c#生成图片缩略图的类(2种实现思路)_.net

第一种

 
/**//// <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(0, 0, 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(); 
} 
} 

关键方法graphics.drawimage见ms-help://ms.netframeworksdkv1.1.chs/cpref/html/frlrfsystemdrawinggraphicsclassdrawimagetopic11.htm
第二种
4个重载方法,有直接返回image对象的,有生成缩略图,并且保存到指定目录的!

复制代码代码如下:

 
using system.io; 
using system.drawing; 
using system.drawing.imaging; 
/// <summary> 
/// 图片处理类 
/// 1、生成缩略图片或按照比例改变图片的大小和画质 
/// 2、将生成的缩略图放到指定的目录下 
/// </summary> 
public class imageclass 
{ 
public image resourceimage; 
private int imagewidth; 
private int imageheight; 
public string errmessage; 
/// <summary> 
/// 类的构造函数 
/// </summary> 
/// <param name="imagefilename">图片文件的全路径名称</param> 
public imageclass(string imagefilename) 
{ 
resourceimage=image.fromfile(imagefilename); 
errmessage=""; 
} 
public bool thumbnailcallback() 
{ 
return false; 
} 
/// <summary> 
/// 生成缩略图重载方法1，返回缩略图的image对象 
/// </summary> 
/// <param name="width">缩略图的宽度</param> 
/// <param name="height">缩略图的高度</param> 
/// <returns>缩略图的image对象</returns> 
public image getreducedimage(int width,int height) 
{ 
try 
{ 
image reducedimage; 
image.getthumbnailimageabort callb=new image.getthumbnailimageabort(thumbnailcallback); 
reducedimage=resourceimage.getthumbnailimage(width,height,callb,intptr.zero); 
return reducedimage; 
} 
catch(exception e) 
{ 
errmessage=e.message; 
return null; 
} 
} 
/// <summary> 
/// 生成缩略图重载方法2，将缩略图文件保存到指定的路径 
/// </summary> 
/// <param name="width">缩略图的宽度</param> 
/// <param name="height">缩略图的高度</param> 
/// <param name="targetfilepath">缩略图保存的全文件名，(带路径)，参数格式：d:images ilename.jpg</param> 
/// <returns>成功返回true，否则返回false</returns> 
public bool getreducedimage(int width,int height,string targetfilepath) 
{ 
try 
{ 
image reducedimage; 
image.getthumbnailimageabort callb=new image.getthumbnailimageabort(thumbnailcallback); 
reducedimage=resourceimage.getthumbnailimage(width,height,callb,intptr.zero); 
reducedimage.save(@targetfilepath,imageformat.jpeg); 
reducedimage.dispose(); 
return true; 
} 
catch(exception e) 
{ 
errmessage=e.message; 
return false; 
} 
} 
/// <summary> 
/// 生成缩略图重载方法3，返回缩略图的image对象 
/// </summary> 
/// <param name="percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param> 
/// <returns>缩略图的image对象</returns> 
public image getreducedimage(double percent) 
{ 
try 
{ 
image reducedimage; 
image.getthumbnailimageabort callb=new image.getthumbnailimageabort(thumbnailcallback); 
imagewidth=convert.toint32(resourceimage.width*percent); 
imageheight=convert.toint32(resourceimage.width*percent); 
reducedimage=resourceimage.getthumbnailimage(imagewidth,imageheight,callb,intptr.zero); 
return reducedimage; 
} 
catch(exception e) 
{ 
errmessage=e.message; 
return null; 
} 
} 
/// <summary> 
/// 生成缩略图重载方法4，返回缩略图的image对象 
/// </summary> 
/// <param name="percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param> 
/// <param name="targetfilepath">缩略图保存的全文件名，(带路径)，参数格式：d:images ilename.jpg</param> 
/// <returns>成功返回true,否则返回false</returns> 
public bool getreducedimage(double percent,string targetfilepath) 
{ 
try 
{ 
image reducedimage; 
image.getthumbnailimageabort callb=new image.getthumbnailimageabort(thumbnailcallback); 
imagewidth=convert.toint32(resourceimage.width*percent); 
imageheight=convert.toint32(resourceimage.width*percent); 
reducedimage=resourceimage.getthumbnailimage(imagewidth,imageheight,callb,intptr.zero); 
reducedimage.save(@targetfilepath,imageformat.jpeg); 
reducedimage.dispose(); 
return true; 
} 
catch(exception e) 
{ 
errmessage=e.message; 
return false; 
} 
} 
} 