Color Management Implementation Method and Experience
Ningbo DSS Intelligent Technology Co., Ltd , https://www.dssking.com
In these years, the author has deepened the experience in helping some companies engage in color management. It is imperative to strengthen color management, which is the only way to bring into play the advanced nature of desktop systems and improve quality and efficiency. At present, many companies have introduced high-end equipment and advanced technology, but they lack color management and operations are not standardized. Therefore, they cannot play the advanced features of high-tech. This situation should be reversed and improved as soon as possible. Although there are still many difficulties in adopting the color management system at present, this is an effective method that has to be adopted and is the fundamental guarantee for improving the quality and efficiency of image reproduction. Therefore, we must take a positive attitude, according to the actual conditions of our unit, adopt methods that are easy to use, difficult to implement, and implement in stages, and gradually improve. We will surely receive results. Do not trust anyone to try it out.
The following briefly introduces some of the practices and experiences of the author in practice for reference by comrades.
First, matching color management system
The color management system (CMS) refers to the software and hardware systems that can implement device calibration, establish a color description file, and implement color conversion between multiple devices throughout the entire process. That is, the color management system is not only software, but also Said that in addition to its core software, it also includes a color management operating system ColorSync 2.0, 2.1; 2 device profile (Profile); 3 support color management applications such as Photoshop5.0FreeHand8.0QuardXPress4.0 ;4 All hardware devices in the process, such as scanners, computers, color displays, digital printers, imagesetters and printers, etc.; 5 Spectral measurement equipment (such as spectrophotometer, transmissive, reflective densitometer, etc.). An effective color management system should include a color management process plan in addition to the above tools.
The current mature color management systems include: Apple ColorSync 2.0, 2.1 (CMS), Kodak Precision CMS (Kcms), Agfa Fototune Flow, Linocolor 5.0, 6.0. Although these different color management softwares have different control points and roles, their basic goals are the same. Therefore, the color management system should be selected according to the hardware and software system of the unit.
The author applied in practice is the color management system designed by Linotype-Hell and Apple's ColorSync2.0. It includes the following three aspects:
1.ColorSync software, including ColorSync, ColorSync System Profile, ColorSync Profile. These files are part of the Apple operating system and are provided by Apple with the operating system.
2. Scanners, monitors, imagesetters, printers, and other device profiles. Linotype-Hell provides a complete set of software/hardware solutions to measure and calculate the profile of a single device, a total of three:
1View Open lCC is used to generate profile files for the shaker. It contains a set of View Open lCC programs and a colorimeter to measure the screen colors.
2Scan Open lCC for scanners to generate profile files, including a set of Scan Open lCC programs and three major manufacturers Kodak, Fuji, Agfa transmission, reflection IT8 standard color standard.
3Print Open lCC, used to generate Profile files for color printers or printing processes, contains a set of Print Open lCC programs and a spectrophotometer.
3. Implementation of color management application software version Linocolor4.1,5.0,6.0.
Linocolor installed on the Macintosh, with the Mac CTU card to control the Doha, S3400 and other scanners. CTU is an abbreviation for Color Transform Unit and is a color space conversion card that rapidly converts color data in RGB, CMYK, and CIE Lab color spaces. The CTU card is highly computationally intensive, enabling large computational operations of color conversions to be performed instantaneously and quickly scanning color separations (that is, converting scanned image data from one color space to another) to ensure high quality Separation. The Mac CTU card has 3 functions:
1 Ensure that the scanned image data can quickly change to CIE Lab color mode for high-quality, fast color correction.
2 Turn CIE Lab's image data into RGB data for real-color display on the monitor in real time.
The final task of the 3CTU card is to convert the image data that enters the CIE Lab color space into printed CMYK four-color data to ensure the high quality of color and the accuracy of color reproduction. This fully shows that the current development of new technologies has made great breakthroughs in the mutual conversion of color space and has taken a step toward WYSIWYG. The workflow of Linuo Color Management System is shown in Figure 1.
Through the application of Linuo Color Management System in production, the color management system is actually a set of color data management based on computer software. It is a comprehensive job, with a unified color standard, application software and input, Output device support. The system's feature is based on the color perception CIE Lab data of the human eye and the Lab color space to represent the location of the color instead of changing the color model, ie, the original color before conversion is already within the device's color space range. The color remains the same, and if the original color before the conversion is outside the color of the device, the closest color that the device can print is replaced. The system can well perform color conversion between calibrated and characterized devices to achieve good color matching. At the same time, the company's scanning mode also uses Lab color space, which ensures that scan images rarely lose layer information due to different color gamut performance. A data conversion table between Lab and CMYK is also provided to make it easier for the operator to adjust the color hierarchy. 
