Adobe Trapping Technology

Transcription

1 September 2000 Adobe Trapping Technology Adobe s Vision of an All-Digital Trapping Workflow A detailed description of trapping technologies available from Adobe Systems As the graphic arts industry moves to an all-digital workflow, there needs to be a fundamental change in the way we prepare and process files for print production. Highly productive, automated tools are transforming our industry from a labor-intensive craft to a finely tuned manufacturing process. The need for automation of everyday tasks such as printing, spooling, OPI, and preflight is becoming a fundamental requirement in print operations. Specifically, fast, accurate trapping of complex printed pages is becoming a vital component of an all-digital workflow and necessary for a profitable print operation. Over the past several years, Adobe Systems has developed a full set of products to enable the vision of an alldigital workflow. One of these offerings is Adobe trapping technology. Adobe trapping technology consists of three main components: Trapping engine Adobe in-rip trapping and the Adobe Portable Document Format (PDF) Trapper Trapping standards for describing controls and results of trapping Adobe PostScript 3 and Adobe Portable Job Ticket Format (PJTF) technologies Trapping controls included in professional publishing applications like Adobe Acrobat InProduction, Adobe InDesign, and Adobe PageMaker This white paper describes the trapping technologies now available from Adobe Systems and certified OEM partners. This paper explains how Adobe trapping technologies work with Adobe PostScript 3 and Adobe Extreme technologies. This paper also describes both Adobe in-rip trapping and Adobe PDF trapping workflows. Finally, the paper highlights some of the unique features and strengths, as well as, some of the new features of Adobe trapping technology and how users can control these settings. Since the scope of this white paper is limited to a description of trapping technology, you should refer to the Adobe PostScript 3, Adobe Extreme, and PDF for Prepress Workflow and Document Delivery white papers for additional information. These white papers are available on the Adobe Web site at Background Trapping is a prepress term used to describe the compensation for misregistration between printing units on a multicolor press. As the printed sheet passes through each printing unit, a unique ink color is applied. Ideally, each color should touch or butt fit, and there should be no shift during the printing process. Several variables in printing can cause this shift to occur. These variables include the high speed of the printing press and the poor dimensional stability of paper, which stretches as it is moistened by ink and water. This misregistration causes unsightly gaps on the final printed piece. Gaps become especially obvious when two or more elements with contrasting color mixes abut. Trapping involves creating overlaps (spreads) or underlaps (chokes) of objects during the print production process to eliminate misregistration on press. A well-trapped page must have sufficient compensation to avoid visible gaps under the actual printing conditions, without introducing new artifacts that are themselves unsightly. Quality trapping requires detailed analysis of the ink properties, the press characteristics, and the content of the page.

2 2 a. b. Figure 1a: Yellow spreads into cyan. Figure 1b: Yellow chokes into cyan. Trapping Workflow Options Today, users can trap their files in several ways. The most common practice is application-based trapping in page layout applications like Adobe PageMaker or QuarkXPress. Within these applications, trapping is specified at the page or object level. In Adobe Illustrator, users trap their files manually by overprinting stroked elements. Other trapping alternatives include competitive in-rip trapping solutions (both raster- and vector-based methodology) or trapping applications that run on separate trapping workstations and servers. These solutions have limitations and do not allow the user to experience a consistent and predictable method for defining traps. Application-based trapping only allows users to trap elements created in the native application; imported graphic elements and images are ignored. Furthermore, users cannot always correctly trap imported graphic elements against native content of the page layout application. For example, text composed in the layout application cannot be trapped against underlying artwork. Since trapping is specified on an object-by-object basis, trap changes are time-consuming and require user intervention. Finally, in application-based trapping, trapping decisions must be made too early in the print production process before the details of the specific printing conditions are considered. Server-based trapping solutions are capable of trapping all elements in a document. However, their workflows are cumbersome because users must move their large PostScript files across the network to the server for trapping and then back to the output device for imaging. Furthermore, there is a lack of support for native PDF trapping. Trapping solutions must be flexible enough to address many different digital workflows while providing excellent quality and a range of options for imaging, proofing, and viewing. They must also maintain a consistent user experience throughout these variations and accommodate the need for last-minute changes of printing conditions, without depending on time-consuming human intervention. Today s print production systems are moving toward automated and distributed workflows using composite PostScript and PDF files. In this late-binding workflow, device-specific operations are performed at the last moment in the PostScript RIP. This includes activities such as color separations, imposition, and, of course, trapping. In automated and distributed workflows, users are able to use the same page content for multiple purposes, responding to customer changes sooner. Application-based and server-based trapping workflows do not allow for this type of flexibility. Automation of workflow and the flexibility to respond to last-minute changes of device-specific content allows for greater throughput in prepress systems, which results in greater profitability. Adobe Trapping Workflow By implementing a trapping technology designed specifically for the Adobe imaging model, users can execute trapping in various ways in an all-digital workflow. In contrast to trapping solutions, which dictate a single workflow, the selection of an Adobe trapping workflow can be based on user requirements. The choice depends on the type of work being produced and the choice of print production workflow used to produce the work. Some print production requirements, such as packaging or other specialty printing, justify the use of dedicated equipment and operators. Those situations call for prepress workstations that include electronic trapping applications. Solution software providers can choose to build these products based on Adobe trapping technology.

