ASP.NET实现上传图片并生成缩略图的方法

本文实例讲述了asp.net实现上传图片并生成缩略图的方法。分享给大家供大家参考，具体如下：

protected void bt_upload_click(object sender, eventargs e)
{
  //检查上传文件的格式是否有效 
  if (this.uploadfile.postedfile.contenttype.tolower().indexof("image") < 0)
  {
   response.write("上传图片格式无效！");
   return;
  }
  //生成原图 
  byte[] ofilebyte = new byte[this.uploadfile.postedfile.contentlength];
  system.io.stream ostream = this.uploadfile.postedfile.inputstream;
  system.drawing.image oimage = system.drawing.image.fromstream(ostream);
  int owidth = oimage.width; //原图宽度 
  int oheight = oimage.height; //原图高度 
  int twidth = 100; //设置缩略图初始宽度 
  int theight = 100; //设置缩略图初始高度 
  //按比例计算出缩略图的宽度和高度 
  if (owidth >= oheight)
  {
   theight = (int)math.floor(convert.todouble(oheight) * (convert.todouble(twidth) / convert.todouble(owidth)));
  }
  else
  {
   twidth = (int)math.floor(convert.todouble(owidth) * (convert.todouble(theight) / convert.todouble(oheight)));
  }
  //生成缩略原图 
  bitmap timage = new bitmap(twidth, theight);
  graphics g = graphics.fromimage(timage);
  g.interpolationmode = system.drawing.drawing2d.interpolationmode.high; //设置高质量插值法 
  g.smoothingmode = system.drawing.drawing2d.smoothingmode.highquality;//设置高质量,低速度呈现平滑程度 
  g.clear(color.transparent); //清空画布并以透明背景色填充 
  g.drawimage(oimage, new rectangle(0, 0, twidth, theight), new rectangle(0, 0, owidth, oheight), graphicsunit.pixel);
  string ofullname = server.mappath(".") + "/image/" + "o" + datetime.now.toshortdatestring().replace("-", "") + datetime.now.hour.tostring() + datetime.now.minute.tostring() + datetime.now.second.tostring() + datetime.now.millisecond.tostring() + ".jpg"; //保存原图的物理路径 
  string tfullname = server.mappath(".") + "/image/" + "t" + datetime.now.toshortdatestring().replace("-", "") + datetime.now.hour.tostring() + datetime.now.minute.tostring() + datetime.now.second.tostring() + datetime.now.millisecond.tostring() + ".jpg"; //保存缩略图的物理路径 
  try
  {
   //以jpg格式保存图片 
   oimage.save(ofullname, system.drawing.imaging.imageformat.jpeg);
   timage.save(tfullname, system.drawing.imaging.imageformat.jpeg);
  }
  catch (exception ex)
  {
   throw ex;
  }
  finally
  {
   //释放资源 
   oimage.dispose();
   g.dispose();
   timage.dispose();
  }
 }
}

这里再补充一个改进方法：

#region 上传图片 并生成缩略图
/// <summary>
/// 上传图片生成缩略图
/// </summary>
/// <param name="originalimagepath">图片源路径</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) {
  //从路径中获取源图片的文件
  system.drawing.image originalimage = system.drawing.image.fromfile(originalimagepath);
  int towidth = width;
  int toheight = height;
  int x = 0;
   int y = 0;
  //获取图片的宽度
   int ow = image.width;
  //获取图片的高度
   int oh = image.height;
  //生成缩略图的方式
   switch (mode) { 
    case "hw":
    break;
    case "w"://指定宽度 高按比例
    toheight = originalimage.height * width / originalimage.width;
    break;
    case "h"://指定图片的高度 宽按比例
    towidth = originalimage.width * height / originalimage.height;
    break;
    case "cut"://如果为裁减模式 则不变形 
    if ((double)originalimage.width / (double)originalimage.height > (double)towidth / (double)toheight)
    {
     oh = originalimage.height;
     //缩略图片的宽度
     ow = originalimage.height * towidth / toheight;
     y = 0;
     x = (originalimage.width - ow) / 2;
    }
    else {
     ow = originalimage.width;
     //缩略图片的高度
     oh = originalimage.width * toheight / towidth;
     x = 0;
     y(originalimage.height - oh) / 2;
    }
    break;
    default: break;
   }
  //新建一个bmp图片
   bitmap bitmap = new bitmap(towidth, toheight);
  //新建一个画布 以bitmap 宽 高作为画布的大小
   graphics g = graphics.fromimage(bitmap);
  //设置高质量插值法
   g.interpolationmode = interpolationmode.high;
  //以高质量 低速度 呈现
   g.smoothingmode = smoothingmode.highquality;
  //清空画布 以白色背景色填充 
   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(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 (exception ex)
   {
    throw ex;
   }
   finally {
    //释放资源
    originalimage.dispose();
    bitmap.dispose();
    g.dispose();
   }
}
#endregion

希望本文所述对大家asp.net程序设计有所帮助。