c# how to deskew an image

Question

I'm currently working with an OCR program. I'm using tesseract and i need to deskew images to improve the quality of the detected characters. The problem is that the deskew property given by tesseract doesn't produce enough attractive results. So i tried to deskew the image with AForge and Atalasoft, but every time, no matter what, the image is not in the format they require. What am i doing wrong? Or there is a better solution?

This is AForge implementation

        System.Drawing.Bitmap imageToBitmap = AForge.Imaging.Image.FromFile(imagePath);
        Console.WriteLine("before  " + imageToBitmap.PixelFormat);
        System.Drawing.Bitmap NewPicture = imageToBitmap.Clone(new System.Drawing.Rectangle(0, 0, imageToBitmap.Width, imageToBitmap.Height), System.Drawing.Imaging.PixelFormat.Format24bppRgb);
        var dop = AForge.Imaging.Image.Clone(imageToBitmap, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
        Console.WriteLine("after  " + dop.PixelFormat);

        AForge.Imaging.DocumentSkewChecker skewChecker = new AForge.Imaging.DocumentSkewChecker();
        // get documents skew angle
        double angle = skewChecker.GetSkewAngle(dop);
        // create rotation filter
        AForge.Imaging.Filters.RotateBilinear rotationFilter = new AForge.Imaging.Filters.RotateBilinear(-angle);
        rotationFilter.FillColor = System.Drawing.Color.White;
        // rotate image applying the filter
        System.Drawing.Bitmap rotatedImage = rotationFilter.Apply(imageToBitmap);

        rotatedImage.Save("deskewedImage");

This is Atalasoft implementation

        AtalaImage img = new AtalaImage(imagePath);
        AutoDeskewCommand cmd = new AutoDeskewCommand();
        AtalaImage resultImage = cmd.Apply(img).Image;
        resultImage.Save("result.tif", new TiffEncoder(), null);

Possible duplicate of [De-skew characters in binary image](http://stackoverflow.com/questions/30273251/de-skew-characters-in-binary-image) — Spektre, May 12 '17 at 06:33

score 3 · Accepted Answer · answered May 15 '17 at 12:24

I finally managed to understand why it wasn't working: the image should be converted to Format8bppIndexed or the method skewChecker.GetSkewAngle(image) will throw an exception

        Bitmap tempImage = AForge.Imaging.Image.FromFile(imagePath);
        Bitmap image;
        if (tempImage.PixelFormat.ToString().Equals("Format8bppIndexed"))
        {
            image = tempImage;
        }
        else
        {
            image = AForge.Imaging.Filters.Grayscale.CommonAlgorithms.BT709.Apply(tempImage);
        }

        tempImage.Dispose();

        AForge.Imaging.DocumentSkewChecker skewChecker = new AForge.Imaging.DocumentSkewChecker();
        // get documents skew angle
        double angle = skewChecker.GetSkewAngle(image);
        // create rotation filter
        AForge.Imaging.Filters.RotateBilinear rotationFilter = new AForge.Imaging.Filters.RotateBilinear(-angle);
        rotationFilter.FillColor = Color.Black;
        // rotate image applying the filter
        Bitmap rotatedImage = rotationFilter.Apply(image);

        var deskewedImagePath = folderSavePath + filename + "_deskewed.tiff";
        rotatedImage.Save(deskewedImagePath, System.Drawing.Imaging.ImageFormat.Tiff);

        image.Dispose();
        rotatedImage.Dispose();

c# how to deskew an image

1 Answers1