Xerox DocuColor 12 Printer with Fiery EX12 Leaflet

In this table, the shaded areas indicate that 200 ppi is typically the best trade-off 
between image quality and file size. However, higher resolutions (for example, 
250 to 300 ppi) may be necessary for offset printing, when quality is of the utmost 
importance, or for images containing sharp diagonal lines.

To find the best image resolution for your purposes, make test prints of some raster 
artwork at different resolutions. Start with a high-resolution image (400 ppi) and save 
versions at progressively lower resolutions, down to 100 ppi, using a pixel-editing 
application, such as Photoshop. Always save a copy of the original high-resolution 
version, in case you must revert to it. The high-resolution data cannot be recreated 
from a lower resolution version. 

Print the files and examine the output. You will likely begin to see a marked 
deterioration in output quality at resolutions below 200 ppi, while above 200 ppi the 
improvement may be very subtle. 

Raster images prepared for offset printing may need to be at higher resolutions than 
necessary for proofing on your Color Server.