Science & Technology Support-independent production and objections to it
Optimized workflow in digital printing – part 1 Whether printing is offset or digital, data processing for the different procedures is the same. With one important difference, because digital printing has no standard, not even standardized reproduction. However, even digital printing can give optimal results through workflow independent of the support. While in the context of PSO (Process Standard Offset – ISO 12647 http://www.pso,insider.de) there is a description of a standardized, industry-oriented method of offset printing, digital printing totally lacks a corresponding set of standards. FOGRA and ISO are working towards standardization in the digital field, too. For offset printing, the fundamental requisites for getting PSO certification are, on the one hand, creation of pre-print data and, on the other, printing itself. The difference between offset and digital printing lies only in the printing process proper, where you have to compare the most disparate colors and supports and it’s impossible to limit oneself to five classes of paper, as in offset printing. What both processes have in common is data processing. However, in digital printing you have to process data that’s independent of the support, while in offset, instead (and depending on the standards available for classes of paper), you can create unlimited support-based data. Due to the multiplicity of supports and the lack of standards, for digital printing it is inadvisable to process data based on the support. You would have to limit reproduction possibilities and forgo some of the extraordinary advantages digital printing offers! The following analysis compares individual concepts, taking in-depth looks at the pros and cons of support-independent production where digital printing is concerned. Before talking about optimized workflow for processing digital printing data, let’s first try to clear the field of doubts about output not dependent on the support, since experts in the creation and production department always have ready excuses. The concepts. When talking about support-independent printing products you run into various concepts. Here we provide a definition: Data not dependent on the support: this means data memorized in a generic RGB or Lab colorimetric space. Data specific to the support: the data is memorized in the specific colorimetric space of the input or output unit. Color management: a procedure linked to the system in which images, graphics and text can be converted at any time from an original colorimetric space to one of destination. PDF: a universal data format able to combine in a container both support-independent and support-specific data, which can be completely incorporated or referred to
externally. PDF/X: a set of ISO standards used in data exchange between the data creator and the data processor during the printing process, and which supplies technically accurate PDF data. It is impossible to exclude errors in data content and structure! Formats PDF/X-3 and PDF/X-4 in particular are nominated in relation to PDF production, whatever the support. Actual production conditions. Whether you are producing catalogues or ads, for example on textile panels, the approach is the same. In every case we are dealing with images (photos, photomontages or logos in black and white), graphics (illustrations, commercial graphics or logos, all in vector form) and texts. All these elements have to be grouped in a layout and you have to analyze the resolution suitable for output into the colorimetric space specific to the support. Images are generally opened in Adobe Photoshop, processed from the color and content standpoints and converted into the colorimetric space specific to the support. For example: ISOCoated_v2 (known to be the largest colorimetric space for offset printing and therefore ideal for digital). If the image has already been archived in CMYK, it is used as is. Here there is no conversion of the image into the colorimetric space specific to the support and suitable for production because you can decide to use the image as is (even when using another specific colorimetric space). To preserve the original image, it is saved with a new name in TIFF or JPEG format. However, if you want to create photomontages, these are saved under another name, usually in PSD format. Graphics are created almost exclusively in CMYK using vector programs like Adobe Illustrator, FreeHand and CorelDraw and are saved as EPS, PDF or AI files. Texts are written with the text editor and input into the layout program mostly in black, sometimes also in color. The text is “colored” almost exclusively using one of the CMYK colors created in the layout program. In most cases, black texts are input with a loaded black (0|0|0|100). To get an optimal print, certain format titles are input in “deep black” (50|50|0|100). This classic production works fine for offset printing, when everything is done right. However, the same production shows a first essential limitation for digital printing in regard to the possible colorimetric space. Ask yourself the following questions. -
Do you know which support-specific colorimetric
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space the data will be processed for? Do you know what printing material the data has to be printed on? Do you know which printing company and which device will be used for printing? Do you know which method – offset, rotogravure, digital – will be used in printing? Do you know what color profile you have to use on the basis of the support-specific colorimetric space?
