What PPI and DPI is needed for a photographic backdrop printed at 6x4 foot? I have a stock image which is 4000 px across and 300 dpi. Do I need to enlarge that with photoshop before sending to my backdrop printer?
I would use between 72-100 dpi if the image could handle it, although you could maybe drop it down a little further if necessary. .
The longer the distance you view something, the smaller the dpi, at longer distances a higher dpi is wasted. So general rules would be.
Magazine (close up) 300dpi
Banner (medium distance) 72 - 100dpi
Billboard (long distance) 30 dpi
My biggest piece of advice is always best to ask your printer, an experienced printer will always help you get the best possible results.
Check out this previous answers for a little more detail.