In the course of business transactions, it is particularly important to evaluate the quality of the printed matter properly. The complexity of the color printing process is well known. The production of a printed matter often takes more than ten steps to complete, which involves companies, staff, etc., in different environments At different times, the evaluation methods or requirements for printed matter are also different. Therefore, in this process, some specifications and corresponding observation conditions need to be established.
Therefore, we can only subjectively evaluate the printed matter by restricting the external factors of the environment, so as to be fair and objective, and to reduce disputes caused by the environment, so a standard lighting environment and a standard light source are necessary .
Color difference of printed matter
The color difference can be divided into (1) color difference of the original: reproducing the color gradation of the original is the purpose of printing and copying, making the printed matter and the original difficult to distinguish between true and false is the highest standard of subjective evaluation. (2) The same batch of color difference: refers to the same batch of products in the same position in the same hue area, the color error between different printed sheets. (3) Similar and different batches of color difference: refers to the color error between different batches of the same product. If the colors printed in each batch are slightly different, when they are put together, customers will feel that these products are old and new, and even doubt Whether its internal quality will be as unstable as its appearance, it will cause distrust of the goods, and naturally it will cause the manufacturers to be dissatisfied with the quality of the printing plant.
Both customers and printers hope that the value of this color error is preferably zero, but due to the limitations of various aspects in actual production, it is impossible to completely eliminate color errors. Only by strengthening the quality control of each link, the product ’s The difference in color quality is controlled within the prescribed color difference standard. The color tolerance refers to the color difference between the print and the manuscript or proof sheet that the customer can accept.
Subjective evaluation
The subjective evaluation of the color quality of the printed matter uses a visual method. Observers make their own judgment after visually comparing the printed matter and comparing it with the manuscript or the printed sample. The main consideration is to what extent the color quality of the printed matter will be accepted by the customer.
Whether in the printing process or after checking the quality of printing, the printing operator or quality inspector should always use his own feelings and experience to evaluate the color quality of the printed products based on the faithfulness and authenticity of the reproduction.
The faithfulness of reproduction refers to the degree of reproduction of the color tone of the original by the printed matter. The printed matter is a kind of copy. From the pre-press processing to the entire color copying process of printing, the original is the basis of our work, and the reproduction of the color tone of the original is the purpose of printing and copying. It is the highest standard for subjective evaluation to make printed matter and manuscript difficult to distinguish between true and false.
When there is no manuscript for comparison, the color quality of the printed matter is related to the realism, that is, it is required to meet the memory color of most people. Most people have a preconceived habit of common objects. If the main color of the printed matter is different from the color of the real object, this printed matter cannot be called a high-quality copy. In short, the subjective evaluation criteria for the color quality of printed matter is to replicate truth, nature, and coordination. Of course, sometimes it will change slightly according to the customer's intention or the use of the product. [next]
Definition of the original
In the past, most manuscripts came from slides, photographs, and hand-painted color manuscripts of photography. In the process of color separation and manuscript, if the manuscript can be approached, it is regarded as an effective color reproduction. The printing aspect is based on the draft approved by the customer. As long as it can follow 90%, it is generally regarded as qualified. But nowadays, there are more definitions of manuscripts in the computer age. For example, if guests see satisfactory colors on the computer screen or printed manuscripts, they think it is an manuscript. Regardless of any type of manuscript, the colors they record or appear may not be able to be expressed under general printing conditions, because each color reproduction system has its color gamut limitations. In the production process, the real thing is the manuscript for the image ingestor, the color separation platemaker uses the photo taken as the manuscript, and the printer uses the manuscript as the goal of color matching.
objective comment
The objective evaluation of the color quality of the printed matter is to calculate the results of the subjective evaluation by statistical means, and then convert it into the corresponding physical quantity, and use it as the objective evaluation standard. In this way, the influence of human factors in the evaluation can be eliminated, and the color quality of various printed materials can be evaluated fairly by standardized unified standards, which ultimately makes it more in line with the subjective evaluation standards of most people. The objective evaluation method mainly uses specific measuring instruments and tools, and measures some standard elements printed together with the printed image. Only through measurement can automatic control of printing quality become possible to some extent.
Color quality and production control
In order to produce high-quality color prints, it is necessary to strengthen the quality control of the production process, and quality control mainly depends on the objective evaluation standard of the product, that is, to develop a set of strict data specifications, use various instruments to objectively measure and Evaluate the color quality of printed matter and other aspects.
The purpose of color control management is to improve the small gap between manuscripts, proofs and products. In the printing process, if you can spot-check the printed matter at any time, you can find the problem through the deviated data and find out the cause in time, so that the problem can be corrected, so as to ensure the copy quality of the printed matter. In addition to using density as a parameter that reflects the color quality of the printed matter, it is necessary to promote the CIE Lab chromaticity value of the color as the parameter to detect the quality of the print.
Every link must be implemented with data management, and each step must have a testing tool to detect it, otherwise many errors will occur. Today, with the continuous advancement of process technology, the color control methods in printing have also been further developed. The new color management system makes printing color control convenient and more effective.
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