Factors for Controlling Print Quality
There are four control factors for printed products: color, gradation, clarity, and consistency.
Color: Color is the foundation of product quality, directly determining its excellence. Color control or management is consistently a key aspect studied and analyzed by printing professionals.
Gradation: Gradation refers to the recognizable color gradients in the image. It forms the basis for accurately replicating colors.
Clarity: Clarity refers to the sharpness of image details, encompassing the clarity of fine-level details, the sharpness of image contours, and the clarity of image details.
Consistency: Consistency, or uniformity, involves two aspects. Firstly, it refers to the consistency of ink quantity in different parts of the same batch, generally measured by the consistency of the vertical and horizontal solid densities of printed products. This reflects the stability of different parts of printed products produced at the same time. Secondly, it refers to the consistency of density in the same part of different batches, reflecting the stability of the printing press.
For printed products, controlling these four aspects-color, gradation, clarity, and consistency-ensures high-quality printing.
Methods for Controlling Print Quality
One method of print quality control is the use of conventional signal bars, test bars, control bars, and step wedges, combined with testing instruments and charts, for the scientific quantitative control of print quality (including both print product quality and print engineering quality). Various countries use different systems, such as the GATF system in the United States, the Bruennel system in Switzerland, the FOGRA system in Germany, and the Gracol system.
Commonly used detection tools in printing include signal bars, test bars, control bars, and step wedges. Signal bars are mainly used for visual evaluation, expressing information about the appearance quality of printed products. Test bars are multifunctional marking elements primarily for density meter detection and evaluation. Control bars combine the visual evaluation and test evaluation of signal and test bars. Step wedges have equal-density or dot step wedges used to control plate exposure and printing quality.
In the digital environment, color management is crucial. It involves the transmission of color information across different devices and media. The International Color Consortium (ICC) has developed a standard, the ICC Profile, to describe the color performance of devices. Color management systems, utilizing ICC Profile characteristic files, facilitate consistent color reproduction across various devices and materials.
In a digital workflow, data transmission and management are critical due to the increased volume of data. Open Prepress Interface (OPI) and Desktop Color Separation (DCS) specifications have been developed for unified file control in prepress, optimizing data transfer and management on the internet.
Digital proofing, particularly with advancements in Raster Image Processors (RIPs), has become an integral part of the print production process. RIPs enable "rip once, output multiple times," ensuring consistency between proofs and the files used for printing.
Online inspection technologies, including CCD cameras, have become prevalent. These technologies allow continuous monitoring of printed products on the production line, providing real-time feedback for control and quality improvement. Online inspection can cover color detection, layout inspection, character detection, registration, as well as defect detection such as misprints, overprints, and dirty plates.