The Google Cloud Vision API allows developers to easily integrate vision detection features within applications, including image labeling, face and landmark detection, optical character recognition (OCR), and tagging of explicit content.

In this codelab you will focus on using the Vision API with C#. You will learn how to perform text detection, landmark detection, and face detection!

What you'll learn

What you'll need

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Self-paced environment setup

If you don't already have a Google Account (Gmail or Google Apps), you must create one. Sign-in to Google Cloud Platform console (console.cloud.google.com) and create a new project:

Remember the project ID, a unique name across all Google Cloud projects (the name above has already been taken and will not work for you, sorry!). It will be referred to later in this codelab as PROJECT_ID.

Next, you'll need to enable billing in the Cloud Console in order to use Google Cloud resources.

Running through this codelab shouldn't cost you more than a few dollars, but it could be more if you decide to use more resources or if you leave them running (see "cleanup" section at the end of this document).

New users of Google Cloud Platform are eligible for a $300 free trial.

Start Cloud Shell

While Google Cloud can be operated remotely from your laptop, in this codelab you will be using Google Cloud Shell, a command line environment running in the Cloud.

Activate Google Cloud Shell

From the GCP Console click the Cloud Shell icon on the top right toolbar:

Then click "Start Cloud Shell":

It should only take a few moments to provision and connect to the environment:

This virtual machine is loaded with all the development tools you'll need. It offers a persistent 5GB home directory, and runs on the Google Cloud, greatly enhancing network performance and authentication. Much, if not all, of your work in this lab can be done with simply a browser or your Google Chromebook.

Once connected to the cloud shell, you should see that you are already authenticated and that the project is already set to your PROJECT_ID.

Run the following command in the cloud shell to confirm that you are authenticated:

gcloud auth list

Command output

Credentialed accounts:
 - <myaccount>@<mydomain>.com (active)
gcloud config list project

Command output

[core]
project = <PROJECT_ID>

If it is not, you can set it with this command:

gcloud config set project <PROJECT_ID>

Command output

Updated property [core/project].

Before you can begin using the Vision API you must enable the API. Using the Cloud Shell, you can enable the API by using the following command:

gcloud services enable vision.googleapis.com

In order to make requests to the Vision API, you need to use a Service Account. A Service Account belongs to your project and it is used by the Google Client C# library to make Vision API requests. Like any other user account, a service account is represented by an email address. In this section, you will use the gcloud tool to create a service account and then create credentials to authenticate as the service account.

First, you will set an environment variable with your PROJECT_ID which you will use throughout this codelab:

export GOOGLE_CLOUD_PROJECT=$(gcloud config get-value core/project)

Next, create a new service account to access the Vision API:

gcloud iam service-accounts create my-vision-sa \
  --display-name "my vision service account"

Then, create credentials that your C# code will use to log in as your new service account. Create these credentials and save it as a JSON file "~/key.json" by using the following command:

gcloud iam service-accounts keys create ~/key.json \
  --iam-account my-vision-sa@${GOOGLE_CLOUD_PROJECT}.iam.gserviceaccount.com

Finally, set the GOOGLE_APPLICATION_CREDENTIALS environment variable. This is used by the Vision API C# library, covered in the next step, to find your credentials. The environment variable should be set to the full path of the credentials JSON file you created:

export GOOGLE_APPLICATION_CREDENTIALS="/home/${USER}/key.json"

You can read more about authenticating the Google Cloud Vision API.

First, create a simple C# console application that you will use to run Vision API samples:

dotnet new console -n VisionApiDemo

You should see the application created and dependencies resolved:

The template "Console Application" was created successfully.
Processing post-creation actions...
...
Restore succeeded.

Next, navigate to VisionApiDemo folder:

cd VisionApiDemo/

And add Google.Cloud.Vision.V1 NuGet package to the project:

dotnet add package Google.Cloud.Vision.V1
info : Adding PackageReference for package 'Google.Cloud.Vision.V1' into project '/home/atameldev/VisionApiDemo/VisionApiDemo.csproj'.
log  : Restoring packages for /home/atameldev/VisionApiDemo/VisionApiDemo.csproj...
...
info : PackageReference for package 'Google.Cloud.Vision.V1' version '1.2.0' added to file '/home/atameldev/VisionApiDemo/VisionApiDemo.csproj'.

