A Study utilizing halftone based digital proofing systems in the flexographic printing process

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12-1-1996

A Study utilizing halftone based digital proofing

systems in the flexographic printing process

William Hanna

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Recommended Citation

Printing

by

William James Hanna

Athesis submittedinpartialfulfillment ofthe

requirements forthe degreeofMasterofSciencein the

Schoolof_PrintingManagementand Sciencesin theCollege

of_ImagingArts andSciences ofthe

Rochester Instituteof_Technology

December 1996

Rochester Institute of Technology Rochester, New York

Certificate of Approval

Master's Thesis

This is to certify that the Master's Thesis of

William James Hanna

With a major in Printing Technology

has been approved by the Thesis Committee as satisfactory for the thesis requirement for the Master of Science degree

at the convocation of

May 1997

Thesis Committee:

Joseph L.Noga Thesis Advisor

Joseph L.Noga

Graduate Program Coordina tot

Flexographic Printing Process.

I, William James Hanna,prefer to be contactedeach time a request for repro-duction is made. I can be reached at the following address:

William James Hanna 2 Sanford Avenue

Amsterdam, New York 12010

I wish to thank thefollowing:

My friends for theiradviceand _support;

Jamisen _Gingerelli,James_{Recene, Timothy} Conroy,JenniferKerrigan, and Stuart

Gallup.

My advisors for _guidance;

Professor Joseph _Noga,Mr. ChetDaniels (Statistical_Design),Mr. Franz _Sigg

(System_{Calibration),}Professor _BarryLee (Press _Technology) and Professor Len

Leger.

My press crewfor_help above andbeyondtheoriginal scope of_{this project;}

Mr. Phil Fisher (forjust about_{everything imaginable)} and Mr. Dave

Dembrowski.

Thecompanies who _generously supplied the goods and services Ineeded to complete_{this project;}

Ms. _AmyCarpinellaandMr. _AndyKatzat _Optronics,Mr. Mike Rook and Mr. Tim Harrigonat EastmanKodakCompany, Fasson Corporation, and Mr.Jim SmithatEnvironmental Inks.

And _{my familyespeciallymy}mother,MaureenHanna,withoutwhom _my edu cation would nothave beenpossible.

Chapter One

Introduction 1-5

Chapter Two

Theoretical Basis 6-33

Flexography 6-11

The Flexographic_PrintingSystem 7-8

Flexographic_PrintingPlates 8

FlexographicSubstrates 9

Flexographic Inks 9

LimitationsoftheFlexographic Process 9-11

Proofing 12-29

What is aProof? 12

A_Historyin_Proofing 12-16

TypesofDigital Proofers 16-20

AdvantagesofDigital_Proofing 21-23

Limitations ofDigital_Proofing 23-24

TheFutureofDigital_Proofing 25

Halftone_ProofingSystems 25-30

Chapter Three

A Review ofthe Literature 34-42

Flexography: PrinciplesandPractices 34-35

UnderstandingDesktopColor 35-37

Electronic_ProofingTechnologiesfor_Flexography 37-38

OffsettoFlexo 39

Changing Paradigm 39-40

Digital Color_Proofingfor_Flexography 40-41

Chapter Four

Hypothesis 43-46

Chapter Five

Methodology 47-55

Chapter Seven

Summaryand_Conclusions 68-73

Bibliography 74-75

Appendix A

Buildinga Test Page _Usingthe ISOStandard Color Image Data.... 76-92 WhatIstheISO Standard ColorImage Dataand_WhyIs It_BeingUsed? . . 76-77

LegalIssues 77-78

Assemblingthe Page 78-81

Press Calibrationand_{Fingerprinting} 81-89

MatchingtheProofstothePress Sheet 90-92

Appendix B

Dataand Statistics 93-121

Appendix C

Photomicrographs 122-170

Appendix D

Contract_proofingfor_printinghas been _{traditionally}done _bypressproofing. This is costly and _wasteful,notjust intermsof equipment and laborbutalso in

termsof expendables. The advent ofoff-press_proofingwas greeted with some degree of_{uncertaintyby}the_printing industry. Withpress _{proofing, the}proof

was _literallya preview ofwhat wouldhappenon a press. Thepress_proof,

although oftenprinted on a different_{press, generally}used thesame typeof

inks, plates andsubstrate that would characterizethefinal print. Withoffpress

proofing,printers were_comparingapples _{to oranges;}instead of_comparing a

presssheet toa press sheet _theywere_comparing apress sheet toan approxima

tionofa presssheet. _However, overtimeas printers learned toread off-press

proofs, _theybecame accepted as contract proofs. The same situationhasnow

befallen digitalproofs.

Intheparticularcaseofflexography, the_proofingproblem isabit different.

Off-press _analog proofs were designedwith_lithographyin mind,_they were charac terized to simulatelithographic dotgain. In ordertomake a proofthatlooks likea flexographicpress_{sheet, two} sets offilmsare _{required;one which com}

pensatesfor flexographic dot gain(this is theset_from whichthejob wouldbe

printed) andone whichhasextradot gainbuiltinto thehighlight and quarter tones (this is the setthat theproof wouldbemade from). This _{extra set offilms}

iswasteful and time_consuming to generate.

canbe builtintothe _proofingsystem and no extrafilm isrequired to createthe

proof.Atthe most_basic levelthere are two typesofdigitalproofers available;

those whichsimulatehalftone dotsand those thatdo not. Whetherornotthe

dots are_necessaryis opento _{discussion,however,} inthecase of _flexographythe

dots appear tobecrucial. Forthis researchdocument itwas decided that the

halftone dots were preferred.The reasonforthis isthat at about133 lpithe

rosette patterns formed_byhalftone dotsare atthe threshold of resolution_by the humaneye. For more coursescreen rulingsthisis even more critical. Muchof

flexographyisprinted at screen rulings of133 lpior lower, so _veryoftenthe dots canberesolved _bytheeye. _Therefore, themindset atthe_beginning of the

researchwas thatifthe dotscanbe resolved onthepress sheet then the dots

shouldberesolved on theproof.

Themajorthrust ofthis researchwasto observe whether or not a halftone-based

digitalproofer can simulatetheappearance of a flexographicpress sheet. Aflex

ographictestformwas created and printed on afilm based substrate. Apress

sheetwas sentto two vendors whomanufacturehalftoneproofers. The_proofing

systems are notmentioned _{byname; they} are insteadreferred toasDigital Proof Aand B. _They thenattemptedto matchthepress sheet as_closelyas possible.

Thus, throughreverse engineering, thevendorscreated a device profilefor this

set of_printingconditions.Uponreceipt of _{the proofs, they}were comparedto

the press sheet interms of optical density,hue (AE) andhalftone dot size. _Later,

a visual assessmentwas executedto observehow_closely thedigitalproofs

matchedthe press sheet_usinga3M _Matchprint, thathad been alteredto

approximate flexography, as thereference or control proof.

press sheetin someinstances and insignificant differences inothers. In terms of

the physical structure ofthe halftone_dots, the3M Matchprinthadtheclosest

matchtothe press sheetdot structure. Interms of physical dot size;digital proof

Abestmatched the50 and 75% dotsand theMatchprintmatched the5% dots

thebest. In terms of optical _density; digitalproofAbestmatched the_density of

the25% _dots,digitalproofBbestmatchedthe _densityofthe 5% dots and the Matchprintbestmatched the50 and 75% dot patches. Interms ofAE values

(color orhuedifference); theMatchprintmost_closelymatched the press _sheet, digitalproofB wasnext, and digitalproofAwaslast.

