.net图片下载的质量怎么控制？这个程序下西来的总是不清晰

public void DownImage() { WebClient client = new WebClient(); foreach (KeyValuePair<string, string> KeyValue in replace) { FileInfo info = new FileInfo(KeyValue.Value); if (!info.Directory.Exists) info.Directory.Create(); try { client.DownloadFile(KeyValue.Key, KeyValue.Value); System.Drawing.Image image = System.Drawing.Image.FromFile(KeyValue.Value); int width =image.Width; image.Dispose(); if (width>700)ImageFunction.Compress(KeyValue.Value, 700, 0, true); if (width > 200) ImageFunction.WaterMark(KeyValue.Value, MarkPath); } catch(Exception ex) { Log("ImageError:" + ex.Message); } } }