Graphics的DrawImage方法，定义了多种原型，可以在制定位置绘制指定Image对象。利用此方法可以在图片对象上再绘制一个水印图片。结合FreeTextBox方便的图片上传功能，可以实现一个适合图片新闻较多的新闻系统。以下WaterMark方法所带参数为文件流，原始图片名称，水印图片名称，图片保存路径等，对应注释理解代码应该没有多大问题。
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public void WaterMark(Stream inputStream, string fileName, string
markName, string picPath)
{
string WorkingDirectory =
HttpContext.Current.Request.PhysicalApplicationPath + "\\" + picPath;
Stream PhotoStream = inputStream;
string WatermarkName = markName;
string PhotoFinalName = fileName;
//create a image object containing the photograph to watermark
System.Drawing.Image imgPhoto = System.Drawing.Image.FromStream(PhotoStream);
int phWidth = imgPhoto.Width;
int phHeight = imgPhoto.Height;
//create a image object containing the watermark
System.Drawing.Image imgWatermark = new Bitmap(WorkingDirectory + "\\" + WatermarkName);
int wmWidth = imgWatermark.Width;
int wmHeight = imgWatermark.Height;
//Create a Bitmap
Bitmap bmWatermark = new Bitmap(PhotoStream);
bmWatermark.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);
//Load this Bitmap into a new Graphic Object
Graphics grWatermark = Graphics.FromImage(bmWatermark);
ImageAttributes imageAttributes = new ImageAttributes();
//This color manipulation is used to change the opacity of the
//watermark. This is done by applying a 5x5 matrix that contains the
//coordinates for the RGBA space. By setting the 3rd row and 3rd column
//to 0.3f we achive a level of opacity
float[][] colorMatrixElements = {
new float[] {1.0f, 0.0f, 0.0f, 0.0f, 0.0f},
new float[] {0.0f, 1.0f, 0.0f, 0.0f, 0.0f},
new float[] {0.0f, 0.0f, 1.0f, 0.0f, 0.0f},
new float[] {0.0f, 0.0f, 0.0f, 0.3f, 0.0f},
new float[] {0.0f, 0.0f, 0.0f, 0.0f, 1.0f}};
ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);
imageAttributes.SetColorMatrix(wmColorMatrix, ColorMatrixFlag.Default,
ColorAdjustType.Bitmap);
//For this example we will place the watermark in the upper right
//hand corner of the photograph. offset down 10 pixels and to the
//left 10 pixles
int xPosOfWm = ((phWidth - wmWidth)-10);
int yPosOfWm = 10;
grWatermark.DrawImage(imgWatermark,
new Rectangle(xPosOfWm,yPosOfWm,wmWidth,wmHeight), //Set the detination Position
0, // x-coordinate of the portion of the source image to draw.
0, // y-coordinate of the portion of the source image to draw.
wmWidth, // Watermark Width
wmHeight, // Watermark Height
GraphicsUnit.Pixel, // Unit of measurment
imageAttributes); //ImageAttributes Object
//Replace the original photgraphs bitmap with the new Bitmap
imgPhoto = bmWatermark;
grWatermark.Dispose();
//save new image to file system.
imgPhoto.Save(WorkingDirectory + "\\" + PhotoFinalName, ImageFormat.Jpeg);
imgPhoto.Dispose();
imgWatermark.Dispose();
PhotoStream.Close();
}
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FTB的图片上传主要利用HtmlInputFile控件，对应HtmlInputFile类的属性PostedFile，它含有SaveAs方法可以来保存图片。当然我们不希望在图片保存完之后再专门读它建Graphics对象来再次处理，因此查了MSDN，发现PostedFile属性返回的是HttpPostedFile 类的一个实例，而HttpPostedFile 有InputStream对象，通过HtmlInputFile控件上传的文件可以通过该Stream对象获得上传文件流，作为WaterMake的参数实现最终功能。
所以最后只要在FTB中把ftb.imagegallery.aspx文件第77行UploadFile.PostedFile.SaveAs那句注释，并替换为对WaterMake方法的调用就行：WaterMark(UploadFile.PostedFile.InputStream, UploadFileName, "watermark.bmp", "UploadPics");当然还要把WaterMake方法放到代码中。
……