AppendLtd Method

'Declaration
 
Public Sub AppendLtd( _
   ByVal sourceFileName As String, _
   ByVal destFileName As String _
) 

Public Shared Sub AppendLtdExample()
      ' Get a multi-page source file
      Dim sourceFileName As String = GetImageFileName()
      Dim destFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "AppendLtdExample.pdf")
      File.Delete(destFileName)
      ' Use OCR Professional engine
      Using ocrEngine As IOcrEngine = OcrEngineManager.CreateEngine(OcrEngineType.Professional, False)
         ocrEngine.Startup(Nothing, Nothing, Nothing, Nothing)

         ' Get the number of pages in the source file
         Dim pageCount As Integer
         Using imageInfo As CodecsImageInfo = ocrEngine.RasterCodecsInstance.GetInformation(sourceFileName, True)
            pageCount = imageInfo.TotalPages
         End Using

         Console.WriteLine("OCRing {0} pages", pageCount)

         ' Use all possible cores
         Dim maxThreads As Integer = Environment.ProcessorCount
         Console.WriteLine("Machine has {0} cores", maxThreads)

         Dim threadCount As Integer = Math.Min(maxThreads, pageCount)
         Console.WriteLine("Using {0} threads", threadCount)

         ' Initialie the thread parameters
         Dim threadParams(threadCount - 1) As MyThreadParam
         For i As Integer = 0 To threadCount - 1
            threadParams(i) = New MyThreadParam()
            threadParams(i).ThreadFinishedEvent = New AutoResetEvent(False)
            threadParams(i).OcrEngine = ocrEngine
            ' We can re-use the documents, so create them once here
            threadParams(i).OcrDocument = ocrEngine.DocumentManager.CreateDocument()
            threadParams(i).SourceFileName = sourceFileName
            ' We can re-use the LTD files, so get them here once
            threadParams(i).LtdFileName = Path.GetTempFileName()
         Next

         ' This is the LTD file we will use to append all recognition data
         ' from all threads
         Dim mainLtdFileName As String = Path.GetTempFileName()
         File.Delete(mainLtdFileName)

         Dim pageNumber As Integer = 1
         While pageNumber <= pageCount
            Dim queuedUpEvents As New List(Of AutoResetEvent)

            ' Queue up the threads, each thread will have its own
            ' IOcrDocument to recognize one page to a separate LTD file
            Dim ltdCounter As Integer = 0
            For threadIndex As Integer = 0 To threadCount - 1
               If pageNumber <= pageCount Then
                  ' Queue up this page
                  Console.WriteLine("Queing up page {0}", pageNumber)
                  threadParams(threadIndex).PageNumber = pageNumber
                  queuedUpEvents.Add(threadParams(threadIndex).ThreadFinishedEvent)
                  ThreadPool.QueueUserWorkItem(AddressOf MyThreadProc, threadParams(threadIndex))
                  pageNumber = pageNumber + 1
                  ltdCounter = ltdCounter + 1
               End If
            Next

            ' Wait for the queued up threads to finish
            Console.WriteLine("Waiting on queued up pages to finished")
            WaitHandle.WaitAll(queuedUpEvents.ToArray())

            Console.WriteLine("Appending LTDs")
            For i As Integer = 0 To ltdCounter - 1
               ' Notice, first time, the main LTD does not exist, AppendLtd will
               ' just copy the data over from the source file
               ocrEngine.DocumentWriterInstance.AppendLtd(threadParams(i).LtdFileName, mainLtdFileName)
            Next
         End While

         ' We are done, convert the LTD to final format, here, we will
         ' use PDF
         Console.WriteLine("Converting to final format")
         ocrEngine.DocumentWriterInstance.Convert(mainLtdFileName, destFileName, DocumentFormat.Pdf)

         ' Clean-up
         For i As Integer = 0 To threadCount - 1
            threadParams(i).ThreadFinishedEvent.Close()
            threadParams(i).OcrDocument.Dispose()
         Next

         Console.WriteLine("Success, file {0} is created", destFileName)
      End Using
   End Sub

   Class MyThreadParam
      ' Event to trigger when recognition is done
      Public ThreadFinishedEvent As AutoResetEvent
      ' OCR engine to use
      Public OcrEngine As IOcrEngine
      ' OCR Document to use
      Public OcrDocument As IOcrDocument
      ' Source image file
      Public SourceFileName As String
      ' Page number to recognize by this thread
      Public PageNumber As Integer
      ' LTD file to save temporary recognition data
      Public LtdFileName As String
   End Class

   Private Shared Sub MyThreadProc(ByVal state As Object)
      Dim threadParams As MyThreadParam = CType(state, MyThreadParam)
      Console.WriteLine("  Thread {0} is working on pages {1}", Thread.CurrentThread.GetHashCode(), threadParams.PageNumber)

      Try
         ' Delete the LTD file if it exists so we can put fresh data in it
         File.Delete(threadParams.LtdFileName)

         ' Clear any previous pages in this document
         threadParams.OcrDocument.Pages.Clear()

         ' Load the page
         Console.WriteLine("  Thread {0} is loading the page", Thread.CurrentThread.GetHashCode())
         threadParams.OcrDocument.Pages.AddPages(threadParams.SourceFileName, threadParams.PageNumber, threadParams.PageNumber, Nothing)

         ' Get it, it is the last page we added
         Dim ocrPage As IOcrPage = threadParams.OcrDocument.Pages(threadParams.OcrDocument.Pages.Count - 1)

         ' Auto-zone it
         Console.WriteLine("  Thread {0} is auto-zoning the page", Thread.CurrentThread.GetHashCode())
         ocrPage.AutoZone(Nothing)

         ' Recognize it
         Console.WriteLine("  Thread {0} is recognizing the page", Thread.CurrentThread.GetHashCode())
         ocrPage.Recognize(Nothing)

         ' Save it
         Console.WriteLine("  Thread {0} is saving the page", Thread.CurrentThread.GetHashCode())
         threadParams.OcrDocument.Save(threadParams.LtdFileName, DocumentFormat.Ltd, Nothing)
      Finally
         Console.WriteLine("  Thread {0} is done", Thread.CurrentThread.GetHashCode())
         threadParams.ThreadFinishedEvent.Set()
      End Try
   End Sub

   Private Shared Function GetImageFileName() As String
      Dim pageTileTemplate As String = Path.Combine(LEAD_VARS.ImagesDir, "Ocr{0}.tif")
      Dim multiPageImageFileName As String = Path.Combine(LEAD_VARS.ImagesDir, "AppendLtdExample.tif")

      File.Delete(multiPageImageFileName)

      ' Create a multi-page TIF file by stitching OCR1 to OCR4.tif shipped with LEADTOOLS
      Using codecs As New RasterCodecs()
         Dim finalImage As RasterImage = Nothing

         For page As Integer = 1 To 4
            Dim pageImage As RasterImage = codecs.Load(String.Format(pageTileTemplate, page))
            If IsNothing(finalImage) Then
               finalImage = pageImage
            Else
               finalImage.AddPage(pageImage)
               pageImage.Dispose()
            End If
         Next

         ' Save the final image
         codecs.Save(finalImage, multiPageImageFileName, RasterImageFormat.CcittGroup4, 1)
      End Using

      Return multiPageImageFileName
   End Function

Public NotInheritable Class LEAD_VARS
   Public Const ImagesDir As String = "C:\Users\Public\Documents\LEADTOOLS Images"
End Class