真正生成高质量不变形缩略图片

最新推荐文章于 2024-04-19 17:24:11 发布

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本文介绍了一种生成图片缩略图的方法，可以根据不同的需求选择缩放方式，并提供了具体的实现代码。支持多种缩略图生成模式，如指定高宽缩放、指定宽度按比例缩放等。

/// <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)
       {
           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
                   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 "CutA"://指定高宽裁减（不变形）自定义
                   if(ow<=towidth&&oh<=toheight)
                   {
                       x=-(towidth-ow)/2;
                       y=-(toheight-oh)/2;
                       ow=towidth;
                       oh=toheight;
                   }
                   else
                   {
                       if(ow>oh)//宽大于高
                       {
                           x=0;
                           y=-(ow-oh)/2;
                           oh=ow;
                       }
                       else//高大于宽
                       {
                           y=0;
                           x=-(oh-ow)/2;
                           ow=oh;
                       }
                   }
                   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
           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;

           //清空画布并以白色背景色填充
           g.Clear(Color.White);

           //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();
           }
       }