Color Management Applications in Digital Workflows

The full color management of printing includes digital camera input, scanning input, screen correction, digital proofing and digital printing. Color management runs through the entire printing process, and its role has two aspects: one is to ensure the predictability and repeatability of color in the printing process, and the other is to ensure the accuracy of color reproduction.

In practical applications, color management can produce very good results, and it may produce very bad results. In order to play a correct role in color management technology, we must pay attention to the following three major points in practical work:

A. Stable printing process parameters

In the print color management process can not be separated from the professional measurement tools and measurement ladder. Experience alone and without measuring instruments are bad color management tasks. The following are some of the commonly used measurement tools in printing, including the printing plate dot meter, transmission densitometer, reflection densitometer, spectrophotometer, printing ink control spectrophotometer.


1. Stable printing process parameters

The printing process flow chart can be shown as follows:
The target color that color management eventually wants to achieve is the final print color, the full color of the printing

The management process flow chart and the printing process flow chart are exactly the opposite, as shown in the following figure


As can be seen from the figure, the final simulation target of color management is printed matter. In order to realize the true role of color management, the most important thing is the stability of the printing process! The stability of the printing process is an important prerequisite for the function of color management. It is necessary to control the pressure, dot gain, printing paper, ink and other conditions of the printing press to stabilize, digitize and standardize.

In practice, stable printing process parameters must be established to control the following major points:
1. Normalized operation of the film output process
2. Standardized operation of traditional printing process
3. Standardized operation of CTP plate process
4. Standardized operation of printing
5. Establish feasible technical parameters of the company and establish a color management system

1.1 Normalized Operation of Film Output Process

Film quality is a prerequisite for printing quality. A bad image processing is only a part of the print, and the poor quality of the film will affect the entire print! Control film quality includes the following four parameters:

* Highest Density * Foggyness * Hardness * Output Linear Data and Curves There are two main tools required to make the above parameters' data control:
* Transmission Density Meter * Film Output Linear Control Scale

Different output RIP software's film output linear control ladder not necessarily the same, but its role is the same: used to check the output after the film dot and density. Use a transmission densitometer to measure the linear output of the film output slider. Note: The density meter should be calibrated regularly to ensure the accuracy of the measurement.

1.2 Standardization and Parameterization of Data in Traditional Printing Processes

Shaiban is the bridge process of platemaking and printing: on the color separation plate, the next pair of printing. The use of dot control strips and corresponding measurement tools in the plate making process is used for normalization and data control.
The commonly used print control signal bar has 15 steps of gray scale, as shown below.

The Bruner signal strip also includes a print control section.

Producers of plate measuring instruments currently have Swiss FAG companies, American X-RITE companies and Swiss GretagMacbeth companies.

1.3 Standardization of CTP Plate Processes and Its Parameterization

At present, CTP is not very popular in China's printing industry because of price and consumables. The directness and timeliness of computer-to-print printing plates (CTPs) and their superiority over the quality of traditional printing plates are the inevitable trend of digital printing. In the standardized operation of the CTP plate process, it is necessary to use a plate measuring instrument and an electronic version of the plate measurement and control bar to control the output quality of the plate and the stability of the dot output. The dot output linearity of the CTP version should refer to the traditional printing process in order to be well integrated into the existing printing process.

1.4 Standardized Operation of Printing

The standard printing process is the use of standard print quality control strips, using professional measurement tools for instant measurement and control.

There are five control points for the printing normalization operation:

* Printed on-site density value and CIELab value control * Print dot gain value control at 50% * Print dot reproduction curve and print contrast K value control * Printing stability and proof ink uniformity control
1.5 The establishment of the company's feasible technical parameters and the establishment of color management system for different printing presses, printing paper, printing ink corresponding to different printing process parameters. The specific equipment of different companies is not the same. The printing process parameters applied by other companies may not be suitable for their own enterprises. Different companies in actual production should establish technical parameters suitable for their own company and establish a feasible color management system for the company. In order to ensure the correct function of color management technology. $Page break $

High quality equipment color profile

The second major point of the color management system is to establish a high-quality color profile for all devices involved in color management. Device color profile includes:
* Printed color profile * Digital proofing color profile * Screen color profile * Scanner color profile * Digital camera color profile

The printed color profile is the target of all device simulations. Attention must be paid to the choice of printed samples in establishing a high-quality device color profile. In color management, to obtain high-quality device color special files, pay attention to the following three points:

1. Select the print color measurement chart suitable for your company
2. Select printing proofs that correctly reflect the printing conditions
3. Use professional measurement tools and professional software to create high-quality device color profile
2.1. Selecting a Print Measurement Document for Use in the Enterprise

The contents of the applicable print measurement document must include:

* Internationally-used color tables, such as IT873, ECI2002
* Print quality measurement and control strips, such as Bruner signal strips* ISO pictures and pictures that the company often appears in daily printing, such as portrait portraits, home furnishings, ceramics, apparel, photography, Chinese painting, etc. .