3 3 In-RIP trapping The simplest solution for Adobe trapping technology is an Adobe PostScript 3 RIP that includes Adobe in- RIP trapping. With in-rip trapping, users need not change their existing workflow. Users simply print to their output device in the regular manner; files are trapped as part of the PostScript interpretation process. Controls for trapping may be specified at the RIP through a device-specific user interface or through one of the application-based user-interface options described later. Adobe in-rip trapping provides many benefits in a print production workflow, including: Support for composite Adobe PostScript 3 and PDF printing. This includes support for all PostScript 3 features including smooth-shading, DeviceN colorspace, and masked images. Therefore, advance graphic constructs such as Hexachrome color, duotones, and custom color gradients can be trapped in a composite workflow. Automation. Once traps have been specified, there is no additional operator intervention required. Traps are executed in the PostScript RIP before the file is imaged to paper, plate, or film. Speed. Efficient use of CPU and system processing resources, which is integrated with the PostScript interpretation process, minimizes the increase in overall printing time. Quality. In-RIP trapping traps all elements in the document, includes all the necessary features to create quality traps, includes support for unlimited custom colors or varnishes, and supports rich blacks, gradient and imaging trapping, and sliding traps. Ease-of-use. A consistent user interface is available in several desktop applications. In-RIP trapping can be easily integrated into an existing print production workflow without the need for a dedicated or comprehensive prepress system or additional training. PDF trapping Future An additional future workflow option is the Adobe PDF Trapper. PDF trapping is a more robust workflow in which content-specific information is separated from device-specific information to provide greater flexibility in the workflow. The key to the PDF Trapper is the use of the Adobe Portable Job Ticket Format (PJTF). PDF/PJTF-based workflows are the basis of Adobe Extreme technology. Extreme systems use PDF as their internal file format. When trapping a PDF file in an Extreme system, users specify trapping controls in PJTF. The trapping is executed by the PDF Trapper, which generates the traps and stores them as a special annotation in the PDF file. The PDF file can then be printed to the Adobe Printer Job Ticket Processor or an Adobe PostScript 3 RIP. This implementation allows users to selectively print or proof the trapped PDF. Adobe PDF trapping will provide many additional benefits, including: Support for all the features in today s Adobe in-rip trapping Support for trapping composite Adobe PostScript 3 and PDF printing The ability to view trapped PDF files in Adobe Acrobat software Round-tripping, which means traps can be specified, executed, edited, deleted, and stored in a PDF file, and PDF files can be retrapped By building a solution around the same core technology and user-experience, Adobe has enabled production facilities to combine the automated solutions of in-rip trapping and PDF trapping to gain a great deal of flexibility in the workflow. Adobe Trap Engine The Adobe Trap Engine is a vector-based trapping technology. The engine recognizes the outline of vector objects, as well as, bitmap elements and images. This means that traps are applied during the PostScript interpretation process, but prior to rasterization. The engine is designed to work on all text, graphics, and images supported by the Adobe Imaging Model and is implemented within Adobe PostScript 3 and Adobe Extreme.

