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作者： 整理

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。