In terms of a visualmatch, the threeproofs were found to _{be statistically}equal

in their_ability to_visuallymatchthepress sheet. Thevisual match_beingthe

most powerful of_{the criteria;} shows thatthemeasurabledifferencesin the

proofs did not_directly affecttheir _abilitytomatchthepress sheet.

Theresults show thateither ofthe twohalftone digital proofscould have been

used inplace ofthe 3M Matchprint. The results also questionthe needfor

halftone dots ina proof.This is primarilybecausethetwohalftone digital

proofs utilized a different RIPthantheAgfagenerated films forthe 3M

Matchprint andflexographic press sheet.Yetthevisualobservationsmade_by

thejudges couldnot, at a normal_{viewing distance,} discernthis difference. The

conclusionisthat there isnovisual difference betweenthehalftone digital

proofs andthe3MMatchprintproofinterms of

visually matchingthe press

sheet.

Introduction

"The color_proof,which is_usuallymadebefore theproduc

tionrunfor customer_approval, isexpected tobe a reasonable representationofthe printedjob sothecustomer candeter mine what_{modifications,} if_any, areneeded before printing.

Whenapproved itbecomes theguideforpressmentouse during makereadyto derivetheOK sheetthatis used for checking theprinting duringtherun. Ifthe proofdoesnot reproduce the_printing characteristicsoftheprocess thereis the risk of_difficultyin _gettingtheprintedjob tomatch the proof, which can resultinlong, _tedious, expensive corrections on_{the press,} plate _remakes,a dissatisfiedcustomer andpossi blyjob rejection."

Michael H. _Bruno, 19891

Purpose andRational for _Study

Thepurpose ofthisresearchwasto determineifa digitalhalftone proofingsys

tem is able to_successfullypredictthehalftone dot structure,ink densityand

hue _(AE) aswell as_visuallyapproximate a flexographicpress sheet_printingon

aplasticfilm substrate (polypropylene). This isa relevant subjectto _study because_up to now, there hasnotbeen a_proofing systemthathas beenable to

successfullycompensateforthehighamount ofdotgain present inthehigh lightportion ofthe tonescale in the flexographic printing_process,ina _timely fashion. Digital_proofingcould save a great dealof time and materials (especial

proofingis anytypeof_proofingnotdoneon apress;this includes theexposure

based analogsystems and allformsof digitalproofing.

The initial formof_proofingwaspressproofing, which usedthe sameink set

and substrateas thefinal product. Press proofs areconsidered tobethebest method of_predictingthe appearance oftheprintedjob. Press_proofing isnot withoutitsdisadvantages; it isa labor intensive processandplates need tobe made _everytime a proofis made. Ina film based _environment,this means films and plates need tobe made each timea proofistobemade. This is a large amount oftime andmaterialsto waste ina production setting.

Differentpresses are used toproofand_{to print,} "as_tyingup aproduction press for_proofingisnot _economicallyadvisable."2

"All presses are_different, not_only

in _design,butin performance."3 _{Even if}

thedesign oftheproofpress wassimi larto the designofthe flexographicproduction_{press; there} arecertainvariables

such_as, anilox roller and doctor bladecompositions or ages, thatwillprevent

theexact sameresultpress to press.

Inoff-press _analogproofing,a series of exposures are madeto aphotosensitive

material.There aretwocategories ofthis typeof_proof; an_overlayproof and an integralorsingle sheet proof. For _proofingcritical_color,the _{overlay proofing}

systems arenot accurate. This is dueto a_graying effectcaused_by eachsucces

sive color_beinglayed down. With integralproofs, color_layers are laminated to

dot gain on press and one hasadditional dot gainbuiltinto it. Thefilm withthe

additionaldot gainis thenused tomake _{the proof;} ifthedesire isto match the

proofdot sizeto thepress sheet.

The dotgain present inthe midtoneportion ofthe tonescale canbe compensat

ed for inthe _exposingprocess. Michael Brunostates that the polyesterbase on

the3MMatchprint, "actsasa spacerbetween theproof and thesubstrate which produces optical dotgain of about20-24% inthemiddletones. Thisis equivalent

to the mechanical dotgainexperienced inaverage magazine_printing . .

However, the dot gaininthehighlightsofanimageprinted_{by flexography} can

notbeaccounted forin anexposurebased _{analog proofingsystem,}withoutthe

use ofmultiple exposuresand masks or _generatingmultiple films. Themask

insures that thehighlights areexposed _{independently}ofthe rest ofthe image.

Exposingwithout _{the mask,} inan attempttomatch the_highlights, willresultin distortingthe midtonegain this istrue regardlessofwhether apositiveor a

negative system is inuse.

Ifahalftone digital_proofingsystem could_accuratelypredictthehue_(AE), den

sity,dotsize,and_visuallyapproximate aflexographic press _{sheet, then}press proofsor off-press_analogproofs would notberequired-thus _savingvaluable

productiontime andmaterials (platesand film).

operator what_theyneed to know. This is _{especially true in}flexography,the

highlight areas onthe continuous tone proof might_onlybear a slight resem

blance to thehighlights onthe presssheet. This is a problembecausea contract

proof; whichis _legallybinding,issupposed to bean accurate representation of

whatwill come off thepress.

Thereare severalhalftone based digital _proofingsystems onthe markettoday.

Eachuses different _imaging schemes andcolor control varies from systemto

system,buteachonepromises a dot for dotrepresentation of theprinted page.

Two systems were_studied; in the interestof each ofthecompanies investments

-none wereidentified_byeither_companyor_by product name(inthe results section). _Theyinstead were referred toas Digital _Proofing SystemAand B. A brief descriptionof eachis used todifferentiate betweenthe technologies that

driveeach system.Athird systemwasto be studied;butthemanufacturer dropped out oftheproject. Itwaslater determined that the 3M Matchprint

would beused as a referenceandbecame thethird (althoughnot _digital)proof ing system.

This researchinvestigatedthethree systems todeterminetheir_abilityto simu late the reproductionofaflexographic pressrun intermsofhalftone dot_size, density,hue (AE) and invisualappearance.Apressrun was performed ona

polypropylene substrateknown as _Primax,which ismanufactured_byFasson. The results ofthispressrunwere used asthestandard press sheetfor the digital

1 _{Bruno, Michael. Principles}

ofColorProofing. Gama _{Communications,} Salem. 1986. _p 1.

2 _{Sigg, Franz. Personal interviewconducted at RITonNovember 20,} 1995.

3

Bruno, Michael. Principles _ofColorProofing. Gama_{Communications,} Salem. 1986. _p4.

