关于Graphics绘图后如何本地保存问题！
string pngFileName=this.txt_KeyWord.Text+".png";
//利用graphviz绘图
//命令格式：dot baoxiao.txt -T png -o baoxiao.png
call(@"D:\常用软件\Graphviz\bin\dot.exe", scriptFileName + " -T png -o " + pngFileName);

System.Threading.Thread.Sleep(10000);

Image a = Image.FromFile(pngFileName);

Bitmap bit = new Bitmap(pictureBox1.Width, pictureBox1.Height);
Graphics g = Graphics.FromImage(bit);
g.DrawImage(a, new Rectangle(0, 0, bit.Width, bit.Height), new Rectangle(0, 0, a.Width, a.Height), GraphicsUnit.Pixel);
pictureBox1.SizeMode = PictureBoxSizeMode.AutoSize;
pictureBox1.Image = bit;
结果如下图：


请问如何讲右边pictureBox1中的图片保存到本地，急急急 Bitmap 图片 Graphics 保存
[解决办法]
bitmap.Save("c:\\");