[C#]產生縮圖

        /// <summary>
        /// 產生縮圖
        /// </summary>
        /// <param name="sourceImagePath">原圖片路徑(絕對路徑)</param>
        /// <param name="thumbnailImageWidth">縮圖的寬度（高度與按源圖片比例自動產生）</param>
        public Image ToThumbnailImages(string sourceImagePath, int thumbnailImageWidth)
        {
            Image Retimage = null;

            string SourceImagePath = sourceImagePath;
            int ThumbnailImageWidth = thumbnailImageWidth;
            string sExt = SourceImagePath.Substring(SourceImagePath.LastIndexOf(".")).ToLower();
            //從 原圖片 建立 Image 對象
            Stream FS = new FileStream(sourceImagePath, FileMode.Open);
            System.Drawing.Image image = System.Drawing.Image.FromStream(FS);
            FS.Close();
            //System.Drawing.Image image = System.Drawing.Image.FromFile(sourceImagePath);
            int num = ((ThumbnailImageWidth / 4) * 3);
            int width = image.Width;
            int height = image.Height;
            //計算圖片的比例
            if ((((double)width) / ((double)height)) >= 1.3333333333333333f)
            {
                num = ((height * ThumbnailImageWidth) / width);
            }
            else
            {
                ThumbnailImageWidth = ((width * num) / height);
            }
            if ((ThumbnailImageWidth < 1) || (num < 1))
            {
                return Retimage;
            }
            //用指定的大小和格式初始化 Bitmap 類的新執行個體
            Bitmap bitmap = new Bitmap(ThumbnailImageWidth, num, PixelFormat.Format32bppArgb);
            //從指定的 Image 對象建立新 Graphics 對象
            Graphics graphics = Graphics.FromImage(bitmap);
            //清除整個繪圖面並以透明背景色填充
            graphics.Clear(Color.Transparent);
            //在指定位置並且按指定大小繪製 原圖片 對象
            graphics.DrawImage(image, new Rectangle(0, 0, ThumbnailImageWidth, num));
            Retimage = image.Clone() as Image;
            image.Dispose();
            bitmap.Dispose();
            graphics.Dispose();

            return Retimage;
        }