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Tech Corner: Digital Printing and Image Size

TIP Calculate the square root of your megapixels to determine their real dimensions.

What's my aspect ratios size?

  • Printing Size
  • Easy Square Roots Converter
  • Make a Print of a Calculated Image Size

Printing and Image Size

One aspect of digital photography that seems to confuse people is the issue of image size. The marketing boys love to boast about megapixel size but in practice this number isn’t very informative. Every digital camera produces images of a certain maximum size in one of the following formats:
  • jpegs
  • tiffs
  • RAW
The easiest way to determine the real dimensions of your megapixels is to calculate their square root. For example, let’s take a 24 megapixel camera. The square root of 24, says Siri is: 4898.98. Now that’s for a square image but most cameras produce images in rectangular format, usually with an aspect ratio of 3:2 (for more about aspect ratios, read Andrew Gibson's The Art of Using Aspect Ratios in Digital Photography). So, to make things easy, there’s a handy online converter that will do all the math for you. Go to Wayne Fulton’s Scantips to utilize his Image Dimension Calculator Tool  and enter the megapixels and aspect ratio of your camera, and presto your file dimensions are revealed. In the above example, 24 MP at 3:2 aspect ratio produces a file size of 6000 x 4000 pixels. Now that you know the file size, what comes next is equally as important.

To Make a Print of Your Image

We’re going to assume you want to make a print of this file. For starters, let’s find the size print we can make from the file. For this we need to know how many of those pixels your printer needs for each inch of print. Printers these days seem to have settled at 300 pixels per inch (ppi) and this is true whether you’re home brewing or uploading to an online lab. So, using our maximum dimension of 6000 x 4000, we divide each number by 300. This gives us a 20 x 13¼ print. That’s a good-sized print using all those camera-original pixels. Smaller Print? If you want a smaller print, software will enable resampling to downsize your file. It uses some high cotton math (algorithms) to accomplish the conversion, but the resulting file will print just fine. To learn more about resampling, visit the Real World Adobe Photoshop CS5 for Photographers Fundamentals: Resampling in Photoshop CS5. Larger Print? If you want a print larger than 13 x20, then the resampling magic will do the trick just as well. I’ve made very beautiful 40 x 60 inch prints from my 24MP files. If you’re willing to invest some time and diligence learning about printing, the rewards of making a well-crafted print are enduring. I recommend you give it a try. More later, Tony Roberts
(Tony Roberts' photographs have been published in every major golf magazine, and his photos have graced over 300 covers. He was voted two times by the International Network of Golf (IGN) as golf photographer of the year. You can see Tony Robert's iconic shot of Tom Watson's chip-in on the 17th hole at Pebble Beach during the final round during the 1982 U.S. Open on Tom Watson's official site.)
Visit Tony Roberts bio to read more.
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