C# Graphics 生成缩略图

[wangxiaofeiwuqiao]

我在页面放一个fileupload控件，ID: File2，一个Button控件，点击Button控件上传图片，目的：上传一个原图后，根据原图生成缩略图，问题：上传是成功了，也生成了缩略图，只有10k,但是缩略图没有图象，请教高手！代码：
protected void Button2_Click(object sender, EventArgs e)
{
//原图1
Random ran = new Random();
string san = ran.Next(1000, 9999).ToString();
string File2_filePath = File2.PostedFile.FileName; //获取上传文件物理路径
string File2_ExtName = File2_filePath.Substring(File2_filePath.LastIndexOf(".") + 1);
string File2_FileName = san + File2_filePath.Substring(File2_filePath.LastIndexOf("\\") + 1);

if (File2.PostedFile.FileName != "")
{
if ((File2_ExtName == "jpg" || File2_ExtName == "jpeg"))
{
//原图
string File2_Path = Server.MapPath(@"~\images\"); //保存到指定路径（展示图片）
File2.PostedFile.SaveAs(File2_Path + File2_FileName); //保存到服务器（展示图片）

//生成缩略图
System.Drawing.Bitmap objNewBitMap = new Bitmap(File2_Path + File2_FileName);

//从指定的 Image 对象创建新 Graphics 对象
Graphics objGraphics = Graphics.FromImage(objNewBitMap);
//清除整个绘图面并以透明背景色填充
objGraphics.Clear(Color.Transparent);
//在指定位置并且按指定大小绘制 原图片 对象
objGraphics.DrawImage(objNewBitMap, new Rectangle(0, 0, 100, 120));
objNewBitMap.Save(File2_Path + "sl_" + File2_FileName);

}

string str = "insert into tb_Image(ImageBit,ImageBig) values('" + (@"~\images\" + ("sl_" + File2_FileName)) + "','" + (@"~\images\" + (File2_FileName)) + "')";
Base.SqlCom(str);
Response.Write("<script>alert('添加成功')</script>");
}
}

问题可能出在：objGraphics.Clear(Color.Transparent); 但是试了很多方法不行。

[Micao_tong]

可以參考：
http://dotnet.aspx.cc/article/45e7e33c-f149-450e-b5d5-832958c20538/read.aspx

[wanghao3616]

//清除整个绘图面并以透明背景色填充
objGraphics.Clear(Color.Transparent);


你都清除了 还怎么有啊

[wangxiaofeiwuqiao]

那要怎么改？

[BossFriday]

这样的代码,网上很多.
注意点:
1,原图作水印logo的处理
2,对于图片的操作最好在内存中完成,这样对于server的HD耗损会小很多
3,对于图片,最好分析头文件,防止用户改改文件的扩展名,就能上传其他乱七八糟的东西,这样对于站点的安全很重要.

目前我这边写的上传部分,就是考虑这3点.

[BossFriday]

这样的代码,网上很多.
注意点:
1,原图作水印logo的处理
2,对于图片的操作最好在内存中完成,这样对于server的HD耗损会小很多
3,对于图片,最好分析头文件,防止用户改改文件的扩展名,就能上传其他乱七八糟的东西,这样对于站点的安全很重要.

目前我这边写的上传部分,就是考虑这3点.

[wanghao3616]

public void Page_Load(object sender, EventArgs e)
{

System.Drawing.Image image = default(System.Drawing.Image);
System.Drawing.Image aNewImage = default(System.Drawing.Image);
int width = 0;
int height = 0;
int newwidth = 0;
int newheight = 0;
System.Drawing.Image.GetThumbnailImageAbort callb = default(System.Drawing.Image.GetThumbnailImageAbort);

//生成缩略图
image = System.Drawing.Image.FromFile(Server.MapPath("classpic/" + "rs1.jpg"));
width = image.Width;
height = image.height;
if (width > height) {
newwidth = 110;
newheight = image.height / image.Width * newwidth;
}
else {
newheight = 110;
newwidth = image.Width / image.height * newheight;
}

aNewImage = image.GetThumbnailImage(newwidth, newheight, callb, new System.IntPtr());
aNewImage.Save(Server.MapPath("smallpic/" + "rs1.gif"));
image.Dispose();

}

给你个生成缩略图的

[the_pain]

