In my own tests where I inspect PDF differences in python, I iterate through the pages, if the number of pages is the same, I convert each of them with PIL to bitmap, get the diff (ImageChops.difference is black for everything same and colored for diffs) and find the content of the diff with `getbbox`. This gives me the coordinates of the rectangle where changes appeared, I then use those to also print the page with a colored rectangle and print out the crops.
I give out the original page, the original rectangle, the original page with colored rectangle, the new page and the new rectangle, the diff cropped and uncropped only after which I start using my caveman eyeballs
I also pixelate it a bit and have a brightness cutoff for the diff to see if the diff actually matters and i also try if re-cropping a bit so shifting by a limited amount of pixels makes it look like an ignorable difference because everything just moved to the left a bit but that is optional.
I also recommend exporting the new pdf from the CI/CD tool to be put back into the test as reference. Even between Linux distros and versions small changes in fonts and stuff like that make a difference
I give out the original page, the original rectangle, the original page with colored rectangle, the new page and the new rectangle, the diff cropped and uncropped only after which I start using my caveman eyeballs
I also pixelate it a bit and have a brightness cutoff for the diff to see if the diff actually matters and i also try if re-cropping a bit so shifting by a limited amount of pixels makes it look like an ignorable difference because everything just moved to the left a bit but that is optional.
I also recommend exporting the new pdf from the CI/CD tool to be put back into the test as reference. Even between Linux distros and versions small changes in fonts and stuff like that make a difference