C#压缩图片算法

using System.IO;  
using System.Drawing;  
using System.Drawing.Imaging;  
using System;  
namespace Bll  
{  
    /// <summary>  
    /// 图片处理类  
    /// 1、生成缩略图片或按照比例改变图片的大小和画质  
    /// 2、将生成的缩略图放到指定的目录下  
    /// </summary>  
    public class ImageHepler  
    {  
        public Image ResourceImage, ReducedImage;  
        private int ImageWidth;  
        private int ImageHeight;  
        public string ErrMessage;  
  
        /// <summary>  
        /// 类的构造函数  
        /// </summary>  
        /// <param name="ImageFileName">图片文件的全路径名称</param>  
        public ImageHepler(string ImageFileName)  
        {  
            ResourceImage = Image.FromFile(ImageFileName);  
            ErrMessage = "";  
        }  
  
        public bool ThumbnailCallback()  
        {  
            return false;  
        }  
  
        /// <summary>  
        /// 生成缩略图，返回缩略图的Image对象  
        /// </summary>  
        /// <param name="Width">缩略图的宽度</param>  
        /// <param name="Height">缩略图的高度</param>  
        /// <returns>缩略图的Image对象</returns>  
        public Image GetReducedImage(int Width, int Height)  
        {  
            double LengthLong;          //存储（长和宽中）较短的长度  
            int widthOK, heightOK;      //存储实际要生成的图片的长宽  
            if (Width < Height)         //判断输入的长和宽那个较短  
            {  
                LengthLong = Width;     //把较短的存储在 LengthLonh 用于计算  
            }  
            else  
            {  
                LengthLong = Height;  
            }  
            try  
            {  
                //判断原图片 长和宽   
                //原图比较长的一个边要和缩略图的边相等  
                if (ResourceImage.Width > ResourceImage.Height)  
                {  
                    widthOK = (int)LengthLong;  
                    heightOK = (int)(LengthLong / ResourceImage.Width * ResourceImage.Height);  
                }  
                else  
                {  
                    heightOK = (int)LengthLong;  
                    widthOK = (int)LengthLong / ResourceImage.Height * ResourceImage.Width;  
  
                }  
                Image ReducedImage;  
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);  
                ReducedImage = ResourceImage.GetThumbnailImage(widthOK, heightOK, callb, IntPtr.Zero);  
                return ReducedImage;  
            }  
            catch (Exception e)  
            {  
                ErrMessage = e.Message;  
                return null;  
            }  
        }  
  
        /// <summary>  
        /// 生成缩略图，将缩略图文件保存到指定的路径  
        /// </summary>  
        /// <param name="Width">缩略图的宽度</param>  
        /// <param name="Height">缩略图的高度</param>  
        /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>  
        /// <returns>成功返回true，否则返回false</returns>  
        public bool GetReducedImage(int Width, int Height, string targetFilePath)  
        {  
            double LengthLong;          //存储（长和宽中）较短的长度  
            int widthOK, heightOK;      //存储实际要生成的图片的长宽  
            if (Width < Height)         //判断输入的长和宽那个较短  
            {  
                LengthLong = Width;     //把较短的存储在 LengthLonh 用于计算  
            }  
            else  
            {  
                LengthLong = Height;  
            }  
            try  
            {  
                //判断原图片 长和宽   
                //原图比较长的一个边要和缩略图的边相等  
                if (ResourceImage.Width > ResourceImage.Height)  
                {  
                    widthOK = (int)LengthLong;  
                    heightOK = (int)(LengthLong / ResourceImage.Width * ResourceImage.Height);  
                }  
                else  
                {  
                    heightOK = (int)LengthLong;  
                    widthOK = (int)LengthLong / ResourceImage.Height * ResourceImage.Width;  
                }  
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);  
                ReducedImage = ResourceImage.GetThumbnailImage(widthOK, heightOK, callb, IntPtr.Zero);  
                ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);  
                //ReducedImage.Dispose();  
                return true;  
            }  
            catch (Exception e)  
            {  
                ErrMessage = e.Message;  
                return false;  
            }  
        }  
  
        /// <summary>  
        /// 生成缩略图，返回缩略图的Image对象  
        /// </summary>  
        /// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>    
        /// <returns>缩略图的Image对象</returns>  
        public Image GetReducedImage(double Percent)  
        {  
            try  
            {  
                Image ReducedImage;  
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);  
                ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);  
                ImageHeight = Convert.ToInt32(ResourceImage.Width * Percent);  
                ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);  
                return ReducedImage;  
            }  
            catch (Exception e)  
            {  
                ErrMessage = e.Message;  
                return null;  
            }  
        }  
  
        /// <summary>  
        /// 生成缩略图，返回缩略图的Image对象  
        /// </summary>  
        /// <param name="Percent">缩略图的宽度百分比 如：需要百分之80，就填0.8</param>    
        /// <param name="targetFilePath">缩略图保存的全文件名，(带路径)，参数格式：D:\Images\filename.jpg</param>  
        /// <returns>成功返回true,否则返回false</returns>  
        public bool GetReducedImage(double Percent, string targetFilePath)  
        {  
            try  
            {  
                Image.GetThumbnailImageAbort callb = new Image.GetThumbnailImageAbort(ThumbnailCallback);  
                ImageWidth = Convert.ToInt32(ResourceImage.Width * Percent);  
                ImageHeight = Convert.ToInt32(ResourceImage.Width * Percent);  
                ReducedImage = ResourceImage.GetThumbnailImage(ImageWidth, ImageHeight, callb, IntPtr.Zero);  
                ReducedImage.Save(@targetFilePath, ImageFormat.Jpeg);  
                //ReducedImage.Dispose();  
                return true;  
            }  
            catch (Exception e)  
            {  
                ErrMessage = e.Message;  
                return false;  
            }  
        }  
    }  
}  

原作者不详，转自【http://www.open-open.com/lib/view/open1391348644910.html】