4_Ibid,

Theoretical Basis

Flexography

Flexographyis a direct rotary printingmethod which uses reliefimageplates

made of a photopolymer or rubber. Unlikehard metal_plates; flexo plates are

displaceable. Sincetheprocess isadirect _{rotaryprocess;} for_everyrevolution of

the cylinder animage isproduced. CharlesWeigand said,"the plates are

affix-ableto plate cylinders ofvarious repeat _lengths,inked_bya cell-structured

ink-meteringroll,with orwithout a reverse-angledoctor_blade, and_carryinga fast

dryingfluid ink toplatesthatprintonto_{virtually anysubstrate,} absorbent or

nonabsorbent."1

Flexographyhasthe advantage of_beingabletoprintona _varietyof_substrates;

fromnewsprintto plasticbased filmssuch aspolyethylene. Both spot color and

process color are often used byflexographicprinters. Theprocess is often used

in the _packagingportions of the_printingindustry. In_fact, as Richard Neumann

pointedoutin Flexo & GravureInternational; thepercentage ofpackage print

sists of the following: ₁₎ ink_{fountain, 2)} ink-fountain roller, 3) doctor blade

(unless thepress contains a two-roller system),4) anilox or _ink-metering roller,

5) printingplate_{cylinder, 6)} thedesired substrate, and ₇₎ the impressioncylin der (see fig. ₁₎

fig. 1 flexographicroller system

Theink-fountainroller takes inkfromthe inkfountain _transferringitto the

anilox roller. Theanilox rollhas cellsengravedinto _it, thesize and _frequency of these cells meterthe amount ofinktransferred ontotheplate. Thedoctor blade

is used to scrape off_anyexcess inkontheanilox rollerto insurethata uniform

amountofink istransferred to the_printingplate cylinder. Theamount ofink

transferredto the plateis _directlyrelated to thenumberand type ofcells

engraved intothe roller. The highfrequencycell counts contain_manycells,

whichare smallerin circumferenceand shallower indepthwhencomparedto courser cell counts. The highercell counts are _generallyused for higherfrequen

cy halftone line screens.

Ina two-rollerflexographic system, onewithout adoctorblade,the ink-fountain

roller ₍₂₎ runs slowerthanthe anilox roller _(4);the excess inkis_actually

a doctorbladeis used ornot; the next actionis ink_beingcarriedto theplate then to the desired substrate (6),while_using theimpression roller₍₇₎ to support

thesubstrate.

Flexographic_PrintingPlates. Exposure of platesis a_verycritical processin _flexog

raphy (this is trueof_{any printing process),}so theexposure processwillbe

examinedhere. _Printing plates fortheflexoprocess are madeof either a rubber

or a photopolymer substance. "Rubber platesare _flexible,resilient and havethe

printingimage inrelief."3_These

plates are duplicates madefrom a _matrix,

whichis fromanoriginal patternplate. Thebasicprocedure for_producingrub

berplates is as follows: _{"1) making}master pattern metalengravings or hard

durometerphotopolymer plates_byexposure through aphotographic negative

and_processingby acid_{etching (metals)} orsolvent wash _{(photopolymers),2)}

makinga phenolic matrixmold ofthemaster pattern_plate,3) rubberplate

molding fromthe matrixmold."4

Aphotopolymerisa lightsensitive material, thatis usedin_{many printing}

processes for printingplates, filmsand _proofingmaterials.Photopolymers are

available inboth liquid formand solid sheets intheneeded platethickness. The

procedure for_producingphotopolymer platesis asfollows: _"1)backexposure

ofbase toUV lightto harden_(cure) floorand establish relief_{depth, 2)} face expo

sure ofsurface toUVlightthrough the negative toharden _{(cure) printing}

images,3) washoutin appropriate solventtoremove unexposed polymer and

leave printingimages inrelief,_{4) dry}to remove absorbed solventandrestore

gaugethickness, 5) postexposeto finalcure of floorandcharacter _shoulders,6)

print on_{many different}typesof substrates. However,when _lookingatthe two

leaders; paper and film-based stocks,it appearsthatfilmisbecomingmore _pop

ular. Inthe_July 1995 issueofFlexo,CatherineHeckman cited "requests for film

facestockapplicationshaveincreased more_rapidly than thosefor paper, _averag

ing 15 to20 percentversuspaper growth at8to 10 percent,with thelargest

growth dominated_bythe _{health/beauty}industry."6

FlexographicInks. As withall_printingprocesses_{using inks,} flexographic inks

have three components: _{1) the colorant, 2) the vehicle,}and₃₎ additives. Thecol

orantis theportion oftheink fromwhichit getsitscolor or hue. Thematerial

usedas the colorantis either a dye or apigment; themaindifferencebetween

the two _beingthat dyesare soluble inthevehicle. Thevehicle is a_nearlycolor

less fluid thatis expectedto_carrythe colorantfromthe _inkingsystemto the

substrate. Flexographic inksare fluid inksthat_{dry quickly}between _printingsta

tions on a multicolor press.

Limitations _ofthe Flexographic Process. The biggestproblemin_flexography seems

tobe the highamountofdotgainwhen compared to otherconventional print

ingprocesses. This is duetothe physical_makeup ofthe_{printingplate;} as stated

earlier, the flexographicplate ismade ofrubber or a photopolymer whichcanbe

easily compressed. This compressioniscaused _bythepressurebetweenthe

plate cylinder andthe impression cylinder. The resultis thatthedots are

"squashed"

and print largerthanthefilm dots orthe dotsonthe plate when not

halftone dots are the smallestand will distortto a greaterextent than the

mid-tone and shadow areaswhenexposed toanequal amount of pressure.Aprocess

such as offset_lithographydoesnot encounterthis as DonAlldianstated, "...

conversely, the offset plate is hard or rigid and therefore doesnot experience the

same _squeezingeffect."7

Thisamount ofdotgain_is, ofcourse, inadditionto thenormal amounts of opti

cal andmechanical dotgainassociated with_{any printing}process. _According to

Gary Field, mechanicalorphysical dotgain is"the gain inthe dotarea" and

optical dotgain is _"darkeningofthewhitepaper around thedotcaused _bylight

scatterwithin the substrate."8_The

darkeningthatMr. Fieldrefers tois in regard

to lithography. Optical dot gain will occurregardless ofsubstrate _type, color or

printingprocess.

Anotherconsiderationis imagedistortion dueto plate curvature. All_printing

plates, regardless of construction will distorttheprint tosome extent when

curved around the plate_{cylinder,however,} flexographicplatedistortionis more

noticeable. Inorderto _remedythis situationthe_followingequation couldbe

used:

factor based on platethickness

printed repeatlength = _{percentelongation}

The factor forplatethicknessdiffers _depending onwhetherornottheplate was

separatelymounted to a stickyback or premounted.Stickyback platemountingis done_{by mounting}the_printingplate onto an adhesivestickybackwhichisthen

attached to theplatecylinder. _Premounting theplate or conventional plate

was mounted _{separately, thefactor}is 3.1416 _(n) times twicetheplatethickness.

Ifthe plate wastopremounted the factorwould ben timesthe platethickness. The actual distortioncompensationcould beaccomplished either

photomechan-ically or _{electronically} (onthedesktop).

Trappingis also anissuein flexography. _First,a distinctionneeds tobe made between a prepress _trap and a press trap. Aprepress_trap iswhat usedto be

more_{commonly known}as

"spreading"

and "choking". _"Trapping istheover lapping of variouscolors ina design to preventtheir_separatingas a result of

registration movement_during printing."9

Apress_trap is how well alayer ofinktransfers onto a substrateor another layer

ofink. The_trap thatisaddressedin thisresearchisthe prepresstrap. _Trapping is more critical in flexothan in_lithographyThis isbecause flexopresses gener

ally operate athigherspeeds. "The flexopress, therefore, needstohave addi tionalcolor-to-color tolerancesasopposed to theoffsetpress."10_The

accepted

trap amount in flexo is0.031 (1/32)ofaninch.

