生成高清晰缩略图

关于生成缩略图的做法,网上搜了一下,大多数都是采用如下的做法:

        public void GenerateThumbnailImage(System.Drawing.Image img,int wi,int hi,string imgDir,string imgName,System.Drawing.Image.GetThumbnailImageAbort callb,string saveDir)
        ...{
            int width,height,newwidth,newheight;  
            System.Drawing.Image newImg;
            img=System.Drawing.Image.FromFile(Server.MapPath(imgDir + imgName));
            width =img.Width;
            height=img.Height;

            if(width>height) 
            ...{ 
                newwidth=wi; 
                newheight=(int)(wi*height/width); 
            } 
            else 
            ...{ 
                newheight=hi; 
                newwidth=(int)(hi*width/height); 
            } 
            newImg=img.GetThumbnailImage(newwidth,newheight,callb,new System.IntPtr());
            newImg.Save(Server.MapPath(saveDir));

        }

上面代码很容易就生成了缩略图,但是效果很不理想,图片很模糊.于是又搜了一遍,结果搜到如下代码,到底出自哪位仁兄就忘了:

        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
        ...{
            System.Drawing.Image originalImage = System.Drawing.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
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            //新建一个画板
            System.Drawing.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(System.Drawing.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 System.Drawing.Rectangle(0, 0, towidth, toheight),
                new System.Drawing.Rectangle(x, y, ow, oh),
                System.Drawing.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();
            }
        }

照搬下去试了一下,结果执行到保存文件这一步总出现"GDI+ 中发生一般性错误 ",google了一下,都是说要么没权限,要么image没有Dispose,该加的都加进去,权限也得到保证,可依然没什么改观,重复了N次,就是没发现哪里出现问题,就在要放弃的时候,才发现原来出现不可原谅的错误:文件保存的路径不对!当场狂凑了自己一顿!把路径改过来之后果然那鬼门关顺利的通过,生成渴望已久的缩略图.(^_^)

以下是几种方法得到的不同效果,当然最模糊的就是第一种啦!