or only in the exit stage? Let’s try to briefly describe the work stages and imagine where conversion is generally possible. Images and graphics can be found in any colorimetric space. Opening this file, colors may already have been converted or simply assigned profiles. In the application itself, by creating colors or transforming them it is possible to
If you’ve answered yes to all these questions, then you’re able to execute the classic production method correctly. Now ask yourself these other questions: Do you know from the start which support-specific colorimetric space and which printing process the data has to be processed for? Have you converted ALL the CMYK images existent in the support-specific colorimetric space? Have you put all the correlated documents (images, graphics and the layout document itself) into the destination colorimetric space? Have you just ONE version of each image or have you memorized several images for each support-specific colorimetric space? If you’ve answered yes to these questions too, then you can continue to successfully use the classic production method, whatever the increase in data it requires. Especially in offset printing, due to standardization in the PSO context, the user can get great prints. But in digital printing, even when you’ve gotten the profiles of the printing material from the company that will do the work, support-dependent production would not let you achieve your goal because in the RIP of digital units it’s possible to take special steps to optimize “blacking”, “color conversion” and “print color drafting”. In supportdependent production you would have to forgo these optimization steps. The existence of data independent from the support is fundamental to digital output! What’s the purpose of workflow independent of the support? The purpose of remaining independent of the support is to leave all options open in order to be able to convert colors even at the last minute so they can be adapted to the most diverse output processes, whether offset or digital. Color can be managed at various points and therefore modified as needed. Is color management needed right now, earlier, later
bring images and graphics into any colorimetric workspace. In the end, the files are memorized in a colorimetric space. Converting colors to a previous condition creates no big problems in offset printing. On the other hand, in digital printing you have to foresee limitations to optimized output for almost every procedure. Page creation: in programs for layouts and graphics colors can be converted only at certain points. Color conversion does not occur while importing images and graphics. Nonetheless, the original profiles may be ignored during this process, so later color compensation might occur on the basis of erroneous information. Transforming colorimetric space from RGB to CMYK can be done in programs only for certain objects and therefore never for positioned images and graphics. PDF creation: whether printing on a color printer, creating a PostScript file or exporting in an EPS or PDF file you may encounter all possible transformations of the colorimetric space. PDF processing: starting from Adobe’s Acrobat 6, color conversion can be done in Acrobat with all the tools
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Science & Technology available. Various plug-in suppliers offer further ways of transforming colorimetric space. While printing or exporting in a PostScript or EPS file a new conversion may occur, like during page creation. Output: since output requires 4c data, even when output is being produced it must be possible to transform the colorimetric space. Even some software tools for trapping and reducing transparencies can cause colors to convert. At the latest in the RIP or PDF-Renderer – Adobe’s PDF Print Engine – all the information has to be transferred, with or without special colors, into the CMYK output colorimetric space. It’s possible to convert colors at various times, and with the right tools you can get the same results. During the output process, color conversion can occur at any time – in creating printing data (early binding), in creating and processing output files such as PDF (intermediate binding) or just in output (late binding). While in offset printing colors are converted as desired by the data creator (naturally in accord with the print supplier), in digital printing it is absolutely necessary to forgo advance color conversion because otherwise the parameters based on the material (which cannot be described through a classic ICC profile) would not be taken into consideration. They could be input through manual retouching but if the colors were already eliminated in advance through conversion it is longer possible to add them. Processing ISOCoated v2 data on the basis of the support? ISO Coated_v2 is the biggest colorimetric space in classic CMYK offset printing. Surely this colorimetric space is large enough for digital printing? The answer is NO. As you can see in the chart, the digital print color range (the colored area) goes far beyond that for offset (grid model). However, compared to offset, digital printing shows clear disadvantages in intensity. The deeper the color tones, the less definition can be reproduced. And precisely in regard to digital printing, customers continue to hear from print suppliers that they have to process CMYK data in ISO Coated v2! If you want to be surprised by black surfaces devoid of definition and at the same time want to forgo bright, saturated colors, just follow that instruction. If, instead, you want to get the best from printing, process the data independently from the support. The doubts of data creators. Why not put the original processed images into a support-independent RGB, assigning them the corresponding origin profile? That way, color conversion into the support-specific colorimetric space could be done whenever, guaranteeing for which output support the data should be processed! The doubts are well known: Colors cannot be corrected in RGB! – Learn! There are various possibilities; the work method has to be adjusted. I don’t see the final version on the monitor! – Then get the output profile of the printing material desired and
