string imgPath = @"C:\ZHM01000001400001-01 青龙 白虎.tif";

Image img = Image.FromFile(imgPath);

Bitmap tmpbitmap = new Bitmap(img);

img = tmpbitmap;

string savePath = Path.Combine(Path.GetDirectoryName(imgPath), Path.GetFileNameWithoutExtension(imgPath) + "sl.jpg");

//可以选择格式

img.Save(savePath, System.Drawing.Imaging.ImageFormat.Jpeg);