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Ifra1 sp ecial Report 2.23 - WAN-IFRA

1. Other Using a third party colour engine e g Linotype Hell Kodak Other e g using Photoshop Viewing conditions Preferred environmental illumination Maximum and minimum illuminance e g 10 40 lux Max Min Colour temperature Kelvin Type of lamps Other environmental factors Painting of walls and ceiling Monitor outlook Framing Colour Is a special viewing light booth needed in the calibration and operation of the system Booth size Illumination control colour temperature illuminance level Colour Brightness Viewing geometry monitor booth Monitor Booth Measurement of illumination Page description formats accepted as input PostScript Portable Document Format pdf TIFF IT Other formats 28 IFRA Darmstadt Input devices of final pages to the system Device type Imagesetter PostScript RIP Facsimile equipment Film plate scanner Web inspection cameras Other Colour space of input device CMYK RGB CIE Other Resolution delivered by input device Pixels in x direction Pixels in y direction Colour accuracy bits pixel Other information delivered by input device Product identification product name edition printing location other Page identification page number
2. separation Coding of identification physical bar code etc digital e g CIP3 IFRA Darmstadt 29 Workflow and working practices Which personnel uses the system Editor Prepress Platemaker Press operator Advertiser Other Where is the equipment used Editorial department Repro Fax receiver Plate making Press room Signing of the monitor proof Who does it How is it arranged How are comments marked on the proof Page visualising software Operating system Windows Windows 95 Windows NT Macintosh Unix Standard visualising program Adobe Photoshop Adobe PageMaker Quark Xpress Other Proprietary visualising program SS GG me fen 2 ve 30 IFRA Darmstadt Visualising properties Thumbnails CMYK components separately Product categories editions history Production tracking data Other Auxiliary properties Calculation of ink settings of printing press Other Support of hardcopy devices list below ok Usability Ink and paper settings By changing colour settings in software By editing the colour profile By recharacterisatio
3. Marking of comments on the proof 7 Usability Yes text and voice Only mouse no keyboard Human interaction mode Ink and paper settings Under development Only mouse no keyboard By changing colour settings in software By recharacterisation printing test sheet Yes Yes Yes System speed fastest response time 1 9 seconds 1 4 seconds 2 seconds 1 2 seconds Peak production max pages products No limitation No limitation 400 pages No limitation 100 products On line help Yes also helpline No Number of language versions of user manual Table Id Comparison of page visualisation software and usability The colour gamut of the systems is evaluated from the graph in figure 9 It can be seen that the Para visual and PRIMA gamut covers almost all the print ing colours whereas Pagevision has a slightly smaller gamut Table 2 lists the strengths and weaknesses ofthe commer cial proofing systems The factors distinguighing the sys tems from one another are stressed not the c mmon ones As can be seen the choice of the Barco monitor puts the PRIMA system in the forefront with regard to the moni tor On the other hand this monitor is the most expensive one The spatial uniformity compensation used by the Sony monitor in the Paravisual system is a clear strength The gamut of the Sony is also as wide as that of Barco Pagevision uses a monitor wi
4. the application 3 6 Input devices of final pages to the system The monitor proofing systems used in newspapers should show the final page after it has been put together The information needed for the monitor proofing includes visual information on the appearance of the final pages the page image as well as product and page identifi cation information Page information is accessible from several places across the production chain see figure 8 3 6 1 Imagesetter The RIP unit takes the PostScript data and converts it into bitmaps for outputting The RIP is often integrated into the local Imagesetter A convenient way to get the monitor proofing information is to utilise the ripped pixel maps that some RIP imagesetter combinations pro vide b 3 6 2 PostScript A pixel map is not available from all output devices In this case the only way is to use a parallel RIP that sim ulates the functions of the real RIP a The problem is that abnormalities for example missing fonts in the real ripping are not necessarily simulated The handling of parallel page versions is also a bit cumbersome The simulating RIP can also be a considerable cost factor A low cost solution is to convert PostScript into the Acrobat page description language pdf which is soft ripped as a part of the viewing operation in the Acrobat Reader or Acrobat Exchange The pdf page format can also drive the production RIP because more an
5. able to handle additional colour separations in addition to the conventional CMYK proc ess separations In the coldur transforms special notice has be paid to reproduce critical spot colours more accu rately than the average process colours There should be possibilities to easily simulate paper and ink changes by changing parameters in the software It should be possible to view the pages in detail even down to the screening structure The product identifications should cover all distinctions needed by the editorial and production personnel Han dling of the Acrobat data format should be included Annotations to the proofs both as text and voice should be possible The annotation tools should include proce dures for signing Current systems which start at a price of about 30 000 do not include facilities like light booths enabling 23 controlled viewing conditions Even if the user can ar range such conditions the solutions should be an integral part of the proofing system Further more an integration with the various production control systems of the news paper is needed This would enable utilisation of produc tion information attached to the digital page file like in 8 References Barco Reference Calibrator Product brochure 12 pp Bar Berns 93 Berns R S Motta M J Gorzynski M E CRT Colorimetry Colour Research and Application Vol 18 Num 5 Oct 1993 pp 299 325 Bas 95 Bassemir R
6. bits RGB channel Bits Refresh rate e g 80 Hz noninterlaced Hz Interlaced Noninterl Maximum brightness candela m2 Candela m Electromagnetic emissions MPRII and TCO standards Proofing properties Contrast ratio luminance of black paper white Colour gamut of the monitor CIEXYZ Red primary X Y Z Green primary X Y Z Blue primary X Y Z Monitor white point X Y Z Warm up period e g 4 hours Hours Estimated lifetime e g white page hours Hours Colour consistency over time and between monitors e g AH AE ab Manually adjustable settings parameters colour temperature Screen finish antireflecting properties Calibration procedure Calibration measurement device colorimeter spectrophotometer Colorimetric Spectrophot Measured units luminance phosphor characteristics ambient light Calibration interval e g every 200 hour of usage Hours Adjustment method analogue digital inside the graphic board Analogue Digital Tools for aligning several monitors e g by a common measurement method Automatic calibration stabilisation Continuously user triggered 26 IFRA Darmstadt Colour matching methods used by the system Default Colour Management System OS CMS Proprietary Default Proprietary How is the printing process profiled characterization Customized CMS profile by measuring test print CMS ICC standard propriet
7. correct colours In USA CGATS Committee for Graphic Arts Technology Standards has chosen Acrobat as the transfer format for advertisements Dun 96 The embedding of the pdf technology in monitor proofing systems has still to be done Even if there are common features for example thumbnails the Acrobat Reader must be considerably extended to include the layout and retrieval features of current page monitor proofing sys tems In spite of these difficulties such systems are likely 13 to emerge over the next years as the popularity of the pdf format continues to grow 3 5 3 TIFF IT TIFF IT is a format for ripped bitmaps that RIPs or CEPS repro systems produce The format is based on the com mon TIFF Tagged Image File Format It was initiated in USA by DDAP Digital Distribution of Advertising for Publications and standardised by the American standard isation body ANSI Its main use is in the digital distribu tion of advertisements Even if it is an open question how successful this format will be it is beneficial for a mon itor proofing system to be able to handle it 3 5 4 Other formats Current monitor proofing systems use a mix of standard formats and proprietary page image formats In addition to TIFF TGA initially a format of Truevision and Mi crosoft s BMP are common image formats The proofing systems typically use modifications of the standard for mats that make it difficult to export the images outside of
8. deliver the page information as a set of monochrome colour separated images Cyan C Magenta M Yellow Y and Black K Key The number of separations can be one black and white page two black one process colour three black two process colours or four CMYK colour page In addition there is a clear need for the soft proof ing systems to handle spot colours that are not printed with the standard CMYK colour inks IFRA 90 Howev er none of the systems currently on the market can handle these real spot colours PostScript source a in figure 8 is the only source that is able to deliver the images in another colour space than CMYK PostScript Level 2 and 3 support CIE spaces and therefore device independent colour 3 6 7 Resolution delivered by input device The spatial resolution varies from about 400 x 600 pixels from certain plate scanners up to thousand of pixels per side from RIP units The RIPs convert the v ctor graphics text line art into pixel maps of an arbitrary resolution The facsimile equipment delivers screened bitmaps whose resolution decreases in the conversion to grey level pixels Typically the conversion averages binary areas of the size of 8 x 8 dots or 16 x 16 dots causing the spatial resolution to decrease correspondingly The colour resolution also called pixel depth varies from I bit per pixel of the screened bit maps up to the usual IFRA Darmstadt 8 bit pixel per colour
