Image processing: How to detect orientation of document image?

In This Topic

VintaSoft Imaging .NET SDK and VintaSoft Document Cleanup .NET Plug-in provide commands for processing and cleanup images of documents.

The GetTextOrientationCommand command purpose is to detect orientation of images, which contain Latin text rotated on 90, 180 or 270 degrees.
GetTextOrientationCommand is not suitable for processing of:

images, which do not contain text
images, which contain non-Latin text
images, which contain Latin text with capital letters only
images, which are rotated on angle different from 0, 90, 180 or 270 degrees (use DeskewCommand command to deskew the image before detection of its orientation)
images, which contain just few words (this is not enough to make a decision about image orientation)

VintaSoft Imaging .NET SDK and VintaSoft OCR .NET Plug-in provideGetTesseractOcrTextOrientationCommand command, which purpose is to detect orientation of document image using Tesseract OCR engine. The GetTesseractOcrTextOrientationCommand command can detect orientation of any image with text (does not have limitations like GetTextOrientationCommand command), but GetTesseractOcrTextOrientationCommand command works up to 5 times slower than GetTextOrientationCommand command.

Based on the stated above it is necessary to use GetTextOrientationCommand command or GetTesseractOcrTextOrientationCommand command depending on type of input document images.

Also it is possible to use both commands together, specifically:

detect the orientation of image using GetTextOrientationCommand command (performs faster and detects orientation correctly for the majority of documents with Latin text)
if GetTextOrientationCommand command cannot detect the orientation of document image, detect orientation of image using GetTesseractOcrTextOrientationCommand command (performs slower, but detects orientation correctly for almost all documents)

Combined use of both commands allows to get the maximum efficiency and quality of document image orientation detection.

Here is example that demonstrates how to detect orientation of document image using GetTextOrientationCommand command:

/// <summary>
/// Returns an orientation angle of document image using statistics for Latin symbols.
/// </summary>
/// <param name="filename">The path to a file with document image.</param>
public static void GetDocumentImageOrientationUsingLatinSymbolStat(string filename)
{
    // create an image collection
    using (Vintasoft.Imaging.ImageCollection images = new Vintasoft.Imaging.ImageCollection())
    {
        // add images from file to the image collection
        images.Add(filename);

        // create an instance of GetTextOrientationCommand class
        Vintasoft.Imaging.ImageProcessing.Info.GetTextOrientationCommand getTextOrientationCommand1 =
            new Vintasoft.Imaging.ImageProcessing.Info.GetTextOrientationCommand();

        // for each image in image collection
        for (int i = 0; i < images.Count; i++)
        {
            // get image
            Vintasoft.Imaging.VintasoftImage image = images[i];

            // determine orientation of document image using statistics for Latin symbols
            getTextOrientationCommand1.ExecuteInPlace(image);

            // write result to the console
            System.Console.WriteLine(string.Format("Filename: {0}, page: {1}, page orientation: {2}, confidence: {3}",
                System.IO.Path.GetFileName(filename),
                i,
                getTextOrientationCommand1.Orientation,
                getTextOrientationCommand1.Confidence));
        }

        // free images
        images.ClearAndDisposeItems();
    }
}

VB.NET

''' <summary>
''' Returns an orientation angle of document image using statistics for Latin symbols.
''' </summary>
''' <param name="filename">The path to a file with document image.</param>
Public Shared Sub GetDocumentImageOrientationUsingLatinSymbolStat(filename As String)
    ' create an image collection
    Using images As New Vintasoft.Imaging.ImageCollection()
        ' add images from file to the image collection
        images.Add(filename)

        ' create an instance of GetTextOrientationCommand class
        Dim getTextOrientationCommand1 As New Vintasoft.Imaging.ImageProcessing.Info.GetTextOrientationCommand()

        ' for each image in image collection
        For i As Integer = 0 To images.Count - 1
            ' get image
            Dim image As Vintasoft.Imaging.VintasoftImage = images(i)

            ' determine orientation of document image using statistics for Latin symbols
            getTextOrientationCommand1.ExecuteInPlace(image)

            ' write result to the console
            System.Console.WriteLine(String.Format("Filename: {0}, page: {1}, page orientation: {2}, confidence: {3}", System.IO.Path.GetFileName(filename), i, getTextOrientationCommand1.Orientation, getTextOrientationCommand1.Confidence))
        Next

        ' free images
        images.ClearAndDisposeItems()
    End Using
End Sub

Here is example that demonstrates how to detect orientation of document image using GetTesseractOcrTextOrientationCommand command:

