Question

I’m using WIA 2.0 to scan images from a HP scanner. The problem is that saved TIFFs are around 9MBs big (A4 page at 300dpi, grayscale). I convert WIA’s ImageFile that contains scan in TIFF format to BitmapSource like this:

    public static BitmapSource ConvertScannedImage(ImageFile imageFile)
    {
        if (imageFile == null)
            return null;

        // save the image out to a temp file
        string fileName = Path.GetTempFileName();

        // this is pretty hokey, but since SaveFile won't overwrite, we
        // need to do something to both guarantee a unique name and
        // also allow SaveFile to write the file
        File.Delete(fileName);

        // now save using the same filename
        imageFile.SaveFile(fileName);

        BitmapFrame img;

        // load the file back in to a WPF type, this is just
        // to get around size issues with large scans
        using (FileStream stream = File.OpenRead(fileName))
        {
            img = BitmapFrame.Create(stream, BitmapCreateOptions.None, BitmapCacheOption.OnLoad);

            stream.Close();
        }

        // clean up
        File.Delete(fileName);

        return img;
    }

Anybody have an idea how to reduce image size, if possible in-memory (because I have a lsit of scans that you can preview and rotate)? Thanks.

Answer 1

Use compression. This example Ccitt4 is for black and white fax compression, the compression factor is huge but there are other versions if you want to keep the grey scale.

using System.Windows.Media.Imaging;


public static byte[] ConvertBitmapSourceToByteArray(BitmapSource imageToConvert, ImageFormat formatOfImage)
{
    byte[] buffer;
    try
    {
        using (var ms = new MemoryStream())
        {
            switch (formatOfImage)
            {
                case ImageFormat.Png:
                    var bencoder = new PngBitmapEncoder();
                    bencoder.Frames.Add(BitmapFrame.Create(imageToConvert));
                    bencoder.Save(ms);
                    break;

                case ImageFormat.Tiff:
                    var tencoder = new TiffBitmapEncoder();
                    tencoder.Compression = TiffCompressOption.Ccitt4;
                    tencoder.Frames.Add(BitmapFrame.Create(imageToConvert));
                    tencoder.Save(ms);
                    break;
            }
            ms.Flush();
            buffer = ms.GetBuffer();
        }
    }
    catch (Exception) { throw; }

    return buffer;
}

Then to write the image

doc.SaveDirectory = DestinationDirectoryImages;
doc.Filename = fName;
doc.Image = ImageConversion.ConvertBitmapSourceToByteArray(img.Image, ImageFormat.Tiff);

and the implementation of .Image is…

private byte[] _image;
/// <summary>
/// Bytes for Image. Set to null to delete related file.
/// </summary>
public virtual byte[] Image
{
    get
    {
        if (_image == null)
        {
            if (SaveDirectory == null) throw new ValidationException("SaveDirectory not set for DriverDoc");
            string fullFilename = Path.Combine(SaveDirectory, Filename);
            if (!string.IsNullOrEmpty(fullFilename))
                if (File.Exists(fullFilename))
                    _image = File.ReadAllBytes(fullFilename);
                else
                    _image = File.ReadAllBytes("Resources\\FileNotFound.bmp");
        }
        return _image;
    }
    set
    {
        if (_image == value) return;
        _image = value;
        if (SaveDirectory == null) throw new ValidationException("SaveDirectory not set for DriverDoc");
        string fullFilename = Path.Combine(SaveDirectory, Filename);
        if (_image != null)
        {
            if (!string.IsNullOrEmpty(fullFilename))
            {
                _image = value;
                File.WriteAllBytes(fullFilename, _image);
            }
        }
        else
        {
            if (!string.IsNullOrEmpty(Filename) && File.Exists(fullFilename))
                File.Delete(fullFilename);
        }
    }
}