Code
 1 /**//// <summary>
 2        /// 生成缩略图
 3        /// </summary>
 4        /// <param name="originalImagePath">源图路径（物理路径）</param>
 5        /// <param name="thumbnailPath">缩略图路径（物理路径）</param>
 6        /// <param name="width">缩略图宽度</param>
 7        /// <param name="height">缩略图高度</param>
 8        /// <param name="mode">生成缩略图的方式</param>    
 9        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
10        {
11            Image originalImage = Image.FromFile(originalImagePath);
12            
13            int towidth = width;
14            int toheight = height;
15        
16            int x = 0;
17            int y = 0;
18            int ow = originalImage.Width;
19            int oh = originalImage.Height;        
20
21            switch (mode)
22            {        
23                case "HW"://指定高宽缩放（可能变形）                
24                    break;
25                case "W"://指定宽，高按比例                    
26                    toheight = originalImage.Height * width/originalImage.Width;
27                    break;
28                case "H"://指定高，宽按比例
29                    towidth = originalImage.Width * height/originalImage.Height;                    
30                    break;        
31                case "Cut"://指定高宽裁减（不变形）                
32                    if((double)originalImage.Width/(double)originalImage.Height > (double)towidth/(double)toheight)
33                    {
34                        oh = originalImage.Height;
35                        ow = originalImage.Height*towidth/toheight;
36                        y = 0;
37                        x = (originalImage.Width - ow)/2;
38                    }
39                    else
40                    {
41                        ow = originalImage.Width;
42                        oh = originalImage.Width*height/towidth;
43                        x = 0;
44                        y = (originalImage.Height - oh)/2;
45                    }
46                    break;                    
47                default :
48                    break;
49            }    
50            
51            //新建一个bmp图片
52            Image bitmap = new System.Drawing.Bitmap(towidth,toheight);
53
54            //新建一个画板
55            Graphics g = System.Drawing.Graphics.FromImage(bitmap);
56
57            //设置高质量插值法
58            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
59
60            //设置高质量,低速度呈现平滑程度
61            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
62
63            //清空画布并以透明背景色填充
64            g.Clear(Color.Transparent);        
65
66            //在指定位置并且按指定大小绘制原图片的指定部分
67            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight), 
68                new Rectangle(x, y, ow,oh),
69                GraphicsUnit.Pixel);
70
71            try
72            {            
73                //以jpg格式保存缩略图
74                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
75            }
76            catch(System.Exception e)
77            {
78                throw e;
79            }
80            finally
81            {
82                originalImage.Dispose();
83                bitmap.Dispose();                        
84                g.Dispose();
85            }
86        }
87