The following figure shows an example of a printed measurement file. The measurement files used by different companies to measure the printed color profile are not necessarily the same, but must include international universal color meters and print quality control bars for measurement. The measuring tool and the universal color table are arranged in different order.


2.2. Select printing proofs that correctly reflect printing conditions

By analyzing the following five data of the printing proofs, the printing proofs that can correctly reflect the printing conditions are selected.
* Print contrast * Dot enlargement at 50% * Print uniformity of proofs, including both overall and single-sheet printing * Print black colorimetric values ​​and curves * Printed trichromatic and inter-subtle color tonality curves

2.3. Use professional measuring tools and professional software to create high-quality device color profile

The color profile of the overall printing equipment includes the following aspects:

2.3.1 Printing Color Profile
2.3.2 Digital Proofing Color Profile
2.3.3 Screen Color Profile
2.3.4 Scanner Color Profile
2.3.5 Digital camera color profile Here we simply describe the process of creating a color profile of different devices. In practical applications, it should be noted that before the device's color profile can be established, the device must be calibrated. Otherwise, the characteristic description file that correctly reflects the color of the device cannot be obtained.

2.3.1 Printing Color Profile


Use professional spectrophotometer to measure the measurement color table in printing sample that can correctly reflect the printing conditions, such as IT873 color table, ECI2002 color table, use professional ICC generation software, such as the GreaseMacbeth company's Profile Maker software to measure the colorimetric data Turn into a color profile.


2.3.2 Digital Proofing Color Profile

A professional spectrophotometer is used to measure measurement color tables printed under non-color management conditions, such as the IT873 color table and ECI2002 color table, and the measured color data is converted into a color profile using professional ICC generation software.

2.3.3 Screen Color Profile

A professional spectrophotometer was used to measure the measurement color patches that appeared on professional screens controlled by professional color management software, and professional ICC generation software was used to convert the measured colorimetric data into a color profile.

2.3.4 Scanner Color Profile

Scanners that support color management scan IT8.7/2 standard color samples without color management and use professional ICC generation software to convert measured colorimetric data into color profiles.

2.3.5 Digital Camera Color Profile

A digital camera that supports color management captures a standard color table in a standard lighting environment, and professional ICC generation software is used to convert the photographed standard color table into a color profile. $Page break $

III. Standardization and Dataization of Process Parameters for Overall Print Color Management

By applying the device's color profile to a corresponding calibrated device, the color management system (CMS) can be used to color manage the device. The effect of ideal color management should be "WYSIWYG", but the current color management products, including measurement tools and software (color management software, digital proofing software, digital printing software, etc.), in the actual use of the process Fine edits that still require human involvement. In order to achieve true "what you see is what you get", you must establish the process parameters of the overall printing color management in the actual application, and standardize and digitize the overall operation process to achieve true color reproduction accuracy and repeatability. . The specific operations of different processes may not be the same, but the data to be controlled must include the following aspects:

3.1. Calibration of equipment
3.2. Finely edited black balance color parameters
3.3. Finely edited ink balance color parameters
3.4. Fine-edited color table deviation values ​​and the reduction rate of the color table
3.1. Linear Calibration of Plate Making Equipment

The prerequisite for all equipment involved in color management: calibration. Among the printing processes involved are screen calibration, scanner calibration, digital proofer calibration, and digital printer calibration. The calibrated equipment, in addition to the screen can only be visually measured can not provide specific calibration data, other equipment, such as scanners, digital proofing machines and digital presses, can get the specific data after calibration.

3.2. Finely edited black balance color parameters

In practical applications, in order to ensure the accuracy and reproducibility of color reproduction, the finely edited equipment is better for reducing the gray balance. The specific implementation of different devices is not the same. The following are some of the examples we used in practical applications:

* Scanner gray balance color parameters

Application ICC color management sweep

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