我期望是1*1的黑色图片，放大为一个50*50像素的黑色图片，但是现在出现的结果是从左上角开始逐渐变淡的图片，如果我用2*2的黑色的图片，就没有这个问题，这是什么原因

如何生成高清略缩图不失真
//上传图片
    protected void imgBtnLoad_Click(object sender, ImageClickEventArgs e)
    {
        if (!fulPhoto.HasFile)
        {
            lbMessage.Text = “请选择上传图片！”;
            return;
        }
        else
        {
            try
            {
                //获取上传文件路径
                string filePath = fulPhoto.PostedFile.FileName;
                //获取上传文件后缀
                string fileExt = filePath.Substring(filePath.LastIndexOf(“.”) + 1);
                //限定上传格式
                if (fileExt.ToLower() == “gif” || fileExt.ToLower() == “jpg” || fileExt.ToLower() == “bmp” || fileExt.ToLower() == “png”)
                {
                    if (fulPhoto.PostedFile.ContentLength > 5120000)
                    {
                        lbMessage.Text = “限定上传图片的大小不能超出5M！”;
                        return;
                    }
                    else
                    {
                        //根据时间生成文件名
                        string nowTime = Album.CreateDateTimeString();
                        string fileName = nowTime + “.” + fileExt;
                        //源文件保存路径
                        string savePath = Server.MapPath(“UpFile/”);
                        //缩略图保存路径
                        string imgPath = Server.MapPath(“UpSmall/”);
                        //上传图片
                        fulPhoto.PostedFile.SaveAs(savePath + fileName);
                        //创建自定义Album类对象实例
                        Album am = new Album();
                        //根据图片的宽、高比例生成缩略图
                        System.Drawing.Image img = System.Drawing.Image.FromFile(savePath + fileName);
                        if (img.Width >= img.Height)
                        {
                            am.GetThumbnail(savePath + fileName, imgPath + fileName, 400, 300, “Cut”);
                        }
                        else
                        {
                            am.GetThumbnail(savePath + fileName, imgPath + fileName, 320, 350, “Cut”);
                        }
                        //文件类型
                        string p_type = fulPhoto.PostedFile.ContentType;
                        //文件大小
                        int p_size = fulPhoto.PostedFile.ContentLength;
                        int categoryId = Convert.ToInt32(ddlCategory.SelectedValue);
                        //调用类方法将数据插入到数据库
                        int result = am.AddPhoto(tbName.Text.Trim(), tbDescript.Text.Trim(), fileName, p_type, p_size, categoryId);
                        ScriptManager.RegisterStartupScript(UpdatePanel1, typeof(UpdatePanel), “scriptname”, “alert(“图片上传成功！”);”, true);
                    }
                }
                else
                {
                    lbMessage.Text = “只允许上传gif，jpg，bmp，png格式的图片文件!”;
                    return;
                }
            }
            catch (Exception ex)
            {
                throw new Exception(ex.Message, ex);
            }
        }
    }//codego.net/tags/11/1/
//调用自定义方法生成略缩图
    public void GetThumbnail(string serverImagePath, string thumbnailImagePath, int width, int height, string p)
    {
        System.Drawing.Image serverImage = System.Drawing.Image.FromFile(serverImagePath);
        //画板大小
        int towidth = width;
        int toheight = height;
        //缩略图矩形框的像素点
        int x = 0;
        int y = 0;
        int ow = serverImage.Width;
        int oh = serverImage.Height;
        switch (p)
        {
            case “WH”://指定高宽缩放（可能变形）                
                break;
            case “W”://指定宽，高按比例                    
                toheight = serverImage.Height * width / serverImage.Width;
                break;
            case “H”://指定高，宽按比例
                towidth = serverImage.Width * height / serverImage.Height;
                break;
            case “Cut”://指定高宽裁减（不变形）                
                if ((double)serverImage.Width / (double)serverImage.Height > (double)towidth / (double)toheight)
                {
                    oh = serverImage.Height;
                    ow = serverImage.Height * towidth / toheight;
                    y = 0;
                    x = (serverImage.Width – ow) / 2;
                }
                else
                {
                    ow = serverImage.Width;
                    oh = serverImage.Width * height / towidth;
                    x = 0;
                    y = (serverImage.Height – oh) / 2;
                }
                break;
            default:
                break;
        }
        //新建一个bmp图片
        System.Drawing.Image bm = new System.Drawing.Bitmap(towidth, toheight);
        //新建一个画板
        System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bm);
        //设置高质量插值法
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
        //设置高质量,低速度呈现平滑程度
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        //清空画布并以透明背景色填充
        g.Clear(System.Drawing.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(serverImage, new System.Drawing.Rectangle(0, 0, towidth, toheight),
            new System.Drawing.Rectangle(x, y, ow, oh),
            System.Drawing.GraphicsUnit.Pixel);
        try
        {
            //以jpg格式保存缩略图
            bm.Save(thumbnailImagePath, System.Drawing.Imaging.ImageFormat.Jpeg);
        }
        catch (System.Exception e)
        {
            throw e;
        }
        finally
        {
            serverImage.Dispose();
            bm.Dispose();
            g.Dispose();
        }
    }
/div>

与其纠结于为啥放大N倍就有失真问题，为啥不考虑改变策略，提供不同比例的图片，按需取对应图片，因为图片失真这是没办法的事情，你还需要了解下图片失真跟图片保存方式之间的关系

现在是用两个像素的图片放大替代了，放大两个像素的图片没有问题，只是想了解一下这个原因。

            base.OnPaint(e);
            Bitmap bmp = new Bitmap(1,1);
            using(Graphics g = Graphics.FromImage(bmp))
            {
                g.Clear(Color.Red);
                //g.FillEllipse(Brushes.Black, new Rectangle(0, 0, 10, 10));
            }
            System.Drawing.Imaging.ImageAttributes attr = new System.Drawing.Imaging.ImageAttributes();
            attr.SetWrapMode(WrapMode.Tile);  //这个是关键
            e.Graphics.DrawImage(bmp,new Rectangle(0,0,50,100), 0,0,bmp.Width,bmp.Height,GraphicsUnit.Pixel, attr,null,IntPtr.Zero);
/pre>

你想”放大”后不失真,应该自己获取它的颜色然后填充进新的图像里,而不是直接调用系统函数让它自己”放大”