 |
|||||||
|
|||||||
|
 |
||
Color management for packaging faces special challenges as many packages require bright and bold colors that are beyond the gamut capabilities of process inks. Typically, the gamut of process CMYK inks may be expanded through the use of special colors such as red, green, or violet. Apart from gamut issues, another reason to use special colors is to provide more consistency, as a single special color is easier to control on press over a long run (as opposed to maintaining a four-color process mix). Reproducing a design in a special color keeps registration issues to a minimum. Special colors are much easier, especially when a packaging product is to be printed across all three print processes— gravure, flexo, litho. Packaging jobs are often designed in many layers and are ultimately printed as multichannel separations. In prepress, we must seek special tools when dealing with multichannel graphics. We are faced with inadequate multichannel support in Photoshop, which causes many users to adopt proprietary systems such as EskoArtwork, formed from ArtWork Systems and Esko-Graphics. Some companies are turning to solutions based on the new Pantone Goe system or an in-house palette system. In this article, we explore these solutions and ICC color-management solutions that address the needs of the packaging community. We see that an X-Rite product, ProfileMaker 5, can provide an ICC-based solution for packaging—and has a fix for Photoshop! Most of the color-management systems for packaging are based on spectral data. We, therefore, define the oft talked about “spectral” issue. It is well-known that packaging requires bright and bold colors, designed to jump off the supermarket shelf, with the message, “Buy me—I contain fresh ingredients or an exciting product.” The colors of a package should not differ among different packages on the shelf. The images should not fade as the poor appearance of the package may be construed to relate to the package content. The package will be viewed in store lighting, but may be enjoyed in the home or outdoors, so do different inks on the package match in the store, but not at home due to metamerism? Finally, does the package match the color of the actual cookie, chocolate bar, or tomato soup? This article examines the color management challenges and solutions for the packaging printer.
Figure 1: The Pantone Digital Library (dots) is compared to the gamut of GRACoL commercial offset printing (solid volume). Note that some Pantone colors can be recreated using CMYK process colors, but some are out of the print gamut. Pantone inks can be used to “extend the print gamut." Pantone Matching System
Figure 2: The Pantone system consists of different swatch books – the basic formula guide (left), the tints book (centre) and a book that compares Pantone to its CMYK equivalent (right). The Pantone system consists of three main components—the swatch books (shown in the figure), the digital libraries found in the Adobe Creative Suite or RIPs, and cans of ink. The swatch books may be printed on coated (C), uncoated (U), or matte (M) substrates. There are different swatch books for different functions. One swatch book deals with the basic formulation, another set deals with Pantone tints, from 80 percent to 0percent, and yet another version of the Pantone books compares a pure Pantone color ink with its recreation via CMYK process inks. The Pantone system has recently been relaunched with a newer system called “Goe.” The new system contains 2058 colors (compared to 1114 colors in the existing system), and if you buy the new printing inks, they are made from 10 base colors and are supposed to behave better on press. The new inks work better with UV and water-based coatings. The Pantone system is well established in prepress systems. The Pantone Digital Library exists in Photoshop, InDesign, and other prepress products such as QuarkXPress. Photoshop allows the same Pantone color to be recreated in CMYK, or a Pantone color can exist as a separate Pantone channel, to ultimately create its own film or plate separation. The Pantone system has its benefits, but also its inconveniences. The system is proprietary and requires that the product you are using is “Pantone compliant.” To work efficiently, everybody has to have, and refer to, a swatch book. And, the books become dirty and need replacing on a regular basis. Let us look at some of the other solutions for managing colors in packaging that co-exist with Pantone.
Figure 3: The Pantone system is well established in prepress systems. In Photoshop, the same Pantone color may be recreated in CMYK, the duller color, or it can exist as a separate Pantone channel and create its own plate separation. Spectral Data The spectrum is the most complete measurement of a color sample. From spectral data, it is possible to calculate density, CIELAB, and dot percent. X-Rite (previously GretagMacbeth) and other color-management products that are spectrally based are able to offer features such as metamerism predictions, swapping of colorants, swapping of substrate, predictions of color mixing, and compensation for UV fluorescence. Products that use spectral data are able to make allowance for different lighting conditions. Lighting is an important factor as packaging is displayed and purchased in store lighting, but may be proofed and designed in prepress standards for D50 or D65.
Figure 4: All these instruments are spectrophotometer— i1 Pro, 530, i1 iSis. They all measure and can report the spectrum of a sample (far right). Most measuring instruments today are spectrophotometers—i.e., they measure and can report the spectrum of a sample. The spectrum is the most complete descriptor of a color and is a plot of the reflectance of the sample in all wavelengths from blue to green to red. From spectral data, these instruments compute and report the L*a*b* values of a sample. Mathematical functions are applied to the spectral data, and the full spectrum is distilled into L*, a*, and b* values that represent the color of the sample. It is important to note that spectral data can be converted into L*a*b*, but L*a*b* cannot be converted back into the spectral data. In order to offer the benefits that spectral data can offer, it is essential that a program retain and save full spectral data within their internal operations. Spectral data is used in Heidelberg’s Prinect Profile Toolbox. The software suite combines the programs PrintOpen and Quality Monitor. PrintOpen can adjust for changes in the white point of the substrate. This feature is used in the situation where the customer or printer changes the substrate as we are getting ready to go to press. By spectral measurement of the new substrate type, color-matching calculations can be done to adjust the image colors to take into account the new substrate.
