Colour Management White Paper

COLOR MANAGEMENT IN THE GRAPHIC ARTSHarlequin RIP Solutions ® Introduction Color printing using a printing press has been around for slightly over 100 years using a variety of techniques from stones and grease pencils to films and plates to more recently using “digital” processes for page design, imaging and plate making. We see color because of the RGB sensitive cones in our eyes and sophisticated processing in our brains.To observe color there must be a light source, an object that the light source is illuminating and an observer that is viewing the object.The color of light is defined in terms such as wavelengths and radiation whereby different wavelengths produce different colors within the human visual spectrum. This white paper details Global Graphics' Color Management solutions using the Harlequin RIP. The term color management has recently been used to describe the digital transforms from different color spaces in the digital revolution. In actuality, any manipulation of the separations to be printed either through etching of printing stones, changes of exposure times when using process cameras, or changing calibration curves in a digital system are all forms of color management since they all are intended to change/improve the color output of the final printed piece. It is beyond the scope of this white paper to go into the history of how color was produced and enhanced in previous pre-press systems. Rather this white paper will define current color management concepts and offerings from Global Graphics with regards to color workflows that require color management. Photographic & Printing Principles In today’s graphic arts market images are still captured on film and scanned but there is a steady growth in digital cameras as well.This in a way is putting the scanner in the camera.The result in either case is an original scene captured in color through a lens, either via the scanner lens when scanning film or a digital camera lens captured into a digital file format. In most cases this is a RGB color space. Some scanners can generate a CMYK file however this will limit the re-usability in later design work and therefore will not be included in the discussion.The captured digital file is typically viewed on a RGB monitor for editing incorporating enhancements that may include sharpening, color correction and cropping.This would be considered the starting point in a pre-press workflow where this original scene capture is going to be used in a future printed piece. Color management if implemented, could already be in use in this scenario by mapping the RGB colors in the original file into the monitor’s color space, or stated another way, the best representation of those original colors within the color gamut limitations of the monitor.What this concept suggests is that the scene brightness or dynamic range in the original is often larger than the RGB color space that has been used to render it and therefore color management must be used to compress the colors in such a way as to keep the visual 1 These databases insure that customer colors are printed accurately but also that digital proofs can accurately print these custom colors when proofs are part of the workflow and approval process. In general the number of colors printable in a CMYK print space is considerably smaller than a RGB emissive space so once again the original scene must be further compressed. the inks together subtract wavelengths of light. magenta. Coated Paper Color Space Often times a design includes a company logo or artwork that has a specific color requirement for example colors that are from a proprietary library like Pantone or a combination of CMYK colors that are known to be within the press gamut of the printing system and must be printed in such a way as to achieve a specified color.This system therefore is a subtractive color model.The quality of this process from original scene to printed image on a printing press.This form of image representation is known as additive and is emissive since the monitor is emitting light. Company Logos.Graphic arts printing makes use of CMY (K) inks which are cyan. an area that Global Graphics and the Harlequin RIP have been at the forefront of since the beginning of printing color digitally. It requires a combination of color software specifications. Color management can be one way of further compressing the colors in the original scene in such a way that insures the printed image looks visually correct and is representative of the original scene. Mixing colors together when printing a color image. appearance of the original scene on the monitor as close as possible to that original scene. thus the more ink on the paper the darker the color. ink and paper combinations gamut. is really color engineering. yellow and black inks. If the CMY inks were spectrally pure one could print all colors very accurately and black would not be necessary. in today’s digital world.The Harlequin RIP includes colorimetric lookup tables for almost all of the Pantone colors in named databases and additional color databases can be added. 2 . industry specific standards and tools to build the color components of a pre-press workflow. Artwork. Primarily due to costs in their manufacture printing inks are not pure so a combination of CMYK inks will provide the best opportunity to print the greatest number of colors within a press. as opposed to the RGB additive model. Illustration 1 below is an example of a RGB monitor space and a smaller CMYK print space typical of magazine printing. CMYK colors are produced by reflected light. and Black and White images Illustration 1 – RGB Monitor Color Space vs. The solid ink densities at the time of printing would also likely be different. that comprise a color management system for the graphic arts contains at a basic level a source/input profile. a black and white profile could be installed in the RIP and then applied to all black & white images. In some workflows this would be okay and nothing more would be needed but in many modern digital workflows often times the final output device is not known at the design stage. which then gives the appropriate CMYK values to print a specific color on the printer or press sheet (via the plate and press) as needed. Device Independence Both RGB and CMYK color spaces are known as color