public static Image GenThumbnail(Image imageFrom, int width, int height, int quality)
        {
            // 源图宽度及高度 
            int imageFromWidth = imageFrom.Width;
            int imageFromHeight = imageFrom.Height;

            // 生成的缩略图实际宽度及高度 
            if (width >= imageFromWidth && height >= imageFromHeight)
            {
                return imageFrom;
            }
            else
            {
                // 生成的缩略图在上述"画布"上的位置 
                int X = 0;
                int Y = 0;

                decimal wpercent = (decimal)width / imageFromWidth;
                decimal hpercent = (decimal)height / imageFromHeight;
                if (wpercent > hpercent)
                {
                    width = (int)(imageFromWidth * hpercent);
                }
                else if (wpercent < hpercent)
                {
                    height = (int)(imageFromHeight * wpercent);
                }

                // 创建画布 
                Bitmap bmp = new Bitmap(width, height, PixelFormat.Format24bppRgb);
                bmp.SetResolution(imageFrom.HorizontalResolution, imageFrom.VerticalResolution);
                using (Graphics g = Graphics.FromImage(bmp))
                {
                    // 用白色清空 
                    g.Clear(Color.White);

                    // 指定高质量的双三次插值法。执行预筛选以确保高质量的收缩。此模式可产生质量最高的转换图像。 
                    g.InterpolationMode = InterpolationMode.HighQualityBicubic;

                    // 指定高质量、低速度呈现。 
                    g.SmoothingMode = SmoothingMode.HighQuality;

                    // 在指定位置并且按指定大小绘制指定的 Image 的指定部分。 
                    g.DrawImage(imageFrom, new Rectangle(X, Y, width, height), new Rectangle(0, 0, imageFromWidth, imageFromHeight), GraphicsUnit.Pixel);

                    return bmp;
                }
            }
        }

------解决方案--------------------

试试锐化方案：
C# code

        /// <summary>
        /// 锐化
        /// </summary>
        /// <param name="b">原始Bitmap</param>
        /// <param name="val">锐化程度。取值[0,1]。值越大锐化程度越高</param>
        /// <returns>锐化后的图像</returns>
        public static Bitmap KiSharpen(Bitmap b, float val)
        {
            if (b == null)
            {
                return null;
            }

            int w = b.Width;
            int h = b.Height;

            try
            {

                Bitmap bmpRtn = new Bitmap(w, h, PixelFormat.Format24bppRgb);

                BitmapData srcData = b.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
                BitmapData dstData = bmpRtn.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);

                unsafe
                {
                    byte* pIn = (byte*)srcData.Scan0.ToPointer();
                    byte* pOut = (byte*)dstData.Scan0.ToPointer();
                    int stride = srcData.Stride;
                    byte* p;

                    for (int y = 0; y < h; y++)
                    {
                        for (int x = 0; x < w; x++)
                        {