怎样裁剪图片的局部

Image newImage = Image.FromFile("c:\\temp.bmp");  
Rectangle destRect = new Rectangle(0, 0,300, 300);  
Graphics g = pictureBox1.CreateGraphics(); 
g.DrawImage(newImage, destRect); 

Image newImage = Image.FromFile("c:\\temp.bmp");  
Rectangle destRect = new Rectangle(0, 0,300, 300);  
Bitmap bmpTarget=new Bitmap(300,300,System.Drawing.Imaging.PixelFormat.Format24bppRgb);
Graphics gg = System.Drawing.Graphics.FromImage(bmpTarget);
gg.DrawImage(newImage, destRect);
bmpTarget.Save("c:\\f4.jpg");