtually, a future building or facility.

    In the construction industry, building information modeling (BIM) is a critical component of presentations to clients. BIM allows construction companies like The Walsh Group to represent the functional characteristics of a facility digitally. While this is mostly effective, Wirtz wanted something that would really “wow” his clients. He wanted a way for them to not only see the drawings, but to bring the buildings to life by allowing clients to explore the blueprints themselves.

    Ubi's interactive display being used during a presentation in a Microsoft conference roomWirtz found the solution he had been seeking when he stumbled upon an article about Ubi. At Ubi Interactive, we provide the technology to transform any surface into an interactive touch screen. All the user needs is a computer running our software, a projector, and the Kinect for Windows sensor. Immediately, Wirtz knew Ubi was something he wanted to implement at Walsh: “I contacted the guys at Ubi and told them I am very interested in purchasing the product.” Wirtz was excited about the software and flew out to Seattle for a demo.

    After interacting with the software, Wirtz was convinced that this technology could help The Walsh Group. “Ubi is futuristic-like technology,” he noted—but a technology that he and his colleagues are able to use today. Wirtz immediately saw the potential: Walsh’s building information models could now be interactive displays. Instead of merely presenting drawings to clients, Walsh can now set up an interactive 3-D blueprint on the wall. Clients can walk up to the blueprint and discover what the building will look like by touching and interacting with the display. In use at Walsh headquarters since June 2012, Ubi Interactive brings client engagement to an entirely new level.

    Similarly, Evan Collins, a recent graduate of California Polytechnic State University, used the Ubi software as part of an architecture show he organized. The exhibition showcased 20 interactive displays that allowed the fifth-year architecture students to present their thesis projects in a way that was captivating to audience members. Collins said the interactive displays, “…allowed audience members to choose what content they interacted with instead of listening to a static slideshow presentation.”

    Twenty Ubi Interactive displays at California Polytechnic University 
    Twenty Ubi Interactive displays at California Polytechnic University

    Wirtz’s and Collins’ cases are just two ways that people are currently using Ubi. Because the solution is so affordable, people from a wide range of industries have found useful applications for the Ubi software. Wirtz said, “I didn’t want to spend $10,000. I already had a projector and a computer. All I needed to purchase was the software and a $250 Kinect for Windows sensor. With this small investment, I can now turn any surface into a touch screen. It’s a powerful piece of technology.”

    In addition to small- and mid-sized companies, several Fortune 500 enterprises like Microsoft and Intel are also using the software in their conference rooms. And the use of the technology goes beyond conference rooms:

    • Ubi Interactive makes it possible for teachers to instruct classes in an interactive lecture hall.
    • Shoppers can access product information on a store’s window front, even after hours.
    • Recipes can be projected onto kitchen countertops without having to worry about getting anything dirty.
    • Children can use their entire bedroom wall to play interactive games like Angry Birds.
    • The possibilities are endless.

    At Ubi Interactive, it is our goal to make the world a more interactive place. We want human collaboration and information to be just one finger touch away, no matter where you are. By making it possible to turn any surface into a touch screen, we eliminate the need for screen hardware and thereby reduce the cost and extend the possibilities of enabling interactive displays in places where they were not previously feasible—such as on walls in public spaces. Our technology has implications of revolutionizing the way people live their lives on a global level. After private beta evaluation with more than 50 organizations, the Ubi software is now available for ordering at ubi-interactive.com.

    Anup Chathoth
    Co-Founder and CEO, Ubi Interactive

    Key links

  • Kinect for Windows Product Blog

    Joshua Blake on Kinect and the Natural User Interface Revolution (Part 1)


    The following blog post was guest authored by K4W MVP, Joshua Blake. Josh is the Technical Director of the InfoStrat Advanced Technology Group in Washington, D.C where he and his team work on cutting-edge Kinect and NUI projects for their clients. You can find him on twitter @joshblake or at his blog, http://nui.joshland.org.

    Josh recently recorded several videos for our Kinect for Windows Developer Center and will be contributing three posts this month to the blog.

    I’ve been doing full-time natural user interface (NUI) design and development since 2008:  starting with multi-touch apps for the original Microsoft Surface (now called “PixelSense") and most-recently creating touch-free apps using Kinect. Over this time, I have learned a great deal about what it takes to create great natural user interfaces, regardless of the input or output device.

    One of the easiest ways to get involved with natural user interfaces is by learning to create applications for the Kinect for Windows sensor, which has an important role to play in the NUI revolution. It is inexpensive enough to be affordable to almost any developer, yet it allows our computers see, hear, and understand the real-world similar to how we understand it. It isn’t enough to just mash up new sensors with existing software, though. In order to reach the true potential of the Kinect, we need learn what makes a user interface truly ‘natural’.

    The Kinect for Windows team generously offered to record several videos of me sharing my thoughts on natural user interface and Kinect design and development. Today, you can watch the first three of these videos on the Kinect for Windows Developer Center.

    Introduction to Natural User Interfaces and Kinect

    In this video, I present the most important ideas and concepts that every natural user interface designer or developer must know and give concrete examples of the ideas from Kinect development. This video covers: what natural user interfaces are, what ideas to consider when designing a natural user interface, and the difference between gestures and manipulations.



    Kinect PowerPoint Control

    This pair of videos covers my Kinect PowerPoint Control sample project. The “Design” video quickly demonstrates the features of the application, and the “Code Walkthrough” video explains the most important parts of the code. The project source code is available under an open source license at https://kinectpowerpoint.codeplex.com.

    I use this app all the time to control my PowerPoint presentations (such as the Intro to NUI video above) with Kinect. The app demonstrates the bare minimum code required to do simple custom gesture recognition using Kinect skeleton data and how to respond to basic voice commands using Kinect speech recognition. I have found many Kinect developers have trouble getting started with gesture recognition, so the features in the sample are kept minimal on purpose so that the code is easy to read and learn from.


    Community Sample: Kinect PowerPoint Control – Design (1:41)



    Community Sample: Kinect PowerPoint Control – Code Walkthrough (3:30)



    Keep watching this blog next week for part two, where I will share more videos showing advanced features of the Kinect SDK.  I will introduce two more of my sample Kinect projects including a completely new, previously unpublished sample that uses Kinect Fusion for object scanning.


    @joshblake | joshb@infostrat.com | mobile +1 (703) 946-7176 | http://nui.joshland.org

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