One of the biggest challenges with producing any custom product is setting the customer’s expectation before production begins. This is true in many industries and it is no less of a challenge in printing. The reason for this is that the equipment that produces a single printed proof typically uses a different printing method and material than the press that will produce the piece in high volumes.
A contract proofer typically uses an inkjet printing method whereas high-volume commercial presses use lithographic (offset) or flexographic printing methods. There are also toner-based digital printers that can be used for both proofing and production. Inkjet printers spray ink onto specialized stocks compatible with inkjet technology. Lithographic and flexographic presses use a series of rollers to transfer ink to paper. Inkjet proofers typically use 6 to 11 colors to produce full-color images. A lithographic press usually uses only 4 colors–cyan, magenta, yellow, and black–to produce full-color images. These different methods of production naturally result in differences in color, finish, and capability. The type of paper also plays a roll in the color that will be produced. A gloss sheet will have vibrant, high-contrasting color, and an uncoated sheet will have lighter, more muted colors. The challenge is both targeting each piece of equipment to a given standard (or to each other) and hitting that target with consistency.
We accomplish this by first fine-tuning the prepress and press operations including PDF workflow, CtP calibration, plate linearization, ink consistency, press consumables, press mechanics, and press operation consistency. If the process and elements involved in producing color is constantly changing then it does no good to hit a given target when the starting point could be different from day to day. Much like leveling a house on an unstable foundation. Once this process is stable with an established baseline we use a combination of dot gain curves and ICC profiles to adjust the color. Color charts with thousands of patches are scanned and analyzed to create ICC profiles. This process usually takes several rounds to get the printed result off press to a G7 colorspace standard. A similar process is then applied to the proofer and digital presses. There are two ways to go at matching the proofer to the press. One could use the output of the press as the target for the proofer. This would tend to be more accurate within a company for a given press, but could result in the proofer having a higher Delta E than it could achieve for the standard target. It would also isolate that company’s color to its press as opposed to meeting a global standard. Another way is to use the same G7 standard as the target for the proofer. As long as the press is able to achieve a low Delta E for the same target then this would allow the press and proofer to rely on each other as a common reference with the proofer having the lowest Delta E possible for the standard target. There are different standards for coated and uncoated papers and coincidentally separate processes to achieve and/or simulate the color standard on each.
There are different proofing stocks for inkjet printers for simulating coated versus uncoated products. Coated stocks will have a glossy surface and uncoated (typically called matte for inkjet media) will have a rougher non-glossy surface. One element that limits an ICC’s ability to simulate color between the proof and press is the base white point of the proofing stock. This is measured in whiteness, which is a paper’s ability to reflect all colors equally under D65 lighting conditions, and brightness, which is the amount of blue light the stock reflects. Brightness is also affected by the amount of optical brightening additives in the paper, which can make the paper appear bluer. It is important that the white point of the proofing stock be as close as possible to the white point of the offset stock. This establishes a comparable base between the two media and allows the proofer to more closely simulate the full color gamut of the press.
Phillips Printing uses an 11-color inkjet proofer to produce contract proofs that very closely simulate the color we can achieve with our offset presses on both coated and uncoated stocks. Our offset press, proofer, and digital presses all meet an Idealliance colorspace standards. Setting our clients expectations at the proofing stage has proven to be a valuable asset by greatly limiting any surprises with the finished product. It also allows us to fine tune graphics with accuracy to make sure our clients get what they want. To learn more about proof-to-print and G7 grayscale/colorspace certifications visit idealliance.com or contact us.