In the last article, we showed how to call the Project Oxford Emotions API via REST in order to determine the emotions of every person in a picture.

In this article, I will show you how to use a .NET library to call this API. A .NET library simplifies the process by abstracting away HTTP calls and providing strongly-typed objects with which to work in your .NET code.

As with the REST call, we begin by signing up for Project Oxford and getting the key for this API, which you can do at

Figure 1: Key

To use the .NET library, launch Visual Studio and create a new Universal Windows App (File | New | Project | Windows | Blank (Universal Windows))

Add the Emotions NuGet Package to your project (Right-click project | Manage NuGet Packages); then search for and install Microsoft.ProjectOxford.Emotion. This will add the appropriate references to your project.

In your code, add the following statement to top of your class file.

using Microsoft.ProjectOxford.Emotion;
using Microsoft.ProjectOxford.Emotion.Contract; 

To use this library, we create an instance of the EmotionServiceClient class, passing in our key to the constructor.

var emotionServiceClient = new EmotionServiceClient(emotionApiKey);

The RecognizeAsync method of this class accepts the URL of an image and returns an array of Emotion objects.

Emotion[] emotionResult = await emotionServiceClient.RecognizeAsync(imageUrl); 

Each emotion object represents a single face detected in the picture and contains the following properties:

FaceRectangle: This indicates the location of the face

Scores: A set of values corresponding to each emotion (anger, content, disgust, fear, happiness, neutral, sadness, and surprise) with a value indicating the confidence with which Oxford thinks the face matches this emotion. Confidence values are between 0 and 1 and higher values indicate a higher confidence that this is the correct emotion.

The code below returns a string indicating the most likely emotion for every face in an image.

var sb = new StringBuilder();
var faceNumber = 0;
foreach (Emotion em in emotionResult)
    var scores = em.Scores;
    var anger = scores.Anger;
    var contempt = scores.Contempt;
    var disgust = scores.Disgust;
    var fear = scores.Fear;
    var happiness = scores.Happiness;
    var neutral = scores.Neutral;
    var surprise = scores.Surprise;
    var sadness = scores.Sadness; 
    var emotionScoresList = new List();
    emotionScoresList.Add(new EmotionScore("anger", anger));
    emotionScoresList.Add(new EmotionScore("contempt", contempt));
    emotionScoresList.Add(new EmotionScore("disgust", disgust));
    emotionScoresList.Add(new EmotionScore("fear", fear));
    emotionScoresList.Add(new EmotionScore("happiness", happiness));
    emotionScoresList.Add(new EmotionScore("neutral", neutral));
    emotionScoresList.Add(new EmotionScore("surprise", surprise));
    emotionScoresList.Add(new EmotionScore("sadness", sadness)); 
    var maxEmotionScore = emotionScoresList.Max(e => e.EmotionValue);
    var likelyEmotion = emotionScoresList.First(e => e.EmotionValue == maxEmotionScore); 
    string likelyEmotionText = string.Format("Face {0} is {1:N2}% likely to experiencing: {2}\n\n", 
        faceNumber, likelyEmotion.EmotionValue * 100, likelyEmotion.EmotionName.ToUpper());
var resultsText = sb.ToString(); 

This will return a string similar to the following:

Face 1 is 99.36% likely to experiencing: NEUTRAL

Face 2 is 100.00% likely to experiencing: HAPPINESS

Face 3 is 95.02% likely to experiencing: SADNESS

You can download this Visual Studio 2015 Universal Windows App project from here.

Full documentation on the Emotion library is available here. You can find a more complete (although more complicated) demo of this library here.

In this article, you learned how to use the .NET libraries to call the Project Oxford Emotion API and detect emotion in the faces of an image.