9. have reacted very positively to the system The viewing environment is set to 5000 Kelvin The light ing is sufficient for simultaneous viewing of monitor and print but not too bright in order to avoid reflection from the monitor screen Diffuse light and a cap covering the O IFRA Darmstadt upper edge of the monitor reduces reflections The walls and ceilings are painted in a neutral grey At the moment only page fax input is in use but in the future more input devices will be considered as well as new data formats like pdf No signing of monitor proofs is used or planned Signing requires that the elements are available early enough before printing starts which is not the case with page proofs The user interface is very good but the system mainte nance is a bit difficult in its current version A weakness is that spot colours are not handled in the system The measurement of spot colours with densitometers is diffi cult as well as their analogue proofing Therefore monitor spot colour proofing is required 6 4 Berlingske Tidende ParaVisual Manager Eric Christensen Berlingske Tidende publishes three newspapers the daily broadsheet Berlingske Tidende the tabloid BT and the weekly edition Weekend Avisen Parascan WYDNET formerly a Crosfield product transmits the pages from the editorial department in the centre of Copenhagen to one printing plant in southern Copenhagen and to another one in Jylland S x ParaVisual
10. printing process profile is more complex and typical ly contains a LUT with up to a thousand entries obtained by measurements of as many CMYK patches as are on a test print chart The test print chart may be standard such as ISO 12642 or proprietary A spectrophotometer robot reduces the workload of measuring such an amount of patches The CMS software may include default profiles repre senting the device under factory calibrated conditions When used in practice the device may deviate from these conditions and therefore requires a customised CMS profile obtained through repeated calibration Especially an unstable newspaper offset printing process needs a quick and fluent recalibration which ideally demands remeasuring only a part of the about 1000 colour patches on the test print In customisation special profile editors can be useful 3 3 1 Matching the colour spaces of monitor and print The colour matching that is gamut mapping is performed according to three methods 1 Using the colour engine of the operating system Mac intosh ColorSync 2 Windows 95 ICM 2 Using a third party colour engine for example from Linotype Hell Kodak 3 Other for example using Photoshop The main task of a colour engine called CMM in the terminology of the ICC is to perform a transformation between colour spaces Colour engines should preferably parse third party standard profiles and choose so called rendering intents ICC The
11. provide a more accurate colour signature of the monitor However spectrophotometers are normally more expen sive than colorimeters Even spectrophotometers do not guarantee accurate results if they do not sample the spec trum accurately enough Especially the red phosphor re flection spectrum is very irregular As a recommendation use moderately priced colorimeters with accurate CIE defined filters if you only measure monitors Consider spectrophotometers if you want to profile both the mon itor and the printing process with the same measuring device A typical calibration interval is reached after 200 hours of usage A too short interval will in practice lead to over looking of the procedure The RGB values are adjusted either analogically after the D A conversion or digitally inside the display control board before the D A conver sion takes place The latter reduces to the dynamic range of the picture In soft proofing systems the basic procedure to character ise the monitor with a colorimeter or a spectrophotometer includes several steps Berns 93 A user friendly system should perform most of these operations automatically Most high class monitors have an automatic continuous calibration The beam intensity is continuously measured and the measurements control the current status of the beam cathode beam current feed back This has a signif icant stabilising effect because monitors tend to fluctuate at least with their
12. the press control system enables an automatic display of the page for which the ink settings are prepared newspaper production IFRA Special Report 6 19 Darmstadt 1995 26 pp IFRA 94 IFRA Colour Quality Club Evaluation 1994 The production of spot colours in news papers from process colours IFRA Special Report 3 13 Darmstadt 1990 36 pp IFRA 90 ISO 75a ISO 2846 1975 Set of Printing Inks for Offset Printing Colorimetric Characteristics 5 pages ISO 75b ISO 3664 1975 Photography Illumination Conditions For Viewing Colour Transparencies and Their Reproductions 4 pp Joh 95 Johnson T A Complete Colour Reproduction Model for Graphic Arts TAGA Proceedings 1995 vol 2 Rochester New York pp 1061 1076 Kon 95 Konrak Helm J Colour proofing Is it real or an illusion Newspaper amp Technology April 1995 I p Mael 97 Joel Maelfeyt personal communication February 1997 Par Parascan System ParaVisual product brochure 4 p www inforamp net poynton poynton inforamp net ee Pre 95 PressScript Version 1 0 Draft Language Specification RIT Research Corporation June 21 1995 16 pp Rosenberg A Reasons and Ways for the Revision of the International Standard for Four Colour Offset Printing TAGA Proceedings 1994 Rochester New York Ros 94 Sch 96 Schl pfer K Widmer E How to Test a Colour Management System TAGA 96 IFRA Darms
13. Costello G DiBernardo A DiPiazza J Kuna D Paulius K Rybny C Zawacki W A Comparison of Visual and Spectrophotometric Evaluations of Paired Colour Prints The 1995 TAGA Proceedings Vol I Rochester New York pp 558 578 CIE 96 Expert Symposium 96 Colour Standards for Image Technology Dat Data Oy Presetting measurement and page previewing Product brochure 4 pp Dau 95 Daun S Lucas G Sch nhut J Specification of the CIP3 Print Production Format Version 1 0 International Cooperation for Integration of Prepress Press and Postpress Fraunhofer IGD May 1995 39 pp Appendices Dun 96 Dunn Report Volume 14 Number 3 1996 GAT 96 GATF and R R Donelley amp Sons Apply for Patent for Flat Panel Display for Colour Proofing System GATF News Release March 1996 4 pp ICC ICC Profile Format Specification Version 3 2 November 20 1995 International Colour Consortium t 4 Colour Management Systems TFRA Special Report 2 18 June 1996 20 pages IFRA 96 IFR 95a IFRA newspaper techniques Special issue on colour management March 1995 IFRAtrack a recommendation for the interchange of status information between local and global tracking systems in IFR 95b 24 Poynton the emerging CIP3 standard as well as visualising proc ess tracking information like IFRAtrack Information about the expected job structure can then be shown to the user Integration with
14. MA only interfaces to a RIP PRIMA acquires job identifica tion information needed in retrieval fairly extensively even if there are clear weaknesses Print location and dates are missing in Paravisual and ProofNet whereas Pagevision does not make a distinction between different dates production publishing Only ProofNet and Pagevision read physical coding from film respectively plate I The ProofNet and the Pagevision software ar multi plat form as they run on both Windows and Macintosh Par avisual and Pagevision calculate the ink settings for the press PRIMA is the only to offer annotation capabilities like text and voice PRIMA also compares received and expected values by using a link to the job management system As regards usability the systems are easily oper ated solely by mouse Paravisual and Aqua Four have the fastest response time Pagevision offers its manual in most languages IFRA Darmstadt Pagevision PRIMA Paravisual Newspaper D50 Paravisual white Pagevision white 0 Jn mem 0 0 1 0 2 0 3 0 4 Figure 9 The colour gamut of three soft proofing systems in the CIE xy space 21 6 Practical experiences and advices Expert users from the following newspapers have been interviewed to give practical experiences of soft proofing systems Helsingin Sanomat FIN Aftonbladet S Los Angeles Times USA Berlingske Tidende DK 6 1 The Helsing
15. ain at many newspapers in order to provide ink con sumption information for presetting the ink keys of the press These scanners can fairly easily be modified to provide also image data for proofing purposes The proof ing system scans the films or printing plates as mono chrome images and combines them into colour images The combination handles the shifting and rotations be tween the separations This is because the films or plates do not pass the scanner at exactly the same positions or at an identical orientation The system reads the page iden tification from the codes included on the film or plate possibly through the press management system 3 6 5 Web inspection cameras The last phase to obtain page information is by imaging the running printed web with cameras f Web video and register density control systems have been on the market for some years for quality control In theory these imag ing devices could deliver information for proofing In practice many technical problems must be solved before on line imagers may provide sufficient geometrical and accurate colour information for proofing An on line proof could complement the proofs obtained from the sources a e On the contrary soft proofs could guide the camera of a web inspection system S d 96 With this concept a closed loop control based on prepress information would be achieved 3 6 6 Colour space of input device Currently the input devices listed above
