convert bitonal TIFF to bitonal PNG in C#

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天涯浪人
天涯浪人 2021-01-12 10:00

I need to convert bitonal (black and white) TIFF files into another format for display by a web browser, currently we\'re using JPGs, but the format isn\'t crucial. From rea

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  • 2021-01-12 10:29

    Have you tried saving using the Image.Save overload with Encoder parameters?
    Like the Encoder.ColorDepth Parameter?

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  • 2021-01-12 10:36

    I believe the problem can be solved by checking that resized bitmap is of PixelFormat.Format1bppIndexed. If it's not, you should convert it to 1bpp bitmap and after that you can save it as black and white png without problems.

    In other words, you should use following code instead of resized.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Jpeg);

    if (resized.PixelFormat != PixelFormat.Format1bppIndexed)
    {
        using (Bitmap bmp = convertToBitonal(resized))
            bmp.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Png);
    }
    else
    {
        resized.Save(outputFilename, System.Drawing.Imaging.ImageFormat.Png);
    }
    

    I use following code for convertToBitonal :

    private static Bitmap convertToBitonal(Bitmap original)
    {
        int sourceStride;
        byte[] sourceBuffer = extractBytes(original, out sourceStride);
    
        // Create destination bitmap
        Bitmap destination = new Bitmap(original.Width, original.Height,
            PixelFormat.Format1bppIndexed);
    
        destination.SetResolution(original.HorizontalResolution, original.VerticalResolution);
    
        // Lock destination bitmap in memory
        BitmapData destinationData = destination.LockBits(
            new Rectangle(0, 0, destination.Width, destination.Height),
            ImageLockMode.WriteOnly, PixelFormat.Format1bppIndexed);
    
        // Create buffer for destination bitmap bits
        int imageSize = destinationData.Stride * destinationData.Height;
        byte[] destinationBuffer = new byte[imageSize];
    
        int sourceIndex = 0;
        int destinationIndex = 0;
        int pixelTotal = 0;
        byte destinationValue = 0;
        int pixelValue = 128;
        int height = destination.Height;
        int width = destination.Width;
        int threshold = 500;
    
        for (int y = 0; y < height; y++)
        {
            sourceIndex = y * sourceStride;
            destinationIndex = y * destinationData.Stride;
            destinationValue = 0;
            pixelValue = 128;
    
            for (int x = 0; x < width; x++)
            {
                // Compute pixel brightness (i.e. total of Red, Green, and Blue values)
                pixelTotal = sourceBuffer[sourceIndex + 1] + sourceBuffer[sourceIndex + 2] +
                    sourceBuffer[sourceIndex + 3];
    
                if (pixelTotal > threshold)
                    destinationValue += (byte)pixelValue;
    
                if (pixelValue == 1)
                {
                    destinationBuffer[destinationIndex] = destinationValue;
                    destinationIndex++;
                    destinationValue = 0;
                    pixelValue = 128;
                }
                else
                {
                    pixelValue >>= 1;
                }
    
                sourceIndex += 4;
            }
    
            if (pixelValue != 128)
                destinationBuffer[destinationIndex] = destinationValue;
        }
    
        Marshal.Copy(destinationBuffer, 0, destinationData.Scan0, imageSize);
        destination.UnlockBits(destinationData);
        return destination;
    }
    
    private static byte[] extractBytes(Bitmap original, out int stride)
    {
        Bitmap source = null;
    
        try
        {
            // If original bitmap is not already in 32 BPP, ARGB format, then convert
            if (original.PixelFormat != PixelFormat.Format32bppArgb)
            {
                source = new Bitmap(original.Width, original.Height, PixelFormat.Format32bppArgb);
                source.SetResolution(original.HorizontalResolution, original.VerticalResolution);
                using (Graphics g = Graphics.FromImage(source))
                {
                    g.DrawImageUnscaled(original, 0, 0);
                }
            }
            else
            {
                source = original;
            }
    
            // Lock source bitmap in memory
            BitmapData sourceData = source.LockBits(
                new Rectangle(0, 0, source.Width, source.Height),
                ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
    
            // Copy image data to binary array
            int imageSize = sourceData.Stride * sourceData.Height;
            byte[] sourceBuffer = new byte[imageSize];
            Marshal.Copy(sourceData.Scan0, sourceBuffer, 0, imageSize);
    
            // Unlock source bitmap
            source.UnlockBits(sourceData);
    
            stride = sourceData.Stride;
            return sourceBuffer;
        }
        finally
        {
            if (source != original)
                source.Dispose();
        }        
    }
    
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  • 2021-01-12 10:39

    Trying jaroslav's suggestion for color depth doesn't work:

    static void Main(string[] args)
    {
            var list = ImageCodecInfo.GetImageDecoders();
            var jpegEncoder = list[1]; // i know this is the jpeg encoder by inspection
            Bitmap bitmap = new Bitmap(500, 500);
            Graphics g = Graphics.FromImage(bitmap);
            g.DrawRectangle(new Pen(Color.Red), 10, 10, 300, 300);
            var encoderParams = new EncoderParameters();
            encoderParams.Param[0] = new EncoderParameter(Encoder.ColorDepth, 2);
            bitmap.Save(@"c:\newbitmap.jpeg", jpegEncoder, encoderParams);
    
    }
    

    The jpeg is still a full color jpeg.

    I don't think there is any support for grayscale jpeg in gdi plus. Have you tried looking in windows imaging component?

    http://www.microsoft.com/downloads/details.aspx?FamilyID=8e011506-6307-445b-b950-215def45ffffd8&displaylang=en

    code example: http://www.codeproject.com/KB/GDI-plus/windows_imaging.aspx

    wikipedia: http://en.wikipedia.org/wiki/Windows_Imaging_Component

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  • 2021-01-12 10:39

    Have you tried PNG with 1 bit color depth?

    To achieve a size similar to a CCITT4 TIFF, I believe your image needs to use a 1-bit indexed pallette.

    However, you can't use the Graphics object in .NET to draw on an indexed image.

    You will probably have to use LockBits to manipulate each pixel.

    See Bob Powell's excellent article.

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  • 2021-01-12 10:43

    This is an old thread. However, I'll add my 2 cents.

    I use AForge.Net libraries (open source)

    use these dlls. Aforge.dll, AForge.Imaging.dll

    using AForge.Imaging.Filters;
    
    private void ConvertBitmap()
    {
        markedBitmap = Grayscale.CommonAlgorithms.RMY.Apply(markedBitmap);
        ApplyFilter(new FloydSteinbergDithering());
    }
    private void ApplyFilter(IFilter filter)
    {
        // apply filter
        convertedBitmap = filter.Apply(markedBitmap);
    }
    
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