生面缩略图通用函数(c#)

做网站有时图片很大，直接引有原图网页下载速度会很慢，这样的图不多还好，或者直接影响网站访问速度；如商品展示类网站就需要生成很多缩略图,以减小图片大小，减少网页下载时间。

文件上传，文件下载，生成缩略图等功能,这样的代码都可以模块化或组,供以后使用

生成缩略图函数：

 

/**/ /// <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">生成缩略图的形式(HW,指定高宽缩放（可能变形）; W,指定宽，高按比例; H,指定高，宽按比例; Cut,指定高宽裁减(不变形);)</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.ToUpper())
            ...{ 
                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格式保存缩略图片
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);//originalImage.RawFormat
            }
            catch(System.Exception e)
            ...{
                throw e;
            }
            finally
            ...{
                originalImage.Dispose();
                bitmap.Dispose(); 
                g.Dispose();
            }
        }

 

调用:

//一
   //生成原图
   System.IO.Stream Stream = this.UploadFile.PostedFile.InputStream;
   System.Drawing.Image Image = System.Drawing.Image.FromStream(Stream);
   int Width = Image.Width; //原图宽度
   int Height = Image.Height; //原图高度
   Common.MakeThumbnail(源图路径,缩略图路径,Width,Height,"W");
   //生成缩略图
   Common.MakeThumbnail(源图路径,缩略图路径,100,100,"W");