Convert PDF Pages to Images and Recognize Barcodes

PDF documents usually comprise text, images, tables, attachments, graphs, annotations and other objects. Some of our customers need to embed barcodes in documents and then identify barcodes in the PDF file. The following article explains how to transform the pages in a PDF file to images and identifying barcodes in the images with Aspose.Barcode for .NET.

Converting Pages to Images and Recognizing Barcodes

Aspose.PDF for .NET is very powerful product for managing PDF documents. It makes it easy to convert pages in PDF documents to images. Aspose.BarCode for .NET is an equally powerful product for generating and recognizing barcodes.

The class PdfConverter under the Aspose.Pdf.Facades namespace supports converting PDF pages to various image formats. The PngDevice under the Aspose.Pdf.Devices namespace supports converting PDF pages to PNG files. Either of these classes can be used to transform pages of PDF file into images.

When the pages have been converted to an image format, we can use Aspose.BarCode for .NET to identify barcodes inside them. The code samples below show how to convert pages using either PdfConverter or PngDevice.

Using Aspose.Pdf.Facades

The PdfConverter class contains a method named GetNextImage which generates the an image from the current PDF page. To specify the output image format, this method accepts an argument from the System.Drawing.Imaging.ImageFormat enumeration.

Aspose.Barcode contains a namespace, BarCodeRecognition, which contains the BarCodeReader class. The BarCodeReader class lets you read, determine, and identify barcodes from image files.

For the purposes of this example, first convert a page in a PDF file into an image with Aspose.Pdf.Facades.PdfConverter. Then use the Aspose.BarCodeRecognition.BarCodeReader class to recognize the barcode in the image.

private static void IdentifyBarcodesConverter()
{
    // The path to the documents directory
    string dataDir = RunExamples.GetDataDir_AsposePdf_DocumentConversion();

    // Create a PdfConverter object
    var converter = new Aspose.Pdf.Facades.PdfConverter();

    // Bind the input PDF file
    converter.BindPdf(dataDir + "IdentifyBarcodes.pdf");

    // Specify the start page to be processed
    converter.StartPage = 1;

    // Specify the end page for processing
    converter.EndPage = 1;

    // Create a Resolution object to specify the resolution of resultant image
    converter.Resolution = new Aspose.Pdf.Devices.Resolution(300);

    // Initialize the convertion process
    converter.DoConvert();

    // Create a MemoryStream object to hold the resultant image
    using (var imageStream = new MemoryStream())
    {
        // Check if pages exist and then convert to image one by one
        while (converter.HasNextImage())
        {
            // Save the image in the given image Format
            converter.GetNextImage(imageStream, System.Drawing.Imaging.ImageFormat.Png);

            // Set the stream position to the beginning of the stream
            imageStream.Position = 0;

            // Instantiate a BarCodeReader object
            var barcodeReader = new Aspose.BarCodeRecognition.BarCodeReader(imageStream, Aspose.BarCodeRecognition.BarCodeReadType.Code39Extended);

            // String txtResult.Text = "";
            while (barcodeReader.Read())
            {
                // Get the barcode text from the barcode image
                var code = barcodeReader.GetCodeText();

                // Write the barcode text to Console output
                Console.WriteLine("BARCODE : " + code);
            }

            // Close the BarCodeReader object to release the image file
            barcodeReader.Close();
        }

        // Close the PdfConverter instance and release the resources
        converter.Close();
    }
}

In above code snippets the output image is saved to a MemoryStream object. The image can also be saved to disk. To do so, replace the MemorStream object with a string object that represents the file path to the PdfConverter class’ GetNextImage method.

Using the PngDevice Class

In the Aspose.Pdf.Devices, is the PngDevice. This class lets you convert pages in PDF documents to PNG images.

For the purpose of this example, load the source PDF file into the Document] cument’s pages into PNG images. When the images have been created, use the BarCodeReader class under the Aspose.BarCodeRecognition to identify and read barcodes in the images.

The code samples given here traverses through the pages of the PDF document and tries to identify barcodes on each page.

private static void IdentifyBarcodes()
{
    // The path to the documents directory
    string dataDir = RunExamples.GetDataDir_AsposePdf_DocumentConversion();

    // Open the PDF document
    using (var document = new Aspose.Pdf.Document(dataDir + "IdentifyBarcodes.pdf"))
    {
        // Traverse through the individual pages of the PDF file
        for (int pageCount = 1; pageCount <= document.Pages.Count; pageCount++)
        {
            using (var imageStream = new System.IO.MemoryStream())
            {
                // Create a Resolution object
                var resolution = new Aspose.Pdf.Devices.Resolution(300);

                // Instantiate a PngDevice object while passing a Resolution object as an argument to its constructor
                var pngDevice = new Aspose.Pdf.Devices.PngDevice(resolution);

                // Convert a particular page and save the image to stream
                pngDevice.Process(document.Pages[pageCount], imageStream);

                // Set the stream position to the beginning of Stream
                imageStream.Position = 0;

                // Instantiate a BarCodeReader object
                var barcodeReader = new Aspose.BarCodeRecognition.BarCodeReader(imageStream, Aspose.BarCodeRecognition.BarCodeReadType.Code39Extended);

                // String txtResult.Text = "";
                while (barcodeReader.Read())
                {
                    // Get the barcode text from the barcode image
                    var code = barcodeReader.GetCodeText();

                    // Write the barcode text to Console output
                    Console.WriteLine("BARCODE : " + code);
                }

                // Close the BarCodeReader object to release the image file
                barcodeReader.Close();
            }
        }
    }
}

For further information on topics covered in this article go to:

• Convert PDF Pages to Different Image Formats (Facades)
• Convert all PDF pages to PNG Images
• Read Barcodes