Confused About DPI vs Pixel Size When Exporting PDFs to Images

[haileywilson]

Hello,

I’m testing PDF-Tools for converting PDF pages into images and ran into some confusion regarding output quality.

When exporting, I can change the DPI value, but I don’t see a way to directly control the pixel dimensions of the final image. For example, I’d like to export a page exactly at 1200 × 800 px, but the result changes only when I adjust DPI.


So my questions:

Is there a way to export to a specific pixel resolution rather than only DPI?

Does page size in inches affect the final pixel output?

What is the recommended method to get consistent image dimensions for web use?

If I’m looking in the wrong place in the export dialog, please point me in the right direction.

Thanks for your help!

[Daniel - PDF-XChange]

Hello, haileywilson

At the moment there is no way to do so. Generally speaking, the majority of PDF files are stored at 72dpi (meaning there are 72 pixels per inch - so you can do a bit of a calculation to translate the image to match the "physical size" inside the document) - but not all PDF files do this, and so it is not strictly a reliable fact. The images in place on the page could also have been resized, allowing one image to be much higher DPI than the rest of the page content, further skewing this capability - leading to reduced image quality if for example, the image on the page was squished, and effectively a 600dpi image - but you are exporting it at 72dpi)

Finally, the chosen export format will have an effect on the actual physical size used, and not all image formats support a DPI value, so getting the correct final output can be difficult as well.

I have passed this up to the Dev team and while it was accepted, it is also a low priority item currently, so I cannot promise a timeline for this implementation - but it is at least in line to be created in the future!
RT#7716: FR: DPI/Pixel on image export

Kind regards,