private Bitmap ReadRGBA(string filename)
{
	if (string.IsNullOrEmpty(filename))
		throw new ArgumentException(filename);
	Bitmap source = new Bitmap(filename);
    Bitmap result = new Bitmap(source.Width, source.Height, PixelFormat.Format24bppRgb);
    for (int i = 0; i < source.Width; i++)
    {
    	for (int j = 0; j < source.Height; j++)
        {
        	var color = source.GetPixel(i, j);
            result.SetPixel(i, j, Color.FromArgb(color.A, color.B, color.G, color.R));
        }
    }
    return result;
}