C# 获取图片一部分

Bitmap   mybit=new   Bitmap(100,100);//局部大小 
Graphics   g=Graphics.FromImage(mybit); 
g.DrawImage(oldbit/*原图*/, 
        new   Rectangle(new   Point(0,0),new   Size(100,100)),//目标位置 
        new   Rectangle(new   Point(startX,startY),new   Size(100,100)),//原图位置 
        GraphicsUnit.Pixel);