When process-colour separations are printed, the rows of dots for each process-colour ink are printed at an angle so that the ink dots don't print on top of each other. Instead, the dots form a symmetrical pattern, called a rosette pattern, which the human eye easily merges into desired colours. If one of the process colour inks prints at an incorrect angle, the rosette pattern prints incorrectly. The resulting pattern is called a moire pattern. Moire patterns are unattractive and disrupt the illusion of multiple colours being created by the process colours.
QuarkXPress contains a standard set of screen angles which are applied to the four process colours. The set of screen angles used depends on the line screen (lpi) specified for the document. The OverrideSeps XTension allows the user to create custom sets of screen angles and indicate separate lpi settings for the best quality output possible. By letting the user save and easily access sixteen separate sets of separation preferences, OverrideSeps gives the user the maximum control over the line screen and screen angle of high-resolution output from XPress.
