A detailed discussion on the problem of color reproduction in packaging printing (on)

Color box packaging products often appear in the actual production of color reduction issues, such as neutral gray cast color, affecting product quality, which in addition to the equipment itself, production personnel technical level of problems, the key issue is that the company did not Can perform effective color management and reasonable use of ink.

The concept and necessity of color management

Color management is the management of people's perception of color, the purpose is to enable the conversion between different colors in the entire process of image reproduction in order to ensure that the appearance of the image color from the input display to the output is matched as much as possible, eventually reaching the original In harmony with the color of the replica.

Image copying needs to undergo various stages of image acquisition, processing, color separation, and printing. At each stage, the color information will be expressed according to the color rendering principle and color description characteristics of the currently used device. Different scanning and display devices will have different color representations of the same original. In addition, the use of different color expression capabilities between RGB three-color display screens and four-color printing inks, coupled with different application software to convert RGB data into CMYK also lacks consistency, using different paper and ink, The resulting prints are also different. Therefore, color management must be used to control color reproduction on various devices and media in the production system.

Color management content

Establishing the device's color profile is the core of color management. The representative file has representative color features of each device, such as the chromaticity characteristic curve, the output color gamut characteristic curve, etc. The color management system uses these to represent Sexual color features enable the matching and conversion of the color space of each device.

Color management must follow a series of prescribed operating procedures in order to achieve the desired results. Color management is divided into three steps in principle, referred to as "3C", namely Calibration, Characterization, and Conversion.

Calibration: In order to ensure the stability, reliability, and sustainability of the color information transfer process, calibration of the input, display, and output devices is required to ensure that they are in standard operating conditions. The input correction includes the brightness, contrast, and correction of black and white fields of the scanner and the like. To ensure that for the same original, whenever scanning, you should be able to obtain the same image data.

By setting the display's brightness, contrast, color temperature, and the gamma value of the entire display system, it accurately displays colors. The output correction includes the correction of printers, imagesetters, printers, and proofers. After correcting the characteristics, the device can be output according to the factory-standard characteristics.

Characterization: Recording the corrected characteristics of all devices is a characteristic process. These feature description files are bridges from device color space to standard device-independent color space (PCS).

Conversion: Based on the calibration of the system equipment, using the device description file, the standard device-independent color space is used as the medium to achieve the correct conversion between the color spaces of the devices. Since the color gamut of the output device is narrower than the color gamut of the original document, scanner, and display, the color gamut needs to be compressed during color conversion. In the ICC protocol, color gamut compression has absolute colorimetry and relative colorimetry. Highlight four methods of saturation and sensory methods.

Implementation of color management

Generally speaking, for a packaging and printing company to do a good job in color management, it needs a standard ambient light source; high-quality color profile generation software; advanced color management system; standard measuring instruments and testing tools; standard color target Standard print management; standard remote digital proofing color management; standard scan reduction, digital camera color management; standard monitor correction and screen soft proofing. In the specific implementation process of color management, we should do the following aspects well: do a good job of standardization, standardization, and data-based production management of all processes throughout the printing process. This is the premise and basis for the application of ICC color management.

Enterprises should strictly establish the quality standards for fine products, standards for raw and auxiliary materials and equipment such as paper and ink, standards for measuring tools and ambient light sources, and formulate standardized management documents, and require that everyone strictly follow the standards. Monitors, soft proofing, printer ICC files, printer parameters, etc. must be standardized, and quantified within standards and specifications. Wherever data can be expressed, test data can be summarized and summarized. The three complement each other and depend on each other to ensure stable, high-quality, high-efficiency production.

Prepress image processing technology is the basis and key link of print reproduction quality. The monitor must be professional, the scanning of originals and the processing of digital manuscripts shall be guided by the four basic standards of copy quality (gray balance, tone reproduction, color correction, and sharpness enhancement), and the four standard parameters shall be standardized through experiments. . After the completion of the scanning of documents, it is necessary to make adjustments and artistic processing for the defects of non-compliant manuscripts so as to make the printed matter more abundant and achieve better results than the originals. For remotely-printed companies, profile management of remote digital proofing ensures that the digital proofs of the two locations are the same color.

The choice of color management system

There are many color management systems on the market today, such as Adobe's Photoshop color management system, Apple's ColorSync color management system, and Kodak's color management system. Different color management systems have different capabilities for the color management of the devices and they all have their own parts. Therefore, companies must first determine which devices require consistent colors in order to make choices.

Second, to determine the self-describing file in the color management system, and whether to support the establishment of description files in the open system; if it is a closed system, the factory must create a description file, so you need to determine whether it can withstand the establishment of the description file The required fee. It is necessary to compare and test various performances such as system availability, device support capability, scalability, compatibility, and ease of use against the company's own situation. The same color manuscript can be used to test which system is to be observed. Under the operating environment, the best effect can be obtained with the original. (to be continued)