Written by:
Jeff Horbinski
jhorbinski@gpo.gov

In many cases involving printing government jobs, customers get samples after their jobs have been delivered only to see something that does not appear as they intended. What generally happens next is that the phone starts ringing off the hook in GPO's Customer Service Department. "What in the world is wrong with my picture on page 'X' of my publication!?!" Frequently, the picture they are referring to looks bitmapped, has bad color, and has a general lack of detail. Is it a bad photo? Did the contractor make a mistake? What happened to that page that looked so great on the computer screen? Actually, it's none of the above. The usual offender in this situation is the use of a graphic that's intended for use on the web.

Web graphics are a great thing... for the web! But GPO has noticed that these fabulous little files mysteriously find their way into print publications where they have no business being. What is it about web graphics that causes the problem? Resolution, also known in the print world as Dots Per Inch (dpi) on press or Pixels Per Inch (PPI) when referring to an electronic file. (From here on I will refer to resolution as dpi only for simplicity reasons.) Web graphics are created for viewing on a computer monitor or printing to a printer in your home or office. The optimum resolution for this work is 72 dpi. Graphics for publication on the other hand, require much higher resolution. Printing presses output your product at much higher detail levels than your computer monitor can output or your desktop printer can produce. In fact, GPO requests that all color and grayscale graphic files be sent to us at 300 dpi at final size (1 to 1 ratio) in .eps or .tif format to ensure proper output. As a side note, any line art should be scanned at 800 to 1240 dpi.

As you can plainly see from the two examples on the left, the difference between 72 dpi and 300 dpi is large. Therefore, if you force a low-resolution image through a high-resolution output device you will see the bitmap distortion on the final piece. Quite simply, the Raster Image Processor (RIP) the printer uses to prepare films or plates must work with what is input to it. In that input, a 72 dpi image does not have enough detail to make up the 300 dpi output. The higher the output, the more noticeable the problem.

To avoid the pitfalls inherent to web graphics, be cautious. Know where your images are supplied from. If you do not prepare the images for printing yourself, speak with your designer or file management technician to identify the sources of your graphics. A great way to catch a web graphic being slipped to you from someone else is to check the file extensions. Any file that is a .jpg is very likely to be a low-resolution web graphic. If you are the primary designer, make sure your color and grayscale files are 300 dpi. Do note that taking a 72 dpi file and increasing the resolution to 300 dpi in a program like Photoshop is not recommended. This process increases the numeric reading of dpi by mathematically adding dots to your file, but does not increase the actual detail, in fact, images that have resolution added to them (called interpolating) become soft and fuzzy. If the image is only available electronically at 72 dpi, a re-scan of the original image should be your next step. If the original is unavailable and all you have on hand is the 72 dpi image, we highly recommend a different image be selected for your product.

Web graphics are great at what they do. In the world of printing and publishing though, web graphics can cause quite a headache by finding their way into your next project. A bitmapped, mottled photo is no way to get your message across. Knowing where your files come from and what resolution they are set at is your best defense against the low-res blues. While re-scanning or choosing different pictures for your next job may be time consuming, the benefits of a sharp publication outweigh the costs or a possible reprint. So remember to keep those 72 dpi files in solitary confinement on the web!

Example Images

Output from high resolution file.

Output from low resolution file.