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ExtractText - .NET Core C#

This tutorial shows how to extract text data from an image using the LEADTOOLS Cloud Services in a C# .NET Core console application.

Overview
Summary	This tutorial covers how to use LEADTOOLS Cloud Services to make `ExtractText` request in a C# .NET Core program.
Completion Time	30 minutes
Project	Download tutorial project (2 KB)
Platform	LEADTOOLS Cloud Services API
IDE	Visual Studio 2019
Language	C# .NET Core
Development License	Download LEADTOOLS
Try it in another language	C#: .NET Core Python: Python Node.JS: Node.JS

Required Knowledge

Be sure to review the following sites for information about LEADTOOLS Cloud Services API.

Service Plans

LEADTOOLS Service Plan offerings:

Service Plan	Description
Free Trial	Free Evaluation
Page Packages	Prepaid Page Packs
Subscriptions	Prepaid Monthly Processed Pages

To further explore the offerings, refer to Pricing Information for LEADTOOLS Hosted Cloud Services > Service Plan Terms.

For pricing details, refer to https://www.leadtools.com/sdk/products/hosted-services#pricing > Page Packages and Subscriptions.

To obtain the necessary Application ID and Application Password, refer to Create an Account and Application with the LEADTOOLS Hosted Cloud Services.

Create the Project and Add the Required Dependencies

In Visual Studio, create a new C# .NET Core Console project, and add the following required NuGet package:

Newtonsoft.Json

Add the ExtractText Code

With the project created and the package added, coding can begin.

In the Solution Explorer, open Program.cs. Add the following statements to the using block at the top.

// Using block at the top 
using System; 
using System.Text; 
using System.Threading.Tasks; 
using System.Net; 
using System.Net.Http; 
using System.Net.Http.Headers; 
using System.IO; 
using Newtonsoft.Json.Linq;

Add the class string variable called hostedServicesUrl and an async Task called ExtractText(). This sends an ExtractText request to the LEADTOOLS Cloud Services API, if successful a unique identifier (GUID) will be returned and then a query using this GUID will be made.

private string hostedServicesUrl = "https://azure.leadtools.com/api/"; 
 
public async Task ExtractText() 
{ 
    var client = InitClient(); 
 
    //The first page in the file to mark for processing 
    int firstPage = 1; 
 
    //Sending a value of -1 will indicate to the service that all pages in the file should be processed. 
    int lastPage = -1; 
 
    // If using URL to the file 
    string fileURL = "http://demo.leadtools.com/images/cloud_samples/ocr1-4.tif"; 
    string recognitionUrl = string.Format("Recognition/ExtractText?firstPage={0}&lastPage={1}&fileurl={2}", firstPage, lastPage, fileURL); 
    var result = await client.PostAsync(recognitionUrl, null); 
 
    /* 
    //If uploading a file as multi-part content: 
    HttpContent byteContent = new ByteArrayContent(File.ReadAllBytes(@"path/to/file")); 
    byteContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data") 
    { 
        Name = "attachment", 
        FileName = "file-name" 
    }; 
    var formData = new MultipartFormDataContent(); 
    formData.Add(byteContent, "formFieldName"); 
 
    string recognitionUrl = string.Format("Recognition/ExtractText?firstPage={0}&lastPage={1}", firstPage, lastPage); 
    var result = await client.PostAsync(recognitionUrl, formData); 
    formData.Dispose(); 
    */ 
 
    if (result.StatusCode == HttpStatusCode.OK) 
    { 
        //Unique ID returned by the services 
        string id = await result.Content.ReadAsStringAsync(); 
        Console.WriteLine("Unique ID returned by the services: " + id); 
        await Query(id, client); 
    } 
    else 
        Console.WriteLine("Request failed with the following response: " + result.StatusCode); 
}

Next, create an async Task called Query(string id, HttpClient client) that utilizes the GUID provided by the ExtractText task. If successful the response body will contain all the request data in JSON format.

private async Task Query(string id, HttpClient client) 
{ 
    string queryUrl = string.Format("Query?id={0}", id.ToString()); 
    HttpResponseMessage result; 
    string returnedContent; 
    JObject returnedData; 
    int fileStatus; 
    do 
    { 
        result = await client.PostAsync(queryUrl, null); 
        returnedContent = await result.Content.ReadAsStringAsync(); 
        returnedData = JObject.Parse(returnedContent); 
        fileStatus = (int)returnedData.SelectToken("FileStatus"); 
        //The file is still being processed -- we will sleep the current thread for 5 seconds before trying again. 
        await Task.Delay(5000); 
    } while (fileStatus == 100 || fileStatus == 123); 
 
    Console.WriteLine("File has finished processing with return code: " + returnedData.SelectToken("FileStatus")); 
    if ((int)returnedData.SelectToken("FileStatus") != 200) 
        return; 
 
    ParseJson(returnedData.SelectToken("RequestData").ToString()); 
}

Then, create the function ParseJson(string json) to process the returned JSON data.

private void ParseJson(string json) 
{ 
    JArray requestArray = JArray.Parse(json); 
    foreach (var requestReturn in requestArray) 
    { 
        Console.WriteLine("Service Type: " + requestReturn.SelectToken("ServiceType")); 
        Console.WriteLine("Returned Data:" + requestReturn.SelectToken("data")); 
        Console.WriteLine(); 
    } 
}

Finally, create the function InitClient() to create a client connection to request the GUID and JSON data through.

private HttpClient InitClient() 
{ 
    string AppId = "Replace with Application ID"; 
    string Password = "Replace with Application Password"; 
 
    HttpClient client = new HttpClient(); 
    client.BaseAddress = new Uri(hostedServicesUrl); 
    client.DefaultRequestHeaders.Accept.Clear(); 
    client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); 
 
    string authData = string.Format("{0}:{1}", AppId, Password); 
    string authHeaderValue = Convert.ToBase64String(Encoding.UTF8.GetBytes(authData)); 
    client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", authHeaderValue); 
 
    return client; 
}

Run the Project

In order to test run this code be sure to add ExtractText().GetAwaiter().GetResults(); to the static void Main section.

Run the project by pressing F5, or by selecting Debug -> Start Debugging.

If the steps were followed correctly, the console appears and the application displays the parsed text information from the returned JSON data.

Wrap-up

This tutorial showed how to extract text information via the LEADTOOLS Cloud Services API.