Handy Display & Banner Resolution Calculator

Jul 23, 2010

A lot of people ask “What resolution do I need for my banner” or else “Look at that digital camera image “weaselfoot.tif”, how big can we blow it up?” Or maybe you need to figure how big to make a drum scan, but not too much larger than what is really needed. Well, Andrew Gregory has a great section on resolution at his site, explaining all the details about this and more. Through Andrew’s mathematical wizardry using radians, tans, and arcs, he’s been able to calculate the average angle of human visual acuity*, and from that, give us the magic number: 3438.

ppi = 3438 ÷ Minimum Viewing Distance

You simply divide this number by the desired viewing distance in inches to get the minimum resolution needed for average conditions, or calculate a minimum viewing distance of an existing image if you know its resolution. At this distance and beyond, a normal human could not distinguish any difference with increased resolution. Typical resolutions for large banners are usually 60-100ppi at final size.

Of course, other factors can also come into play, so it pays to have a little understanding. For example, a soft image is more tolerant of lower resolution than one with finer detail. A hazy landscape and sky will fare much better than a crisp shot of lace and a face. Keep this in mind and maybe add a little resolution headroom in your figures when it might help.

If you’re like me, you like to get things done quickly, and if you’re a Mac user who wonders about resolution, you’re in luck. I’ve written a simple Applescript called RezDistance where you can enter in the resolution of an image and it’ll tell you how close you can view it, or you can enter a distance, and it calculates the minimum resolution you could probably get away with before the image might not look optimal.

Here’s a little clip so you can decide if RezDistance might be of use in your work:

RezDistance 16KB (it’s free) Mac only (Applescript application)

* 0.000290888 radians (θ)