/// <summary>
/// Returns an orientation angle of document image using Tesseract OCR.
/// </summary>
/// <param name="filename">The path to a file with document image.</param>
/// <param name="tesseractOcrDllDirectory">A path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located.</param>
public static void GetDocumentImageOrientationUsingTesseractOCR(string filename, string tesseractOcrDllDirectory)
{
    // create an image collection
    using (Vintasoft.Imaging.ImageCollection images = new Vintasoft.Imaging.ImageCollection())
    {
        // add images from file to the image collection
        images.Add(filename);

        // create an instance of GetTesseractOcrTextOrientationCommand class
        using (Vintasoft.Imaging.ImageProcessing.Ocr.Tesseract.GetTesseractOcrTextOrientationCommand getTextOrientationCommand =
            new Vintasoft.Imaging.ImageProcessing.Ocr.Tesseract.GetTesseractOcrTextOrientationCommand())
        {
            // specify path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located
            getTextOrientationCommand.TesseractOcrDllDirectory = tesseractOcrDllDirectory;

            // for each image in image collection
            for (int i = 0; i < images.Count; i++)
            {
                // get image
                Vintasoft.Imaging.VintasoftImage image = images[i];

                // determine orientation of document image using Tesseract OCR
                getTextOrientationCommand.ExecuteInPlace(image);

                // write result to the console
                System.Console.WriteLine(string.Format("Filename: {0}, page: {1}, page orientation: {2}",
                    System.IO.Path.GetFileName(filename),
                    i,
                    getTextOrientationCommand.Orientation));
            }
        }

        // free images
        images.ClearAndDisposeItems();
    }
}

VB.NET

''' <summary>
''' Returns an orientation angle of document image using Tesseract OCR.
''' </summary>
''' <param name="filename">The path to a file with document image.</param>
''' <param name="tesseractOcrDllDirectory">A path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located.</param>
Public Shared Sub GetDocumentImageOrientationUsingTesseractOCR(filename As String, tesseractOcrDllDirectory As String)
    ' create an image collection
    Using images As New Vintasoft.Imaging.ImageCollection()
        ' add images from file to the image collection
        images.Add(filename)

        ' create an instance of GetTesseractOcrTextOrientationCommand class
        Using getTextOrientationCommand As New Vintasoft.Imaging.ImageProcessing.Ocr.Tesseract.GetTesseractOcrTextOrientationCommand()
            ' specify path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located
            getTextOrientationCommand.TesseractOcrDllDirectory = tesseractOcrDllDirectory

            ' for each image in image collection
            For i As Integer = 0 To images.Count - 1
                ' get image
                Dim image As Vintasoft.Imaging.VintasoftImage = images(i)

                ' determine orientation of document image using Tesseract OCR
                getTextOrientationCommand.ExecuteInPlace(image)

                ' write result to the console
                System.Console.WriteLine(String.Format("Filename: {0}, page: {1}, page orientation: {2}", System.IO.Path.GetFileName(filename), i, getTextOrientationCommand.Orientation))
            Next
        End Using

        ' free images
        images.ClearAndDisposeItems()
    End Using
End Sub

Here is example that demonstrates how to detect orientation of document image using GetTextOrientationCommand command and GetTesseractOcrTextOrientationCommand command:

/// <summary>
/// Returns an orientation angle of document image using statistics for Latin symbols and using Tesseract OCR.
/// </summary>
/// <param name="filename">The path to a file with document image.</param>
/// <param name="tesseractOcrDllDirectory">A path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located.</param>
public static void GetDocumentImageOrientationUsingLatinSymbolStatAndOcrTesseract(string filename, string tesseractOcrDllDirectory)
{
    // create an image collection
    using (Vintasoft.Imaging.ImageCollection images = new Vintasoft.Imaging.ImageCollection())
    {
        // add images from file to the image collection
        images.Add(filename);

        // create an instance of GetTextOrientationCommand class
        Vintasoft.Imaging.ImageProcessing.Info.GetTextOrientationCommand getTextOrientationCommand1 =
            new Vintasoft.Imaging.ImageProcessing.Info.GetTextOrientationCommand();