There isalso a certain amount of_difficultyin_holding a vignettein thehigh lights. Inother wordsthe _abilityto "taperthesize ofthehighlight dotsuntil

only thebase colorofthesubstrate

shows."11 _Whatthis

means inthe case of a

halftone image is that,therewill bea "cut

off"

in thehighlights. Sincethehigh

light dots are

"squashed"

on_{the plate, they}printlargerthan_they are supposed

to. The_tapering isnot as effective asinlithography, in _flexographythehighlight dots gain to abouta 10-14% dot, thusthere isnot a _taperingtransition from

Proofing

What is a Proof?

Aproof, inthe graphic_arts, is_essentiallya prediction oftheappearance ofthe

final printed product. Thereare severalmethods of_doingthis; one_way is_using

a _printingpressto generate a proof underconditions similarto those thatwould

beused forthefinalprinted product. Anothermethodis offpress _proofing,

which canbeeither _analogordigital. _Analogoff-press proofs are film_based, while digitalproofs donot requirefilm. Whether_analogor _digital,bothutilize tonersor dyesto simulate theinks of a given_printingprocess. Yetanother

method of_proofing iscalled soft_proofing, which_{involves viewing} aCRTcali

brated for a given set of_printingconditions.

A_History in Proofing:

Press Proofing. Theoldestmethod of_proofing is_printingunderconditions _very

closeto those ofthe productionpressrun. Althoughtheclosest method of pre

dictingthe outcome ofthepress_{run, this} approach isnottime ormaterials

AnalogOff-press Proofing. The firstphotomechanical off-press proofwaspro duced_by the United States_{Army during}WorldWarII. This wasan_overlaysys

tem called _Watercote and was oftenused _bymap makers tochecktheir line

work and color. The Watercote system wascreated _by Direct Reproduction Corporation.As experimentswith off-press _proofingsystems continued, _they became more _complex;halftones andprocess colorsbeganto find their_{way into}

color proofing._According to_HarveyT_Holzapple, "halftoneproof[s] in process

colors, _presenting ... an exact statement oftheoriginal separation negatives

thatwill show _exactlywhat _[image] thereis on yourplates."12

The3M_Company introducedthe Color_KeySystemin 1960. Itutilized dyesto

approximate theprocess color inkset. The Color_KeySystem isstill used _today, inorderto checkpage_layout, colorbreaks andthe densitiesof colors. It is _not, however, used tocheckforcolor accuracy.

In _1971, theDuPont_CompanyintroducedtheCromalin_ProofingSystem. Prior

tothis, most customersdemanded actualpress proofs inorder to_{verify final}

films. The Cromalin_proofing systemis a compositeor integralproofin which

colorlayers arelaminated together toform a single sheet. "Becausethe

Cromalin overcame_manyproblems associated withoverlays such as the

grayed whites andtinted highlightsthat resultfrom lightabsorption and reflec tion_amongmultiplelayers of polyester film. Itwas _graduallyaccepted as an

Thesefilm based_proofing systems use light_(generallyUV) exposures to image

onto animage carrier of some _description, onefor eachofthe process colors.

The integral_proofingsystemslike theCromalin ortheMatchprint are often

used as contract proofs inplace ofa pressproof._They are quite accuratein

regardsto halftone dot_size, inkhueand density, aswell as_{visually predicting}

what apress sheetwill look like. Some ofthesesystems proof _directlyonto the

final substrate,while others simulatethe finalsubstrate. These systems were

created tobeused withlithography. _Therefore,their inherentcharacteristics

more_closelymatch alithographic press run. Thiscanposeproblems when_they

areused for flexography.

Today, there are_manyproducts that competeinthe_{analog proofing} circle 3M

Matchprint, Enco _Pressmatch,Fuji_ColorArt, and KodakContractProofarejust

a few. Thecompanies that manufacturethese_proofingsystemshave developed

or are_developing digital_proofingsystems.

Digital Proofing. The initialpurpose ofdigital_proofingwasto emulatethestruc

tureofthe halftonedot; _includingadjustable line _rulings,dot shapes and

rosettes. Thiswas dropped infavorof less_costlycontinuous _{tone methods,}after

several companies lostlargeamountsof_moneyin failed R&D.

During the 1980's,a numberof companies were _working on a new_technology

thatwould_eventually lay thefoundationfor adigital_proofingsystem. In _1987,

DuPontand Xeroxteamed _up toproduce theDX (DuPont_/Xerox) system. _By

justifythe expense of_bringingit to themarket. "It was feltthatif thesystem were not_{rapidlyperfected,} cheaperones [digitalproofs] wouldarrive and

undermine the marketsdesire forhalftonebased digital proofs."14

Meanwhile,the 3M_companyworkedon a digital_{proofingtechnology} and dubbed itthe Digital Matchprint which promisedto _accurately reproduceboth colorand_halftone dots. Other companieshave continuedto explorethe realms

of digital _{proofingincluding; Kodak,} Polaroidand Optronics. "These. . . sys

tems differin theirbasic technologies _rangingfrom Kodak Approval'selec trophotographic engine [author's_{note; the}Approval_actually uses a laser] to Optronics IntelliProofs_imagesettinglaser;but_theyare all_extremelycapable

andhavepricetags thatreflect it $245,000andup."15

Only fairlylarge and

successfulfirms canafford a systemlike this. In _1994, 3Mdiscontinued the

Digital Matchprintproduct _statingthatitwould be too_costlytoupgradethe

product.

AsDuPontand Xerox had feared, othertechnologieshave emerged and lowered the demand for digitalhalftone dots. Two types ofdigitalproofers that are_pop

ular inthe market atthis time are; inkjetand dye sublimation. _Theyrangein price; frominexpensivedesktop office printers tohighpriced proofers,suitable for _advertising agencies anddesign firms.

priced between_$245,000 to_350,000, while production grade continuoustone

inkjets sell for about$40,000 to_125,000; and dyesublimation printers arepriced

between $10,000 to25,000.

Types of Digital Proofers:

Accordingto Dr. Patrick _King(VPof_TechnologyatPolaroid Graphics _Imaging),

digitalproofers canbe dividedinto three categories; ₁₎ digitalcolor_printer,2)

digitalpreprooferand ₃₎ digitalcolorproofers or halftone digitalproofer.A_dig

italcolor printerisbestsuited foran office environment ratherthan ingraphic

arts. _{Xerox, Canon,} andHewlett-Packardare _amongthecompanies involved in

producingcolor printers.

"The four basic technologiesat thislevel of price and_qualityare

ink_jet, laser (electrostatic), thermalwax transferand dye subli

mation. Thesetechnologiesenable themanufactureof low-cost

devicesin volume.

The performance capabilities andspecifications _identifythese

devicesascolor printers. _They can_certainlybe employed for

conceptproofing,butone shouldbe realistic andmaintainthe

lowest level of_qualityexpectations."16

Adigitalpreprooferis amore expensive version of a color printer. Whatthis

means is that the digitalpreproofer_hasa higher degree of control over color

matchinganda moreadvanced color engine. Preproofersusethesame four

dyesublimation and inkjet. Two popularmodels ofpreproofersare the3M

Rainbow andthe Iris3024.