16. ally missing pages inter change of pages wrong pairing of tabloid pages shift ing of pages At present Aftonbladet sees no need for any closer colour matching between screen and print because the colour quality is not checked at the sending site The resolution of Pagevision is not sufficient for reading normal text but this is not considered to be any problem either Pagevision is not meant for proof reading 6 3 Los Angeles Times ParaVisual Quality director Niko Ruokosuo Paravisual viewing stations are installed at all press con trol points 15 monitors in all plate preparation depart ments 3 stations in three printing plants in all repro departments 3 stations and in the editorial department Los Angeles Times developed a Photoshop based colour matching scheme in co operation with Parascan The de veloped matching scheme is now part of the Paravisual system EE Before the Paravisual system was installed the operators at Los Angeles Times proofed all colour pages in all printing plants which required a lot of labour and mate rial Material costs alone were tens of thousands dollars a year With Paravisual physical proofs are made only in the repro departments The printing plants get the monitor proofs immediately after the fax transmission that is before the printing starts The press operators can famil iarise themselves with the pages in advance which makes the printing process easier The users
17. an information source In some cases ripping and transmission errors have been detected from the soft proof The risk of ripping errors has grown since advertisements are arrivirig from many sources in digital form Also intermixing of colour sepa rations because of erroneous or missing bar codes have been detected at the Pagevision system 6 2 Aftonbladet Pagevision Technical expert Pierre Gunnarsson The evening tabloid Aftonbladet with its numerous sup plements and editions is transmitted to 5 satellite printing 22 plants situated around Sweden through the WydNet trans mission system Aftonbladet uses Pagevision in the edito rial department in Globen in Stockholm to manage the complex transmission operation The system has two viewing stations situated close to each other In addition to the WydNet interface the system is interfaced to a RIP feeding a separate network for transmission of magazines to gravure printing plants The production managers use Pagevision to check that correct pages go to the right printing plants The check takes place before but also after the transmission The high transmission speed page per 20 seconds makes it impossible to check everything in advance However Pagevision makes it easier for the editorial personnel to discuss the quality of the films that the plant operators observe to be erroneous Pagevision detects errors like missing page elements missing images wrong or tot
18. ary ICC Proprictary Type of test print ISO ANSI standard own other Standard Own Other Number of colour patches on test print Number of reference points used by interpolation of final values Measuring device and accuracy Average AE pp Device AE op How often is the measurement repeated profile maintenance Hours How many patches have to be measured in maintaining the profile Software program used e g profile editor Other e g using Photoshop printing ink set up values How is the monitor profiled characterisation Default profile ICC standard proprietary Default Proprietary Customised profile by measuring colour fields displayed by monitor CMS ICC standard proprietary ICC Proprietary Number of measurement fields Number of reference points used in interpolation of final values Measurement device product name accuracy Name AE How often is the measurement repeated Software program used e g profile editor Hours Calculated characteristics RGB primaries eal RGB gamma RGB Same gamma White point Ambient light gr Other e g using Photoshop monitor set up Values O IFRA Darmstadt 27 How are the colour spaces of monitor and print matched Using the colour engine of the operating system Macintosh ColorSync 2 Windows 95 ICM Inter Color Matching
19. ay hardware and CRT display figure 2 The host computer manipulates the image values pixels and pass es the digital pixel values to the frame buffer on the graphics board display controller The D A converters of the Video Signal Generator linear ly transform the numerical pixel values in the frame buff er to video voltages Standard voltage intervals exist for Computer System Frame Buffer Video Signal E Generator 5 2 8 Figure 2 A generic display sys tem Berns 93 IFRA Darmstadt various applications Typically they follow Electronic In dustries Association EIA standards Manually adjusta ble display settings include parameters like colour tem perature brightness contrast spatial properties RGB gun voltage and convergence The size of the monitor vertically and horizontally has an effect on the simulation of the printed page Newspa per pages look different on small monitors In practice proofing a broadsheet page demands at least a 20 inch monitor However bigger monitors need a higher band width compared to smaller monitors to maintain the frame refresh rates and to prevent flickering One possibility to prevent flickering in the past was to select long persist ence phosphors Nowadays vendors do not offer long persistence phosphors because of small market needs and of technical weaknesses short life time low light out put The graphics board settings define spatial resol
20. d more RIPs are accepting pdf as input In this case no parallel versions of the page have to be created However the pdf format has several problems as it comes to handling of colour and page identification data that make current implementa tions difficult see chapter 5 3 6 3 Facsimile equipment l The page information can also be tapped at certain page facsimile senders as screened two level bitmaps c Al ternatively the bitmaps may be available from a wide area network like WydeNet from Crosfield that connects the RIP and the page facsimile sender In both cases the screened bitmaps must be converted into grey level pix els before the page image is displayed on the monitor This conversion usually averages the bitmaps In remote printing plants the information can be obtained directly from the page facsimile receiver as screened bit maps d 3 6 4 Film plate scanner Film and plate scanners e offer additional locations to tap the page information They are used in the production PostScript Page facsimile Page facsimile Film plate Web RIP scanner gt receiver gt scanner inspection pdf sender recorder Simulating RIP i e g Acrobat Imagesetter I Reader a b c d e f Y Y y Y Monitor proofing of newspaper pages Figure 8 Input devices to a soft proofing system 14 IFRA Darmstadt ch
21. ddition to luminance phosphor Ambient light based upon the Paravisual system at Los Angeles Times Table Ib Comparison of colour matching 3 Page description formats as input PostScript Yes Yes with RIP option Portable Document Format pdf TIFF T No Yes No Yes Yes Other formats At least 16 At least 6 Bitmaps 4 Input devices to the system Imagesetter including RIP Yes PostScript RIP Yes Facsimile equipment I 4 Yes Yes Film plate scanner Plate scanner Video from film 5 Identification delivered by input Product identification in addition to name edition printing location print date ET Peg Yes Yes Coding of identification physical digital Table Ic Comparison of inputs IFRA Darmstadt Yes from plate Yes No File name Yes from film Yes 19 6 Page visualising software Product name Pagevision Paravisual ProofNet Windows Macintosh Windows Windows Windows Macintosh Operating system Visualising program Proprietary Proprietary Proprietary Proprietary Yes No CMYK components separately Yes Yes Yes Yes Yes Product categories editions history Yes Yes Expected received job information from management syst Production tracking data Yes Calculation of ink settings of press No
22. e applications into account In particular the recommenda tions deal with the measuring and visual assessment of the colour matching accuracy IFRA Darmstadt The researchers together with an expert working group have worked out the selection criteria The study evalu ates existing systems for soft proofing according to these criteria Expert users have provided experiences of soft proofing systems VTT Information Technology in Espoo Finland has car ried out the research work as a commission of IFRA The project leader was Prof Caj S derg rd and the expert on image processing was Mr Ari Siren M Sc the project co ordinator was Dr Ulf Lindqvist An expert working group with the following members conducted the project Les Bovelander Scitex Europe Waterloo B Alain Bezy Le Republicain Lorrain Metz F Aytun Erdentug Parascan Redwich GB Boris Fuchs IFRA Darmstadt D Sulo Nuutinen Sanoma Corporation Helsinki FIN Ron Johnson Aqua 4 Corporation San Clemente USA BARCO Kortrijk B Data Engineering Helsinki FIN IFRA Darmstadt D IFRA Darmstadt D Moderator Associated Media Base London GB Joel Maelfeyt Ilkka Yl koski Andy Williams Manfred Werfel Ian Withers 2 The use of monitor proofing in newspapers Monitor proofing is already in use to a certain degree in several production stages at newspapers figure 1 Each production stage has its own requirements of the monitor proof I
23. e smaller than 6 AE This accuracy enables the monitor proof to reveal and visualise the colour fluctuations during the print run The best European newspapers print with an average colour error of 8 9 AE units IFRA 94 The fluctuations for the IFRA Colour Quality Club member newspapers are 7 1 13 AE ibid This requirement is also in line with the standard for offset inks Ros 94 ISO 75 that allows tolerances of 3 5 AE units for CMYK process colours The human eye perceives colour differences depending on hue from 0 3 grey to 5 0 yellow AE units Bas 95 This requirement can be covered by current technology The best monitors on the market reproduce the IT8 7 target colours within 1 AE Wan 95 Current profiling CMYK to XYZ XYZ to RGB and gamut mapping algo rithms have an accuracy of AE John 95 The gamut mapping is fairl exact in monitor proofing of newspaper prints because the printed gamut is almost completely inside the monitor gamut Of course the fulfilment of these requirements has to be considered against its costs Therefore the final accuracy is a matter of agreement between the customer and the system supplier 4 2 Visual assessment of colour matching accuracy A group of people evaluates the colour matching accura cy between monitor proof and print The following test pictures are recommended the IT8 7 test target four photographs The evaluation is made under controlled su
