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Recognizing Barcodes in PDF and TIFF Documents

Multipage business documents and reports sometimes use barcodes to aid in routing and indexing. Using the DotImage .NET PDF Reader, .NET TIFF Codec, and Barcode Recognition for .NET Add-on, it's easy to read the barcodes and use them to automate workflows or find these documents in a repository.

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Multipage business documents and reports sometimes use barcodes to aid in automated routing and indexing. Using the DotImage .NET PDF Reader, .NET TIFF Codec, and Barcode Recognition for .NET Add-on, it’s easy to read the data encoded in these barcodes and use them to automate workflows or find these documents in a repository.

Reading a Page from a PDF

Generally, a page in a PDF will either be an imaged page that might have come from a scanner or instead be made up of various elements (text, drawings, images, etc.). If it’s an imaged page, we would want to extract the page from the PDF at the stored resolution. If it’s composed, we need to rasterize the page to a single image, making sure to do it at a high resolution to preserve the quality of the barcodes.

Here is a C# function that retrieves a page from a PDF at the best resolution for barcode reading:

        private AtalaImage GetPdfPage(Stream stream, int pageNum)
        {
            AtalaImage img = null;            

            // check to see if this page is an image
            using (Document pdfDoc = new Document(stream))
            {
                Page pdfPage = pdfDoc.Pages[pageNum];
                if (pdfPage.SingleImageOnly)
                {
                    // if it's an image, extract it from the PDF at its
                    // stored resolution
                    img = pdfPage.ExtractImages()[0].Image;
                }
            }

            // if the page is not an image, rasterize it at high enough
            // resolution to read the barcodes
            if (img == null)
            {   
                PdfDecoder pdfReader = new PdfDecoder();
                pdfReader.Resolution = 300;
                stream.Position = 0;
                img = pdfReader.Read(stream, pageNum, null);
            }
            return img;
        }

Here is the function in VB.NET

    Private Function GetPdfPage(ByVal stream As Stream, 
                ByVal pageNum As Integer) As AtalaImage
        Dim img As AtalaImage = Nothing

        ' check to see if this page is an image
        Using pdfDoc As New Document(stream)
            Dim pdfPage As Page = pdfDoc.Pages(pageNum)
            If pdfPage.SingleImageOnly Then
                ' if it's an image, extract it from the PDF at its
                ' stored resolution
                img = pdfPage.ExtractImages()(0).Image
            End If
        End Using

        ' if the page is not an image, rasterize it at high enough
        ' resolution to read the barcodes
        If img Is Nothing Then
            Dim pdfReader As New PdfDecoder()
            pdfReader.Resolution = 300
            stream.Position = 0
            img = pdfReader.Read(stream, pageNum, Nothing)
        End If
        Return img
    End Function

Reading a Page from a TIFF

Reading a page from a tiff is easier since it will already be rasterized at a specific resolution. In DotImage, we simply need to construct an AtalaImage object, passing the stream with the encoded image and the page number. Incidentally, this will work for any raster image type, not just TIFF. This C# function detects if a file is PDF, and if so, calls the previous function. If it isn’t a PDF, it simply reads the page and returns it.

        private AtalaImage GetDocumentPage(string file, int pageNum)
        {
            AtalaImage img = null;
            PdfDecoder pdfReader = new PdfDecoder();            
            using (Stream stream = File.OpenRead(file))
            {
                if (pdfReader.IsValidFormat(stream))
                {
                    stream.Position = 0;
                    img = GetPdfPage(stream, pageNum);
                }
                else
                {
                    stream.Position = 0;
                    img = new AtalaImage(stream, pageNum, null);
                }
            }
            return img;
        }

And, here is the function in VB.NET

    Private Function GetDocumentPage(ByVal fileName As String, 
                ByVal pageNum As Integer) As AtalaImage

        Dim img As AtalaImage = Nothing
        Dim pdfReader As New PdfDecoder()
        Using stream As Stream = File.OpenRead(fileName)
            If pdfReader.IsValidFormat(stream) Then
                stream.Position = 0
                img = GetPdfPage(stream, pageNum)
            Else
                stream.Position = 0
                img = New AtalaImage(stream, pageNum, Nothing)
            End If
        End Using
        Return img
    End Function

Reading Barcodes from an Image

Once you have an AtalaImage, DotImage makes it easy to read any barcode from it. Here is the C# code:

        private BarCode[] ReadBarcodesFromPage(AtalaImage img)
        {
            BarCodeReader reader = new BarCodeReader(img);
            ReadOpts opts = new ReadOpts();
            opts.Symbology = Symbologies.All;
            return reader.ReadBars(opts);
        }

And, here it is in VB.NET

    Private Function ReadBarcodesFromPage(ByVal img As AtalaImage)
                 As BarCode()
        Dim reader As New BarCodeReader(img)
        Dim opts As New ReadOpts()
        opts.Symbology = Symbologies.All
        Return reader.ReadBars(opts)
    End Function

The ReadOpts class allows you to control the barcode reading in a lot of ways. You could specify the type (symbology) of the barcode that you want to find, the direction that it should appear on the page, the number of barcodes you expected to be there. Any of these options can be used to speed up the recognition by having the reader do less work. This code just tries to find any barcode in any direction.

Processing the Barcodes

Once you have the array of BarCode objects, you just need to loop through them and get the recognized text from them. Here it is in C#:

            // Get the page and read the barcodes
            AtalaImage img = GetDocumentPage(fileName, pageNum);            
            BarCode[] bars = ReadBarcodesFromPage(img);            

            // show the barcodes in the list
            foreach (BarCode bar in bars)
            {
                Console.WriteLine(bar.DataString);
            }

And VB.NET:

        ' Get the page and read the barcodes
        Dim img As AtalaImage = GetDocumentPage(fileName, pageNum)
        Dim bars As BarCode() = ReadBarcodesFromPage(img)

        ' show the barcodes in the list
        For Each bar As BarCode In bars
            Console.WriteLine(bar.DataString)
        Next

DotImage

The DotImage .NET Imaging SDK contains everything you need to read document imaging formats and recognize the barcodes in them. Download a 30-day evalulation.

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License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Lou Franco
Atalasoft, Inc.
United States United States
Lou Franco is the Director of Engineering at Atalasoft, provider of the leading .NET Imaging SDK (DotImage) and the Document Viewer for SharePoint (Vizit).
 
http://atalasoft.com/products/dotimage
http://vizitsp.com

Comments and Discussions

 
QuestionOptical Mark Recognition with DotImage PinmemberKatsina Aliyu7-Jan-14 0:28 
General[My vote of 2] Commercial Pinmembermaxxnostra7-Oct-09 6:28 
GeneralRe: [My vote of 2] Commercial PinmemberLou Franco7-Oct-09 6:54 
GeneralRe: [My vote of 2] Commercial Pinmembermaxxnostra14-Oct-09 13:26 
GeneralRe: [My vote of 2] Commercial PinmemberLou Franco15-Oct-09 1:43 

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