ASP.NET生成高质量缩略图通用函数(代码)

在网站开发时,生成缩略图是一个非常常见和实用的功能.以前在asp里只能借助com组件实现,现在在.net里可以利用框架的强大的类库轻松实现.下面帖出完整的代码(带详细注释),参考了网上的一些文章及.net sdk相关内容.QQROOM网络家园的图片上传用到了所有的4种生成方式. 
        /// <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(); 
            } 
        }