Scanning 4x5 film to make 60 foot poster

[Jim Blomfield]

Question for a friend: An artist creates room size sculptures and then photographs them... and then turns it into a billboard type of image (so close you can see all the little pixels and then from far away you see the whole image). What file size and resolution is needed if she has a 4x5 piece of film? What resolution should it be scanned at so enlarging it to 60 feet will give the right dpi? Would 60dpi for 60 feet work? Any help would be appreciated.

 

[Lachlan Young]

I've done this in a similar context at about 4x5 metres - 2000ppi from a high end CCD/ Flextight scan of 4x5 came to about a 25lpi screen, aka 50ppi. A regular line screen ended up looking better than the stochastic/ 'grain' screen on the billboard paper. Using the more standard billboard lpi's of 10-20 (20-40ppi), it could have perhaps gone to 40+ ft without major issue.

Bear in mind that most high end/ drum scanners will max out at about 4-5500ppi which will translate to perhaps 30ppi (15lpi) of information in your case from your 4x5 original - as long as your computer doesn't choke on the files, it'll not be terribly difficult to do. Alternatively, take a 2000ppi scan & run it through 'preserve details 2.0' upres in PS which can be pretty startlingly good up to about 2x original. You'll need to finesse in some sharpening etc.

 

[Pieter12]

Billboards can typically be printed at 15 lpi (that's lines per inch, a graphics measurement of halftone dots). Up close, the dots are quite noticeable, but from the usual viewing distance of 20 ft, they disappear.

 

[Luckless]

Of course "Billboard sized" and "actual billboards" are not exactly the same thing, and the important part to establish to answer this question is "How pixelated do you want the image to be when viewing close up?"

I suggest getting a big monitor and a test image, then zoom in or enlarge a small section to the point where the pixels are as big as you want them to be in the final image, and then use that to sort out your required resolution for the total image. [Be careful to use a measuring device that won't mar or scratch the display if you need to manually measure it...]

Examples:
- If you find that huge distinct 1x1 inch pixels are what you're after, then you're actually only looking at 720 pixels across a 60 foot wide image.
- If you want 1/8th inch pixels, then a 60 foot wide image would need 5760 pixels.

Of course, that assumes you're printing with a method that will actually produce distinct pixels, and not some other pattern. Not all very large format printing is done in the same way.