Recently, color management has become a more important requirement for wide-format signs and displays. The technology is maturing, becoming easier to use, and customers are more aware of the advantages in delivering consistent, accurate color.
There are two key components to wide-format color management. One is accuracy—the ability to replicate colors to a standard or the brand and product colors for cosmetics, fashion, etc. The other key is consistency between printers. One digital printer is comparatively easy to color manage, but multiple printers are a challenge. When using multiple, different digital printers, a flexo press and an offset press, the objective is still consistency between the print processes, but the task becomes insurmountable without the right tools.
Science Replaces Skill
Many companies become experts in image editing in order to output consistent color. This method requires lots of skill. The operator outputs a proof, goes into the ‘adjust image’ function of a photo editing program, and experiments with the image until the output matches the required colors. This interactive, skills-based approach takes an inordinate amount of time and many operators don’t have such skills. Meanwhile, as the operator fixes some colors in the image, something else in the image gets ‘broken’. The whole approach is based on subjective visual assessment and no one ever gets all the ‘stars’ to line up.
Similarly, when printing with different inks (solvent, aqueous, etc.), on different machines, with different RIPs (Colorburst, EFI, Onyx, and others), centralized color management is far better than individual printer-based systems. Ultimately, after the system is up and running, all a printer needs is a spectrophotometer and a measuring process that virtually anyone can follow.
A good centralized color management system also supports using a single, standards-based, color corrected image file that can be safely sent to any printer as a PDF file. This approach also delivers files more ‘forgiving’ to changing conditions. Some color management systems additionally deliver customized separations optimized to the specific printer, ink, and media. This produces more consistency, ink savings, improved drying and better adhesion to the substrate.
Because a centralized color-managed system is based on scientific measurement, it is more reliable. Once installed, anyone can run the system. The incremental costs are for software, an automated spectrophotometer, hardware (an existing computer may be suitable), installation and training.
How it’s Done
The workflow is quite simple:
The first step shuts off color management on all RIPs. The RIPs will receive color-managed files, so they do not need to perform this function. However, the RIP still performs basic printer to media calibration for each media type. This involves printing a tone scale for each color, and making adjustments to optimize the match between requested and printed values. Once calibration is complete, the device is linearized.
The final step is creating a reference or “fingerprint” of the printer or press. A reference chart is printed and ‘read’ with a spectrophotometer. This allows the software to understand both what colors your printer can reproduce as well as how it produces them. Good color management software takes the printer color output, compares it to a preferred standard (GRACoL, for example) and creates a link to correlate the printer’s color capabilities to the color standard. Printers with a broader range of colors (gamut) support a better match to the color standard or original color being matched.
With the right software and training, you can deal with special circumstances. For example, some customers print the backside of polycarbonate then laminated over the print with a white film. The resulting color gamut is considerably smaller than GRACoL. In this type of case it is possible to compress the input color range to fit the available gamut.