等比例缩放图片（C#）

1. private Bitmap ZoomImage(Bitmap bitmap, int destHeight, int destWidth)  
2. {  
3.     try  
4.     {  
5.         System.Drawing.Image sourImage = bitmap;  
6.         int width = 0, height = 0;  
7.         //按比例缩放             
8.         int sourWidth = sourImage.Width;  
9.         int sourHeight = sourImage.Height;  
10.         if (sourHeight > destHeight || sourWidth > destWidth)  
11.         {  
12.             if ((sourWidth * destHeight) > (sourHeight * destWidth))  
13.             {  
14.                 width = destWidth;  
15.                 height = (destWidth * sourHeight) / sourWidth;  
16.             }  
17.             else  
18.             {  
19.                 height = destHeight;  
20.                 width = (sourWidth * destHeight) / sourHeight;  
21.             }  
22.         }  
23.         else  
24.         {  
25.             width = sourWidth;  
26.             height = sourHeight;  
27.         }  
28.         Bitmap destBitmap = new Bitmap(destWidth, destHeight);  
29.         Graphics g = Graphics.FromImage(destBitmap);  
30.         g.Clear(Color.Transparent);  
31.         //设置画布的描绘质量           
32.         g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;  
33.         g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;  
34.         g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;  
35.         g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);  
36.         g.Dispose();  
37.         //设置压缩质量       
38.         System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();  
39.         long[] quality = new long[1];  
40.         quality[0] = 100;  
41.         System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);  
42.         encoderParams.Param[0] = encoderParam;  
43.         sourImage.Dispose();  
44.         return destBitmap;  
45.     }  
46.     catch  
47.     {  
48.         return bitmap;  
49.     }  
50. }