How to turn a background image into a watermark by changing the transparency?

Question

Java

I want to make background image transparent using iText.
Here is the image code:

string root = Server.MapPath("~");
string parent = Path.GetDirectoryName(root);
string grandParent = Path.GetDirectoryName(parent);
string imageFilePath = parent + "/Images/logo.png";
iTextSharp.text.Image jpg = iTextSharp.text.Image.GetInstance(imageFilePath);
jpg.ScaleToFit(1700, 800);
jpg.Alignment = iTextSharp.text.Image.UNDERLYING;
jpg.SetAbsolutePosition(100, 250);
jpg.ScaleAbsoluteHeight(500);
jpg.ScaleAbsoluteWidth(500);

How to do it?

Answer 1

See the BackgroundTransparent example . This is a variant of the BackgroundImage
example. In your code, you add Imageto the Document. There is nothing wrong with this, but if you want to make the image transparent, you need to create a soft mask. It's not difficult, but there's an easier way to make the background transparent: add an image directly to the content, and then define transparency with PdfExtGState:

PdfCanvas canvas = new PdfCanvas(pdfDoc.addNewPage());
ImageData image = ImageDataFactory.create(imgSrc);
canvas.saveState();
PdfExtGState state = new PdfExtGState();
state.setFillOpacity(0.6f);
canvas.setExtGState(state);
canvas.addImage(image, 0, 0, pageSize.getWidth(), false);

You can compare the results of the examples above and see the difference.
My example is written in Java, but it's easy to modify for C#.