Thermal Wax. ThermalWax proofersutilize colored_ribbons, eitherCMY or

CMYK,to image ontoa special substrate._According to MichaelKieran, the rib

bon is butted against a drum "which has been divided _up intoa grid ofindivid

ually addressablepixels,_typically 300perlinearinch. Eachpixel for a given

colorheats_{up, melting}thewax into thepaper."17

Thermal Waxproofers are_fairly inexpensivebutare slow in_{actually outputting}

a proof. Thedifference between_usingthreeor four ribbonsis _mainlyoneof

speed,butthe CMYK option wouldbe desirable ifalarge amount ofblackis to

be presentin theproof.

Thermal Waxproofers use an _imagingtechnique knownas errordiffusionor

dithering. Conventionalhalftone dots arenot _created,therefore_attemptingto

matcha halftonescreen patternisnot possible. _Theyhavethe _abilitytoproof on

mostlyofficesized _stocks-uptoabout 11"

x _17",but thesesubstrates are made

specifically forthe proofer.

Laser (Electrostatic). Color Electrostatic devices commonlyknown as "color

copiers",aresimilar totheirblack and whitecounterparts; _theybothuse a

pho-toconductorinthe _imagingprocess. "The majordifference [between color and

B&W] is thatfour tonersare _used, one eachforcyan,magenta, yellow,and

Most ofthesedevices use_dithering inorder tocreate theimage;however, when

certainRasterImageProcessors _(RIPs) areused inconjunctionwith thedevice a simulatedhalftonepatterncanbecreated. This halftonepattern should notbe mistaken as thepatternthat willappear on thepresssheet. Most "color

copiers"

can support substrate sizes _up to 11" x 17".

Dye Sublimation. Adye sublimationproofis identified _by rich vibrant colorsthat

arewell suited for compsorscatterproofs. Dye sublimation was the first tech nologytobeadopted_by large advertisingagenciesand designstudios. "Dye sublimationworks with a special set ofdyescarried on a page sizeribbon. Whenwarmed_by theprinthead variable-intensity heat_{source, the} dyes turn to

gas andevaporate from the ribbon. _They thendiffuse into a _speciallycoated thermalactivated paper_(varying inweightfroma _slightlyheavierthanfax paperto actual photographic_{qualitypaper)} and revertto a solid. Differenthues

aredetermined_byheatintensity; withhigher temperatures. . . more dye is applied to thepage . . .sinceup to256 differenttemperature levels are available for eachcolor,it's possibleto obtain_veryprecisecolorcontrol."19

Adyesublimation _proofingsystemlays downa grid of pixels at a _relativelylow

resolution (150to 300 _dpi) butappears as acontinuous toneimage. Dyesubli mation_proofingsystemsare convenient and flexible because_they are able to read,RIP, and process directlyfrom the designer's disk. Theyare also ableto proofon _manysizes ofpaperfrom

8" x

10"

to 11" x17". Most dyesublimation

quality fromthesesystems isbetterthan the_qualityof a colorcopier (laser or

electrostatic _device) or a low-end inkjetproofer. "... beforeabsolute color accu

racy is critical,_they [dyesub] give a good _feeling for how a designis progress

ing, and_theydo socosteffectively"20

Aserious drawbackto these systemsis

thehighcost of consumablesdue to theneed for a specific type of paper.

Inkjet Proofers. Inkjetproofers "range from inexpensive_desktopunitsto those

usedin final stages of_{proofingbyprinters, tradeshops,}publishers and service

bureaus."21 _{Inkjet digital}

proofers are considered themiddle ground ofthe

realm ofdigitalproofing. Animage that isproduced_bya productionlevel

modelresembles a photographinits _{sharpness, clarity}of color and _subtletyof

tone.An inkjetprooferproduces variable size dotsthatare toosmalltobe seen

individually apparent resolutionishigherthanactual resolution. For _example;

300 dotsper inchwould appear as 1200to 1800 dotsperinch.

"Inkjetimages arecreated withmicroscopic dropletsofink _{cyan, magenta,} yel

low,andblack thatare sprayed fromultra finenozzles to formdotsof color on

the page."22_{Thesedots do not}form_conventionalhalftone

dots,therefore these

devices cannot predictdot behaviorsuch as dot gain. Inkjetproofers use

water-based dyesandmost substrates offilm orpapercapable of_absorbingwater

based inks canbeused.

These _proofingsystemsdonot attempt toreproducehalftone dotsor predict

moire. Detailand color is quite consistent_usinginkjetsystems. Theseproofs are

repeata-bility. Althoughthe initial costforan inkjet_proofing system is quitehigh, the

operational andmaintenancecosts are_fairly inexpensive butrequire frequent

cleaning andcalibrationprocedures.

Adigitalcolor prooferor direct digitalcolor_proofer, or more_specifically a

halftone based digitalcolor_proofer, imageshalftone dots onto a substrate in

order tomatchthe dot gain ofa specified_printingcondition. These systems

have_differingamounts of color control.

DigitalHalftone Proofers. Thecurrenthighend digitalproofers are thehalftone

basedsystems. Thesehalftone proofers _accordingtoMac _Byrd, "presentan

accurate representation of whatthepresssheet will look_like,since _theyshow

actualhalftone dots printed inSWOP dye. They're also more consistent. . .

They simulatethe halftonestructureat_extremelyhigh resolutions _(upto2400

dpi)and fine screen rulings _(up to200 lpi)._They alsocontrolscreen anglesand

dot gain,show certaintypes ofmoire', andcalibrate outputtoreflect_many

types ofpaper characteristicsand _printingconditions. _Theycan alsobe lin

earized and calibratedfor a specific deviceprofileor "fingerprint"of aparticu

lar printingpress.

There are a_variety ofdigitalhalftone proofing devices onthe market and_they

do not share acommon_technologybase. Some uselasers toimage the device

specific films or papers. Othersuse laserswithtoners toproof onvarious com

mon typesofsubstrates, and still othershavereplaced inkand tonerwith a _dry

Advantages of _Digital Proofing:

Analogproofing fromthe actualfilms used for_platemakingis a good_proofing

method for _evaluatingthecolors ofthe images and the_qualityand _accuracyof

the separationfilms. _However,it is _very time consuming,labor-intensive and

consumes_costly materials. Itisalso prone toerrorsinherentto itsnature; such

as fluctuations in_{the exposure, thechemistry}and development time, theregis

terofthe separationfilms, and a_varietyof operator errors. _Byreducingsome of

thevariables of the_analog process, digital_proofing isconsideredmore consis

tentandrepeatable fromproofto proof. Because ofitsconsistent _nature,users of

digital_proofingmethods are ableto gain experienceand a more reliable under

standing ofthe_relationship betweenproof and press.

"Because so_manyprintjobs nowremainfilmless until _platemaking . . . digital

proofing seemsan obvious and even_necessary componentoftoday'soverall

creative/productive process.This is especiallytrue when ajob involves several

rounds ofproofing."24

With full-scale computer electronicprepress systems (CEPS), a digitalproofer

can translateRGB files toCMYK, simulateSWOPstandards,incorporate custom

color_setups, and manipulate image data toaccommodatepaper_{characteristics,}

ink types, and specificpressconditions. This also allows theusertocreate

proofsthat can predict a_varietyofconditions apartfrom thedataused topro

ducethe separationfilms, such as differentpress_{configurations,} differentpaper

Another advantage ofdigital_proofingisthetime savedin _sendingjobs from

customer_{to printer,}when thefiles are digital. Theprocess of_making an_analog

proofis _{verylengthy,considering} thetime to RIP, imageset,and process the

film, then tohand registerandexposeeach separation film. It isnowfasterand

easier tofindproblemswith image _quality and placement and color_trapping

withdigitalproofing. Acustomer canlookat numerous rounds ofproofs before

the finalsign-offandbefore_committingthepagetofilm. This can_greatlyallevi

atethe bottleneckatthe RIPand _imagesetter,as wellas reducethefilmcosts.