24. eproduction than in page visualisation except if the colour gamut of the monitors is exceptionally small Still there can be difficulties in rendering the cyan region of the newsprint In addition the dark tones might disappear if the viewing conditions do not follow the stand ards or if the monitor black level is incorrect Relative colorimetric transformations force the input and output devices to the same white point The saturation intent preserves the saturation at the expense of accuracy in hue and lightness The absolute colorimetric intent renders the output colours identically to the input colours cropping those values that do not fit into the output gamut This is why this intent is used for all proofing methods 3 4 Viewing conditions Viewing conditions are usually overlooked in soft proofing Ambient light is reflected both from the printed page and from the monitor screen The main effect on the screen is that the display loses in contrast Although some press oper ators use a standard viewing booth for inspecting the printed page monitors are placed practically at random Viewing booths in the graphic industry are standardised in ISO 3664 ISO 75b The standard defines the colour temperature of light typically 5000 K maximum and minimum illuminance and viewing geometry For softproofs the illuminance level of the viewing booth should be set so that the light intensity of the monitor white equals the reflected lig
25. er 13 TIFFIT 6 2 4 2 22 22 80a rear ER 14 Other formats u a sites en unten sei da 14 Input devices of final pages to the System nennen 14 magesetter under snout bubyabsseataronanoeareiee 14 PostScript anne nahe 14 Facsimile equipment iurssesesrerserrarnrnnnnnerenenenentavsvsvsenssevennsnenvasesesenaneseseenesesennenn 14 Film plate scanner sesseersvorennsesvssenensernnsnsnrsnenenrnnnssserersnsenesenennsannsnsnenesnvnanesessensernser 14 Web inspection Cameras msrreresnrnsnnneneneressnrsanenenenrnrnrnrnrannnnennnnnaravevsvenasessseseserenenenee 15 gt Colour space of input device seen nansns 15 Resolution delivered by input device neeeeneenenensenennenesnenenne rennen 15 Other information delivered sessseeessnennneesnnnnenennnnnneneneenennnenn es onsnsten 15 Workflow and working practices eneeeneeneenenenenseeesenesenensen seen 15 Page visualising software een essen 15 Usability REE SE EN 16 Testing criteria for a monitor proofing system a een 17 Evaluation of the colour matching accuracy een 17 Visual assessment of colour matching accuracy ueeeeneeeererennnete 17 Evaluation of existing soft proofing systems EE ee a 18 Short description of existing systems 18 Evaluation of the systems au aaa 18 Practical experiences and advices nennen 22 The Helsingin Sanomat Forssa printing plant Pagevision een 22 Aftonbladet Pagevision eneeeneenenenn PENNE ER 22 Los A
26. ered Because the procedure requires special equipment and computer programs not available to the typical system buyer testing services of research laboratories are one possibility to elvaluate a soft proofing system The system manufacturer should be urged to supply results of their own testings 4 1 Evaluation of the colour matching accuracy The deviations between monitor proof and print are meas ured as AE differences calculated over all patches of the IT8 7 test target The following steps are recommended a The IT8 7 test slide is scanned colour separated out put on film or plate and printed by the potential buyer as part of the normal production procedure b The CIE values of all 289 colour patches of the test print are measured with an accurate measurement de vice A spectrophotometer is recommended c The processed test target is input to the monitor proof ing system as a digital CMYK file PostScript bit maps and displayed on the monitor d The colour patches displayed are measured with an accurate measurement device A spectroradiometer with dense sampling is the ideal device for this e The AE differences for all IT8 7 patches are calculat ed and the result is given as average AR ap standard deviation of AE maximum AE The average AE calculated in this way should be smaller than 3 units The standard deviation of AE should be smaller than 1 unit The maximum error should b
27. files N A under development accurate visual matching no measuring of print accurate visual matching aligning of monitors measurement of ambient light black level contrast no measuring of print Page description formats as input af many formats several formats no PostScript pdf all relevant devices Input devices to the system only RIP all except fax receiver all except film plate scanners extensive multiple dates missing Job identification extensive no physical print location dates physical missing 4 physical multiple platforms calculation of ink settings Page visualising software text voice annotation expected values from manage ment system calculation multiple platforms of ink setting Usability easy operation mouse manual in several languages only English manual easy operation mouse fast response only English manual easy operation mouse fast response Table 2 Strengths and weaknesses of commercially available soft proofing systems the analysis is based upon table 1 does not accept PostScript Pagevision has interfaces to all relevant input device categories RIP imagesetter facsimile sender receiver and plate scanner Paravisual and ProofNet are almost equally well interfaced PRI
28. haviour of a Sony monitor for a white screen For lower grey levels the deviations are greater and the stabilisation time is longer Screen savers should be turned off so as not to slow down the warm up process 1 4 1 2 1 0 T 2 0 8 E 4 a 0 6 0 4 Figure 4 a The effects of the warm up period on monitor 02 brightness for a white screen 0 0 b The colour error in CIELAB E ab units after changing a white a ls 20 m 9 2 i 5 e 120 screen to middle grey Berns 93 Ban IFRA Darmstadt 9 150 100 L cdm L cdm 50 DAC counts Figure 5 a Gain and b offset adjustment changes gamma that is the tube gun voltage lumi nance relation Berns 93 255 DAC In addition to warm up variations monitors also start to fluctuate when the display content radically changes Changes between two different displays may need more than one minute to stabilise This has to be considered when calibrating and characterising monitors Figure 4 b presents the chromatic error after a white blank screen changed to middle grey The stabilisation took about 90 seconds Berns 93 Monitors also show normal short time variations with out any external reason Keeping the digital values un changed the CIELAB values can vary in some unstabi lised monitors between 0 5 1 0 E units This short time variation might disturb calibration Display controllers use look up tables to linearise the mo
29. he screen picture is renewed Typically the rate should be at least 70 times a second or 70 Hz non inter laced to avoid flickering The maximum brightness should be high enough to pre serve a good contrast ratio Brightness depicts the phys iological sensation of light intensity The corresponding psychophysical measure is luminance that is expressed as candela m or nit A typical maximum luminance value is 120 150 candela m giving an operational luminance of 80 100 candela m This is in line with the emerging standards in graphic arts proofing that recommend a maximum illumination of 500 lux see below Electro magnetic emissions should fit into common standards Gengrally low emission monitors follow the Swedish government s SWEDAC Swedish Board for Technical Accreditation MPR II specifications or the stricter TCO Swedish Confederation of Professional Employees standards Both limit the emissions of VLF Very Low Frequency and ELF Extremely Low Fre quency electric and magnetic fietds Although new mon itor technology generates less radiation than older units additional active and passive shielding mechanisms re duce emissions even further The majority of monitors produced now falls within the MPR II specifications al though some still do not The price differential between regular and low emission units has declined substantially The basic specifications can be retrieved from the internet www noradcorp com swedish h
30. hor The rest of the energy dissi pates as heat from the mask As a result shadow mask monitors are prone to colour purity problems as they heat up due to slight shifts in the position of the holes relative to the phosphor dots The Trinitron tubes have shadow masks with vertical slits instead of holes leading to a higher penetration of electrons and subsequently less heating However modern INVAR monitors come close to the Trinitrons in colour purity Channel independence means that the RGB values do not affect each other Constant phosphors keep their chro maticity when the excitation level of the phosphor chang es and constant channels do not interfere with other chan nels In practice only dedicated fully stabilised monitors with independent RGB amplifiers have totally independ ent channels Usually the red channel electronic beam strikes only red phosphors but in some displays the red beam strikes also green or blue phosphors Berns 93 The same is true for the green and blue beams Macro spatial independence of RGB pixcls means that surrounding pixels do not affect the selected pixel inten sities Most commonly poor spatial independence is due to unstabilised power supply An accuracy of 25 V over the 27 kV black to white interval guarantees good inde pendence Fortunately the problem is easily detected by showing a test image on the screen with a white square about 5 cm each side in the middle of the screen while the surr
