Printing Color Management Technology (I)

First, color management technology

(1) Adobe's Photoshop Color Management System

Adobe's Photoshop color management system is Adobe's most famous image processing software. Photoshop has an irreplaceable position in image processing. At the same time, Adobe also strives to develop Photoshop into a complete color management system. The color management features of Photoshop software are controlled by the Monitor Setup, Printing Inks Setup, and Separation settings.

(2) Apple's ColorSync color management system

Apple's ColorSync color management system is a color management system released by Apple. It adopts the ICC standard and uses the Lab color space as the standard reference space. It is a system-level color management software applied under the Mac operating system. It is an open color management system, users can use ColorSync's Plug-in module to perform color conversion between different color management systems. The ColorSync system consists of three components, an ICC standard color profile, a color matching method (CMM), and an application software interface (API).

(3) Kodak's color management system

Kodak's Kodak color management system is a color management system that supports both PC and Mac platforms. Unlike Apple ColorSync and Adobe's Photoshop, Kodak's color management system tends to perform color management in a modular manner, and provides several localized modules that can be combined to form a complete color management system. . The Kodak color management system generally includes four modules: KPCMS, DCP, PICC and PCS100, which can be used separately or combined into a complete color management system.

(4) QuarkXPress Color Management System

QuarkXPress's color management window offers a different approach to management. With Quark software, you can choose to convert only objects and images in the RGB format without converting the CMYK format, and you must specify which ICC profile the monitor uses. Adobe’s products are automatically recognizable. After the 5th edition - this time, Quark had some color failures, but it didn't happen very often. If you use non-TIFF PICT or JPG files, each file will be separated in different ways. It still uses the CMYK output device as the final output tool.

These color management systems are basically based on ICC color management technology. The goal of ICC technology is to create a standard format for color look-up tables - such as profile files - that primarily translates between different devices (such as scanners, displays, and output devices). The quality of this profile is uncertain, and it mostly depends on the software developer's expertise. Today ICC still appears on the standard of digital proofing. However, further investigation shows that ICC cannot obtain good quality and cannot meet the requirements of the same sheet.

ICC color management technology has the following deficiencies:

1 Chaos mapping

There are four different mapping methods for each profile (sense, chroma, absolute chroma, saturation). If two different profiles (such as proofs and sheets) are merged together, 4×4=16 blending options will be generated.

2 Black Channel issues

The use of ICC profiles in the gamut space conversion does not yield the results you expect, because the CMYK data in the target gamut space is calculated using the CIELab transformation gamut space. Lab color space is a three-dimensional color space, so the characteristics of the black channel are lost in the Lab color space. Therefore, in the ICC environment, the calculated CMYK data lead to different proofing or printing results and cannot meet the consistency requirements of color transfer.

3 Non-standard color matching method (CMM)

There are many program softwares on the market that can generate ICC profiles. There are also different color matching methods (CMM), some of which are implemented in the operating system or used by various application software. They assume that the profile is generated from the ideal initial data using different characterization methods and is interpreted using a different color matching method (CMM), resulting in biased results. This deviation is very noticeable when displaying detailed textures such as hair in highlights and shadows.

4 Did not separate calibration and characterization

In the ICC world, printer calibration and characterization are not strictly separated. Changes in temperature, climate, humidity, paper, or ink, or as the printer's use time increases, must continually generate new profiles.

5 does not apply to high-end professional needs

In general, ICC's method of generating and editing color profiles is relatively simple. However, if the user's requirements for proofs and operational reliability are relatively high, the ICC method is more troublesome. When ICC began in the field, it was necessary to constantly create optimized profiles for the proofing vehicles, and to manually edit them, the ICC became very troublesome.

6 Net gain is not taken into account

The ICC standard does not take into account the dot gain, which results in a worse proof quality. If the proof dot gain does not match the printed sheet, the printed sheet cannot be simulated optimally.

7 does not apply to remote proofing

Since calibration and characterization are not always performed separately, remote proofing using ICC-based systems is difficult. The goal of remote proofing is to produce the same identical sheet at the long distance B as at the original position A. Using ICC-based systems to obtain the same quality, manual editing, which requires very experienced staff, but generally is not the color management training staff at B, so it can not achieve the same remote proofing. If you still want to use ICC-based systems for remote proofing, the cost of optimizing the necessary ICC profiles in multiple locations must also be taken into account.

(5) GMG's four-dimensional color conversion technology

The core technologies of GMG's color management system are its own R&D, especially printer calibration and 4D color space conversion engine technology (4D).

a, printer closed-loop calibration technology

In the actual production process, when the color of the printer is found to have changed, the printer is calibrated. When using the GMG printer closed-loop correction technology, the user only needs to run a simple printer calibration program, and the software will perform calibration according to the steps. According to the control of the printer's ink jet volume, the difference between the new print color table and the initial color difference is realized. Unite. The cycle-accurate approach ensures a repeatable and stable printing system. The specific correction process is shown in Figure 2.

The original and target values ​​of GMG's unique four-dimensional color conversion technology are directly calculated in CMYK (different from the color space conversion using CIELab in the ICC Profile color conversion process), so that the black channel characteristics of the original data are always maintained very Balanced conversions ensure consistent, high-quality visual images in the target CMYK color space. The concrete implementation process of the four-dimensional color conversion technology is shown in Figure 3.

After accurate closed-loop color correction, the printed dot gain rate can also be obtained from the measurement process through the measurement of prints, so as to control the unification of the printer's simulated dot proofs and the printed dot gains to ensure the security of dot proofing. The consistency of color.

Based on the above two technologies, the company has a color management system that runs through the entire printing process:
1. GMG CamFlow -- RGB Color Management
2. GMG FileOut -- CMYK Color Management
3. GMG ColorProof - Color proofing
4. GMG DotProof - Dot Proofing
5. GMG FlexoProof - Packaging/Flexographic Proofing
6. GMG ProofControl - Color Check Tool
7. GMG InkOptimizer -- Printing Machine Ink Optimization
8. GMG Profile Editor

At present, although the color management system supplier has provided a full-scale digital proofing solution for printing-line-industry, in the actual production process, many printing companies/output centers only use the color management system for digital proofing. And digital proofing technology is one of the hottest technologies in the prepress industry in recent years. Compared with traditional proofing, digital proofing has unique advantages, not only in terms of stability, consistency, and speed, but also in the breadth and investment of proofing. The cost also has unparalleled advantages.