将图片等比例缩小不影响图片的分辨率

#region 生成缩略图
///
/// 生成缩略图
///
/// 传入图片的路径
private void SaveImage(string filePath)
{
string fileName = Path.GetExtension(File1.PostedFile.FileName).ToLower();
string _filename = DateTime.Now.ToString("yyMMddHHmm");

System.Drawing.Image image = null, aNewImage = null;

//下面是生成缩略图
int newwidth = 0, newheight = 0;
image = System.Drawing.Image.FromFile(filePath);
System.Drawing.Image.GetThumbnailImageAbort callb = new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback);

//取高和宽
int phWidth = image.Width;
int phHeight = image.Height;

//设置缩略的宽度和高度
if (phWidth > 110)
{
//指定宽度
newwidth = 110;
//根据宽度算出高度
newheight = phHeight * newwidth / phWidth;
}
aNewImage = image.GetThumbnailImage(newwidth, newheight, callb, new System.IntPtr());
//将缩略图重新命名并保存
aNewImage.Save(Server.MapPath("~/upload/") + "Avaster_" + DateTime.Now.ToString("yyMMddHHmm") + fileName);
image.Dispose();
}

#endregion