        // create an instance of GetTesseractOcrTextOrientationCommand class
        using (Vintasoft.Imaging.ImageProcessing.Ocr.Tesseract.GetTesseractOcrTextOrientationCommand getTextOrientationCommand2 =
            new Vintasoft.Imaging.ImageProcessing.Ocr.Tesseract.GetTesseractOcrTextOrientationCommand())
        {
            // specify path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located
            getTextOrientationCommand2.TesseractOcrDllDirectory = tesseractOcrDllDirectory;

            // for each image in image collection
            for (int i = 0; i < images.Count; i++)
            {
                // get image
                Vintasoft.Imaging.VintasoftImage image = images[i];

                // determine orientation of document image using statistics for Latin symbols (works for Latin text only)
                getTextOrientationCommand1.ExecuteInPlace(image);
                // if orientation is detected and orientation result has high confidence
                if (getTextOrientationCommand1.Orientation != Vintasoft.Imaging.ImageProcessing.Info.ImageOrthogonalOrientation.Undefined &&
                    getTextOrientationCommand1.Confidence > 0.3)
                {
                    // write result to the console
                    System.Console.WriteLine(string.Format("Filename: {0}, page: {1}, page orientation: {2}, confidence: {3}",
                        System.IO.Path.GetFileName(filename),
                        i,
                        getTextOrientationCommand1.Orientation,
                        getTextOrientationCommand1.Confidence));
                }
                // if orientation is not detected or orientation result has low confidence
                else
                {
                    // determine orientation of document image using Tesseract OCR (works for any text)
                    getTextOrientationCommand2.ExecuteInPlace(image);

                    // write result to the console
                    System.Console.WriteLine(string.Format("Filename: {0}, page: {1}, page orientation: {2}, confidence: {3}",
                        System.IO.Path.GetFileName(filename),
                        i,
                        getTextOrientationCommand2.Orientation,
                        getTextOrientationCommand2.Confidence));
                }
            }
        }

        // free images
        images.ClearAndDisposeItems();
    }
}

VB.NET

''' <summary>
''' Returns an orientation angle of document image using statistics for Latin symbols and using Tesseract OCR.
''' </summary>
''' <param name="filename">The path to a file with document image.</param>
''' <param name="tesseractOcrDllDirectory">A path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located.</param>
Public Shared Sub GetDocumentImageOrientationUsingLatinSymbolStatAndOcrTesseract(filename As String, tesseractOcrDllDirectory As String)
    ' create an image collection
    Using images As New Vintasoft.Imaging.ImageCollection()
        ' add images from file to the image collection
        images.Add(filename)

        ' create an instance of GetTextOrientationCommand class
        Dim getTextOrientationCommand1 As New Vintasoft.Imaging.ImageProcessing.Info.GetTextOrientationCommand()

        ' create an instance of GetTesseractOcrTextOrientationCommand class
        Using getTextOrientationCommand2 As New Vintasoft.Imaging.ImageProcessing.Ocr.Tesseract.GetTesseractOcrTextOrientationCommand()
            ' specify path to a directory, where Tesseract5.Vintasoft.xXX.dll files are located
            getTextOrientationCommand2.TesseractOcrDllDirectory = tesseractOcrDllDirectory

            ' for each image in image collection
            For i As Integer = 0 To images.Count - 1
                ' get image
                Dim image As Vintasoft.Imaging.VintasoftImage = images(i)

                ' determine orientation of document image using statistics for Latin symbols (works for Latin text only)
                getTextOrientationCommand1.ExecuteInPlace(image)
                ' if orientation is detected and orientation result has high confidence
                If getTextOrientationCommand1.Orientation <> Vintasoft.Imaging.ImageProcessing.Info.ImageOrthogonalOrientation.Undefined AndAlso getTextOrientationCommand1.Confidence > 0.3 Then
                    ' write result to the console
                    System.Console.WriteLine(String.Format("Filename: {0}, page: {1}, page orientation: {2}, confidence: {3}", System.IO.Path.GetFileName(filename), i, getTextOrientationCommand1.Orientation, getTextOrientationCommand1.Confidence))
                Else
                    ' if orientation is not detected or orientation result has low confidence
                    ' determine orientation of document image using Tesseract OCR (works for any text)
                    getTextOrientationCommand2.ExecuteInPlace(image)

                    ' write result to the console
                    System.Console.WriteLine(String.Format("Filename: {0}, page: {1}, page orientation: {2}, confidence: {3}", System.IO.Path.GetFileName(filename), i, getTextOrientationCommand2.Orientation, getTextOrientationCommand2.Confidence))
                End If
            Next
        End Using

        ' free images
        images.ClearAndDisposeItems()
    End Using
End Sub

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