[C#] 圖片縮圖

System.Drawing namespace 提供對 GDI+ 基本繪圖功能的存取，可以方便處理圖片的操作，下面是一個處理圖片縮圖的範例:

原始碼

1. //using System.Drawing; 
2.  
3. var image = Image.FromFile(@"D:\001.jpg"); 
4.  
5. int width = 120, height = 100; 
6. float targetRatio = (float)width / (float)height; 
7. float imageRatio = (float)image.Width / (float)image.Height; 
8.  
9.  
10. if(imageRatio < targetRatio) 
11. { 
12.    width = Math.Max(1, height * image.Width / image.Height); 
13. } 
14. else 
15. { 
16.    height = Math.Max(1, width * image.Height / image.Width);  
17. } 
18.  
19.  
20. var thumbnail = image.GetThumbnailImage(width, height, null, IntPtr.Zero); 
21.  
22. thumbnail.Save(@"D:\thumb.jpg"); 

//using System.Drawing;

var image = Image.FromFile(@"D:\001.jpg");

int width = 120, height = 100;
float targetRatio = (float)width / (float)height;
float imageRatio = (float)image.Width / (float)image.Height;


if(imageRatio < targetRatio)
{
    width = Math.Max(1, height * image.Width / image.Height);
}
else
{
    height = Math.Max(1, width * image.Height / image.Width); 
}


var thumbnail = image.GetThumbnailImage(width, height, null, IntPtr.Zero);

thumbnail.Save(@"D:\thumb.jpg");

這個方式可以容易的做到圖片縮圖，但使用這個方式會很佔用記憶體，在處理尺寸大的圖片時有可能會出現 out of memory，而且在 MSDN 有以下的警示:

Classes within the System.Drawing namespace are not supported for use within a Windows or ASP.NET service. Attempting to use these classes from within one of these application types may produce unexpected problems, such as diminished service performance and run-time exceptions. For a supported alternative, see Windows Imaging Components.