Getting Started with Web API OCR Processor

14 Aug 20264 minutes to read

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

To include the .NET OCR library in your ASP.NET Core Web API, please refer to the NuGet Packages Required or Assemblies Required documentation.

Prerequisites

Version Compatibility

• Syncfusion.PDF.OCR.Net.Core supports .NET 8.0 and later versions.

Supported Inputs

The OCR processor supports the following input formats:

• Single-page and multi-page PDF documents
• Scanned images in common formats (JPEG, PNG, TIFF)
• Recommended DPI: 200 DPI or higher for optimal OCR accuracy

Register the License Key

NOTE

Starting with v16.2.0.x, if you reference Syncfusion® assemblies from trial setup or from the NuGet feed, you must add the Syncfusion.Licensing assembly reference and register a license key in your application. For more information, see the licensing documentation.

Include the following code in the Program.cs file to register the license key:

C#

using Syncfusion.Licensing;

// Register Syncfusion license at application startup
SyncfusionLicenseProvider.RegisterLicense("YOUR LICENSE KEY");

NOTE

1. Beginning from version 21.1.x, the TesseractBinaries and Tesseract language data folders are now included by default; you no longer have to set these paths explicitly.
2. The current NuGet package includes Tesseract 5.0, which provides support for 100+ languages.

Steps to perform OCR on an entire PDF document in ASP.NET Core Web API

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

Step 2: In the project configuration window, select your target framework (.NET 8.0 or later), name your project, and click Create.

Step 3: Install the Syncfusion.PDF.OCR.Net.Core NuGet package into your ASP.NET Core Web API project from NuGet.org.

Step 4: Build the project to ensure all NuGet packages are properly restored. Press Ctrl+Shift+B or go to Build > Build Solution.

Step 5: Add a new API controller empty file in the project.

Step 6: Include the following namespaces in the PdfController.cs.

C#

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

Step 7: Include the following code sample in PdfController.cs using the PerformOCR method of the OCRProcessor class.

C#

[HttpGet("/api/Pdf")]
public IActionResult ConvertOCR()
{
    //Initialize the OCR processor.
    using (OCRProcessor processor = new OCRProcessor())
    {
        FileStream fileStream = new FileStream("Input.pdf", FileMode.Open, FileAccess.Read);
        //Load an existing PDF document.
        PdfLoadedDocument document = new PdfLoadedDocument(fileStream);
        //Set the Tesseract version.
        processor.Settings.TesseractVersion = TesseractVersion.Version5_0;
        //Set OCR language.
        processor.Settings.Language = Languages.English;
        //Perform OCR with input document and tessdata (Language packs).
        processor.PerformOCR(document);
        //Create memory stream.
        MemoryStream stream = new MemoryStream();
        //Save the document to memory stream.
        document.Save(stream);
        stream.Position = 0;
        fileStream.Dispose();
        document.Dispose();
        return File(stream, "application/pdf", "Output.pdf");
    }
}

Step 8: Navigate to the Swagger UI, expand the GET /api/Pdf API, click Execute, and then download the response output.

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

A complete working sample can be downloaded from Github.

Click here to explore the rich set of Syncfusion^® PDF library features.