Perform OCR in ASP.NET Core

11 Jan 20233 minutes to read

The Syncfusion .NET OCR library is used to extract text from the scanned PDFs and images in the ASP.NET Core application with the help of Google’s Tesseract Optical Character Recognition engine.

Steps to perform OCR on entire PDF document in ASP.NET Core application

Step 1: Create a new C# ASP.NET Core Web Application project.

Step 2: In configuration windows, name your project and click Next.

Step 3: Install the Syncfusion.PDF.OCR.NET NuGet package as a reference to your .NET Standard applications from NuGet.org.

Step 4: Tesseract assemblies are not added as a reference. They must be kept in the local machine, and the assemblies location is passed as a parameter to the OCR processor.

C#

OCRProcessor processor = new OCRProcessor(@"Tesseractbinaries/Windows");

Step 5: Place the Tesseract language data {E.g, eng.traineddata} in the local system and provide a path to the OCR processor. Please use the OCR language data for other languages using the following link.

Tesseract language data

C#

OCRProcessor processor = new OCRProcessor(@"Tesseractbinaries/Windows");
processor.PerformOCR(lDoc, "tessdata/");

Step 6: A default controller with the name HomeController.cs gets added to the creation of the ASP.NET Core MVC project. Include the following namespaces in that HomeController.cs file.

C#

using Syncfusion.OCRProcessor;
using Syncfusion.Pdf.Parsing;

Step 7: Add a new button in index.cshtml as follows.

C#

@{Html.BeginForm("PerformOCR", "Home", FormMethod.Post);
   {
      <div>
         <input type="submit" value="Perform OCR" style="width:150px;height:27px" />
      </div>
   }
   Html.EndForm();
}

Step 8: Add a new action method named PerformOCR in the HomeController.cs and use the following code sample to perform OCR on the entire PDF document using PerformOCR method of the OCRProcessor class.

C#

//Initialize the OCR processor by providing the path of tesseract binaries(SyncfusionTesseract.dll and liblept168.dll).
using (OCRProcessor processor = new OCRProcessor("Tesseractbinaries/Windows"))
{
   FileStream fileStream = new FileStream("Input.pdf", FileMode.Open, FileAccess.Read);
   //Load a PDF document.
   PdfLoadedDocument lDoc = new PdfLoadedDocument(fileStream);
   //Set OCR language to process.
   processor.Settings.Language = Languages.English;
   //Process OCR by providing the PDF document and Tesseract data.
   processor.PerformOCR(lDoc, "tessdata/");
   //Create memory stream.
   MemoryStream stream = new MemoryStream();
   //Save the document to memory stream.
   lDoc.Save(stream);
   lDoc.Close();
   //Set the position as '0'
   stream.Position = 0;
   //Download the PDF document in the browser.
   FileStreamResult fileStreamResult = new FileStreamResult(stream, "application/pdf");
   fileStreamResult.FileDownloadName = "Sample.pdf";
   return fileStreamResult;
}

By executing the program, you will get a PDF document as follows.

A complete working sample can be downloaded from the Github.