using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication1

    public static Bitmap cropAtRect(this Bitmap b, Rectangle r)
{
    Bitmap nb = new Bitmap(r.Width, r.Height);
    Graphics g = Graphics.FromImage(nb);
    g.DrawImage(b, -r.X, -r.Y);
    return nb;
}