调用：

1 int width = 190;2 int height = 190;3 Bitmap source = new Bitmap("c:\\someimage.jpg");4 System.Drawing.Image thumb = source.GetThumbnailImage(width,height,null,IntPtr.Zero);5 thumb.Save("C:\\someimageshot.jpg");6 thumb.Dispose();

 

函数：

1 public static Bitmap CreateThumbnail(Bitmap source, int thumbWi, int thumbHi, bool maintainAspect) 2         { 3             if (source.Width < thumbWi && source.Height < thumbHi) return source; 4             System.Drawing.Bitmap ret = null; 5             try 6             { 7                 int wi, hi; 8  9                 wi = thumbWi;10                 hi = thumbHi;11 12                 if (maintainAspect)13                 {14                     if (source.Width > source.Height)15                     {16                         wi = thumbWi;17                         hi = (int)(source.Height * ((decimal)thumbWi / source.Width));18                     }19                     else20                     {21                         hi = thumbHi;22                         wi = (int)(source.Width * ((decimal)thumbHi / source.Height));23                     }24                 }25                 ret = new Bitmap(wi, hi);26                 using (Graphics g = Graphics.FromImage(ret))27                 {28                     g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;29                     g.FillRectangle(Brushes.White, 0, 0, wi, hi);30                     g.DrawImage(source, 0, 0, wi, hi);31                 }32             }33             catch34             {35                 ret = null;36             }37 38             return ret;39         }

另类用途：

比如某张云图特别大。要在首页上缩小显示。第一想法就是强制设定img的width和height。这个方法对ie8完美运行。但是ie7和6会出现图片压缩严重失真现象。这时就可以用大图转成缩略图来实现。读取大图的时候生成缩略图，并读取缩略图。下次再thumb.Save同一个缩略图文件。这样也不占用空间。