Fast Bitmap conversation

[jonasfj]

The ZBar.Image constructor that imports from Image should use Mashal.Copy directly from underlying Bitmap data to unmanaged memory for the image, see set in Zbar.Image.Data.

It might also be good to have a constructor that takes a System.Drawing.Bitmap as argument, to avoid painting, but this would require FourCC codes for each entry in System.Drawing.Imaging.PixelFormat.