31. house Pressman remote Agency editor Technician Inhouse Low High Pressman remote 6 Printing Pressman Inhouse remote Figure 1 Monitor proofing in different production stages at a newspaper The focus for this study is on stages 4 and 5 Fe IFRA Darmstadt 3 Evaluation criteria for a monitor proofing system The potential buyer has to consider a set of criteria when evaluating the feasibility of monitor proofing systems The evaluation uses the documentation provided by the system vendors The criteria are printed below as a check list Not all criteria might be applicable to a certain sys tem A proofing system might come with several different monitors In this case each monitor is separately evaluat ed 3 1 Monitor 3 1 1 Technical properties Soft proofing technology is currently based on CRT mon itors even if LCD displays with carefully designed filters promise a very good colour matching accuracy GAT 96 CRT monitors work by aiming a beam of electrons at a blob of phosphor which in turn glows This glow is what we perceive as a pixel on the screen A standard colour monitor has three dots dot triad at each location on the screen red green and blue RGB There is a correspond ing electron gun for each colour that emits an electron beam of varying intensity this corresponds to colour brightness A generic display system consists of a computer graphics displ
32. ht from the blank paper It is better to adjust the illuminance level of the booth than the luminance of the monitor because the latter will decrease the dynamic range of the page simulation Fherefore a viewing booth with illumination control istpreferable The walls and ceilings should be painted in neutral grey and windows should be covered 3 5 Page description formats accepted as input 3 5 1 PostScript Adobe PostScript is by far the most frequently used page description language It models the page document as a IFRA Darmstadt set of drawing commands making it resolution independ ent The importance of the PostScript is growing as the pagination is becoming more and more fully digital and as the pages are transmitted to the printing locations in PostScript form instead of as facsimile pages PostScript has two standardised levels Level 1 and Level 2 whereas Level 3 is announced Level 2 includes several extensions compared to Level 1 among which the support for CIE based independent colour and image compression are most important tor proofing purposes Modern RIPs and imagesetters accept Level 2 The typical EPS format En capsulated PostScript includes a low resolution viewing file in raster format TIFF or PICT which however is too crude both in spatial and colour resolution for proofing PostScript Level 3 offers advanced page processing en hanced image technology for example handling of the full colour spectrum i
33. ifra Special Report 2 23 Materials 1 Pre Press 2 Press 3 Mailroom and Distribution 4 Electronic Communication 5 General 6 Soft proofing of full newspaper pages This graphic shows the small size of a newspaper printing colour gamut compared with an RGB colour gamut both displayed within the CIE colour space Hard copy colour proofing has never been very popular with newspaper printers It is time and cost consuming And in many cases the proof results are hardly comparable to the final print As the entire prepress workflow is now definitely on the way to full digitisation and automation there is almost no more slot left for the chance of hard copy proofing This is why IFRA looked into the possibilities of soft proofing of newspaper pages prior to full page output either computer to film or to plate What are the criteria a soft proofing system for newspaper production has to fulfill Which monitors should be used How does calibration work and how is colour management involved Which data formats and which input devices are supported How is the soft proofing workflow arranged This report compares those requirements to the specifications of available systems on the market Practical experiences of users from different countries conclude this Special Report A detalled evaluation check list is also attached With this report we want
34. in Sanomat Forssa printing plant Pagevision Plant Manager Risto Lehto Helsingin Sanomat publishes the daily broadsheet Hel singin Sanomat the evening tabloid newspaper Iltasano mat and the weekend magazine NYT The papers are printed at 3 satellite printing plants Vantaa near Hel sinki Forssa western Finland and Varkaus eastern Finland The pages are transmitted to Forssa and Var kaus over 2 Mbit s lines There are several transmission chains film telecom line film RIP telecom line film repro system telecom line film editorial system telecom line RIP film Pagevision is used in both Forssa and Varkaus In Forssa Pagevision is connected to two parallel production lines All production data pass the system Two viewing sta tions are used in two printing control rooms The main use of the system is providing a visual reference for the press operators It helps keeping the production quality constant over long production runs Every page is checked visually The colour match between the screen and the print is judged to be good enough The point is that the soft proof is a stable reference over time In addition Pagevision functions as a colour communica tion device between the graphic designer and the press operator The designers of the weekend magazine come to the printing plant to discuss the forthcoming issue with the press operators using the Pagevision visualisations as
35. inance level of the monitor has to be close to the illumination of environment The colour proofing environment in printing industry has cur rently been standardised CIE 96 An old ISO 3664 standard recommended very high illumination of 2000 lux 1270 lux for transparencies that does not match viewing conditions in the graphic industry An updated standard ISO 13655 will recommend a lower illumina tion level of 500 lux that better approximates industrial viewing conditions and the luminance levels of the mon itors The ICC standard also addresses this problem of equal brightness between different media The proposed PCS Profile Connection Space has enough bright and dark areas to represent all device colour spaces However ICC does not recommend any brightness values Lumi nance is most easily measured with a low cost photo meter but can also be measured with more expansive colorimeters and spectrophotometers The colour gamut depicts how large a colour space the monitor can display The colour space is a three dimen sional body luminance hue saturation centred around the luminance axis At minimum black and maximum white luminance the chromaticity is zero The gamut is a predominant factor determining how well pages are simulated on screen Particularly green phosphors seem to be critical for simulating cyan colours on the screen Green phosphors will not widen the gamut enough in typical cyan process colour regions fig
36. l standard values for example brightness as well as the states of other monitors and devices Charac terisation describes these states mathematically making it possible to simulate the behaviour of the device Colour characterisation defines how different image processing components interpret colour by the use of device inde pendent colour values that is CIELAB Characterisation or profiling produces so called colour profiles as a report of the colour interpretation A summary of steps in mon itor calibration and profiling is shown in figure 7 Use accurate calibration measurement devices The sim plest case is when the monitor stabilisation and calibra tion procedures only require luminance measurements Wan 95 Use the factory chromaticity values in these schemes However monitors age individually and the phosphor emission and channel constancy characteristics F7 Check macro spatial independence measure small squares of various grey levels against black white background in CIELAB Check micro spatial independence display a small saturated coloured square against different shades of grey Figure 7 Flow diagram of cali bration and profiling with a soft proofing system CMS Colour Management System IFRA Darmstadt calibration Monitor profiling put contrast control to minimum adjust the brightness control and lock t Adjust colour temperature white
37. luminance values Bar 3 3 Colour matching methods used by the system Good colour matching requires that the printing process is colour characterised i e profiled A Colour Manage ment System CMS carries out the profiling A CMS has three main tasks IFRA 96 e Provide and handle colour profiles of different devices e Colour gamut mapping bringing the colours recorded with the input device into the gamut of the output device For soft proofing this is fairly easy because the input space the printing process fits almost totally into the output space monitor t e Colour space transformations between tlie device de pendent RGB CMYK and device independent CIE colour spaces Matrix transforms look up table based interpolation and colour mixing equations such as Neugebauer are the most used algorithms The International Colour Consortium ICC has standard ised the colour profiles Most commercial CMS software products recognise ICC profiles The ICC profiles use the CIEXYZ space as a so called Profile Connection Space 12 PCS The Colour Management Module CMM exe cutes the colour transformations according to the algo rithms mentioned above The profile of a colour monitor may consist of only 9 values because the conversion from RGB to XYZ with a 3 x 3 matrix is fairly exact see above The measurement device measures typically RGB gamma white point phosphors and in some cases ambient light The
