根据原图片生成等比缩略图#region 根据原图片生成等比缩略图        /// <summary>          /// 根据源图片生成缩略图          /// </summary>          /// <param name="imgPath_old">源图(大图)物理路径</param>          /// <param name="imgPath_new">缩略图物理路径(生成的缩略图将保存到该物理位置)</param>          /// <param name="width">缩略图宽度</param>          /// <param name="height">缩略图高度</param>          /// <param name="mode">缩略图缩放模式(取值"HW":指定高宽缩放,可能变形；取值"W":按指定宽度,高度按比例缩放；取值"H":按指定高度,宽度按比例缩放；取值"Cut":按指定高度和宽度裁剪,不变形)；取值"DB":等比缩放,以值较大的作为标准进行等比缩放</param>          /// <param name="type">即将生成缩略图的文件的扩展名(仅限：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":  //指定高宽压缩                    if ((double)img.Width / (double)img.Height > (double)width / (double)height)//判断图形是什么形状                    {                        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":  //指定宽，高按比例                       toheight = img.Height * width / img.Width;                    break;                case "H":  //指定高，宽按比例                      towidth = img.Width * height / img.Height;                    break;                case "Cut":   //指定高宽裁减（不变形）                       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":    // 按值较大的进行等比缩放（不变形）                       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;            }            //新建一个bmp图片              System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);            //新建一个画板              System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);            //设置高质量插值法              g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;            //设置高质量,低速度呈现平滑程度              g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;            //清空画布并以透明背景色填充              g.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              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格式保存缩略图                 switch (imageType.ToLower())                {                    case "gif":                        img.Save(imgPath_new, ImageFormat.Jpeg);//生成缩略图                        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;                }                ////保存缩略图                  // bitmap.Save(imgPath_new);            }            catch (System.Exception e)            {                throw e;            }            finally            {                img.Dispose();                bitmap.Dispose(); g.Dispose();            }        }        #endregion