models that are device dependent.org) or proprietary formats that are capable of providing additional parameters unavailable within the ICC profile specification. the destination for output can change and an acceptable print can be produced on a variety of output devices. and is called a Color Management Module (CMM). if I am a designer do I turn on color management in image 3 .This is known as device independent color and used in some graphic arts workflows.Thus if you view the same RGB image on two different monitors they will look different. So.The input profile defines the colors in the source or input space in such a way as to align RGB or CMYK values to LAB (a uniform intermediary color space). should one have multiple black & white images within a layout. In the CMYK print space if the same CMYK values are sent to two different printers the printed pieces would likely look different because the inks are different.This is because the monitors likely have slightly different white and black points and therefore the internal gamuts are different as well. Marketing people have also recognized the inherent advantages and often tout that their products(s) in the workflow chain. the color bits if you will.They would produce predictable color on a single device but the CMYK file would produce different colors on a different device. another reason the printed pieces would look different.Black & White images are often found in design layouts and with the Harlequin RIP these can be handled differently than color work.This again can be handled with color management if engineered properly. In other words. hardware and measurement devices used in colorimetry and likely has somewhat different definitions.This can be corrected using color management. Device Dependence vs. Obviously a pre-press system could be optimized if the output destination is known along with the ability to produce color accurate digital proofs but the principle is that once a color space is converted to LAB via a profile and CMM. Part of the challenge in succeeding at printing in the digital age is to understand the elements that must be controlled and “engineered” to insure predictable and color accurate prints that meets the requirements of one’s clients. be it software or hardware is color management capable.The profiles mentioned can be ICC profiles based on the ICC specification (more information can be found at www. from different sources.Late Binding/Early Binding The term Color Management has gained in popularity when talking about software.The CMM contains the Profile Connection Space (PCS) which is a conversion color space.Thus the CMYK values in the file are device dependent.The destination or output profile takes the LAB values that the CMM has identified in the source image and profile.The processing engine is the intermediary place to process/convert the profiles.This would insure the tonality of these black & white images are consistent throughout the publication. a CMM and a destination/output profile. Color Management Elements The elements. The power in this solution and working model is a designer working in RGB does not have to know where their work is going to be printed and still obtain a quality print within the gamut limitations of the output device.color. looks them up in the table of LAB to CMYK values in the output profile. Defining Workflows . The Harlequin RIP recognizes PDF/X file formats. For many types of printing a digital color proof is required to insure that the designer. PDF/X file formats developed to improve file submission accuracy to printers can have a profile and specific color requirements.The Harlequin RIP CMM would be considered late-binding as all of the color management decisions are performed at the last stage of the workflow. and when color management would best be applied.With the advent of the digital revolution this process has caused a great deal of confusion. The Harlequin RIP is fully capable of performing all of the necessary color management because it can make use of ICC profiles and Harlequin HQ profiles (which contain extra color information unavailable in ICC profiles). to convert between color spaces as needed on the way to the intended output device. provides pertinent information as to file contents and RIP configuration insuring that color management is honored and handled correctly. the graphic arts standards bodies continue to develop standards that define different printing conditions for different industry segments.The Harlequin RIP continues to be engineered to insure these standards are implemented properly thereby insuring that the color meets a given standard and client’s expectation. Finally. the elements involved. Building Workflows The key to predictable color is the ability to configure the pre-press workflow such that files prepared for printing when arriving at the RIP will be color managed appropriately.Yet some other examples of the components of a color management capabilities of the Harlequin RIP with a properly engineered workflow includes the ability to accurately color manage pre-press workflow".manipulation software.This requires considerable engineering to insure that the digital proofs are 4 . mixed color space files where perhaps the pictorial images are in RGB and the advertisements are in CMYK. that of converting the page files or PDL into a raster form. all RGB a combination of color images can be handled and optimized properly at the RIP. Thus a designer who receives digital images from a digital camera in a RGB color space can place those images on a page layout and provided the workflow is designed properly and the correct profiles are either "Color management requires attached to the images or installed and made available in the RIP. and the secret is understanding what it takes to build a color managed workflow. Recently for example we obtained SWOP® certification on an ink proofing device to demonstrate our capability in this area. Global Graphics is an active participant in these trend setting industry standard groups. Perhaps a last minute press change is required. One avenue is via a JDF front end which contains instructions on how files are to be managed be it fonts. and tools to build the color There are options to use additional profiles to produce color accurate proofs to a variety of output devices. again with either software