Withthe sizes available fordigital_{proofers, the}customer isabletoreview com

plete pages with typeandcolorimages in _place, insteadof randomproofs of

eachimage separately. Even thesmaller size_proofingsystems can accommodate

2to4page spreads thatcanbeevaluated as contractproofsand full-sized rough

proofsthatcanbeused tocheck_imposition, general cleanlinessand colorbar

positioning. Once_{again, the ability}tocheck afull page orimpositionfor errors

willreduce the wasteoftimeand materials associated witherrorsfoundintra

ditional _analogmethods.

DotsorNo Dots?

The largest issue in the debateover the _qualityof_analogversus _digital,is

whetherhalftone dots are_necessary ina proof. Traditionally,_analogproofs have

had halftone dotssimilartothosefound onthe press sheet. _Manypeople

believe thatfora digitalprooftobeusedas acontract_proof; it must alsohave

halftone dots similar to thoseonthepresssheet. Others believethatif acontinu

be acceptableas a contractproof. The focusofthis research was onhalftone

based digital_proofing systems; _originallytheauthor feltthat_theywere superior

to the continuous tonesystems. Based on theconclusionsshown in later_chap

ters; thisbeliefhasbeen questioned.

Concerningnewer technologieslike_frequency modulated _screening (FM),

matchingconventionalhalftone patternsisnolonger_necessary,but_matching

the FMdots wouldbe nice. The FMscreenhas a largeramount of dot gain;but,

the _{analog proofing}materials _{(laminates, toners, inks, etc.)} weredeveloped for

the tone reproductioncharacteristics of conventional halftonescreens. The small

size oftheFM dotand the greaternumber ofdotspose problemsfor _analog

proofingsystems. To make an_analogproof of aFMscreened _image,2sets of

filmsare made one toproof and one toprint and _relating theproofto the

printtakes considerabletime, effort and experience. With digital _data, the

proofer can manipulate thestochastic screeninformationtoproof with the same

tonereproductionand dotgain characteristicsas thepress itself.

Limitations of Digital Proofing:

"Digital_{proofing is}somewhatofa problemforus atthemomentbecause there

is reallynoproduct onthe marketthatdoeswhat we need it todo."25 Wewant

all theattributes ofan_analogproofinhalfthetime and athalfthe cost. The

problem is thata _(generally non-halftone_based) digitalproofiscreated _directly

fromthe electronicfile and _onlyprovidesan estimate ofthe informationand the

prob-lemswiththe _imagesetter, outof register films,variances indotdensities from

the _imagingor

processingsystem, variancesin filmemulsion, dirt and scratches

onthe final _films,colorshiftsor moirepatternscaused _byusingdifferentRIP's

for _{generating films} or_{proofs, incorrect linescreening,} and _anyoperator errors.

Anotherconcernwith digital_proofingis that the "connection betweentheproof

andthe film isbroken."26_Files

canbe changed _{purposely (oraccidentally),} after

the finalproofhasbeenchecked andbeforethe films are_{made,creating}a prob

lemwhenthe erroris detected onpress. Thiscanbe alleviated _byrepeated

proofing,proper trafficcontrol ofthe filesand adequate _qualitymanagement of

the final films.

Digital proofing, like all new_{technologies,}struggleswith_gainingrespectand

acceptance notbecauseitis _inferior,butratherit is _very difficulttochangethe

mindsetofthe industry. Press _operators, customersand art _directorshave expe

rience _{reading analog} proofsand _analyzingthe translationof_{type, color,} and

imageryto the press.Ittook timeforpeople to learnto read all ofthevariations

thatcanbepresent within a given _{analog proofing}system andwhenthisnew

technologywasintroduceditwas not understood andconsidered problematic.

As withthe introductionof_analogsystems, digitalsystems will takesometime

to becomemainstreamed. In fact, adigitalproofis better suitedto previewa

final imagebecausethe electronic data canbemanipulated to _actually "finger

print"

the characteristics ofthepress. This offersthe consumer a moreaccurate

resemblanceofthe finalprinted piece. Itwill_simplytake time tobecomemore

The Future of_Digital Proofing:

The futureof digital_{proofing is}based onthe needforcultural changein the

industry andfor manufacturercooperationtoestablish standards to better facili

tate the_technologythat_already exists. "Ifpressescanbe calibrated to anagreed

upon standard . . . thencolor management softwarecould [theoretically] be

usedto matchthe finalpress output"27_In

a _fullycalibrated _{system, the}color on

the designer's screenshould matchthe finalpress output.All printouts,

pre-proof and pre-proof would alsomatch and technicalproblemslike incorrecttrapsor

overprints couldbe marked_bythesoftware. Inthis scenario, jobscould _stay

digitalall the_way toplate orpaper. There wouldno longer be a needfor film or

filmproofs. "Ina film freeworld, a similar_proofing arrangement_{may be}

offeredforplatemakers, where thesame machinewill createbothplates and

proofs . . . platemakervendors

alreadynote theirmachines canbe used to gen

eratefilmto makea traditional

proof." 28

Halftone _Proofing Systems

Thepurposeofthis document isto testthe_ability ofhalftone digitalproofersto

represent a flexographicpress sheet._Therefore, the remainder ofthis document

will concernitselfwithinformationpertinenttothe actual execution ofthe

experiment. Short discussionson each ofthe three_proofingsystems are present

edbelow. The chapterfollowingthis willdealwithworkin the field, this is

The Optronics IntelliProof. The IntelliProofisa device thatiscapable of _producing

both filmandproofs. The IntelliProof is a digital_proofing systemthatresides

withinthe vendors_imagesetter, whichisan external drumcolor laserimageset

ter.

Accordingto the vendor, "TheIntelliProofalso increasesthe levelof_certainty in

digitalproofing. Unlikesomedigital_proofing deviceswhich simulate halftone

dots,the IntelliProof employsthesame _screeningalgorithms toproduce the dot

as the ColorSetter _{(imagesetter)} uses to produce film. As such, theIntelliProof

matches the actual dotrather than_{emulatingit, producing}a proofinwhich pre

press professionals can haveconfidence."29

TheIntelliProofis thefirstDirect Color_Proofingsystemthatutilizes thesame

colorlaser imagesetter in theproductionofboth separationfilm and large-for

mat, full-colorproofs withlasergeneratedhalftone dots. _"Bytakingadvantage

ofthe samelaser imaging, rasterimage _processor, 2000or 4000dpi _resolution,

andhalftone_screening technologiesused_bythe ColorSetterto image filmsepa

rations, theIntelliProofsystem_presently provides the_onlyalldigital means

available to_closelypredicthow aPostScript jobwillbeprinted on a four-color

press."30

Redand greenheliumneon laserswere added to the standard_blue argonion

used inthe ColorSetter. The greenheliumneon laser is formed_by

modulating

the signalofthenormal redheliumneon. Theargonion laseris used to image

pro-ducecyan,magenta, and yellowhalftonedots respectively. Theblack halftone

dots are produced_by allthree lasers_actingtogether.

