ASP.NET(C#)图片上传压缩成缩略图的代码

// 按模版比例生成缩略图（以流的方式获取源文件）
//生成缩略图函数
//顺序参数：源图文件流、缩略图存放地址、模版宽、模版高
//注：缩略图大小控制在模版区域内
public static void MakeSmallImg(System.IO.Stream fromFileStream,string fileSaveUrl,System.Double templateWidth,System.Double templateHeight)
{
//从文件取得图片对象，并使用流中嵌入的颜色管理信息
System.Drawing.Image myImage = System.Drawing.Image.FromStream(fromFileStream,true);

//缩略图宽、高
System.Double newWidth = myImage.Width , newHeight = myImage.Height;
//宽大于模版的横图
if(myImage.Width>myImage.Height || myImage.Width==myImage.Height)
{
if(myImage.Width > templateWidth)
{
//宽按模版，高按比例缩放
newWidth = templateWidth;
newHeight = myImage.Height * (newWidth/myImage.Width);
}
}
//高大于模版的竖图
else
{
if(myImage.Height > templateHeight)
{
//高按模版，宽按比例缩放
newHeight = templateHeight;
newWidth = myImage.Width * (newHeight/myImage.Height);
}
}

//取得图片大小
System.Drawing.Size mySize = new Size((int)newWidth,(int)newHeight);
//新建一个bmp图片
System.Drawing.Image bitmap = new System.Drawing.Bitmap(mySize.Width,mySize.Height);
//新建一个画板
System.Drawing.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;
//清空一下画布
g.Clear(Color.White);
//在指定位置画图
g.DrawImage(myImage , new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height) ,
new System.Drawing.Rectangle(0, 0, myImage.Width,myImage.Height) ,
System.Drawing.GraphicsUnit.Pixel);

///文字水印
//System.Drawing.Graphics G=System.Drawing.Graphics.FromImage(bitmap);
//System.Drawing.Font f=new Font("宋体",10);
//System.Drawing.Brush b=new SolidBrush(Color.Black);
//G.DrawString("myohmine",f,b,10,10);
//G.Dispose();

///图片水印
//System.Drawing.Image copyImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath("pic/1.gif"));
//Graphics a = Graphics.FromImage(bitmap);
//a.DrawImage(copyImage, new Rectangle(bitmap.Width-copyImage.Width,bitmap.Height-copyImage.Height,copyImage.Width, copyImage.Height),0,0, copyImage.Width, copyImage.Height, GraphicsUnit.Pixel);

//copyImage.Dispose();
//a.Dispose();
//copyImage.Dispose();

//保存缩略图
bitmap.Save(fileSaveUrl , System.Drawing.Imaging.ImageFormat.Jpeg);

g.Dispose();
myImage.Dispose();
bitmap.Dispose();
}