38. n printing a test chart and measuring the values Other System speed Fastest response time s per display resolution Dimensioning for peak production Maximum number of pages Maximum number of products How is the user assisted On line help Other How is the quality of the technical manual Number of language versions System training and technical support Other usability factors list below IFRA Darmstadt 3l
39. n evaluation questionnaire see Appendix that the system manufacturers have filled in Because PURUP did not provide information about their Preview system we could not include it in the evaluation Mixes of different systems are possible For example different systems can use the same kind of monitor Parascan Aqua Four Product name Pagevision Basic properties PRIMA Paravisual ProofNet Monitor used NEC XP21 Barco Reference Calibrator Hitachi SONY Multiscan 2002 Radius Sony NEC Philips Barco etc Spatial resolution 1280 x 1024 1600 x 1200 1280 x 1024 1280 x 1024 Maximum brightness 65 cd square meter 120 cd square meter N A Colour gamut of the monitor Medium fig 9 Large fig 9 Large fig 9 N A Manually adjustable white point N A 100K N A 5000 20 000 K 3000 9300 K Monitor stabilisation and calibration Permanent measurement device Colorimeter part of monitor Colorimeter part of monitor Own colorimeter Black level and contrast calibration Calibration interval None None Yes 300 h Adjustment method Tools for aligning several monitors Analogue No 600 h Digital No 720 h Digital Own patented method Spatial uniformity compensation No Yes 81 points No Notice to user about calibration need Yes No No Continuous autocalibration beam curren
40. n this study the focus has been on examining proofing solutions that visualise the digital page descriptions be fore or after the RIP as well as showing the content of the output film and plate This kind of monitor proof provides the following benefits to the user who most often is a technician a press operator but in some cases also an editor or an advertising agency Production What is proofed Proof quality The proof e shows the PostScript interpretation errors e shows page transmission errors like missing lines e shows colour separation mix ups mostly caused by misread ID codes from plates e offers the printing press operator a colour reference to stick to over the production run The reference repre sents the average print run e allows the press operator to get himself familiar in advance with the work to be printed e is acommunication vehicle between the page designer and the press operator e provides auxiliary functions like production tracking and ink presetting Who proofs In house Resolution stage to proof Page Full element page Scanner Digital camera Ad design or remote required Technician In house Operator Photographer Designer In house Ad agency remote Page make up Technician Inhouse Editor remote Ad agency Page description or output on RIP Output on film plate Technician In
41. ncreased networking and remote printing over Internet Because PostScript is a programming language and not a static data structure a Raster Image Processor RIP converts its drawing algorithms into a viewable or print able data file Even if there are several soft RIP pro grams on the market the problerh for proofing is that these programs do not necessarily simulate the produc tion RIP CIP3 production information data are PostScript com ments 3 5 2 Portable Document Format Adobe has developed its PostScript language into a Portable Document Format pdf The Adobe Acrobat software generates the pdf format from any PostScript file The Acrobat Reader program displays the pdf docu ment on the monitor at all major computer platforms Windows Macintosh Unix The document shows up exactly in the same form on monitor as on paper because fonts can be embedded in the pdf document Compressing the images reduces the file size The Reader contains several tools for convenient viewing thumb nails book marks zoom article threads as well as antialiased grey level fonts to make small text clearer The viewing can even take place inside an internet browser like Netscape The pdf document can contain annotations links com ments The recent version 3 of Acrobat has support for colour that has been missing from earlier versions As a result the conversion from CMYK to monitor RGB performed in the encoding phase produces fairly
42. ngeles Times ParaVisual neeeneseneeeseennnnnenenn 22 Berlingske Tidende ParaVisual mmrererrrrrerrrrrrsernrrnenevavevsvererrersererersrsesssesererenenene 23 Conclusions u en nad nes enger 23 References anainn ie hig NA ea teachin leiten iin 24 Appendix Evaluation check list for soft proofing systems 26 3 1 Introduction Soft proofing of newspaper pages saves time material and money when compared to traditional photomechan ical proofs and digital hard copies It also enables a better management of the production process For modern full colour newspapers physical proofing is not viable For FM screened pictures FM Frequency Modulated Screening and computer to plate processes physical proofs are not feasible at all It has been the scope of this study to specify the technical demands of a monitor proofing system for full pages The study compares the demands to the technical specifica tions of soft proofing systems on the market and specifies the development of software needed to overcome the gaps In order to offer useful information to the printer the study identifies the places for monitor proofs in the news paper reproduction chain Moreover the study presents a method of evaluating the performance of the monitor proof The main application areas for soft proofing are produc tion tracking layout and colour accuracy inspection The recommendations are as simple as possible taking thes
43. nitor s behaviour In addition offset and gain controls adjust the driving signals These settings are usually in side the monitor housing unreachable for casual users Berns 93 Adjusting gain and offset setting changes the monitor gamma function figure 5 Gamma depicts the relationship between driving voltage approximately the digital input to the D A converter and the luminance of the monitor Black level control is sometimes wrongly called bright ness control The black level should be set so that the black picture content shows up as true black on the monitor Improper adjustment of this control is the most common problem of poor picture quality The contrast setting determines the intensity of a full white input signal After setting the black level contrast is selected to get a comfortable viewing bright ness The black level raises or lowers the entire luminance curve The control affects mostly the dark areas In elec trical terms black level controls the bias or offset of the video signal 1 72 Contrast control determines the light intensity produced for white with intermediate values towards black being scaled appropriately In a well designed monitor the monitor maintains correct black setting and preserves the correct greyscale when adjusting the contrast The easiest way to adjust the black level and the contrast of a monitor is to perform the following three steps in sequence Poynton 1 Turn the c
44. ontrast control to minimum and display a black picture 2 Adjust the black level brightness control to repro duce black correctly 3 Adjust the contrast control to display the maximum luminance level white that you desire It is important to adjust the black level to reach the max imum dynamic range of the CRT In the third phase the luminance is determined to be close to the illumination level used for viewing the printed page After the black level and the brightness adjustments the contrast ratio luminance of black paper white can be measured A good contrast ratio needs proper ambient Light 5 7 b Out Ai Light fOut Gray Pedestal RE l z Black Video Signal White aki Black Figure 6 Too low a and too high black level settings b affect Video Signal White 10 the image qualitv of monitor O IFRA Darmstadt illumination Too bright ambient light wipes out the im age contrast on the screen Colour consistency over time and between different monitors is measured as E deviations from the reference colours of a test chart like IT8 7 1 3 2 Stabilisation calibration and characterisation procedures The concepts of stabilisation calibration and characteri sation profiling are frequently intermixed Stabilisa tion keeps the device monitor scanner proofer to its current state Calibration ensures that these stabilised states equa
45. ounding is black Measuring this small square for example in CIELAB and comparing it with the same measurement when the white page covers the whole screen reveals monitors spatial independence Monitors with poor spatial independence should not be used Low ering the monitor luminance improves the spatial inde pendence However this makes it difficult to compare soft proof with hard copy proofs and printed colour imag es because the viewing illumination of a monitor is nor mally high Berns 93 Micro spatial independence is the absence of inter action between RGB signal channels and is even more essential than macro independence Mael 97 It is pos sible to detect missing micro independence in the follow ing way Display a saturated colour rectangle about IO cm horizontal and 2 cm vertical against a back ground of different shades of grey for exan ple 5 50 and 100 No colours should appear on tHe grey back ground f The bandwidth MHz of the monitor determines the spatial resolution vertical and horizontal and the refresh rate of the monitor image Colour resolution bits RGB channel expresses how accurately the colours are coded The resolution depends on the graphics board s D A con verter and on the display memory size Typical depths are 8 bits per RGB colour However if the monitor is digitally calibrated with look up tables LUTs 8 bits per colour are not enough The refresh rate depicts how often t
