The DPI Dilemma

Resolution basics for beginners

measure resolution
There are many ways to measure resolution. We'll call them dots for convenience. © J. Bear

Resolution, scanning, and graphics size is a vast and often confusing topic, even for experienced designers. For those new to desktop publishing it can be overwhelming. Before you panic at the thought of what you don't know about resolution, focus on what you do know and some basic, easy to understand facts.

Warning! If you are a resolution pro easily offended by the misuse of DPI and related resolution terms — back away from this article. I'm not trying to avoid proper terminology but I do aim to introduce the subject of resolution from the point of view of a beginner who has heard a few terms (however erroneously used) and is, understandably, confused.

What is Resolution?
As it is used in desktop publishing and design, resolution refers to the dots of ink or electronic pixels that make up a picture whether it is printed on paper or displayed on-screen. The term DPI (dots per inch) is probably a familiar term if you've bought or used a printer, a scanner, or a digital camera. DPI is one measure of resolution. Properly used, DPI refers only to the resolution of a printer.

Dots or Pixels or Something Else?
Other initials you will encounter that refer to resolution are PPI (pixels per inch), SPI (samples per inch), and LPI (lines per inch). There are two important things to remember about these terms:

  1. Each term refers to a different type or measure of resolution.
  2. Fifty percent or more of the time you encounter these resolution terms, they'll be used incorrectly, even within your desktop publishing or graphics software.

In time, you'll learn how to determine from the context which resolution term applies.

In this article, we'll simply refer to resolution as dots to keep things simple. (But, dots and DPI are not the proper term for anything other than output from a printer. It's simply familiar and convenient.)

How Many Dots?

  • Whether printed on paper or displayed on your computer screen, a picture is made up of tiny little dots.
  • There are color dots and there are black dots. In black & white printing, the size and shape of the black dots and how close or far apart they are printed creates the illusion of shades of gray.
  • The more little dots that are used (up to a point) the clearer the picture.
  • The more dots in a picture, the larger the size of the graphic file.
  • Resolution is measured by the number of dots in a horizontal or vertical inch.
  • Each type of display device (scanner, digital camera, printer, computer monitor) has a maximum number of dots it can process and display no matter how many dots are in the picture.

    Resolution Examples

  • A 600 DPI laser printer can print up to 600 dots of picture information in an inch. A computer monitor can typically display only 96 (Windows) or 72 (Mac) dots of picture information in an inch.
    When a picture has more dots than the display device can support, those dots are wasted. They increase the file size but don't improve the printing or display of the picture. The resolution is too high for that device.
  • A photograph scanned at both 300 DPI and at 600 DPI will look the same printed on a 300 DPI laser printer. The extra dots of information are "thrown out" by the printer but the 600 DPI picture will have a larger file size.
    When a picture has fewer dots than the display device can support, the picture may not be as clear or sharp.
  • Pictures on the Web are usually 96 or 72 DPI because that is the resolution of most computer monitors. If you print a 72 DPI picture to a 600 DPI printer, it won't usually look as good as it does on the computer monitor. The printer doesn't have enough dots of information to create a clear, sharp image. (However, today's inkjet home printers do a pretty decent job of making low-resolution images look good enough much of the time.)

Connect the Dots of Resolution

When you're ready, delve deeper into the mysteries of resolution where you can learn the proper resolution terminology and the relationship between DPI, PPI, SPI, and LPI as measures of resolution. You may also want to learn more about halftone printing, which is related to the topic of resolution.

Pick Your Path to Desktop Publishing
Get Started:Basic Guidelines and Requirements for Desktop Publishing
Choose Software:Desktop Publishing and Design Software
Make Something:Things to Make Using Desktop Publishing
Tips & Tutorials:How to Do Desktop Publishing
Training, Education, Jobs:Careers in Desktop Publishing
In the Classroom:Back to School With Desktop Publishing
Use Templates:Templates for Print and Web Publishing