Graphics如何压缩图像质量

Question

在写一个多张图片拼合的程序时，遇到个问题，生成后的PNG图高达370多KB，任务需求里要求必须在100KB左右，我试了Graphics里的几个属性，输出的图片还是370KB，小弟学艺不精，请各位指点下。
附上代码：Image Idol_Bg = Image.FromFile(pde.Idol_Bg);//背景图片                Image Idol_Face = Image.FromFile(pde.Idol_Face);//偶像脸图层                Image Idol_Hair = Image.FromFile(pde.Idol_Hair);//偶像头发图层                Image Idol_Eyes = Image.FromFile(pde.Idol_Eyes);//偶像眼睛图层                Image Idol_Mouth = Image.FromFile(pde.Idol_Mouth);//偶像嘴巴图层                Graphics gs = Graphics.FromImage(Idol_Bg);                gs.SmoothingMode = SmoothingMode.AntiAlias;
                gs.CompositingQuality = CompositingQuality.HighSpeed;
                gs.InterpolationMode = InterpolationMode.Bilinear;
                //gs.Clear(Color.Transparent);                gs.DrawImage(Idol_Face, new System.Drawing.Point(0, 0));
                gs.DrawImage(Idol_Hair, new System.Drawing.Point(0, 0));
                gs.DrawImage(Idol_Eyes, new System.Drawing.Point(0, 0));
                gs.DrawImage(Idol_Mouth, new System.Drawing.Point(0, 0));                gs.DrawString("Photo By Yzone", new System.Drawing.Font("宋体", 18), System.Drawing.Brushes.Black, new System.Drawing.PointF(1,1));                Idol_Bg.Save(HttpContext.Current.Server.MapPath("images/PaperDol/"+pde.Idol_Id+"_Big.png"),ImageFormat.Png);
                Idol_Face.Dispose();
                Idol_Hair.Dispose();
                Idol_Eyes.Dispose();
                Idol_Eyes.Dispose();
                Idol_Mouth.Dispose();
                Idol_Bg.Dispose();
                gs.Dispose();

Answer 1

可以考试生产文件的缩略图,当然这样会损失一定的图像质量。/**//**//// <summary>
         /// 生成缩略图
         /// </summary>
         /// <param name="originalImagePath">源图路径（物理路径）</param>
         /// <param name="thumbnailPath">缩略图路径（物理路径）</param>
         /// <param name="width">缩略图宽度</param>
         /// <param name="height">缩略图高度</param>
         /// <param name="mode">生成缩略图的方式</param>    
         public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
         {
             Image originalImage = Image.FromFile(originalImagePath);
            
             int towidth = width;
             int toheight = height;
        
             int x = 0;
             int y = 0;
             int ow = originalImage.Width;
             int oh = originalImage.Height;                     switch (mode)
             {        
                 case "HW"://指定高宽缩放（可能变形）                
                     break;
                 case "W"://指定宽，高按比例                    
                     toheight = originalImage.Height * width/originalImage.Width;
                     break;
                 case "H"://指定高，宽按比例
                     towidth = originalImage.Width * height/originalImage.Height;                    
                     break;        
                 case "Cut"://指定高宽裁减（不变形）                
                     if((double)originalImage.Width/(double)originalImage.Height > (double)towidth/(double)toheight)
                     {
                         oh = originalImage.Height;
                         ow = originalImage.Height*towidth/toheight;
                         y = 0;
                         x = (originalImage.Width - ow)/2;
                     }
                     else
                     {
                         ow = originalImage.Width;
                         oh = originalImage.Width*height/towidth;
                         x = 0;
                         y = (originalImage.Height - oh)/2;
                     }
                     break;                    
                 default :
                     break;
             }    
            
             //新建一个bmp图片
             Image bitmap = new System.Drawing.Bitmap(towidth,toheight);             //新建一个画板
             Graphics g = System.Drawing.Graphics.FromImage(bitmap);             //设置高质量插值法
             g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;             //设置高质量,低速度呈现平滑程度
             g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;             //清空画布并以透明背景色填充
             g.Clear(Color.Transparent);                     //在指定位置并且按指定大小绘制原图片的指定部分
             g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight), 
                 new Rectangle(x, y, ow,oh),
                 GraphicsUnit.Pixel);             try
             {            
                 //以jpg格式保存缩略图
                 bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
             }
             catch(System.Exception e)
             {
                 throw e;
             }
             finally
             {
                 originalImage.Dispose();
                 bitmap.Dispose();                        
                 g.Dispose();
             }
         }

Answer 2

生成PNG图片，貌似不能压缩太多。

Answer 3

 图像压缩比例是可以控制的你百度一下。
 System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)100)