C# 生成等比缩略图的类

public  class BitmapHelper
    {
         ///   <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,  string type)
        {
            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;
                 case  " DB ": // 等比缩放（不变形，如果高大按高，宽大按宽缩放） 
                     if (( double)originalImage.Width / ( double)towidth < ( double)originalImage.Height / ( double)toheight)
                    {
                        toheight = height;
                        towidth = originalImage.Width * height / originalImage.Height;
                    }
                     else
                    {
                        towidth = width;
                        toheight = originalImage.Height * width / originalImage.Width;
                    }
                     break;
                 default:
                     break;
            }

             // 新建一个bmp图片
            Image bitmap =  new Bitmap(towidth, toheight);

             // 新建一个画板
            Graphics g = 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
            {
                 // 保存缩略图
                 if (type.ToUpper() ==  " JPG ")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
                }
                 if (type.ToUpper() ==  " BMP ")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Bmp);
                }
                 if (type.ToUpper() ==  " GIF ")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Gif);
                }
                 if (type.ToUpper() ==  " PNG ")
                {
                    bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Png);
                }
            }
             catch (System.Exception e)
            {
                 throw e;
            }
             finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
        }

         /**/
         ///   <summary>
         ///  在图片上增加文字水印
         ///   </summary>
         ///   <param name="Path"> 原服务器图片路径 </param>
         ///   <param name="Path_sy"> 生成的带文字水印的图片路径 </param>
         public  static  void AddShuiYinWord( string Path,  string Path_sy)
        {
             string addText =  " Sxmobi ";
            Image image = Image.FromFile(Path);
            Graphics g = Graphics.FromImage(image);
            g.DrawImage(image,  0,  0, image.Width, image.Height);
            Font f =  new Font( " Verdana ",  16);
            Brush b =  new SolidBrush(Color.Blue);

            g.DrawString(addText, f, b,  15,  15);
            g.Dispose();

            image.Save(Path_sy);
            image.Dispose();
        }

         /**/
         ///   <summary>
         ///  在图片上生成图片水印
         ///   </summary>
         ///   <param name="Path"> 原服务器图片路径 </param>
         ///   <param name="Path_syp"> 生成的带图片水印的图片路径 </param>
         ///   <param name="Path_sypf"> 水印图片路径 </param>
         public  static  void AddShuiYinPic( string Path,  string Path_syp,  string Path_sypf)
        {
            Image image = Image.FromFile(Path);
            Image copyImage = Image.FromFile(Path_sypf);
            Graphics g = Graphics.FromImage(image);
            g.DrawImage(copyImage,  new Rectangle(image.Width - copyImage.Width, image.Height - copyImage.Height, copyImage.Width, copyImage.Height),  0,  0, copyImage.Width, copyImage.Height, GraphicsUnit.Pixel);
            g.Dispose();

            image.Save(Path_syp);
            image.Dispose();
        }
    }