Biegral Blog

转自：http://www.codefans.net/articles/234.shtml

• C#缩略图生成类，采用高质量插值法实现缩略图生成，高质量,低速度呈现平滑程度，可以保持缩略图纵横比，在获取缩略图的时候一开始就根据百分比获取图片的尺寸、根据设定的大小返回图片的大小，并高质量保存缩略图图片，为原图片设置EncoderParameters 对象。

  以下为类文件，建议保存文件名为：ImageHelper.cs
  

  using System;
  using System.Collections.Generic;
  using System.Drawing;
  using System.Drawing.Imaging;
  namespace HtmlSnap
  {
      public static class ImageHelper
      {
          /// 获取缩略图
          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>
          /// <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>
          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>
          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>
          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();
          }
     }
  }

  
  
  
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