46. point put contrast to 80 of maximum compare to paper white and select the closest colour temparature Monitor feasibility check Adjust black level show a black screen Monitor Print process profiling Adjust contrast keep the brightness setting locked adjust the contrast control to get proper white adopted to environment illumination Print test chart with a large number of colour patches e g ISO 12642 x level y t Correct for missing spatial uniformity measure luminance at different spots Measure test chart with a spectrophotometer or colorimeter and CMS software t v Profile the monitor with a measurement device colorimeter spectrophotometer and CMS software which displays colours in sequence and calculates a colour profile to be used with soft proofing Let CMS software calculate a colour profile ICC or proprietary to be used with soft proofing Note Let always the monitor warm up 1 hour before measuring and leave minute for the monitor i stabilise after the scene content has changed 11 change over time Therefore monitor calibration and characterisation need a colour measuring device A well designed 3 or 4 channel colorimeter is an adequate col our measuring device Spectrophotometers measure the visible spectrum through considerably more channels than colorimeters typically 30 channels and therefore
47. r aging 16 x 16 binary pixels of the transmitted page In the printing plants Faxlink and Imagemaker deliver the setup values for the ink feed to the printing press control sys tem The main advantage of Paravisual is that it provides the editorial personnel a visualisation of the digitally com posed page It gives an assurance that all page elements are in place and that the RIP process has been successful In the printing plants the soft proof also assures that the fax transmission has succeeded It also gives the preset ting values for the ink feed a feature that has shortened the make ready time of the presses considerably The new colour matching module Colour Manager is not yet installed and therefore the colour match between screen and print at the moment is not corrected by the colour values of the paper shade The system indicates spot colours if the user has properly set up the system Both CMYK and spot colours are dealt with The spatial resolution allows reading of the body text but this is not considered to be a purpose of the system The system has continuously developed as a result of the co operation between Berlingske Tidende and Parascan colour fidelity requirements stated in this report In spite of this they are useful as their numerous installations show In addition to better colour fidelity there are several other improvements to be done to the systems currently on the market They should be
48. rendering intent is an in struction code for gamut Mapping It tries to degrade the image quality degradation gracefully if the colour gamut of the original image exceeds that of the printed images The rendering intents supported by the ICC standard are 1 Perceptual 2 Relative Colorimetric 3 Saturation 4 Absolute Colorimetric Perceptual rendering is in most cases the preferred meth od It compresses or expands the gamut of the input de vice to fill the gamut of the destination device It pre serves the grey balance but not necessarily the chromatic values However ICC rendering definitions are not fully satisfactory Proprietary colour management systems and their colour engines could extend the ICC capabilities Sch 96 These proprietary systems can be added as IFRA Darmstadt so called private sections to the CMM module The per ceptual intent is based on a selection of psychophysical criteria which are widely accepted in the graphic indus try Those are in order of importance Stone 88 1 The grey tones of the input image should be pre served Maximum luminance contrast is desirable Few colours should lie outside the destination gamut 4 Hue and saturation shifts should be minimised 5 It is better to increase than to decrease the colour saturation 2 3 The relative importance of these criteria may change as the content and purpose of the image changes Colour rendering is more a problem in r
49. rrounding illu mination conditions that resemble those of production The printed proof should be examined either in produc tion like illumination or in a viewing light booth with standard light The latter is recommended if a viewing light booth is used in calibration and operation of the system In a more exact analysis the DE values are calculated separately for light middle and dark tones see Wan 95 Calculated on the basis of 72 colour patches of the IT8 7 target IFRA Darmstadt 17 5 Evaluation of existing soft proofing systems Existing soft proofing systems on the market are evaluat ed below according to the criteria developed in this re port The evaluation is based on the documentation sup plied by the vendors and by interviews with users The systems have not been tested The price of a typical minimum configuration consisting of input interface server and viewing station is about 35 000 The average price of an installed system is about 100 000 5 1 Short description of existing systems The following products in alphabetical order are evalu ated Manufacturer Data Oy Harland Simon Data Engineering Oy Pagevision Harland Simon PRIMA Parascan Technologies Ltd Paravisual Aqua Four Corporation Proof Net the monitor proof ing part is licensed from WillowSix Inc 5 2 Evaluation of the systems Technical data of the systems is listed in tables la Id The data is based on a
50. separation In the future the pixel depth will grow to 12 and even 16 bit pixel High end colour scanners in prepress and also in systems for auto matic inspection and control already use this accuracy 3 6 8 Other information delivered To be able to retrieve and display the proofing informa tion the system needs product and page identification The product identification includes product name and number date edition name and number date printing lo cation name and number The page identification includes page number and colour separation CMYK A useful additional information is the time of generation of the page image which for example tells when the page was received on the fax or when the plate passed the plate scanner The product and page identification codes are normally positioned on the upper edge of the page The coding which typically resembles a bar code is positioned out side the printable area but is present on the film and plate A pattern recognition program interprets the code The code typically varies from one newspaper to another which requires the recognition algorithm to be custom ised to suit a certain installation An elegant way to deliver the identification data to a monitor proofing system is to use a standardised digital format like CIP3 International Cooperation for Integra tion of Prepress Press and Postpress CIP 95 or PressS cript Pre 95 The CIP3 format embeds the product and page struc
51. t feed back gene tert ur Yes Colour consistency over time and between monitors DE 1 5 3 0 based upon the Paravisual system at Los Angeles Times Table la Comparison of the monitors of commercial soft proofing systems for final pages The information is based on evaluation sheets filled in by the manufacturers 18 IFRA Darmstadt 2 Monitor colour print colour matching Matching method Measurement visual comparison Under development comparison aa i Visual Visual omparison Test print Standard e g IT8 7 Under development Own Number of colour patches on test print Colour Management System f gt 250 Proprietary Under development Standard e g IFRA A gt 200 500 ICM under Windows planned T Proprietary Proprietary Photoshop used for matching Yes No Yes Yes Separate Printing process profiling Yes Under development No _t No Using measuring device Spectrophotometer Using default values Yes Separate monitor colour profiling Yes Under development 2 Yes Yes Measurement device Number of measurement fields shown in sequence Colorimeter Adjustable 12 764 W K different grades of RGB Colorimeter Own patented colorimeter 5 plaques grey 2 x white point black point grey balance Measured units in a
52. tadt Sch 88 Sey 95 Stone 88 S d 96 Wan 95 Wil Schl pfer K Shao Y Braun R Bewertung von Farbmonitoren UGRA Bericht 103 St Gallen December 1988 50 pages Willow Six goes after soft copy proofing Seybold Report February 1995 pp 32 33 Stone M C Cowan W B Beatty J C Colour Gamut Mapping and Printing digital Colour Images ACM Transactions on Graphics Oct 1988 Vol 7 No 3 pp 249 292 S derg rd C Launonen R ik s J Inspection of Colour Printing Quality International Journal of Pattern Recognition and Artificial Intelligence Vol 10 No 2 1996 pp 115 128 Wandelt M Large Screen Monitors PrePress Number 10 1995 pp 4 8 Willowsix Inc MonitorRightproof Prepress Monitor Proofing and Colour Monitor Calibrator Introduction amp Guide product brochure 25 pp IFRA Darmstadt 25 9 Appendix Evaluation check list for soft proofing systems Monitor used Technical properties Basic technology CRT LCD CRT LCD Size monitor size vertically and horizontally Horizontal Vertical Type of shadow mask Shadow Slot Dot or aperture pitch of shadow mask e g 0 28 mm mm Bandwidth MHz MHz Spatial resolution e g 1024 x 768 pixels Horizontal Vertical Colour resolution
53. thout stabilisation and with restricted gamut and brightness which are clear weak nesses 20 English As regards the matching of monitor colours to print col ours only Pagevision measures test prints in addition to visual comparison Paravisual and ProofNet use solely visual comparison combined with Photoshop for carry ing out the matching ProofNet applies a common meas uring device to align monitors to each other which is a clear advantage All systems use sensors to measure the monitor colours ProofNet measures even ambient light which allows the balancing of monitor brightness and ambient light ProofNet is the only system to include black level and contrast adjustments in the calibration scheme Most systems accept a variety of page description for mats Pagevision having the largest repertoire Notable is that ProofNet is the only system that accepts the Acrobat format that is becoming more and more important Par avisual does not include any RIP which means that it IFRA Darmstadt Manufacturer Data Oy Harland Simon Parascan Aqua Four Product name Pagevision no stabilisation gamut brightness 1 Monitor PRIMA colour fidelity stabilisation resolution price Paravisual ProofNet spatial uniformity accurate white control gamut brightness Monitor colour print colour matching measures monitor print accurate monitor pro
