How to get the image DPI in PDF?

How can I read the width/height/scale of an image and be confident about the result?

I'm trying to get information about scanned images that are saved into PDF files through iText (using Java). I can get width and height (either through Matrix, or through BufferedImage). The idea was to use the answer here to calculate the DPI, but I am a bit lost. Are these values (width and height) in pixels or points? Is there any other way to achieve this? There are a lot of answers on how to scale and save an image to a PDF file, but I didn't find any on how to read the width/height/scale of an image and be confident about the result.

Posted on StackOverflow on Aug 28, 2014 by Finik

Now you don’t need to calculate the DPI values yourself. There is an ImageData class in iText 7 with built-in methods to solve your problem:

ImageData image = ImageDataFactory.create(IMG);
int x = image.getDpiX();
int y = image.getDpiY();

Click How to get the image DPI in PDF? if you want to see how to answer this question in iText 5.