Xamarin.Cognitive.Face is a client library that makes it easy to work with the Microsoft Cognitive Services Face API on Xamarin.iOS, Xamarin.Android, and Xamarin.Forms and/or Portable Class Library (PCL) projects.

Resources about the Face API and what it is:

• Learn about the Face API
• Documentation
• Face API Reference

Xamarin.Cognitive.Face is available as a NuGet package to be added to your Xamarin.iOS, Xamarin.Android, or Xamarin.Forms project(s).

The included PCL assembly is compiled against Profile 111, which is currently the same profile used for Xamarin.Forms shared PCLs. In the case of Xamarin.Forms or any other PCL situation, you must install the package to the PCL project as well as any platform (iOS/Android) projects - this package uses the Bait & Switch PCL pattern.

This library uses two separate binding projects to native libraries:

• Cognitive-Face-iOS-Xamarin - a binding for the native iOS Microsoft Face API: iOS Client Library
• Cognitive-Face-Android-Xamarin - a binding for the native Android Microsoft Face API: Android Client Library

These bindings can of course be used individually in your Xamarin.iOS and/or Xamarin.Android projects if you want to build and use them directly.

The Xamarin.Cognitive.Face package contains pre-compiled versions of these bindings that you can use directly if so desired:

iOS: Use the types in the Xamarin.Cognitive.Face.iOS namespace, such as MPOFaceServiceClient. Documentation and usage is demonstrated in the Microsoft Face API: iOS Client Library.

Android: Use the types in the Xamarin.Cognitive.Face.Droid namespace, such as FaceServiceRestClient. Documentation and usage is demonstrated in the Microsoft Face API: Android Client Library.

Xamarin.Cognitive.Face brings the above bindings together into a single NuGet package and adds a unified API that can be called from either platform projects or shared code (shared project or portable class library).

This higher-level library contains a number of value-adds and niceties that make it easy to work with the Face API:

• Full async/await support across the API, for awesome and responsive apps.
• A full set of extended domain/model classes that improve upon the native classes.
• Extensions to ease working with and consuming native images (UIImage/Bitmap) on each platform.
• Simple support for storing face thumbnail images "on disk."
• Data caching on retrieved items like PersonGroup lists, etc.
• API equivalnce on both platforms, i.e. the ability to also use the client library's API in a Shared Project.

• Xamarin.Cognitive.Face.Sample.iOS
• Xamarin.Cognitive.Face.Sample.Droid

These samples exercise most areas of the Face API, including Person/PersonGroup/Face management, face detection, person identification, verification, face grouping, and more.

These samples are based off of and heavily influenced by the original samples found in the native client libraries (linked above), but have been heavily updated to Xamarin-ize and use the [Xamarin Client Library](#Xamarin Client Library).

• Windows UWP support
• There's no unified API for or samples showing FaceLists
• Performance and/or memory profiling has not been done, so buyer beware!

If you'd like to address any of the above, we're happy to review and merge any quality pull requests!

1. Add the NuGet package to your Xamarin.iOS and/or Xamarin.Android project, and any PCL project where the Xamarin.Cognitive.Face library is needed.

2. The Xamarin.Cognitive.Face client is exposed as a Singleton that can be referenced via FaceClient.Shared.

   Initialize the FaceClient with a subscription key (get one here!), and, optionally, set the endpoint (defaults to WestUS):

   FaceClient.Shared.Endpoint = Endpoints.WestUS;
   FaceClient.Shared.SubscriptionKey = faceApiKey;

   NOTE: Subscription keys are tied to a specific endpoint, so pay attention when creating a new key.

   At this point, the FaceClient is configured and ready to use.

3. Use the FaceClient to interact with the Face API. You can do things such as:

   • Get all PersonGroup

      List<PersonGroup> groups = await FaceClient.Shared.GetPersonGroups ();

     This operation will cache the list of groups the first time and continue to return the cahced list until your next session, or you tell it to refresh the cache:

      List<PersonGroup> groups = await FaceClient.Shared.GetPersonGroups (true); //true == force refresh

   • Detect faces in an image

      List<Face> detectedFaces = await FaceClient.Shared.DetectFacesInPhoto (SourceImage.AsJpegStream);

     Or, with facial landmarks and face attributes specified:

      List<Face> detectedFaces = await FaceClient.Shared.DetectFacesInPhoto (
      						SourceImage.AsJpegStream,
      						true, //return landmarks
      						FaceAttributeType.Age,
      						FaceAttributeType.Gender,
      						FaceAttributeType.Hair,
      						FaceAttributeType.FacialHair,
      						FaceAttributeType.Makeup,
      						FaceAttributeType.Emotion,
      						FaceAttributeType.Occlusion,
      						FaceAttributeType.Smile,
      						FaceAttributeType.Exposure,
      						FaceAttributeType.Noise,
      						FaceAttributeType.Blur,
      						FaceAttributeType.Glasses,
      						FaceAttributeType.HeadPose,
      						FaceAttributeType.Accessories);

     SourceImage can be either a Bitmap (Android) or UIImage (iOS).

   • Person Identification

     To identify a face to a Person within a PersonGroup:

      PersonGroup MyPersonGroup;
      Face MyFaceToIdentify;
      
      List<IdentificationResult> results = await FaceClient.Shared.Identify (MyPersonGroup, MyFaceToIdentify);

   ...And much more. Take a look at the Sample Apps to see the usage of these and more features.

It is not possible to retrieve stored Face images via the Face API. If your use case requires working with face thubnail images, Xamarin.Cognitive.Face provides simple support for working with and storing any persisted Face images to the local file system on both platforms.

The following extensions are available on the Face class:

iOS:

• UIImage CreateThumbnail (this Model.Face face, UIImage sourceImage)

• List<UIImage> GenerateThumbnails (this List<Model.Face> faces, UIImage photo, List<UIImage> thumbnailList = null)

• void SaveThumbnail (this Model.Face face, UIImage thumbnail)

• void SaveThumbnailFromSource (this Model.Face face, UIImage sourceImage)

• UIImage GetThumbnailImage (this Model.Face face)

  Example:

   Person myPerson;
   PersonGroup myPersonGroup;
   Face myFace;
   UIImage sourceImage;
   ...
   await FaceClient.Shared.AddFaceForPerson (myPerson, myPersonGroup, myFace, sourceImage.AsStream);
   face.SaveThumbnailFromSource (sourceImage);

Android:

• Bitmap CreateThumbnail (this Model.Face face, Bitmap sourceImage)

• List<Bitmap> GenerateThumbnails (this List<Model.Face> faces, Bitmap photo, List<Bitmap> thumbnailList = null)

• void SaveThumbnail (this Model.Face face, Bitmap thumbnail)

• void SaveThumbnailFromSource (this Model.Face face, Bitmap sourceImage)

• Bitmap GetThumbnailImage (this Model.Face face)

  Example:

   Person myPerson;
   PersonGroup myPersonGroup;
   Face myFace;
   Bitmap sourceImage;
   ...
   await FaceClient.Shared.AddFaceForPerson (myPerson, myPersonGroup, myFace, sourceImage.AsStream);
   face.SaveThumbnailFromSource (sourceImage);

On either platform, if you already have a cropped face thumbnail image (via CreateThumbnail()), you may call face.SaveThumbnail (thumbnail) rather than SaveThumbnailFromSource(sourceImage).

NOTE: Any images persisted via the SaveThumbnail* methods will be stored on disk at the path found on the ThumbnailPath property of the Face. These thumbnails will only be available (via GetThumbnailImage ()) for the life of the app on a given device, i.e. they will not persist across app removals, etc. If you desire long-term face thumbnail storage, we suggest using another storage option for your thumbnail images.

The Face API throws a handful of exceptions for most API methods. A list of possible exceptions that may be thrown for a given operation can be found in the API documentation.

Any API exception received from the Face API will be raised to the caller in the form of an ErrorDetailException.

A common example of one of these exceptions is a "rate limit exceeded" exception. Too many API calls made within a window of time may result in this exception being returned. In this case, the caller will receive an ErrorDetailException wrapping an Error similar to this:

Error
{
	Code: "429",
	Message: "Rate limit is exceeded. Try again in XXX seconds"
}

Contributions are welcome. Feel free to file issues and pull requests on the repo and we'll address them as time permits.

• Created by Nate Rickard
• Contributions from Colby Williams (iOS binding & packaging) and Roberto Cervantes (work on the Android sample app)

Licensed under the MIT License (MIT). See LICENSE for details.

Microsoft will receive the images you upload and may use them to improve Face API and related services. By submitting an image, you confirm you have consent from everyone in it.