这个C#类可以生成各种形式的缩略图，可以自动保持图片比例缩略，可以根据百分比获得图片尺寸等

using System;  using System.Collections.Generic;  using System.Drawing;  using System.Drawing.Imaging;      namespace HtmlSnap  {      public static class ImageHelper      {               /// <summary>          /// 获取缩略图          /// </summary>          /// <param name="image"></param>          /// <param name="width"></param>          /// <param name="height"></param>          /// <returns></returns>          public static Image GetThumbnailImage(Image image, int width, int height)          {              if (image == null || width < 1 || height < 1)                  return null;                  // 新建一个bmp图片              //              Image bitmap = new System.Drawing.Bitmap(width, height);                  // 新建一个画板              //              using (Graphics g = System.Drawing.Graphics.FromImage(bitmap))              {                      // 设置高质量插值法                  //                  g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;                      // 设置高质量,低速度呈现平滑程度                  //                  g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;                                      // 高质量、低速度复合                  //                  g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.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(image, new Rectangle(0, 0, width, height),                      new Rectangle(0, 0, image.Width, image.Height),                      GraphicsUnit.Pixel);                      return bitmap;              }          }              /// <summary>          /// 生成缩略图，并保持纵横比          /// </summary>          /// <param name="image"></param>          /// <param name="width"></param>          /// <param name="height"></param>          /// <returns>生成缩略图后对象</returns>          public static Image GetThumbnailImageKeepRatio(Image image, int width, int height)          {              Size imageSize = GetImageSize(image, width, height);              return GetThumbnailImage(image, imageSize.Width, imageSize.Height);          }              /// <summary>          /// 根据百分比获取图片的尺寸          /// </summary>          /// <param name="picture"></param>          /// <param name="percent"></param>          /// <returns></returns>          public static Size GetImageSize(Image picture, int percent)          {              if (picture == null || percent < 1)                  return Size.Empty;                  int width = picture.Width * percent / 100;              int height = picture.Height * percent / 100;                  return GetImageSize(picture, width, height);          }              /// <summary>          /// 根据设定的大小返回图片的大小，考虑图片长宽的比例问题          /// </summary>          /// <param name="picture"></param>          /// <param name="width"></param>          /// <param name="height"></param>          /// <returns></returns>          public static Size GetImageSize(Image picture, int width, int height)          {              if (picture == null || width < 1 || height < 1)                  return Size.Empty;                  Size imageSize;                  imageSize = new Size(width, height);                  double heightRatio = (double)picture.Height / picture.Width;              double widthRatio = (double)picture.Width / picture.Height;                  int desiredHeight = imageSize.Height;              int desiredWidth = imageSize.Width;                      imageSize.Height = desiredHeight;              if (widthRatio > 0)                  imageSize.Width = Convert.ToInt32(imageSize.Height * widthRatio);                  if (imageSize.Width > desiredWidth)              {                  imageSize.Width = desiredWidth;                  imageSize.Height = Convert.ToInt32(imageSize.Width * heightRatio);              }                  return imageSize;          }                  /// <summary>          /// 获取图像编码解码器的所有相关信息          /// </summary>          /// <param name="mimeType">包含编码解码器的多用途网际邮件扩充协议 (MIME) 类型的字符串</param>          /// <returns>返回图像编码解码器的所有相关信息</returns>          public static ImageCodecInfo GetCodecInfo(string mimeType)          {              ImageCodecInfo[] CodecInfo = ImageCodecInfo.GetImageEncoders();              foreach (ImageCodecInfo ici in CodecInfo)              {                  if (ici.MimeType == mimeType) return ici;              }              return null;          }              public static ImageCodecInfo GetImageCodecInfo(ImageFormat format)          {              ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders();                  foreach (ImageCodecInfo icf in encoders)              {                  if (icf.FormatID == format.Guid)                  {                      return icf;                  }              }                  return null;          }              public static void SaveImage(Image image, string savePath, ImageFormat format)          {              SaveImage(image, savePath, GetImageCodecInfo(format));          }              /// <summary>          /// 高质量保存图片          /// </summary>          /// <param name="image"></param>          /// <param name="savePath"></param>          /// <param name="ici"></param>          private static void SaveImage(Image image, string savePath, ImageCodecInfo ici)          {              // 设置 原图片 对象的 EncoderParameters 对象              //              EncoderParameters parms = new EncoderParameters(1);              EncoderParameter parm = new EncoderParameter(Encoder.Quality, ((long)95));              parms.Param[0] = parm;                  image.Save(savePath, ici, parms);              parms.Dispose();          }          }  }