54. thumbnails display of CMYK components separately product categories edi tions history and production control data They may also have auxiliary properties like calculation of ink settings of the press and production tracking Support for hard copy devices is a natural property 3 9 Usability The software should handle changes of printing process parameters ink paper in two ways e by changing colour settings in software e by printing a new test sheet and measuring the values recalibration 16 The system should be fast enough typically the system response should be shorter than 3 seconds The system should be dimensioned for peak production with a max imum number of pages and products The user should be assisted by on line help and preferably by a help line The technical manual should be in the native language of the user The vendor should provide system training and technical support The system should be easy to use also by personnel not skilled in computers This is possible by designing the user interface around the use of the mouse IFRA Darmstadt 4 Testing criteria for a monitor proofing system The testing focuses on the colour matching between screen and print which is critical for monitor proofing The recommended tests both include objective measure ments and subjective assessments In analysing the test results the relations between the objective and subjective evaluations should be consid
55. tm 3 1 2 Proofing properties The soft proof should fulfil three criteria of quality and usability These criteria are also used in print quality assessments Sch 96 1 Colour gamut 2 Tonal range 3 Resolution Proofing quality Digital pixel values usually have a linear relation to mon itor driving voltages HoWever different display con trollers have different slopes and intercepts in the rela tionship between digital values and voltages The EIA standard determines tolerances that most display control lers adapt to and which a voltmeter can measure Toler ances as small as 0 1 V affect the monitor characterisa tion This means that monitors should be characterised together with their display controllers unless the control ler provides a possibility to adjust the voltage signal with offset and gain controls individually for selected moni tors Monitors are not spatially uniform This is due to diffi culties in compensating increased path length towards the edges of the screens phosphor nonuniformities on the faceplate and external effects such as changes in temper ature and magnetic fields Some monitors allow for com IFRA Darmstadt pensation of nonuniformities by measuring the monitor at several different parts in the calibration phase However significant distortions are difficult to compensate compu tationally because the compensation produces wrinkles on the images The brightness that is lum
56. to assist those 6f our members who look for a fast and reliable soft proofing system i May 1997 Andy Williams Manfred Werfel Research Engineer Repro Research Manager For IFRA members only IFRA Washingtonplatz D 64287 Darmstadt Tel 49 6151 733 6 Fax 49 6151 733 800 IFRA Darmstadt Table of contents Introduction ioeina aaea aaaeei eani iiae seia inasar eia ko S ia ta enai 5 The use of monitor proofing in newsp pers eneeneenntnen 6 Evaluation criteria for a monitor proofing system een 7 Monitor emeenvrrreessrenasnrerprensenrsseannrssrassrssesnannnnennnenennrnvsnennnsssansdanensnankserassrensennnesvevnenn 7 Technical properties mmseverrvrvrrnrvrrreverrererrrnrnerersenernenerennarsnsnssevarnenneveervensnnansnne 7 Proofing properties emsrnrrnrrasvnnrnnnnnnrnrnrnnnnsrvrevereenenenevsvsersvnsanessavesasersenenenrenenersrsenene 8 Stabilisation calibration and characterisation procedures nenn 11 Colour matching methods used by the system msmereerrrrererrenererernrveraverevrererarreverenn 12 Matching the colour spaces of monitor and print 12 Viewing conditions esemersrsreserenensnnensersnenensessrsvennsssrenenenssensanenenensevsvssnsnvnevnsssserseeenen 13 Page description formats accepted as input eeensenensesseenenenn 13 PostScript snur ambassade An alerede 13 Portable Document Format rrmrrronnnnvrnnenonnvevnnnsnvnenevnnnsenrrrnrnnsnanenssnnnnnsvenrsennansnvrenr
57. ture information in PostScript as comments Thus this format is suitable for the case when the source of the proofing information is a PostScript file source a in figure 8 A more general format is IFRAtrack IFR 95b that enables the processing devices to exchange pro duction status information The proofing process could use this information At this writing March 1997 no monitor proofing system has yet applied these communi cation formats 3 7 Workflow and working practices The press operator is the main user of a full page monitor proofing system but also the editor and advertiser are potential users Correspondingly the equipment is used in the editorial department in the repro at the fax receiv er in platemaking and in the pressroom or at remote locations in the advertisement agency It should be possi ble to enhance the proof with annotations at different stages These annotations may include tools for signing the proof or parts of it as a signal to start the production 3 8 Page visualising software Because computers with different operating systems Windows Macintosh Unix are used in newspaper pro duction it is a benefit if the proofing system can be used cross platform The visualising program is normally 15 proprietary because standard pagination programs like PageMaker and Quark Xpress are not designed for con venient page proofing The program should include sev eral visualising properties like
58. ure 3 The colour gamut can be smaller and its shape might change after adjustments of the white balance Therefore phosphor chromaticities should be measured after the white point adjustment or the colour gamut should be specified to a selected white point Monitor stabilisation as well as the matching of white and other colours to the paper white usually D50 and print colours demand a transformation of the monitor RGB values This transformation is usually computed 0 6 0 5 0 4 v 0 3 0 2 e Gravure printing a Hitachi 0 1 1 a Barco a Newspaper 1 x Newspaper 2 0 l _ 0 0 1 0 2 0 3 0 4 0 5 u Figure 3 Press and monitor Hitachi CM211ME and Barco CDCT 5351 colour gamut as a CIE uv projection of the three dimensional CIE Luv space VTT Information Technology has made the measure ments and calculations for all devices except Barco The Barco values are taken from the literature Sch 88 with a simple 3 by 3 matrix mainly for speed reasons However this transformation reduces the colour gamut leading to an underuse of the phosphor colour space This is especially true if the transformation is digital Usability The warm up time is very individual for different mon itors and can vary from 15 minutes to 3 or more hours During the warm up period both the luminance and chro maticity values change Figure 4 a depicts the warm up be
59. ution for example 1024 x 768 pixels The settings should corre spond to the monitor s shadow masks and the resolution of the monitor A high resolution for example 1600 x 1200 leads to small fonts if the physical monitor is not big enough It may also lead to lower refresh rates and therefore to heavier flickering and lower visual quality The shadow mask of the monitor affects the picture quality It ensures that the electrons from each gun strike the corresponding phosphor The three electron beams arrive at slightly different angles from the three separate electron guns It is therefore possible to construct and align the shadow mask so that the electron beam from one gun will strike the correct phosphor dot but the other two phosphors will be in shadow In this way the intensity of Raster Scan CRT Deflection Image Geometry Convergence and Power Supply Circuits Video Signals Y Yb N phosphor a Screen CRT Video Signal Interface Amplifiers A red green and blue signals v to control grids B beam current feedback from gun cathodes C 2nd RGB grids focus screens and deflection yokes D cathode heater red green and blue is separately controlled at each dot triad location The shadow mask is usually an INVAR mask 64 iron 36 nickel which is a thin plate with small holes punched in it Only about 20 30 of the electron beam actually pass through the holes in the mask and hit the screen phosp
60. viewing stations are in use in the editorial department 4 in the Copenhagen printing plant and 3 in the Jylland plant 7 Conclusions As the main use of soft proofing is to provide a colour reference for the person operating the press an accurate simulation of the printed colours on the screen is a vital requirement Using colorimetry this accuracy demand can be stated in numerical terms The average difference between the monitor colours and the print colours must not exceed 3 AE units as calculated over all patches of the standard test target IT8 7 To meet this requirement a high class monitor must be used To maintain accurate colour values over time the monitor must apply autocalibration beam current feed back as well as enable regular manual measuring of the monitor colours In addition the monitog phosphors should be individually measured at the factofy It is also important that the monitor has a sufficient farge colour gamut to embrace as many of the printing colours as possible A good monitor is not enough The colour fidelity also requires good colour matching algorithms that use colori metric measurements to profile both the monitor and the printing process One crucial element is the gamut mapping method that handles out of gamut colours Current commercial proofing systems do not reach the IFRA Darmstadt The Paravisual stations are connected to WYDENET The Faxlink interface unit forms the input image by ave

Ifra1 sp ecial Report 2.23 - WAN-IFRA

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