.net等比缩放生成缩略图的方法

生成缩略图是一个十分常用功能，找到了一个方法，重写部分代码，实用又好用，.net又一个生成缩略图的方法，不变形

/// <summary>    /// 为图片生成缩略图   /// </summary>    /// <param name="phyPath">原图片的路径</param>    /// <param name="width">缩略图宽</param>    /// <param name="height">缩略图高</param>    /// <returns></returns>    public System.Drawing.Image GetHvtThumbnail(System.Drawing.Image image, int width, int height)   {     Bitmap m_hovertreeBmp = new Bitmap(width, height);     //从Bitmap创建一个System.Drawing.Graphics      Graphics m_HvtGr = Graphics.FromImage(m_hovertreeBmp);     //设置      m_HvtGr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;     //下面这个也设成高质量      m_HvtGr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;     //下面这个设成High      m_HvtGr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;     //把原始图像绘制成上面所设置宽高的缩小图      Rectangle rectDestination = new Rectangle(0, 0, width, height);     int m_width, m_height;     if (image.Width * height > image.Height * width)     {       m_height = image.Height;       m_width = (image.Height * width) / height;     }     else     {       m_width = image.Width;       m_height = (image.Width * height) / width;     }     m_HvtGr.DrawImage(image, rectDestination, 0, 0, m_width, m_height, GraphicsUnit.Pixel);     return m_hovertreeBmp;   }

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();    }  }}