缩略图

 public Bitmap ToThumbnailImages(string sourceImagePath, string thumbnailImagePath, int thumbnailImageWidth)
        {
            //string SourceImagePath = sourceImagePath;
            //string ThumbnailImagePath = thumbnailImagePath;
            //int ThumbnailImageWidth = thumbnailImageWidth;
            //string sExt = SourceImagePath.Substring(SourceImagePath.LastIndexOf(".")).ToLower();
            //if (SourceImagePath.ToString() == System.String.Empty) throw new NullReferenceException("SourceImagePath is null!");
            //if (!CheckValidExt(sExt))
            //{
            //    throw new ArgumentException("原图片文件格式不正确,支持的格式有[ " + AllowExt + " ]", "SourceImagePath");
            //}
            //从 原图片 创建 Image 对象
            System.Drawing.Image image = System.Drawing.Image.FromFile(sourceImagePath);
            int num = ((thumbnailImageWidth / 4) * 3);
            int width = image.Width;
            int height = image.Height;
            //计算图片的比例
            if ((((double)width) / ((double)height)) >= 1.3333333333333333f)
            {
                num = ((height * thumbnailImageWidth) / width);
            }
            else
            {
                thumbnailImageWidth = ((width * num) / height);
            }
            if ((thumbnailImageWidth < 1) || (num < 1))
            {
                return null;
            }
            //用指定的大小和格式初始化 Bitmap 类的新实例
            Bitmap bitmap = new Bitmap(thumbnailImageWidth, num, PixelFormat.Format32bppArgb);
            //从指定的 Image 对象创建新 Graphics 对象
            Graphics graphics = Graphics.FromImage(bitmap);
            //清除整个绘图面并以透明背景色填充
            graphics.Clear(Color.Transparent);
            //在指定位置并且按指定大小绘制 原图片 对象
            graphics.DrawImage(image, new Rectangle(0, 0, thumbnailImageWidth, num));
            image.Dispose();
            graphics.Dispose(); 
            return bitmap;
            //image.Dispose();
            //try
            //{
            //    //将此 原图片 以指定格式并用指定的编解码参数保存到指定文件
            //    string savepath = (ThumbnailImagePath == null ? SourceImagePath : ThumbnailImagePath);
            //    SaveImage(bitmap, HttpContext.Current.Server.MapPath(savepath), GetCodecInfo((string)htmimes[sExt]));
            //}
            //catch (System.Exception e)
            //{
            //    throw e;
            //}
            //finally
            //{
            //    bitmap.Dispose();
            //    graphics.Dispose();
            //}
        }