private void AddCheckStateBitmap(ImageList il, string key, CheckBoxState boxState)
{
Bitmap b = new Bitmap(il.ImageSize.Width, il.ImageSize.Height);
Graphics g = Graphics.FromImage(b);
g.Clear(il.TransparentColor);
Point location = new Point(b.Width / 2 - 5, b.Height / 2 - 6);
CheckBoxRenderer.DrawCheckBox(g, location, boxState);
il.Images.Add(key, b);
}