c# 改变图片的大小（w,h）

本文介绍获取网络上的图片将其大小尺寸改成自己想要的

   /// <summary>
        /// 图片大小裁剪
        /// </summary>
        /// <param name="filePath"></param>
        /// <returns></returns>
        public byte[] ResizeImage(string filePath)
        {

            WebRequest request = (WebRequest)HttpWebRequest.Create(filePath);
            WebResponse response = request.GetResponse();
            using (Stream stream = response.GetResponseStream())
            {
                Bitmap bm = (Bitmap)Image.FromStream(stream);

                bm = GetThumbnail(bm, 50, 40);
                MemoryStream ms = new MemoryStream();
                bm.Save(ms, System.Drawing.Imaging.ImageFormat.Bmp);
                byte[] bytes = ms.GetBuffer();  //byte[]   bytes=   ms.ToArray(); 这两句都可以，至于区别么，下面有解释
                ms.Close();
                return bytes;
            }

        }

  /// <summary>
        /// 修改图片的大小
        /// </summary>
        /// <param name="b"></param>
        /// <param name="destHeight"></param>
        /// <param name="destWidth"></param>
        /// <returns></returns>
        public Bitmap GetThumbnail(Bitmap b, int destHeight, int destWidth)
        {
            System.Drawing.Image imgSource = b;
            System.Drawing.Imaging.ImageFormat thisFormat = imgSource.RawFormat;
            int sW = 0, sH = 0;
            // 按比例缩放           
            int sWidth = imgSource.Width;
            int sHeight = imgSource.Height;
            if (sHeight > destHeight || sWidth > destWidth)
            {
                if ((sWidth * destHeight) > (sHeight * destWidth))
                {
                    sW = destWidth;
                    sH = (destWidth * sHeight) / sWidth;
                }
                else
                {
                    sH = destHeight;
                    sW = (sWidth * destHeight) / sHeight;
                }
            }
            else
            {
                sW = sWidth;
                sH = sHeight;
            }
            Bitmap outBmp = new Bitmap(destWidth, destHeight);
            Graphics g = Graphics.FromImage(outBmp);
            g.Clear(Color.Transparent);
            // 设置画布的描绘质量         
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.DrawImage(imgSource, new Rectangle((destWidth - sW) / 2, (destHeight - sH) / 2, sW, sH), 0, 0, imgSource.Width, imgSource.Height, GraphicsUnit.Pixel);
            g.Dispose();
            // 以下代码为保存图片时，设置压缩质量     
            EncoderParameters encoderParams = new EncoderParameters();
            long[] quality = new long[1];
            quality[0] = 100;
            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
            encoderParams.Param[0] = encoderParam;
            imgSource.Dispose();
            return outBmp;
        }

 asp.net mvc 前台调用

 /// <summary>
        /// 得到图像
        /// </summary>
        /// <param name="path"></param>
        /// <returns></returns>
        public FileResult GetAvator(string path)
        {
            return File(service.ResizeImage(path), "image/png");
        }