C＃将TIFF JPEG压缩转换为TIFF压缩CCITT4会产生很多噪音

Question

For a OCR engine I need to feed the OCR engine with TIFF files with CCITT4 Compression. Our scanner outputs TIFF files with JPEG compression. I want to convert these files with C#, using System.Drawing.Imaging.

This results in images with a lot of Noise. How can I reduce the noise?

My Code:

        List<byte[]> fRet = new List<byte[]>();
        ImageCodecInfo fImageCodecInfo = GetEncoderInfo("image/tiff");
        EncoderParameters fEncoderParameters = new EncoderParameters(3);
        fEncoderParameters.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Compression, (long)EncoderValue.CompressionCCITT4);
        fEncoderParameters.Param[1] = new EncoderParameter(System.Drawing.Imaging.Encoder.ScanMethod, (int)EncoderValue.ScanMethodNonInterlaced);
        fEncoderParameters.Param[2] = new EncoderParameter(System.Drawing.Imaging.Encoder.RenderMethod, (int)EncoderValue.RenderNonProgressive);

        //

        Image fOrgTiff = Image.FromStream(pInputTiff);
        Guid objGuid = fOrgTiff.FrameDimensionsList[0];
        FrameDimension objDimension = new FrameDimension(objGuid);
        int frameCount = fOrgTiff.GetFrameCount(objDimension);
        for (int i = 0; i < frameCount; i++)
        {
            MemoryStream ms = new MemoryStream();
            fOrgTiff.SelectActiveFrame(objDimension, i);
            fOrgTiff.Save(ms, fImageCodecInfo, fEncoderParameters);
            ms.Position = 0;
            fRet.Add(ms.GetBuffer());
        }
        return fRet;

Answer 1

As Brannon said, Ccitt4 is a binary format (black/white) so your image is automatically binarized. The documentation says: " The Ccitt3, Ccitt4, and Rle require that the PixelFormat value be set to BlackWhite . Setting the PixelFormat to any other value resets the Compression property value to Default. "

You can try to reduce the noise by choosing a better binarization threshold. You can look at algorithms provided by open-source imaging libraries like AForge.Net or EmguCV .