specifications. CMYK image data can be also color managed accurately at the RIP. or color management.The Harlequin RIP has been developed to handle a variety of situations by providing flexibility in setup of color managed workflows. Again if the appropriate profiles have been installed an emulation workflow can be color managed to redirect/repurpose the data for a different press condition keeping the colors accurate.The Harlequin RIP is JDF compliant and remains current with the JDF specifications as it evolves. screening. appropriate for the intended output device. the answer depends. customer and printer are all working towards the same end point. then my page layout application then my RIP? Isn’t this going to insure that my color elements are color managed properly? Well. PDF/X files are also color managed correctly in the Harlequin RIP as the profiles industry specific standards selected for output and identified in the PDF/X format are honored. properly attached profiles or profiles that are in the RIP. Harlequin ColorPro ColorPro is the GUI interface to the Harlequin RIP kernel where all color managed workflow decisions are setup. This window is feature rich and has evolved to be useable by novice users as well as for operators needing to design complex color managed workflows. It should be mentioned again that setting up a color managed workflow at the RIP stage is known as late-binding and offers very powerful control over the color management of jobs when the source is known.This insures both installation and color accuracy as the profiles have been optimized for the Harlequin RIP and press or proof condition being characterized. In fact Harlequin SetGoldPro provides the ability to work with a specific RIP so that when the data has been imported and a profile generated. Harlequin SetGoldPro uses patented gray balance techniques along with sophisticated algorithms to build profiles that are optimized for the Harlequin RIP . Illustration 2 – Color Spaces and Color Conversion Routes Harlequin SetGoldPro™ Part of the success of developing color managed workflows is the building of profiles that capture the color space/gamut of a device accurately and then have these profiles available to the RIP . the resultant profile is placed in the appropriate location within RIP and also made available in Harlequin ColorPro within the RIP for immediate use. screening and resolution. For each combination of paper. It is also very controllable even when jobs files from unknown sources (a new customer for example) need to be accurately output in preparation for printing or plate making. In addition to the feature set found in the Harlequin ColorPro window many additional features can be initiated via PostScript® 5 . A source/input profile must be created for the press and a destination/output profile must be created for the proofing device. ink. Illustration 2 below highlights some workflow options using profiles and a variety of input color spaces. Once the color characterizations are built into profiles for each printing condition they can be installed into the Harlequin RIP and used in a variety of Harlequin ColorPro™ setups to meet customer requirements.representative of future printing. the printing characteristics of the printing device changes and therefore the color will change as well. USA Tel: +1 703 266 9588 Fax: +1 703 266 9582 Global Graphics Software Ltd. 2nd Floor. If one is receiving job files that are not tagged for specific printing application these files will need conversion. Global Graphics makes no warranty and accepts no liability for any loss or damage arising from the useof information or particulars in this document. Adobe and PostScript are a trademarks of Adobe Systems. and a decision on where the color transforms take place.This example would be through emulation as seen in illustration 2 and is a way one can repurpose data or optimize data prepared for one press that at the last minute needs to be printed on a different press. which may be registered in certain jurisdictions. SetGold and ColorPro are trademarks of Global Graphics Software Limited which may be registered in certain jurisdictions.A. Building 2030 Cambourne Business Park Cambourne. For more information please refer to the Harlequin ColorPro User’s Guide for the Harlequin RIP. If one needs color accurate proofs the obvious location is at the RIP.VA 20120. 5875 Trinity Parkway. Using the Harlequin RIP and color tools optimized for the RIP insures that any workflow challenges can be accurately configured at the RIP prior to printing. Again the Harlequin RIP is ideally suited for this purpose as all of the color bits can be loaded and configured to correct color issues within files (wrong or no profile attached to the submitted images). ONE TECHNOLOGYTO SUPPORT ONE SCALABLE ARCHITECTURE ONE SOURCE Global Graphics Software Inc. 6 . Genesis Release.globalgraphics. Suite 110 Centreville.ColorPro GUI commands to even further control how page elements within a file are color managed. Conclusion Color Management is a combination of color engineering and correct workflow setup. the Harlequin logo. All rights reserved. Copyright © 2006 Global Graphics Software Limited. which may be registered in certain jurisdictions. Keeping these color decisions available to the latest possible stage helps limit mistakes and provides a greatest flexibility to optimizing jobs that may have been setup for one print condition but now need to run in a different set of conditions.The Harlequin ColorPro window was designed to allow for most operations but not so complicated as to have limited usability. Cambridge CB23 6DW UK Tel: +44 (0)1954 283100 Fax: +44 (0)1954 283101 September 2007 www. plating or proofing. Global Graphics is a trademarkof Global Graphics S.com Global Graphics KK Level 14. All other brand and product names are trademarks or registered trademarks of their respective owners. Inc. Japan Tel: +81-3-5532-7340 Fax: +81-3-5532-7373 the smarter alternative.. Harlequin. Hibiya Central Building 1-2-9 Nishi-Shimbashi. Minato-ku Tokyo 105-0003. applications to build those transforms into profiles. If one needs to change the printing condition the job files will need conversion. Eclipse Release. All specifications subject to change without notice.This includes the necessary transforms to move between different color spaces.