Proofing is the basis for ensuring accurate and stable output color

A color management system running on a color desktop system ensures that the output film, plate, proofing and printing remain accurate, with consistent color and tone. To achieve this goal, color proofing proofs, whether analog or digital proof proofs, whether it is prepress proofs or proof proofs, are the key to monitor image reproduction technology. Color-accurate proofs can be used as the basis for adjusting the colors of screens, scanners, and digital printers; they can also provide standards for printers to adjust ink density, gray balance, and color saturation.

To output accurate color proofs, you must have a proofer. The printer performs corrections, stabilizes suitability conditions, and establishes a proofing profile. It also has a number of profiles that describe each piece of paper. The ink composition of the color characteristics and color range.

Traditional Proofing In terms of traditional offset press proofing, the color of four-color ink proofs must be accurate and stable. There are three links that must be controlled and standardized.
1. Equipment Calibration of the equipment, including pressure, platen temperature and performance adjustment of the air-cushion blanket, ensures that the proofer is in the best working condition.
2. Materials (1) The specification uses the same brand, the same series of inks. The use of four-color inks with different brands will cause different profiles between the proofs and the scanner, directly affecting the accuracy of color correction, and failure to obtain correct image files;
(2) Specification paper: In principle, the same kind of paper should be used for proofing and printing. If proofing and printing use one type of ink and use multiple types of paper, a variety of characteristic documents must be established.
3. Quality Standards (1) Specification of the on-site density value of the four-color inks, which is the core of the proofing and color management of the entire prepress work, because the change in the value of the solid density has a great influence on the proof tone;
(2) Regulate the relative contrast (K value) of printing. This is an important index to measure whether the density of the proofing (printing) is sufficient and whether the dot gain is within the scope of the standard. Generally, high quality proofs are used, and the K value should be above 0.40.
At present, some proof companies generally have the following two problems. First, one-sided pursuit of dot gains is minimal. However, this can easily cause a small white hole at the center of the outlet, resulting in the inability of printing to catch up. There should be a specific standard range for proofing dot gains, and one can't ignore the printing and unilaterally pursue the minimization of dot gains. Practice has proved that 50% of the outlets increase, C and M are 8% to 10%, and Y and K are 12% to 13%. Second, the ink used for proofing is far from the ink used for printing, resulting in a large gap between the printed matter and the proofs. Therefore, it is very important to standardize the use of the same brand of ink for printing and printing, and to establish the profile of this ink, because prepress operations must create conditions for the final printing of good products.

Digital proofing
As far as digital proofing is concerned, first the printer should be able to simulate the color effects of the traditional proofs (prints) and create a printer profile. The method is as follows.
(1) By correcting the printer, ensure that the printer is in the best working condition and that the printing paper used meets the requirements.
(2) Use standard proofing to produce a standard proof of ISO/IT 8.7.3 color standard for digital proofing machine to automatically correct color. The ISO/IT 8.7.3 color scale contains 928 color patches containing the total number of ink overprint areas used to detect the ink overprint effect. Y\M\C\K scale for measuring the density of solids, overprint area for detecting gray balance CMY, etc.
(3) Use a colorimeter or spectrodensitometer to measure the chromaticity values ​​of 928 color patches on the ISO/IT 8.7.3 color scale.
(4) The measured data is input into the printer property file generating software. The property file generating software compares and analyzes the chromaticity data of the original color patch and the output patch to generate a new printer characteristic file.
In summary, only the output proofing standardization and the establishment of multiple ICC Profiles for proofing environment can ensure the accuracy and stability of the output color.




Source: Shanxi Datong Tongbao Company Printing Factory (Li Hongri)