.Net 实现图片缩略图上传通用方法

/// <summary>
 /// 生成缩略图或质量压缩
 /// </summary>
 /// <param name="sourcePath">源图路径（物理路径）</param>
 /// <param name="targetPath">缩略图路径（物理路径）</param>
 /// <param name="width">缩略图宽度，如果宽度为0则不缩略</param>
 /// <param name="height">缩略图高度，如果高度为0则不缩略</param>
 /// <param name="mode">生成缩略图的方式,默认为空,为空则不缩略高宽[HW 指定高宽缩放（不变形）；W 指定宽，高按比例；H 指定高，宽按比例；CUT 指定高宽裁减（不变形）]</param> 
 /// <param name="flag">压缩质量（数字越小压缩率越高）1-100</param>
 /// <param name="size">压缩后图片的最大大小,0为不限制大小</param>
 public static void MakeThumbnail(string sourcePath, string targetPath, int width = 0, int height = 0, string mode = "", int flag = 100, int size = 0)
 {
 Image sourceImage = null;
 Image bitmap = null;
 Graphics g = null;
 EncoderParameters ep = null;
 EncoderParameter eParam = null;
 try
 {
 sourceImage = Image.FromFile(sourcePath);
 int toWidth = 0;
 if (width > 0)
 {
 toWidth = width;
 }
 else
 {
 toWidth = sourceImage.Width;
 }
 int toHeight = 0;
 if (height > 0)
 {
 toHeight = height;
 }
 else
 {
 toHeight = sourceImage.Height;
 }
 int x = 0;
 int y = 0;
 int ow = sourceImage.Width;
 int oh = sourceImage.Height;
 if (width > 0 && height > 0 && !string.IsNullOrWhiteSpace(mode))
 {
 switch (mode.ToUpper())
 {
 case "HW"://指定高宽缩放（不变形）
 int tempheight = sourceImage.Height * width / sourceImage.Width;
 if (tempheight > height)
 {
 toWidth = sourceImage.Width * height / sourceImage.Height;
 }
 else
 {
 toHeight = sourceImage.Height * width / sourceImage.Width;
 }
 break;
 case "W"://指定宽，高按比例 
 toHeight = sourceImage.Height * width / sourceImage.Width;
 break;
 case "H"://指定高，宽按比例
 toWidth = sourceImage.Width * height / sourceImage.Height;
 break;
 case "CUT"://指定高宽裁减（不变形） 
 if ((double)sourceImage.Width / (double)sourceImage.Height > (double)toWidth / (double)toHeight)
 {
 oh = sourceImage.Height;
 ow = sourceImage.Height * toWidth / toHeight;
 y = 0;
 x = (sourceImage.Width - ow) / 2;
 }
 else
 {
 ow = sourceImage.Width;
 oh = sourceImage.Width * height / toWidth;
 x = 0;
 y = (sourceImage.Height - oh) / 2;
 }
 break;
 }
 }
 //新建一个bmp图片
 bitmap = new Bitmap(toWidth, toHeight);
 //新建一个画板
 g = Graphics.FromImage(bitmap);
 g.CompositingQuality = CompositingQuality.HighQuality;
 //设置高质量插值法
 g.InterpolationMode = InterpolationMode.HighQualityBicubic;
 //设置高质量,低速度呈现平滑程度
 g.SmoothingMode = SmoothingMode.HighQuality;
 //清空画布并以透明背景色填充
 g.Clear(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(sourceImage, new Rectangle(0, 0, toWidth, toHeight),
 new Rectangle(x, y, ow, oh),
 GraphicsUnit.Pixel);
 //以下代码为保存图片时，设置压缩质量
 ep = new EncoderParameters();
 long[] qy = new long[1];
 qy[0] = flag;//设置压缩的比例1-100
 eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
 ep.Param[0] = eParam;
 ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();//获取图像编码器的信息
 ImageCodecInfo jpegICIinfo = null;
 for (int i = 0; i < arrayICI.Length; i++)
 {
 if (arrayICI[i].FormatDescription.Equals("JPEG"))
 {
 jpegICIinfo = arrayICI[i];
 break;
 }
 }
 if (jpegICIinfo != null)
 {
 bitmap.Save(targetPath, jpegICIinfo, ep);
 FileInfo fiTarget = new FileInfo(targetPath);
 if (size > 0 && fiTarget.Length > 1024 * size)
 {
 flag = flag - 10;
 MakeThumbnail(sourcePath, targetPath, width, height, mode, flag, size);
 }
 }
 else
 {
 //以jpg格式保存缩略图
 bitmap.Save(targetPath, ImageFormat.Jpeg);
 }
 }
 catch (System.Exception ex)
 {
 throw ex;
 }
 finally
 {
 if (sourceImage != null)
 {
 sourceImage.Dispose();
 }
 if (bitmap != null)
 {
 bitmap.Dispose();
 }
 if (g != null)
 {
 g.Dispose();
 }
 if (ep != null)
 {
 ep.Dispose();
 }
 if (eParam != null)
 {
 eParam.Dispose();
 }
 }
 }