生成缩略图

 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        System.Drawing.Image originalImage = System.Drawing.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        System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
53
54        //新建一个画板
55        System.Drawing.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(System.Drawing.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 System.Drawing.Rectangle(0, 0, towidth, toheight),
68            new System.Drawing.Rectangle(x, y, ow, oh),
69            System.Drawing.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