asp.net改变上传图片的物理大小，能否实现。。

Question

上传图片太大，能否在上传后改变图片的物理大小，不改变图片原来的尺寸，也不很大影响图片的原来画质。
  求解...

Answer 1

都是生成了那种改变了图片尺寸的，没有找到可以缩小图片物理大小
比如一张图片100KB，把图片改小成小于100KB

Answer 2

refer this:
你可以在上传时改变它。或是上传时不改变，而是在显示改变。还有一种选择，显示时显示小图，当用户点击再显示大图：http://www.cnblogs.com/insus/articles/2060601.html

Answer 3

导入ps，保持为gif或者jpeg，调低品质

Answer 4

给你一段代码吧：
 /// <summary>
        /// 上传图片生成缩略图
        /// </summary>
        /// <param name="originalImagePath">源图片</param>
        /// <param name="thumbnailPath">缩略图保存路径</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="mode">缩略模式</param>
        public static void MakeThumbnail(byte [] originalImageByte, string thumbnailPath, int width, int height, string mode)
        {
            System.IO.Stream imageStream = new System.IO.MemoryStream(originalImageByte);
            System.Drawing.Image originalImage = System.Drawing.Image.FromStream(imageStream);            int towidth = width;
            int toheight = height;            int x = 0;
            int y = 0;
            int ow = originalImage.Width;
            int oh = originalImage.Height;            switch (mode)
            {
                case "HW"://指定高宽缩放（可能变形）                
                    break;
                case "W"://指定宽，高按比例                    
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut"://指定高宽裁减（不变形）                
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                default:
                    break;
            }
            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
            //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;
            //清空画布并以透明背景色填充
            g.Clear(Color.Transparent);
            //在指定位置并且按指定大小绘制原图片的指定部分
            g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
                new Rectangle(x, y, ow, oh),
                GraphicsUnit.Pixel);            try
            {
                //以jpg格式保存缩略图
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                g.Dispose();
            }
        } 
    }   

Answer 5

  /// <summary>
        /// 执行: 压缩原图 System.Drawing.Bitmap 对象保存到文件 (JPEG格式压缩)
        /// </summary>
        /// <param name="source">原图 System.Drawing.Bitmap 对象: System.Drawing.Bitmap</param>
        /// <param name="level">压缩等级(值越高图像质量越好,文件越大,范围在1~100之间): int</param>
        /// <param name="path">保存路径(包含完整路径,文件名及其扩展名): string</param>
        public void Compress(Bitmap source, int level, string path)
        {
            if (level < 1 || level > 99)
                throw new ArgumentException("压缩等级值范围在0~100之间");
            long[] quality = new long[1];
            quality[0] = level;
            using (EncoderParameters Parameters = new EncoderParameters())
            {
                using (EncoderParameter Parameter = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality))
                {
                    Parameters.Param[0] = Parameter;
                    source.Save(path, ImageCodecInfo.GetImageEncoders()[1], Parameters);                }
            }        }

Answer 6

 /// <summary>
        /// 压缩到指定尺寸
        /// </summary>
        /// <param name="oldfile">原文件</param>
        /// <param name="newfile">新文件</param>
        public bool Compress(string oldfile, string newfile)
        {
            try
            {
                System.Drawing.Image img = System.Drawing.Image.FromFile(oldfile);
                System.Drawing.Imaging.ImageFormat thisFormat = img.RawFormat;
                Size newSize = new Size(100, 125);
                Bitmap outBmp = new Bitmap(newSize.Width, newSize.Height);
                Graphics g = Graphics.FromImage(outBmp);
                g.CompositingQuality = CompositingQuality.HighQuality;
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                g.DrawImage(img, new Rectangle(0, 0, newSize.Width, newSize.Height), 0, 0, img.Width, img.Height, GraphicsUnit.Pixel);
                g.Dispose();
                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;
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo jpegICI = null;
                for (int x = 0; x < arrayICI.Length; x++)
                    if (arrayICI[x].FormatDescription.Equals("JPEG"))
                    {
                        jpegICI = arrayICI[x]; //设置JPEG编码
                        break;
                    }
                img.Dispose();
                if (jpegICI != null) outBmp.Save(newfile, System.Drawing.Imaging.ImageFormat.Jpeg);
                outBmp.Dispose();
                return true;
            }
            catch
            {
                return false;
            }
        }