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(); }
