ILLUSTRATION: MARK FISHER
My graphics company often refers to "target resolution." What does that mean, and how is it calculated?
"Target resolution" is the resolution (DPI or PPI) of a graphic at its final printed size. DPI stands for dots per inch; PPI means pixels per inch. DPI and PPI are ratios, so
an image doesn't have "resolution" until it is assigned a specific size for printing. Look at the image properties in the graphics file, and you'll be able to see how many pixels wide by pixels tall it is (e.g., 2,400 by 3,300). You can print that image at the size of a postage stamp and get a high resolution. However, if you print that image for your exhibit graphics, you will get a low resolution. And as a rule of thumb, the target resolution for a print ad is about 300 DPI, while for larger exhibit graphics, the ideal target resolution is 100 DPI.
To put that into context, here's a real-world example. Suppose your team members send you the image file for their latest 8.5-by-11-inch print ad and tell you they want to use the same image for exhibit graphics sized at 30-by-40 inches. However, this one image file won't work for both the print ad and exhibit graphics due to the size and resolution. It will likely appear blurry or pixilated when sized up to the exhibit-graphic dimensions.
To calculate the minimum size image you will need for the exhibit graphics, multiply both measurements by the target resolution, which in this case is 100. (So multiply 30 inches by 100 and 40 inches by 100.) Your answer is 3,000-by-4,000 PPI, and this is the minimum resolution of the file you need in order to print a quality large-scale graphic.
— Brian Baker, vice president, Highmark TechSystems, Fort Wayne, IN