Xerox 96 NPS manual Device-dependent operators, Gray shading-setscreen and setcolorscreen

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ADJUSTING PRINT QUALITY AND SPEED

Device-dependent operators

Some PostScript operators result in device-dependent PostScript files. “Device dependence” means that devices having different output characteristics may produce different-looking output even though they use the same software. This section documents the most serious examples of device dependence. The PostScript Language Reference Manual, second edition, lists all of the graphics state operators that are considered device-dependent.

Note: Depending on the emitter used, color-related operators may be used even for monochrome jobs. On DocuPrint NPS, color jobs undergo a color to monochrome mapping process. Therefore, if these operators are included in the PostScript jobs, they can affect the output.

Gray shading—setscreen and setcolorscreen

The PostScript operators setscreen and setcolorscreen control the PostScript halftone software that simulates various intensity levels of gray and color inks. Since each PostScript product may have a different default halftone definition, the halftone patterns and gray scale range may differ also. Because setscreen is inherently device dependent (especially when used for pattern fills), PostScript masters look different on almost every different model of PostScript printer.

The operators are also used to perform pattern fills, since PostScript Level 1 does not have a pattern fill operator. (PostScript Level 2 has pattern fill operators.) As stated in the PostScript Language Reference Manual, first edition, “Remember that everything pertaining to halftones is, by definition, device-dependent. In general, when an application provides its own halftone specifications, it sacrifices portability. Associated with every device is a default halftone definition that is appropriate for most applications.”

In addition to the device-dependent nature of halftoning, a spot function is used by setscreen and setcolorscreen to determine the order of pixel darkening in the halftone cell. When two pixels have the same spot function value, their ordering values are determined arbitrarily. Duplicate spot function values are very common. In fact, almost all the various default spot functions generate duplicate values. Therefore, different PostScript implementations yield different halftone patterns, resulting in visual differences in the output.

Gray shading—settransfer and transfer function

The PostScript operators settransfer and setcolortransfer are used to change the procedure for mapping perceived color values in the output of the print device into specified color values in the PostScript master. PostScript devices use an internal transfer array or procedure that takes into account the printing characteristics of their marking engines in order to produce levels of color.

Transfer functions are called by the setcmykcolor, setbsbcolor, setrgbcolor, and setgray operator before processing of the desired color level that is specified in the master. The transfer function takes a value from the stack and leaves another value on the stack for each color component (red, green, blue, and gray).

XEROX DOCUPRINT 96/4635/180 NPS TROUBLESHOOTING GUIDE

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Contents Version 7.1 August 2000 721P86651 Page Operation safety Laser safetyOzone information Xerox Docuprint 96/4635/180 NPS Troubleshooting Guide Table of contents Correcting stacking problems System unresponsive Index Introduction ContentsAbout this guide Conventions DocuPrint NPS Interactive Customer Documentation CD Related publicationsPage Information to have on hand when calling for service Calling for serviceEnabling and disabling the modem for remote service Fault masking Fault List screen Troubleshooting Xerox Client Software installation Troubleshooting Xerox Client Software Installation Pserver problems Problem Probable Cause Resolution Troubleshooting a Novell implementationPASSWORDS=ON at Problem Probable Cause Resolution Rprinter problems Problem Probable Cause Resolution Page Clearing paper misfeeds and jams Clearing a feeder tray faultClearing Paper Misfeeds and Jams Frequent misfeeds Clearing paper jams Checking job integrity following a paper jam Fault InstructionsArea Printer areasArea Area Area Area Area Area Area Area Area Clearing bypass transport paper jams Area Measuring the paper curl Paper curl and paper jamsDecurler lever Adjusting the decurler leverPaper curl chart Arguments None Using sample documentsListing and printing sample documents List Sample DocumentsPS-oplist sample documents Print Sample DocumentArguments Document Using Sample Documents Page Installing the custom transfer assist blade Adjusting print quality and speedCorrecting skewed printing Adjusting the registration transport roll leversAdjusting Print Quality and Speed Measuring performance Calculating throughput Enter Start Printing Minimizing the start-up latency 99995163.ps, November 19, 1996 35222 pm PST Dpi versus 600 dpi performance Product features that affect print quality Setting page orderProprietary PostScript extensions Gray shading-setscreen and setcolorscreen Device-dependent operatorsGray shading-settransfer and transfer function Scan conversion-fill, eofill, and stroke Settransfer, or SetcolortransferSmooth curves-setflat Invisible strokes-0 setlinewidthSymptom Probable cause Action Correcting stacking problemsPage System unresponsive Configuring and Managing the System forPage Numerics IndexIndex
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