activate Proof Simulation in the program: this way you will see what you would have seen converting the image into the destination colorimetric space. I can’t be sure that the digital printer will perform the same conversion! – Okay! PDF workflow independent of the support can work only if each person in the production chain is aware of its possibilities and uses them correctly. It is not advisable to share support-independent PDF workflow with “unknown” companies or persons. But what happens when you proceed independently from the support and only at the last minute – when the data leaves your premises – are colors converted into the specific colorimetric space? Data control would remain on your premises – even if the optimum has not yet been reached. Why not put vector data into an RGB colorimetric space independent from the support? The doubts here concern: Logos have to be printed with precise CMYK values. And we mean precise. Creating vector data independent from the support and converting them as late as possible into the colorimetric space specific to the support would inevitably lead to a different rendering of colors (from the numerical standpoint). However, it would ensure a technical visual conversion of color reproduction. De facto: we remain with vector data created in CMYK and for RGB output forms we create a corresponding pendant. Two logos in two colorimetric spaces are allowed! If the logos are created in association with color images we’re in hot water. On the one hand, the images have to be created independently from the support in association with the CMYK vertical objects; on the other, this very condition could pose problems in color compensation since there might be interruptions in color between the vector data and images. Solution: if the images are entirely associated with vector data – the logo as the result of a whole image – then the vector data and images have to be saved as independent from the support. If, instead, images and vectors are independent from one another in a vector file, then the image has to be created as independent from the support and the vector as support-specific. Both statements surely hold true for offset printing. For digital printing (especially ink-based systems) and for largeformat particularly, there are totally different requirements. Is there exact reproduction of color values or the expectation that this will happen for the colors being reproduced? Should black surfaces be reproduced solely as black or also as “deep black”? And is it sure that reproduction will also produce the same deep black? In digital printing vector data can be processed as in offset printing. In some situations, however, a support-independent reproduction of colored vector constants would make it possible to meet the goal. This decision has to be assessed and taken case by case. Why not create layout files independent from the support? Here, too, there are doubts: As for vector data, the same holds true for colored surfaces, variations (variants) and colored texts to be
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Science & Technology reproduced created in layout programs. The colors are created as support-specific because the layout file is the output point of every PDF and so up to the last minute it is possible to create or correctly modify support-specific colors. After color conversion, objects in black (including texts) appear in all four color selections and the reproduction of a deep black surface might not be precisely regulated. Even for layout data there are the same doubts and the same technical requirements for production. What’s essential, however, is that, in saving, all the support-independent data be assigned a corresponding origin profile and that color management in the layout application be set to conserve all the original colorimetric spaces and all the information. This way there is no obstacle to producing a supportindependent PDF. For the time being it is still not important at what point conversion occurs in the support-specific colorimetric space. Using DeviceLink profiles it is possible to also use colorimetric space conversions from RGB to CMYK in an optimal way. Container for support-independent data. The PDF/X standard (X-1a; X-3; X-4) in which data are finally exchanged between parties depends on the point at which colors are converted. If the colors are not converted in the printing plant, the best solution is the PDF/X-1a format. All the objects are compensated for in the colorimetric space of the printing support and in addition all the transparencies and levels are “flattened”. If you’ve produced “dead” printing data, one hopes (there is only one hope!) that the output colorimetric space is correct! In digital printing it’s impossible to even think of optimizing at output time.
variation is the PDF/X-4 format. For pre-printing, creating PDF/X-4 files is the only variant for support-independent printing (but also for support-dependent), by means of which it is still possible in the output stage to optimize printing specifications. The PDF/X-4 format is also a presupposition for PDF/VT - Variable Data Printing Standard. Result. To optimize workflow in digital printing, it is necessary to create data independent from the support, assign origin profiles and place them in a neutral container. It is necessary to dispel the doubts of data creators, while printing personnel need to have the skills and right tools to process such data. The choice of container is obvious: PDF/X-4. It is necessary to learn how to interpret and process support-independent data. In digital printing, the interaction between data creator and print supplier has to follow rules. In the next issue of Process we will learn the steps and measures to take.
Author: Hans Peter Schneeberger, MD of Nixberg Consulting GmbH, Caibrate Workflow Consulting(www.calibrate.at), Professor at FH Hagenberg (Austria), author of various books on Adobe SW packages, particularly re InDesign Cs3,Cs4,Cs5: Pdf Workflow in prepress, etc.
If color optimization, conversion and reduction of transparencies are done solely at the printing plant, the only
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