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在网站开发时,生成缩略图是一个非常常见和实用的功能.以前在asp里只能借助com组件实现,现在在.net里可以利用框架的强大的类库轻松实现.下面帖出完整的代码(带详细注释),参考了网上的一些文章及.net sdk相关内容.QQROOM网络家园的图片上传用到了所有的4种生成方式.

        
/// <summary>
        
/// 生成缩略图
        
/// </summary>
        
/// <param name="originalImagePath">源图路径(物理路径)</param>
        
/// <param name="thumbnailPath">缩略图路径(物理路径)</param>
        
/// <param name="width">缩略图宽度</param>
        
/// <param name="height">缩略图高度</param>
        
/// <param name="mode">生成缩略图的方式</param>    

        public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
        
{
            Image originalImage 
= Image.FromFile(originalImagePath);
            
            
int towidth = width;
            
int toheight = height;
        
            
int x = 0;
            
int y = 0;
            
int ow = originalImage.Width;
            
int oh = originalImage.Height;        

            
switch (mode)
            
{        
                
case "HW"://指定高宽缩放(可能变形)                
                    break;
                
case "W"://指定宽,高按比例                    
                    toheight = originalImage.Height * width/originalImage.Width;
                    
break;
                
case "H"://指定高,宽按比例
                    towidth = originalImage.Width * height/originalImage.Height;                    
                    
break;        
                
case "Cut"://指定高宽裁减(不变形)                
                    if((double)originalImage.Width/(double)originalImage.Height > (double)towidth/(double)toheight)
                    
{
                        oh 
= originalImage.Height;
                        ow 
= originalImage.Height*towidth/toheight;
                        y 
= 0;
                        x 
= (originalImage.Width - ow)/2;
                    }

                    
else
                    
{
                        ow 
= originalImage.Width;
                        oh 
= originalImage.Width*height/towidth;
                        x 
= 0;
                        y 
= (originalImage.Height - oh)/2;
                    }

                    
break;                    
                
default :
                    
break;
            }
    
            
            
//新建一个bmp图片
            Image bitmap = new System.Drawing.Bitmap(towidth,toheight);

            
//新建一个画板
            Graphics g = System.Drawing.Graphics.FromImage(bitmap);

            
//设置高质量插值法
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;

            
//设置高质量,低速度呈现平滑程度
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;

            
//清空画布并以透明背景色填充
            g.Clear(Color.Transparent);        

            
//在指定位置并且按指定大小绘制原图片的指定部分
            g.DrawImage(originalImage, new Rectangle(00, towidth, toheight), 
                
new Rectangle(x, y, ow,oh),
                GraphicsUnit.Pixel);

            
try
            
{            
                
//以jpg格式保存缩略图
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }

            
catch(System.Exception e)
            
{
                
throw e;
            }

            
finally
            
{
                originalImage.Dispose();
                bitmap.Dispose();                        
                g.Dispose();
            }

        }


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