在内存中动态生成缩略图

public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "image/jpeg";
        //url传来的图片名
        string img = context.Request.QueryString["img"];
        if (!string .IsNullOrEmpty(img))
        {
            //获取图片的物理路径
            string path = context.Request.MapPath("images/"+img);
            //加载大图
            Image big = Image.FromFile(path);

            int oldWidth = big.Width;
            int oldHeigth = big.Height;
            int newWidth = 150;
            int newHeigth = 100;
            //保持纵横比例
            if (oldWidth > oldHeigth)
            {
                newHeigth = newWidth * oldHeigth / oldWidth;
            }
            else
            {
                newWidth = newHeigth * oldWidth / oldHeigth;
            }
            
            //生成小图
            Bitmap bitmap = new Bitmap(newWidth,newHeigth);

            Graphics g = Graphics.FromImage(bitmap);
            //把大图，画到小图上
            g.DrawImage(big,0,0,bitmap.Width,bitmap.Height);
            //释放资源
            g.Dispose();
            //把bitmap输出到浏览器
            bitmap.Save(context.Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);
            
        }
       
    }