| title | Perform OCR on PDF and image files in Azure Vision | Syncfusion |
|---|---|
| description | Learn how to perform OCR on scanned PDF documents and images in Azure Vision using Syncfusion .NET OCR library. |
| platform | document-processing |
| control | |
| documentation | UG |
| keywords | Assemblies |
The Syncfusion® .NET OCR library supports external engines (Azure Computer Vision) to process the OCR on images and PDF documents.
Step 1: Create a new .NET Console application project.
In project configuration window, name your project and select Next.
Step 2: Install Syncfusion.PDF.OCR.Net.Core and Microsoft.Azure.CognitiveServices.Vision.ComputerVision NuGet packages as reference to your .NET application from nuget.org.
N> 1. Beginning from version 21.1.x, the default configuration includes the addition of the TesseractBinaries and Tesseract language data folder paths, eliminating the requirement to explicitly provide these paths. N> 2. Starting with v16.2.0.x, if you reference Syncfusion® assemblies from trial setup or from the NuGet feed, you also have to add "Syncfusion.Licensing" assembly reference and include a license key in your projects. Please refer to this link to know about registering Syncfusion® license key in your application to use our components.
Step 3: Include the following namespaces in the Program.cs file.
{% highlight c# tabtitle="C#" %} using Syncfusion.OCRProcessor; using Syncfusion.Pdf.Parsing; {% endhighlight %}
Step 4: Use the following code sample to perform OCR on a PDF document using PerformOCR method of the OCRProcessor class with Azure Vision.
{% highlight c# tabtitle="C#" %}
//Initialize the OCR processor. using (OCRProcessor processor = new OCRProcessor()) { //Load an existing PDF document. FileStream stream = new FileStream("Input.pdf", FileMode.Open); PdfLoadedDocument lDoc = new PdfLoadedDocument(stream); //Set OCR language. processor.Settings.Language = Languages.English; //Initialize the Azure vision OCR external engine. IOcrEngine azureOcrEngine = new AzureExternalOcrEngine(); processor.ExternalEngine = azureOcrEngine; //Perform OCR. processor.PerformOCR(lDoc); //Create file stream. FileStream outputStream = new FileStream("OCR.pdf", FileMode.CreateNew); //Save the document into stream. lDoc.Save(outputStream); //If the position is not set to '0' then the PDF will be empty. outputStream.Position = 0; //Close the document. lDoc.Close(true); outputStream.Close(); }
{% endhighlight %}
Step 5: Create a new class named AzureExternalOcrEngine to get the image stream from the PerformOCR method and process the image stream with an external engine. It returns the OCRLayoutResult for the image.
N> Provide a valid subscription key and endpoint to work with Azure computer vision.
{% highlight c# tabtitle="C#" %}
class AzureExternalOcrEngine : IOcrEngine
{
private string subscriptionKey = "SubscriptionKey";
private string endpoint = "Endpoint link";
public OCRLayoutResult PerformOCR(Stream imgStream)
{
ComputerVisionClient client = Authenticate();
ReadResult azureOcrResult = ReadFileUrl(client, imgStream).Result;
OCRLayoutResult result = ConvertAzureVisionOcrToOcrLayoutResult(azureOcrResult);
return result;
}
public ComputerVisionClient Authenticate()
{
ComputerVisionClient client = new ComputerVisionClient(new ApiKeyServiceClientCredentials(subscriptionKey))
{
Endpoint = endpoint
};
return client;
}
public async Task<ReadResult> ReadFileUrl(ComputerVisionClient client, Stream stream)
{
stream.Position = 0;
var textHeaders = await client.ReadInStreamAsync(stream);
string operationLocation = textHeaders.OperationLocation;
const int numberOfCharsInOperationId = 36;
string operationId = operationLocation.Substring(operationLocation.Length - numberOfCharsInOperationId);
//Extract the text
ReadOperationResult results;
do
{
results = await client.GetReadResultAsync(Guid.Parse(operationId));
}
while ((results.Status == OperationStatusCodes.Running || results.Status == OperationStatusCodes.NotStarted));
ReadResult azureOcrResult = results.AnalyzeResult.ReadResults[0];
return azureOcrResult;
}
private OCRLayoutResult ConvertAzureVisionOcrToOcrLayoutResult(ReadResult azureVisionOcr)
{
Syncfusion.OCRProcessor.Line ocrLine;
Syncfusion.OCRProcessor.Word ocrWord;
OCRLayoutResult ocrlayoutResult = new OCRLayoutResult();
ocrlayoutResult.ImageWidth = (float)azureVisionOcr.Width;
ocrlayoutResult.ImageHeight = (float)azureVisionOcr.Height;
//Page
Syncfusion.OCRProcessor.Page normalPage = new Syncfusion.OCRProcessor.Page();
//Lines
foreach (var line in azureVisionOcr.Lines)
{
ocrLine = new Syncfusion.OCRProcessor.Line();
//Word
foreach (var word in line.Words)
{
ocrWord = new Syncfusion.OCRProcessor.Word();
Rectangle rect = GetAzureVisionBounds(word.BoundingBox);
ocrWord.Text = word.Text;
ocrWord.Rectangle = rect;
ocrLine.Add(ocrWord);
}
normalPage.Add(ocrLine);
}
ocrlayoutResult.Add(normalPage);
return ocrlayoutResult;
}
private Rectangle GetAzureVisionBounds(IList<double?> bbox)
{
Rectangle rect = Rectangle.Empty;
PointF[] pointCollection = new PointF[bbox.Count / 2];
int count = 0;
for (int i = 0; i < bbox.Count; i = i + 2)
{
pointCollection[count] = new PointF((float)bbox[i], (float)bbox[i + 1]);
count++;
}
float xMin = 0;
float yMin = 0;
float xMax = 0;
float yMax = 0;
bool first = true;
foreach (PointF point in pointCollection)
{
if (first)
{
xMin = point.X;
yMin = point.Y;
first = false;
}
else
{
if (point.X < xMin)
xMin = point.X;
else if (point.X > xMax)
xMax = point.X;
if (point.Y < yMin)
yMin = point.Y;
else if (point.Y > yMax)
yMax = point.Y;
}
}
int x = Convert.ToInt32(xMin);
int y = Convert.ToInt32(yMin);
int w = Convert.ToInt32(xMax);
int h = Convert.ToInt32(yMax);
return new Rectangle(x, y, w, h);
}
}
{% endhighlight %}
By executing the program, you will get a PDF document as follows.
A complete working sample can be downloaded from Github.
Click here to explore the rich set of Syncfusion® PDF library features.