/// <summary>
    /// 上传文件
    /// </summary>
    /// <param name="fulFile">上传控件 </param>
    /// <param name="DirectionName">文件所放的父文件夹 </param>
    /// <returns> </returns>
    [WebMethod]
    public void FileUpLoad(FileUpload fulFile,string DirectionName)
    {
        string FileName;
        string FileSavePath;
        FileName = fulFile.FileName;
        FileSavePath = Server.MapPath("~/File/");

        if (fulFile.HasFile) 
        {
            string name = fulFile.PostedFile.FileName;
            FileInfo file = new FileInfo(name);
            string newFileName = GetRandomString(10) + file.Extension;
            //FileSavePath += DirectionName;
            //DirectoryInfo direction = new DirectoryInfo(FileSavePath);
            if (!File.Exists(FileSavePath+"\\"+DirectionName))
            {
                Directory.CreateDirectory(FileSavePath+"\\"+DirectionName);
            }
            FileSavePath += DirectionName+"\\"+ newFileName;
           
            //string path = Server.MapPath(FileSavePath);
            if (!File.Exists(FileSavePath))
            {
                try
                {
                    fulFile.SaveAs(FileSavePath);
                }
                catch (Exception Error)
                {
                    HttpContext.Current.Response.Write(" <script>alert('" + Error.Message + "') </script>");
                    return;
                }
            }
            else
            {
                HttpContext.Current.Response.Write(" <script>alert('该文件已存在') </script>");
                return;
            }
        }
        else
        {
            HttpContext.Current.Response.Write(" <script>alert('请选择要上传的文件') </script>");
            return;
        }
        HttpContext.Current.Response.Write(" <script>alert('文件上传成功') </script>");
    }

[the_pain]

/// <summary>
    /// 生成缩略图
    /// </summary>
    /// <param name="originalImagePath">源图路径（物理路径） </param>
    /// <param name="thumbnailPath">缩略图路径（物理路径） </param>
    /// <param name="width">缩略图宽度 </param>
    /// <param name="height">缩略图高度 </param>
    /// <param name="mode">生成缩略图的方式 </param> 
    public static void MakeThumbnail(string originalImagePath, string thumbnailPath, int width, int height, string mode)
    {
        System.Drawing.Image originalImage = System.Drawing.Image.FromFile(originalImagePath);

        int towidth = width;
        int toheight = height;

        int x = 0;
        int y = 0;
        int ow = originalImage.Width;
        int oh = originalImage.Height;

        if (ow < towidth && oh < toheight)
        {
            originalImage.Save(thumbnailPath);
        }
        else
        {

            switch (mode.ToUpper())
            {
                case "HW"://指定高宽缩放（可能变形）         
                    break;
                case "W"://指定宽，高按比例           
                    toheight = originalImage.Height * width / originalImage.Width;
                    break;
                case "H"://指定高，宽按比例
                    towidth = originalImage.Width * height / originalImage.Height;
                    break;
                case "CUT"://指定高宽裁减（不变形）         
                    if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
                    {
                        oh = originalImage.Height;
                        ow = originalImage.Height * towidth / toheight;
                        y = 0;
                        x = (originalImage.Width - ow) / 2;
                    }
                    else
                    {
                        ow = originalImage.Width;
                        oh = originalImage.Width * height / towidth;
                        x = 0;
                        y = (originalImage.Height - oh) / 2;
                    }
                    break;
                case "AUTO": //自动适应高度
                    if (ow > oh)
                    {
                        //newwidth = 200;
                        toheight = (int)((double)oh / (double)ow * (double)towidth);
                    }
                    else
                    {
                        //newheight = 200;
                        towidth = (int)((double)ow / (double)oh * (double)toheight);
                    }
                    break;
                default:
                    break;
            }

            //新建一个bmp图片
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);

            //新建一个画板
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bitmap);

            //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(originalImage, 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
                bitmap.Save(thumbnailPath, System.Drawing.Imaging.ImageFormat.Jpeg);

            }
            catch (System.Exception e)
            {
                throw e;
            }
            finally
            {

                bitmap.Dispose();
                g.Dispose();
            }
        }
        originalImage.Dispose();
    }

[wangxiaofeiwuqiao]

GetThumbnailImage这个方法我会，效果不好，图片比较模糊，还比较大，所以我考虑用Graphics

[Roc_Lee]

帮顶，关注

[wangxiaofeiwuqiao]

谢谢5，6楼，不过如果能在我那里的代码改下最好。

[wangxiaofeiwuqiao]

那位哥哥做过这方面的，帮帮忙。

[oranrry]

你如果对图片的质量没有太大的要求的话
你把
objGraphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
objGraphics.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
//下面这个设成High
objGraphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
不要设成High不就行了

[wangxiaofeiwuqiao]

我缩略的图片也有40-50K那么大，是不是也是正常的?

[violinacl]

帮顶

[jidubushuang]