End the chaos of color control

With the advancement of science and technology, people have higher and higher requirements for the quality of printed matter. To achieve WYSIWYG, to ensure the stability and accuracy of color reproduction results is an important task before us. The color management of printing companies can save a large amount of original rework due to color inconsistencies (such as redisaction, plate making), It can also reduce the printing time. Color management and process control can end the chaotic state of the printing process and provide more reliable color reproduction results.

1. Color management is part of quality management

In order to obtain accurate copying effects, color management is used as a quality control throughout the entire printing process: from the manuscript to the final copy. Take screen printing as an example, including display calibration, linearization of the imagesetter, keeping the film production process stable and consistent, controlling screen tension and stencil coating stability, maintaining effective printing pressure distribution, maintaining stable ink viscosity, and keeping an eye on production All variables in the process.

Apple Computer is the earliest part of color management as an operating system, Wundows platform computer also has some degree of color management capabilities, Apple color management is more suitable for image design. Microsoft also registered color management technologies similar to Apple's, enabling color descriptions that can only be printed, scanned, etc., on the Mac, and can also be transferred between different systems.

2. Hardware and software requirements for color management

Take the Mac machine as an example to see how color management works.

2.1 Hardware Needs

The color measurement equipment and evaluation software necessary for color management are combined to create a production environment for implementing color management. The color measurement equipment should have the following functions:

1. Correct the monitor

2. Measure the film's copy characteristics and dot density

3. Measure the reflection characteristics and color of the copied results.

Currently, the price of instruments that can perform the above functions varies from 1,200 to 1,2000. Expensive instruments can provide some degree of automation. Cheaper devices require manual operation. In fact, low-cost instruments can also be well managed. The best color measurement equipment on the market is colortron II. The price is about 1200. It can be used as a display corrector, a reflective light instrument or a color transfer instrument. The colortron II can read spectral values, density values, and dot range, which can be used to measure the color of a real object, and then transmitted to the computer in the form of light data. Based on the data obtained, colortron software can create color ranges and supply software to create color lookup tables (such as PhotoShop software). For high-efficiency production, Gretag-MacBrth's Spectroscan can be used, which eliminates the need to read hundreds of thousands of color sample blocks, provides automatic reading capabilities, and can save a lot of time for dedicated color management. Spectroscan sells for 10, Around 000, it can be used as a tool to measure the display, and it can also complete reflection and transmission reading.

2.2 Software needs

At present, a large number of color management software includes display calibration, scanner calibration, and printing/proofing description providing modules. The software is used in conjunction with a color measurement instrument to create a description for color management and to make the system work. The most important software supports almost all color measurement devices on the market, so there is no need to use a special device for a specific software package. There is usually a pull-down menu in the software that allows the user to select the provided device. This software package allows the entire system to function as a color management unit.

The most efficient software is the LinoColor description software package. The software package contains a monitor, scanner and printing/proofing description software. It was developed by LinoColor's color experts after many years of hard work. It can produce the most complex scanners and software for the printing industry. The descriptors provide excellent tools for printing production. The PrintOpen in the description includes more advanced Complex color separation control, conventional color separation methods and gray component replacement (GCR) functions.

3. Preparation for color management

Before applying color management to an image, it must be categorized according to the different components of the system and then corrected for them. The purpose of the correction is to create a profile of each device and to coordinate the descriptions with each other to achieve the expected results in the film output and printing stages. In general, the corrections the system has to do are:

Display correction

Correction of input devices (such as scanners or digital cameras)

Correcting the proofing and printing methods used in actual production

3.1 Display Calibration

Display calibration is easier to implement. For example, a cup-type suction reading device dedicated to the screen can be used to run calibration software programs. Through a series of color projections, the instrument generates the display's response. The instrument sends the data back to the computer through the cable, and the computer then calculates the corresponding description for the display.

The description created by the correction software is called display description and stored in the computer's system software. It is also called the system description. The system software is used to control the display color. Once the system description is established, it will work until it is updated or replaced.