Konica, a _leadingmanufacturer ofphotographic supplieshas produced a photo

sensitive paper thatapproximates a coated sheet. _According toa Product

Managerat_{Optronics, they}didnot_initiallyintend on_usingthe IntelliProofas a

device for_producingcontractproofs. However, _manyoftheircustomers have

beensuccessful in _utilizingtheproofs as contractproofsfor theircustomers.

Thissuccess hasbeen_partlyattributed to the gooddesign ofthe photopaper.

Proofs canbeoutput_{automatically}toa special lighttightcassette or _directlyto

a user supplied or optional in-lineprocessor. "A_varietyof color_controls, are

alsosupportedto ensurecolor _{consistency from}proofto finishedproduct,

includingreferences toSWOP/GAAstandards, aswellas adjustable dot gain

controls to ensure thatthehalftone dotsintheproofare_{substantially}the same

size asthehalftone dots created_bythe_printing process."31 _Look

up tables

(LUTs) areused to interpolatethelook of_{many widely}used and accepted con

ventional _{(analogproofing} systems).

The Kodak Approval. The Kodak Approval is a devicethatoutputs screened

halftone proofs imageddirectly ontothesubstratethatwouldbe used forthe

press run. Thissubstrate, at thispoint in_time,is restrictedto paperthatis

between 30#-110#stockand between and inthickness.

The systemalso allows forcontrol ofdotgainfrom 3%-97% in 1%_increments,

choose from five_differentscreen_shapes, andcontrol of solid _densityofthe col

orant; all in aneffortto attemptto match a set of_printingconditions.

Accordingto the _{vendor, "CMYK} donormaterials arebroughtintocontact with

the intermediate receiverand are _digitallyexposed _bya thermallaser."32Color

dyes arethen transferredto the intermediateas halftone dotsorline work. The

intermediate isloaded ontothe drum and doesnotchangepositionforthe

entire _proofingprocess.

"Thethermal lasertransferscolordyes fromeach donorto the receiverinthe

exact amounts neededto reproduce pixelsat 1800dpi."33The donor materials

utilized_by the KodakApprovalare advertised as _beingcloselymatchedto

SWOPorISOcolorants.

In_{early 1996,} Kodakannounced theApprovalPS whichis PostScript driven

ratherthanDolev drivenasithasbeeninthe past.This eliminatestheneed for

a Scitexsystem andbringstheApprovalinto the_desktop environment. _{The PS} versionwastheversionused forthis research project.

The Polaroid_DryTech. The Polaroid_DryTech is unique_amongthe threesystems

researched inthatituses dried printinginksas itscolorant. The _printinginks

are then transferred _utilizing a laserto thesubstrate. The_proofingsubstrateis

the _generallythesameas the_{final printing}substrate this should alsoinclude

The system also includestheoption ofcustomcolors;which wouldhelpout

greatlywhen

attempting to matchspotcolors on packaging. Sincenot all ofthe

other proofers havethe _abilityto usecustomcolors (mostdigital proofing sys

temsuseCMY orCMYK _colorants)this pointwillnotbeaddressed in the

research andpressrun.

Digital _proofing isa link _{for direct-to-plate}and direct-to-print technology,thisis

especiallytrue inthe case oftheIntelliProof. If thevendors platesetterwas

equipped withthe IntelliProof itwould endtheneed forfilm; and thesame

imagesetterwould beused, _usingthesame files,_using thesameRIPto image

both the color proof and the_printingplate.

Film_{has already}beeneliminated inthe gravure_printingprocess and similar

technologycanbe used toeliminate theneed forfilminother processes. Inthis

environment, digital proofingwillbe the_only practicalalternativeto press

proofing becausethere wouldbeno sense in_taking anelectronic _file,making

analog films for proofingand returningtoelectronic data forprinting. Digital

technologyisalsomuchmore compatible withnew_screeningtechnologies and

itiseasier tomanipulate digitaldatatoemulate other "untraditional" prepress

and _printingconditions.

Finally,itseems the standards ofthegraphic arts _industryare changing. _Quality

colorreproductionand_printingwasonce much lessaccessible_by thecommon

market. Withtechnology becomingmore "user

friendly"

and the reductionin

"All jobsare not equal in importanceand therefore,all do not requirethesame

level of_monitoring andpreviewprior to_printing ... asconfidencebuilds inour

collective _ability to"read" digital _proofs, customers willbe _{increasinglywilling}

Endnotes for Chapter 2

1

Siconofli, Frank. Flexography:Practicesand Principles.

FoundationofFlexographic TechnicalAssociation,

Ronkonkoma. 1991. _p 4.

2

Neumann, Richard. "Flexography-the Print Process ofthe Future for the Packaging Industry". Flexo & Gravure International. _January 1995. _p 7.

3

Siconofli,Frank. Flexography: PracticesandPrinciples.

FoundationofFlexographicTechnical_Association,

Ronkonkoma. 1991. _p 104.

4 _Ibid,

p 104.

5 _Ibid,

p 104-105.

6 _{Heckman, Catherine. "Film Facestock} Update"

Flexo, July 1995. _p 24.

7

Alldian, Don. "OffsettoFlexo" Flexo, March 1995. _p 164.

8_{Field, Gary. Color}andIts Reproduction.

Graphic ArtsTechnicalFoundation,Pittsburgh. 1992. _p 338.

9

Alldian, Don. "OffsettoFlexo" Flexo, March 1995. _p 167.

10_Ibid,

p 167.

11 _Siconofli, Frank. Flexography:Practices andPrinciples. Foundation ofFlexographic TechnicalAssociation,

12

Hogg,Charles. "DirectDigital ColorProofing"

ElectronicPrepress Section_{ofPIA., Alexandria,} VA. 1994. _p 8.

13_Ibid,

p 9.

14_Ibid,

p 10.

15_Ibid,

p 10.

16

King,Patrick. _"ProofingTechnologies forFlexography"

Flexo, March 1995. _p 146.

17

Kieran,Michael. _{UnderstandingDesktop} Color. Peachpit_Press, Berkeley. 1994. _p447.

18_Ibid,

p 453.

19

Hogg,Charles. "Direct Digital ColorProofing"

ElectronicPrepress Section ofPIA., Alexandria,VA. 1994. _p 14.

20

Byrd,Mac. "Direct Digital Proofing" Pre, _May/June, 1994. _p46.

21

Abraham, Matthew. Personal interview conducted atRIT in_January of 1995.

22

Hogg,Charles. "Direct DigitalColorProofing"

Electronic Prepress Section ofPIA., Alexandria, VA. 1994. _p 16.

23

Byrd, Mac. "Direct Digital Proofing" Pre, May/June, 1994. _p46.

24

Hogg, Charles. "Direct Digital ColorProofing"

Electronic Prepress Section ofPIA., Alexandria, VA. 1994. _p 11.

25

Hogers,Hans. "TheDigital Proof"

26

Hogg, Charles. "DirectDigitalColorProofing"

Electronic Prepress Section _{ofPIA., Alexandria,}VA. 1994. _p 15.

27

Hogers, Hans. "The Digital Proof" Canadian Printer. April 1994. _p 25.

28_Ibid,

p 25.

29 _{Optronics Product Literature.} "Intelliproof"

Optronics: An IntergraphDivision. 1994.

