This question already has an answer here:
If I purchase a scenic photo from Shutterstock that says 5586px x 3724px, and 18.6" x 12.4" @ 300 dpi, can this photo be enlarged to a huge 40ft x 6ft banner without appearing extremely pixelated? This banner will be used outdoor and will mostly be viewed from a 10ft to 15ft distance.
I asked the actual printer, they told me to open photoshop and insert the photos at 50 dpi and view it at 100%, if that is acceptable then that's how it would print on the banner.
Since this is not a graphic design, I'm assuming a photo can not be vectorized, so What is the general rule for enlarging photos to extreme large sizes? what are the formulas to calculate how big can you enlarge without loosing the pixilation too much?