Quickstart: Detect faces in an image using C#

In this quickstart, you detect human faces in an image using the Face API.

Prerequisites

You need a subscription key to run the sample. You can get free trial subscription keys from Try Cognitive Services.

Detect faces in an image

Use the Face - Detect method to detect faces in an image and return face attributes including:

  • Face ID: Unique ID used in several Face API scenarios.
  • Face Rectangle: The left, top, width, and height indicating the location of the face in the image.
  • Landmarks: An array of 27-point face landmarks pointing to the important positions of face components.
  • Facial attributes including age, gender, smile intensity, head pose, and facial hair.

To run the sample, do the following steps:

  1. Create a new Visual C# Console App in Visual Studio.
  2. Replace Program.cs with the following code.
  3. Replace <Subscription Key> with your valid subscription key.
  4. Change the uriBase value to use the location where you obtained your subscription keys, if necessary.
  5. Run the program.
  6. At the prompt, enter the path to an image.

Face - Detect request

using System;
using System.IO;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;

namespace CSHttpClientSample
{
    static class Program
    {
        // Replace <Subscription Key> with your valid subscription key.
        const string subscriptionKey = "<Subscription Key>";

        // NOTE: You must use the same region in your REST call as you used to
        // obtain your subscription keys. For example, if you obtained your
        // subscription keys from westus, replace "westcentralus" in the URL
        // below with "westus".
        //
        // Free trial subscription keys are generated in the westcentralus region.
        // If you use a free trial subscription key, you shouldn't need to change
        // this region.
        const string uriBase =
            "https://westcentralus.api.cognitive.microsoft.com/face/v1.0/detect";

        static void Main()
        {
            // Get the path and filename to process from the user.
            Console.WriteLine("Detect faces:");
            Console.Write(
                "Enter the path to an image with faces that you wish to analyze: ");
            string imageFilePath = Console.ReadLine();

            if (File.Exists(imageFilePath))
            {
                // Execute the REST API call.
                try
                {
                    MakeAnalysisRequest(imageFilePath);
                    Console.WriteLine("\nWait a moment for the results to appear.\n");
                }
                catch (Exception e)
                {
                    Console.WriteLine("\n" + e.Message + "\nPress Enter to exit...\n");
                }
            }
            else
            {
                Console.WriteLine("\nInvalid file path.\nPress Enter to exit...\n");
            }
            Console.ReadLine();
        }


        /// <summary>
        /// Gets the analysis of the specified image by using the Face REST API.
        /// </summary>
        /// <param name="imageFilePath">The image file.</param>
        static async void MakeAnalysisRequest(string imageFilePath)
        {
            HttpClient client = new HttpClient();

            // Request headers.
            client.DefaultRequestHeaders.Add(
                "Ocp-Apim-Subscription-Key", subscriptionKey);

            // Request parameters. A third optional parameter is "details".
            string requestParameters = "returnFaceId=true&returnFaceLandmarks=false" +
                "&returnFaceAttributes=age,gender,headPose,smile,facialHair,glasses," +
                "emotion,hair,makeup,occlusion,accessories,blur,exposure,noise";

            // Assemble the URI for the REST API Call.
            string uri = uriBase + "?" + requestParameters;

            HttpResponseMessage response;

            // Request body. Posts a locally stored JPEG image.
            byte[] byteData = GetImageAsByteArray(imageFilePath);

            using (ByteArrayContent content = new ByteArrayContent(byteData))
            {
                // This example uses content type "application/octet-stream".
                // The other content types you can use are "application/json"
                // and "multipart/form-data".
                content.Headers.ContentType =
                    new MediaTypeHeaderValue("application/octet-stream");

                // Execute the REST API call.
                response = await client.PostAsync(uri, content);

                // Get the JSON response.
                string contentString = await response.Content.ReadAsStringAsync();

                // Display the JSON response.
                Console.WriteLine("\nResponse:\n");
                Console.WriteLine(JsonPrettyPrint(contentString));
                Console.WriteLine("\nPress Enter to exit...");
            }
        }