4 4 Some trapping technologies available on the market today, first convert vectors objects to bitmaps, then analyze for traps on a pixel-by-pixel basis. However, the Adobe Trapping Engine uses patented technology to create traps for both vector objects and bitmap elements without rasterization. This significantly improves the quality of the resulting trap shape, as well as, the overall speed and accuracy of trapping. In addition, the trapping engine provides features whereby trap settings can be controlled by trapping zones. A trapping zone is composed of a region of the page, or the entire page, and the parameters for trapping in that region. The result from the trapping engine is a trapping network. This network is an overlay of small fills that add traps to the current page. In the case of in-rip trapping, the trap network is imaged along with the file. In the case of the future PDF Trapper, the trap network is placed in the PDF file in the annotation layer. When the PDF file is viewed or printed, the traps in the annotation layer are included. By building a family of solutions around the same trap engine, Adobe offers the assurance of consistent results, regardless of the specific workflow. Specifying Traps The modular architecture of Adobe trapping technology allows for a consistent user interface for trap specification in a wide range of environments. Trapping parameters can be specified through plug-in interfaces to applications like Adobe Acrobat InProduction, Adobe InDesign, or Adobe PageMaker*. Dedicated tools such as an Adobe Acrobat plug-in or desktop trapping applications will have the same user-interface attributes. Independent software developers can also offer prepress solutions that integrate control for trapping using a similar user-experience. Figure 2: The Adobe InDesign in-rip trapping plug-in, Trap Style dialog box. Users of an Adobe trapping solution are presented with three basic tasks. They must describe the properties of the inks to be used, select the parameters for trapping, and designate zones or regions in which to enable or disable trapping. By basing all user interface experiences on the same three aspects, there is no challenge when moving from one trapping solution to another. In some implementations of the Adobe trapping technology, trapping parameters are specified in the PostScript RIP, either in the user-interface customized by the licensing partner or through the use of user definable hot folders, which are also used as print queues. Ink properties The definition of ink properties is purely descriptive. For each ink, users must specify the ink density and transparency/opacity of the ink as well as the order of ink lay-down. These parameters are all selected through an ink settings dialog box. Adobe trapping technology supports trapping of unlimited process and custom color inks, including varnishes. Information about the printing or lay-down order of the inks is used to determine the correct behavior of opaque inks, such as custom or metallic colors. Inks placed on the paper first will always spread or choke

5 5 under overlying opaque inks. This ensures that the resulting traps are concealed by the overlaying opaque ink. Trapping parameters Trapping parameters are defined via trap styles. Each trap style describes a set of parameters, including trap width, image trapping, trapping of gradients, and others elements. Once trap styles are created, they can be used throughout a document or saved and exported for use in future documents. Furthermore, trap styles let users apply different settings not only to different jobs, but also to different trap zones (pages or groups of pages) within a single document. * The Adobe PageMaker plug-in for in-rip trapping is available free of charge from the Adobe Web site at Trap Zones Finally, users specify trap zones. By default, a trap zone is the size of page. However, for greater trapping control a user may wish to apply a different trap style to a particular section of a page or element on a page. In this instance, regional trap zones must be created. In application(s) such as Adobe Acrobat InProduction, regional trap zones can be defined within the page using the rectangle and polygon trapping tool. In either case, once users define trap zones, they can assign a different trap style to each zone. Figure 3: Regional trap zones defined in Adobe Acrobat InProduction. Unique Features and Product Strengths Adobe PostScript 3 and Adobe Extreme Adobe trapping technology works in conjunction with the latest Adobe PostScript 3 and Adobe Extreme technology. This includes support for PostScript 3 features such as masked images, DeviceN colorspace and smooth shading, as well as composite PostScript and PDF printing, and in-rip separations. The DeviceN colorspace is used to define Hexachrome color, custom color gradients, and multitone images (duotones) in a composite PostScript printing workflow. Both Adobe Photoshop 5.02 or later, and Adobe Illustrator 8.01 applications use the DeviceN colorspace to define these application features. Corner mitering Corner mitering is a unique feature of the Adobe trapping technology that enhances the quality production of trapped elements. As discussed earlier, the trapping engine creates traps by calculating additional PostScript paths that it adds to the job stream or, in the case of the future PDF Trapper, by annotating a PDF file. As part of this calculation, the trapping engine applies a corner mitering formula at line intersection points. This corner mitering formula ensures that unsightly spikes do not appear in documents after being trapped. Rich blacks and black width To make large areas of black as dark as possible on a printed sheet, users commonly add layers of other color inks to a 100 percent black background, such as 60 percent cyan or magenta. Such blacks are described as having support screens or being rich blacks. To keep these support screens from showing along the edges of an object, the trapping engine chokes back the support screen colors. In addition, when black abuts other colors, it is common to create traps by spreading the other inks into the black area. The trapping engine allows the user to specify a black width setting for both of these situations.

