C#生成高清縮略圖的方法

   /// <summary>
   /// 為圖片生成縮略圖  
   /// </summary>
   /// <param name="phyPath">原圖片的路徑</param>
   /// <param name="width">縮略圖寬</param>
   /// <param name="height">縮略圖高</param>
   /// <returns></returns>
   public System.Drawing.Image GetThumbnail(System.Drawing.Image image, int width, int height)
   {
       Bitmap bmp = new Bitmap(width, height);
       //從Bitmap創建一個System.Drawing.Graphics
       System.Drawing.Graphics gr = System.Drawing.Graphics.FromImage(bmp);
       //設置 
       gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
       //下面這個也設成高質量
       gr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
       //下面這個設成High
       gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
       //把原始圖像繪制成上面所設置寬高的縮小圖
       System.Drawing.Rectangle rectDestination = new System.Drawing.Rectangle(0, 0, width, height);
 
       gr.DrawImage(image, rectDestination, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel);
       return bmp;
   }

調用方法

  HttpPostedFile file = photoFile.PostedFile;
        if (!file.ContentType.Contains("image"))
        {
　　　　　　return "照片格式不合法";
        }
        string ext = Path.GetExtension(file.FileName).ToLower();
        if (ext != ".jpg" && ext != ".gif" && ext != ".png" && ext != ".jpeg")
        {
　　　　　　return "請您上傳jpg、gif、png圖片";
        }
        if (file.ContentLength > 5 * 1024 * 1024)
        {
　　　　　　return "請您上傳512字節內的圖片";
        }
        string newName = Guid.NewGuid().ToString();
        string tempPath = "upload/";
        string img = tempPath + newName + ext;
        string filePath = Server.MapPath(img);
        if (!Directory.Exists(tempPath))
        {
            Directory.CreateDirectory(tempPath);
        }
        using (System.Drawing.Image originalImage = System.Drawing.Image.FromStream(file.InputStream))
        {
            GetThumbnail(originalImage, 504, 374).Save(filePath);
        }