Count
Quarters
By Mike Pasini, EditorImaging Resource Newsletter
How big does your image have to be to order an 8 x 10-inch print from online photo printers like Ofoto, Shutterfly, or Print@Kodak? One way of (roughly) calculating the biggest size you can get from your image is to double your image file's smallest dimension (in pixels) and divide by 250.
Part of the trick to this formula is that these photofinishers use output devices with a resolution of about 250 pixels (dots) per inch. So if your image is 768 x 512 pixels, you would double the 512 to get 1,024, and then divide by 250 to get roughly 4 inches, giving you a 4 x 6-inch print
512 x 2 = 1,024 pixels ÷ 250 (ppi) = 4.096 inches
It's easier than it looks. In fact, it's just like counting quarters to find out how many dollars you have.
A 1,536 x 1,024 pixel image would give you a little over 2,000 on the small dimension, which like $2 has 8 quarters, so you could get an 8 x 10 out of it.
A 1,280 x 960 pixel image doubles the 960 to give you 1,920, which (like $19.20) has 7 quarters, so you can get a 5 x 7 out of it, but an 8 x 10 would be a stretch (remember, you're going for the 5 and 8 sides, not the 7 and 10).
It's not impossible to go larger. You're just crossing the quality line. But now, at least, you know where it is.
This article is reprinted from The Imaging Resource Digital Photography Newsletter,
Beginner's Flash Column, published October 6, 2000