Color management and proofing in flexo

Color Management in flexo

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What is color management and proofing in flexo and how is it done ?

The wide variety of substrates, lack of standard ink hues, and unique dot gain characteristics all contribute to the difficulty of communicating and reproducing color by the flexographic process. Commonly for color management and proofing in flexo, Color Management Systems (CMS), such as Agfa’s ColorTune 3.0 are software systems to ensure color consistency among different input and output devices so that printed results match originals. The use of these systems aid in the color communication process by correlating colors on computer monitors and proofing devices with the actual or expected color results from the printing press. Because a color monitor can produce a much wider gamut of colors than the inks on a printing press, the designer needs to know the range of printable colors vailable on the computer.

To find this range, a color specialist can run a CMS test on the flexographic printingpress under controlled conditions, using the same ink, plates, mounting tape, and anilox rolls required for the actual production run. Since each substrate affects color in a different way, a new test needs to be run for each new type of material. The results of the test are entered into the CMS software, which sets up calibration tables and builds press profiles. Digital cameras, scanners, monitors, and proofing devices are all adjusted by the CMS, based on the colors printed by the individual press. Input devices such as cameras and scanners, and prepress output devices including monitors and proofing systems are adjusted according to the predicted outcome on press.

Test Targets

Color Management Systems build profiles by analysing standard color data from test targets. The IT8 series of test targets can be used to calibrate prepress input devices (such as scanners), and output devices (such as proofing devices), monitors, and the press itself. The IT8 7/1, IT8 7/2, and the IT8 7/3 (shown above) test targets all contain the same standard color information, but each uses a different format.IT8 7/1 is a reflective color test target input to calibrate scanners for reflective art in a color management system. IT8 7/2 is a transparency of the same format as IT8 7/1, but used to calibrate scanners for reading transparencies, rather than reflective art. IT8 7/3 is a digital file of the same format used to calibrate imagesetters.

To build a press profile, the imagesetter is calibrated and the IT8 7/3 file is output to film. Plates are made and mounted, and the IT8 7/3 is then printed under the actual production conditions. Printed samples are measured for density, dot gain, and colorimetric values, and the resulting data is entered into the color management system. CMS software then recalibrates monitors, digital proofing devices, and imagesetters to correlate the output at each of these devices with the expected output from the actual press run. There are several color measurement tools used by flexographers to measure printed samples. Used primarily in the press room, the reflection densitometer can only truly measure reflectance. It is used by the flexographer to measure solid ink density for process color printing. The colorimeter, important because it assigns numerical values to all colors in the gamut, measures hues printed as either spot colors or screen tint combinations of CYMK. The spectrophotometer is most useful for ”fingerprinting“ specific hues of CYMK and base colors used for ink mixing.

Proofing

In flexography, proofing for halftone accuracy and color matching can be difficult and inexact. A digital or film-based proofing method used in offset lithography may not be suitable for different kinds of substrates, for matching spot colors, or for reproducing flexographic dot gain. Accurate proofing may require using two or more methods. Substrates Most proofing methods are limited to a small number of substrates. Because ink colors are affected by the absorption and color of the substrate, proofing to another material cannot provide accurate color matching. Spot Colors Since most film-based and digital proofing methods apply toner in CMYK colors, spot colors often cannot be accurately produced. If matching spot colors is critical to a job, some printers can provide a catalog of colors that they can consistently print on a variety of substrates.

Catalogs may contain specially formulated colors, or use systems similar to Pantone® or FocolToneTM. Sometimes it is possible to request samples. To ensure accurate matching, spot colors should also be evaluated by a color measurement instrument. Dot Gain Adjustments for flexographic dot gain are often not available in proofing systems designed to mimic the dot gain found in offset lithography. For this reason, halftone images and smaller type may not be accurately reproduced in the proof. However, once a characterized profile is established for a given press using a color management system, dot gain can be simulated by a digital proofing system. 

Proofing for Flexography :

 Soft Proof

Soft Proof

During preliminary design, proofing starts with a monitor, sometimes  called a soft proof. A monitor can provide an overall view of the design, but RGB colors on a monitor will probably not match CMYK or spot colors printed on the substrate. Higher color fidelity is possible by calibrating the monitor and by using a color management system.

Digital Print Proof

Digital print proof

Flexographic printers often provide mock-up packages, using proofs from digital laser printers. Many high-end digital proofing methods meet industry color standards for prepress proofing systems. Inexpensive desktop color printers can also give an approximation of specified colors. When used with a color management system, digital printers can provide contract proofs. Most digital systems are based on CMYK toner applications, so spot colors may not be accurate.

Film Proofs

Film Proofs

Plate Proof

For many years, flexographic printers have used a plate proof created on a mounterproofer during plate mounting to verify plate register, quality, and content. Though expensive and not intended for customer approval, the plate proof today is mostly used on wide web presses. Plate proofs can be created for

color matching, but they more commonly use ink hues that are not intended to match press colors. Color matching from a plate proof is very difficult due to the differences between proofing and press equipment.

Plate proof

Press Proof

Printed on the press, a press proof is the most accurate method, but because it is also the most expensive, it is not common.

These were the basic of color management in flexo.

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