iText Image and transparency - image

Question

I'm trying to add a PNG image to an existing pdf, but the transparency is converted to black color.
PdfReader reader = new PdfReader(pdfPath);
File f = new File(pdfPath);
String result = f.getParent() + File.separator + UUID.randomUUID().toString() + ".pdf";
PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(result));
Image image = Image.getInstance(ImageIO.read(new File(imagePath)), null);
PdfImage stream = new PdfImage(image, null, null);
PdfIndirectObject ref = stamper.getWriter().addToBody(stream);
image.setDirectReference(ref.getIndirectReference());
image.setAbsolutePosition(30, 300);
PdfContentByte canvas = stamper.getOverContent(1);
canvas.addImage(image);
stamper.close();
reader.close();
How can I keep transparency?

Answer 1

First this: I am violating the policy at iText Software by answering this question. You are using an old version of iText, and the policy dictates that voluntary support on iText 5 or earlier has stopped. You should either use iText 7, or you should get a support contract if you still want support for an old iText version.
However, I am curious. I want to know where you found this clunky code (or why you decided to write this code):
Image image = Image.getInstance(ImageIO.read(new File(imagePath)), null);
PdfImage stream = new PdfImage(image, null, null);
PdfIndirectObject ref = stamper.getWriter().addToBody(stream);
image.setDirectReference(ref.getIndirectReference());
image.setAbsolutePosition(30, 300);
PdfContentByte canvas = stamper.getOverContent(1);
canvas.addImage(image);
You don't need ImageIO and you don't need to create a PdfImage, nor do you need to add that image to the body of a PDF file. The code you are using is code specialists would use for a very particular purpose. If you know that particular purpose, please explain.
If adding an image at an absolute position is all you want to do (that's a general purpose, not a particular purpose), your code should be as simple as this:
Image image = Image.getInstance(imagePath);
image.setAbsolutePosition(30, 300);
PdfContentByte canvas = stamper.getOverContent(1);
canvas.addImage(image);
In this case, you don't have to worry about the image mask; iText will take care of that for you.
Please also explain why you're using an outdated version of iText instead of iText 7. If you want your application to be future-proof, you should upgrade to iText 7 now (to avoid wasting time later).