Figure 5: The X-Rite iSis was used to measure the paper white of an inkjet paper, with and without UV. Notice how in UV light, the optical brighteners cause a boost in the blue part of the spectrum. A new system from Sun Chemical is aimed at the brand owner. SmartColour uses spectral data from an extensive ink-on-substrate database to organize and optimize your brand palette. Often we find an unwieldy collection of in-house colors. The SmartColour system is designed to “organize and harmonize” these collections. Spectral data is used to compute mixes for solids, tints, and overprints. The SmartColour system consists of different parts including a DigiBase (Photoshop plug-in digital library), swatch books called “DigiGuides,” and proofs called “DigiProofs.” The Sun Chemical SmartColour system is based on spectral measurements of samples. Spectral data is useful in the analysis of UV-based fluorescence. Substrate manufacturers use optical brightening agents (OBAs, which work by absorbing light in the UV (invisible) part of the spectrum and emitting that in the blue (visible) part of the spectrum. This boost in the blue part of the spectrum makes the substrate more appealing by making it both bluer and brighter. We also see the use of spectral data in the light booths. Light booths are not perfectly D50, and a spectral measurement of the light in the booth can be used in software to make a more accurate color management ICC profile. ICC Profiles and Packaging
The ICC specification allows input, monitor, and printer profiles to be used with different color spaces. Profiles are most commonly used to convert data from RGB to L*a*b* to CMYK. However, the specification also allows profiles to contain more than four color channels. Thus, a six-channel ICC profile can deal with the situation of four process colors and two special colors. An ICC profile can have anywhere from 2 to 15 color channels. In conversation, these are referred to as “n-channel” or “multichannel” profiles, but in a profile, the precise number is listed—e.g., six-color, seven-color, eight-color, etc. To build an n-channel profile, it is necessary to use a special test target with n-colors and a profiling product that supports the creation of n-channel profiles. The special colors may be local variations of CMYK process colors, such as substituting process cyan with Pantone 435, or they may be in addition to CMYK colors so that we may seek a profile for a job that will be printed using process colors and some spot colors. Conventional CMYK targets, such as the ECI 2002, are designed in CMYK and, thus, contain a good distribution of colors in CMYK coordinates. One way of dealing with special colors is to use a conventional target and simply replace the four process colors by special colors. This does not always provide the best solution. CMYK targets are adequate for process inks, but the target is not designed for non-CMYK colorants. So even if the job has only four colorants, it is not optimum to simply substitute special colorants for CMYK in this test target. If you have special colorants, you should use a specially designed test target, and if you have more than four channels, you have to use a special test target. Specially designed test targets take into account the colorants being used and generate a set of patch values that will best capture the press response. It is likely that you can get a better characterization (fingerprint) of the press with a test target that has been optimized for the colorant set. A specially designed test target may use less patches, thus reducing press sheet real estate and measuring time. X-Rite/GretagMacbeth MeasureTool will allow the user to input the colorants and design a test target based on the actual colorant values. Figure 7: The ECI 2002 target is designed for CMYK (left). For a six-color profile, we can use GretagMacbeth ProfileMaker to design a special printer target (right). X-Rite/GretagMacbeth ProfileMaker 5 Packaging Consider an image with four channels—two Pantone colors and two process colors. In this instance, we may use a four-channel ICC profile. In Photoshop, the image colors are not displayed correctly, making it necessary to use MultiColor Separation, a third-party plug-in from ProfileMaker 5 Packaging, to perform the separation and soft proof the image with correct colors.
(a) (b) (c) Figure 8: This packaging job consists of two Pantone colors and two process colors. Photoshop initially displays the wrong colors (b), but with the ProfileMaker 5 MultiColor plug-in we can view accurate color (c). A very exciting offering from X-Rite is the ProfileMaker 5 Packaging solution that meets the color management needs of the imaging workflow in the packaging market for gravure, flexo, offset, and inkjet proofing environments. It has a number of tools that are intended to deal with the everyday issues facing packaging printers. X-Rite is able to do this through clever use of spectral data—an X-Rite ICC profile now stores full spectral data for each measurement of every single test chart patch. Proper use of the ProfileMaker 5 Packaging can increase the accuracy and reduce the time spent on preparing extended gamut work jobs in packaging printing. If you are a packaging printer, you need to look at this product. The ICC specification allows n-channel profiles, and products such as X-Rite ProfileMaker Packaging and Monaco Profiler can make n-channel ICC profiles, but the rest of the imaging chain such as Photoshop, the OS, and the RIP must also be n-channel compliant. Unfortunately, n-channel profiles are more the exception than the norm, and we must wait as vendors update their products for n-channel support. Most color management solutions today are based on spectral data. In packaging we have the need to evaluate and predict the effect of colorants and substrates on the final color - this is only possible using the full spectral description of a color. The best solutions on the market are spectral-based products. About Ryerson University
The Heidelberg School of Graphic Communications Management is housed in a 30,000 sq. ft., state-of-the-art press and prepress facility that was completed in 2003. The School offers the only B.Tech. in Graphic Communications Management in Canada and has an enrolment of 400 students at the undergraduate level. The reputation of the School ensures 100 percent internship placement and 100 percent employment of students upon graduation. Abhay Sharma is Chair of the School of Graphic Communications Management. Ian Baitz is Associate Chair of the program and is leading the development of the flexo/packaging curriculum within the school. Prof Baitz will lead a team from Ryerson University at the Phoenix College Challenge, FFTA 2008 Annual Forum, April 2008, Dallas. Copyright 2008 GravurExchange |