6 6 a. b. Figure 4a: With no black width, support screens may show through. Figure 4b: Adding a black width chokes back the support screen. Sliding traps Adobe trapping technology uses neutral density of inks as its method of comparison for lightness and darkness. Neutral density is a measure of ink s light-stopping ability or, more simply, a measure of its opacity. When colors have similar neutral densities, neither color determines the direction of the trap. To trap these colors, the trapping engine adjusts (slides) the trap position from spreading the lighter color into the darker one by straddling the centerline between them. A sliding trap prevents abrupt shifts in trap placement, for example, along a gradient edge. Gradients are also known as blends, degradées, or vignettes. a. b. Figure 5a: A gradient touching a solid color can cause traps to shift abruptly. Figure 5b: Using a sliding trap creates a gradual centerline trap. Trap Join Styles In September 2000, Adobe released a new version of Adobe in-rip Trapping Version 305. This release is based on an entirely new Adobe Trap Engine. Version 305 includes a number of powerful new features, as well as, continued performance improvements. One of these new features is the ability to select a different trap join style. A trap join is the shape the outside edge of the trap makes when it joins another trap. Different trap join styles may be used depending on the printing conditions, the type of ink, or the substrate being used. In Adobe in-rip Trapping 305, the following trap join styles are available: miter, round, or bevel. If no trap join style is selected, the default trap join style miter will be used, in order to ensure compatibility with previous versions of Adobe trapping products. Earlier versions of Adobe in-rip Trapping, only supported miter trap join styles. Figure 6a: Miter trap join. Figure 6b: Round trap join. Figure 6c: Bevel trap join. Trap End Styles Trap End Styles is another new feature supported in Adobe in-rip Trapping 305. A trap end style is a trapping parameter that specifies how the Adobe Trapping Engine forms the intersection of a trap. Version 305 supports two different types of trap end styles miter and overlap. In a miter trap end style, the end of the trap keeps away from the trap intersection. In an overlap trap end style, the lightest trap is wrapped around the intersection.

