Apply OCR to Vector Graphic PDF in C# and .NET
OCR (Optical Character Recognition) is a technology that allows you to convert various types of documents, such as scanned paper documents, PDF files or images captured by a camera, into editable and searchable data.
In this article, we will look at how to use the SautinSoft.Pdf library.NET to perform OCR on a PDF document containing text in the form of vector graphics using C# and .NET.
Step-by-step guide:
- Add SautinSoft.PDF from NuGet.
- Load a PDF document.
- Save the vectorized content as image objects.
- Perform OCR.
- Save the document in DOCX format.
Input file: simple text.pdf
Output result:
Complete code
GitHubusing SautinSoft.Pdf;
using SautinSoft.Pdf.Content;
using SautinSoft.Pdf.Objects;
using System;
using Tesseract;
using System.Collections.Generic;
using System.IO;
using System.Linq;
namespace OCR
{
class OCR
{
/// <summary>
/// OCR a PDF document containing text as vector graphics
/// </summary>
/// <remarks>
/// Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/ocr-a-pdf-document-containing-text-as-vector-graphics.php
/// </remarks>
static void Main()
{
try
{
string tesseractLanguages = "eng";
string tesseractData = Path.GetFullPath(@".\tessdata");
string tempFile = Path.Combine(tesseractData, Path.GetRandomFileName());
PdfDocument pdfDocument = PdfDocument.Load(@"..\..\..\Vectorized text.pdf");
MemoryStream ms = new MemoryStream();
pdfDocument.Save(ms, new ImageSaveOptions());
pdfDocument = new PdfDocument();
PdfFormattedText text = new PdfFormattedText();
using (Tesseract.TesseractEngine engine = new Tesseract.TesseractEngine(tesseractData, tesseractLanguages, Tesseract.EngineMode.Default))
{
var pdfPage = pdfDocument.Pages.Add();
engine.DefaultPageSegMode = Tesseract.PageSegMode.Auto;
{
byte[] imgBytes = ms.ToArray();
using (Tesseract.Pix img = Tesseract.Pix.LoadFromMemory(imgBytes))
{
using (var page = engine.Process(img, "Serachablepdf"))
{
var st = page.GetText();
double scale = Math.Min(pdfPage.Size.Width / page.RegionOfInterest.Width, pdfPage.Size.Height / page.RegionOfInterest.Height);
using (var iter = page.GetIterator())
{
iter.Begin();
do
{
do
{
do
{
iter.TryGetBoundingBox(PageIteratorLevel.TextLine, out Rect liRect);
text.FontSize = liRect.Height * scale;
//text.Opacity = 0;
text.Append(iter.GetText(PageIteratorLevel.TextLine));
pdfPage.Content.DrawText(text, new PdfPoint(liRect.X1 * scale, pdfPage.Size.Height - liRect.Y1 * scale - text.Height));
text.Clear();
} while (iter.Next(PageIteratorLevel.Para, PageIteratorLevel.TextLine));
} while (iter.Next(PageIteratorLevel.Block, PageIteratorLevel.Para));
} while (iter.Next(PageIteratorLevel.Block));
}
}
}
}
}
pdfDocument.Save(@"text.docx");
System.Diagnostics.Process.Start(new System.Diagnostics.ProcessStartInfo(@"text.docx") { UseShellExecute = true });
}
catch (Exception e)
{
Console.WriteLine();
Console.WriteLine("Please be sure that you have Language data files (*.traineddata) in your folder \"tessdata\"");
Console.WriteLine("The Language data files can be download from here: https://github.com/tesseract-ocr/tessdata_fast");
Console.ReadKey();
throw new Exception("Error Tesseract: " + e.Message);
}
finally
{
}
}
}
}Imports SautinSoft.Pdf
Imports SautinSoft.Pdf.Content
Imports System
Imports Tesseract
Imports System.Collections.Generic
Imports System.IO
Imports System.Linq
Namespace OCR
Friend Class OCR
''' <summary>
''' OCR a PDF document containing text as vector graphics
''' </summary>
''' <remarks>
''' Details: https://sautinsoft.com/products/pdf/help/net/developer-guide/ocr-a-pdf-document-containing-text-as-vector-graphics.php
''' </remarks>
Public Shared Sub Main()
Dim liRect As Rect = Nothing
Try
Dim tesseractLanguages = "eng"
Dim tesseractData = Path.GetFullPath(".\tessdata")
Dim tempFile As String = Path.Combine(tesseractData, Path.GetRandomFileName())
Dim pdfDocument As PdfDocument = PdfDocument.Load("..\..\..\Vectorized text.pdf")
Dim mss As List(Of MemoryStream) = New List(Of MemoryStream)()
Dim ms As MemoryStream = New MemoryStream()
pdfDocument.Save(ms, New ImageSaveOptions())
pdfDocument = New PdfDocument()
Dim text As PdfFormattedText = New PdfFormattedText()
Using engine As TesseractEngine = New TesseractEngine(tesseractData, tesseractLanguages, EngineMode.Default)
Dim pdfPage = pdfDocument.Pages.Add()
engine.DefaultPageSegMode = PageSegMode.Auto
If True Then
Dim imgBytes As Byte() = ms.ToArray()
Using img = Pix.LoadFromMemory(imgBytes)
Using page = engine.Process(img, "Serachablepdf")
Dim st = page.GetText()
Dim scale = Math.Min(pdfPage.Size.Width / page.RegionOfInterest.Width, pdfPage.Size.Height / page.RegionOfInterest.Height)
Using iter = page.GetIterator()
iter.Begin()
Do
Do
Do
iter.TryGetBoundingBox(PageIteratorLevel.TextLine, liRect)
text.FontSize = liRect.Height * scale
'text.Opacity = 0;
text.Append(iter.GetText(PageIteratorLevel.TextLine))
pdfPage.Content.DrawText(text, New PdfPoint(liRect.X1 * scale, pdfPage.Size.Height - liRect.Y1 * scale - text.Height))
text.Clear()
Loop While iter.Next(PageIteratorLevel.Para, PageIteratorLevel.TextLine)
Loop While iter.Next(PageIteratorLevel.Block, PageIteratorLevel.Para)
Loop While iter.Next(PageIteratorLevel.Block)
End Using
End Using
End Using
End If
End Using
pdfDocument.Save("text.docx")
Process.Start(New ProcessStartInfo("text.docx") With {
.UseShellExecute = True
})
Catch e As Exception
Console.WriteLine()
Console.WriteLine("Please be sure that you have Language data files (*.traineddata) in your folder ""tessdata""")
Console.WriteLine("The Language data files can be download from here: https://github.com/tesseract-ocr/tessdata_fast")
Console.ReadKey()
Throw New Exception("Error Tesseract: " & e.Message)
Finally
End Try
End Sub
End Class
End Namespace
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