        /// <summary>
        /// Returns the contents of the specified file as a byte array.
        /// </summary>
        /// <param name="imageFilePath">The image file to read.</param>
        /// <returns>The byte array of the image data.</returns>
        static byte[] GetImageAsByteArray(string imageFilePath)
        {
            using (FileStream fileStream =
                new FileStream(imageFilePath, FileMode.Open, FileAccess.Read))
            {
                BinaryReader binaryReader = new BinaryReader(fileStream);
                return binaryReader.ReadBytes((int)fileStream.Length);
            }
        }


        /// <summary>
        /// Formats the given JSON string by adding line breaks and indents.
        /// </summary>
        /// <param name="json">The raw JSON string to format.</param>
        /// <returns>The formatted JSON string.</returns>
        static string JsonPrettyPrint(string json)
        {
            if (string.IsNullOrEmpty(json))
                return string.Empty;

            json = json.Replace(Environment.NewLine, "").Replace("\t", "");

            StringBuilder sb = new StringBuilder();
            bool quote = false;
            bool ignore = false;
            int offset = 0;
            int indentLength = 3;

            foreach (char ch in json)
            {
                switch (ch)
                {
                    case '"':
                        if (!ignore) quote = !quote;
                        break;
                    case '\'':
                        if (quote) ignore = !ignore;
                        break;
                }

                if (quote)
                    sb.Append(ch);
                else
                {
                    switch (ch)
                    {
                        case '{':
                        case '[':
                            sb.Append(ch);
                            sb.Append(Environment.NewLine);
                            sb.Append(new string(' ', ++offset * indentLength));
                            break;
                        case '}':
                        case ']':
                            sb.Append(Environment.NewLine);
                            sb.Append(new string(' ', --offset * indentLength));
                            sb.Append(ch);
                            break;
                        case ',':
                            sb.Append(ch);
                            sb.Append(Environment.NewLine);
                            sb.Append(new string(' ', offset * indentLength));
                            break;
                        case ':':
                            sb.Append(ch);
                            sb.Append(' ');
                            break;
                        default:
                            if (ch != ' ') sb.Append(ch);
                            break;
                    }
                }
            }

            return sb.ToString().Trim();
        }
    }
}

Face - Detect response

A successful response is returned in JSON, for example:

[
   {
      "faceId": "f7eda569-4603-44b4-8add-cd73c6dec644",
      "faceRectangle": {
         "top": 131,
         "left": 177,
         "width": 162,
         "height": 162
      },
      "faceAttributes": {
         "smile": 0.0,
         "headPose": {
            "pitch": 0.0,
            "roll": 0.1,
            "yaw": -32.9
         },
         "gender": "female",
         "age": 22.9,
         "facialHair": {
            "moustache": 0.0,
            "beard": 0.0,
            "sideburns": 0.0
         },
         "glasses": "NoGlasses",
         "emotion": {
            "anger": 0.0,
            "contempt": 0.0,
            "disgust": 0.0,
            "fear": 0.0,
            "happiness": 0.0,
            "neutral": 0.986,
            "sadness": 0.009,
            "surprise": 0.005
         },
         "blur": {
            "blurLevel": "low",
            "value": 0.06
         },
         "exposure": {
            "exposureLevel": "goodExposure",
            "value": 0.67
         },
         "noise": {
            "noiseLevel": "low",
            "value": 0.0
         },
         "makeup": {
            "eyeMakeup": true,
            "lipMakeup": true
         },
         "accessories": [

         ],
         "occlusion": {
            "foreheadOccluded": false,
            "eyeOccluded": false,
            "mouthOccluded": false
         },
         "hair": {
            "bald": 0.0,
            "invisible": false,
            "hairColor": [
               {
                  "color": "brown",
                  "confidence": 1.0
               },
               {
                  "color": "black",
                  "confidence": 0.87
               },
               {
                  "color": "other",
                  "confidence": 0.51
               },
               {
                  "color": "blond",
                  "confidence": 0.08
               },
               {
                  "color": "red",
                  "confidence": 0.08
               },
               {
                  "color": "gray",
                  "confidence": 0.02
               }
            ]
         }
      }
   }
]

Next steps

Learn how to create a WPF Windows application that uses the Face service to detect faces in an image. The application draws a frame around each face and displays a description of the face on the status bar.