How can I tell the resolution of scanned PDF from within a shell script?

Question

I have a large collection of documents scanned into PDF format, and I wish to write a shell script that will convert each document to DjVu format. Some documents were scanned a

Answer 1

I guess that the scans are included as images in the PDF, so you could use pdfimages to extract them first. Then, identify should be able to find the correct data.