.NET 等寬、等高、等比例、固定寬高生成縮略圖 類

#region 根據原圖片生成等比縮略圖
        /// <summary>  
        /// 根據源圖片生成縮略圖  
        /// </summary>  
        /// <param name="imgPath_old">源圖(大圖)物理路徑</param>  
        /// <param name="imgPath_new">縮略圖物理路徑(生成的縮略圖將保存到該物理位置)</param>  
        /// <param name="width">縮略圖寬度</param>  
        /// <param name="height">縮略圖高度</param>  
        /// <param name="mode">縮略圖縮放模式(取值"HW":指定高寬縮放,可能變形；取值"W":按指定寬度,高度按比例縮放；取值"H":按指定高度,寬度按比例縮放；取值"Cut":按指定高度和寬度裁剪,不變形)；取值"DB":等比縮放,以值較大的做爲標準進行等比縮放</param>  
        /// <param name="type">即將生成縮略圖的文件的擴展名(僅限：JPG、GIF、PNG、BMP)</param>  
        public static void MakeThumbnail(string imgPath_old, string imgPath_new, int width, int height, string mode, string imageType, int xx, int yy)
        {
            System.Drawing.Image img = System.Drawing.Image.FromFile(imgPath_old);
            int towidth = width; int toheight = height;
            int x = 0; int y = 0; int ow = img.Width;
            int oh = img.Height; switch (mode)
            {
                case "HW":  //指定高寬壓縮
                    if ((double)img.Width / (double)img.Height > (double)width / (double)height)//判斷圖形是什麼形狀
                    {
                        towidth = width;
                        toheight = img.Height * width / img.Width;
                    }
                    else if ((double)img.Width / (double)img.Height == (double)width / (double)height)
                    {
                        towidth = width;
                        toheight = height;
                    }
                    else
                    {
                        toheight = height;
                        towidth = img.Width * height / img.Height;
                    }
                    break;
                case "W":  //指定寬，高按比例   
                    toheight = img.Height * width / img.Width;
                    break;
                case "H":  //指定高，寬按比例  
                    towidth = img.Width * height / img.Height;
                    break;
                case "Cut":   //指定高寬裁減（不變形）   
                    if ((double)img.Width / (double)img.Height > (double)towidth / (double)toheight)
                    {
                        oh = img.Height;
                        ow = img.Height * towidth / toheight;
                        y = yy; x = (img.Width - ow) / 2;
                    }
                    else
                    {
                        ow = img.Width;
                        oh = img.Width * height / towidth;
                        x = xx; y = (img.Height - oh) / 2;
                    } break;
                case "DB":    // 按值較大的進行等比縮放（不變形）   
                    if ((double)img.Width / (double)towidth < (double)img.Height / (double)toheight)
                    {
                        toheight = height;
                        towidth = img.Width * height / img.Height;
                    }
                    else
                    {
                        towidth = width;
                        toheight = img.Height * width / img.Width;
                    } break;
                default:
                    break;
            }
            //新建一個bmp圖片  
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
            //新建一個畫板  
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);
            //設置高質量插值法  
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            //設置高質量,低速度呈現平滑程度  
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            //清空畫布並以透明背景色填充  
            g.Clear(System.Drawing.Color.Transparent);
            //在指定位置而且按指定大小繪製原圖片的指定部分  
            g.DrawImage(img, new System.Drawing.Rectangle(0, 0, towidth, toheight),
            new System.Drawing.Rectangle(x, y, ow, oh),
            System.Drawing.GraphicsUnit.Pixel); try
            {
                //以jpg格式保存縮略圖 
                switch (imageType.ToLower())
                {
                    case "gif":
                        img.Save(imgPath_new, ImageFormat.Jpeg);//生成縮略圖
                        break;
                    case "jpg":
                        bitmap.Save(imgPath_new, System.Drawing.Imaging.ImageFormat.Jpeg);
                        break;
                    case "bmp":
                        bitmap.Save(imgPath_new, System.Drawing.Imaging.ImageFormat.Bmp);
                        break;
                    case "png":
                        bitmap.Save(imgPath_new, System.Drawing.Imaging.ImageFormat.Png);
                        break;
                    default:
                        bitmap.Save(imgPath_new, System.Drawing.Imaging.ImageFormat.Jpeg);
                        break;
                }
                ////保存縮略圖  
                // bitmap.Save(imgPath_new);
            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {
                img.Dispose();
                bitmap.Dispose(); g.Dispose();
            }
        }
        #endregion