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22.1 Displaylanguages:PostScript,PDF,andSVG
interpreter code), on-RIPcolor separaration(for spead and portability), on-RIP imagecompression
(e.g.,JPEG),compositefonts(important forAsianlanguageswithlargecharactersets),bettersupport
foroutputdevices(largesetofprinterdescriptionfiles)andimprovedscreeningalgorithms.
•1999:PostScriptlevel3
PostScript level3waspublisedinFebruary1999. emainadditionsare support for morethan256
graylevelspercolor,furtheradvancesinon-RIPcolorseparation(introductionofnewcolorspaces,in-
RIPtrapping),morehalones,smoothshading,andsupportforPDF(PostScript3RIPscaninterpret
PDFfilesnatively).
22.1.1.2 PostScript:anoverviewofitsfeature
PostScript[2](
www.adobe.com/products/postscript/pdfs/PLRM.pdf
)isapagedescription
language. Itprovides amethodforexpressingtheappearance ofa printed page,includingtext,lines,
andgraphics.
Adevice-and resolution-independent, general-purpose, programminglanguage, PostScript de-
scribes a complete“output page”. elanguage is stackorientedand uses “reversePolish”or postfix
notation.Itincludesloopingconstructs,procedures,andcomparisonoperators,anditsupportsmany
datatypes,includingreals,Booleans,arrays,strings,andcomplexobjectssuchasdictionaries.
PostScript programsaregenerallywrittenintheformof ASCIIsourcetext,which iseasytocre-
ate,edit,transmit,andmanipulate.BecausePostScriptisresolutionanddeviceindependent,thesame
ASCIIfilecanbeviewedonacomputerdisplaywithapreviewer,suchas
ghostview
,andprintedona
smalllaserprinterorahigh-resolutionphototypesetter.
InthePostScriptlanguagethefollowingfeaturescanbefreelycombined:
• Arbitraryshapes,whichcanbeconstructedfromlines,arcs,andcubiccurves.eshapesmay
self-intersectandcontaindisconnectedsectionsandholes.
• Paintingprimitives,whichpermitshapestobeoutlinedwithlinesofanythickness,filledwithany
color,orusedasaclippingpathtocropanyothergraphic.
• Textcharacters,whicharetreatedasgraphicalshapesthatmaybeoperatedonbyanyofthelan-
guage’sgraphicsoperators.isisfullytrueforPostScriptType3fonts,wherecharactershapesare
definedasordinaryPostScriptlanguageprocedures.Incontrast,Adobe’sPostScriptType1format
definesaspecialsmallerlanguagewherecharactershapesaredefinedbyusingspeciallyencoded
procedures¹
• Images(suchasphotographsorsyntheticallygeneratedimages),whichcanbesampledatanyres-
olutionandwithavarietyofdynamicranges.PostScriptprovidesfacilitiestocontroltherendering
ofimagesontheoutputdevice.
• Severalcolormodels(devicebased:RGB,HSB,CMYK;standardbased:CIE)andconversionfunc-
tionsfromonemodeltoanother.
• Ageneralcoordinatesystemfacility,whichsupportsallcombinationsoflineartransformations,
includingscaling,rotation,reflection, andskewing.esetransformationsapplyuniformlytoall
pageelements,includingtext,graphicalimages,andsampledimages.
• Dictionariesforcolorspaces,fonts,forms,images,half-tones,andpatterns.
• Compressionfilters,suchasJPEGandLZW.
¹Forcomplexlanguageswithmanythousandsofcharacters(e.g.,ChineseandJapanese),compositeType0fontscanbe
used.SeeSections21.1.1,21.1.4,and21.2.6formoreinformationonPostScriptfonttechnology.
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