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无法从带有索引像素格式的图像创建graphics对象

news 来源：原创 2024/5/3 17:41:58

大家在用 .NET 做图片水印功能的时候， 很可能会遇到 “无法从带有索引像素格式的图像创建graphics对象”这个错误，对应的英文错误提示是“A Graphics object cannot be created from an image that has an indexed pixel format"

这个exception是出现在 System.Drawing.Graphics g = System.Drawing.Graphics.FromImage("图片路径")  

这个调用的语句上，通过查询 MSDN， 我们可以看到如下的提示信息：

 

通过上面的错误解释，我们可以看到，原因是因为图片是索引像素格式的。为了避免此问题的发生，我们在做水印之前，可以先判断原图片是否是索引像素格式的，如果是，则可以采用将此图片先clone到一张BMP上的方法来解决：

private static PixelFormat[] indexedPixelFormats = { PixelFormat.Undefined, PixelFormat.DontCare,
                PixelFormat.Format16bppArgb1555, PixelFormat.Format1bppIndexed, PixelFormat.Format4bppIndexed,
                PixelFormat.Format8bppIndexed};
    /**/
    /// <summary>
    /// 判断图片的PixelFormat 是否在 引发异常的 PixelFormat 之中
    /// </summary>
    /// <param name="imgPixelFormat">原图片的PixelFormat</param>
    /// <returns></returns>
    private static bool IsPixelFormatIndexed(PixelFormat imgPixelFormat)
    {
        foreach (PixelFormat pf in indexedPixelFormats)
        {
            if (pf.Equals(imgPixelFormat)) return true;
        }

        return false;
    }

    protected void btnUpload_Click(object sender, EventArgs e)
    {
        if (FileUpload1.HasFile)
        {
            string fileContentType = FileUpload1.PostedFile.ContentType;
            if (fileContentType == "image/bmp" || fileContentType == "image/gif" || fileContentType == "image/pjpeg")
            {
                string name = FileUpload1.PostedFile.FileName;                  // 客户端文件路径
                /** <summary>
                /// 会产生graphics异常的PixelFormat
                /// </summary>
                
                FileInfo file = new FileInfo(name);
                string fileName = file.Name;                                    // 文件名称
                string fileName_s = "x_" + file.Name;                           // 缩略图文件名称
                string fileName_sy = "text_" + file.Name;                         // 水印图文件名称（文字）
                string fileName_syp = "water_" + file.Name;                       // 水印图文件名称（图片）
                string webFilePath = Server.MapPath("ImgUpload/"+Request.QueryString["id"]+"/" + fileName);        // 服务器端文件路径
                string webFilePath_s = Server.MapPath("ImgUpload/" + Request.QueryString["id"] + "/" + fileName_s);　　// 服务器端缩略图路径
                string webFilePath_sy = Server.MapPath("ImgUpload/" + Request.QueryString["id"] + "/" + fileName_sy);　// 服务器端带水印图路径(文字)
                string webFilePath_syp = Server.MapPath("ImgUpload/" + Request.QueryString["id"] + "/" + fileName_syp);　// 服务器端带水印图路径(图片)
                string webFilePath_sypf = Server.MapPath("sy.png");　// 服务器端水印图路径(图片)
                string iPath = Server.MapPath("ImgUpload/" + Request.QueryString["id"]);
                if (!File.Exists(webFilePath))
                {
                    try
                    {
                        if (!System.IO.Directory.Exists(iPath))//判断文件夹是否已经存在
                        {
                            System.IO.Directory.CreateDirectory(iPath);//创建文件夹
                        } 
                        FileUpload1.SaveAs(webFilePath);                                // 使用 SaveAs 方法保存文件
                        AddWater(webFilePath, webFilePath_sy);
                        AddWaterPic(webFilePath, webFilePath_syp, webFilePath_sypf);
                        MakeThumbnail(webFilePath, webFilePath_s, 130, 130, "Cut");     // 生成缩略图方法
                        Label1.Text = "提示：文件“" + fileName + "”成功上传，并生成“" + fileName_s + "”缩略图，文件类型为：" + FileUpload1.PostedFile.ContentType + "，文件大小为：" + FileUpload1.PostedFile.ContentLength + "B";
                    }
                    catch (Exception ex)
                    {
                        Label1.Text = "提示：文件上传失败，失败原因：" + ex.Message;
                    }
                }
                else
                {
                    Label1.Text = "提示：文件已经存在，请重命名后上传";
                }
            }
            else
            {
                Label1.Text = "提示：文件类型不符";
            }
        }
    }
    /**/
    /// <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;

        switch (mode)
        {
            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;
            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
        {
            originalImage.Dispose();
            bitmap.Dispose();
            g.Dispose();
        }
    }

    /**/
    /// <summary>
    /// 在图片上增加文字水印
    /// </summary>
    /// <param name="Path">原服务器图片路径</param>
    /// <param name="Path_sy">生成的带文字水印的图片路径</param>
    protected void AddWater(string Path, string Path_sy)
    {
        string addText = "KV";
        System.Drawing.Image image = System.Drawing.Image.FromFile(Path);
        System.Drawing.Font f = new System.Drawing.Font("Verdana", 60);
        System.Drawing.Brush b = new System.Drawing.SolidBrush(System.Drawing.Color.Green);
        //如果原图片是索引像素格式之列的，则需要转换
        if (IsPixelFormatIndexed(image.PixelFormat))
        {
            Bitmap bmp = new Bitmap(image);
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp);                        
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            g.DrawImage(bmp, 0, 0);
            
            g.DrawString(addText, f, b, 35, 35);
            g.Dispose();
            bmp.Save(Path_sy);
        }
        else
        {
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);
            g.DrawImage(image, 0, 0, image.Width, image.Height);            
            g.DrawString(addText, f, b, 35, 35);
            g.Dispose();
            image.Save(Path_sy);

        }
        
        image.Dispose();
    }

    /**/
    /// <summary>
    /// 在图片上生成图片水印
    /// </summary>
    /// <param name="Path">原服务器图片路径</param>
    /// <param name="Path_syp">生成的带图片水印的图片路径</param>
    /// <param name="Path_sypf">水印图片路径</param>
    protected void AddWaterPic(string Path, string Path_syp, string Path_sypf)
    {
        System.Drawing.Image image = System.Drawing.Image.FromFile(Path);
        System.Drawing.Image copyImage = System.Drawing.Image.FromFile(Path_sypf);
        //如果原图片是索引像素格式之列的，则需要转换
        if (IsPixelFormatIndexed(image.PixelFormat))
        {
            Bitmap bmp = new Bitmap(image);//.Width, image.Height, PixelFormat.Format32bppArgb
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(bmp);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
            g.DrawImage(copyImage, new System.Drawing.Rectangle(bmp.Width - copyImage.Width, bmp.Height - copyImage.Height, copyImage.Width, copyImage.Height), 0, 0, copyImage.Width, copyImage.Height, System.Drawing.GraphicsUnit.Pixel);          

            g.Dispose();
            bmp.Save(Path_syp);
        }
        else
        {            
            System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(image);
            g.DrawImage(copyImage, new System.Drawing.Rectangle(image.Width - copyImage.Width, image.Height - copyImage.Height, copyImage.Width, copyImage.Height), 0, 0, copyImage.Width, copyImage.Height, System.Drawing.GraphicsUnit.Pixel);
            g.Dispose();
            image.Save(Path_syp);

        }     
        
        
        image.Dispose();
    }

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