.net等比缩放生成缩略图的方法

/// <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;
 }

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();
 }

 }
}