Document conversion workflow

Conversion of multipage documents

If you want to take advantage of multithreading, you can use the interface IPageQueue or its implementation CRangedPageQueue to start the multipage document conversion right at the beginning of the OCR processing.

Image 1. Document conversion workflow using CRangedPageQueue

So you can use the processed pages as soon as the output document engine has retrieved them.

Code snippets

Note

The code snippet does not show exception handling to keep it simple.

Usign CRangedPageQueue in a multithreaded document conversion workflow with C++ API and OpenMP instructions

// Create the ranged page queue with an appropriate size, according to available
// memory and number of OCR threads.
CRangedPageQueue objRangedPageQueue = CRangedPageQueue::Create ( 9 );
omp_set_nested ( 1 );
#pragma omp parallel sections num_threads(2)
{
  // First thread will start document output
  #pragma omp section
  {
    CDocumentOutput objDocumentOutput = CDocumentOutput::Create ( CIDRS::Create ());
    objDocumentOutput.Save ( strOutputPath, objOutputParameters, objRangedPageQueue );
  }
  #pragma omp section
  {
    // The 3 other threads will be performing OCR
    const int iProcessingThreadCount = 3;
    #pragma omp parallel num_threads(iProcessingThreadCount)
    for ( ... )
    {
      // Retrieve the number of the next page to process
      IDRS_INT iPageToProcess = ( ... );

      // Load and process it
      CPage objPage = CPage::Create ( ... );

      // ...

      // Once process is done, wait until the queue is able to store this page
      // before starting processing of a new one
      while ( ! objRangedPageQueue.TryAddPage ( objPage, iPageToProcess ))
      {
        Sleep ( 50 );
      }
    }
    // When the end of the document is reached, close the page queue
    // to complete document creation.
    objRangedPageQueue.Close ();
  }
}

Using CRangedPageQueue in a multithreaded document conversion workflow with .NET API

// Create the ranged page queue with an appropriate size, according to available
// memory and number of OCR threads.
CRangedPageQueue objRangedPageQueue = new CRangedPageQueue(9);

// Start document output in a separate thread
Thread objOutputThread = new Thread(() =>
{
  CDocumentOutput objDocumentOutput = new CDocumentOutput(new CIDRS());
  objDocumentOutput.Save(strOutputPath, objOutputParameters, objRangedPageQueue);
});
objOutputThread.Start();

// Then start OCR in 3 other threads
const int iProcessingThreadCount = 3;
Parallel.For(...,
  new ParallelOptions { MaxDegreeOfParallelism = iProcessingThreadCount },
  ... =>
{

  // Retrieve the number of the next page to process
  UInt32 uiPageToProcess = (...);

  // Load and process it
  using (CPage objPage = new CPage(...))
  {
    // ...

    // Once process is done, wait until the queue is able to store this page,
    // before starting processing of a new one
    while (!objRangedPageQueue.TryAddPage(objPage, uiPageToProcess))
    {
      Thread.Sleep(50);
    }
  }
});

// When the end of the document is reached, close the page queue
// to complete document creation.
objRangedPageQueue.Close();

// Wait for the document output thread completion before exiting
objOutputThread.Join();