OCR text detection with google APIs C#

- May 14, 2016

After searching more than 3 hrs to know how to implement text detection using google API i decided to write this post, hope it help c# developer to know how to use and implement Vision API,
Source Code : https://github.com/msm2020/OCR-google-APIs

1- Create server key on google console

Go to http://console.developers.google.com/ and create new project or use existing project

From Overview page enable vision API

You need to create new bill information to use vision API, it's fully free for 1st 1000 request/ month you can check https://cloud.google.com/vision/docs/pricing
After Enable Google Cloud Vision API go to Credentials page and create new server key

Create key by fill all requested data and download Json file

2- Create Visual studio project I'll use vs 2015 and .NET framework 4.5

Add google Nuget packages : Google.Apis.Vision.v1 by right click on project and then manage nuget package .

Add json file to your project and from properties windows change copy to output directory to true
Now create new class and add path of your file to use

 privatestring JsonKeypath
{
     get { return Application.StartupPath + "\\your file name.json"; 
}

We need to create credential object to call with our api

private GoogleCredential CreateCredential()
{
    using (var stream = new FileStream(JsonKeypath, FileMode.Open, FileAccess.Read))
          {
              string[] scopes = {  VisionService.Scope.CloudPlatform };
              var credential = GoogleCredential.FromStream(stream);
              credential = credential.CreateScoped(scopes);
              return credential;
}

And create service for vision to request api

        private VisionService CreateService(GoogleCredential credential)
        {
                var service = new VisionService(new  BaseClientService.Initializer()
                {
                     HttpClientInitializer = credential,
                     ApplicationName =ApplicationName,
                     GZipEnabled = true,
                });
                return service;
        }

API need language code reference here : https://cloud.google.com/translate/v2/translate-reference#supported_languages
Create batch request to upload image and get result :

BatchAnnotateImagesRequest batchRequest = new BatchAnnotateImagesRequest();
batchRequest.Requests = new List();
batchRequest.Requests.Add(new AnnotateImageRequest()
{
 Features = new List() { new Feature() { Type = "TEXT_DETECTION", MaxResults = 1 }, },
 ImageContext = new ImageContext() { LanguageHints = new List() { language } },
 Image = new Image() { Content = Convert.ToBase64String(file) }
});

Vision api have a lot of type like face detection and other types I use text_detiction https://cloud.google.com/vision/reference/rest/v1/images/annotate#Type
Excute request to get result

 var annotate = service.Images.Annotate(batchRequest);
 BatchAnnotateImagesResponse batchAnnotateImagesResponse = annotate.Execute();

Response result have Error variable and different type of classes related to Type uses on the api call and will use annotateImageResponse.TextAnnotations to get result and values

Output