缩放图片之后，都成了像素点.为什么？？？

Question

 原始图片的W为3072，H为2304.System.Drawing.Image myImage = System.Drawing.Image.FromStream(Request.Files["Filedata"].InputStream);
 System.Drawing.Image thumbImageB = myImage.GetThumbnailImage
           (1024, 768, null, System.IntPtr.Zero);从高像素缩略到低像素的，不应该出现这种情况啊，哪里出错了，或者是语句不对。
就是很模糊，为什么模糊呢。

Answer 1

/// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath">原图片地址</param>
        /// <param name="thumNailPath">缩略图地址</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="model">生成缩略的模式</param>
        /// <param name="smoothingMode">平滑程度</param>
        /// <param name="interpolationMode">查值法</param>
        public void MakeThumNail(string originalImagePath, string thumNailPath, int width, int height, string model, System.Drawing.Drawing2D.SmoothingMode smoothingMode, System.Drawing.Drawing2D.InterpolationMode interpolationMode)
        {
            System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);            int thumWidth = width;      //缩略图的宽度
            int thumHeight = height;    //缩略图的高度            int x = 0;
            int y = 0;            int originalWidth = originalImage.Width;    //原始图片的宽度
            int originalHeight = originalImage.Height;  //原始图片的高度            switch (model)
            {
                case "HW":      //指定高宽缩放,可能变形
                    break;
                case "W":       //指定宽度,高度按照比例缩放
                    if (width < originalImage.Width)
                    {
                        thumHeight = originalImage.Height * width / originalImage.Width;
                    }
                    else
                    {
                        thumWidth = originalWidth;
                        thumHeight = originalHeight;
                    }
                    break;
                case "H":       //指定高度,宽度按照等比例缩放
                    thumWidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "Cut":
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)thumWidth / (double)thumHeight)
                    {
                        originalHeight = originalImage.Height;
                        originalWidth = originalImage.Height * thumWidth / thumHeight;
                        y = 0;
                        x = (originalImage.Width - originalWidth) / 2;
                    }
                    else
                    {
                        originalWidth = originalImage.Width;
                        originalHeight = originalWidth * height / thumWidth;
                        x = 0;
                        y = (originalImage.Height - originalHeight) / 2;
                    }
                    break;
                default:
                    break;
            }            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(thumWidth, thumHeight);            //新建一个画板
            System.Drawing.Graphics graphic = System.Drawing.Graphics.FromImage(bitmap);            //设置高质量查值法
            graphic.InterpolationMode = interpolationMode;            //设置高质量，低速度呈现平滑程度
            graphic.SmoothingMode = smoothingMode;            //清空画布并以透明背景色填充
            graphic.Clear(System.Drawing.Color.Transparent);            //在指定位置并且按指定大小绘制原图片的指定部分
            graphic.DrawImage(originalImage, new System.Drawing.Rectangle(0, 0, thumWidth, thumHeight), new System.Drawing.Rectangle(x, y, originalWidth, originalHeight), System.Drawing.GraphicsUnit.Pixel);            try
            {
                bitmap.Save(thumNailPath);
                //bitmap.Save(thumNailPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            catch (Exception ex)
            {                throw ex;
            }
            finally
            {
                originalImage.Dispose();
                bitmap.Dispose();
                graphic.Dispose();
            }
        }        /// <summary>
        /// 生成缩略图
        /// </summary>
        /// <param name="originalImagePath">原图片地址</param>
        /// <param name="thumNailPath">缩略图地址</param>
        /// <param name="width">缩略图宽度</param>
        /// <param name="height">缩略图高度</param>
        /// <param name="model">生成缩略的模式</param>
        public void MakeThumNail(string originalImagePath, string thumNailPath, int width, int height, string model)
        {
            MakeThumNail(originalImagePath, thumNailPath, width, height, model, System.Drawing.Drawing2D.SmoothingMode.Default, System.Drawing.Drawing2D.InterpolationMode.Default);
        }

Answer 2

重点在这： //设置高质量查值法
            graphic.InterpolationMode = interpolationMode;            //设置高质量，低速度呈现平滑程度
            graphic.SmoothingMode = smoothingMode;