asp.net上传图片生成缩略图

在asp.net中，上传图片功能或者是常用的，生成缩略图也是常用的。baidu或者google，c#的方法也是很多的，但是一用却发现缩略图不清晰啊，缩略图片太大之类的事情，下面是我在处理图片上的代码，效果不错，所以拿出来分享，(效果能达到一些绘图软件的效果)

代码如下：

/// <summary> 
    /// asp.net上传图片并生成缩略图 
    /// </summary> 
    /// <param name="upImage">HtmlInputFile控件</param> 
    /// <param name="sSavePath">保存的路径,些为相对服务器路径的下的文件夹</param> 
    /// <param name="sThumbExtension">缩略图的thumb</param> 
    /// <param name="intThumbWidth">生成缩略图的宽度</param> 
    /// <param name="intThumbHeight">生成缩略图的高度</param> 
    /// <returns>缩略图名称</returns> 
    public string UpLoadImage(HtmlInputFile upImage, string sSavePath, string sThumbExtension, int intThumbWidth, int intThumbHeight) 
    { 
        string sThumbFile = ""; 
        string sFilename = "";        
        if (upImage.PostedFile != null) 
        { 
            HttpPostedFile myFile = upImage.PostedFile; 
            int nFileLen = myFile.ContentLength; 
            if (nFileLen == 0) 
                return "没有选择上传图片";            
            //获取upImage选择文件的扩展名 
            string extendName = System.IO.Path.GetExtension(myFile.FileName).ToLower(); 
            //判断是否为图片格式 
            if (extendName != ".jpg" && extendName != ".jpge" && extendName != ".gif" && extendName != ".bmp" && extendName != ".png") 
                return "图片格式不正确"; 
            
            byte[] myData = new Byte[nFileLen]; 
            myFile.InputStream.Read(myData, 0, nFileLen);
            sFilename = System.IO.Path.GetFileName(myFile.FileName); 
            int file_append = 0; 
            //检查当前文件夹下是否有同名图片,有则在文件名+1 
            while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename))) 
            { 
                file_append++; 
                sFilename = System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) 
                    + file_append.ToString() + extendName; 
            } 
            System.IO.FileStream newFile 
                = new System.IO.FileStream(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename), 
                System.IO.FileMode.Create, System.IO.FileAccess.Write); 
            newFile.Write(myData, 0, myData.Length); 
            newFile.Close();
            //以上为上传原图
            try 
            { 
                //原图加载 
                using (System.Drawing.Image sourceImage = System.Drawing.Image.FromFile(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename))) 
                { 
                    //原图宽度和高度 
                    int width = sourceImage.Width; 
                    int height = sourceImage.Height; 
                    int smallWidth; 
                    int smallHeight;
                    //获取第一张绘制图的大小,(比较 原图的宽/缩略图的宽 和 原图的高/缩略图的高) 
                    if (((decimal)width) / height <= ((decimal)intThumbWidth) / intThumbHeight) 
                    { 
                        smallWidth = intThumbWidth; 
                        smallHeight = intThumbWidth * height / width; 
                    } 
                    else 
                    { 
                        smallWidth = intThumbHeight * width / height; 
                        smallHeight = intThumbHeight; 
                    }
                    //判断缩略图在当前文件夹下是否同名称文件存在 
                    file_append = 0; 
                    sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) + extendName;
                    while (System.IO.File.Exists(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sThumbFile))) 
                    { 
                        file_append++; 
                        sThumbFile = sThumbExtension + System.IO.Path.GetFileNameWithoutExtension(myFile.FileName) + 
                            file_append.ToString() + extendName; 
                    } 
                    //缩略图保存的绝对路径 
                    string smallImagePath = System.Web.HttpContext.Current.Server.MapPath(sSavePath) + sThumbFile;
                    //新建一个图板,以最小等比例压缩大小绘制原图 
                    using (System.Drawing.Image bitmap = new System.Drawing.Bitmap(smallWidth, smallHeight)) 
                    { 
                        //绘制中间图 
                        using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap)) 
                        { 
                            //高清,平滑 
                            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; 
                            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; 
                            g.Clear(Color.Black); 
                            g.DrawImage( 
                            sourceImage, 
                            new System.Drawing.Rectangle(0, 0, smallWidth, smallHeight), 
                            new System.Drawing.Rectangle(0, 0, width, height), 
                            System.Drawing.GraphicsUnit.Pixel 
                            ); 
                        } 
                        //新建一个图板,以缩略图大小绘制中间图 
                        using (System.Drawing.Image bitmap1 = new System.Drawing.Bitmap(intThumbWidth, intThumbHeight)) 
                        { 
                            //绘制缩略图 
                            using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap1)) 
                            { 
                                //高清,平滑 
                                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High; 
                                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality; 
                                g.Clear(Color.Black); 
                                int lwidth = (smallWidth - intThumbWidth) / 2; 
                                int bheight = (smallHeight - intThumbHeight) / 2; 
                                g.DrawImage(bitmap, new Rectangle(0, 0, intThumbWidth, intThumbHeight), lwidth, bheight, intThumbWidth, intThumbHeight, GraphicsUnit.Pixel); 
                                g.Dispose(); 
                                bitmap1.Save(smallImagePath, System.Drawing.Imaging.ImageFormat.Jpeg); 
                            } 
                        } 
                    } 
                } 
            } 
            catch 
            { 
                //出错则删除 
                System.IO.File.Delete(System.Web.HttpContext.Current.Server.MapPath(sSavePath + sFilename)); 
                return "图片格式不正确"; 
            } 
            //返回缩略图名称 
            return sThumbFile; 
        } 
        return "没有选择图片"; 
    }

HtmlInputFile控件我想大家都应该知道的，就是input type=file....这个会在后面的一起学asp.net章节中讲解