Figure 1 Work Flowchart of Linuo Color Management System
Practice has proved that even the color management system can be well matched with the CMS color management system, thereby effectively improving the quality of image replication.
Second, establish a standard color environment
The implementation of color management first requires a stable color environment, so that the effect of observing the original color, screen color, and print color is consistent.
1. Use standard ambient light
Observe the color can not be separated from the light source, in order to accurately distinguish the color, you should use a standard light source. At present, many companies do not use standard light sources, seriously affecting the observation of reflected drafts and printed materials. Therefore, due to the difference in the color temperature of the ambient light of the observed sample, the color difference caused by the customer is often caused by the error. Therefore, it is important to use a standard ambient light source to keep the light in the room constant.
One of the key components of the standard light source is a high color temperature. Currently, domestic and international regulations require that the color temperature of the light source used for the observation of reflective samples be 5000K or 6500K. The second is a high color rendering index, usually >95% of fluorescent tubes. The life of the standard light source fluorescent tube is generally 2000 hours, more than 2000 hours, its color temperature, color rendering index will be reduced, the observed color is not accurate, it should be replaced.
The fluorescent lamp of the German JUST company is generally used. Its color rendering index is 97%, and it can basically completely project the true color of the object.
2. Use standard transmission light source
Observe the transmission of the original must use a transmission standard light source, so that it is consistent with the observation of printed matter, domestic and foreign regulations using 5000K (D50) fluorescent tubes. Some units use the CPM (Mini) series of transmission standard light sources. Its illumination is very uniform and soft, and the structure is small and exquisite. Its thickness is only 4 centimeters and weighs only a few kilograms. It is vivid when viewed on the side of the workstation to observe color reversal films. Color adjustment accuracy.
The use of standard light sources is not only the need for color management, but also the need for customers to correct color, as well as the need for enterprise progress. Today, it is time for such an important standard light source with a small investment, and it is time for improvement. I hope relevant business leaders will pay attention and adopt it.
Third, full color measurement instruments and control tools
Image copying is a systematic project. Scanning color separation, screen display, output film, printing PS printing, proofing and printing are the original documents. They are related and interact with each other. Quantitative and precise data control, which requires the use of professional color measurement instruments and tools, to effectively detect, control the replication process, to ensure the quality of the quality and stability. The following measuring instruments and control tools are essential.
1. Spectrophotometer
The most accurate way to perform color management is to obtain spectral data and use a spectrophotometer to measure the color of the 928 color samples in the IT8-7.3 standard color scale produced by the output device. The obtained results are compared with the standard data and obtained. New spectral information to create an output device profile file. If the investment is difficult or not, you can use the spectrophotometer provided by the company when buying a digital proofing system.
Generally used in the United States X-Rite DTP41 automatic scanning spectrophotometer, which can provide spectral data, a variety of density values ​​and colorimetric function, can measure 480 color in 5 minutes on A4 paper or within 8 minutes 800 color patches on A3 paper.
2. Screen calibrator
It is used to correct the screen color, and it is adsorbed on the screen by the sampling head of the calibration instrument. The screen is sampled. If the RGB three-color ratio is imbalanced and there is color cast, it can be adjusted by software to balance it. Generally used the United States X-Rite Color Monitor Optimi Zer screen calibration, some spectrophotometers can also be used as screen correction.
3. Reflectance Density Meter
It is used to measure the density value, dot gain value, overprint rate and relative contrast value of proofing and printing four-color ink to control and stabilize the quality of proofing and printing.
The newly-developed DigiDens T6CR handheld color reflection/black-and-white transmission densitometer, used by the author, is a multi-functional device with the latest sensors and micro-processing technology that can accurately measure various functions such as density values. There are 5 different display modes in the color reflection operation mode, the reflection density range is greater than 2.5, and the four-color density can be displayed at the same time.
4. Transmission Densitometer
For the linearization of the laser imagesetter, one is to measure the maximum density value of the output film and the bottom ash value of the white film base; the other is to measure the network value from 2%, 50%, 98% at all levels to control the network points at all levels. Reach the standard value.
The commonly used DigiDens T6CR black and white transmissive/reflective densitometer can accurately measure the density value and dot value, the transmission density is greater than 6.0, the density deviation is ±0.01, and the dot percentage deviation is ±0.5%.
5. Bruner control bar
Used for measuring and controlling the technical parameters of proofing and printing density values, dot gains and other technical parameters. It is a control tool prescribed by the national printing industry. It is generally used to lengthen the 85-type control strip and has five functions: four-color overprint color marking section. Neutral gray balance section, multi-use circular control section, print control section, relative contrast control section.
6. Printing control bar
It is used to control the correct exposure time and development time of the printing plate. Currently, it is widely used at home and abroad.