3.2 Scanner Characterization

Input devices such as scanners and digital cameras should also be calibrated to better meet the needs of color management. Corrections to the input device are made by scanning IT-8 originals to obtain uncorrected data, scanning correction software including similar originals, and providing comparative measurement standards. The correction software is used to compare the actual value of the scan with the theoretical value of the original, and then use the measurement standard to construct the scanner description file as a basis for correcting the subsequent scan results. Make it consistent with the original. Therefore, the scanner description file enables the operator to accurately scan the original.

But what if the operator wants to correct the original image, such as removing a tone or creating a color tone, during the scanning process? In a color management system, this can also be achieved, but usually the image processing work is done in a computer because the computer processing makes the results more reliable, measurable, repeatable, and more efficient.

After the calibration of the display and the description of the scanner are completed, the display can reproduce the colors better, so that the operator can use the digital control with repeatability to process and control the images in the computer.

3.3 Film output, proofing, and printing/printing process corrections

This process can be divided into several steps. The first thing to do is to ensure that the imagesetter produces a linearized output. The linearization of the imagesetter is a critical step in managing color. Because it will affect the size (or line width) of the dot, the dots will be enlarged in the subsequent sequence and affect the printing result. Most imagesetters come with some linearization software at the time of purchase. For those that do not have linearization software, they can use the color correction software used by specialized publishing services. These software can complete the linearization of most imagesetters with accuracy of 1 Within %, you can create a correction function in RIP to make the output stable and reliable.

Once the imagesetter has been linearized, the same color separations as the manuscript can be produced. The manuscript is composed of 80-1000 color patches. Then the plate is made, printed, and finally the color characteristics of the image are measured with the instrument. The color reading on the print image corresponds to the number of colors on the original. This information creates a description, which describes a specific set of printing. How variables are duplicated.

Different color management software is not consistent with the number of colors that should be used in a proof or print description. There are 210 colors in LinoColor PrintOpen's manuscript, and it takes about one hour to measure all the color blocks with LinoColor. The fully automated Spectroscan takes only 15 minutes without human intervention.

Description The software creates a description for the proofing device or printing based on an assessment of the readings of the color measurement device, tells the application software, uses a technique, and corrects the colors in the post-process printing to match the expected color.

In addition to considering color information for management, it is also necessary to correct all changes in the printing process. Because the data obtained by the color measurement device is from the actual printed sample, the color-related information in the original file can be measured by the instrument, which includes dot gain, loss of highlights, the color of the substrate itself, and other changes in the dot value.

4. Apply various descriptions throughout the system

After the above steps are completed, the formal color management process can be entered.

The first thing to consider is how the image is used and then decide when to apply color management. Due to the wide range of image applications and the different printing processes, the entire process should be managed in color until the end. A certain image can be used for offset printing, screen printing, ink jet printing and implementation on the Internet. And each printing process or display environment has its own characteristics. Most of the current digital color management vendors use Apple ColorSync to connect with PhotoShop, then transfer the processed images to other applications to create color separation films. PhotoShop plug-in software allows images to be imported and exported in PhotoShop.

Another method is to use the page layout language to build a complete work. PageMaker also supports ColorSync, allowing users to apply color descriptions to documents that are output to the imagesetter. Quark Xpress's latest version 4.0 also supports ColorSync, which uses monitors, scanners, proofing/printing equipment descriptions to maximize color correction, and its color management rules are similar to those in PageMaker, but it includes a The advanced network cable preprocessing function can display the change of printing color in a certain process. It first defines the source description and then tells the software how the colors are specified. In some cases, it can be seen in advance how to complete the color processing in printing.

The specific process is: When ColorSync is activated, the driver in ColorSync converts the color of each pixel in the file to be processed to the device-independent space L*a*b*, and then the L*a* of each point. The b* value is passed to the processor, remapping the new color value within the allowed copy range of the output device. The calculation of hue and saturation will compensate color shift due to scanning, printing, and display devices.

Color conversion between multiple devices is very time consuming. Usually, all pixels in a 2MB image are mapped accordingly. It takes several minutes. This is a math problem that is difficult to solve at present. But with the increase of computer efficiency, the speed of the processor will also become faster, and the speed of color management will also accelerate.

Color management is part of process control. Throughout the entire process of print production, consistent and reliable replication results are obtained. The entire system is often tested. Periodically monitor and calibrate the monitor, and maintain real-time control of the proofing and plate-making process to ensure stable quality and end color confusion as soon as possible.