The Problem of Specification of Color Management in Digital Proofing

The core problem of color management is to determine its true color meaning based on a known color information, such as RGB or CMYK values, and to replicate the true color sense on another device by changing the color value transmitted. The effectiveness of color management depends on the accuracy of the device's feature file. If the device's characteristics change, the profile will no longer be accurate, and we will not be able to accurately get the color you want to copy. Therefore, in order to maintain the consistency of product color in production for a long time, it is necessary to standardize the operating environment, which is also the premise of the role of color management technology.

Calibration in three steps of color management is the basis for implementing a color management system. Calibration is a method of adjusting each device (display, scanner, proofer, etc.) to a defined standard state. The purpose is to achieve consistent device behavior. It is the device's profile that describes it correctly so that proper color management can be performed. jobs.

I. Implementation Procedures for Color Management in Digital Proofing

Second, establish a standardized operating environment

The standardized operation should be started from the beginning step by step. Only according to standardized and standardized operating procedures, the entire digital proofing process can be based on evidence, in order to effectively improve the proofing quality and achieve a perfect match with the printed proofs.

1. The specification of the printer

The quality of digital proofing is closely related to print software, printers, ink, and paper. Only by determining the standard parameters of various processes can the equipment achieve a good working condition and it is possible to achieve the stable process conditions required for color management.

1 experimental conditions

EPSON STYLUS 10600 color inkjet printer, EYE-ONE spectrophotometer;
Founder smooth color management software, generate ICC file software Profile maker5.0;
EPSON Digital Proofing Paper, EPSON's original six-color ink.

2 experimental steps

Establish the basic linearization of the printer, which determines the physical characteristics of the paper and ink together, and obtain the largest possible color density with the smallest possible amount of ink, providing the foundation and optimization features for the creation of printer paper ICC profiles. Thus established the basis for color management.

Take Founder Flow as an example, that is, print a four-color gray scale directly and test it with a spectrophotometer to directly generate the basic linearity of the printer. The total amount of ink is then printed, and the total ink volume of the printer is determined from the printed sample sheet.

After the basic linearization is done, the ECI2002 color standard is first printed out, and the color block L*a*b* is tested with a spectrophotometer. Then, the profile maker software is used to generate an ICC profile file that reflects the printability.

2. Specifications of the printing press

The color management of digital proofing must first establish a standard printing status. Based on this, the ICC Profile generated can accurately reflect the ability of equipment and printed materials to express color. The digital proofing thus produced is truly practical in practical production. .

1 prepress process specification

The film output from the imagesetter requires the quality standard of the output film. Including phototypesetting machine exposure, linearization cycle, flushing time, flushing temperature, compensation, field density, fog and other process parameters of the standardization. It is required that the error of each point of the film output is ±1%, and the maximum density is ≥4.0, and the output dot curve is linear.

In addition to the factors that should be considered in the photolithography process, the photolithography process also includes the adjustment of the exposure amount. The adjustment of the exposure is mainly determined by the gray scales, micro-line blocks, and outlets on the print control strips (mostly FOGRA). 3% -98% of outlets are better.

2 printing process specification

The printing process specifications mainly include: performance parameters of paper ink, ambient temperature and humidity, selection of printing blanket, printing color sequence, printing speed, printing pressure, and field density.

A software profile maker and an eye-one spectrophotometer were used to test the L*a*b* values ​​of the color patches of the ECI2002 color patches printed under standard conditions, and an ICC profile file reflecting printability was generated.

Third, the analysis of color management applications

The previously acquired ICC Profile reflecting the characteristics of the printing process and the ICC profile reflecting the characteristics of the color printer are placed in the streamer, and the color matching module (CMM) in the stream is used for file matching, so that the digital proofing is simulated. The effect of printing is to create an ICC Profile that ultimately reflects the effect.

If we are not satisfied with the effect of the proofing system we are using, we can choose a paper with printability between various paper properties and use this combination of paper/ink/printer as a target to create a profile. Once the printer has been characterized under such conditions and the target value of the paper/ink/printer combination is established, the proofing device can be characterized for this target value. During proofing, the color is converted from the printer profile to the profiler's profile, and the dot expansion of different papers is compensated by the curve on the imagesetter or the platesetter, so that the use of this single press profile can be satisfied. Different proofing effects.

But only one color space conversion can't do the exact color conversion. According to the actual situation, the printer's ICC file needs to be modified and edited several times, and the dot gain rate, gray balance data, UCR and GCR parameters of the ICC file can be modified. The total ink volume of the ink, etc., can also be adjusted to the four-color curve of yellow, blue, green, and black, respectively. To ensure the consistency of the simulation results, the data is re-measured after a period of time, and a new characteristic file with a slight adjustment of the black version curve is made. .