30 _{Ibid. 1994.}

31_{Ibid. 1994.}

32_{Kodak ProductLiterature.} "Approval"

EastmanKodak Company. 1993.

33_{Ibid. 1993.}

34

Hogg, Charles. "Direct Digital ColorProofing"

Chapter 3

A Review of the Literature

Flexography: Principles andPractices

The_book, Flexography: Principles and_Practices, isfull ofinformationconcern

ing everyfacet ofthe flexographic process, from artgenerationto inkformula

tions,press specifications to_convertinginformationfor packaging. The book

refers tobothpress and off-press_proofingmethods insome detail,off-press

proofing is whatis of concern at this point. Below isa quote_concerningproof

ing,in general, forthe flexographicprocess.

"Traditionalproblemsin_proofing for_flexographyhaven't

been in editorial orgraphics contentbutinimage quality. This

is _especially truein_proofingprocesscolor. The objectivehere

is tohave a proofthat_visuallymatches_printingfrom thepro

ductionpress. _Proofingimage_quality requires_simulating

[press] imagequality. To obtain avisualmatch of a proofto productionpress requires _matchingthevariablesthataffect

color reproduction. Allthesevariables canbeclassified under

three headings: _{hue, density} and dotsize. Ifwe can match

thesevariables inthe proofto theproductionpress,we can

obtain a visual match to theproductionpress."1

Thebooknext discussesthe problemswith off-press_proofing methods;_citing

simu-late offsetprinting."2

This means thateven ifthere isa hueand _densitymatch to

flexography, a _{conventionaloff-press}

proofingsystem will notbe ableto mimic

the dot gain of_{flexography-atleast notwithout}

alteringtheproofingoperation.

Althoughthere are ways of_dealing with_this;such as _givingdifferentexposures

usingmasks or_by

changing thedotsizes in_Photoshop, this istime _consuming

andwasteful. _Creating a _{photographic maskin ordertoexpose areas}

selectively

isno smalltask._Altering the dot sizesin _Photoshop

usingthe transfercurve

functionis _{easy enough,}butrequiresthat two setsoffilms be output. _Changing

the dotsizesin_Photoshop, is similartowhatdigital proofing devices allowthe

userto do to matcha given set of_printingconditions-butdigital_{proofing does}

not requirean extra setoffilms.

Understanding Desktop Color

This is an excellent reference for anyoneinterested indigitalprepress;itcovers

theentire spectrumofelectronic _imaging devices usedinthe graphic arts _today

Theauthor Michael Kierancovers quite abit information_{concerning digital}

proofing.

Mr. Kieran identifieshalftone based digital proofers aselectrophotographic

printers, and says of_them, "... their output consistsof_{halftone dots exactly like}

those onthe printed sheet.Inthisrespect_they are closerthan_{any digital}printer

to traditionalfilmproofs."3_{He then}

goes onto mentionthata_bigpayoffisthat

DigitalProofs. Kierangoes onto statethat digitalproofs arebotha

"challenge'

andan "opportunity".

"Thechallenge isin _learning to interpret_{them properly, especially}

with_cheap pre-proofs fromthermalwaxprintersor intermediate

proofs produced ondyesublimation_printers, ratherthanwith con tractdigitalproofs created on_{more expensive ink jet}or electrophoto

graphic printers.

The _opportunitycomes fromthe factthatdigitalproofsallow youto

create_{workingcomposites,} or_comps, priorto_{plotting film,}which

resultsin significant_{savings, especially}ifyou end_{up making}changes to thejob priorto _going topress. After_all, if_reviewinga filmproof

leadsyou to decideto make _changes,you end_{up throwingaway both}

the proof andfourpieces of film.With digitalproofing, you still toss

awaythe proof, butno film isproduced untilyou're confident (based

onthe digital_proof) that_everythinglooks right."4

Limitations _ofdigital proofs. Kieranlists some"potential

pitfalls"

of digitalproof

ing, the onemostimportant for halftone based digital_proofing systemsiswhere

andhowthe filesare ripped. Hestates, "... becausethe rasterimage processor

used to createthe _{film is usually different}than thatused to createthe _{proof, the}

screen angles,screen _frequencies,and dot shape can _{vary between film}and

proof. . Kierangoes ontosay thatthiscould result inundesirable effects such

asundetected moire patterns and color shifts.

Where's thedot? Thelast portionofKieran's discussionondigital_proofingis

concerned with whetherornothalftone dotsare _necessaryin acontract proof.

His decision is thathalftone dots are necessary.Kieran states thatmost digital

acommercial printer's standpoint. _"The results [froma non-halftone _proofer]

may lookgood,butareoflittleuse to the pressoperator,who makes assess

ments of_quality noton subjective groundsbutonhow closely thehalftone dots

on the press sheet match thoseontheproof."6

Electronic_{Proofing Technologies for}

Flexography

This is an article written_by Dr. Patrick_King, that appeared intheMarch 1995

issueof_Flexo magazine. Dr. _Kingbegins_byquotingBritishphilosopherJohn

MichaelOsbourne's_piece, The Road to _Nowhere, as anexampleof a prevalent

feelingmanypeoplehave regarding digitalproofing.

Dr. _King statesthat_analogor exposure film-based proofing systems competefor

the marketshare_byclaimingto _effectively mimicthepress sheets ofa _printing

process. He then _flatlystates _that, "the fact is_theycan never_preciselysimulate a

press _{sheet,particularly for} all flexographicneeds."7

On the subject ofdigital_proofing, Dr. _King feelsthat the initialexpectation ofa

digital _proofingsystem is thatitwould offerthe sametype of control overthe

imageasimagesetters do. "Thisisa naturalassumption,since _theyare often

drivenoffthe sameterminalas animagesetter. Theoretically, thisassumption is

correct, but in_realitymostDDCP [direct-digital color_proofing] systemslimit

the operators _abilityto replicate thepress sheetprecisely"8

This isablanket

statement, obviouslythe halftonebased systemsallow formorecontrolthan

Onthe topic ofhalftone _dots, Dr. _Kinghas this to _sayaboutnon-halftonebased

proofing systems:

"Most dyesublimation systems donot create dotsbutrather

color_{using dyes imaged}atvariousdensities. Inkjetand

laser-based _proofingsystems _generallycreate spots _(typically300

dpi) whoseshapes do not even_closelymatchthedots on a

press sheet._Thermalwax transfer systemsform images_using

extremelycourse,_fuzzyaddresses ofcolorthat shouldnot even

be construed asdots ... thevast

majorityof DDCPsystemsdo

not possess sufficient control over the tonereproductioncurve

to_{be accurately fingerprinted} toan offset_press, letalonea

flexo press."9

The Ideal DDCP. Dr. _Kingexplains thathe feelsthat there are certainfunctions

that the ideal digital_proofing systemshould have: anopen architecturesystem;

sufficienttonecurve control tomimic a_printingsystem (this includes midtone

control to simulate dotgain for_lithography orhighlightcontrolto simulate dot

gain in flexography); itshould produce dots of_manyscreen_{rulings, shapes,} or

type (AMorFM). "Thereshouldbenocompromise."10

Controlof thecolorant_density isalso importantbecause differentprocesses will

have _differing amounts ofsolid density,evenpresseswithinthesame_printing

process are subjectto _{slightly different} solidinkdensities.Also, controlofthe

actual colordata (CIELab) is desirable because a magentaink in flexography