解决GDI+的图像质量的问题

最近在完成一个文章发布系统时需要给图片添加水印，采用GDI+的DrawString后发现图像质量非常糟糕，后来从其他地方找到如下代码，经过试验 图像质量大幅提高：

//上传成功，加水印    
                        
                        string path=UploadFileDestination + UploadFileName;
                        System.Drawing.Image img = System.Drawing.Image.FromFile(path);
            System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;

            //Size newSize = NewSize(maxWidth, maxHeight, img.Width, img.Height);
            //Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height);
            Graphics g = Graphics.FromImage(img);

            // 设置画布的描绘质量
            g.CompositingQuality = CompositingQuality.HighQuality; 
            g.SmoothingMode = SmoothingMode.HighQuality; 
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;

            g.DrawImage(img, 0, 0, img.Width, img.Height);
                
            Font f = new Font("Arial",9);
                Brush b = new SolidBrush(Color.Black);
                Brush c = new SolidBrush(Color.White);
                string addText = ".com在线";
                
                g.DrawString(addText, f, b, 3, 3);
                g.DrawString(addText, f, c, 2, 2);
                
                g.DrawString(addText, f, b, img.Width-140, img.Height-15);
                g.DrawString(addText, f, c, img.Width-141, img.Height-16);
                g.Dispose();        
            

            // 以下代码为保存图片时，设置压缩质量
            EncoderParameters encoderParams = new EncoderParameters();
            long[] quality = new long[1];
            quality[0] = 100;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[0] = encoderParam;

            //获得包含有关内置图像编码解码器的信息的ImageCodecInfo 对象。
            ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo jpegICI = null;
            for (int x = 0; x < arrayICI.Length; x++)
            {
                if (arrayICI[x].FormatDescription.Equals("JPEG"))
                {
                    jpegICI = arrayICI[x];//设置JPEG编码
                    break;
                }
            }

            string newPath = (UploadFileDestination+RNDFile())+newext;

            if (jpegICI != null)
            {
                img.Save(newPath, jpegICI, encoderParams);
            }
            else
            {
                img.Save(newPath, thisFormat);
            }
            
            img.Dispose();
            
                        

                //保存加水印过后的图片,删除原始图片
                

                if(File.Exists(path))
                {
                    File.Delete(path);
                }                            
                    
                        
                    //水印添加完成