Now, you're ready to use Vision API!

Vision API's Text Detection performs Optical Character Recognition. It detects and extracts text within an image with support for a broad range of languages. It also features automatic language identification.

In this example, you will perform text detection on an image of an Otter Crossing.

Open the code editor from the top right side of the Cloud Shell:

Navigate to the Program.cs file inside the VisionApiDemo folder and replace the code with the following:

using Google.Cloud.Vision.V1;
using System;

namespace VisionApiDemo
{
    class Program
    {   
        static void Main(string[] args)
        {
            var client = ImageAnnotatorClient.Create();
            var image = Image.FromUri("gs://cloud-vision-codelab/otter_crossing.jpg");
            var response = client.DetectText(image);
            foreach (var annotation in response)
            {
                if (annotation.Description != null)
                {
                    Console.WriteLine(annotation.Description);
                }
            }
        }
    }
}

Take a minute or two to study the code and see how the Vision API C# library is used to perform text detection.

Back in Cloud Shell, run the app:

dotnet run 

You should see the following output:

CAUTION
Otters crossing
for next 6 miles

Summary

In this step, you were able to perform text detection on an image of an Otter Crossing and print recognized text from the image. Read more about Text Detection.

Vision API's Landmark Detection detects popular natural and man-made structures within an image.

In this example, you will perform landmark detection on an image of the Eiffel Tower.

Navigate to the Program.cs file inside the VisionApiDemo folder and replace the code with the following:

using Google.Cloud.Vision.V1;
using System;

namespace VisionApiDemo
{
    class Program
    {   
        static void Main(string[] args)
        {
            var client = ImageAnnotatorClient.Create();
            var image = Image.FromUri("gs://cloud-vision-codelab/eiffel_tower.jpg");
            var response = client.DetectLandmarks(image);
            foreach (var annotation in response)
            {
                if (annotation.Description != null)
                {
                    Console.WriteLine(annotation.Description);
                }
            }
        }
    }
}

Take a minute or two to study the code and see how the Vision API C# library is used to perform landmark detection.

Back in Cloud Shell, run the app:

dotnet run

You should see the following output:

Eiffel Tower

Summary

In this step, you were able to perform landmark detection on image of the Eiffel Tower. Read more about Landmark Detection.

Face Detection detects multiple faces within an image along with the associated key facial attributes such as emotional state or wearing headwear.

In this example, you will detect the likelihood of emotional state from four different emotional likelihoods including: joy, anger, sorrow, and surprise.

Navigate to the Program.cs file inside the VisionApiDemo folder and replace the code with the following:

using Google.Cloud.Vision.V1;
using System;

namespace VisionApiDemo
{
    class Program
    {   
        static void Main(string[] args)
        {
            var client = ImageAnnotatorClient.Create();
            string[] pictures = {"face_surprise.jpg", "face_no_surprise.png"};
  
            foreach (var picture in pictures)
            {
                var image = Image.FromUri("gs://cloud-vision-codelab/" + picture);
                var response = client.DetectFaces(image);
                foreach (var annotation in response)
                {
                    Console.WriteLine($"Picture: {picture}");
                    Console.WriteLine($" Surprise: {annotation.SurpriseLikelihood}");
                }
            }
        }
    }
}

Take a minute or two to study the code and see how the Vision API C# library is used to perform emotional face detection.

Run the app;

dotnet run

You should see the following output for our face_surprise and face_no_surprise examples:

Picture: face_surprise.jpg
 Surprise: Likely
Picture: face_no_surprise.png
 Surprise: VeryUnlikely

Summary

In this step, you were able to perform emotional face detection. Read more about Face Detection.

You learned how to use the Vision API using C# to perform different detection on images!

Clean up

To avoid incurring charges to your Google Cloud Platform account for the resources used in this quickstart:

Learn More

License

This work is licensed under a Creative Commons Attribution 2.0 Generic License.