Need to enlarge photo for 24' backdrop - help!

[dydee]

Hi,

I'm looking to enlarge a photo for a 24' backdrop. The stock photos are just not large enough to provide the printer with a file that's 1/2 size (146"w) at 72 dpi. When enlarging the photos in PS to the dimensions the biggest one I found was only 42 dpi. Check out the screen shot.

I remember someone at my previous job using a program to rez up images. Anyone know what that is? Any other ideas?

Thanks all!

Dydee

[Guest]

Hi

Not sure if this is the program you're thinking of

https://topazlabs.com/gigapixel-ai/

[dydee]

Ged, thank you for your quick response! I think that was the program, but if not, I believe it will do the trick. Just downloaded a trial and it's looking pretty good. Thank you again! Dydee

[Derek Cross]

42PPI my be acceptable for a large image that's viewed from a distance - check with your printer.

[joanH]

Hi dydes57085107, When I open this posted photograph, I read the size at

64.2

159.214 inches wide

77 inches high

res only 42.779

If you are able to resave this at a higher resolution how far can you enlarge it?

Free transform might let you do it inside the current work-frame. Someone here might know the exact formula you need. Best always, JH

[dydee]

Thank you!

[davescm]

Hi
What distance will you view the backdrop from?  You may not need higher than 42ppi.  The resolution required can be calculated from 6878/Viewing distance in inches *.
So if your are viewing this from say 15 feet away (which is 180 inches) the ppi required is 6878/180 = 38 ppi. Any higher and your eyes cannot resolve it at that distance.

Dave

The math is based on this:

A good human eye can resolve 60 line pairs per degree i.e. pairs of black and white lines.  So in half a degree we would have 60 single lines.

Simple trigonometry means that the width containing those 60 lines can be calculated by:
               Width of 60 lines = Viewing distance x tan(0.5°)

Once we know the width for 60 lines (or pixels) we can calculate how many lines per inch can be seen by using 60/Width of 60 lines.

So putting those together gives us

60/(Viewing distance x tan(0.5°)) = 60/(Viewing distance x 0.0087269)

= 2/(Viewing distance x 0.000291)    

Or

1/(Viewing distance x .0001454)

Or

6878/Viewing distance

[dydee]

Dave, Thanks for your quick response. Appreciate the Math and the information. This helps for sure. Dydee