Asp.net中裁剪，缩小图片(多谢csdn朋友热心帮助) 转载。

private void Page_Load(object sender, System.EventArgs e)
        {
            ImgReduceCutOut(100,120,"1.jpg","2.jpg");
        }
        /// <summary>
        /// 缩小裁剪图片
        /// </summary>
        /// <param name="int_Width">要缩小裁剪图片宽度</param>
        /// <param name="int_Height">要缩小裁剪图片长度</param>
        /// <param name="input_ImgUrl">要处理图片路径</param>
        /// <param name="out_ImgUrl">处理完毕图片路径</param>
        public void ImgReduceCutOut(int int_Width,int int_Height,string input_ImgUrl,string out_ImgUrl)
        {
            // ＝＝＝上传标准图大小＝＝＝
            int int_Standard_Width=160;
            int int_Standard_Height=160;

            int Reduce_Width=0; // 缩小的宽度
            int Reduce_Height=0; // 缩小的高度
            int CutOut_Width=0; // 裁剪的宽度
            int CutOut_Height=0; // 裁剪的高度
            int level = 100; //缩略图的质量 1-100的范围
            
            // ＝＝＝获得缩小，裁剪大小＝＝＝
            if (int_Standard_Height*int_Width/int_Standard_Width>int_Height)
            {
                Reduce_Width=int_Width;
                Reduce_Height=int_Standard_Height*int_Width/int_Standard_Width;
                CutOut_Width=int_Width;
                CutOut_Height=int_Height;
            }
            else if (int_Standard_Height*int_Width/int_Standard_Width<int_Height)
            {
                Reduce_Width=int_Standard_Width*int_Height/int_Standard_Height;
                Reduce_Height=int_Height;
                CutOut_Width=int_Width;
                CutOut_Height=int_Height;
            }
            else
            {
                Reduce_Width=int_Width;
                Reduce_Height=int_Height;
                CutOut_Width=int_Width;
                CutOut_Height=int_Height;
            }

            // ＝＝＝通过连接创建Image对象＝＝＝
            System.Drawing.Image oldimage = System.Drawing.Image.FromFile(Server.MapPath(input_ImgUrl));

            // ＝＝＝缩小图片＝＝＝
            System.Drawing.Image thumbnailImage = oldimage.GetThumbnailImage(Reduce_Width, Reduce_Height,new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero);
            Bitmap bm=new Bitmap(thumbnailImage);

            // ＝＝＝处理JPG质量的函数＝＝＝
            ImageCodecInfo[] codecs=ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo ici=null;
            foreach(ImageCodecInfo codec in codecs)
            {
                if(codec.MimeType=="image/jpeg")
                    ici=codec;
            }
            EncoderParameters ep=new EncoderParameters();
            ep.Param[0]=new EncoderParameter(Encoder.Quality,(long)level);
            
            bm.Save(Server.MapPath("2.jpg"),ici,ep);

            // ＝＝＝裁剪图片＝＝＝
            Rectangle cloneRect = new Rectangle(0, 0, CutOut_Width, CutOut_Height);
            PixelFormat format = bm.PixelFormat;
            Bitmap cloneBitmap = bm.Clone(cloneRect, format);

            // ＝＝＝保存图片＝＝＝
            cloneBitmap.Save(Server.MapPath(out_ImgUrl),ici,ep);
        }

        public bool ThumbnailCallback()
        {
            return false;
        }