Why is Image.Save(Stream, ImageFormat) throwing an exception?

Question

I am trying to convert an image to an icon. My function is:

private Icon GenerateIcon(int width, int height)
{
    using (Bitmap icon = _backingImage.GetThumbnailImage(width, height, () => false, System.IntPtr.Zero) as Bitmap)
    using(MemoryStream imgStream = new MemoryStream())
    {
        icon.Save(imgStream, System.Drawing.Imaging.ImageFormat.Icon);
        return new Icon(imgStream);
    }
}

But when the programme calls the method, it throws an ArgumentNullException("encoder") where I'm calling icon.Save.

I find this odd because I'm not passing in an encoder, I want the framework to figure out what the encoder should be, which is why I'm passing in an ImageFormat.

Is it that there aren't any encoders for ImageFormat.Icon, or is there something I'm doing wrong?

Answer 1

You guessed it right: GDI+ only supports an ICON decoder.

You might want to perform the conversion yourself. In that case, see http://www.codeproject.com/KB/GDI-plus/safeicon.aspx.