It's not so impossible to spot flaws if you're using worst-case testing scenarios. Which are not worthless because such patterns do actually pop up in real world usage, albeit rarely.
One of the album covers being stretched had some kind of fine pattern on it that caused a clearly visible shifting/flashing Moiré pattern as it was being stretched.
Wish I could remember what album cover it was now.
Though really it's simple enough: As long as you can still spot a single dark pixel in the middle of an illuminated white screen, the pixels could benefit from being smaller. (Edit: swapped black and white)