How color management ensures faithful reproduction of high-quality print colors

Everything seems to be ideally implemented: the customer's data is scheduled to be put into production, all pages have been completed, and none of the selected fonts are missing - in short, the task is very satisfactory. However, it suddenly became apparent that the effect was not the same once it was printed. The originals were much brighter, and even the preflight on the screen was much better than what was printed.

Experts believe that "Color Management" can avoid these problems. But what is the real meaning of this term? Simply speaking, color management includes controlling the color to be reproduced accurately and stably, and the result can be predicted. Its purpose is to make the final product as close to the original as possible. This topic may be a cliché for some people, but it is one of the most popular topics in professional seminars, industry symposia, and lectures because of the content of this topic and its ongoing uncertainty.

In publications, a color image usually requires a series of digital workflows. This workflow begins with a scanner or digital camera capturing images, reproducing images on a display screen, proofing with a digital proofing device, and finally preparing for actual printing. There is usually no problem in this process, but there is one point to note: Colors are not easily captured and are more difficult to control precisely.

Color is not a simple physical phenomenon but a complex visual experience influenced by light, including the reflective nature of the surface illuminated by light, and the slightly different psychological factors affecting each person's color perception. It is wrong to think that rainbows contain all colors. Because color is not a unitary single plane, it is far from simple to assign one wavelength to each color. In fact, we cannot see the true color at all. Color is simply the result of a combination of the signals received by the pyramidal cells on our retina in the brain.

Some systems have been tried to describe colors. The color space that we usually refer to is a multidimensional coordinate system, like the widely used CIE color coordinate system, which uses red-green, yellow-blue, and black-white three coordinate axes. But no manufacturer's defined color space can simply correspond to the color space defined by another manufacturer.

Different devices reproduce colors in different ways. Even the same color cannot be recorded and described in the same way. For example, scanners and displays use color space to synthesize various shades of red, green, and blue. On the other hand, proofers and printers combine the CMYK color space to create colors. A typical prepress system can contain a set of different devices from different manufacturers, complicating the color management process.

In previous years, the typical prepress part more or less adopted a self-contained equipment system, and its parts can work in close coordination to ensure full adaptability. However, digital equipment used by pre-press operating systems, which are mostly manufactured by different manufacturers, has also brought problems to color management. At present, it is common to find production lines of equipment produced by different prepress commercial manufacturers, such as scanners from Heidelberg, Kodak, or Itek, or input from Epson, Ricoh, or Nikon digital cameras, or directly from customers. Kinds of hardware and software generated images.

Problems caused by improper matching:

When changing from one color space to another in the workflow, the problem of color management will be more serious. For example, the scanner performs input scans in RGB and output in CMYK. This kind of thing happens in the printing factory every day.

Although different devices use different color spaces to have a certain coverage area, it is still difficult to completely match. Even the two devices that use the same RGB color space have different results. Paper and other substrates also affect the reproduction of colors. These factors also have to be taken into account in color management.

The task of color management:

The goal of color management is to compensate for the color distortion caused by the input and output devices, ensure that the color data is converted in a repeatable manner, and meet professional requirements, and ultimately establish color expression that does not vary from device to device. This is mainly achieved by the "device color calibration" approach.

In theory, the color profile should be based on widely accepted standards. The International Color Consortium has developed such a color space standard ICC-Profile and the necessary Color Management Module for modular hardware and software environments. Through these standard documents, the colors are input or output. Convert to a color space that is not affected by the device.

Apple Computer's MacOS operating system fully supports the ColorSync color management system. ColorSync is based on the technology developed by Linotype-Hell (now the pre-press of Heidelberg) and handles color conversion. This ColorSync software coordinates the operating system, applications, ICC-Profile and CMM, and can even switch between different module systems using different color conversion methods. Microsoft Corporation acquired the permission of the prepress department of Heidelberg and used ICM technology in the Windows operating system.

The truth of color management:

When an image is scanned or photographed with a digital camera, the result must be viewed on the display. Here is the first pass. Both of these devices need to be calibrated and a calibration curve determined to compensate for the difference. To calibrate the input device, a reference file is needed, usually a color slide, containing a color test strip, which should be consistent with the IT8 standard for all device color profiles. The original can be measured with a spectrophotometer, but of course, this step can also be omitted using a measured color value document. The second step, using a spectrophotometer to measure an actual scanned image, compares the results with the previously stored reference data and creates a set of differential values. This is the profile supported by the corresponding software, which can be used to convert the scanned data into a color space that does not vary from device to device. The same method is used to calibrate the display screen, proofer, and final output device.

Printers introduce uncertainties:

Naturally, the final printed output is the final test of color management. Standard color control strips have been designed as the printer color scale, so the color reproduction quality of prints can be verified on printed sheets. However, due to the inherent limitations of the offset printing process itself and the large number of variables that need to be maintained, considerable instabilities are added to this process, and the Profile can only calibrate one device under a specific data set. It is very important that the printing conditions remain unchanged. Ink, ink fountain settings, paper and even temperature and humidity will affect the quality of printed products.

Prospects:

In fact, due to the weaknesses in the process, various devices require different profiles and processing schemes, and color management cannot always achieve the desired results. As long as one link in the production process is not properly calibrated or an incorrect or outdated profile is used, the entire process is compromised. Manufacturers also recognize these issues and have embarked on effective color management solutions, including powerful calibration tools designed for a wide range of devices.

In fact, color management technology has not been widely used. Some people are hesitant about this complex issue. The numerous tools and systems on the market have not only failed to help potential users find directions, but have also made them even more confused. What's more, many of the explanations for "color management" are arbitrarily fluctuating, and various arguments only narrowly address certain aspects, rather than describing the technology as a whole. And, essentially, the fundamental problem of color is completely a subjective phenomenon, which makes it difficult to control.

In any case, however, the days when color management can be used to ensure the faithful reproduction of high-quality print colors are not far off. In fact, as this article explains, there is an urgent need to push color management forward.

Author/Yang Yongfei

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