7 7 Like trap join styles, different trap end styles may be used depending on the printing conditions, the type of ink, or the substrate being used. For example, a miter trap end style may be used in lithographic printing and an overlap trap end style may be used in flexographic printing. If no trap end style is selected, the trap end style miter will be used, in order to ensure compatibility with pervious versions of Adobe trapping products. Earlier versions of Adobe in-rip Trapping, only supported miter trap end styles. Figure 7a: Miter trap end. Figure 7b: Overlap trap end. Trapping Thin Areas Another benefit with Adobe trapping technology is the ability to shape traps in thin areas. Some trapping products can create undesirable traps in thin areas. This is due to their lack of ability to limit trap thickness (trap width) in thin areas. The Adobe Trapping Engine limits the traps in thin areas to either the trap width specified or to 50 percent of the distance between the two boundaries of the thin areas, whichever is smaller. The resulting trap is more desirable, because the trap never extends beyond the opposite boundary of the thin area. Figure 8a: Undesirable results from trapping a thin area. Figure 8b: Desirable results from trapping a thin area. Advanced gradient processing Adobe trapping technology will not trap the tint steps within a gradient because it requires at least 5 percent minimum difference between color areas before it will begin trapping. To avoid unnecessary analysis of each color boundary within a gradient, the trapping engine recognizes the objects that match the definition of gradients and treats them as a single, composite object. By avoiding this unnecessary analysis, object-toobject color analysis performance is greatly enhanced, and unneeded traps within gradients are avoided. Advanced gradient processing improves the quality and speed of both PostScript 3 smooth-shaded blends and legacy PostScript gradients. Late-binding workflow One of the greatest enhancements of the Adobe trapping workflow is the flexibility it gives users to make last-minute changes. Trapping is a uniquely device-specific process. By executing trap instructions in the PostScript RIP, users are not committed to device-specific instructions until they are ready to image the document. If users need to change the trap specification, they can apply new trap styles to the entire document rather than applying new trap settings to individual elements. Furthermore, the PDF Trapper allows users to view traps that have been stored in a special annotation of a PDF document after the interpretation process. In this workflow, traps can be viewed, edited, stored, or even deleted before the file is imaged to the output device.

8 8 Conclusions The Adobe trapping technology that is currently available in Adobe in-rip trapping and the Adobe PDF Trapper is one of the most robust product offerings for trapping available today. This full-featured trapping technology offers a flexible, automated, and distributed workflow that produces quality traps. With implementations of this technology in both Adobe PostScript 3 and Adobe Extreme, this all-digital trapping workflow supports both composite PostScript files and PDF. By continuing to provide a family of solutions around the same trapping technology and utilizing a consistent user-interface, Adobe offers the assurance of consistent results regardless of the specific workflow. Several Adobe licensing partners are shipping Adobe in-rip trapping solutions. They include Agfa Bayer Corporation; Autologic Information International Inc.; FUJIFILM Electronics Imaging; IPTech; RIPit Computer Corporation; and Xitron, Inc. Adobe is working with OEM and ISV partners to develop additional products incorporating Adobe trapping technology. For additional information on Adobe PostScript 3 and Adobe Extreme licensing partners, please refer to the Adobe Web site at Glossary Adobe PostScript 3 is the latest version of Adobe s page description language used for document printing. Adobe Extreme is the most advanced version of Adobe PostScript offering a fast, flexible, scalable, and productive printing architecture for the graphic arts and production printing environment. Extreme accepts both PostScript and PDF, but uses PDF as its internal file format and PJTF as the control mechanism. PDF is an abbreviation for Portable Document Format. PDF files are created in Adobe Acrobat software. They are used to represent a document in a manner independent of the application software, platform, and operating system used to create it. PJTF is an abbreviation for Adobe s Portable Job Ticket Format. PJTF is a format based on PDF that describes the device-specific printing parameters of a PDF document, including trapping parameters. A Portable Job Ticket can reside within a PDF document or as a stand-alone file. Adobe Systems Incorporated 345 Park Avenue San Jose, CA USA Adobe Systems Pty. Ltd. Level 4, 67 Albert Avenue Chatswood, NSW 2047 Australia Adobe Systems Europe Limited Adobe House, Mid New Cultins Edinburgh EH11 4DU Scotland, United Kingdom Adobe Systems Co., Ltd. Yebisu Garden Place Tower Ebisu, Shibuya-ku Tokyo Japan World Wide Web This brochure was created with Adobe PageMaker software and font software from the Adobe Type Library. Adobe, the Adobe logo, Acrobat, Acrobat, Extreme, Illustrator, InDesign, InProduction, PageMaker, Photoshop, PostScript, and PostScript 3 are trademarks of Adobe Systems Incorporated. All other trademarks are the property of their respective owners Adobe Systems Incorporated. All rights reserved. Printed in the USA. BC /00