How to Perform OCR on a PDF Document Using ASP.NET Core

29 Nov 20223 minutes to read

Optical Character Recognition (OCR) is a technology that converts scanned paper documents from PDF files or images into searchable and editable data.

The Syncfusion OCR processor library has extended support to process OCR on scanned PDF documents and other scanned images in the .NET Core platform with the help of the Tesseract OCR engine.

Steps to perform OCR on a PDF document programmatically

1.Create a new C# ASP.NET Core Web application project.

2.In the project configuration window, name your project and select Next.

3.Install the Syncfusion.PDF.OCR.Net.Core NuGet package as a reference to your .NET Standard application from nuget.org.

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

C#

OCRProcessor processor = new OCRProcessor(@"TesseractBinaries\")

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,
https://github.com/tesseract-ocr/tessdata

C#

OCRProcessor processor = new OCRProcessor("Tesseractbinaries\");
processor.PerformOCR(loadedDocument, "tessdata/");

6.A default action method named Index will be present in HomeController.cs. Right-click on Index method and select Go to View, where you will be directed to its associated view page Index.cshtml.
7.Add a new button in the Index.cshtml as shown below.

C#

@{Html.BeginForm("PerformOCR", "Home", FormMethod.Get);
    {
        <div>
            <input type="submit" value="Perform OCR on entire PDF" style="width:200px;height:27px" />
        </div>
    }
    Html.EndForm();
}

8.A default controller with name HomeController.cs is added to the creation of ASP.NET Core project. Include the following namespaces in that HomeController.cs file.

C#

using Syncfusion.Pdf.Parsing;
using Syncfusion.OCRProcessor;
using System.Drawing;

10.Use the following code sample to perform OCR in the ASP.NET Core application.

C#

//Load PDF document as stream
string docPath = _hostingEnvironment.WebRootPath + "/Data/Input.pdf";
FileStream docStream = new FileStream(docPath, FileMode.Open, FileAccess.Read);
//Load the PDF document 
PdfLoadedDocument loadedDocument = new PdfLoadedDocument(docStream);
string tesseractPath = _hostingEnvironment.WebRootPath + "/Data/Tesseractbinaries/Windows";
//Initialize the OCR processor by providing the path of tesseract binaries
using (OCRProcessor processor = new OCRProcessor(tesseractPath))
{
    //Language to process the OCR
    processor.Settings.Language = Languages.English;

    string tessdataPath = _hostingEnvironment.WebRootPath + "/Data/tessdata/";
    //Process OCR by providing loaded PDF document, Data dictionary and language
    processor.PerformOCR(loadedDocument, tessdataPath);
}
//Saving the PDF to the MemoryStream
MemoryStream stream = new MemoryStream();
loadedDocument.Save(stream);
//Close the PDF document 
loadedDocument.Close(true);
//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;

A complete working sample can be downloaded from GitHub.

By executing the program, you will get the text file (contains extracted text) as follows.