When I change the ink in my all-in-one HP ink jet printer, it prints a test page which I then scan in to the printer to self-align the print head. But, how can this be? If the print head is not aligned, then the test page will print crooked, too!
Yes, but it has a scanner, and can measure the locations of the fiducials it prints and calculate the correct offset for each cartridge.
It’s not aligning page registration (whether or not the paper is going through straight) but black vs color ink registration - they’ve simply semi-automated the process where we used to have to print a test page with an assortment of lines and hatches, then click on the groupings that lined up the best in the alignment utility.